Jupiter, if it were sentient, could be wondering what it did to make space rocks dislike it so much, given it has been hit twice in the last five weeks. In fact, such collisions are so common that a gap of more than a month is probably a welcome break for the massive planet, yet capturing them on camera is extremely unusual. If you do not consider the several linked impacts of Shoemaker-Levy, this is the first time two have filmed so close together. On September 13, amateur astronomers all over the world saw a dazzling light when something massive collided with Jupiter. At least five of them recorded the collision. Surprisingly, this was only the seventh human-observed impact event on Jupiter.
Now, on October 15, a Japanese amateur astronomer known as @yotsuyubi21 on Twitter and Dr. Arimatsu Ko of Kyoto University have both reported an impact, making it the ninth recorded incident. This event, which occurs at the 12-second mark in the video below, is considerably fainter, so most of the telescopes that saw the September event may be too small to see it, but it was still bright enough to cause a visible flash as it burned up in Jupiter’s atmosphere. Dr. Ko has even shared photos of the flare at various wavelengths.
Because of Jupiter’s massive gravity and size, it will inevitably be bombarded by more space junk than any other object in the Solar System. In 1994, the first mention of a Jovinian effect was made. Pieces of the comet Shoemaker-Levy 9 had been orbiting Jupiter for a long period in that case, and the pace of its orbital degradation had been calculated in advance. As Jupiter’s rotation brought them around to face Earth, space probes observed the collision and Earth-based observatories recorded the after-effects, giving astronomers the first-ever direct observation of two bodies colliding in the Solar System.
Perhaps astronomers had seen impacts before, but there was no way of knowing until video cameras became widely available. The next filmed incident was in 2009, and each year after then, there has been one. Astronomers calculated that 20-60 incidents large enough to seen from Earth occur each year based on the 2019 collision. Others have given lower estimates, but many of them are on Jupiter’s far side, when the planet is near to the Sun from our perspective or when it is otherwise unlikely to seen. There is still a lot we could theoretically see, and the growing number of amateurs filming through medium-sized telescopes means we are seeing more of them.
Such phenomena may entice more people to gaze at the enormous planet with their cameras, but they can also be scientifically significant. We track molecules left behind by Shoemaker-Levy to determine the speed of the winds in Jupiter’s upper atmosphere. Aside from Shoemaker-Levy, the striking objects are often too small for humans to detect directly at this distance — roughly the size of a house. The flashes they produce as they burn up in Jupiter’s upper atmosphere, on the other hand, can be rather dazzling. Anyone else on Jupiter who captured this – or any other – flash should contact the Organized Autotelescopes for Serendipitous Event Survey (Oases) here.