Unless you happen to be born under the horoscope signs of Gemini or Virgo, which are ruled by the planet Mercury or be a scientist who is interested in astronomy the tiny planet of Mercury might have slipped below your radar.
Mercury seldom makes it into the news as it is far to hot to sustain life and it is literally and figuratively overshadowed by its more glamorous neighbour the Sun. Yet all this could be about to change as on March 17th, 2012, the tiny MESSENGER spacecraft completed its primary mission to orbit and observe the planet Mercury for one Earth-year.
The surfeit of surprises from the mission has completely altered our understanding of the solar system’s innermost planet. Scientists have found that Mercury’s core which was suspected to occupy a greater fraction of the planet’s interior than do the cores of Earth, Venus, or Mars, is larger than anyone guessed, in fact Mercury’s core occupies about 85% of the planetary radius.
Due to its small size, scientists thought the interior should have cooled to the point that the core would be solid. However, subtle motions measured from Earth-based radar, combined with MESSENGER’s newly measured parameters of the gravitational and magnetic fields suggest an active core that is at least partially liquid.
Mercury’s core is totally different from any other planetary core in our Solar System. Earth has a metallic, liquid outer core sitting above a solid inner core. Mercury appears to have a solid silicate crust and mantle overlying a solid, iron sulfide outer core layer, a deeper liquid core layer, and possibly a solid inner core.
So what would the surface of Mercury look like? Well, for a start it would be way too hot for anyone to go there but if you could visit and look about according to MESSENGER’s Mercury Laser Altimeter (MLA) which has provided the first-ever precise topographic model of the planet’s northern hemisphere you might see small rises in the surface.
These are much smaller than the mountains on the Moon or Mars which means there has been large-scale changes to Mercury’s landscape since the earliest phases of the petite planet’s geological history, furthermore, the surface is rough. If you stood by the 960 mile wide interior plains of the Caloris impact basin you would notice that they have been changed over time so that part of the basin floor now stands higher than the rim.
The elevated portion appears to extend for approximately half the planetary circumference at mid-latitudes. These features imply that large-scale changes to Mercury’s topography occurred after the era when the impact basin was formed and the production of Mercury’s volcanic plains had ceased.
Sean Solomon of the Carnegie Institution is delighted with the results from the MESSENGER programme…
“The first year of MESSENGER orbital observations has yielded a wonderful harvest of results…From Mercury’s extraordinarily dynamic magnetosphere and exosphere to the unexpectedly volatile-rich composition of its surface and interior, our inner planetary neighbour is now seen to be very different from what we imagined just a few years ago. The number and diversity of new findings being presented this week to the scientific community in these papers and in presentations at this week’s Lunar and Planetary Science Conference provide a striking measure of how much we have learned to date.”
He is not alone in his enthusiasm, as the mission’s many successes have lead to it to being extended for another year.