GRAIL Impacts the Moon

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  • 
    ID: 4218 Visualization

    Procellarum Rifts for the Cover of <i>Nature</i>

    Oct. 1st, 2014
    (updated May 3rd, 2023)

    Oceanus Procellarum, or the Ocean of Storms, is the largest of the dark maria visible to the naked eye on the near side of the Moon. Its relatively flat surface of basaltic lava covers most of the northwest quadrant of the Moon's disk.The leading explanation of Procellarum's origin is that it is a large, ancient impact basin. But the authors of a paper in the October 2, 2014 edition of the journal Nature suggest instead that this region is the result of the way the lunar crust cooled billions of years ago.The red in the image shown here is part of a pattern of gravity anomalies revealed by data from the Gravity Recovery and Interior Laboratory (GRAIL) mission. Jeffrey Andrews-Hanna and his coathors interpret this rectangular feature as a remnant of the plumbing system that moved magma to the surface of the Moon's near side, flooding low-lying areas with lava.The rectangular shape differs from the circular shape expected for an impact basin. It more closely resembles the pattern of cracks that form in materials subjected to thermal stress. In fact, the paper compares the shape of the Procellarum gravity anomaly with a feature spanning the south pole of Enceladus, the ice-covered moon of Saturn. ||

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  • 
    ID: 4175 Visualization

    GRAIL Gravity Map for the Cover of <i>Geophysical Research Letters</i>

    June 17th, 2014
    (updated Aug. 25th, 2023)

    This print-resolution still image was created for the cover of the May 28, 2014 issue of Geophysical Research Letters. It features a free-air gravity map of the Moon's southern latitudes developed by S. Goossens et al. from data returned by the Gravity Recovery and Interior Laboratory (GRAIL) mission.If the Moon were a perfectly smooth sphere of uniform density, the gravity map would be a single, featureless color, indicating that the force of gravity at a given elevation was the same everywhere. But like other rocky bodies in the solar system, including Earth, the Moon has both a bumpy surface and a lumpy interior. Spacecraft in orbit around the Moon experience slight variations in gravity caused by both of these irregularities.The free-air gravity map shows deviations from the mean gravity that a cueball Moon would have. The deviations are measured in milliGals, a unit of acceleration. On the map, purple is at the low end of the range, at around -400 mGals, and red is at the high end near +400 mGals. Yellow denotes the mean.The map shown here extends from the south pole of the Moon up to 50&deg;S and reveals the gravity for that region in even finer detail than the global gravity maps published previously. The image illustrates the very good correlation between the gravity map and topographic features such as peaks and craters, as well as the mass concentration lying beneath the large Schr&#x00F6;dinger basin in the center of the frame. The terrain in the image is based on Lunar Reconnaissance Orbiter (LRO) altimeter and camera data. ||

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  • 
    ID: 4054 Visualization

    LAMP Observes GRAIL Impact

    March 19th, 2013
    (updated May 3rd, 2023)

    The Gravity Recovery and Interior Laboratory (GRAIL) mission comprised a pair of satellites that together measured the gravity field of the Moon. GRAIL ended its mission with a planned impact into the side of a lunar mountain on December 17, 2012. Lunar Reconnaissance Orbiter (LRO) maneuvered into an orbit that would allow it to observe the impact. One of LRO's instruments, the Lyman-Alpha Mapping Project (LAMP), looked for the chemical signatures of a number of elements, including hydrogen and mercury, in the dust plume kicked up by the impact.This animation shows the relative positions of GRAIL and LRO at the time of the impact, as well as the view from LAMP as it scanned for the dust plume. The LAMP sensor is a 6.0&deg; x 0.3&deg; slit that was positioned to look over the limb of the Moon, so that it would be pointed into the tenuous dust plume with only the sky in the background. This observation was possible, in part, because GRAIL impacted on the night side of the Moon, where there was no concern that LAMP's sensitive detector could be blinded by sunlit terrain. From Earth, the Moon was a waxing crescent at the time of the impact. ||

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  • 
    ID: 11186 Produced Video

    Final Orbit

    Feb. 12th, 2013
    (updated May 3rd, 2023)

    On December 17, 2012, two NASA spacecraft slammed into a ridge near the moon's north pole. The collisions marked the planned end to NASA's GRAIL (Gravity Recovery and Interior Laboratory) mission. Flying in formation, the twin, washing machine-sized probes, named Ebb and Flow, spent 351 days in lunar orbit mapping the moon's gravitational field. The maps revealed features of the lunar surface and interior in incredible detail, providing scientists with new information about the moon's craggy topography and lumpy crust. Using these maps, researchers will be able to peer back at the moon's early history and better understand its origin and development, along with that of Earth and the other rocky bodies in the solar system. The visualization shows the two spacecraft's final three orbits and their mission-ending crash. ||

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  • 
    ID: 4014 Visualization

    GRAIL Primary Mission Gravity Maps (AGU 2012)

    Dec. 5th, 2012
    (updated May 3rd, 2023)

    The Gravity Recovery and Interior Laboratory (GRAIL) mission comprises a pair of satellites launched in September, 2011 and placed in orbit around the Moon in January, 2012. The two satellites, named Ebb and Flow, used radio signals to precisely measure their separation as they flew in formation, one following the other in the same nearly circular polar orbit. These measurements allowed mission scientists to build up an accurate and detailed gravity map of the Moon.If the Moon were a perfectly smooth sphere of uniform density, the gravity experienced by the spacecraft would be exactly the same everywhere. But like other rocky bodies in the solar system, including the Earth, the Moon has both a bumpy surface and a lumpy interior. As the spacecraft fly in their orbits, they experience slight variations in gravity caused by both of these irregularities, variations which show up as small changes in the separation of the two spacecraft.The free-air gravity map shows these variations directly. (Free-air is a historical term; there is, of course, no air on the Moon.) The Bouguer gravity map subtracts the effect of the bumpy surface to show the lumpiness underneath. The elevation maps from the laser altimeter on Lunar Reconnaissance Orbiter (LRO) were used to create a model of what the gravity would be if the Moon were bumpy but not lumpy. This model was then subtracted from the free-air map to produce the Bouguer map. (Note: The Bouguer map shown here was filtered to emphasize smaller features; harmonic degrees 1 to 6 were excluded.)The crustal thickness map is inferred from the Bouguer map: If the density of the crust is assumed to be uniform, then the gravity anomalies visible in the Bouguer gravity map can be explained by variations in the thickness of the crust. Highs in gravity indicate places where the denser mantle is closer to the surface, and hence where the crust is thinner.While aiding navigation for future lunar missions, GRAIL's gravity measurements reveal information about the internal structure of the Moon, improving our understanding of the origin and development of not just the Moon, but also the Earth and the rest of the inner solar system. ||

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