Comets have been in the news a lot recently, with the ongoing investigation of comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft and the close flyby of Mars by comet Siding Spring this past week. But there is also another comet discovery – one much further out from our solar system. With the help of the HARPS instrument, on the European Southern Observatory’s (ESO) 3.6-meter telescope, astronomers have identified nearly 500 comets orbiting the nearby star Beta Pictoris, as part of an unprecedented new survey of exocomets orbiting other stars.
Just like planets, comets appear to be common around other stars, and astronomers have hit pay dirt with the star Beta Pictoris, a young star about 63 light-years away. Being relatively young at an estimated age of only 20 million years, the star is still surrounded by a huge disk of dust and gas (proplyd) — the kind capable of forming planets later on.
Scientists have found evidence for nearly 500 individual comets orbiting Beta Pictoris, which appear to be of two types: old comets which have already made repeated passes by their star and younger comets which are thought to have more recently formed from the collision of other larger objects like asteroids.
The discovery was made using the HARPS instrument at ESO’s La Silla Observatory in Chile. More than 1,000 observations from between 2003 and 2011 were analyzed by the research team to come up with the results. A total of 493 comets were observed, some comets several times and for a few hours.
Astronomers were able to measure the speed and size of the gas clouds containing the comets, and even the shape and orientation of the orbits of some of the comets, as well as their distance from the star.
The existence of comets around Beta Pictoris had been suspected for almost 30 years, due to subtle changes seen in the light of the star over time. Isolated individual comets, being so small, would not have that effect, but a swarm of many comets could, as the collective number of the cometary tails forming when approaching the star could absorb some of the light coming from the star.
According to Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study, “Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system.”
The orbits of the older comets are thought to be controlled by a massive exoplanet, Beta Pictoris b, which orbits about 600 million miles (1 billion kilometers) from the star. Being able to analyze hundreds of comets around another star is a very unique and unprecedented achievement.
“For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago,” Kiefer said.
The older comets seem to show less activity, meaning that they have probably already vented most of their original ice supply after making multiple trips close to the star. The younger comets are more active and also appear to have similar orbits. This suggests they share a common origin, such as the disintegration of a much larger object.
As Kiefer concluded, “For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago.”
The new findings were presented in the paper “Two families of exocomets in the Beta Pictoris system” which was published in the journal Nature on 23 October 2014.
This article was first published on SpaceFlight Insider.