Spotlight on Mercury!
5/6/16

On Monday May 9, we will be able to observe a transit of Mercury in front of the Sun, that is to say, an observable passage of the planet between the Earth and our star. While this is a very rare event, two recent publications shed new light on the history of the planet closest to the Sun.

Using data gathered by the American probe MESSENGER, geologists at the University of Liege have recreated “samples” of Mercury in the laboratory in order to better understand the formation and evolution of the rocks that make up the planet. From extraction from the core to the eruption of very ancient lavas covering its surface, the magmatic history of Mercury is revealed by experiments conducted in extreme conditions.

Mercure large

“When the MESSENGER probe orbited Mercury, I was engaged in post-doctoral studies at MIT”, recalls Bernard Charlier, who is currently developing an experimental petrology laboratory at the University of Liege. “I therefore had access to the first data available on the composition of the planet’s surface.  In 2013 we published a first analysis based on this preliminary data but we needed more in-depth analysis which we completed in Liege. This resulted in the publication of two recent articles” (1).

MESSENGER did an outstanding job in providing a chemical mapping of the planet thereby supplying data on many tens of thousands of analysis points on Mercury’s crust. Bernard Charlier continues, “In 2013, we only had 11 analysis points on which to base our conclusions, today, our conclusions are based on 49,000 points”!

Mercury: a window on the formation of the solar system

The rocks on the surface of Mercury, in the form of lava, were deposited 3.7 to 4.2 billion years ago. By way of comparison, the surface of the Earth is very recent, 200,000 years maximum even though there are rock outcrops dating back to 4 billion years ago. The existence of very old rocks on the surface evidently provide information on the initial stages of formation of the planet. At the moment of its formation, a planet is composed of two parts, a core (essentially of iron) surrounded by a silicate mantle. The silicated part partially remelts producing the lavas that will go on to form the crust on the surface.
Earth-Mercury mantle

(1) Namur O, Collinet M, Charlier B, Grove TL, Holtz F, McCammon C (2016) Melting processes and mantle sources of lavas on Mercury. Earth and Planetary Science Letters 439: 117-128. http://www.sciencedirect.com/science/article/pii/S0012821X16000522

Namur O, Charlier B, Holtz F, Cartier C, McCammon C (sous presse) Sulfur solubility in reduced mafic silicate melts: Implications for the speciation and distribution of sulfur on Mercury. Earth and Planetary Science Letters.

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