Mercury: “A world in and of its own”

In March this year Nasa’s Messenger probe became the first spacecraft to orbit Mercury.  And, as the BBC reports, a few days ago Nasa released the scientific observations and data collected during the first three months of its scheduled year-long mission.  In the process a number of hypotheses about the innermost planet were consigned to the “dust bin of science”.  Mercury is not like the Moon, nor like the Earth, and it’s not “the burnt-out cinder of the solar system”. [All images credit: NASA/The Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington]

Here’s the press conference via NASAtelevision.

And a stunning image of the Degas crater on Mercury

This spectacular view of the crater Degas was obtained as a high-resolution targeted observation (90 m/pixel). Impact melt coats its floor, and as the melt cooled and shrank, it formed the cracks observed across the crater. For context, Mariner 10’s view of Degas is shown at left. Degas is 52 km in diameter and is centered at 37.1° N, 232.8° E.

With the improved view from orbit, they’ve found evidence of volcanic activity and tectonic deformation. 

MESSENGER’s orbital images have been overlaid on an image from the second flyby shown in Image 1.2a. Even for previously imaged portions of the surface, orbital observations reveal a new level of detail. This region is part of the extensive northern plains, and evidence for a volcanic origin can now be seen. Several examples of “ghost” craters, preexisting craters that were buried by the emplacement of the plains, are seen near the center of the mosaic.

Polar crater floors that are in permanent shadow and which could contain more water ice than our own Moon. 

A portion of a northern hemisphere mosaic of Mercury’s surface (500 m/pixel) on which the radar image in Image 3.3 has been superposed. The prominent impact crater circled in red hosts an area of polar deposits and was profiled several times by MLA early in MESSENGER’s science mapping phase. The crater is centered at 82.3°N, 342.8°E, and is 24 km in diameter.

And a surprisingly asymetric magnetic field.

As a result of the north-south asymmetry in Mercury’s internal magnetic field, the geometry of magnetic field lines is different in Mercury’s north and south polar regions. In particular, the magnetic “polar cap” where field lines are open to the interplanetary medium is much larger near the south pole. This geometry implies that the south polar region is much more exposed than in the north to charged particles heated and accelerated by solar wind–magnetosphere interactions. The impact of those charged particles onto Mercury’s surface contributes both to the generation of the planet’s tenuous atmosphere and to the “space weathering” of surface materials, both of which should have a north-south asymmetry given the different magnetic field configurations at the two poles.

Here’s a video from that press conference focusing in on a 13 km wide crater with a distinctively dark impact melt.

All of the multimedia resources used in the conference are available here.

And, because I can, here’s Messenger’s wondrous last look at the Earth.