While astronomers are still hunting for a huge new planet somewhere beyond Neptune, smaller objects have been turning up with surprising regularity lately. Now, a team at the National Astronomical Observatory of Japan has discovered a new class of object that has long been thought to exist in the Kuiper belt on the fringes of the solar system. It's a small body on the scale of a few kilometers.
The new object, with a diameter of 2.6 km (1.6 mi), was spotted using the tried-and-true transit method – essentially, watching stars and waiting for the shadow of an object as it passes between the star and Earth. Since it can be hard to time that right, the researchers brute-forced it by monitoring around 2,000 stars for 60 hours, using two small, 28-cm (11-in) telescopes set up on a rooftop.
This is the first object of its class to have been spotted in the Kuiper belt, the expanse of rocky and icy debris that extends out past Neptune. While there are likely hundreds of thousands of objects out there, we only really know about the big ones. Pluto is the headliner of course, with a diameter of 2,377 km (1,477 mi), but other dwarf planets like Haumea and Makemake, with diameters of 1,632 km (1,014 mi) and 1,430 km (889 mi), respectively, are nothing to sneeze at either. By comparison Ultima Thule, which New Horizons just buzzed a few weeks ago, is a tiny 32 km (20 mi) long.
The majority of objects out there should be even smaller, on the scale of between two and 20 km (1.2 and 12 mi) wide. Unsurprisingly, it's hard to spot objects this small at that distance, so nothing has been found in this range – until now.
The researchers say this object is a kind of "missing link" in planet formation. Planets start life as matter clumping together in disks of dust and gas, and eventually swell to become the full-size objects we see today. It makes sense that intermediate, kilometer-sized objects would need to exist, but this marks the first direct observation of one in the Kuiper belt.
The research was published in the journal Nature Astronomy.
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