Commentary: James W. Head III

Water, organic molecules on Mercury

November 30, 2012  |  Media Contact: Kevin Stacey |  401-863-3766
Mercury, where surface temperatures can reach 800 degrees Fahrenheit, would not be a likely spot to find water ice. James W. Head III, professor of geological sciences, calls Thursday’s news from NASA a “stunning announcement.”

James W. Head III“A stunning announcement” — NASA scientists detect water ice and probable organic molecules on Mercury.James W. Head III
“A stunning announcement” — NASA scientists detect water ice and probable organic molecules on Mercury.
Where do the building blocks of life — water and organic molecules — originate? One would hardly expect answers to this fundamental question to come from Mercury, the planet in our Solar System closest to the Sun.

But in a stunning announcement Thursday accompanying publication of three papers in the journal Science, scientists from the NASA Mercury MESSENGER mission described the detection not only of water ice on Mercury, but probable organic molecules in association with the ice. Found in deep impact craters in the north polar region of Mercury, the ice and organic material form in permanently shadowed “cold traps” on the crater floors, where temperatures can be as cold as minus 370 degrees Fahrenheit.

Mercury is too close to the Sun to hold an atmosphere, and thus the surface can reach 800 degrees Fahrenheit. If a comet containing ice and organic molecules impacts the surface, the molecules migrate to the polar cold trap, the only place where they can remain. Over time, the ice starts to “evaporate” but the organic molecules remain, forming a protective lag and preserving the ice from further loss.

Mercury’s north poleRed areas (from MESSENGER) and yellow areas (from Earth-based radar) are in persistent shadow. Credit: NASA/JPLMercury’s north pole
Red areas (from MESSENGER) and yellow areas (from Earth-based radar) are in persistent shadow. Credit: NASA/JPL
Although life has not been found on Mercury, this discovery underlines the very high likelihood that the building blocks of life are brought to all planetary bodies in their early history by cometary impacts in abundance, and that even in the harshest environments, ice can remain for millions and perhaps billions of years. Indeed, the volume of ice detected on Mercury, between 100 billion and one trillion tons, means that the ice represents a laboratory to study the sources and accumulation of ice over geologic time. Similar types of accumulations are thought to occur on the Earth’s Moon.

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