As boring as the moon?  Just a burned-out cinder?  Not Mercury.  True to tradition for planetary exploration, the MESSENGER spacecraft has served up a plate of surprises about the innermost planet.  In orbit since March, the ship is sending theorists back to the drawing board to figure out a number of puzzling phenomena, some unique to Mercury.  Commentators fall into two categories: those that are flabbergasted, and those who say all is well.

Science magazine published the first seven papers this week since the orbital tour began.  Here were the headlines that resulted on various news outlets:

  • Science Daily: “Mercury Not Like Other Planets, MESSENGER Finds.”
  • PhysOrg: “Epic volcanic activity flooded Mercury’s north polar region”
  • BBC News: “‘Hollows’ mark Mercury’s surface.”  The article begins, “Hands up who thought Mercury was just a dull rock circling close to the Sun?  The latest data returned by Nasa’s Messenger probe shows that view couldn’t be further from the truth.”
  • National Geographic: “Mercury ‘Hollows’ Found—Pits May Be Solar System First.”
  • New Scientist: “Bright ‘hollows’ on Mercury are unique in solar system.”
  • Space.com: “Planet Mercury Full of Strange Surprises”

By contrast, Richard Kerr’s summary article in Science was titled, calmly, “Mercury Looking Less Exotic, More a Member of the Family” (30 September 2011: Vol. 333 no. 6051 p. 1812, DOI: 10.1126/science.333.6051.1812).  Judging from abstracts and reports, the following discoveries seem the most interesting:

  1. Hollows:  The hollows spoken of are unique structures found within some craters.  Irregular in shape and up to miles across, these depressions with sharp rims, often found in clusters and found across Mercury, appear to be collapse pits – as if volatile substances escaped from underground and caused surfaces to fall.  The closest analogues are on Mars, where similarly shaped features result from sublimation of ice at the poles; but here on Mercury there is no ice.  Science Daily called them “an unexpected class of landform on Mercury and suggest that a previously unrecognized geological process is responsible for its formation.”  New Scientist said of them, “They may have been formed by processes still active today, and change our view of the small rocky planet’s history.”  Science Daily quoted a scientist who believes they are actively forming today – further evidence that “Mercury is radically different from the Moon in just about every way we can measure.”  National Geographic quoted David Blewett (Johns Hopkins): “”The old thinking was, Oh, Mercury, it’s an old burned-out cinder and not so interesting… here’s this jaw-dropping thing that nobody ever predicted.”….

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