In our solar system there are many things that revolve around the sun – that is, are in its orbit. The Earth goes around the Sun in 365 days. Seven other planets also circulate around the Sun with their moons, and with them other things, including asteroids and comets. But what is really asteroids and comets? Why do people confuse them? Did it fall – a star, an asteroid or a comet? How to explain to a child what a comet and an asteroid are, how do they differ? Let’s see.
An asteroid is just 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 one that was ever studied was two meters tall.
How many asteroids are in the solar system?
Our system has 780,290 asteroids, but not all of them are made of the same material. Scientists have divided them into three different groups depending on the composition – they can be metal, stony or consist of rocks that are more like clay or contain silicon.
We are still trying to learn more about asteroids. The Japanese Hayabusa-2 probe arrived at Ryugu asteroid. The NASA OSIRIS-REx mission is on its way to another asteroid, Benn. Each mission plans to take a sample from the surface of the asteroid and bring dust and stones to Earth.
Hayabusa-2 has already made many measurements on Ryuga. The spacecraft is circling around the asteroid and has already sent three cars to the surface. One of the machines is the landing module, which did not move much and examined the surface for 17 hours. Scientists on Earth are already exploring the measurement module, to find out more about how this asteroid was formed. The other cars are much smaller and are designed to move across the surface by jumping. They explore the asteroid from September 21.
Asteroids are cool.
But what is a comet?
In the Solar System, the known comets are much smaller than the 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 rather small and remains motionless, passing through the outer limits of the solar system. In comets, as a rule, the orbits go far from the Sun, where it is much colder than closer to the Earth. Sometimes comets come close to the Sun in orbits.
Approaching the sun, the comet heats up, the ice heats up and begins to stream with steam, creating clouds of dust and gas that follow the comet’s core. This coma is the fluffy tail of a comet. As the comet moves, dust and gas remains behind it, creating a tail that can stretch hundreds of thousands of kilometers. Closer to Earth, the tail looks like a bright band in the sky. It does not happen often, but when it happens, it looks amazing. People around the world have been watching comets for thousands of years.
In principle, we ourselves came close to the comets. The mission of Stardust flew through the tail of one of the comets and brought samples to Earth in 2006. The Rosetta mission, which ended in 2016, captured more than 100,000 amazing images of the comet’s surface.
Although several comets pass through 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 with your own eyes, this is a real celebration.
This is the main difference between comets and asteroids – an asteroid consists of stones or metals, and a comet is made of frozen material that melts as it approaches the Sun.