Studying the Moon by starlight

The Moon's south pole by starlight

In a paper published today in the Journal for Geophysical Research, Planets, the science team for Lunar Reconnaissance Orbiter describe how they have used starlight to peer into the permanently shadowed craters of the Moon’s north and south poles. Looking only during the lunar night, they measured the dim albedo of the Moon from reflected starlight. From this very weak signal they were able to cull two interesting facts about these very cold and very dark places.

  • The ground at the bottom of these craters is more porous than the surrounding unshadowed terrain.
  • There is evidence in the spectroscopy of 1 to 2% water frost in these craters.

The first discovery is consistent with other Lunar Reconnaissance Orbiter data that mapped the Moon’s surface using lasers. That data had suggested that the floors of these craters had a very rough terrain. This new data further suggests the existence of what the scientists dub “fairy-castle structures” due to “charging effects.” Since the scientists also note that even if there is water-ice on the floors of these craters it would still be subject to melting and evaporation over the eons due to the harsh conditions, I also wonder if this rough terrain is the result of that melting. Think of what a block of ice looks like after you spray warm water on it. As it melts it leaves behind wild and surreal shapes.

The second discovery is consistent with other data that has suggested there is remnant frozen water hidden in these permanently dark regions. Once again, the value of this “beachfront” property on the Moon has gone up!

In reading this paper, however, I myself can’t help marveling at what these engineers and scientists have managed to do. They have used the practically invisible reflection of starlight from these dark regions to analyze the surface topography and makeup. And they have done it from Earth, using a robot in orbit around the Moon almost a quarter of a million miles away.

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