LAMP detects hydrogen and Hg in GRAIL plumes

Despite skepticism of the possibilities of success, the Lyman-alpha mapping project (LAMP) instrument on-board the Lunar Reconnaissance Orbiter (LRO) managed to detect both singly ionized hydrogen and mercury (a marker for a variety of elements) in the twin plumes following the impacts of the twin GRAIL spacecraft Ebb and Flow as each rose up into sunlight, December 17, 2012. Each plume became visible in the instrument's narrow field of view about 20 seconds apart, as LRO's orbit carried it along a path nearly perpendicular to the GRAIL twin's final course toward impact [VMA/LP].

"Lights are dimming on both coasts," GRAIL principal investigator Maria Zuber reported Tuesday, at a press conference held at the Lunar and Planetary Science Conference near Houston. Continuing digestion of data collected by the GRAIL twin lunar gravity probes "Ebb" and "Flow," long after their successful impacts on the Moon last December, has required the mission's investigators to become "the largest users of supercomputers at NASA, dimming the lights at both Goddard (Space Flight Center in Maryland) and JPL (Jet Propulsion Laboratory in California)."

The latest GRAIL gravity maps of the Moon, to be presented at the conference, are double the resolution of those published only weeks ago, with finer resolutions to come, including fine grained local maps of regions like Mare Orientalis expected late this summer. 

"One of the greatest surprises," Zuber said, "has been the strong correlation between gravity and topography, especially as the spacecraft results continue to increase in resolution."

"Gravity is no longer an impediment to lunar exploration," Zuber said, hinting at the large scale lumpiness of the Moon's composition, where, at low altitudes, "there's no such thing as a stable orbit."

Kurt Retherford of the Southwest Research Institute, principal investigator for the Lyman-alpha mapping project (LAMP) instrument installed on the Lunar Reconnaissance Orbiter (LRO) joined Zuber at the press conference, Tuesday, along with Mark Robinson of Arizona State, principal investigator for the LRO's sensitive Narrow and Wide Angle cameras (LROC NAC and WAC).

Robinson's surprise, reported by LROC earlier on Tuesday (HERE), was the relatively dark material exclusively excavated by both impacts. Investigators have speculated this result, captured during several sequential orbital passes, at 1.6 meters resolution by the LROC NAC, may be due to the presence of hydrocarbon compounds in the small volume of fuel remaining on-board the GRAIL twin spacecraft, or in the composite material used in the construction of the spacecraft themselves.

Retherford summarized a presentation on the LRO's LAMP observations following the GRAIL impacts he was scheduled to deliver at the conference Tuesday afternoon. Despite skepticism from flight planners of seeing anything, because of the geometry of the LRO orbit together with the position of the Sun and the narrow field of view of the LAMP instrument, designed to detect reflected starlight from the areas on the Moon in permanent shadow, Retherford and colleagues reported direct detection of marker spectra of specific elements in the impact plumes of both spacecraft, rising into sunlight soon at a predictable rate following the GRAIL impacts.

"The LAMP detected emissions from both mercury and and hydrogen atoms in these plumes," Retherford reported. "The spectral, spatial, and light-curve analyses used in these gas detections are consistent with previous LAMP observations of the LCROSS impact in 2009."

"The full implication of these very recent detections of material released from a northern high-latitude mountainside is not yet determined, though the transport of volatiles species is known to concentrate them near the poles."

"The detection of atomic hydrogen emission is a first for LAMP, a time dependent detector charge depletion feature has made previous searches for this species difficult. The implications of this detection are still being considered, but its potential relevance to studies of sub-surface volatiles or surface hydratation at high-to-polar latitudes (not necessarily in permanent shadow), is intriguing."