Shooting the Moon

Artwork from Jules Verne’s 1865 novel, From the Earth to the MoonLaunching a spacecraft bound for the Moon with the deliberate intention of striking the Moon in a spectacular impact!

Sounds like something out of a Jules Verne novel... but that's exactly what NASA's up to this year with the upcoming LCROSS (Lunar Crater Observation and Sensing Satellite) mission, scheduled for launch on June 2nd and impact sometime in October-- exact date TBA.

And it's not unprecedented, either: the Lunar Prospector spacecraft back in 1998/1999, whose instruments detected possible signs of water ice in craters around the Moon's poles, was crashed into the Moon's South Pole at the end of its mission. The aim was to blast up a cloud of material from the lunar surface and spectroscopically analyze the plume in search of water vapor. None was detected then, but that's where LCROSS comes in.

LCROSS will seek to verify the presence or absence of water ice and related hydrated materials buried at the bottom of a permanently shadowed crater floor on the Moon's South Pole. Water ice cannot persist on any part of the Moon's surface that is subjected to sunlight, but because of the Moon's low axial tilt with respect to the ecliptic (the Sun's apparent annual path in the sky)-- only about 1.5 degrees-- there are craters at the Moon's poles whose floors never see the light of day, all month long and year round. Water ice could persist near the surface in these places.

LCROSS consists of two pieces: a "Shepherding Spacecraft" that will guide the whole affair to the proper location on the Moon's South Pole, and the Centaur rocket stage that propelled the spacecraft to the Moon. The pair will separate, and the Centaur rocket will become the primary impactor, striking ground and producing a crater and plume of ejected material. Viewing the event from above, the Shepherding Spacecraft will use cameras and other instruments to analyze the plume from a distance, and will then follow the same course as the Centaur, descending four minutes after impact through the ejected plume and analyzing material samples as it falls.

Then, the Shepherding Spacecraft, too, will impact the Moon-- and the plume it kicks up may well be visible through modest sized telescopes on Earth. We're planning to watch the explosion live through our telescopes at Chabot, weather permitting. Keep an eye on our website for details.

Now, back to Jules Verne for a moment. The launching of a projectile with the intent of striking the Moon was indeed the subject of one of his novels, From the Earth to the Moon, published in 1865. Fired from an enormous cannon, the goal of that post Civil War mission was to catch the attention of anyone living on the Moon, to open up a line of communication with their civilization.

My wife asked me if crashing a probe into the Moon would have any harmful effects, particularly if in fact there is any form of life (subsurface microbes or such) living there. Well, certainly, if you happen to be a lifeform living at ground zero of the impact... but the fact is the Moon is frequently struck by meteorites much larger than the LCROSS impactor anyway. To paraphrase Douglas Adams, "that kind of thing goes on all the time."

One last fun tidbit about the Jules Verne novel: the launch site for his cannon-fired projectile was a place in Florida, 50 miles south of Tampa Bay, and only about 135 miles from the Kennedy Space Center, from which LCROSS will be launched...

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