Observations from NASA’s Transiting Exoplanet Survey Satellite (TESS) made an impressive detection just 63.4 light-years away from our Sun. Thirty alien comets (from outside the solar system) were seen transiting the young star Beta Pictoris, with their long tails lighting up the skies of the planets that form there.
Beta Pictoris is home to a dusty planet-forming disk that was discovered in 1983 by IRAS, the Infrared Astronomy Satellite. The disk contains at least two planets, both gas giants. Spectral observations gathered since 1987 point to the presence of comets (or “falling evaporating bodies” as they were referred to at the time) releasing dust and gas in this disk.
In 2019, astronomers led by Sebastian Zieba of the University of Innsbruck in Austria discovered three exocomets transiting Beta Pictoris using TESS data.
Now, a study conducted by another team, led by astronomer Alain Lecavelier des Etangs of the Institute of Astrophysics in Paris, France, has managed to detect another 27, making a total of 30 alien comets.
“These additional exocomet detections are very useful because we now see a lot of different comets of different sizes, which means we can start to compare their size distribution — how many small ones we see compared to larger ones,” said Matthew Kenworthy, an astronomer at the Comets Observatory. Leiden, the Netherlands, and a member of both research teams, in an interview with the website Space.com.
Although Beta Pictoris is not the first star around which exocomets have been discovered, it is the first for which it has been possible to measure the size distribution of comets.
Based on the size of the tails and the amount of dust these comets produce (using the Hale-Bopp comet as a model), Lecavelier des Etangs’ team was able to measure the diameter of the nucleus of each of them, which vary between 3 and 14 kilometers in diameter.
Also according to the new study, the size distribution of exocomets coincides with the size distribution of comets in our solar system.
This pattern suggests that the processes that formed the exocomets around Beta Pictoris are the same processes that formed the comets in our solar system. In turn, the way comet formation reflects on the formation of planets is also likely to be the same. By studying exoplanetary systems, astronomers can learn more about how the planets in the solar system, including Earth, formed.
The prevailing model of planet formation, at least for rocky planets, is that they are the result of collisions and mergers between smaller bodies – comets, asteroids and planetesimals.
If the gravity of the bodies involved in a collision is strong enough, it can shape the resulting debris into a larger body. If the colliding objects are too small, then there won’t be enough gravity to merge them, and instead they will break up and disperse, resulting in smaller bodies. This is exactly what astronomers see in the size distribution of Beta Pictoris’ exocomets.
“The size distribution is remarkably similar to that predicted for a debris population resulting from collision and fragmentation cascades,” said Lecavelier des Etangs.
For scientists, it’s reassuring to get more evidence that planets form in the same way around different stars, so we can draw direct comparisons with our solar system.
“The formation of planets and comets is linked,” Kenworthy said. “So our first measurement of a distribution of comets outside our solar system evolves our understanding of these processes.”
Comets are also believed to be important for the emergence of life, potentially providing water and biological building blocks for the surfaces of planets.
Although Beta Pictoris is only about 25 million years old, this process of comet impacts bringing life ingredients to hitherto invisible rocky planets may have already begun.
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