One of the old favorites for folks looking to understand solar system formation is the star Beta Pictoris. This young star was discovered to have a disk of material around it in the late 1980s, and as our technology progressed, we found more and more cool stuff in this 20 million-year-old planetary system. In recent years, two gas giants were discovered in this system, and now, thanks to data from the TESS mission, individual comets have been seen as well.

I have to admit — I didn’t think we were quite to the point of making this kind of measurement, but last night I read the paper in Scientific Reports, which was led by Alain Lecavelier des Etangs, and I’m a believer.

Beta Pictoris is an edge-on system just over sixty light-years away, and the combination of a large central star and perfect alignment allows us to catch objects passing between us and the star with relative ease, including (just barely) the passage of comets.

In 156 days of observations with TESS, thirty different light dips were detected that are consistent with the passage of comets in front of this hot, A-type star. The depth and length of each dip in light, presumably caused by these comets circling Beta Pictoris, allowed rough sizes to be calculated. Remarkably, the scatter in sizes observed in Beta Pictoris’ comets is statistically similar to the distribution in our own solar system. This seems to reflect comets forming in the same way in that system as they formed in our system.

Now, for those of you asking, “But how do they know they are comets and not something else?” I’m with you. Star spots and other misbehaviors in stars can masquerade as transits. To prove something is a comet, you really want to be watching the star with a spectroscope so that the gases in the star can be measured as they are backlit by the star. And while all thirty presumed comets weren’t watched this way, there have been spectroscopic measurements of comet transits in the past. Here, past behavior is used to inform current interpretations, and the size distribution really makes sense for the answer being comets.

This paper could be proven wrong, but I think they’re right, and until we get even better systems in space, this is the data we have, and this discovery is kind of awesome.

More Information

CNRS press release

“Exocomets size distribution in the Beta Pictoris planetary system,” Alain Lecavelier des Etangs et al., 2022 April 28, Scientific Reports