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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).

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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.

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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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Sometimes if you aren’t watching the heavens (or the news) closely enough, you miss a major astronomical discovery.  For example last summer, astronomers discovered a galaxy which formed only one or two billion years after the Big Bang (so I guess it is unclear whethter I missed this story by one year or by 12 billion).  At any rate, the galaxy hunters used the Hubble space telescope to peer through a powerful gravitational lense far away in space.  Gravitational lenses are areas where timespace is warped like a huge lense by high-gravity phenomena, and a viewer can use them like a huge lense to see far-away objects.  By using the Hubble telescope together with the gravitational lense they were able to see back a dozen billion years in time to the edge of the universe…as it once was not long after creation.  What they saw perplexed them.

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There is a fundamental difference between galaxies.  Galaxies where stars are being formed tend to be blue and spiral shaped (like our own beloved Milky Way!).  Galaxies where stars have largely stopped forming are “red and dead” since the remaining stars tend to be long lived red dwarf stars and the bright young (short-lived) blue stars are mostly gone.  These red galaxies are not shaped like spirals, but tend to be elliptical shaped (like an egg or a football, not like one of those evil gym machines).

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The ancient galaxy at the edge of the universe was neither of those colors or shapes. It was a dense yellow disk.  Stars formed in an (enormous) accretion disk but then, for some reason, new star formation stopped.  The blue stars burned out (“the light that shines twice as bright etc, etc..”), but the yellow middle aged stars were still burning.   The galaxy had three times the mass of the Milky Way but scrunched into a pancake of much smaller area.

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So do galaxies always form as disks and then either become self-renewing blue spirals (maybe by colliding with other galaxies or clouds of dust)or dead red footballs?  Or was this early yellow disk galaxy an abberation? Or is our own galaxy truly new (well…newish…being only a few billion years old)?  I do not understand astrophysics well enough to answer these questions or even formulate them properly (although I get the sense some of these questions may not yet be answered by anyone in any comprehensive way), but I would love to hear what people can add to this rudimentary yet compelling story of shapes and colors.

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Ceres (optimized image from the Hubble Space telescope)

Today’s post topic is located in the depths of space far far away from the bats, pumpkins, and haunted deserts I have been writing about for October. The dwarf planet Ceres is located in the midst of the asteroid belt between Jupiter and Mars.  The only dwarf planet in the inner solar system, Ceres is only 950 km (590 miles) in diameter, but it is sufficiently large to have become spherical from its own gravity (and it is by far the largest asteroid). Named after Ceres (Demeter), the mythological goddess of growing things whose daughter was abducted by Hades and who gave the secrets of agriculture to humankind through the farmer Triptolemus, the dwarf planet was discovered in 1801 by Italian astronomer Giuseppe Piazzi, a Roman Catholic priest of the Theatine order.  Ceres was the first asteroid to be discovered and it comprises a third of the asteroid belt’s total mass.

A comparison of the sizes of the Earth, Moon, and Ceres

The nebular hypothesis proposes that the solar system formed as a great cloud of space dust and gas coalesced into a disk which then further coagulated into small clumps, then into planetesimals, then into moon-sized planetary embryos, and finally into planets. Ceres is one of the few (or maybe the only) planetary embryos which formed four and a half billion years ago but somehow did not get smushed together with other like bodies to form a planet or hurled off into deep space. The dwarf planet probably consists of a rocky core surrounded with an icy mantle of frozen water.  Ceres is believed to contains 200 million cubic kilometers of water–more fresh water than in all the lakes, rivers, clouds, swamps, ponds (and everything else) on Earth. The Hubble telescope has photographed several mysterious surface features on Ceres including a dark spot believed to be a crater (now informally named after Piazzi) and several bright spots, the nature of which is unknown.

Image of the bright spots on Ceres (taken by the Hubble Space telescope)

Astronomers are profoundly curious about Ceres and hope to better understand the history of the solar system by examining this surviving planetary embryo.  Additionally, the chemical makeup of Ceres is similar to that of Earth. Scientists seeking extraterrestrial life have concentrated on Europa and Mars, but Ceres is next on their short list.

Astronomers will soon have some of their answers about Ceres.  The asteroid probe Dawn is currently orbiting the asteroid Vesta–but its mission there is scheduled to end in July of 2012.  At that point Dawn will power up its ion thrusters and fly to Ceres. In February of 2015 Dawn will enter permanent orbit around the little planet and we will finally have some of our answers.

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