Astronomy Blog

The size of Charon

In this week's edition of Nature, there is a report detailing observations of Pluto's moon Charon occulting a background star. The observations were made using part of the Very Large Telescope, the 0.5m Campo Catino Austral Telescope and the 2.5m Jorge Sahade telescope which are all based in South America.

At each of the three sites they saw the star passing behind a different part of Charon and this allowed accurate measurements of the diameter. The diameter is now found to be 603.6 km (±5.0km) which is incredibly accurate for a measurement of something so far away. Once you have a diameter for Charon you can also combine that with the mass of the moon to work out the average density. It turns out to be about 1.7 gm/cm³ which is equivalent to "an icy body with about slightly more than half of rocks". You can listen to this on the Nature podcast or read the ESO press release for more details.

Pluto is making the news quite a lot at the moment. It should get even more exciting soon as the first mission to Pluto should be launching in about 12 days time.