Spotlight on Mercury!
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.
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.
(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.