We're still trying to map the solar system's vast outer reaches beyond Neptune. It's teeming with space rocks, some of which are many miles across, and could at some point become meteors shooting towards Earth.
The outer edges of the solar system is home to countless rocks known as trans-Neptunian objects, or TNOs. Of course, the most famous of these is the former planet Pluto - in fact, for over sixty years, it was the only trans-Neptunian object we knew about other than its moon Charon. In the last two decades, we've discovered 1,000 new TNOs, and 200 of them have now earned minor planet status.
Of course, that's probably only a small fraction of all the rocks that are out there in the Kuiper Belt, scattered disk, and vast Oort Cloud, the three main regions of the trans-Neptune solar system. The rocks are incredibly faint, with average magnitudes between 25 and 27. To put that in some perspective, that sort of magnitude is 100 million times fainter than anything we could hope to see with the naked eye. And that's just the bigger rocks - the really tiny one are even fainter and even more impossible to detect.
Now astronomers have combed through old Hubble Space Telescope archives to identify fourteen new TNOs. They did this by watching for evidence of slight movement of objects in the photographs, indicating the objects were in our solar system. They then combined data about the distance and brightness of the object to figure out the size of the TNOs, as well as a rough estimate of their orbits.
The newly discovered TNOs range from 25 to 60 miles in diameter, which makes them about 2 to 4% the size of Pluto. A particularly intriguing pair appear to be in a binary orbit much like Pluto and Charon, as the two TNOs orbit each other while revolving around the Sun. This first study examined only a third of a square degree of the sky, so there's plenty more space to explore and potentially hundreds more new TNOs to be found.