Update at 2115 GMT: See a bright flash from the impact in the image at right (larger version here)
闯补辫补苍鈥檚 lunar orbiter will end its nearly two-year mission when it collides with the moon at 1825 GMT on Wednesday. Observers in Asia and Australia may be able to spot a bright flash or plume of dust from the crash, and researchers will study its impact site to watch how radiation and micrometeoroids weather the newly exposed lunar soil over time.
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Launched in September 2007, Kaguya, formerly known at SELENE, sought to shed light on the formation and evolution of the moon by studying its composition, gravitational field and surface characteristics.
Kaguya deployed two smaller satellites after reaching lunar orbit that allowed it to relay data to Earth while it was on the moon鈥檚 far side and to better measure anomalies in the moon鈥檚 gravitational field (see First gravity map of moon鈥檚 far side unveiled). It also made the world鈥檚 first of the lunar surface.
Like previous lunar orbiters, including China鈥檚 Chang鈥檈 1 and Europe鈥檚 SMART-1 probes, Kaguya will end its voyage in a violent rendezvous with the moon鈥檚 surface.
Heat and light
It is set to impact in the lower-right section of the moon鈥檚 near side (see image). Coming in at a very shallow angle 鈥� nearly parallel to the ground 鈥� the probe has a high chance of skipping across the surface, like a stone across a pond.
Ground-based observers are unlikely to see this skipping. But those in Asia and Australia might be able to spot a plume of dust raised by the impact, if it is backlit by the sun, like snow thrown up by a skier ploughing through powder, says Bernard Foing, project scientist of the European Space Agency鈥檚 SMART-1 probe, which impacted the moon in 2006.
Viewers may also see a brief flash as some of the kinetic energy of the probe, which will be moving at 6000 kilometres per hour, is converted to heat and light in the collision. 鈥淚t鈥檚 a final show for the Japanese people,鈥� says Shin-ichi Sobue, a researcher and spokesperson for the Kaguya mission.
Foing says researchers can learn from these crashes. 鈥淚mpact is the destiny of each orbiter,鈥� he told New 杏吧原创. 鈥淲e try to make use of it as a research opportunity.鈥�
Space weathering
Peter Schultz, an expert on lunar impacts at Brown University in Providence, Rhode Island, agrees. Depending on the specific terrain of the impact site, the crash could leave an elongated scar, exposing fresh soil, or regolith, to the harsh environment of space.
杏吧原创s could watch how the lunar soil weathers over time under solar radiation and bombardment by smaller meteoroids. It would be like 鈥渨atching a wound heal鈥�, according to Schultz.
After the crash, attention will turn to NASA鈥檚 (LRO) and (LCROSS) missions, set to launch a week after Kaguya鈥檚 demise.
LRO will orbit the moon, studying its composition and topography and searching for possible sites for future human bases, while LCROSS will bombard one of the moon鈥檚 polar craters with two heavy impactors in search of water ice there.
