Shadows have been known throughout history to be excellent hiding places. They may even be hiding unexpected things off the Earth as well. According to a new NASA study, there might be water that moves from shadow to shadow on the moon – even in daylight.
Scientists have long accepted the fact that there is water on the moon – especially in the permanently shadowed craters at the poles, which is part of the reason they recently funded a “hopper” mission to go investigate. But there are parts of the Moon that are sometimes exposed to the sun, and sometimes cloaked in shadow. Previously, scientists thought it would have been difficult for water ice to exist in these environments, but it turns out they might have been wrong.
UT video discussing some of the lunar environment.
Data from SOFIA, one of NASA’s airliner-based observatories, confirmed that water does exist on the surface of the moon exposed to daylight. But models suggested that any water that might have existed there should have been burned away by the Sun. There was one critical hint in the data, which then led to a hypothesis leveraging two other factors in the lunar environment.
That critical hint was that the amount of water measured by SOFIA decreases in the lunar “morning” and then increases in the lunar “afternoon”. If it was simply being burned away, the amount would have steadily decreased throughout the time. It also ruled out the water being trapped in rock formations by a previous meteor impact. But one explanation that fit the data is that the water is migrating to different parts of the moon throughout the course of a lunar day. To figure out if that was possible, scientists at the Jet Propulsion Laboratory started to look at lunar environmental conditions.
Map of some of the track water ice on the moon, primarily in shadowed craters.
Credit – Shuai Li, University of Hawaii SOEST/ HIGP
One focal point of their study were the “jagged” shadows that lay across the lunar surface and move with the sun’s position in the sky. These shadows are primarily formed by rocks or cliffs rather than crater walls, and usually aren’t very big. While the sun blasts these areas it dramatically increases their temperature, up to 120° C in some cases. After the sun moves on and an area is again cast into shadow, the temperature can go down to -210° C. Heat is not transferred between these two areas effectively, even though they might be literally touching each other, as there is little to no atmosphere to provide the thermal conductance necessary to even out temperatures, like there is on Earth.
Pockets of water ice are certainly possible at those frigid temperatures in shadow, but what about the change in amount over the course of a lunar day? Though there isn’t enough atmosphere to perform thermal transfer on the moon, there might be enough to perform hydro transfer.
Graphic showing the the new mechanism (right) and what scientists though might have been holding the water on the moon’s surface previously (left).
Credit – NASA / JPL-Caltech
Despite the common perception of the Moon being a completely airless desert, it does have an “exosphere” which is composed of trace amounts of gasses that are gravitationally bound to the lunar surface before they are blasted away by solar winds.