Star systems are not just suns and planets, they can also comprise moons, asteroids, and even comets. And thanks to painstaking analyses by astronomers and citizen scientists, the catalog of objects orbiting other stars has grown and grown. Now we can add three exocomets to the count.
The objects orbit the star Beta Pictoris, a very young and bright star 63.4 light-years from Earth. The star was the first one found to have an exocomet back in 1987, years before the first exoplanet was discovered. Now, researchers have discovered more exocomet signatures thanks to NASA’s latest planet hunter TESS, which uses the different approach of studying how the light of a star dips as a comet’s coma and tail pass in front of it. The findings will be published in Astronomy & Astrophysics and are currently available on arXiv.
“This discovery is really important for the science of extrasolar comets for several reasons,” co-author Dr Grant Kennedy, from the University of Warwick, said in a statement. “Beta Pictoris had been thought to host exocomets for three decades from a different technique, and the TESS data provide long overdue and independent evidence for their existence.”
Researchers took the light signals from Beta Pictoris and eliminated the underlying changes expected from such a variable star. However, the corrected signal was not perfectly constant. It showed three asymmetric dips, which the researchers believe to be consistent with the signature of evaporating comets.
“What we are seeing is not the comet nucleus itself, but the material blown off the comet and trailing behind it," explained co-author Professor Konstanze Zwintz of the University of Innsbruck. "So the TESS data do not tell us how big the comets were, since the extent of the dust tail could be very big and not very dense, or less big and more dense. Both situations would give the same light curve.”
The light curve of comets might give intriguing insights into the composition of other systems and the researchers are now planning to extend the search to other stars. They are especially intrigued by young systems. Beta Pictoris is just 23 million years old.
“In the future, we want to find answers to the question of how often exocomets occur and whether their number really decreases with the age of a star," added Professor Zwintz. "Information about this is important because by analysing the comets around a young star we can also draw conclusions about the history of our own Solar System. Because we know that our solar system showed considerably more comets in 'young years'.”
TESS, which stands for Transitioning Exoplanet Survey Satellite, is currently studying 500,000 stars including the 1,000 closest red dwarfs and is expected to discover 20,000 exoplanets in its two-year primary mission which ends next year.