We found water on the moon!
The Moon is not dry. Its surface conceals billions of billions of water molecules ...
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Sylvestre Huet
The Moon is not dry. Its surface contains billions of billions of water molecules! They nestle just on the surface, about a millimeter thick. What to harvest ... half a liter per football field. There would therefore be - the conditional relating only to the precise quantity - a few billion liters of water on the star of the night.
This is the incredible discovery announced by NASA. It is published tomorrow in a series of three scientific articles in the journal Science.
One of the favorite subjects of planetologists, space engineers, astronauts and Science Fiction writers is the search for water on the Moon. Logic. Because if the presence or absence of water plays a considerable role in the destinies of the celestial bodies, it is not for nothing that we have named H20 the molecule of life. Without water, no life. Occupying the Moon, or using it as a base to explore the solar system, with first flights to Mars, presupposes having solved the water problem. If possible without turning to the worst solution: route it from the bottom of the earth's gravity well using rockets.
So the lunar water is fantasizing. Captain Haddock and Tintin found some on the star. Heinlein (Revolt on the Moon) and other SF authors used it to colonize the Moon. But...
But the rocks brought back by the astronauts of the Apollo missions never showed the least trace of water. But terrestrial radars like lunar probes - Clementine in 1994 (Nasa), Lunar Prospector (Nasa), en or Smart One (Esa) - sometimes led scientists to believe that they had found water, in the form of ice mingled in the basement, but each time hope vanished. Finally, two probes have just found them reliably: the Indian Chandrayaan and especially the Deep Impact probe from Nasa. Ironically, the research was sent into space to observe ... the bombing of a comet!
About bombing: it is October 9 that NASA will send the impactor of the LRO probe to the bottom of a crater to see if ... there is not hiding ice there. LRO - Lunar reconnaissance orbiter - which began its work on hyper-precise mapping of the star.
The Indian Chandrayaan probe, launched in October 2008, allowed India to make its mark on lunar soil with the brutal arrival of an impactor. Since November 2008, its instruments have been scanning the star. One of them, the Moon mineralogy mapper, supplied by JPL, the famous jet propulsion laboratory of Nasa installed in Pasadena (California), startled its scientists. Its infrared spectrometer, by drawing a map of the Moon, detects emissions typical of two molecules, OH and H2O. A broadcast diffused on the star, but more intense towards the coldest zones (poles and funds of craters badly lit). Enough to sing songs of joy in the labs.
But MMM's spectrometer stops right at 3 microns. However, to get a clearer picture, eliminate any risk of instrumental artefacts and distinguish between the two molecules, an infrared spectrometer was needed going beyond 3 microns in wavelength in order to properly frame the typical emission of the single H20 molecule between 2,8 and 3,6 microns ... precisely the case of that of the Deep Impact probe. Incredible luck, the latter, after her operation "I bombard a comet and I take a photo" which made the front page of Liberation on July 4, 2005, not too far from the Moon - 6 million kilometers all the same, last May . Luck too: the world of planetologists is not huge. Thus, the astrophysicist Jessica Sunshine is part of the scientific team of MMM ... and that of Deep Impact. Suffice to say that the junction takes place illico presto.
"My first email on this case dates from the beginning of May" tells me Olivier Groussin, from the Marseille astrophysics laboratory (INSU / CNRS, University of Provence), who has been part of the scientific team of Deep Impact for several years. He participated in the comet bombing operation. And now works as part of the extension of the mission, called EPOXY whose objective is the overflight of comet 103P / Hartley 2, in November 2010. “We had to make observations of the Moon anyway, especially to check the how the instruments work, but we changed the program to get the most information from the infrared spectrometer. ”
The result was, he insists, "unambiguous". In English, the term used by scientists in their articles is "strong evidence". Especially that a third space instrument ... had already seen it! Yes, when an interplanetary probe leaves Earth to visit Jupiter or Saturn, we take advantage of the proximity of the Moon to test the instruments at the start of the journey. When the Cassini probe left for Saturn in 1997, it made several detours, including one not far from the Moon in 1999. And there, its infrared spectrometer had detected traces of water. But it was only after the discovery of Chandrayaan that we went to verify this data. Ironically also, to realize that each time that we sent into space a telescope carrying a precise infrared detector and having good spectral coverage (IRAS, ISO, Spitzer) ... the astrophysicists mainly programmed telescopes for not observing the Moon. Why ? Simply because the Moon would have simply dazzled the telescope, saturating the detector and prohibiting any analysis.
Known physics tells them with certainty: there is water. But how much, and most importantly, how did it get there? This is where the conditional starts.
How ? Olivier Groussin has agreed to carry out calculations that are not in the articles. And which give results to be taken as orders of magnitude because the measurement uncertainties are significant. So: “about 1 liter of water per 10.000 square meters, or to be more visual 0.5 liters per soccer field. Extrapolated to the surface of the Moon, that means about 4 billion liters of water, equivalent to a few million cubic meters. ”
How did she get there? Planetologists can only advance the only plausible hypothesis, compatible with known physics and chemistry. It is the protons of the solar wind (nothing to do with the wind from here, they are electrically charged particles, especially protons) which would be at the origin of this water. A proton is a hydrogen ion, that is to say a hydrogen atom deprived of its electron. When this proton strikes the lunar soil, it can dissociate oxygen atoms from it, some of which are therefore free to recombine with it. The process would form OH (hydroxyl) atoms and ... H20O, water. The image opposite illustrates this idea. After its formation, the water molecule is adsorbed (weakly attached to the surface) on the dust. But this water molecule is not eternal. If the temperature on the ground rises enough for it to be desorbed, the photons of the Sun will then dissociate it. The process is therefore not cumulative.
This plausible explanation is not only based on physics and chemistry. But also on the spatio-temporal distributions recorded by Deep Impact. Thus, there is almost no water at the equator and we find more and more going towards the poles. In addition, we find the same gradient ... in the lunar "day". There is more water formation in the morning and in the evening, and more destruction under the midday sun - the process is illustrated by the image opposite.
However, underlines Olivier Groussin, it should be emphasized that “if the presence of water seems solidly established, but the process of its formation, and of its destruction, as of a possible migration, falls under the assumption and must be put at the conditional, even if for the moment we have no alternative to oppose it ”.
Can astronauts hope to drink this water? In theory, why not. To recover it, it is "enough" to heat the lunar soil every morning, and to recover the water molecules which will then detach from it. Easy to say ... This is probably a good field "manipulation" for a future mission, on tiny dimensions, but almost impossible to do on a large scale. In addition, with half a liter per football field treated in this way, we do not go far.
In short, it is likely that NASA will use this discovery to fuel its prophetic discourse on the "New Frontier", and its requests for funds for manned flights, but it is more reasonable to think that, if the astronauts return to the Moon, it will be with a few bottles of water from home .... and a recycling system for their wastewater and urine. Sorry for the not glamorous side at all ... but more realistic.
It is quite funny to note that NASA and the journal Science had imposed an embargo until 20 p.m. this evening (Paris time), for a press conference by American scientists. But the La Provence website, probably unfamiliar with the respect that scientific journalists give to embargoes, released the subject last night, toasting everyone. This morning, an email from the journal Science sent to journalists accredited to the journal informed me that, suddenly, it was breaking the embargo ...
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