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March 11, 2014

The object known as Quaoar is in a bit of limbo. It’ll probably be designated as a dwarf planet — an object similar to Pluto. One key factor in determining its qualification as a dwarf planet is its size. Estimates have ranged by quite a bit. But some observations made last year are helping narrow that range.

Artist's concept of Quaoar [NASA]Artist's concept of Quaoar [NASA]Measuring Quaoar’s size is difficult in part because it’s a long way out — close to four billion miles. And no matter what its exact size is, it’s small — probably no more than a third the diameter of the Moon. Measuring something that small at such a great range is tough. So estimates have ranged from about 525 to 775 miles.

Astronomers have used several techniques to zero in on Quaoar’s size. For one, they’ve used Hubble Space Telescope to make a physical measurement of its size. Since Hubble is above Earth’s blurring atmosphere, it sees objects more clearly than most ground-based telescopes, so it produces better size measurements.

Astronomers have also used infrared telescopes to measure the amount of heat that Quaoar pumps into space, which helps narrow down the range.

And last year, they watched as Quaoar passed in front of a distant star. Timing how long it blocked the star from view produced another measurement of its size — roughly 700 miles. But the measurement didn’t reveal its shape. To be considered a dwarf planet, Quaoar also must be nice and round — just like Pluto.


Script by Damond Benningfield, Copyright 2014

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