KAGUYA plunges into the Moon
Published on Jun 10, 2009 at 10:05 am.
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Filed under moon, space exploration.
The KAGUYA (formerly SELENE) spacecraft is at the end of its mission. As with several other recent missions to the Moon, KAGUYA’s final action will be a deliberate plunge into the lunar surface. The orbit has already been altered, and at this late time, there is not much that could stop it from slamming into the Moon. JAXA, the Japanese space agency, has released a map showing the anticipated impact site (reproduced here).
The impact will be near the far southwestern limb of the Moon (as seen from Earth). The impact time will be 18:25 UT (that is 1:25 pm Central Daylight Time here in the US). When the probe hits the Moon, it may create a flash or small plume. JAXA and astronomers are interested in any observations of anything that anybody sees. At the time of impact, though, the Moon will not be visible from here. In fact, it will be on the opposite side of the world. Observers in Asia, Europe, Africa, and Australia will have the best view. In fact, I’d imagine that India and Australia would be in prime position, with the Moon high in the sky at the time. I don’t expect any flash or plume to be visible in binocular, and certainly not with the naked eye. Most likely, you’d need at least what would be a medium or large amateur astronomer sized telescope to see anything.
This is not the first time that spacecraft have slammed into the lunar surface. In fact, the first spacecraft to reach the lunar surface, the Soviet Luna 2 spacecraft, did just that on September 13, 1959. Since it is easier to just run into the Moon than to try to land on it, the first American spacecraft to the lunar surface (the Ranger program) also was designed to crash into the lunar surface, a maneuver refered to as a hard landing. Ranger 4 was the first to actually accomplish this, on April 26, 1962. Ranger 4 ran into the far side of the Moon, making it impossible for data to be returned to Earth. Actually, the spacecraft had failed and was sending little data back, so it really would not have mattered. The first Ranger to actually run into the Moon with the cameras running and sending information back to Earth was Ranger 7, which impacted on July 31, 1964.
The first attempts to reach the lunar surface were hard landers because that is easier than trying to land intact. Eventually soft landings occurred, too, of course. But, you can learn a lot from studying a body from orbit. So, many missions to the Moon were placed into orbit around it. In the 1960s, both American and Soviet unmanned spacecraft were placed into lunar orbit. At the end of their missions, the American spacecraft were generally given a command to plunge into the Moon. Many of the Soviet spacecraft continued to orbit until the spacecraft was no longer functioning. This was a point of contention between the two respective nations and their space programs. After all, NASA was in the midst of a very public race to land men on the Moon by the end of the decade. The Soviets were also trying to send men to the Moon, but their manned lunar program was not progressing as well as the American one, and ultimately failed. There was some concern expressed that all of the orbital debris around the Moon from leftover spacecraft could pose a hazard to the Apollo missions. The concern was further compounded by the fact that there was no way to reliably track spacecraft in lunar orbit once they had ceased to transmit. It was hard enough to track Earth orbiting space debris. But, the Moon was simply too far away to be able to track of all of the debris orbiting it. The Soviets, of course, pointed out that the likelihood of one of the handful of old spacecraft orbiting the Moon hitting anything else was extremely small. Still, this was a point of contention between the two nations (one of many in those days).
Soon after the end of the Apollo missions, the Soviets quit sending Luna spacecraft to the Moon, too. For nearly two decades the Moon received very little attention. Things changed, though, with the Navy’s Clementine spacecraft. A testbed for technology, the Clementine mission used instruments that revealed a great deal of detail on the Moon, and renewed scientists interests in that nearby world. A startling finding, though, was that radar reflected from some of the craters in the southern polar region of the Moon that seemed to indicate the possibility of ice on the Moon. The discovery is significant, because the Moon rocks brought back by the Apollo astronauts show that the Moon is amazingly deficient in water. The ice in the polar regions would presumably be the result of trapped water vapor resulting from the impact of comets on the lunar surface. Ice on the Moon may have been somewhat unexpected, but it wasn’t totally surprising. A few years earlier, the Arecibo radio telescope had found similar deposits in the polar craters of Mercury. Still, the finding was something significant.
So, when NASA sent another spacecraft to the Moon in 1998, the Lunar Prospector, one of its goals was to look for evidence of ice in the polar craters. Lunar Prospector failed to find the ice that the Clementine data suggested. At the end of the mission, the Lunar Prospector was deliberately crashed into the lunar surface into one of the craters that was suspected of having ice in it. The hope was that a cloud of material spit out by the impact would show the spectral signature of water. However, water was not found. Later missions have continued to look for ice in the southern lunar craters, without finding the large amount that had been hoped for. Further radar studies of the Moon suggest that the radar data from the Clementine mission may have been misinterpreted, and that large deposits of ice may not exist on the Moon after all. But, the hunt for possible ice still goes on.
More recently, the European SMART-1 spacecraft also plunged into the Moon on September 3, 2006. Rather than slamming into a polar region, though, SMART-1 crashed into the face of the Moon in a spot visible from Earth. Large telescopes on Earth were able to observe the flash of the impact, and the impact site itself has been subsequently studied. The impact site is an artificially created crater, exposing fresh material onto the surface of the Moon. Much of the surface material has been slightly altered by eons of exposure to the Sun and cosmic rays, so this gives an opportunity to see lunar material that is fresh.
Like these recent missions, the impact of KAGUYA is seen as not only getting rid of space debris, but an opportunity to study the Moon by observing what gets thrown out by the impact itself. This is a very clever way of disposing of an old space probe, using the kinetic energy of the body of the fast moving spacecraft to excavate material.
-Astroprof
Image courtesy JAXA
