Planet Closest to the Sun - Universe Today Universe Today Planet Closest to the Sun Article Updated: 24 Dec , 2015 by Jerry Coffey [/caption]Mercury, the planet closest to the Sun, is a study in extremes and offers many surprises. The extremes of the planet have made it an understudied body in our Solar System, though the MESSENGER mission is trying to change that as you are reading this article. In addition to being the planet closest to the Sun, Mercury is also the smallest by mass. If you ignore the former planet Pluto, it is also the smallest by surface area, as well. The planet has the most eccentric orbit: at perihelion it is 46,001,200 km from the Sun and at aphelion it is 69,816,900 km. The planet’s short orbital period(87.969 Earth days) and slight axial tilt combine to make the day on Mercury(116 Earth days) longer than the year. The average temperature on the planet is 442.5°K.

Because of the planet’s thin atmosphere there is a wide temperature range, 100°K to 700°K. The temperature at the equator can be as much as 300°K more than the temperature at the poles. Despite its proximity to our central star, the poles of the planet are thought to have water ice hidden within impact craters. Claims for water ice are substantiated by observations by the 70 m Goldstone telescope and the Very Large Array. There are areas of very high radar reflection at the pole areas so, since water is highly reflective of radar, astronomers believe that water ice is the most likely cause of this reflection. Due to its size and average temperatures, the planet’s gravity can not retain a significant atmosphere over a long period. It does have a negligible surface-bounded exosphere that is dominated by hydrogen, helium, oxygen, sodium, calcium, and potassium. Atoms are continuously being lost and replenished from this exosphere. Hydrogen and helium atoms are thought to derive from the solar wind that buffets the planet. These elements diffuse into Mercury’s magnetosphere before escaping back into space. Radioactive decay within the crust is a source of helium, sodium, and potassium.

Mercury has been explored by two mission: Mariner 10 and MESSENGER. Mariner 10 was able to map 40-45% of Mercury’s surface through more than 2,800 photos. It revealed a more or less moon-like surface, a slight atmosphere, a magnetic field, and a large iron rich core. MESSENGER was launched in August of 2004. After a 31/2 year flight, it made its first flyby in January 2008 and arrived in orbit on March 18, 2011. So far, the probe has discovered large amounts of water in the exosphere, evidence of past volcanic activity, and evidence of a liquid planetary core. As the MESSENGER mission continues, the closest planet to the Sun should continue to reveal more surprises for the scientists at NASA. It appears a new age of discovery has begun for Mercury. We have an extensive section just on Mercury on Universe Today. And did you know there’s a spacecraft visiting Mercury called MESSENGER? You can read news about this mission here . Here’s a link to NASA’s Solar System Exploration Guide on Mercury.

We have recorded an episode of Astronomy Cast just about the Sun called The Sun, Spots and All . References: Order of the Planets From The Sun – Planet Closest Distance to the Sun – PlanetFacts.org The Moon Order of the Planets From The Sun The solar system is a group of celestial bodies orbiting around the dwarf star called the Sun. The main members of the solar system are eight major planets, and their satellites. Other interesting members are comets, meteors and meteorites and dwarf planets. The order of the planets from the Sun from nearest to the farthest is Mercury, Venus, earth, Mars, Jupiter, Saturn Uranus, and Neptune. 1. The nearest planet to the Sun is Mercury. Though it is very near to the Sun, it is not the hottest planet at all. The smallest among the inner planets has actually temperature of 450 degrees Celsius during day time while it drops to a very frigid negative 170 degrees Celsius at night. It is named after the Roman messenger of the Gods as it orbits the Sun once every 88 days. 2. The second planet from the Sun is named after the Roman Goddess of Beauty, Venus.

True to its name, this beautiful planet is also called the evening star. It is also the hottest planet in the solar system due to clouds of toxic gas with temperatures over 460 degrees Celsius. It rotates backward and makes one complete revolution around the Sun in 225 days. 3. The third planet from the Sun is Earth, the beautiful blue planet blessed with a diversity of living organisms of varying shapes and sizes. It is the only planet known to sustain life. It makes a complete revolution around the Sun for 365 days. It has one satellite called the Moon. 4. Mars is the fourth planet from the Sun. It is named after the Roman God of War. It is usually called the red planet. A Martian year is equivalent to 687 Earth days. It is usually the third brightest object of the night sky after Earth’s moon and Venus. The possibility of life on Mars is still a subject of probes and studies. By the way, Mars has similar seasons as here on Earth. 5. The biggest planet, Jupiter is the fifth planet from the Sun. Although it has the greatest volume among the planets, it has the lowest density.

It is separated from the inner planets by the asteroid belt where many other interesting heavenly bodies orbit around the Sun. 6. Saturn is the second of the outer planets and is the sixth in order from the Sun. Many astronomers tag it as the most beautiful planet because of its prominent rings made up of ice, dust, gas, and other particles. 7. Uranus is the third of the outer planets, the seventh in order from the Sun. This planet has a very low density and is made up of a large proportion of gas. It is also referred to as an ice giant because a decent percentage of its gases are trapped in ice form. It has faint rings. 8. Neptune is the fourth among the outer planets and the farthest planet away from the Sun. It is also made up of frozen gases like its neighboring planet Uranus. A great percentage of these gases are methane making it appear as a blue planet. What was once recognized as the ninth solar planet, Pluto, was just recently reclassified as a dwarf planet. It was placed in this category along with Eris, Vespa, and Ceres. Awesomeninja 18hunter235 StarChild: The planet Mercury Mercury: Planet Closest to the Sun Guess what?

Due to Mercury's rotation and highly elliptical orbit , the Sun appears to rise briefly, set, and rise again before it travels westward across the sky. At sunset, the Sun appears to set, rise again briefly, and then set again. Mercury is only about one-third the size of the Earth. It is smaller than any other planet. Mercury is very close to the Sun and has no substantial atmosphere . These factors contribute to the fact that the surface of Mercury has the greatest temperature range of any planet or natural satellite in our solar system . The surface temperature on the side of Mercury closest to the Sun reaches 427 degrees Celsius , a temperature hot enough to melt tin. On the side facing away from the Sun, or the night side, the temperature drops to -183 degrees Celsius. Scientists have detected a magnetic field surrounding Mercury, though it is not as strong as the field around the Earth. Scientists theorize that Mercury's field is due to an iron-bearing core or possibly to the solar winds . Mercury's atmosphere is very thin and is composed of helium and sodium.

The surface of Mercury has been shaped by three processes: impact cratering where large objects struck the surface resulting in crater formation, volcanism where lava flooded the surface, and tectonic activity where the planet's crust moved in order to adjust to the planetary cooling and contracting. Mercury does not have any naturally occurring satellites. Mercury A Question What is the difference in the temperature of Mercury's surface when it is facing towards and away from the Sun? Planet Mercury: Facts About the Planet Closest to the Sun Planet Mercury: Facts About the Planet Closest to the Sun By Charles Q. Choi, Space.com Contributor | November 30, 2016 08:44pm ET MORE This view is one of the first from the MESSENGER probe's Oct. 6, 2008 flyby of Mercury. Credit: NASA/JHUAPL/CIW Mercury is the closest planet to the sun. As such, it circles the sun faster than all the other planets, which is why Romans named it after their swift-footed messenger god. The Sumerians also knew of Mercury since at least 5,000 years ago. It was often associated with Nabu, the god of writing .

Mercury was also given separate names for its appearance as both a morning star and as an evening star. Greek astronomers knew, however, that the two names referred to the same body. Heraclitus believed that both Mercury and Venus orbited the sun, not Earth. [ Latest Photos: Mercury Seen by NASA's Messenger Probe ] Mercury's physical characteristics Because the planet is so close to the sun, Mercury's surface temperature can reach a scorching 840 degrees Fahrenheit (450 degrees Celsius). However, since this world doesn't have a real atmosphere to entrap any heat, at night temperatures can plummet to minus 275 F (minus 170 C), a temperature swing of more than 1,100 degrees F (600 degree C), the greatest in the solar system. Mercury is the smallest planet — it is only slightly larger than Earth's moon. Since it has no significant atmosphere to stop impacts, the planet is pockmarked with craters.

About 4 billion years ago, an asteroid roughly 60 miles (100 kilometers) wide struck Mercury with an impact equal to 1 trillion 1-megaton bombs, creating a vast impact crater roughly 960 miles (1,550 km) wide. Known as the Caloris Basin, this crater could hold the entire state of Texas. Another large impact may have helped create the planet's odd spin . As close to the sun as Mercury is, in 2012, NASA's MESSENGER spacecraft discovered water ice in the craters around its north pole, where regions may be permanently shaded from the heat of the sun. The southern pole may also contain icy pockets, but MESSENGER's orbit did not allowed scientists to probe the area. Comets or meteorites may have delivered ice there, or water vapor may have outgassed from the planet's interior and frozen out at the poles. [Related: First Photos of Water Ice on Mercury Captured by NASA Spacecraft ] As if Mercury isn't small enough, it not only shrank in its past but is continuing to shrink today . The tiny planet is made up of a single continental plate over a cooling iron core.

As the core cools, it solidifies, reducing the planet's volume and causing it to shrink. The process crumpled the surface, creating lobe-shaped scarps or cliffs, some hundreds of miles long and soaring up to a mile high. In the past, the surface was constantly reshaped by volcanic activity , some fairly recently in the planet's past. "The young age of the small scarps means that Mercury joins Earth as a tectonically active planet with new faults likely forming today as Mercury's interior continues to cool and the planet contracts," Tom Watters, Smithsonian senior scientist at the National Air and Space Museum in Washington, D.C., said in a statement . Mercury is the second densest planet after Earth, with a huge metallic core roughly 2,200 to 2,400 miles (3,600 to 3,800 km) wide, or about 75 percent of the planet's diameter. In comparison, Mercury's outer shell is only 300 to 400 miles (500 to 600 km) thick. The combination of its massive core and abundance of volatile elements has left scientists puzzled for years.

A completely unexpected discovery Mariner 10 made was that Mercury possessed a magnetic field. Planets theoretically generate magnetic fields only if they spin quickly and possess a molten core. But Mercury takes 59 days to rotate and is so small — just roughly one-third Earth's size — that its core should have cooled off long ago. "We had figured out how the Earth works, and Mercury is another terrestrial, rocky planet with an iron core, so we thought it would work the same way," Christopher Russell, a professor at the University of California, Los Angeles, said in a statement . An unusual interior could help to explain the differences in Mercury's magnetic field when compared to Earth. Observations from MESSENGER revealed that the planet's magnetic field is approximately three times stronger at its northern hemisphere than at its southern. Russell co-authored a model that suggests that Mercury's iron core may be turning from liquid to solid at the core's outer boundary rather than the inner. "It's like a snow storm in which the snow formed at the top of the cloud and middle of the cloud and the bottom of the cloud too," said Russell.

"Our study of Mercury's magnetic field indicates iron is snowing throughout this fluid that is powering Mercury's magnetic field." The discovery in 2007 by Earth-based radar observations that Mercury's core may still be molten could help explain its magnetism, though the solar wind may play a role in dampening the planet's magnetic field. Although Mercury's magnetic field is just 1 percent the strength of Earth's, it is very active. The magnetic field in the solar wind — the charged particles streaming off the sun — periodically touches upon Mercury's field, creating powerful magnetic tornadoes that channel the fast, hot plasma of the solar wind down to the planet's surface. Instead of a substantial atmosphere, Mercury possesses an ultra-thin "exosphere" made up of atoms blasted off its surface by solar radiation, the solar wind and micrometeoroid impacts. These quickly escape into space, forming a tail of particles. Mercury's orbital characteristics Mercury speeds around the sun every 88 Earth days, traveling through space at nearly 112,000 mph (180,000 km/h), faster than any other planet.

Its oval-shaped orbit is highly elliptical, taking Mercury as close as 29 million miles (47 million km) and as far as 43 million miles (70 million km) from the sun. If one could stand on Mercury when it is nearest to the sun, it would appear more than three times as large as it does when viewed from Earth. Oddly, due to Mercury's highly elliptical orbit and the 59 Earth-days or so it takes to rotate on its axis, when on the scorching surface of the planet, the sun appears to rise briefly, set, and rise again before it travels westward across the sky. At sunset, the sun appears to set, rise again briefly, and then set again. Mercury is the closest planet to the sun and has a thin atmosphere, no air pressure and an extremely high temperature. Take a look inside the planet.

Credit: Karl Tate, SPACE.com Solar System Planets: Order of the 8 (or 9) Planets Solar System Planets: Order of the 8 (or 9) Planets By Robert Roy Britt | January 22, 2016 12:35pm ET MORE The planets of the solar system as depicted by a NASA computer illustration. Orbits and sizes are not shown to scale. Credit: NASA Ever since the discovery of Pluto in 1930, kids grew up learning about the nine planets of our solar system. That all changed starting in the late 1990s, when astronomers began to argue about whether Pluto was a planet. In a highly controversial decision , the International Astronomical Union ultimately decided in 2006 to call Pluto a “dwarf planet,” reducing the list of “real planets” in our solar system to eight. However, astronomers are now hunting for another planet in our solar system, a true ninth planet , after evidence of its existence was unveiled on Jan. 20, 2016.

The so-called "Planet Nine," as scientists are calling it, is about 10 times the mass of Earth and 5,000 times the mass of Pluto. [ Solar System Pictures: A Photo Tour ] If you insist on including Pluto , then that world would come after Neptune on the list; Pluto is truly way out there, and on a wildly tilted, elliptical orbit (two of the several reasons it got demoted). Interestingly, Pluto used to be the eighth planet, actually. More on that below. Terrestrial planets The inner four worlds are called “ terrestrial planets ,” because, like Earth, their surfaces are all rocky. Pluto, too, has a solid surface (and a very frozen one) but has never been grouped with the four terrestrials. Jovian planets The four large outer worlds — Jupiter, Saturn, Uranus, and Neptune — are known as the “Jovian planets” (meaning “Jupiter-like”) because they are all huge compared to the terrestrial planets, and because they are gaseous in nature rather than having rocky surfaces (though some or all of them may have solid cores, astronomers say).

According to NASA , "two of the outer planets beyond the orbit of Mars — Jupiter and Saturn — are known as gas giants; the more distant Uranus and Neptune are called ice giants." This is because, while the first two are dominated by gas, while the last two have more ice. All four contain mostly hydrogen and helium. Dwarf planets The IAU definition of a full-fledged planet goes like this: A body that circles the sun without being some other object's satellite, is large enough to be rounded by its own gravity (but not so big that it begins to undergo nuclear fusion, like a star) and has "cleared its neighborhood" of most other orbiting bodies. Yeah, that’s a mouthful. The problem for Pluto, besides its small size and offbeat orbit, is that it shares its space with lots of other objects in the Kuiper Belt , beyond Neptune. Still, the demotion of Pluto remains controversial . The IAU planet definition puts other small, round worlds in the dwarf planet category, including the Kuiper Belt objects Eris , Haumea , and Makemake . Also now a dwarf planet is Ceres , a round object in the Asteroid Belt between Mars and Jupiter.

Ceres was actually considered a planet when discovered in 1801 and then later deemed to be an asteroid. Some astronomers like to consider Ceres as a 10th planet (not to be confused with Nibiru or Planet X ), but that line of thinking opens up the possibility of there being 13 planets, with more bound to be discovered. The planets Below is a brief overview of the eight primary planets in our solar system , in order from the inner solar system outward: Mercury The closest planet to the sun, Mercury is only a bit larger than Earth's moon. Its day side is scorched by the sun and can reach 840 degrees Fahrenheit (450 Celsius), but on the night side, temperatures drop to hundreds of degrees below freezing. Mercury has virtually no atmosphere to absorb meteor impacts, so its surface is pockmarked with craters, just like the moon. Over its four-year mission, NASA's MESSENGER spacecraft has revealed views of the planet that have challenged astronomers' expectations.

Discovery: Known to the ancients and visible to the naked eye Named for: Messenger of the Roman gods Diameter: 3,031 miles (4,878 km) Orbit: 88 Earth days Venus' southern hemisphere, as seen in the ultraviolet. Credit: ESA Venus The second planet from the sun, Venus is terribly hot, even hotter than Mercury. The atmosphere is toxic. The pressure at the surface would crush and kill you. Scientists describe Venus’ situation as a runaway greenhouse effect. Its size and structure are similar to Earth, Venus' thick, toxic atmosphere traps heat in a runaway "greenhouse effect." Oddly, Venus spins slowly in the opposite direction of most planets. The Greeks believed Venus was two different objects — one in the morning sky and another in the evening. Because it is often brighter than any other object in the sky — except for the sun and moon — Venus has generated many UFO reports.

Discovery: Known to the ancients and visible to the naked eye Named for: Roman goddess of love and beauty Diameter: 7,521 miles (12,104 km) Orbit: 225 Earth days An image of the Earth taken by the Russian weather satellite Elektro-L No.1. Credit: NTsOMZ Earth The third planet from the sun, Earth is a waterworld, with two-thirds of the planet covered by ocean. It’s the only world known to harbor life. Earth’s atmosphere is rich in life-sustaining nitrogen and oxygen. Earth's surface rotates about its axis at 1,532 feet per second (467 meters per second) — slightly more than 1,000 mph (1,600 kph) — at the equator. The planet zips around the sun at more than 18 miles per second (29 km per second).

Diameter: 7,926 miles (12,760 km) Orbit: 365.24 days Day: 23 hours, 56 minutes Related: Mars researchers are focusing both Earth-based and planet orbiting sensors to better understand sources of methane on the red planet. Image Credit: Space Telescope Science Institute Mars The fourth planet from the sun, is a cold, dusty place. The dust, an iron oxide, gives the planet its reddish cast. Mars shares similarities with Earth: It is rocky, has mountains and valleys, and storm systems ranging from localized tornado-like dust devils to planet-engulfing dust storms. It snows on Mars. And Mars harbors water ice. Scientists think it was once wet and warm, though today it’s cold and desert-like. Mars' atmosphere is too thin for liquid water to exist on the surface for any length of time. Scientists think ancient Mars would have had the conditions to support life, and there is hope that signs of past life — possibly even present biology — may exist on the Red Planet.

Discovery: Known to the ancients and visible to the naked eye Named for: Roman god of war Diameter: 4,217 miles (6,787 km) Orbit: 687 Earth days Day: Just more than one Earth day (24 hours, 37 minutes) Related: Close-up of Jupiter's Great Red Spot as seen by a Voyager spacecraft. Credit: NASA/JPL-Caltech Jupiter The fifth planet from the sun, Jupiter is huge and is the most massive planet in our solar system. It’s a mostly gaseous world, mostly hydrogen and helium. Its swirling clouds are colorful due to different types of trace gases. A big feature is the Great Red Spot, a giant storm which has raged for hundreds of years. Jupiter has a strong magnetic field, and with dozens of moons, it looks a bit like a miniature solar system.

Discovery: Known to the ancients and visible to the naked eye Named for: Ruler of the Roman gods Diameter: 86,881 miles (139,822 km) Orbit: 11.9 Earth years The shadow of Saturn's moon Mimas dips onto the planet's rings and straddles the Cassini Division in this natural color image taken as Saturn approaches its August 2009 equinox. Credit: NASA/JPL/Space Science Institute Saturn The sixth planet from the sun is known most for its rings . When Galileo Galilei first studied Saturn in the early 1600s, he thought it was an object with three parts. Not knowing he was seeing a planet with rings, the stumped astronomer entered a small drawing — a symbol with one large circle and two smaller ones — in his notebook, as a noun in a sentence describing his discovery. More than 40 years later, Christiaan Huygens proposed that they were rings. The rings are made of ice and rock. Scientists are not yet sure how they formed. The gaseous planet is mostly hydrogen and helium. It has numerous moons .

Discovery: Known to the ancients and visible to the naked eye Named for: Roman god of agriculture Diameter: 74,900 miles (120,500 km) Orbit: 29.5 Earth years Day: About 10.5 Earth hours Related: Near-infrared views of Uranus reveal its otherwise faint ring system, highlighting the extent to which the planet is tilted. Credit: Lawrence Sromovsky, (Univ. Wisconsin-Madison), Keck Observatory Uranus The seventh planet from the sun, Uranus is an oddball. It’s the only giant planet whose equator is nearly at right angles to its orbit — it basically orbits on its side. Astronomers think the planet collided with some other planet-size object long ago, causing the tilt. The tilt causes extreme seasons that last 20-plus years, and the sun beats down on one pole or the other for 84 Earth-years. Uranus is about the same size as Neptune. Methane in the atmosphere gives Uranus its blue-green tint. It has numerous moons and faint rings.

Discovery: 1781 by William Herschel (was thought previously to be a star) Named for: Personification of heaven in ancient myth Diameter: 31,763 miles (51,120 km) Orbit: 84 Earth years Neptune’s winds travel at more than 1,500 mph, and are the fastest planetary winds in the solar system. Credit: NASA/JPL Neptune The eighth planet from the sun, Neptune is known for strong winds — sometimes faster than the speed of sound. Neptune is far out and cold. The planet is more than 30 times as far from the sun as Earth. It has a rocky core. Neptune was the first planet to be predicted to exist by using math, before it was detected. Irregularities in the orbit of Uranus led French astronomer Alexis Bouvard to suggest some other might be exerting a gravitational tug. German astronomer Johann Galle used calculations to help find Neptune in a telescope. Neptune is about 17 times as massive as Earth. Discovery: 1846 Pluto and its moons orbit the sun near the edge of our solar system.

Learn all about Pluto's weirdly eccentric orbit, four moons and more in this Space.com infographic . Credit: SPACE.com/Karl Tate Pluto (Dwarf Planet) Once the ninth planet from the sun, Pluto is unlike other planets in many respects. It is smaller than Earth's moon. Its orbit carries it inside the orbit of Neptune and then way out beyond that orbit. From 1979 until early 1999, Pluto had actually been the eighth planet from the sun. Then, on Feb. 11, 1999, it crossed Neptune's path and once again became the solar system's most distant planet — until it was demoted to dwarf planet status. Pluto will stay beyond Neptune for 228 years. Pluto’s orbit is tilted to the main plane of the solar system — where the other planets orbit — by 17.1 degrees. It’s a cold, rocky world with only a very ephemeral atmosphere. NASA's New Horizons mission performed history's first flyby of the Pluto system on July 14, 2015.

[Related: New Horizons' Pluto Flyby: Latest News, Images and Video ] Discovery: 1930 by Clyde Tombaugh Named for: Roman god of the underworld, Hades Diameter: 1,430 miles (2,301 km) Orbit: 248 Earth years NASA Solar System Exploration: Dwarf Planets Planet Nine Planet Nine orbits the sun at a distance that is 20 times farther out than the orbit of Neptune. (The orbit of Neptune is 2.7 billion miles from the sun at its closest point.) The strange world's orbit is about 600 times farther from the sun than the Earth's orbit is from the star. Scientists have not actually seen Planet Nine directly . Its existence was inferred by its gravitational effects on other objects in the Kuiper Belt, a region at the fringe of the solar system that is home to icy objects left over from the birth of the sun and planets. Mercury, the closest planet to the Sun email this page to a friend Mercury, the closest planet to the Sun Mercury is the innermost planet in our solar system. Because of its small size � a diameter of 3030 miles � it is not the easiest of planets to observe.

German scientist Johannes Hevelius (1611 - 1687) was among the first to observe a Mercurial transit and discovered the Mercurial phases. Most of our information has been collected by the Mariner 10 space probe that made three successful passes of the planet (March 29 1974, September 21 1974, and March 16 1975) before losing contact with Earth. Averaging an orbital velocity of 47.87 km per second, Mercury is the fastest-moving planet in our solar system. Because of its low escape velocity, Mercury hasn't much of an atmosphere. Based on information from Mariner 10, its surface pressure is ten billionths of a millibar. This barely extant atmosphere includes trace amounts of hydrogen and helium from the solar wind. In 1991, very powerful radio telescopes noticed large sheets of ice contained on the poles, areas unseen by Mariner 10. Due to its 3600 km iron core, Mercury has the greatest density in our Solar System apart from Earth.

Composed of 70% iron and 30% rock, Mercury has a molten core, a 600-km thick mantle, and a crust of silicates. Its largest known surface feature is the Caloris Basin with a 1350 km diameter. Mariner 10 also detected a magnetosphere with a 1% surface value of Earth's. Mercury's magnetic field is inclined at 11% to its rotational axis and has the same polarity as Earth's � just enough to protect it from the full force of the solar wind. Mercury's 0.06 albedo is due to a dark-coloured, rough, porous rock that does not reflect much light; its climate indicates a slim chance life could exist there. Due to the small difference between Mercury's orbital and rotational periods, the interval between night and day on the planet itself is 88 Earth days. This leads to a few peculiarities. As a result of orbital eccentricity, the temperature as measured at perihelion is two and a half times the heat received at aphelion.

To an observer situated on the planet's hot pole at aphelion during a sunrise, the Sun would approach the zenith (getting larger as it does so), but since the orbital angular velocity is greater than the constant-spin angular velocity for a time, the Sun appears to stop, retreat backward for 8 Earth days, stop again, and then resume its original course. The $427 million Mercury Messenger probe , launched August 2004 aboard a Boeing Delta 2 rocket, will arrive at Mercury in 2011 to explore the planet's atmospheric and magnetic environments, crust structure and composition, geological history, polar areas, and core. Of all the inner rocky planets, Mercury is the least explored with only 45% of its surface photographed by Mariner 10. Though it is two thirds iron, the actual reason for this is a mystery for Messenger to solve. Some scientists believe it was originally a rocky planet that somehow lost its exterior. Messenger will also help scientists find out why Mercury and Earth are the only rocky planets with global magnetic fields.

Equatorial temperatures on Mercury can reach 450°C and though signatures of ice craters have been detected at high latitudes with temperatures reaching below -184°C, some scientists believe the 'ice' might just be super-frozen silicon. Coated with heat-resistant ceramic fabric, the room-temperature probe carries a total of seven scientific instruments. Weighing 1.2 tons, Messenger will only briefly encounter Mercury's hotter regions. Order Of the Planets From The Sun - Universe Today Universe Today Order Of the Planets From The Sun Article Updated: 31 Jan , 2016 by Nancy Atkinson First the quick facts: Our Solar System has eight “official” planets which orbit the Sun. Here are the planets listed in order of their distance from the Sun: Mercury , Venus , Earth , Mars , Jupiter , Saturn , Uranus , and Neptune . An easy mnemonic for remembering the order is “My Very Educated Mother Just Served Us Noodles.” If you add in the dwarf planets, Ceres is located in the asteroid belt between Mars and Jupiter, while the remaining dwarf planets are in the outer Solar System and in order from the Sun are Pluto , Haumea , Makemake , and Eris .

There is, as yet, a bit of indecision about the Trans-Neptunian Objects known as Orcus , Quaoar , 2007 O10 , and Sedna and their inclusion in the dwarf planet category. A mnemonic for this list would be “My Very Educated Mother Could Just Serve Us Noodles, Pie, Ham, Muffins, and Eggs” (and Steak, if Sedna is included.) You can find more tricks for remembering the order of the planets at our detailed article here. Now, let’s look at a few details including the definition of a planet and a dwarf planet, as well as details about each of the planets in our Solar System. Artistic impression of the Solar System, with all known terrestrial planets, as giants, and dwarf planets. Credit: NASA What is a planet? In 2006, the International Astronomical Union (IAU) decided on the definition of a planet. The definition states that in our Solar System, a planet is a celestial body which: is in orbit around the Sun, has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), has “cleared the neighborhood” around its orbit. is not a moon.

This means that Pluto, which was considered to be the farthest planet since its discovery in 1930, now is classified as a dwarf planet. The change in the definition came after the discovery three bodies that were all similar to Pluto in terms of size and orbit, (Quaoar in 2002, Sedna in 2003, and Eris in 2005). With advances in equipment and techniques, astronomers knew that more objects like Pluto would very likely be discovered, and so the number of planets in our Solar System would start growing quickly. It soon became clear that either they all had to be called planets or Pluto and bodies like it would have to be reclassified. With much controversy then and since, Pluto was reclassified as a dwarf planet in 2006. This also reclassified the asteroid Ceres as a dwarf planet, too, and so the first five recognized dwarf planets are Ceres, Pluto, Eris, Makemake and Haumea. Scientists believe there may be dozens more dwarf planets awaiting discovery.

Later, in 2008, the IAU announced the subcategory of dwarf planets with trans-Neptunian orbits would be known as “plutoids.” Said the IAU, “Plutoids are celestial bodies in orbit around the Sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit.” This subcategory includes Ceres, Pluto, Haumea, Makemake, and Eris. The Planets in our Solar System: Having covered the basics of definition and classification, let’s get talking about those celestial bodies in our Solar System that are still classified as planets (sorry Pluto!). Here is a brief look at the eight planets in our Solar System. Included are quick facts and links so you can find out more about each planet. Mercury: Mercury is the closest planet to our Sun, at just 58 million km (36 million miles) or 0.39 Astronomical Unit (AU) out.

But despite its reputation for being sun-baked and molten, it is not the hottest planet in our Solar System (scroll down to find out who that dubious honor goes go!) Mercury, as imaged by the MESSENGER spacecraft, revealing parts of the never seen by human eyes. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Mercury is also the smallest planet in our Solar System, and is also smaller than its largest moon (Ganymede, which orbits Jupiter). And being equivalent in size to 0.38 Earths, it is just slightly larger than the Earth’s own Moon. But this may have something to do with its incredible density, being composed primarily of rock and iron ore. Here are the planetary facts: Diameter: 4,879 km (3,032 miles) Mass: 3.3011 x 1023 kg (0.055 Earths) Length of Year (Orbit): 87.97 Earth days Length of Day: 59 Earth days. Mercury is a rocky planet, one of the four “terrestrial planets” in our Solar System.

Mercury has a solid, cratered surface, and looks much like Earth’s moon. If you weigh 45 kg (100 pounds) on Earth, you would weigh 17 kg (38 pounds) on Mercury. Mercury does not have any moons. Temperatures on Mercury range between -173 to 427 degrees Celcius (-279 to 801 degrees Fahrenheit) Just two spacecraft have visited Mercury: Mariner 10 in 1974-75 and MESSENGER, which flew past Mercury three times before going into orbit around Mercury in 2011 and ended its mission by impacting the surface of Mercury on April 30, 2015. MESSENGER has changed our understanding of this planet, and scientists are still studying the data. Find more details about Mercury at this article on Universe Today, and this page from NASA. Venus: Venus is the second closest planet to our Sun, orbiting at an average distance of 108 million km (67 million miles) or 0.72 AU. Venus is often called Earth’s “sister planet,” as it is just a little smaller than Earth.

Venus is 81.5% as massive as Earth, and has 90% of its surface area and 86.6% of its volume. The surface gravity, which is 8.87 m/s², is equivalent to 0.904 g – roughly 90% of the Earth standard. A radar view of Venus taken by the Magellan spacecraft, with some gaps filled in by the Pioneer Venus orbiter. Credit: NASA/JPL And due to its thick atmosphere and proximity to the Sun, it is the Solar Systems hottest planet, with temperatures reaching up to a scorching 735 K (462 °C). To put that in perspective, that’s over four and a half times the amount of heat needed to evaporate water, and about twice as much needed to turn tin into molten metal (231.9 °C)!

Diameter: 7,521 miles (12,104 km) Mass: 4.867 x 1024 kg (0.815 Earth mass) Length of Year (Orbit): 225 days Length of day: 243 Earth days Surface temperature: 462 degrees C (864 degrees F) Venus’ thick and toxic atmosphere is made up mostly of carbon dioxide (CO2) and nitrogen (N2), with clouds of sulfuric acid (H2SO4) droplets. Venus has no moons. Venus spins backwards (retrograde rotation), compared to the other planets. This means that the sun rises in the west and sets in the east on Venus. If you weigh 45 kg (100 pounds) on Earth, you would weigh 41 kg (91 pounds) on Venus. Venus is also known and the “morning star” or “evening star” because it is often brighter than any other object in the sky and is usually seen either at dawn or at dusk. Since it is so bright, it has often been mistaken for a UFO! More than 40 spacecraft have explored Venus.

The Magellan mission in the early 1990s mapped 98 percent of the planet’s surface. Find out more about all the missions here. Find out more about Venus on this article from Universe Today , and this page from NASA. Earth: Our home, and the only planet in our Solar System (that we know of) that actively supports life. Our planet is the third from the our Sun, orbiting it at an average distance of 150 million km (93 million miles) from the Sun, or one AU. Given the fact that Earth is where we originated, and has all the necessary prerequisites for supporting life, it should come as no surprise that it is the metric on which all others planets are judged. Earth, pictured by the crew of the Apollo 17 mission. Credit: NASA Whether it is gravity (g), distance (measured in AUs), diameter, mass, density or volume, the units are either expressed in terms of Earth’s own values (with Earth having a value of 1) or in terms of equivalencies – i.e. 0.89 times the size of Earth.

Here’s a rundown of the kinds of Diameter: 12,760 km (7,926 miles) Mass: 5.97 x 1024 kg Length of Year (Orbit): 365 days Length of day: 24 hours (more precisely, 23 hours, 56 minutes and 4 seconds.) Surface temperature: Average is about 14 C, (57 F), with ranges from -88 to 58 (min/max) C (-126 to 136 F). Earth is another terrestrial planet with an ever-changing surface, and 70 percent of the Earth’s surface is covered in oceans. Earth has one moon. Earth’s atmosphere is 78% nitrogen, 21% oxygen, and 1% various other gases. Earth is the only world known to harbor life. Find out more about Earth at a series of articles found here on Universe Today , and on this webpage from NASA. Mars: Mars is the fourth planet from the sun at a distance of about 228 million km (142 million miles) or 1.52 AU.

It is also known as “the Red Planet” because of its reddish hue, which is due to the prevalence of iron oxide on its surface. In many ways, Mars is similar to Earth, which can be seen from its similar rotational period and tilt, which in turn produce seasonal cycles that are comparable to our own. Global image of the planet Mars. Credit: NASA The same holds true for surface features. Like Earth, Mars has many familiar surface features, which include volcanoes, valleys, deserts, and polar ice caps. But beyond these, Mars and Earth have little in common. The Martian atmosphere is too thin and the planet too far from our Sun to sustain warm temperatures, which average 210 K (-63 ºC) and fluctuate considerably. Diameter: 6,787 km, (4,217 miles) Mass: 6.4171 x 1023 kg (0.107 Earths) Length of Year (Orbit): 687 Earth days. Length of day: 24 hours 37 minutes.

Surface temperature: Average is about -55 C (-67 F), with ranges of -153 to +20 °C (-225 to +70 °F) Mars is the fourth terrestrial planet in our Solar System. Its rocky surface has been altered by volcanoes, impacts, and atmospheric effects such as dust storms. Mars has a thin atmosphere made up mostly of carbon dioxide (CO2), nitrogen (N2) and argon (Ar).If you weigh 45 kg (100 pounds) on Earth, you would weigh 17 kg (38 pounds) on Mars. Mars has two small moons, Phobos and Deimos. Mars is known as the Red Planet because iron minerals in the Martian soil oxidize, or rust, causing the soil to look red. More than 40 spacecraft have been launched to Mars. You can find out more about missions to Mars here. Find out more about Mars at this series of articles on Universe Today , and at this NASA webpage. Jupiter: Jupiter is the fifth planet from the Sun, at a distance of about 778 million km (484 million miles) or 5.2 AU.

Jupiter is also the most massive planet in our Solar System, being 317 times the mass of Earth, and two and half times larger than all the other planets combined. It is a gas giant, meaning that it is primarily composed of hydrogen and helium, with swirling clouds and other trace gases. Io and Jupiter as seen by New Horizons during its 2008 flyby. (Credit: NASA/Johns Hopkins University APL/SWRI). Jupiter’s atmosphere is the most intense in the Solar System. In fact, the combination of incredibly high pressure and coriolis forces produces the most violent storms ever witnessed. Wind speeds of 100 m/s (360 km/h) are common and can reach as high as 620 km/h (385 mph). In addition, Jupiter experiences auroras that are both more intense than Earth’s, and which never stop.

Diameter: 428,400 km (88,730 miles) Mass: 1.8986 × 1027 kg (317.8 Earths) Length of Year (Orbit): 11.9 Earth years Length of day: 9.8 Earth hours Temperature: -148 C, (-234 F) Jupiter has 67 known moons, with an additional 17 moons awaiting confirmation of their discovery – for a total of 67 moons. Jupiter is almost like a mini solar system! Jupiter has a faint ring system, discovered in 1979 by the Voyager 1 mission. If you weigh 45 kg (100 pounds) on Earth, you would weigh 115 kg (253) pounds on Jupiter. Jupiter’s Great Red Spot is a gigantic storm (bigger than Earth) that has been raging for hundreds of years. However, it appears to be shrinking in recent years. Many missions have visited Jupiter and its system of moons, with the latest being the Juno mission will arrive at Jupiter in 2016. You can find out more about missions to Jupiter here.

Saturn’s relatively thin main rings are about 250,000 km (156,000 miles) in diameter. (Image: NASA/JPL-Caltech/SSI/J. Major) Saturn: Saturn is the sixth planet from the Sun at a distance of about 1.4 billion km (886 million miles) or 9.5 AU. Like Jupiter, it is a gas giant, with layers of gaseous material surrounding a solid core. Saturn is most famous and most easily recognized for its spectacular ring system, which is made of seven rings with several gaps and divisions between them. Diameter: 120,500 km (74,900 miles) Mass: 5.6836 x 1026 kg (95.159 Earths) Length of Year (Orbit): 29.5 Earth years Length of day: 10.7 Earth hours Temperature: -178 C (-288 F) Saturn’s atmosphere is made up mostly of hydrogen (H2) and helium (He).

If you weigh 45 kg (100 pounds) on Earth, you would weigh about 48 kg (107 pounds) on Saturn Saturn has 53 known moons with an additional 9 moons awaiting confirmation. Five missions have gone to Saturn. Since 2004, Cassini has been exploring Saturn, its moons and rings. You can out more about missions to Saturn here. Find out more about Saturn at this series of articles on Universe Today and at this webpage from NASA. Uranus: Uranus is the seventh planet from the sun at a distance of about 2.9 billion km (1.8 billion miles) or 19.19 AU. Though it is classified as a “gas giant”, it is often referred to as an “ice giant” as well, owing to the presence of ammonia, methane, water and hydrocarbons in ice form. The presence of methane ice is also what gives it its bluish appearance. Uranus as seen by NASA’s Voyager 2 space probe. Credit: NASA/JPL Uranus is also the coldest planet in our Solar System, making the term “ice” seem very appropriate!

What’s more, its system of moons experience a very odd seasonal cycle, owing to the fact that they orbit Neptune’s equator, and Neptune orbits with its north pole facing directly towards the Sun. This causes all of its moons to experience 42 year periods of day and night. Diameter: 51,120 km (31,763 miles) Mass: You can find out more about Uranus at this series of articles on Universe Today and this webpage from NASA . Neptune: Neptune is the eighth and farthest planet from the Sun, at a distance of about 4.5 billion km (2.8 billion miles) or 30.07 AU. Like Jupiter, Saturn and Uranus, it is technically a gas giant, though it is more properly classified as an “ice giant” with Uranus. Neptune photographed by the Voyager 2 space probe. Credit: NASA/JPL Due to its extreme distance from our Sun, Neptune cannot be seen with the naked eye, and only one mission has ever flown close enough to get detailed images of it.

Nevertheless, what we know about it indicates that it is similar in many respects to Uranus, consisting of gases, ices, methane ice (which gives its color), and has a series of moons and faint rings. Diameter: 49,530 km (30,775 miles) Mass: 1.0243 x 1026 kg (17 Earths) Length of Year (Orbit): 165 Earth years Length of day: 16 Earth hours Temperature: -214 C (-353 F) Neptune is mostly made of a very thick, very hot combination of water (H2O), ammonia (NH3), and methane (CH4) over a possible heavier, approximately Earth-sized, solid core. Neptune’s atmosphere is made up mostly of hydrogen (H2), helium (He) and methane (CH4). Neptune has 13 confirmed moons and 1 more awaiting official confirmation. Neptune has six rings. If you weigh 45 kg (100 pounds) on Earth, you would weigh 52 kg (114 pounds) on Neptune. Neptune was the first planet to be predicted to exist by using math.

Voyager 2 is the only spacecraft to have visited Neptune. You can find out more about this mission here. Find out more about Neptune at this series of articles on Universe Today and this NASA webpage. We have written many articles about the planets for Universe Today. Here are some facts about planets , and here’s an article about the names of the planets .If you’d like more info on the Solar System planets, dwarf planets, asteroids and more, check out NASA’s Solar System exploration page , and here’s a link to NASA’s Solar System Simulator .We’ve also recorded a series of episodes of Astronomy Cast about every planet in the Solar System. Start here, Episode 49: Mercury .Venus is the second planet from the Sun, and it is the hottest planet in the Solar System due to its thick, toxic atmosphere which has been described as having a “runaway greenhouse effect” on the planet. Now you know! And if you find yourself unable to remember all the planets in their proper order, just repeat the words, “My Very Educated Mother Just Served Us Noodles.” Of course, the Pie, Ham, Muffins and Eggs are optional, as are any additional courses that might be added in the coming years!

Astronomy Cast also has some cool episodes about the Solar System. Here’s Episode 68: Pluto and the Icy Outer Planets , Episode 306: Accretion Discs , and Episode 159: Planet X . What is the closest planet to the sun? | Reference.com What is the closest planet to the sun? A: Quick Answer Mercury is the closest planet to the sun. The next closest planet is Venus, followed by Earth. Full Answer Being closest to the sun, Mercury has the shortest orbit of approximately 88 days long. Unlike some other planets, Mercury has no moons or rings. Due to having a near non-existent atmosphere, the surface temperature of Mercury varies widely. The surface can reach up to a temperature of 800 degrees Fahrenheit during the day, and as low as -280 degrees at night. Every two full orbits around the sun, Mercury revolves exactly three times. This means that the days on Mercury are extremely long compared to days on Earth. Earth Closest To Sun On Jan. 2, As Our Planet Reaches 'Perihelion' | The Huffington Post Earth Closest To Sun On Jan.

2, As Our Planet Reaches 'Perihelion' 01/02/2013 12:35 pm ET By: Geoff Gaherty Published: 01/02/2013 08:12 AM EST on SPACE.com If the sun looks a little larger than usual today, you're not seeing things. Today (Jan. 2) marks the time when the Earth is at perihelion, the point in its orbit at which it is closest to the sun. During perihelion, the Earth is exactly 91,402,560 miles (147,098,161 kilometers) from the sun.In actuality, you most likely can't see any difference between the apparent size of the sun today and its appearance at aphelion (when the Earth will be farthest from the star).The difference is only 3.4 percent, too small to be detected with the naked eye. On average, the Earth is about 93 million miles (150 million km) from the sun.

It will be farthest from the sun on July 5, when the Earth reaches aphelion, a point 94,508,960 miles (152,097,427 km) from the sun. The closest and farthest differences from the sun are very similar because the Earth’s orbit is very close to being circular. In fact, as planetary orbits go, ours is close to perfect. The eccentric Earth Only Venus and Neptune have more circular orbits than the Earth. On the other hand, if you look at the diagram of the orbits of the four inner planets accompanying this story, you may easily see that Mercury and Mars have orbits which are seriously eccentric. Astronomers use the term "eccentric" in its original mathematical sense, meaning "away from the center." A perfect circle has an eccentricity of 0. A straight line would have an eccentricity of 1. Everything else in between is an oval of some kind.

Here's a look at the innermost planets of the solar system in order of increasing eccentricity: Venus: 0.006785 Mars: 0.093277 Mercury: 0.205649 Looking at the diagram, the orbits of Earth and Venus look almost perfectly circular, while that of Mars is slightly closer to the sun towards the bottom. Mercury's orbit is very much closer to the sun on the right. If you look closely, there is a little tick mark on the orbits to indicate where perihelion lies. Don't confuse this mark with the little wedges which denote the orbital nodes, the points where the orbits cross the plane of the ecliptic. The Earth appears right next to the tick mark on its orbit marking perihelion in the image. Closer to the sun So what is the difference for the inhabitants of Earth when our planet is at perihelion instead of aphelion? The Earth is slightly warmer than it would be otherwise, about 4 degrees Fahrenheit (2.3 degrees Celsius). [ Earth Quiz: How Well Do You Know Our Planet?

] This perihelion effect is very minor compared to the effects of the tilt of our planet's axis. During December in the Northern Hemisphere, the North Pole is tilted away from the sun so that we receive less sunlight every day. At the same time, the South Pole is tilted towards the sun, so the Southern Hemisphere receives more sun and experiences summer. In June, the situation is reversed and we have summer in the northern hemisphere and winter in the southern hemisphere. The only effect of perihelion is that the winters in the Northern Hemisphere are very slightly milder than the winters in the southern hemisphere at the equivalent latitudes. Not as many people live as close to the South Pole as do close to the North Pole, so humanity isn't affected much. So enjoy that "big" January sun, and look forward to the longer days to come as Earth moves around its orbit to the point where we really receive more sun and spring arrives. This article was provided to SPACE.com by Starry Night Education , the leader in space science curriculum solutions. Follow Starry Night on Twitter @StarryNightEdu .

Question: Which planet is nearest to the Sun?
Answer: Mercury