In our solar system, there are many things that revolve around the sun - that is, are in its orbit. The Earth revolves around the Sun in 365 days. Seven other planets also orbit the Sun, along with their satellites, and with them other gizmos, including asteroids and comets. But what exactly are asteroids and comets? Why do people confuse them? Was it a star, an asteroid or a comet? How to explain to a child what a comet and an asteroid are, how are they different? Let's figure it out.
An asteroid is simply a rock orbiting the sun. Asteroids are smaller than planets, but some of them can be very large. The largest, according to scientists, is Vesta - more than 550 kilometers across. The smallest ever studied was two meters high.
How many asteroids are there in the solar system?
There are 780,290 asteroids in our system, but not all of them are made of the same material. Scientists have divided them into three different groups depending on their composition - they can be metallic, rocky, or composed of rocks that look more like clay or contain silicon.
We are still trying to learn more about asteroids. The Japanese probe Hayabusa-2 arrived at the asteroid Ryugu. NASA's OSIRIS-REx mission is en route to another asteroid, Bennu. Each mission plans to take a sample from the surface of an asteroid and bring dust and rocks back to Earth.
Hayabusa 2 has already taken many measurements on Ryugu. The spacecraft is circling the asteroid and has already sent three vehicles to the surface. One of the machines is a lander, which did not move much and explored the surface for 17 hours. Scientists on Earth are already investigating the module's measurements to find out more about how this asteroid formed. Two of the other machines are much smaller and are designed to move on the surface by jumping. They have been exploring the asteroid since September 21st.
Asteroids are cool.
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But what is a comet?
In the solar system, there are much fewer known comets than asteroids - 3526.
A comet, unlike an asteroid, looks more like a dirty piece of ice than a rock. The middle of the comet, called the nucleus, is quite small and remains stationary as it passes through the outer reaches of the solar system. Comets tend to orbit far from the Sun, where it is much colder than closer to Earth. Sometimes comets come close to the Sun in orbits.
As it approaches the Sun, the comet heats up, the ice heats up, and steam begins to flow, creating clouds of dust and gas that follow the comet's nucleus. It's a coma - the fluffy tail of a comet. As the comet moves, dust and gas remain behind it, creating a tail that can stretch hundreds of thousands of kilometers. Closer to Earth, the tail looks like a bright streak in the sky. It doesn't happen often, but when it happens it looks amazing. Humans all over the world have watched comets for thousands of years.
In principle, we ourselves came close to comets. The Stardust mission flew over the tail of one of the comets and brought samples back to Earth in 2006. The Rosetta mission, which ended in 2016, captured over 100,000 stunning images of the comet's surface.
Although several comets zip near the Earth every year, many of them can only be seen through a telescope. When a comet has such a bright coma that you can see it with your own eyes, it is a real holiday.
This is the main difference between comets and asteroids - an asteroid is made of stones or metals, while a comet is made of frozen material that melts as it approaches the Sun.
Ilya Khel
