Mercury May Be Meteor Like
Geologists at MIT have traced part of Mercury’s cooling history and based on their findings have determined that the planet likely has the composition of a meteorite.
Cecil and Ida Green Professor of Geology in MIT’s Department of Earth, Atmospheric, and Planetary Sciences, Timothy Grove says this new information on Mercury’s past is of interest for tracing Earth’s early formation.
The team utilized data collected by NASA’s MESSENGER spacecraft, (The MErcury Surface, Space ENvironment, GEochemistry, and Ranging probe) which orbited Mercury between 2011 and 2015, and collected measurements of the planet’s chemical composition with each flyby.
“It’s true of all planets that different age terrains have different chemical compositions because things are changing inside the planet,” Grove says. “Why are they so different? That’s what we’re trying to figure out.”
In an effort to answer that question, Grove started by recreating Mercury’s lava deposits in the lab using MESSENGER’s 5,800 compositional data points, and selected two extremes: one representing the older lava deposits and one from the younger deposits.
The team found a surprising disparity in the two samples: The older rock melted deeper in the planet, at 360 kilometers, and at higher temperatures of 1,650 C, while the younger rock melted at shallower depths, at 160 kilometers, and 1,410 C. The experiments indicate that the planet’s interior cooled dramatically, over 240 degrees Celsius between 4.2 and 3.7 billion years ago—a geologically short span of 500 million years.
“Mercury has had a huge variation in temperature over a fairly short period of time, that records a really amazing melting process” Grove says. “We now know something like an enstatite chondrite was the starting material for Mercury, which is surprising, because they are about 10 standard deviations away from all other chondrites.”
Grove concluded by saying “The next thing that would really help us move our understanding of Mercury way forward is to actually have a meteorite from Mercury that we could study. That would be lovely.”
Grove and his colleagues, including researchers from the University of Hanover, in Germany; the University of Liége, in Belgium; and the University of Bayreuth, in Germany, have published their results in Earth and Planetary Science Letters.