The chief scientist for the Mercury MESSENGER mission reminisces its findings and upcoming finale
April 28, 2015 | and |Water ice is present at Mercury's south pole.
On April 30, after more than four years in orbit around Mercury, NASA's MESSENGER probe will plunge to its doom. Out of fuel and long past its intended one-year mission, the spacecraft will crash into the planet's surface at a speed of 3.9 kilometres a second.
Mission head Sean Solomon, a planetary scientist and director of the Lamont-Doherty Earth Observatory in Palisades, New York, sat down with to talk about what MESSENGER has accomplished since it launched in 2004. The following interview has been edited and condensed.
Why did you want to send a mission to Mercury?
What does it look like close up?
The hollows were a landform we didn't expect. They are bright depressions created by the loss of near-surface material. They are some of the youngest features on the planet, and speak to some sort of unstable material whose identity we are still working out.
What did you find at its poles?water ice at both poles.
There is dark material covering the polar deposits, which we have identified tentatively as organic-rich material of the sort that we see in the outer Solar System, in organic-rich meteorites and comets. I don’t think anybody could count Mercury as habitable. But it is a witness to the delivery of the ingredients for habitability, from the outer Solar System to the inner Solar System.
What about its weird magnetic field?
Which MESSENGER findings surprised you?how Mercury got put together predicted that it would be depleted in volatiles, much like the Moon. But instead, we see sulphur [at] ten times the average for Earth. We see sodium and potassium. We see chlorine, one of the most volatile elements that we have the ability to measure.
That means we really didn't understand the particular way that Mercury became an iron-rich planet. It wasn't a process with sustained high temperatures that drove off the volatile elements. I don't think the final chapter has been written on what the most likely explanation is for the formation of Mercury.
In 2017, the European and Japanese space agencies plan to launch the BepiColombo mission to Mercury. What's left for it to discover?
What will MESSENGER’s impact day be like?
I have worked on the mission for 19 years. It's like losing a member of the family. Even pre-knowledge doesn't prepare you completely for the loss.
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