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Airplane silhouette in front of the moon (the machine is not the "Sofia" observatory)
Photo: Toby Melville / REUTERS
In the Lufthansa Technik hangar at Hamburg Airport there is a unique aircraft for regular inspection these days: The "Sofia" flying observatory, a 43-year-old Boeing 747SP, will be serviced in Fuhlsbüttel until the beginning of next year.
The special thing about the machine is that it carries an infrared telescope and other scientific equipment inside.
With them you can look far into space during research flights, beyond the disturbing water vapor in the earth's atmosphere.
To do this, a large door is opened on the side of the jet through which the 2.7-meter telescope can see outside.
The flying observatory is a joint project of the US space agency NASA and the German Aerospace Center (DLR).
But it has been a topic of discussion for years.
The Americans have threatened several times to withdraw from the project.
From their point of view, the scientific output in the form of publications was not convincing enough.
On Monday, however, at a press conference that was set at short notice, NASA announced an "exciting new discovery" - as it previously advertised - which would not have been possible without further ado without "Sofia".
A team led by Casey Honniball from NASA's Goddard Space Flight Center in Greenbelt (US state Maryland) has already detected molecular water on the surface of the moon during a measurement flight on August 31, 2018 - including in areas of the earth's satellite that were the sun are shining.
The "Sofia" measurements took place at the Clavius crater in the southern highlands of the moon.
It has a diameter of about 225 kilometers, making it the second largest crater that can be seen from Earth.
Future missions may be interested in the water
The researchers also report on their discovery in the journal "Nature Astronomy".
The corresponding manuscript was already received there last November, but has only now been published.
The journal's scientific reviewers may have requested revisions.
The article now reports on water molecules trapped in tiny glass spheres and between the grains of moon dust.
The concentration of the molecules is low - there are 100 to 400 of them for every million other molecules on the surface.
And yet: the water is there.
"The amount of water that 'Sofia' discovered is roughly equivalent to the content of a 0.33 liter beverage can spread over the surface of a soccer field," explains Alessandra Roy, "Sofia" project scientist at DLR Space Administration Honniball's research was involved.
"The moon remains drier than the deserts on earth, but the amount of water found could still be important for future astronautical space missions."
Nasa has announced that it intends to return to the moon with humans by the middle of the decade.
Numerous tenders are currently running for the necessary technology, which is also to be purchased by private companies.
The outcome of the presidential election will also determine how the corresponding "Artemis" program continues.
With a possible change of government - as has happened several times in the past - the work of the space agency could be realigned.
It's not entirely clear why the water is still there
Regardless of this, however, the Chinese, for example, are drawn to the moon, and Russia is also reporting long-term plans.
And whoever lands on the earth's satellite will endeavor to use the resources available there for the mission - because freight transport from the earth is extremely expensive.
Water would not only be of interest to astronauts, but also as rocket fuel if you want to fly further from the moon into the solar system.
For a good ten years there have been indications that the moon is not as dusty dry as one might assume.
The "Chandrayaan-1", "Deep Impact" and "Cassini" space probes have made similar observations.
However, in these measurements it was not easily possible to differentiate between water molecules - they consist of two hydrogen and one oxygen atoms - and so-called hydroxyl radicals, in which only one hydrogen and one oxygen atom are connected.
This was due to the wavelength of the infrared radiation that was measured at the time.
This was characteristic of both water molecules and hydroxyl radicals.
The measurements by Honniball and her colleagues now took place at a different wavelength, which the researchers believe can be used to identify the water as such without any doubt.
The interesting question is why the water molecules are actually still there - it would be expected that they would have long since evaporated from the sun's rays and would have escaped into space, never to be seen again.
There are several theories as to why they are still detectable: On the one hand, it could be that micrometeorites constantly bring small amounts of water to the moon.
This could be deposited in the rock.
Or else, larger impacts carry water upwards from the deeper layers of the lunar soil.
Another possibility would be that the solar wind brings hydrogen atoms to the moon, which combine with the existing hydroxyl radicals to form a water molecule.
And then there is the ice on the poles
In addition to the finely distributed water molecules in the soil, there are also larger deposits of water on the moon - in the form of ice that has survived, for example, in the shady interior of lunar craters.
In another article in "Nature Astronomy", a group of scientists led by Paul Hayne from the University of Colorado in Boulder reports that much larger areas than previously thought could act as so-called cold traps.
This means that so little heat from the sun reaches these places that ice can persist there permanently.
According to the researchers, it is cold enough on around 40,000 square kilometers of the moon's surface.
The team had worked with data from the "Lunar Reconnaissance Orbiter".
During modeling, the researchers found that, from their point of view, the number of small cold traps in particular has been underestimated so far.
Pieces of ice could survive even in areas only one centimeter in diameter.
"Our results suggest that the water trapped at the lunar poles could be more widespread and accessible as a resource for future missions than previously thought," she concluded.
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