After almost 2 years of scientific harvesting, the Japanese lunar probe Kaguya marked the end of its mission by crashing on our natural satellite.
Artist’s impression of Kaguya. The probe was accompanied by two microsatellites used for taking various measurements, notably of the Moon’s field of gravity. Credit: JAXA
18:30 (UTC - Co-ordinated Universal Time) on 10 June 2009 Kaguya collided with the Moon at a latitude of 65° south. This crash was in no way the result of an error in navigation; the manoeuvre was planned and could even provide additional scientific data. The impact was confirmed by the japanese space agency (JAXA) on 11 June.
From SELENE to Kaguya Kaguya is yet another sign of the way in which the Japanese space programme is being stepped up. Remember that in January 1990, the Land of the Rising Sun sent a first probe, Hiten who only weighed 197 kg at lift-off, to the Moon. Kaguya weighed a total of almost 3 tonnes prior to its launch on 14 September 2007, which is 15 times more! But instead of Kaguya, we ought to say SELENE for SELenological and ENgineering Explorer, the original name for this mission that the Japanese Space Agency, JAXA, was then to qualify as “the most important mission to the Moon since the Apollo programme”. The patronymic Kaguya (Moon goddess from Japanese folklore) was adopted shortly before the launch and resulted from a public survey. But although the name was changed, the scientific ambitions remained the same with 15 onboard instruments (cameras, spectrometers, laser altimeter, etc.) and the desire to obtain a better understanding of the Moon’s formation and its evolution. Kaguya's data is still currently subject to intense interpretation although the first results have already been published. Thus, scientists connected with the mission estimate that lunar volcanism on the dark side of the Moon is more recent than we thought. It would have congealed 2.5 billion, and not 3 billion, years ago.
The Moon in high-definition In addition to a robust scientific programme, the interest of the general public in this mission has not been forgotten. With this in mind, the Japanese Space Agency, in partnership with the Japanese television channel NHK, has fitted the probe with a high-definition camera. The most spectacular sequences show the Earth rising and setting (video below) with the lunar horizon in the foreground.
Said rising and setting of the Earth are, however, illusions. Whilst the Moon orbits the Earth, it also turns on its own axis in such a way that the same side is always facing our planet. Consequently, an astronaut who is looking at the Earth from the surface of the Moon will never see the Blue Planet rise or set; it will remain immobile in the sky. If Kaguya has filmed the Earth in the process of “rising” and “setting”, it is because the probe moves through its orbit. The phenomenon is similar to that of a sailor out at sea who watches dry land appear on the horizon as his boat advances.
Why a crash? Kaguya was turning around the Moon at an attitude of approx. 100 km. Such a low orbit means frequently resorting to trajectory corrections using small rockets. But once fuel reserves are exhausted, the spacecraft becomes uncontrollable and finishes by crashing into the Moon anyway. But, by deciding to carry out the last necessary manoeuvres before running out of fuel, Kaguya’s controllers were able to determine precisely where and when the probe collided with the lunar surface on 10 June. The impact resulted in a flash of light. By analysing this brief flash of lightning with powerful telescopes on the ground, we can try and deduce the composition of the soil and subsoil in this spot. It would have been a shame not to exploit such a scientific bonus. This is not, however, the first time that this type of manoeuvre has been used with this purpose in mind. On 31 July 1999, the American probe Lunar Prospector targeted a crater at the South Lunar Pole (in order to detect the presence of water, without success). The European Smart-1 also crashed into our natural satellite on 3 September 2006. More recently, the Chinese probe Chang’e 1 plunged to a similar fate on 1 March 2009. And the same reasoning will be put back on the agenda with the American LCROSS (Lunar Crater Observation and Sensing Satellite) which is to lift-off with the LRO (Lunar Reconnaissance Orbiter) probe on 17 June 2009. The impact, itself, is to take place in October.
An image of the Moon taken by Kaguya’s HDTV camera. See this photograph and others in this Enjoy Space portfolio. Credit: JAXA/NHK
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