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Astronomers Have Detected a Curious Object at The Edge of Our Solar System

For over 70 years, scientists have been predicting the existence of a certain kind of object in the outer Solar System. Small in size, these potential bodies are thought to constitute an important early step in the planet formation process.

Since these hypothetical objects are only between 1 and 10 kilometres in radius (0.6 to 6.2 miles), it's tricky to spot them from where we sit. But now astronomers think they have done it. By staring at the sky for hours, they've obtained evidence of an object just 1.3 kilometres (0.8 miles) in radius, in the vicinity of Pluto's orbit. The find could finally be a representative of this proposed class of small, 'kilometre-sized' Kuiper Belt objects.

Given their small size and dimness, the objects can't be seen directly. So astronomers from the National Astronomical Observatory of Japan tried another method - occultation. This means essentially lying in wait and staring at a star, waiting for an object to pass in front of it and block some of its light. They picked out 2,000 stars, and spent a total of 60 hours observing them with the help of two small, 28-centimetre (11-inch) telescopes. The work paid off - the team found evidence of a tiny body called a planetesimal orbiting the Sun at a distance of 32 astronomical units (AU). This actually places it within Pluto's orbital range, which is between 29 and 49 AU.

[...] And the team isn't done yet. They have their sights on a much more distant prize. "Now that we know our system works, we will investigate the Edgeworth-Kuiper Belt in more detail," [NAOJ astronomer Ko] Arimatsu said. "We also have our sights set on the still undiscovered Oort Cloud out beyond that."

Also at Space.com.

A kilometre-sized Kuiper belt object discovered by stellar occultation using amateur telescopes (DOI: 10.1038/s41550-018-0685-8) (DX)

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