If you think that the asteroid risk is high on Earth, you wouldn’t want to be on Jupiter. According to preliminary results, the largest planet in the Solar System is hit on average 6.5 times every year.
This latest estimate, though, presented at an international workshop on Jupiter, actually significantly reduces the expected number of impacts on the gas giant from previous studies. Revaluating this number was only possible thanks to the extensive observations of Jupiter by a group of 60 non-professional astronomers around the world.
The value of 6.5 was calculated statistically based on the few observed impacts compared to the many observations of Jupiter. If more than 6.5 impacts happened every year, we should have detected many more.
“Dramatic impacts with Jupiter can be captured with standard amateur equipment and analyzed with easy-to-use software,” said Marc Delcroix, who coordinates the group of astronomers, in a statement. “But to get a good estimate of how often these events occur, we need observers around the world who are willing to collaborate to create a programme of more-or-less continuous monitoring of Jupiter.”
The monitoring of Jupiter by the group started 3 years ago. They collected more than 1,344 hours of footage in 53,000 videos, which were analyzed by other citizen scientists from Europe, the U.S., and Australia. In the videos, they didn’t find a single fireball.
It might sound peculiar, but not seeing something is just as scientifically important as seeing something. The group was able to provide an extensive but not at all complete surveillance of Jupiter, enough to provide statistics on the number of impacts. If impacts were more common they would have seen them.
The project was set up by Isshi Tabe and Dr. Jun-chi Watanabe following the observations of a fireball hitting Jupiter on August 20, 2010, by four Japanese amateur astronomers. Including this one, there have only been four recorded impacts on Jupiter.
Previous fireball flashes were spotted when comet Shoemaker-Levy collided in 1996, and during the 2009 impact. The latest one was observed on March 17 this year by amateur astronomers Gerrit Kernbauer and John McKeon. McKeon was luckily filming Jupiter at the time, so there’s capture footage of the impact as it happened.
More observation campaigns are currently planned to both refine the estimate and potentially spot more fireballs. Jupiter is believed to protect the central Solar System from large impacts, so understanding exactly what goes on will lead to a deeper understanding of how the planets and planetesimal interact in the Solar System.