Geothermal History of Mars

Within the various different studies on Mars, another very interesting one is the study of thermal history of the planet. There are some theories on whether Mars cooled off faster or slower than Earth. One theory for a slower cooling rate of Mars is based on the fact that it is only 1/3 the size of the Earth. But a paper from the Royal Society of Chemistry can proves that the cooling rate of Mars is actually slower than that of Earth.

Size comparison of Earth and Mars

This paper incorporates data that was collected from the gamma ray spectrometer (GRS) on the Mars Odyssey spacecraft. The GRS are used for elemental and isotopic analysis in airless environments, and work by measuring the distribution of the intensity of gamma radiation versus the energy of each photon. The GRS was specifically used to collect data of thorium, silicon, and iron from volcanic regions on Mars. The concentration of each elements helps the scientists learn something about Mars. 

• Thorium - A good indicator of how much the interior of the planet has melted. 
• Silicon - Found in silicon dioxide, this compound is good for measuring the depth at which melting occurs
• Iron - Useful for validating interference between thorium and silicon data

Incoming cosmic rays excite atoms in the soil which cause them to eventually release gamma radiation, which is what the GRS captures.

According to Michael Toplis, one of the French scientists working on this paper, the scientists converted the chemical composition into temperature and pressures to see hot the Martian mantle is and quantified the planet's rate of cooling. 

The potential temperature of the mantle, the temperature had there been no enthalpy change while extracting the elements, is 1400ºC, similar to that of Earth. And between older and younger volcano sites on Mars, there is only about 80ºC difference in temperature, showing that the planet would only have cooled about 80ºC during the last two or three billion years. 

Mars Odyssey Artistic Concept

It is amazing how even the Odyssey Orbiter, while not even on the surface of the planet, could gather such detailed data that scientists use to explain phenomenon in a logical method through chemistry. And interestingly, the Odyssey Orbiter is also the longest running Mars mission, being deployed on 2001 and besides making its own scientific observations, is used as a communications relay for robots on the surface.