A New Moon for Neptune

Did you know it has been 30 years since a spacecraft swung by Neptune?  Voyager II was the first and last spacecraft to visit the strange ice world which (with the demotion of Pluto) is the outermost planet of our solar system.  A ball of gas, ice, rock and iron 17 times the size of Earth, Neptune is the third most massive planet and is the most dense of all the giant planets. However we know surprisingly little about this distant neighbor–a fact which was vividly demonstrated this week when astronomers discovered an unexpected new moon orbiting the planet.  This new moon brings the tally of Neptune’s moons to 14. Mark Showalter, a researcher at the SETI institute in California, discovered the little satellite accidentally, while working on another project and the new body was confirmed with the Hubble Space telescope (which is also still out there, by the way).

Neptune’s largest moon is the retrograde Triton.  The second largest moon is Proteus, an irregular polyhedron with a diameter of 420 kilometers, named after the shape-shifting old man of the sea.  The new moon, which is named “Hippocamp”, after a seahorse like Greek sea monster (above) has a diameter of about 20 kilometers (about the length of Manhattan) and seems to have been formed from ejecta left over from when some primordial body slammed into Proteus.

Astronomers have spent comparatively little time studying Uranus and Neptune compared to the other planets of the solar system–which is somewhat ironic since most of the exoplanets we are finding are ice giants.  It seems like they might be noticing this gap in their knowledge.  A new mission to the ice giants is the third top mission priority in a vote-based ranking of proposed probe missions (by astrophysicists…nobody asked me what I want *cough*  balloon mission to Venus’ atmosphere).  Hopefully we will get our act together and launch a modern robot out to the big blue ice worlds in the not-too-distant future.

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