There are no comets in the solar system alone. For decades, scientists have known that there are exocects: comets that revolve around other stars.
Do you know the exoplanets, but do you know the exocometers? However, scientists have known them for 35 years. This Thursday, April 28, 2022, a new step has been taken with a more in-depth analysis of 30 “exocomets” located in a young planetary system, that of the star β Pictoris. A study, broadcast by the CNRS, was published in Scientific reports.
Comets, but outside the solar system
What exactly are we talking about? ” The exocetus is by definition a comet that is not in the solar system, but in an extrasolar system. In the same way that exoplanets are planets in extrasolar systems “Astrophysicist Alain Lecavelier, director of research at the CNRS, summarizes with Numerama. Therefore, they are comets, but in orbit around stars other than the Sun.
Comets are highly studied objects because they are true remnants of the formation of the solar system. More than 3,740 comets are known, each with its own specifics. But each can be described as ” a small rocky core a few kilometers in diameter, composed of rocks and ice, in an elongated orbitExplain Alain Lecavelier. During the period when it is close to its star, the ice it contains evaporates. It is these ejections that give rise to these splendid cometic tails that can be seen in the solar system. Lucky observers can even admire the tails of comets at a glance; this was the case for the C / 2020 F3 (NEOWISE) during the summer of 2020.
Here, it is thanks to a space satellite, TESS (“Transiting Exoplanet Survey Satellite”) that scientists were able to study in more detail the characteristics of 30 exocometers orbiting β Pictoris. They have been known since 1987, but now we know that they are between 3 and 14 kilometers in diameter.
” Until then, the gas envelope surrounding the core had been observed by spectroscopy. “, emphasizes the scientist (that is, the study of spectra resulting from electromagnetic radiation, a very useful method in astrophysics to determine the chemical composition of a body). With the TESS data, we saw the tail of dust passing in front of the star, like the transits of exoplanets in front of its star. The star becomes a little less bright for a few hours. »
Observing the dusty tail of comets in this way is an important breakthrough, because this is what has allowed scientists to estimate the size of the nuclei of these exocomets. Impossible to expect to see these pieces of rock, which are too small.
Exocometers have bears the scars of a violent past “
” Which also interests uscontinues Alain Lecavelier, is the size distribution of objects: knowing how many large exocomets there are compared to the number of small ones. It is a tracer of fragmentation phenomena. This measure of the size distribution of the objects that make up the β Pictoris system is the first to be made outside the solar system. An important interest then is to make comparisons with what we know about the solar system. ” It turns out it’s incredibly similar. All these objects have a very important history of collisions and fragmentations, as they have preserved the scars of this violent past.. »
Work on exocetus (or even comets) is far from over. ” There are now two extensions: to find other stars around which there are exocomets; study in more detail the comets and comets we already know “Space experts can still use non-TESS space telescopes: Hubble, of course, but also James Webb, which should be operational in the summer of 2022.