02.20.2007
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| A simplified view of the interactions between incoming cosmic rays and elements on the surface of Mercury, which produce fast neutrons, slow neutrons, and gamma rays. (Image Credit: K. Garver) |
Understanding if ice exists on the surface of Mercury, and if so what types, will mark an important component of the investigations by the MESSENGER spacecraft about the origin and evolution of the solar system's inner planets. This month, instrument engineers at the Johns Hopkins University Applied Physics Laboratory in Laurel, MD, turned on the Neutron Spectrometer (NS)-one of several sensors aboard MESSENGER that will be key to sorting out the mystery of Mercury's surface.
The NS will collect data about the composition of the uppermost tens of centimeters of Mercury's crust by measuring the numbers and energies of neutrons that reach the MESSENGER probe as it passes near the planet. The NS together with a gamma ray sensor make up the Gamma-Ray and Neutron Spectrometer (GRNS) instrument.
The NS will map variations in the fast, thermal, and epithermal neutrons Mercury's surface emits when struck by cosmic rays. "Fast" neutrons shoot directly into space; others collide with neighboring atoms in the crust before escaping. If a neutron collides with a small atom (like hydrogen), it will lose energy and be detected as a slow (or thermal) neutron. Scientists can look at the ratio of thermal to epithermal (slightly faster) neutrons across Mercury's surface to estimate the amount of hydrogen-possibly locked up in water molecules-and other elements.
The NS will remain on during most of MESSENGER's cruise phase and return data from Venus flyby 2 in June, three Mercury flybys in 2008 and 2009, and one Earth year in Mercury orbit starting in 2011.
For more complete information on the instrument, click here.
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