# Wikijunior:Solar System/Saturn

```{=html}
<div style="float:right;  border:2px solid #aaaaaa; width:250px; margin-left:0.2em; padding:0.4em">
```
!♄.svg "♄"){width="80"} **Saturn Facts**:

-   If you could find a bathtub big enough, Saturn would float in it.
-   Some of Saturn\'s moons control the width of its rings. These are
    known as shepherd moons.
-   Although it is made mostly of gases, scientists believe Saturn has a
    small rocky core.

```{=html}
</div>
```
**Saturn** is the sixth planet from the sun, and is one of the *gas
giants*.

{{  }}

## How big is the planet?

!Comparison of the size of Saturn and the
Earth
Saturn is 120,536 km or 9.449 Earths wide at the **equator**.[^1]

## What is its surface like?

Saturn is mostly gas and liquid.[^2] Saturn may have a small core of
rock and ice.[^3] The **atmosphere** has bands, but they are not as
colorful as Jupiter\'s.

## What are its rings like?

!Saturn casts a shadow on its
rings
Saturn\'s rings are composed of rock and ice particles ranging in size
from specks of dust to the size of a house. Some particles might even be
a few kilometers wide! The particles in the rings are actually spaced
far apart. It would be easy to pass through the rings.[^4]

## What are its moons like?

!Map of the Saturn system
(NASA)") Saturn has 56
moons, and many of them have names.[^5]The size of Saturn\'s moons and
the size of the chunks of ice in its rings are similar, which means that
we can never know the exact number of moons. [^6] New moons are still
being discovered. Saturn\'s biggest moon is named Titan, and is large
enough to be a planet in its own right!

### Shepherd moons

There are small potato-shaped moons in or near Saturn\'s rings. They
control the ring particles with their gravity. That is why they are
called shepherd moons. Six of them are known, and there may be more.[^7]

### Mimas

Mimas is mostly made of water ice with a small amount of rock.[^8] It
has a large **crater** for its size called *Herschel*. It is 130 km
across, making it about a third as big as Mimas.[^9] The crater makes
Mimas look like the Death Star from the *Star Wars* movies.

### Enceladus

Enceladus is made of ice. It is **denser** than the other icy moons.
That suggests it also has some rock inside.[^10] It has smooth areas,
cracks and some craters. The smooth areas are younger. Craters there
have been erased within the past 100 million years. Water vapor was
found over a smooth area around the south pole. The cracks and grooves
suggest **tectonics** similar to Ganymede\'s. Some ridges similar to
Europa\'s ridges were also found. Those suggest oceans like Europa\'s
under some areas of Enceladus.[^11]**Tidal forces** from Dione could be
powering some of this activity. It is because Enceladus orbits Saturn
twice for every orbit by Dione. This makes Dione and Saturn tug on
Enceladus. This is similar to how Europa and Ganymede\'s tidal forces on
Io power Io\'s volcanoes.[^12]

### Tethys

!Tethys imaged by the Cassini
spacecraft.
Tethys is an icy moon that has many craters, including the huge
*Odysseus*. It is 400 km across, 1/5th as big as Tethys is. The crater
had become flattened because the icy material does not hold its shape as
well as rock would. There is also a large valley called *Ithaca Chasma*.
It is 3 to 5 km deep, 100 km wide and 2000 km long, three fourths of the
way around Tethys.[^13]

There are two moons, Telesto and Calypso, which share Tethys\' orbit.
Telesto is ahead of Tethys and Calypso is behind it.[^14]

### Dione

Dione is made of lots of ice and there may be some rock in its **core**.
It has lots of craters. The craters are flattened because the ice does
not hold their shape as well as rock. One side has bright white lines
that are fractures. Two moons share Dione\'s orbit. Helene is ahead of
Dione and Polydeuces is behind it.[^15]

### Rhea

Rhea is an icy moon similar to Dione with some rock in the core. It has
many craters mostly on one side, and the other side has some bright
white icy areas.[^16]

### Titan

!Titan imaged by the Cassini
spacecraft.
Titan is the largest moon of Saturn and the second largest one in the
solar system.[^17] It is the only moon in the Solar System that has a
thick atmosphere. The atmosphere is made of **nitrogen**, **argon**,
**methane** and various **organic compounds**.[^18] Its surface has
light and dark areas and few craters. The Cassini probe discovered a
huge crater 440 km wide.[^19]

### Hyperion

Hyperion is made of water ice with a little rock. It is potato shaped.
It wobbles instead of rotating in the same way other moons do.[^20]

### Iapetus

!Mosaic of Iapetus images taken by the Cassini
spacecraft.
Iapetus is almost entirely ice.[^21] It has a light area called
*Roncevaux Terra* that has craters.[^22] There is a big dark area called
*Cassini Regio* that covers half of Iapetus. The dark material may be
from Phoebe. Some of it is on the bottom of craters. Some huge craters
and a ridge have been discovered in *Cassini Regio* by the Cassini
probe. The ridge stretches 1300 km along the equator. It is up to 20 km
high, which is over 2.26 times higher than Mount Everest.[^23] More huge
craters were found in *Roncevaux Terra* when Cassini went by Iapetus
again.[^24]

### Phoebe

Phoebe is made of ice and rock. It looks dark because it has a layer of
dark material on the outside. It also looks rough.[^25]

### Other moons

There are two groups of small outer moons. Phoebe is part of the second
outermost group.[^26]

## How long is a day on this planet?

One day on Saturn is about 10 hours and 39 minutes in Earth time.[^27]

## How long is a year on this planet?

One year on Saturn is about 29.46 Earth years long. That is 10,760 Earth
days![^28]

## What is it made of?

Saturn has a rocky core. Around the core, there is ice. Above the ice is
liquid metallic **hydrogen**. On top of that is gaseous hydrogen. There
is no place where the hydrogen suddenly turns from a gas to a liquid.

The gaseous hydrogen makes up most of Saturn\'s atmosphere. Other gases
there include **helium** and some other gases. There may be rain made of
helium falling through the hydrogen. There is also ammonia on the
surface.[^29]

## How much would Saturn\'s gravity pull on me?

If you were floating close to the cloud tops of Saturn, it would pull
you down with a force only a little stronger than the force of Earth\'s
gravity.[^30] The effects of Saturn\'s large **radius** and its **mass**
almost cancel each other out, making the force only a little bigger. So,
if you weighed 100 lbs. on Earth, you would weigh 106 lbs. on Saturn.

## Who is it named after?

Saturn is named after the most important Roman god of agriculture and
harvest time. He taught people how to farm. He was the father of
Jupiter. Saturday is named after him.[^31]

Uranus

ar:ويكي الأطفال:نظام
شمسي/زحل bs:Wiki junior
Sunčev sistem/Saturn
de:Wikijunior_Sonnensystem/\_Saturn
es:Wikichicos/Sistema_Solar/Saturno
fr:Wikijunior:Système_solaire/Saturne
nl:Wikijunior:Zonnestelsel/Saturnus
pl:Wikijunior:Układ_Słoneczny/Saturn
fi:Wikijunior_Aurinkokunta/Saturnus

## References

```{=html}
<references/>
```
de:Wikijunior Sonnensystem/
Saturn
nl:Wikijunior:Zonnestelsel/Saturnus

[^1]: <http://www.nineplanets.org/saturn.html>;
    <http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html>

[^2]: <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=OverviewLong>

[^3]: <http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=166>

[^4]: <http://www.nineplanets.org/saturn.html>;
    <http://www.solarviews.com/eng/saturnrings.htm>;
    <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Rings>

[^5]: <http://www.nineplanets.org/saturn.html>

[^6]: <http://www.factmonster.com/ce6/sci/A0860937.html>

[^7]: <http://saturn.jpl.nasa.gov/faq/saturn.cfm#q13>

[^8]: <http://www.nineplanets.org/mimas.html>

[^9]: <http://www.nineplanets.org/mimas.html>

[^10]: <http://saturn.jpl.nasa.gov/multimedia/products/pdfs/20050830_CHARM_Esposito.pdf>;
    <http://www.ifa.hawaii.edu/faculty/jewitt/kb/phoebe.html>

[^11]: <http://www.nineplanets.org/enceladus.html>;
    <http://www.nasa.gov/home/hqnews/2005/jul/HQ_05208_cassini_watery_world.html>;

[^12]: <http://www.bbc.co.uk/science/space/solarsystem/saturn/enceladus.shtml>;
    <http://www.spacedaily.com/news/cassini-01e3.html>

[^13]: <http://www.nineplanets.org/tethys.html>

[^14]: <http://apod.gsfc.nasa.gov/apod/ap020519.html>

[^15]: <http://www.nineplanets.org/dione.html>;
    <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Dione>;
    <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Polydeuces>

[^16]: <http://www.nineplanets.org/rhea.html>;
    <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Rhea>

[^17]: <http://www.nineplanets.org/titan.html>;
    <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Titan>

[^18]: <http://www.nineplanets.org/titan.html>;
    <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Titan>

[^19]: <http://www.nineplanets.org/titan.html>;
    <http://www.nasa.gov/mission_pages/cassini/media/cassini-021605.html>

[^20]: <http://www.nineplanets.org/hyperion.html>

[^21]: <http://www.nineplanets.org/iapetus.html>

[^22]: <http://www.seasky.org/solarsystem/sky3g8.html>

[^23]: <http://www.solarviews.com/cap/pia/PIA06166.htm>;
    <http://www.solarviews.com/eng/iapetus.htm>;
    <http://www.nineplanets.org/iapetus.html>;
    <http://antwrp.gsfc.nasa.gov/apod/ap030831.html>

[^24]: <http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=2763>

[^25]: <http://www.solarviews.com/eng/phoebe.htm>

[^26]: <http://www.factmonster.com/ce6/sci/A0860937.html>

[^27]: <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Facts&System=Metric>

[^28]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html>

[^29]: <http://www.nineplanets.org/saturn.html>;
    <http://www.solarviews.com/eng/saturn.htm>;
    <http://www.seasky.org/solarsystem/sky3g1.html>

[^30]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html>

[^31]: <http://www.pantheon.org/articles/s/saturn.html>;
    <http://coolcosmos.ipac.caltech.edu/cosmic_kids/AskKids/saturn_name.shtml>


# Wikijunior:Solar System/Uranus

Uranus, the seventh planet from the Sun, was discovered by William
Herschel on March 13, 1781.[^1]

!Uranus as seen from Voyager
2
{{/Coolfacts\|
!⛢.svg "⛢"){width="80"}\|Uranus Facts:\|

-   Uranus\'s rings look white in pictures, but they are really made of
    asphalt-colored material.
-   When it was first discovered, Uranus was mistaken for a star. It was
    named \"34 Tauri\".
-   Uranus rotates on its side It is the only planet to do so.

}}

## How big is Uranus?

!Comparison of the size of Uranus and the
Earth
Uranus is 51,118 kilometers or about four Earths wide. It is the third
widest and fourth heaviest planet in the Solar System.\

## What is the surface of Uranus like?

Uranus does not have a surface that you could stand on without going
deep into the **atmosphere**. Under the atmosphere, there may be an even
mixture of rock and ice.[^2]

## What are the rings around Uranus like?

Uranus has eleven rings. They are dark in colour and very hard to see.
They were discovered by accident in 1977. Scientists were studying a
bright star near Uranus. However, the star\'s light was blocked before
and after it disappeared behind Uranus. From this, they figured out that
Uranus has a ring system.[^3]

## What are its moons like?

right\|thumb\|Uranus\'s rings and
moons

Uranus has 27 known moons, which places it third in the Solar System for
number of moons. The five main ones are Miranda, Ariel, Umbriel, Titania
and Oberon.[^4]

### Miranda

Miranda is the smallest and closest of Uranus\'s major moons. It is
mainly made of ice and rock. Miranda\'s surface has grooves, cliffs, and
valleys. The moon was named after a character in *The Tempest*, a play
by Shakespeare.[^5]

### Ariel

Ariel is made of rock and ice. Ariel has many valleys, but not many
craters. Ariel was named after a character in the poem *The Rape of the
Lock* by Alexander Pope. Ariel is also a spirit in *The Tempest* by
Shakespeare.[^6]

### Umbriel

Umbriel is made of lots of ices and some rock. It is also the darkest of
Uranus\'s major moons. Umbriel was named after a character in the poem
*The Rape of the Lock* by Alexander Pope.[^7]

### Titania

Titania is the largest moon of Uranus. It is mostly ice and rock. The
surface is covered with canyons. It was named after the Queen of the
Fairies in *A Midsummer\'s Night Dream*, a play by Shakespeare.[^8]

{{  }}

### Oberon

Oberon is the outermost of the major moons of Uranus. It is made of the
same things as Titania. It has many craters. Some of them have white
rays around them and dark crater floors. It was named after the King of
the Fairies in *A Midsummer\'s Night Dream*.[^9]

### Other Moons

There are 13 tiny moons known to be **orbiting** Uranus inside
Miranda\'s orbit. Nine more tiny moons are known to be in big orbits
beyond Oberon\'s orbit.[^10]

## How long is a day on Uranus?

One day on Uranus is about 17.24 Earth hours long. Uranus spins on its
side, maybe because of a big impact early in the history of the Solar
System.[^11]

## How long is a year on Uranus?

One year on Uranus would be 30,708 days or 84 years on Earth.[^12]

## What is Uranus made of?

Unlike Jupiter and Saturn, Uranus is thought to be made mostly of rock
and ice. The gases in its atmosphere are 83% **hydrogen**, 15%
**helium**, and 2% **methane**. Other gases found in smaller amounts are
ammonia, water, and **methane**.[^13] Uranus\' blue color comes from
**methane** clouds, which absorb red light and reflect blue light.[^14]

## How much would Uranus\'s gravity pull on me?

If you were floating close to the cloud tops of Uranus, you would be
pulled down with a force about 89% of Earth\'s gravity.[^15]

## Who is Uranus named after?

Uranus was named after Ouranos, the Greek name for the sky. Ouranos was
the ancient Greek deity of the heavens, the earliest supreme God.
According to Greek mythology, Ouranos was the husband and son of Gaia,
Mother Earth.[^16]

Next Topic: Neptune

## References

```{=html}
<references/>
```
ar:ويكي الأطفال:نظام
شمسي/أورانيوس
de:Wikijunior Sonnensystem/
Uranus
nl:Wikijunior:Zonnestelsel/Uranus
pl:Wikijunior:Uklad_Sloneczny/Uran

[^1]: <http://www.nineplanets.org/uranus.html>

[^2]: <http://www.solarviews.com/eng/uranus.htm>;
    <http://www.nineplanets.org/uranus.html>

[^3]: <http://www.solarsystem.org.uk/uranus/>

[^4]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/index.html>;
    <http://www.nineplanets.org/uranus.html>

[^5]: <http://www.nineplanets.org/miranda.html>;
    <http://www.bbc.co.uk/science/space/solarsystem/uranus/miranda.shtml>

[^6]: <http://www.nineplanets.org/ariel.html>;
    <http://www.bbc.co.uk/science/space/solarsystem/uranus/ariel.shtml>

[^7]: <http://www.nineplanets.org/umbriel.html>;
    <http://www.bbc.co.uk/science/space/solarsystem/uranus/umbriel.shtml>

[^8]: \[<http://www.nineplanets.org/titania.html>;
    <http://www.nineplanets.org/titania.html>\];
    <http://www.bbc.co.uk/science/space/solarsystem/uranus/titania.shtml>

[^9]: <http://www.nineplanets.org/oberon.html>;
    <http://www.bbc.co.uk/science/space/solarsystem/uranus/oberon.shtml>

[^10]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/uraniansatfact.html>

[^11]: Gierasch, Peter J., and Philip D. Nicholson. \"Uranus.\" World
    Book Online Reference Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar577720>;
    <http://www.nasa.gov/worldbook/uranus_worldbook.html>

[^12]: Gierasch, Peter J., and Philip D. Nicholson. \"Uranus.\" World
    Book Online Reference Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar577720>;
    <http://www.nasa.gov/worldbook/uranus_worldbook.html>

[^13]: <http://www.nineplanets.org/uranus.html>;
    <http://www.solarviews.com/eng/uranus.htm>

[^14]: <http://www.solarviews.com/eng/uranus.htm>

[^15]: Gierasch, Peter J., and Philip D. Nicholson. \"Uranus.\" World
    Book Online Reference Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar577720>;
    <http://www.nasa.gov/worldbook/uranus_worldbook.html>

[^16]: <http://www.nineplanets.org/uranus.html>


# Wikijunior:Solar System/Neptune

!Neptune as seen from Voyager
2
{{/Coolfacts\|=
1\|!♆.svg "♆"){width="80"}\|= 2\|Neptune
Facts:\|= 3\|\*Wind speeds on Neptune can reach 450 meters per second.

-   Neptune was discovered because its gravitational field was affecting
    the orbit of Uranus.
-   Neptune is sometimes farther from the Sun than Pluto.

}}

## How big is this planet ?

{{  }} !Comparison of the size of Neptune
and the
Earth
Neptune is very similar to Uranus in size. Its diameter is only slightly
smaller, at 49,528 km wide. [^1] It is almost as big as four Earths in
length.[^2]

## What is its surface like?

The **atmosphere** of Neptune has some dark blue spots. When the Voyager
probe went by Neptune in 1989, it saw a large one called the Great Dark
Spot. In 1994, it vanished, but later reappeared.[^3] There is also a
large white cloud nicknamed \"Scooter.\" It goes around Neptune every 16
hours.[^4] The winds of Neptune are very fast, blowing at up to 2000 km
per hour(the fastest in the entire solar system).[^5] That is about four
times faster than the fastest recorded tornado on Earth.

## What are its rings like?

Neptune has some faint rings that are dark and hard to see. There are
clumps in some parts of the rings where the material is **denser**.[^6]

## What are its moons like?

Neptune has 13 moons. There could be more.[^7]

### Inner Moons

There are five small potato-shaped moons **orbiting** close to Neptune.

#### Proteus

Proteus is a dark moon about 418 km across. It has an irregular shape.
In Roman mythology Proteus was a sea-god who could change into any shape
he wanted.[^8]

#### Triton

Triton is the largest moon of Neptune. Scientists think that it is a lot
like Pluto. It is 2700 km across. It is made of rock and ice. It has a
surface temperature of −235 °C Triton has a very thin atmosphere made up
of **nitrogen** and a little **methane**.

There are volcanoes that have eruptions of liquid nitrogen, dust or
methane compounds. The eruptions happen because of the seasons. There
are few **craters** because the eruptions cover them up. There are ice
caps that change sizes with the seasons. There are also **ridges** and
**valleys**. They may have formed because of repeated freezing and
thawing.

An interesting thing about Triton\'s orbit is that it goes around
Neptune in the opposite direction that Neptune\'s rotates. Because of
this, scientists think that Triton was captured by Neptune long ago. In
Roman mythology, Triton was the son of Neptune.[^9]

#### Nereid

Nereid is an irregularly shaped moon about 340 km across. Its orbit is
very eccentric or noncircular. It may have been captured by Neptune or
moved into the eccentric orbit by Triton\'s gravity when Triton got
captured. In Roman mythology Nereids were sea nymphs.[^10]

### Outer Moons

There are five other known moons. They are small potato-shaped moons far
from Neptune. There might be more we haven\'t seen yet.

## How long is a day on this planet?

A day on Neptune lasts 16 hours and 7 minutes.[^11]

## How long is a year on this planet?

One year on Neptune is about 165 Earth years, or 60,265 days.[^12]

## What is it made of?

Neptune is made of rock and metal in the **core**. The core is probably
bigger than Uranus\'s because Neptune weighs more, but is the same size.
Around the core is rock, water, **ammonia** and **methane**. The
atmosphere is made of **hydrogen** and **helium**. Lower down in the
atmosphere, there is methane and ammonia too. The methane makes Neptune
look blue-green.[^13] !Artistic impression of the mythological
Neptune.jpg "Artistic impression of the mythological Neptune")

## How much would Neptune\'s gravity pull on me?

If you were floating close to the cloud tops of Neptune, it would pull
you down with a force only a little stronger than the force of Earth\'s
gravity.[^14] The effects of Neptune\'s larger **radius** and its
**mass** almost cancel out, making the force only a little bigger.

## Who is it named after?

Neptune is named after the Roman god of the seas, also known as Poseidon
in ancient Greece. [^15]

Next Topic: Pluto

## References

```{=html}
<references/>
```
ar:ويكي الأطفال:نظام
شمسي/نبتون de:Wikijunior
Sonnensystem/ Neptun
nl:Wikijunior:Zonnestelsel/Neptunus
pl:Wikijunior:Układ_Słoneczny/Neptun

[^1]: Smith, Bradford A. \"Neptune.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^2]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html>

[^3]: Smith, Bradford A. \"Neptune.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^4]: <http://www.nineplanets.org/neptune.html>;
    <http://www.moreheadplanetarium.org/index.cfm?fuseaction=page&filename=science_resources_neptune.html>

[^5]: <http://www.nineplanets.org/neptune.html>;
    <http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level1/neptune.html>

[^6]: Smith, Bradford A. \"Neptune.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^7]: <http://www.nineplanets.org/neptune.html>

[^8]: <http://www.nineplanets.org/proteus.html>

[^9]: <http://www.nineplanets.org/triton.html>

[^10]: <http://www.nineplanets.org/nereid.html>

[^11]: Smith, Bradford A. \"Neptune.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^12]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html>;
    Smith, Bradford A. \"Neptune.\" World Book Online Reference Center.
    2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^13]: <http://www.nineplanets.org/neptune.html>;
    Smith, Bradford A. \"Neptune.\" World Book Online Reference Center.
    2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar386900>;
    <http://www.nasa.gov/worldbook/neptune_worldbook.html>

[^14]: Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 281. West Publishing
    Company.

[^15]: Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 282. West Publishing
    Company.


# Wikijunior:Solar System/Pluto

Pluto is a dwarf planet that was discovered by the astronomer Clyde W.
Tombaugh in Arizona on February 18, 1930.[^1] !Pluto, as seen from the
*New Horizons*
spacecraft.

```{=html}
<div style="float:right; border:2px solid #aaaaaa; width:250px; margin-left:0.2em; padding:0.4em">
```
!♇.svg "♇"){width="80"} **Pluto Facts**:

-   Pluto is a dwarf planet, smaller even than Earth\'s Moon.
-   Pluto sometimes moves closer to the sun than Neptune.

```{=html}
</div>
```
## How big is Pluto?

!Comparison of the sizes of Pluto, Charon, the Moon and
Earth
Pluto\'s **mass** is about 12,500,000,000,000,000,000,000 kilograms.[^2]
While this may seem large, it\'s only about 1/500th of the Earth\'s
mass. Pluto is between 2200 and 2400 kilometers across.[^3] Its
**surface area** is about 17,950,000 square kilometers (or 1/30th of the
Earth\'s).[^4] Its **volume** is 7,150,000,000 km^3^ (or 1/150th of the
Earth\'s).[^5]\
{{  }}

## What is its surface like?

!The surface of
Pluto..jpg "The surface of Pluto.")
Pluto\'s surface is covered with ice.[^6] It is very cold, at about -230
°C.[^7] Pluto also has a very thin **atmosphere** which freezes when
Pluto moves far away from the Sun.[^8]

The image above on the right shows Pluto\'s color.

## What are Pluto\'s moons like?

Pluto has three known moons. The largest is called Charon. Charon is
about half as wide as Pluto. Because Pluto and Charon are so close in
size, they are sometimes called a \"double planet\".[^9] Charon\'s
surface is covered in water ice.[^10] Two other moons were discovered in
2005. They have been named Nix and Hydra.[^11]

## How long is a day on Pluto?

One day on Pluto is about 6.487 Earth days long. Like Uranus, Pluto also
spins on its side.[^12]

## How long is a year on Pluto?

One year on Pluto would be about 90,613 days or 248 years on Earth![^13]

## What is it made of?

Scientists believe Pluto is made mostly of rock and ice,[^14] but they
will not be sure until more research is done. The discovery of Charon
helped scientists estimate the **density** of Pluto. The information
collected told them what Pluto was and was not made out of. If Pluto
were made out of heavy solids, it would have a very high density. If it
were made of gases, it would have a low density. Pluto is somewhere in
between, so it is probably made of rock and ice.

## How much would Pluto\'s gravity pull on me?

If you were on Pluto, gravity would be only 0.06 times as strong as it
is on Earth. [^15] This means you could do really high jumps---even more
than people could on the Moon!

## Who is Pluto named after?

Pluto was named after the Roman god of the underworld. In Roman
mythology, he kidnapped Proserpina (Persephone) so he could marry her.
This made her mother, Ceres, the goddess of agriculture, very sad,
causing winter. To end winter, Jupiter, the king of the gods and her
brother, decreed that Proserpina could return to the surface as long as
she hadn\'t eaten any food of the Underworld. However, she had eaten six
pomegranate seeds, so Jupiter decided she had to spend six months in the
underworld each year. This is the Roman myth of winter. When she goes to
the Underworld, everything stops growing. When she comes back, her
mother is happy again, and life returns.[^16]

In Roman mythology, Charon took dead souls across the river Acheron to
the land of the dead.[^17]

## Is Pluto a planet?

Pluto has been officially classified as a dwarf planet, which is
different from a regular planet. One reason is its small size - although
it is the tenth largest known object that revolves around the sun, it is
smaller than many moons, including Earth\'s moon. Scientists used to
think that Pluto was a lot larger than it actually is,[^18] and it was
thought of as the ninth planet for many years.

Another key reason is that Pluto is part of a large group of objects
called the Kuiper Belt, which all revolve around the Sun in the area
beyond Neptune. In January 2005 another object \"Eris\" was discovered
in the Kuiper Belt. Eris is larger than Pluto. Scientists think there
are even more Pluto-sized objects in this part of the solar system, as
well as millions of smaller objects. Because of this, the International
Astronomical Union (IAU) defined the term \'planet\' for the first time.
Under the definition, both Eris and Pluto (along with Ceres, Haumea and
Makemake) are dwarf planets.

In spite of this, some people continue to hold on to the idea that Pluto
is a regular planet because of tradition. Also, some textbooks and
references are not up to date, and still list Pluto as the ninth planet.

Next Topic: Comets

## References

```{=html}
<references/>
```
ar:ويكي_الأطفال:نظام_شمسي/بلوتو
de:Wikijunior Sonnensystem/
Pluto
nl:Wikijunior:Zonnestelsel/Pluto
pl:Wikijunior:Układ_Słoneczny/Pluton

[^1]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html>

[^2]: Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 285. West Publishing
    Company. ;
    <http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html>

[^3]: Spinrad, Hyron. 2004 \"Pluto.\" World Book Online Reference
    Center. 2004. World Book, Inc.
    <http://www.worldbookonline.com/wb/Article?id=ar435500>;
    <http://www.nasa.gov/worldbook/pluto_worldbook.html>; Snow, Theodore
    P. (1996) \"The Outer Planets.\" In *The Dynamic Universe: An
    Introduction to Astronomy*. pp. 285. West Publishing Company.
    ;
    <http://amazing-space.stsci.edu/resources/fastfacts/pluto.php.p=Astronomy+basics@,eds,astronomy-basics.php&a=,eds>

[^4]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html>

[^5]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html>

[^6]: Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 287. West Publishing
    Company. ;
    <http://www.nasa.gov/worldbook/pluto_worldbook.html>

[^7]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html>;
    Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 285. West Publishing
    Company. ;
    <http://www.nasa.gov/worldbook/pluto_worldbook.html>

[^8]: Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 287. West Publishing
    Company. ;
    <http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html>

[^9]: <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Plu_Charon>

[^10]: <http://seds.lpl.arizona.edu/nineplanets/nineplanets/pluto.html>

[^11]: <http://www.space.com/scienceastronomy/060621_nix_hydra.html>

[^12]: <http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html>;
    <http://www.nineplanets.org/pluto.html>

[^13]: <http://solarsystem.nasa.gov/planets/profile.cfm?Object=Pluto&Display=Overview>

[^14]: <http://seds.lpl.arizona.edu/nineplanets/nineplanets/pluto.html>

[^15]: Snow, Theodore P. (1996) \"The Outer Planets.\" In *The Dynamic
    Universe: An Introduction to Astronomy*. pp. 285. West Publishing
    Company. ;
    <http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html>

[^16]: <http://www.windows.ucar.edu/tour/link=/mythology/persephone_seasons.html>;
    <http://www.pantheon.org/articles/p/persephone.html>

[^17]: <http://www.pantheon.org/articles/c/charon.html>

[^18]: Sobel, Dava (2005) \"The Planets.\" pp. 220. Harper Perennial
    Publishing Company.


# Wikijunior:Solar System/Comets

{{/Coolfacts\|= 1\|\|=
2\|80px\|☄.svg "wikilink") Comet
Facts\|= 3\|

-   Comets are often described as giant \"dirty snowballs\" because they
    are mostly made up of ice and some dirt.
-   Comets have two \"tails\", one made up mostly of rocks and dust, the
    other mostly made of gas.
-   Comet tails always point *away* from the
    Sun.

}}

## What is a Comet?

!The Hale Bopp comet
Think of a comet as a big, dirty, gassy snowball. Comets are formed in
the ring of rocks, dust, and ice that orbits the
Sun beyond Pluto called
the Kuiper Belt. Comets form when rocks,
dust, and ice `<i>`{=html}condense`</i>`{=html} -- that is, join
together . As a comet grows larger, it starts to be pulled towards and
around the Sun. Comets in our Solar System usually take many years to go
around the Sun -- from a few dozen years to many thousands of years.
This is because they start to orbit the sun from very far away. They
make long, egg-shaped orbits around the Sun instead of almost circular
ones like the planets.\

## What does a Comet look like?

{{  }} !The strange surface of
Churyumov-Gerasimenko, a comet. Photograph taken by the Rosetta space
craft.
The comets that can be seen in the sky without telescopes are unusual
because they are the biggest and brightest comets of all. You might have
the chance to see one once or twice during your life. Most comets can
only be seen with a telescope. The few that can be seen with human eyes
are usually just hazy streaks or faint smudges in the night sky.

When comets are very far away from the Sun, they are covered in a
coating of icy, black rocks and dust. As a comet approaches the Sun,
however, the ice starts to melt. This creates large amounts of water and
gas that break through the coating, freeing some of the dust and rocks.
Sometimes this water, gas, rocks, and dust can be seen from the Earth as
one or two tails streaming away from the comet. Even when only one tail
can be seen, there are two, one made from the lighter gas and water, and
the other from the rocks, dust, and chunks of ice.

Comets themselves are usually between a few kilometres and several
hundred kilometres in size, but their tails can be several million
kilometres long.

## Seeing Comets in the Sky

The \"great comets\" that produce particularly spectacular tails are
some of the rarest objects in our solar system. Usually they can only be
seen about once every hundred years, so it is very rare to see one of
these comets. The last great comet appeared in 1910, but it may still be
another hundred years before another one comes near the Earth.
Astronomers can\'t predict exactly how or when they will appear as there
are still things about our Solar System that they don\'t understand. If
you hear about a comet coming into the sky soon, follow the instructions
below to watch it!

1.  Find out if the comet is going to be in your area of the sky.
2.  Get a telescope or binoculars and some chairs to view it. Many of
    the largest comets have never even needed a telescope to see them.
3.  Ask your parents to take you to a park, the woods or another dark
    place away from city lights.
4.  Look up into the sky and enjoy this amazing sight.

Usually the dust making up the comet\'s tail is so faint you can\'t see
it. However, when the Earth\'s orbit takes it through one of these
tails, the dust hits the Earth\'s atmosphere and burns up. These are the
recurring **meteor showers** that happen from time to time, and most
major meteor showers have now been identified either with an existing
comet or the remains of a comet that was observed earlier, usually in
previous centuries. When the Earth travels through this \"swarm\" of
dust left behind, you can see **shooting stars** or **meteors** at
night.

## How many Comets are there?

No one really knows. All comets spend most of their orbit so far away
from the sun that they can\'t be seen \-- even with a telescope.
However, every year amateur
astronomers1
discover over 100 never-seen-before comets that have come close enough
to be discovered2. As of November 2005,
astronomers have discovered 2 857 comets
3. Most of the
comets we see either crash into the Sun, or leave the Solar System
entirely. There might be millions of these comets that sooner or later
will come within range of our telescopes.

Of all the comets that have ever been seen, astronomers only expect 253
comets to ever return 4.

## How is a Comet named?

!Edmond Halley A comet is usually
named after the astronomer who first discovered it. When several people
are involved in its discovery, sometimes you will see multiple names on
a comet, like Comet Hale-Bopp, or Comet Shoemaker-Levy. It is generally
considered to be a great honor to have a comet named after you.\

## What are some famous Comets in history?

right\|thumb\|upright=1.5\|This diagram shows the orbit of Halley\'s
comet around the Sun. There are a few things to note about this orbit.\
\*It is much more elongated than a planet\'s orbit.\
\*It is not in the same plane as the planets.\
\*It goes round its orbit in the opposite direction. This is called
retrograde motion.\

-   Halley\'s Comet - Perhaps the most famous of all comets, and this
    was the first comet to be identified as a recurring comet.
-   Comet Encke - The second comet to be identified as a recurring
    comet.
-   Comet Shoemaker-Levy 9 - This was the first comet to have been
    observed hitting another body in the Solar System. In this case, it
    smashed into the planet Jupiter in what was possibly the most
    studied astronomical event in history.

## Do comets bring bad luck?

In ancient times people didn\'t have a very good understanding of what
comets really were or where they came from. They were seen as very
unusual objects in the sky, and very temporary in nature as well. In
some societies it was often a sign of bad events in the future when a
comet arrived, associated with the death of a king or a significant
military defeat. In other countries comets were considered to bring good
luck, bringing increased fertility and more food. The ancient Chinese
astronomers seem to have done the best job of actually recording when
comets appeared in the sky, and left detailed descriptions of what they
looked like and approximately where in the sky each comet was seen.

Even as recently as the 1910 appearance of Halley\'s Comet there was
widespread panic when it was discovered that the Earth might pass
through the tail of that comet. The panic was over the possibility of
gases from the comet flooding the atmosphere of the Earth with poison.
The reality was that there is so little gas in a comet tail that there
is no measurable effect in the content of the Earth\'s atmosphere when
an event like this occurs. Next Topic: Kuiper
Belt

## References

-   \"What is a comet?\"
    5
-   \"What does a comet look like?\"
    6
    7
    8
    9
-   \"Seeing comets in the sky\"
    10
    11
    12
-   \"How many comets are there?\"
-   \"How is a comet named?\"
    13
    14
-   \"Do comets bring bad luck?\"
    15


# Wikijunior:Solar System/Kuiper Belt

```{=html}
<div style="float:right;  border:2px solid #aaaaaa; width:250px; margin-left:0.2em; padding:0.4em">
```
**Kuiper Belt Facts**:

-   The Kuiper belt is the most recently discovered section of the Solar
    System.

```{=html}
</div>
```
Beyond the **orbit** of Neptune lies the Kuiper belt. It extends outward
an additional three billion kilometers away from the Sun. The belt
contains different-sized lumps of icy mixtures. These lumps are called
Kuiper belt objects. The biggest are called minor planets or dwarf
planets. The Kuiper belt may have formed when the gravity of the young
planet Jupiter hurled the objects out to where they are now. The Kuiper
belt is named after Gerard Kuiper (rhymes with \"viper\"), one of
several astronomers who hypothesized about a field of small objects
beyond Neptune.

### What are Kuiper belt objects?

The objects in the Kuiper belt are frozen mixtures of dirt, ice and
**organic compounds**. They are a lot like **comets**. Some of the
objects have a reddish color and others are gray. {{
 }}

### How big are the Kuiper belt objects?

Scientists consider Pluto to be one of the largest Kuiper belt objects.
It is 2390 km across and is a dwarf planet. The next largest known
Kuiper belt objects are Orcus, 2003 EL61 and 2005 FY9. Orcus is about
1600 km (1,000 miles) across; 2003 EL61 is 70% the size of Pluto and
2005 FY9 is about 50% to 70% of Pluto\'s size.

Recently, scientists found another dwarf planet named Eris that is even
bigger than Pluto. The scientists don\'t know its exact size, but they
think it is about 20% larger than Pluto. At the time it was found, it
was almost 100 times further away from the Sun than the Earth. It can
come about as close to the Sun as Pluto. Eris has a moon named Dysnomia.
The orbit of Eris is tilted almost 45 degrees compared to Earth\'s
orbit. Pluto\'s orbit is only tilted by 17 degrees.

Other large Kuiper belt objects about or over 1000 km across are
Pluto\'s moon Charon, Quaoar, Varuna, Ixion, 1996 TL66, 2002 TX300, 2002
TC302, 2002 UX25 and 2002 AW197. Ceres, the largest **asteroid** in the
asteroid belt, is about 950 km across.

There are many other Kuiper belt objects that are only a few kilometers
or tens of kilometers across.

### How many Kuiper belt objects are there?

Over a thousand Kuiper belt objects had been found by astronomers.
Scientists think that there might be more than seventy thousand large
objects in the Kuiper belt. Even though there are so many objects in the
Kuiper belt, it is very light, weighing between ^1^/~25~ and ^1^/~30~ of
Earth\'s mass.

### What is it named after?

After the first object in the belt other than Pluto and its moon Charon
was spotted from the Mauna Kea Observatory in Hawaii in 1992, the belt
was named after the astronomer Gerard Kuiper. Back in 1951 this
scientist wrote that he thought this belt might exist, but there was no
proof at that time. Other astronomers, including Frederick Leonard,
Kenneth Edgeworth, and Julio Fernandez, also thought that the belt
existed. For this reason some astronomers call it the Edgeworth-Kuiper
belt.

### What are the Kuiper belt objects named after?

When an object is discovered in space, it is given a temporary name
called a \"provisional designation\". This temporary name begins with
the year the object was discovered, followed by some letters and numbers
that tell in what month and in what order it was discovered. Later on,
important objects are given formal names, often taken from mythology.

The Kuiper belt objects Orcus, Charon, and Varuna were all named after
mythological gods of the underworld. Ixion was named after a
mythological person in the underworld. Quaoar was named after a creation
god of the Native American Tongva people.

Next Topic: Oort Cloud

de:Wikijunior Sonnensystem/
Kuipergürtel


# Wikijunior:Solar System/Oort Cloud

{{/Coolfacts\|= 1\|\|= 2\|Oort cloud
Facts:\|= 3\|\* The Oort cloud is as far from the Sun as you can go
without leaving the Solar System.

-   It is believed that most comets originate in the Oort cloud before
    \"falling\" toward the Sun.

}} The Oort cloud is a huge halo made of millions of comets that lies at
the outermost edge of the Solar System.

## What is the Oort Cloud?

Scientists say there is a distant group of objects, made of rock and
ice, that forms a cloud-like region surrounding our Solar System. It is
a cloud of comet-like objects orbiting far away from the Sun. Even
though the comets are very widely scattered from each other, there many
millions of them. The total mass of all these comets may be up to 100
times the mass of the Earth. The Oort Cloud is named after a Dutch
astronomer Jan Oort who took the
original idea, improved upon it and made it widely known.

!This diagram shows about how far away the Oort cloud might be compared
to the planets of the Solar System. Start in the upper left frame, then
follow the pictures clockwise. Each picture shows a bigger volume of
space.{width="350"}

As a comet makes several passes through the solar system, the Sun slowly
melts and vaporizes the ice and only little bits of solid debris are
left behind. But if the comets are all destroyed when they pass through
the system, then new comets will need to appear. Otherwise we would not
see any more comets. Jan Oort used the idea of the Oort cloud to explain
why new comets keep appearing.

## Where is the Oort Cloud?

If you can imagine the distance from the Earth to the Sun, then the
comets in the Oort cloud are 50,000 to 100,000 times further away! That
is 1,000 times further away from the Sun than is Pluto, and about one
fourth the distance to the nearest neighboring star---Proxima Centauri.
Light takes a year to travel from the Sun to the outer edge of the Oort
Cloud.

{{  }}

## How did the Oort Cloud start?

The Oort cloud objects may have started closer to the Sun during the
Solar System\'s formation. When they passed near the gas giants, the
gravity of those planets hurled the objects into very distant orbits.
The Oort cloud objects were sent in all directions, making the Oort
cloud ball-shaped instead of disk-shaped. The gravity of passing stars
also made the orbits of these objects more circular, and pulled them
further from the Sun. But sometimes the gravity of other far away stars
can send the objects hurtling back toward the Sun. These become the
comets.

## What objects are in the Oort Cloud?

An object named Sedna has been discovered that may belong to the Oort
Cloud (although it is actually between the Kuiper Belt and the Oort
Cloud.) It is from 1,180 to 1,800 km across. Its orbit stretches from 76
to 928 times further from the Sun than does the Earth\'s. Sedna orbits
the Sun about once every 11,250 Earth years. The last time Sedna was
where it is now in its orbit, Earth\'s last Ice Age was ending! Some
scientists think that Sedna should be included in the Kuiper Belt,
making the belt bigger.

Next Page: Glossary

de:Wikijunior Sonnensystem/ Oortsche
Wolke


# Wikijunior:Solar System/Space exploration

## Space exploration --- A long dream

!An illustration of a spacecraft in *From the Earth to the
Moon*
Going into space was always one of the biggest dreams people had, even
thousands of years ago. Many science fiction authors wrote about
traveling in space even before the first airplane flight in 1903. One of
the most famous science fiction books on space travel is *From the Earth
to the Moon* by Jules Verne --- it was written in 1865, more than one
hundred years before the first person walked on the moon. Jules Verne\'s
idea was to use a giant cannon! That might seem silly today, but it
shows how much our ideas on space travel have changed.

## The first exploration of space

!Laika: the first space
traveller Space
begins about 100 km or 62 miles above the earth. A more realistic way to
travel in space is with a **rocket**. Within a rocket is a controlled
explosion. However, exhaust (things left over after burning) is only
allowed to leave the rocket in one direction. As a result, the rocket is
pushed in the other direction. In 1942, the German rocket *A-4* became
the first to reach that height, but it wasn\'t meant to do anything but
fall straight down again and so wasn\'t terribly useful. Still, it was
an advance in rocket technology.

The Soviets were the first to put anything in space that would stay up:
they launched the *Sputnik 1* satellite on October 4, 1957. Within a
month, the Soviets launched *Sputnik 2*, and in that spacecraft was the
first space traveler: a dog called Laika.

The launch of the *Sputnik* started the Space Race, a competition
between the United States and the Soviet Union to obtain more and more
advanced space technology. Americans were very surprised that the
Soviets could have launched \'Sputnik\', and began to design rockets and
satellites of their own. The race would last for the next few decades.

## A man in Space

!Yuri Gagarin_-_Restoration.jpg "Yuri Gagarin") On
April 12, 1961, the first person was sent into space: Yuri Gagarin, a
Soviet, riding in the spacecraft *Vostok 1*. The Soviets would send more
people into space over the next few decades, and so would the Americans,
but it wouldn\'t be until 2003 that a different country would launch
their own spacecraft with a person in it: China, with the *Shenzhou 5*.

## The race to the moon

!An Astronaut on the
Moon. At
the beginning of the 1960s, American president John F. Kennedy made a
famous speech in which he said that the U.S. was going to send people to
the moon within the next 10 years. And that\'s what happened: in July of
1969, Neil Armstrong stepped off the there spacecraft and said \"One
small step for \[a\] man and one giant leap for mankind\". He and Buzz
Aldrin walked on the moon where they put an American flag. Their
footprints are still there because there is no wind or water on the Moon
to wash them away.

## The Space Shuttle

!Launch of a space
shuttle.

After the Apollo program that sent people to the Moon, the U.S. built
the Space Shuttle, that is like a jet-plane that can go to space and
return (with the help of rockets of course)! The Space Shuttle helped to
construct the ISS (International Space Station) among another things.

The last space shuttle mission was on June 28, 2011, but it will be
replaced with new vehicles that will take mankind to the Moon, Mars, and
beyond!

## Spaceships of the future

Right now, spaceships are not very efficient. The Saturn V rocket was
363 feet or nearly 111 meters tall, and it could only take people to the
moon! To get people further, better rockets must be invented. One of the
most popular ideas for a rocket is the **antimatter** rocket. This type
of rocket collides a small amount of **antimatter** with an equal amount
of normal **matter** to create a large amount of energy!

Other ideas for going into space, that do not need rockets, have been
thought of by scientists and astronomers. One of these is a space
elevator. A space elevator is basically a big lift into space. It will
cost a lot less to get things up into space if a space elevator is
built. !Is this what space travel will look like in the
future?
Another idea, a bit like the Jules Verne idea, is an electromagnetic
catapult. This catapult works by accelerating the spaceship along a
rail, similar to a maglev train. Unfortunately, the air on Earth would
set spaceships on fire as they launched, but scientists aren\'t thinking
of putting one there: one could go on the Moon! The catapult on the moon
could send metal and other resources to Earth\'s orbit, where a space
station could collect them.

## Exploration beyond the Solar System

Many people dream of the day when humans can travel to another star and
explore other worlds, some people wonder what\'s out there some belive
that aliens or other life may live on another plant. But, if this ever
does happen probably won\'t happen for a very long time. The stars are
so spread out that there are trillions of miles between stars that are
\"neighbors\". Maybe one day, your great grandchildren will be standing
atop an alien world wondering about their ancient ancestors?

## The eye beyond Earth

!The Hubble Telescope as seen by the space
shuttle.
Many people say the very best invention ever (not just in space
technology) was the Hubble space telescope (HST). Others say it\'s just
the space station being selfish having the best technology in the world.

The Hubble Space telescope is a giant telescope that is in orbit around
the Earth. Because there is no atmosphere, the Hubble Space Telescope
has a clear view of even distant galaxies. One of the pictures the
Hubble space telescope has made is called the \'Hubble Deep Field\'. The
Hubble Deep Field is a picture of some of the most distant galaxies, and
it gives a snapshot of what the universe looked like when it was
younger. !A futuristic space telescope planned for the year
2021.
Even bigger telescopes are also in the planning, so we might be able to
see right to the edge of the universe some day soon.

de:Wikijunior Sonnensystem/
Raumforschung


# Wikijunior:Solar System/Puzzles

### Crypto Quiz

Try to fill in the correct answer for each of the questions below. A
letter should go on each blank line. The numbers underneath the lines
match the entries in the secret message. What does it say?
![](Solar_System_Crypto_Quiz.png "Solar_System_Crypto_Quiz.png"){width="600"}

### Photo Word Scramble

Each of the names of the pictures below have been scrambled. Can you
unscramble the letters to find the correct names?
![](Solar_System_Word_Scramble.png "Solar_System_Word_Scramble.png"){width="400"}

### Word Find

Each of the words except one in the list to the right can be found along
a row, column, or diagonal somewhere inside the box below. See if you
can find which one is missing by finding all the others.
![](Solar_System_Word_Find.png "Solar_System_Word_Find.png"){width="600"}


# Wikijunior:Solar System/Glossary

{{  }}

A glossary of words used in this book:

-   **Antimatter**: the opposite of normal matter. Not usually found
    outside of a laboratory. When mixed with matter they cancel each
    other out and release lots of energy.

```{=html}
<!-- -->
```
-   **Arachnoid**: a scientific term for something shaped like a spider,
    like the legend of the weaving contest.

```{=html}
<!-- -->
```
-   **Asteroid**: a large rocky object that orbits a star, but is too
    small to be a planet. It is found in space.

```{=html}
<!-- -->
```
-   **Astronomer**: a person who studies stars and planets. Also a
    person who explores new planets and solar systems.

```{=html}
<!-- -->
```
-   **Astronaut**: a person who travels beyond the atmosphere of the
    Earth.

```{=html}
<!-- -->
```
-   **Atmosphere**: a layer of gases around a planet.

```{=html}
<!-- -->
```
-   **Atom**: a very tiny particle that is the basic building block of
    matter. It is the tiniest thing on Earth.

```{=html}
<!-- -->
```
-   **Basalt lava**: molten basalt, a kind of rock from a volcano.

```{=html}
<!-- -->
```
-   **Belt**: A name used for bands of dark-colored cloud layers on
    Jupiter.

```{=html}
<!-- -->
```
-   **Binoculars**: a folding pair of small telescopes with an eyepiece
    for each eye.

```{=html}
<!-- -->
```
-   **Carbon dioxide**: a gas that animals breathe out and plants take
    in.

```{=html}
<!-- -->
```
-   **Carbonaceous chondrite**: A type of meteorite that contains a lot
    of water and organic compounds.

```{=html}
<!-- -->
```
-   **Centaur**: an icy planetoid that orbits the Sun between Jupiter
    and Neptune.

```{=html}
<!-- -->
```
-   **Channel**: a groove in the surface of something.

```{=html}
<!-- -->
```
-   **Comet**: a small icy object orbiting a star.

```{=html}
<!-- -->
```
-   **Conjunction**: when two objects orbiting the same body come
    closest together.

```{=html}
<!-- -->
```
-   **Continent**: a huge landmass on a planet, usually made of tectonic
    plates that have locked together.

```{=html}
<!-- -->
```
-   **Convection**: a type of movement in a gas or liquid that carries
    heat toward a cooler location. When the gas or liquid cools, it
    sinks back down again.

```{=html}
<!-- -->
```
-   **Core**: the center of a planet or star.

```{=html}
<!-- -->
```
-   **Corona**: a region of very hot gas that surrounds the photosphere
    of a star.

```{=html}
<!-- -->
```
-   **Crater**: a dent in a planet\'s surface made by a meteorite
    falling on it.

```{=html}
<!-- -->
```
-   **Crust**: the outermost layer of a planet\'s surface.

```{=html}
<!-- -->
```
-   **Dwarf planet**: a rounded body that is in orbit around the Sun. It
    is not a moon and it is not big enough to sweep up the other objects
    along its orbit.

```{=html}
<!-- -->
```
-   **Eclipse**: the shadow made when one object comes between another
    object and the Sun.

```{=html}
<!-- -->
```
-   **Energy**: what you use to do work.

```{=html}
<!-- -->
```
-   **Environment**: the conditions on a planet.

```{=html}
<!-- -->
```
-   **Equator**: an imaginary line around a planet, perpendicular to the
    axis of rotation.

```{=html}
<!-- -->
```
-   **Erosion**: the slow wearing away of a
    surface, usually from wind, water, and temperature changes.

```{=html}
<!-- -->
```
-   **Galaxy**: a huge mix of gas, dust, stars, planets and other
    objects that are held together by their own gravity.

```{=html}
<!-- -->
```
-   **Gas giant**: one of the four outer planets made out of giant balls
    of gas.

```{=html}
<!-- -->
```
-   **Gravity**: the force that pulls on anything with mass (see the
    About gravity, mass, and
    weight
    section).

```{=html}
<!-- -->
```
-   **Hemisphere**: one half of a planet\'s surface.

```{=html}
<!-- -->
```
-   **Ice cap**: A huge body of ice at the pole of a planet.

```{=html}
<!-- -->
```
-   **Lagrange point**: the places where
    the gravity from two orbiting objects balance each other.

```{=html}
<!-- -->
```
-   **Lava**: molten rock above a planet\'s surface.

```{=html}
<!-- -->
```
-   **Latin**: the language of the Roman Empire that was later used by
    scientists to name things.

```{=html}
<!-- -->
```
-   **Mantle**: a layer of molten rock below a planet\'s crust.

```{=html}
<!-- -->
```
-   **Maria**: a large sea of magma that has cooled into solid rock.

```{=html}
<!-- -->
```
-   **Mass**: the amount of matter that something is made of (see the
    About gravity, mass, and
    weight
    section).

```{=html}
<!-- -->
```
-   **Matter**: a scientific word for \'stuff\'.

```{=html}
<!-- -->
```
-   **Meteor**: a small or medium-size rock from space that has entered
    a planet\'s atmosphere but has not reached the ground.

```{=html}
<!-- -->
```
-   **Meteor shower**: a large number of meteors that enter a planet\'s
    atmosphere at about the same time.

```{=html}
<!-- -->
```
-   **Meteorite**: A meteorite that made it through a planet\'s
    atmosphere and landed on the ground.

```{=html}
<!-- -->
```
-   **Methane**: a gas that makes up most of the gas giants.

```{=html}
<!-- -->
```
-   **Near Earth asteroid**: an
    asteroid that has an orbit that brings it very close to the earth.

```{=html}
<!-- -->
```
-   **Newton**: a unit of measurement the describes how hard gravity is
    pulling you down (see the About gravity, mass, and
    weight
    section).

```{=html}
<!-- -->
```
-   **Observatory**: A special building where astronomers keep their
    telescopes ready for use.

```{=html}
<!-- -->
```
-   **Orbit**: the path that an object takes around a larger object.

```{=html}
<!-- -->
```
-   **Orbit System**: a planet and its moons rotating around a star.

```{=html}
<!-- -->
```
-   **Organic compounds**: compounds (collections of atoms) containing
    carbon.

```{=html}
<!-- -->
```
-   **Phase**: how a planet or moon looks to us at some part of its
    orbit, when it is lit by the Sun.

```{=html}
<!-- -->
```
-   **Planet**: the celestial body that has a greater mass than all
    other objects of the same orbit system together and that describes a
    well-defined, special orbit around a star.

```{=html}
<!-- -->
```
-   **Planetary nebula**: a great cloud of gas that was blown off by an
    old star.

```{=html}
<!-- -->
```
-   **Photosphere**: the layer of a star that releases light and other
    energy into space.

```{=html}
<!-- -->
```
-   **Prominence**: an eruption of hot gas at the surface of the Sun.

```{=html}
<!-- -->
```
-   **Provisional designation**: a temporary name given to a newly-found
    object. Later a permanent name may be picked.

```{=html}
<!-- -->
```
-   **Radar**: radio waves used to find distances to and make maps of
    things.

```{=html}
<!-- -->
```
-   **Regolith**: loose soil on the Moon created by rocks hitting the
    surface at very high speed.

```{=html}
<!-- -->
```
-   **Retrograde motion**: a rotation that is the opposite way from the
    rotation of most of the Solar System.

```{=html}
<!-- -->
```
-   **Retrograde orbit**: an orbit that is the opposite way from the
    orbit of most of the planets and moons in the Solar System.

```{=html}
<!-- -->
```
-   **Ring**: A flat, circular band of many small, loose objects that
    orbit a planet.

```{=html}
<!-- -->
```
-   **Rotate**: to spin around on an axis.

```{=html}
<!-- -->
```
-   **Satellite**: an object in a stable orbit around a much larger
    object.

```{=html}
<!-- -->
```
-   **Scarp**: a type of cliff.

```{=html}
<!-- -->
```
-   **Sidereal day**: the time for a planet or moon to rotate so that a
    distant star overhead is again overhead.

```{=html}
<!-- -->
```
-   **Silicate**: an object composed mostly of
    the element silicon, which makes rocks.

```{=html}
<!-- -->
```
-   **Shooting star**: another name for a meteor.

```{=html}
<!-- -->
```
-   **Solar day**: the time for a planet or moon to rotate so that the
    Sun is again overhead.

```{=html}
<!-- -->
```
-   **Solar wind**: a very hot gas that is being blown away from the Sun
    at a high speed.

```{=html}
<!-- -->
```
-   **Spacesuit**: A special sealed suit that protects an astronaut. It
    has its own air supply so the astronaut can breath, and is insulated
    against the cold of space.

```{=html}
<!-- -->
```
-   **Spectrum**: the colored band of light made when white light passes
    through a prism.

```{=html}
<!-- -->
```
-   **Star**: a huge ball of gas that is so heavy that it causes nuclear
    reactions inside itself. This produces heat and light.

```{=html}
<!-- -->
```
-   **Sulfuric acid**: a strong type of acid that is used in car
    batteries, and contains the element sulphur.

```{=html}
<!-- -->
```
-   **Supergiant**: a star near the end of its life that puffs out into
    a huge body many times larger than a normal star.

```{=html}
<!-- -->
```
-   **Surface area**: the area on the outside of something.

```{=html}
<!-- -->
```
-   **Tectonic Plate**: a solid part of
    the crust that very slowly moves across the surface of a planet

```{=html}
<!-- -->
```
-   **Telescope**: a system of lenses or mirrors that are used to see
    distant objects.

```{=html}
<!-- -->
```
-   **Terrestrial planets**: the four planets closest to the Sun.

```{=html}
<!-- -->
```
-   **Tether**: A cord that is used to keep two things attached to each
    other, such as an astronaut to a spaceship.

```{=html}
<!-- -->
```
-   **Tide**: the rise in the surface caused by gravity from another
    object, such as the Moon or Sun.

```{=html}
<!-- -->
```
-   **Tidal lock**: when tides have slowed rotation so that a moon or
    planet is always facing the same side toward the planet or star.

```{=html}
<!-- -->
```
-   **Transit**: When astronomers observe one object pass in front of a
    larger object.

```{=html}
<!-- -->
```
-   **Trojan asteroid**: an asteroid in
    the same orbit as a planet or moon that always stays the same
    distance ahead or behind.

```{=html}
<!-- -->
```
-   **Volcanic**: something that relates to volcanoes.

```{=html}
<!-- -->
```
-   **Volume**: the size of a three-dimensional object.

```{=html}
<!-- -->
```
-   **White dwarf**: a star that has run out of fuel to burn and is
    slowly cooling off.

```{=html}
<!-- -->
```
-   **Zone**: A name used for bands of light-colored cloud layers on
    Jupiter.

it:Wikijunior Il sistema
solare/Glossario
de:Wikijunior Sonnensystem/
Glossar
fr:Wikijunior:Système
solaire/Glossaire


# Wikijunior:Solar System/Test

## Task 1: The Solar System

Below are the eight planets of our solar system, each with a
description. Fill in the blanks in the descriptions.

-   First you have to fill in which planet it is from the sun. For
    example: if you think Jupiter is the seventh planet, fill in *7th*.
-   Secondly you have to fill in if the planet is bigger or smaller than
    Earth. The bigger/smaller question for Earth is about the moon!

  --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  !Venus is the **2nd** planet of our Solar System and it\'s **smaller** than Earth.{width="90"}   !Earth is the **3rd** planet of our Solar System and the moon is **smaller** than Earth.{width="90"}   !Jupiter is the **5th** planet of our Solar System and it\'s **bigger** than Earth.{width="90"}   !Saturn is the **6th** planet of our Solar System and it\'s **bigger** than Earth.{width="90"}   !Neptune is the **8th** planet of our Solar System and it\'s **bigger** than Earth._flatten_crop.jpg "Neptune is the 8th planet of our Solar System and it's bigger than Earth."){width="90"}   !Uranus is the **7th** planet of our Solar System and it\'s **bigger** than Earth.{width="90"}   !Mercury is the **1st** planet of our Solar System and it\'s **smaller** than Earth.{width="90"}   !Mars is the **4th** planet of our Solar System and it\'s **smaller** than Earth.{width="90"}
  --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

*8 points can be earned with this task. Every wrong sentence reduces the
score by 1.*

## Task 2: About the planets

*8 points can be earned with this task. Every right answer gives 1
point.*

## Task 3: Other astronomical objects

Dependent on the previous question:

Dependent on the previous question:

*8 points can be earned with this task. Every right answer gives 1
point.*

## Task 4: Glossary

Define these terms.

*8 points can be earned with this task. A wrong or bad description gives
0 points, a reasonable description gives 1 point, a good description
gives 2 points.*

## Task 5: Space Flight

*8 points can be earned with this task.*

nl:Wikijunior:Zonnestelsel/Eindtoets


# Wikijunior:Solar System/How the Solar System was born

Our **solar system** is part of an entity called our **universe**. There
were many attempts made in the past to explain how our solar system and
universe came into existence as we observe it today. Most scientists use
the **Big Bang Theory**, though some people have other theories.

## Big Bang Theory

This theory is based around the idea that an enormous explosion occurred
about 13.7 billion years ago. That is 13,700,000,000 years ago. This is
three times the age of Earth! The Big Bang was not a usual explosion in
space because space and time themselves were made in the explosion. This
explosion caused the formation of the matter and energy in the universe.
At first, the universe was very hot. The planets, stars and all other
heavenly bodies formed starting some time after the Big Bang after the
universe had cooled down.

The universe had been expanding and cooling since the Big Bang. Most
galaxies are moving further away from our Milky Way galaxy. The
exceptions are the few galaxies that are close enough to the Milky Way
for gravity to overcome the universe\'s expansion.

Scientists can still see the faint light from when the universe was hot.
Over time, the universe\'s expansion stretched out the light, turning it
into weak microwave light. Scientists can detect this microwave light.

## Milky Way Galaxy Formation

## Solar System Formation

The solar system formed out of a big cloud of gas and dust about 4.6
billion years ago.

thumb\|250px\|Eagle Nebula (M16) - Birth of New
Stars

Stars and solar systems that are very similar to the Sun are now forming
in the Eagle Nebula (also known as M16). While this is not a picture of
our own sun, it can give you an idea of what our solar system looked
like billions of years ago. These gas clouds that you see in this image
were formed from earlier stars that exploded and left stuff behind.

Small finger-like parts of these clouds, especially at the \"top\" of
the first column on the left, are the new stars that are forming.
Astronomers who have been watching these stars form have seen changes
happen in just a few years, which is a very rapid change for the life of
a star. Over many millions and billions of years, these stars and any
planets formed with them will look like our Solar System today.

What astronomers think happened after this initial period when the Sun
was created from these huge gas clouds, there were many small and large
rocks that gradually came together because of gravity and formed the
planets, moons, asteroids, and comets that we know about today. Many of
the craters which can be found on the Moon were made when these rocks
came crashing on to the surface.

While the number of small rocks and other stuff from the early history
of the solar system is now less than what it was like right after the
Sun formed, the space between the planets still has many of these rocks,
and they continue to form craters and even come into the Earth\'s
atmosphere. When you see these rocks at night, they are known as either
**Shooting Stars** or **Meteorites**. By watching these items come to
the Earth, you are directly witnessing the process that created the
Earth in the first place.


# Wikijunior:Solar System/What will happen to the Solar System in the future

## The Fate of Our Solar System

Just as the Solar System relies on the Sun as its source of energy, so
too is its fate linked to that of the Sun.

The Sun is right now a middle-aged star. It has existed for about 5
billion years, and will go on shining, pretty much unchanged, for about
another 5 billion more. At that time, it will go through major changes
that will bring an end to the Solar System as we know it. To understand
these changes, we must first understand where the Sun\'s energy comes
from.

## The Power of Fusion

Like all stars, the Sun is made mostly of hydrogen. This is the simplest
of all atoms. Because the Sun is so large and its gravity is so strong,
the hydrogen atoms near the center of the Sun - at its core - are under
extreme pressure, and are squeezed very close together. Sometimes, four
of these atoms are squeezed so tightly together that they collide with
enough force to stick together permanently, forming a new, larger, and
more complex atom: helium. This process is called **nuclear fusion**,
and when it happens, a small amount of energy is released in the form of
heat and light. Due to the massive size of the sun, those small amounts
of energy add up to an enormous amount and nuclear fusion is what powers
the Sun. (The energy output at the sun\'s core per cubic meter is about
the same as common reptiles, so it IS size that matters here!)

## Out of Gas

Eventually, the Sun will burn all of the hydrogen in its core, and the
fusion will stop. Once this happens, the core will shrink under its own
gravity, until it becomes so dense that the helium atoms will begin to
collide to form carbon (from three helium atoms) and oxygen (from four
helium atoms). These collisions produce much more energy than the
hydrogen fusion that powers the Sun today.

The extra energy will cause big changes in the Sun. The core will become
much hotter, causing the Sun to swell to over one hundred times its
present size, swallowing up the planets Mercury and Venus. Even though
the core will be hotter, the surface will be cooler than it is today,
changing in color from yellow to red. A star at this stage is called a
**red giant**.

What about here on Earth? When the Sun expands, the Earth will not be
spared. Like Mercury and Venus, Earth will probably be absorbed by the
expanding Sun. But even if it is not, it will be no place to live. The
oceans will boil, and the atmosphere will be blown away. What is left
will be a charred, barren cinder, unable to sustain life.

## An Unstable Ending

!A Planetary
Nebula{width="320"}Meanwhile,
the helium-burning reaction in the Sun will produce **solar wind** much
stronger than it is today. As it leaves the Sun\'s surface, it will
carry with it some of the hydrogen in its outermost layers, forming a
**planetary nebula**.

As more matter is carried away from the Sun, the solar wind will
continue to strengthen. Eventually, it will blow away so much of the
Sun\'s matter that there will no longer be enough pressure at the core
to keep the helium fusion going. At that point, what\'s left of the Sun
will contract under its own gravity, becoming a much smaller, very dense
star called a **white dwarf**. The white dwarf will radiate off heat
that is left over from the earlier nuclear fusion, but it will no longer
generate any new energy.

## A New Beginning

But will this really be the end? As bleak as this future might sound,
there is a silver lining. All of that matter blown away from the Solar
System during will eventually be compressed again by gravity, along with
the remains of other long-gone stars, into a cloud of gas and dust much
like the one that gave birth to our Solar System. In this cloud, many
new stars will form with planets of their own, and just possibly, some
of these planets may one day produce living beings who will look at the
sky and wonder: where did we come from?


# Wikijunior:Solar System/Is there life out there?

The short answer is \"Nobody knows\" - but it\'s interesting to try to
make some guesses based on what we **do** know!

Scientists who have tried to make good guesses use an equation called
\'The Drake Equation\' which was named after Doctor Frank Drake who
first tried to work this out about forty years ago. The idea is that if
you know how likely it was for life to form on Earth - and if you know
how many planets there are that are more or less like the Earth - then
you can make a good estimate of how much life there is out there.

We can try to do that ourselves.

### How many stars are there in the Universe?

When you look up at the sky on a really dark night - far from the lights
of cities and roads, you can see about five thousand stars and four or
five planets. But nearly all of the stars and planets out there are far,
far away and much too dim to see.

We know that there are eight planets orbiting the Sun and that our sun
is a lot like the other stars out there in our galaxy. Our galaxy (which
we call \"The Milky Way\" because it looks like a splash of milk across
the night sky) has about three hundred **billion** stars in it. But the
Milky Way is a rather small galaxy and there are many, many other
galaxies.

With our very best telescopes we can see about a hundred billion
galaxies. With a hundred billion galaxies - each one with hundreds or
even thousands of billions of stars - astronomers calculate that there
are about fifty thousand, billion, billion stars in the part of the
universe that we can see! That\'s a big number. Written out in numbers
it\'s 50,000,000,000,000,000,000,000 stars!

### Do all of those stars have planets?

Well, it\'s rather hard to tell for sure - but astronomers have looked
carefully at some of the stars in our neighborhood and whilst planets
that are orbiting other stars are too small to see - even with our very
best telescopes, we can sometimes see a slight wobble in the light
coming from a star that is caused by the gravity of one or more planets
that are orbiting it.

Knowing that, we have found that many nearby stars have at least a few
planets that are big enough to wobble the lights from the star enough so
we know they are there. There are probably other planets too small to
produce a big enough wobble for us to measure - so we don\'t know
exactly how many planets to expect. But it seems that there are probably
more planets than stars in the universe, so there could easily be
50,000,000,000,000,000,000,000 planets for life to try to get started
on. That\'s a lot of places and we haven\'t counted moons, asteroids,
comets and dust clouds!

### How often does life actually get started on one of these planets?

This something we can really only guess at. We know that life formed
once on one planet because we are that life and we live on that planet -
but how do we know whether the Earth is just an amazingly special place
or whether there are Earth-like planets orbiting most of the stars in
the sky? Unfortunately, we don\'t know.

-   Many planets must be too hot - like Venus and Mercury in our own
    solar system. Life can\'t survive there because the chemicals that
    life needs don\'t work properly when things are that hot.
-   Other planets might be too cold - so there would not be enough
    sunlight for plants and animals to use as energy. The outer planets
    of our Solar system - Pluto and Neptune - must be far too cold for
    life to exist there.
-   It\'s possible that planets might not have the right mixture of
    life-giving chemicals. There is no life on our Moon because it has
    no atmosphere - in daytime it\'s too hot and at night too cold.
-   Other planets may form and then be destroyed before life has had
    time to form - and on others, life might have formed a long time ago
    and then died out for some reason,

But there are plenty of planets to choose from. Next time you are on a
beach or at a playground with a sand lot, take a handful of sand. There
are an awful lot of tiny sand grains in a fistful of sand - but there
are more stars and planets than there are grains of sand on all the
beaches of all the world! Surely they can\'t all be too hot, too cold,
too dry or too poisonous?

But we humans haven\'t yet looked closely enough in enough places where
life might be to really know for sure what life needs. We\'ve found
bacteria living in boiling hot water near underwater volcanoes. There
are tiny worms who live in the ice near to the South Pole. Bacteria have
been found living inside rocks in the deepest mine shafts. There is
hardly anywhere on earth where live can\'t survive somehow. Astronauts
from Apollo 12 who visited the moon in 1969 visited the Surveyor III
lander that had been sitting on the moon for more than two years. They
found that bacteria that had hitched a ride on Surveyor when it was
launched and were still alive after two years of living on the moon!

It seems then that life can survive and even prosper in some fairly
hostile places - this shows that a planet may not have to be a
comfortable place for humans in order to develop life. However, there
doesn\'t seem to be any native life on the Moon beyond what humans have
put there by accident and our robotic missions haven\'t found life on
Mars or Venus or any of the comets we\'ve looked at closely.

With at fifty thousand billion billion planets in the universe, even if
each planet only had a one in a trillion chance of having life, there
could still be billions of planets teeming with life out there in the
universe. But if the chances are that bad then we might be alone in our
galaxy with the nearest other creatures living hundreds of millions of
light years away. Even if the odds for life are only a million to one
for each planet, we humans and our robots might have to travel for
thousands of years and search millions of planets and moons before we\'d
find them.

### So how many aliens are there?

That is where the drake equation comes into play:

`<big>`{=html}`<big>`{=html}R^\*^ × f~p~ × n~e~ × f~l~ × f~i~ × f~c~ × L
= The number of alien civilisations that we can talk to in our
galaxy`</big>`{=html}`</big>`{=html}

This equation might look complicated, but it\'s actually quite simple
when you understand it.

R^\*^ is how many stars appear a year. So, for example, if there was 10
stars being made every year, then you could scrible out R\* and put at
\'10\' there instead.

f~p~ is the chances that a star has planets. If, on average, there was a
1 in 2 chance that each new star had a planet, then the number that
replaced f~p~ would be 0.5 (1÷2).

n~e~ is the number of planets in each solar system that can have life.
In our solar system, n~e~ would be 1, because we only have one planet
that we know has life on it, Earth.

f~l~ is the chances that these planets have life. If all planets that
could have life have life, then 1 would go in the place of f~l~

f~i~ is the chances that the life on these planets is clever. A 1 in a
hundred chance of life would give us 0.01, 1÷100.

f~c~ is the chance that they will be able to talk to us. This number
might be 1 (100%), because if they are clever they will eventually find
out how to talk to other planets.

Finally, L is how long each alien civilisation will live (or want to
talk to us), in years. Though nobody knows the real value of this, Frank
Drake guessed 10,000 years.

Now, we can multiply them all together. 10×0.5×1×1×0.01×1×10000 = 500
alien civilisations in our galaxy. The values here are just guesses,
though, and other guesses have ranged from only one civilisation in our
galaxy to thousands.

### Little Green Aliens

If so many planets in the universe does this mean that we should expect
little green aliens to be popping out of their flying saucers soon?
Well, perhaps not. For beings living in another galaxy outside of the
Milky Way, if they noticed that we are here and set out to visit us -
traveling at the speed of light, they still wouldn\'t get here for
another 300 million years! They couldn\'t have set out millions of years
ago to visit us because humans haven\'t been on around for nearly that
long.

If we\'re going to be visited by aliens, they\'d have to live on a
nearby star and know how to fly very fast to get here. That means that
if we are to meet alien cultures they must come from within the very few
stars that are within a reasonable travel time. Life would have to be
very common indeed for there to be intelligent beings close enough to
meet us face-to-face.

### SETI - The Search for Extra-Terrestrial Intelligence

One group of scientists are searching for other intelligent life in our
galaxy by listening to the radio. With large radio telescopes they sweep
the stars looking for radio signals with interesting patterns in them
that would not come from natural radio sources. So far, they haven\'t
found anything - but that may mean that they have to keep on looking -
or it might be that the aliens are not transmitting anything in our
direction with enough power for SETI\'s sensitive radio telescopes to
pick up.

### Panspermia - Life from Space?

One other possibility is that life didn\'t just appear on Earth at all.
If life were really common throughout the universe, it\'s possible that
life arrived on Earth after it developed somewhere else. We know that
meteorites found on Earth have come here from the Moon and from Mars -
and probably from other planets too. We also know that debris in the
form of little bits of rock and ice rain down on the Earth from space
all the time. If life existed in that debris when the Earth was young,
there is a good chance that we Earthlings originally came from some
other planet entirely. It could be that all life on Earth originated on
Mars and we are the alien invaders!

### So what **IS** the answer?

We still don\'t know for sure that there is life anywhere beyond the
earth, and even if life were common in the universe, we don\'t know
whether we\'d ever be able to find it if there was.

The search for life beyond Earth is a very new thing. Humans have only
been searching for about 40 years - and we\'ve only been looking in the
most likely places for 10 years. If we humans are going to find signs of
life outside the Earth, it will probably happen in your lifetime. You
may one day be amongst the first humans to encounter alien life or to
hear a message from another world through SETI!


# OpenSSH/Overview

The OpenSSH suite provides secure remote
access and file transfer. Since its initial release, it has grown to
become the most widely used implementation of the SSH protocol. During
the first ten years of its existence, ssh has largely replaced older
corresponding unencrypted tools and protocols. The OpenSSH client is
included by default in most operating system distributions, including
MacOS, Linux, BSD, AIX and Solaris. Any day you use the Internet, you
are using and relying on dozens if not hundreds of machines operated and
maintained using OpenSSH. A survey in 2008 showed that of the SSH
servers found running, just over 80% were OpenSSH. [^1]

OpenSSH was first released towards the end of 1999. It is the latest
step in a very long and useful history of networked commuting, remote
access and telecommuting.

## History of OpenSSH

The first release of OpenSSH was in December 1999 as part of OpenBSD
2.6. The source code was originally derived from a re-write of the last
available open version, ssh 1.2.12 specifically, of SSH[^2]. SSH went on
to become Tectia SSH.

Ongoing development of OpenSSH is done by the OpenBSD group. Core
development occurs first on OpenBSD, then portability teams bring the
changes to other platforms. OpenSSH is an integral part of as good as
all server systems today and a good many network appliances such as
routers, switches and networked storage. The first steps were in many
ways the biggest.

### The Early Days of Remote Access

Some of the tools that inspired the need for SSH have been around since
the beginning, too, or very near the beginning of the Internet. Remote
access has been a fundamental part of the concept since the idea stage
and the nature and capabilities of this access has evolved as the
network has evolved in scale, scope and usage. See the web version of
the *Lévénez Unix Timeline*[^3] by Éric Lévénez for an overview of
systems development and the web version of *Hobbes\' Internet
Timeline*[^4] by Robert H Zakon for an overview of the development of
the Internet.

**1969**

-   Telnet was one of the original ARPAnet application protocols, named
    in RFC 15 from September 1969.
    It was used to access a host at a remote site locally. Telnet was
    described starting two years later in RFC 137, RFC 139, RFC 318 and
    others, including RFC 97. That is as good a turning point as any to
    delineate Telnet.

**1971**

-   Thompson Shell, by Ken Thompson, was an improvement on the old
    text-based user interface, the shell. This new one allowed redirects
    but was only a user interface and not for scripting.
-   In the same year FTP, the file transfer protocol, was described in
    RFC 114. A key goal was to promote use of computers over the net by
    allowing users at any host on the network to use the file system of
    any cooperating host.

**1978**

-   Bill Joy created BSD\'s C shell which is named for the C-like syntax
    it uses. It allows job control, history substitution, and aliases,
    which features we find in today\'s interfaces.
-   In the same year, the Bourne Shell by Steve Bourne at Bell Labs [^5]
    was created. It is the progenitor to the default shells used in most
    distros today: **ksh** and **bash**.

**1983**

-   The remote file copy utility, **rcp**, appeared in 4.2 BSD. **rcp**
    copied files across the net to other hosts using **rsh**, which also
    appeared staring 4.2 BSD, to perform its operations. Like **telnet**
    and **ftp**, all passwords, user names, and data are transmitted
    unencrypted in clear text. Both **rsh** and **rcp** were part of the
    **rlogin** suite.

**1991**

-   PGP, written at MIT by Philip Zimmermann[^6], charted new waters for
    encrypted electronic communications with the goals of preserving
    civil liberties online, ensuring individual privacy, keeping
    encryption legal in the USA, and protecting business communications.
    Like SSH it uses asymmetric encryption with public / private key
    pairs.

**1993**

-   Kerberos V (RFC 1510) authentication service from MIT\'s project
    Athena [^7] provides a means for authentication over an open,
    unsecure network. Kerberos got its original start in 1988.

### SSH - open then closed

**1995**

-   Tatu Ylönen at the then Helsinki University of Technology developed
    the first SSH protocol and programs, releasing them under an open
    license[^8] as per the norm in computer science, software
    engineering, and advanced development. [^9]

**1995?**

-   Björn Grönvall dug out the most recent open version of **ssh**,
    version 1.2.12[^10] [^11]. He and Holger Trapp did the initial work
    to free the distribution, resulting in OSSH

**1996**

-   The SSH2 protocol is defined

### OpenSSH

**1999**

-   OpenSSH begins based on OSSH. Niels Provos, Theo de Raadt, Markus
    Friedl developed the cryptographic components during the port to
    OpenBSD which became the OpenSSH we know today. Dug Song, Aaron
    Campbell and many others provided various non-crypto contributions.
    openssl library issues were sorted by Bob Beck. Damien Miller,
    Philip Hands, and others started porting OpenSSH to Linux. Finally
    OpenSSH 1.2.2 was release shipped with OpenBSD 2.6 in December 1,
    1999.[^12]

**2000**

-   Markus Friedl added SSH 2 protocol support to OpenSSH version 2.0,
    which was released in June.[^13] OpenSSH 2.0 shipped with OpenBSD
    2.7. Niels Provos and Theo de Raadt did most of the checking. Bob
    Beck updated OpenSSL. Markus also added support for the SFTP
    protocol later that same year.
-   In September of 2000, the long wait in the USA for the patents on
    the RSA algorithms to expire was over. In the European Union the
    European Patent Convention of 1972 frees software, algorithms,
    business methods or literature, unlike the unfortunate,
    anti-business situation in the USA. This freedom in Europe hangs by
    a thread at the moment.
-   SSH Tectia changes licenses again.

**2001**

-   Damien Miller completed the SFTP client which was released in
    February.
-   SSH2 became the default protocol

**2008**

-   Built-in chroot support for **sshd**.

**2010**

-   As of OpenSSH 5.4, the legacy protocol SSH1 is finally disabled by
    default.

**2014**

-   As of OpenSSH 6.7, both the base and the portable versions of
    OpenSSH can build against LibreSSL instead of OpenSSL for certain
    cryptographic functions.

**2016**

-   OpenSSH 7.4 removes server support for the SSH1 legacy protocol.

**2023**

-   OpenSSH 9.5 ssh-keygen(1)
    generates Ed25519 keys by default instead of old RSA keys.

Note: OpenSSH can be used anywhere in the whole world because it uses
only algorithms unencumbered by software patents, business method
patents, algorithm patents, and so on. These types of patents do not
apply in Europe, only physical inventions can be patented in Europe, but
there are regions of the world where these problems do occur. Small and
medium businesses in Europe have been active in politics to keep the
advantage.

## Why Use OpenSSH?

A lot has changed since the commercialization of the Internet began in
1996. It was once a University and Government research network and if
you were on the net back then, odds were you were supposed to be there.
Though it was far from being utopia, any misbehavior could usually be
quickly narrowed down to the individuals involved and dealt with easily,
usually with no more than a phone call or a few e-mails. Few, if any,
sessions back then were encrypted and both passwords and user names were
passed in clear text.

By then, the WWW was more than a few years under way and undergoing
explosive growth. The estimated number of web servers online in 1996
grew from 100,000 at the beginning of the year to close to 650,000 by
the end of the same year[^14]. When other types of servers are included
in those figures, the estimated year-end number was over 16,000,000
hosts, representing approximately 828,000 domains.[^15]

Nowadays, hosts are subject to hostile scans from the moment they are
connected to the network. Any and all unencrypted traffic is scanned and
parsed for user names, passwords, and other sensitive information.
Currently, the biggest espionage threats come from private companies,
but governments, individuals, and organized crime are not without a
presence.

Each connection from one host to another goes through many networks and
each packet may take the same or a different route there and back again.
This example shows thirteen hops among three organizations from a
student computer to a search engine:

``` shell-session
% /usr/sbin/traceroute -n www.google.com
traceroute: Warning: www.google.com has multiple addresses; using 74.125.95.106
traceroute to www.l.google.com (74.125.95.106), 30 hops max, 40 byte packets
 1 xx.xx.xx.xx           0.419 ms   0.220 ms    0.213 ms    University of Michigan
 2 xx.xx.xx.xx           0.446 ms   0.349 ms    0.315 ms    Merit Network, Inc.
 3 xx.xx.xx.xx           0.572 ms   0.513 ms    0.525 ms    University of Michigan
 4 xx.xx.xx.xx           0.472 ms   0.425 ms    0.402 ms    University of Michigan
 5 xx.xx.xx.xx           0.647 ms   0.551 ms    0.561 ms    University of Michigan
 6 xx.xx.xx.xx           0.945 ms   0.912 ms    0.865 ms    University of Michigan
 7 xx.xx.xx.xx           6.478 ms   6.503 ms    6.489 ms    Merit Network, Inc.
 8 xx.xx.xx.xx           6.597 ms   6.590 ms    6.604 ms    Merit Network, Inc.
 9 216.239.48.154       64.935 ms   6.848 ms    6.793 ms    Google, Inc.
10 72.14.232.141        17.606 ms   17.581 ms   17.680 ms   Google, Inc.
11 209.85.241.27        17.736 ms   17.592 ms   17.519 ms   Google, Inc.
12 72.14.239.193        17.767 ms   17.778 ms   17.930 ms   Google, Inc.
13 74.125.95.106        17.903 ms   17.835 ms   17.867 ms   Google, Inc.:
```

The net is big. It is not uncommon to find a trail of 15 to 20 hops
between client and server nowadays. Any machine on any of the subnets
the packets travel over can eavesdrop with little difficulty if the
packets are not well encrypted.

### What OpenSSH Does

The OpenSSH suite gives the following:

-   Encrypted remote access, including tunneling insecure protocols.
-   Encrypted file transfer
-   Run remote commands, programs or scripts and, as mentioned,
-   Replacement for **rsh**, **rlogin**, **telnet** and **ftp**

More concretely, that means that the following undesirable activities
are prevented:

-   Eavesdropping of data transmitted over the network.
-   Manipulation of data at intermediate elements in the network (e.g.
    routers).
-   Address spoofing where an attack hosts pretends to be a trusted host
    by sending packets with the source address of the trusted host.
-   IP source routing

As a free software project, OpenSSH provides:

-   Open Standards
-   Flexible License - freedom emphasized for developers
-   Strong Encryption using these ciphers:
    -   AES
    -   ChaCha20[^16]
    -   RSA
    -   ECDSA
    -   Ed25519
-   Strong Authentication, supported methods:
    `gssapi-with-mic, hostbased, keyboard-interactive, none , password`
    and `publickey`[^17]
    -   Public
        Key: can
        authenticate using multiple keys since March 2015 (OpenSSH
        6.8)[^18]
    -   Single Use Passwords
    -   Kerberos
    -   Dongles
-   Built-in SFTP
-   Data Compression
-   Port Forwarding
    -   Encrypt legacy protocols
    -   Encrypted X11 forwarding for X Window System
-   Key Agents
-   Single Sign-on using
    -   Authentication Keys
    -   Agent Forwarding
    -   Ticket Passing
    -   Kerberos
    -   AFS

### What OpenSSH Doesn\'t Do

OpenSSH is a very useful tool, but much of its effectiveness depends on
correct use. It cannot protect from any of the following situations.

-   Misconfiguration, misuse, or abuse.
-   Compromised systems, particularly where the root account is
    compromised.
-   Insecure or inappropriate directory settings, particularly home
    directory settings.

OpenSSH must be properly configured and on a properly configured system
in order to be of benefit. Arranging both is not difficult, but since
each system is unique, there is no one-size-fits-all solution. The right
configuration is dependent on the uses the system and OpenSSH are put
to.

If you login from a host to a server and an attacker has control of root
on either side, he can listen to your session by reading from the
pseudo-terminal device because even though SSH is encrypted on the
network it must communicate in clear text with the terminal device.

If an attacker can change files in your home directory, for example via
a networked file system, he may be able to fool SSH.

Last but not least, if OpenSSH is set to allow everyone in, whether on
purpose or by accident, it will.

## References

[^1]:

[^2]:

[^3]:

[^4]:

[^5]:

[^6]:

[^7]:

[^8]:

[^9]:

[^10]:

[^11]:

[^12]: <https://www.openssh.com/history.html>

[^13]:

[^14]:

[^15]:

[^16]:

[^17]: <https://linux.die.net/man/5/sshd_config>

[^18]: <https://lists.mindrot.org/pipermail/openssh-unix-announce/2015-March/000120.html>