Astrophysics and Astronomy Science

Astronomy and Astrophysics are very similar sciences and are the most important to learn when exploring planets. Why is this you may ask? Well we do not want people exploring gas giants do we now? We need to first learn about how space and planets and their systems work. This is the very first thing anyone who explores space must learn. So what is Astronomy and Astrophysics? What exactly is a gas giant? How do I know which planet to explore? Sit in, it is time to learn science!

***Planet Science:***

What are the types of planets?

Here is a list of Planet types, However we will only be focusing on Terrestrial Planets and Gas Giants for the time being. Be sure to look at the given vocabulary if you are unfamiliar with any words used. So what is a:

**Terrestrial Planet)** This is a planet, much like Earth, made of rock or metals. It has a solid surface and can be land on, usually safely. These planets consist of molten heavy and metal core, few moons and topological features such as craters, volcanoes, mountains etc.

**Gas Giant)** This is a planet, much like Jupiter, made of gas like hydrogen and helium with small rocky cores. They are huge planets with low density, this is because they are made of mostly gas. These planets are not always big, but they all have common characteristics for example: Rings, multiple moons, acid rain, huge storms etc.

**So which are safe to explore and how do you know which is which?**

 Terrestrial planets will not always be inhabited but those that are, are usually safe. Make sure you have special gear to protect yourself from unknown sources or acid rain etc. Please stay clear of gas giants/planets. These are highly dangerous. The pressure is extremely enormous and the atmosphere may be contained with poisonous gases and crystals that when inhaled could kill you. Not to mention you have possible chances of being caught in storms like the red eye of Jupiter.

**How are planets formed?**

Well there are many ways a planet could be formed depending on which type of planet they are and what galaxy they were created in. Lets take a look at the Milkyway galaxy and how their terrestrial planets were formed. (Mercury, Venus, Earth and Mars) One theory is that these planets were formed by the same spinning disc that created the sun named 'Solar Nebula' which was composed of mainly hydrogen and helium. The nebula had a specific amount of angular *momentum* orbiting the forming sun and soon particles started to clump together as gravity attracted one another. Over a few millions of years of this and there were about 110 chunks of objects called *planetesimals*, each with a diameter of about 1000 m. Soon more and more of these chunks collided together creating *protoplanets*. These were about the same size and shape of the Earth's moon. The *accumulation* or gathering of material to form terrestrial planets are called *accretion*. For the specific solar system consisting of Earth, it is thought that the early temperature of the system is the reason why there is terrestrial and gas planets. The inner system was very hot about 2000K while the outer system was low around 50K (K is for Kelvin; A way of measuring temperature). In the inner solar system, only substances with very high melting points would have remained solid. All the rest would have vaoprized. So the inner solar system objects are made of iron, silicon, magnesium, sulfur, aluminum, calcium and nickel. Many of these were present in compounds with oxygen. There were relatively few elements of any other kind in a solid state to form the inner planets. The inner planets are much smaller than the outer planets and because of this have relatively low gravity and were not able to attract large amounts of gas to their atmospheres. In the outer regions of the solar system where it was cooler, other elements like water and methane did not vaporize and were able to form the giant planets. These planets were more massive than the inner planets and were able to attract large amounts of hydrogen and helium, which is why they are composed mainly of hydrogen and helium, the most abundant elements in the solar system, and in the universe.

How do planets work?

What is gravity?

***Vocabulary:***

**Astronomy)** The branch of science which deals with celestial objects, space, and the physical universe as a whole.

**Astrophysics)** The branch of *astronomy* concerned with the physical nature of stars and other celestial bodies, and the application of the laws and theories of *physics* to the interpretation of astronomical observations.

**Galaxy)** A system of millions or billions of stars, together with gas and dust, held together by gravitational attraction.

**Gravity)** The force that attracts a body towards the centre of the earth, or towards any other physical body having mass.

**Planetesimals)** A minute planet; a body which could come together with many others under gravitation to form a planet.

**Accumulation)** The acquisition or gradual gathering of something.

**Accretion)** Growth or increase by the gradual accumulation of additional layers or matter.

**Momentum)** The quantity of motion of a moving body, measured as a product of its mass and velocity