Scientists are studying so-called dark comets. These are mysterious objects that look like asteroids but emit large amounts of gases. It is known that they are of two kinds and at least one of them may be involved in the appearance of water on Earth.
Comets, asteroids and water
There is a lot of water on Earth. There is more water in our seas and oceans than the planet should have received from its environment during its formation. The excess must have come from somewhere else, but scientists have not yet come to a definitive conclusion about where. A new study may have found its source – dark comets.
Most objects in the Solar System are not planets and their satellites at all, but much smaller bodies – comets and asteroids. They often have orbits lying in both the inner and outer parts of the solar system, are composed of gravel, ice, and organic matter in various combinations, and are considered to be their carriers.
At the same time, the difference between comets and asteroids is usually made not by differences in chemical composition, but by the way they manifest themselves. Simply put, comets have tails, while asteroids do not.
Dark comets
And that is where the story of dark comets comes in. As it turns out, many of the asteroids show cometary activity. As a rule, astronomers do not see these emissions themselves, but they can witness their presence because of the acceleration they give to the body.
Usually, the orbit of an asteroid is determined by the impact of large bodies on it, which is relatively easy to calculate. If its vector deviates from the calculations, it means that something is vaporized from the surface, going from the solid state directly into the gaseous state. And that gives it additional momentum.
The non-gravitational acceleration of objects that look like asteroids was first noticed in 2017, when the first interstellar asteroid ʻOumuamua came to us. With its appearance and unusual shape, it already made a lot of noise. And when scientists noticed that the trajectory of the body differed from that which it should have been given by the Sun’s gravity, everyone immediately started talking about an alien ship.
Two populations of dark comets
Of course, Oumuamua was not an alien spacecraft. However, his case interested scientists, and they began to look for other objects that look like asteroids, but experience non-gravitational acceleration. They are called dark comets.
As of today, 14 such objects have been discovered. They form two rather different populations. The first is made up of large bodies with diameters of 1.5-2 kilometers, which orbit far from the Sun. The second is made up of relatively small bodies about 300 meters in diameter orbiting close to the Earth.
It is dark comets that are thought to be the possible source of water on Earth. However, no one knows for sure. Scientists hope that the commissioning of the Vera Rubin telescope will help to learn more about them. In addition, the extended mission of Hayabusa2 could reach one of these objects in 2031 and show what their surface looks like.
Provided by phys.org
