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New analysis of Chandrayaan-1’s lunar orbital data might explain its detection of widespread surface hydrogen on the Moon

The Earth's magnetic field, shaped by the solar wind
The Earth’s magnetic field, shaped by the solar wind

One of the significant finds coming from India’s first lunar orbiter, Chandrayaan-1, was the detection of hydrogen in many places across the entire lunar surface, in places where it seemed impossible for hydrogen to be there, even if it was locked in a molecule like water.

Researchers in Hawaii now think they have found an explanation by linking that data to the Earth’s long magnetotail, formed by the solar wind pushing against the Earth’s magnetic field. The graphic to the right illustrates that process. The scientists focused on the kind of weathering processes that occurred both when the Moon was inside that tail, and when it was not.

Li and co-authors analyzed the remote sensing data that were collected by the Moon Mineralogy Mapper instrument onboard India’s Chandrayaan 1 mission between 2008 and 2009. Specifically, they assessed the changes in water formation as the Moon traversed through Earth’s magnetotail, which includes the plasma sheet.

“To my surprise, the remote sensing observations showed that the water formation in Earth’s magnetotail is almost identical to the time when the Moon was outside of the Earth’s magnetotail,” said Li. “This indicates that, in the magnetotail, there may be additional formation processes or new sources of water not directly associated with the implantation of solar wind protons. In particular, radiation by high energy electrons exhibits similar effects as the solar wind protons.”

In other words, the evidence suggests that the hydrogen signal seen by Chandrayaan-1 might have been a very temporary implacement of that hydrogen by the solar wind, which ceases during the Moon’s periodic passages through the magnetotail. The Moon’s harsh environment then causes that hydrogen to vanish, only to reappear when it is once again exposed to the solar wind.

None of this is confirmed, so some skepticism is required. If true, however, it would provide further evidence that the hydrogen signal seen at the lunar poles that scientists hope is evidence of ice in the permanently shadowed craters might be nothing of the sort, and we shall find little ice there.

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On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

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  • Richard M

    None of this is confirmed, so some skepticism is required. If true, however, it would provide further evidence that the hydrogen signal seen at the lunar poles that scientists hope is evidence of ice in the permanently shadowed craters might be nothing of the sort, and we shall find little ice there.

    This is indeed possible, and would be a great disappointment in regards to prospects for economic development of the Moon.

    But the only way we will know for sure is to go there, to the Poles, and dig around and take a hard look. Fortunately, that’s in the works, with veritable fleets of probes headed to the South Pole over the next several years, even aside from whatever Artemis ends up doing. The one I’m really waiting for is VIPER.

  • pawn

    I’ve hear from several sources that the plume from the Centaur stage that was crashed had a significant amount of water vapor in it. Indeed that crazy experiment kicked off the current “water rush” to the lunar south pole.

    So maybe there’s a good chance that this means nothing as far as water presence.

  • TallDave

    we can eventually use the solar wind to help terraform Venus by putting huge electromagnets around solar shades to create a giant ramscoop

    as Sagan pointed out many decades, even if engineered microbes lock down all the carbon you still have 90 bars of oxygen to account for — and no water

    if we could concentrate the stream of hydrogen Venus currently receives by roughly 100-fold we’d saturate the atmosphere with enough moisture to support more and more airborne life, and also gradually clear out the permanent sulfuric acid cloud cover that makes Venus so hot today

    get enough water cycling and the temperature would fall to the same 23C plateau as on Earth even at ~10 bars

    probably takes millennia even to get that far but it’s still probably cheaper and faster than collecting comets or asteroids, or transporting our polar icesheets

  • J Fincannon

    I listened to this report on the Joh Batchelor show. Pretty surprising negative statements about water.

    As another commenter mentioned, LCROSS/Centaur impacted a vehicle into a PSR and the team measured approximately 341 pounds of water vapor. I have seen it as 5.6 ± 2.9% by mass of the regolith. Sound good to me.

  • J Fincannon: Yup, I remain a skeptic as to the existence of water. I want it to be there, but so far I am unconvinced any has been found. As it has been said, extraordinary conclusions require extraordinary evidence, and that so far has not been presented. It might exist, but I think it is my job to report results both good and bad.

  • J Fincannon


  • Edward

    J Fincannon,
    What they measured was hydrogen. The assumption was that it must be tied up in water, because what else would be able to retain hydrogen on the surface? What hasn’t been measured is actual water.

    This is why so many people and nations want to explore these craters. They want to find real water, not assumed water.

    One thing that I have noticed is that SpaceX’s Mars migration plan does not yet include a stop near the Moon in order to retank the propellant tanks before heading off to Mars. The plans all depend upon retanking only in low Earth orbit. The plan does not include a dependence on a possibly non-existent source of water.

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