April 6, 2015 | David F. Coppedge

Messages from Mercury

With MESSENGER in its final days before impact, the innermost planet has become a familiar place.

NASA’s MESSENGER spacecraft has already made history before its scheduled crash into the planet Mercury on April 30.  After 10 years in space, 4,000 orbits (PhysOrg) and 10 terabytes of science data (see infographic), it will take years to digest the many discoveries made. After a near 40-year hiatus, MESSENGER, managed by the Johns Hopkins Applied Physics Lab (APL), has provided a giant leap in Mercury science since the brief flybys of a far-less-capable spacecraft, Mariner 10, in 1974. MESSENGER’s swan song, a low-altitude campaign, has brought more discoveries to waiting planetary scientists and the public.

A pre-crash news conference will be held on April 16. Results of a previous science conference (March 16) have been posted on PhysOrg.  Among the many surprises were thousands of  “hollows” (ranging in size from tens of meters to several kilometers across and tens of meters deep) that show Mercury is not a dead planet.  Because the “hollows appear to be younger than the planet’s freshest impact craters,” the finding “suggests that Mercury is a planet whose surface is still evolving.” Also, some scarps are thought to be less than 50 million years old, just a 1% fraction of the planet’s assumed 4.5 billion year history.  One more “geologically young” trait was found—young volatiles at the poles:

MESSENGER’s low-altitude campaign has enabled imaging of the polar deposits in the permanently shadowed floors of Mercury’s near-polar craters at higher resolutions than ever previously obtained, says Nancy Chabot, the Instrument Scientist for MESSENGER’s Mercury Dual Imaging System (MDIS) and a planetary scientist with APL.

“Acquired with the broadband filter of MDIS, low-altitude images show that the deposits have sharp, well-defined boundaries and are not disrupted by small, young impact craters,” says Chabot. “These characteristics indicate that the deposits are geologically young. This inference points either to delivery of volatiles to Mercury in the geologically recent past or to an ongoing process that restores the deposits and maintains the sharp boundaries.”

Another mystery was solved, that of Mercury’s dark color. The BBC News and Science Magazine relay the answer: the planet has been spray-painted with comet dust and with carbon from certain carbon-rich meteorites. Because it is so close to the sun, Mercury gets pummeled often by comets and wandering bodies pulled in by the sun’s gravity. The high-speed impacts create amorphous carbon with the darkness of pencil lead (graphite) and soot. The BBC article claims it has been going on for billions of years, but does not explain.  A press release from Brown University says that after billions of years, “Mercury’s surface should be anywhere from 3 to 6 percent carbon.”

As with almost every object in the solar system, actual data provided by visiting spacecraft have been surprising, revolutionary, and contrary to expectations. Usually the data do not fit the A.S.S. assumption. Three evidences of youth are provided above; there are more, such as the magnetic field that should be long gone. Creation scientists freed from the bad A.S.S. of the moyboys may wish to look at the spray-painting by comets and make some projections about how much soot should be there after 4.5 billion years. Perhaps young craters can tell something about the depth of the material.

Two other missions are worth watching for evidence of youth: the Rosetta Mission (ongoing) at a comet, and the July arrival of New Horizons at Pluto. Already, some are expecting it to be “gusty and gassy” according to Space.com.  For something out in the cold reaches of the solar system, that will be difficult for the moyboys to explain (but they will make up a story, as they always do).


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