Asteroids in the outer Solar System
A paper published this week in the Astrophysical Journal presents the first direct observations of small asteroids in the outer solar system. This all began in June, when two amateur astronomers, on different continents, happened to be pointing their telescopes at Jupiter when they both simultaneously observed a two-second flash, apparently in Jupiter's atmosphere. Since then, astronomers have been working to explain what was seen.
It's likely that what was seen was a small meteor burning up in Jupiter's upper atmosphere, and research published this week produces a fairly precise estimate of the size of the object: probably around 10 metres across.
That's fascinating because it's the first time that such a small object has been directly observed at such a distance. We've always suspected that there must be a large number of small rocks in the solar system, but have never been able to see them at these distances or get much idea of how many there might be.
This story was given another exciting twist in August when a second similar flash was observed by another pair of amateur astronomers. It seems highly likely that these events have always been occuring at a rate of a few per year, but that because they've generally been thought impossible to observe, they've gone unrecorded. If so, we may well expect to see a flurry of more similar discoveries in coming months.
If we do, that will be really exciting because we will begin to get an idea of exactly how many asteroid there are around Jupiter, and what the distribution of their sizes looks like. That will really help us to understand how material is distributed in the asteroid belt, and perhaps help us to understand where it came from.