Sunday, November 15, 2009

LCROSS Finds Water On The Moon

Back in September 2009, the LRO discovered the presence of Hydrogen at the Moon's south pole, indicating that there may be water in some of the many permanently shadowed craters.  Well, on 9th October 2009, LCROSS observed the impact of the spent Centaur rocket stage into the Cabeus crater, kicking up a plume of dust that was observed by the trailing LCROSS satellite and also Hubble as well as many telescopes on Earth.  The LCROSS impacted the Moon's surface abiut 5 minutes after the rocket stage, creating a smaller plume.

Well, on 13th November 2009 NASA scientists announced that there was indeed water detected in the plumes from the LCROSS impacts.

That opens the Moon back up as a possibly viable first base for our future space exploration - if there's water there then that will provide not only drinking water for residents, but also cooling and especially rocket fuel needs.  With the gravity of the Moon being about 16.7% of that on Earth that means that instead of needing to overcome 9.81 m/s/s of gravity on Earth, rockets launched from the moon will need to overcome a mere 1.63 m/s of gravity.

Now, the Moon's gravity isn't anywhere near as consistent as that on Earth.  And the gravitational pull of the Earth isn't all that consistent - the accepted nominal or average value at the Earth's surface is 9.80665 m/s/s, however this is 9.78033 m/s/s around the equator and 9.83217 m/s/s due mainly to the centrifugal force at the equator being greater than at the poles (actually, it is non'existent right at the poles) and it varies across the Earth's surface depending on what you're standing (or floating) on.  Now, because of this centrifugal force, the equator bulges outward a little, meaning that when you're standing at ocean/water level on the equator, you're further from the center of the Earth than someone standing on one of its poles at ocean/water level.  No, the Earth is not a (consistent) sphere, but it definitely isn't flat!  :)

Because the Moon doesn't spin on its poles as the Earth does, there's no centrifugal force as we experience here on Earth.  That means that there's no equatorial bulge and the resultant centrifugal variation across the entire surface.  However, the Moon has what's known as "Mascons" across the surface of the moon which can greatly affect its gravity, and these were discovered by NASA's Lunar Orbiter program due to errors in the navigation of these orbiters being greater than the mission specifications had catered for.

These mascons (mass concentrations) are often made up of the dense bodies of impacted asteroids, basaltic lava flows or iron-rich sediments lifting up from the Moon's core.  In 2011, NASA will launch its GRAIL mission to thoroughly measure the Moon's gravity field.  This will result in the Moon's gravity field being more closely mapped than that of the Earth!  The interest in mascons is due to their effect, as discovered with the Lunar Orbiters, on all missions around and to the surface of the Moon - and if we're going to be launching future space missions from the Moon, we need to know how these mascons will affect trajectories.


The Outspoken Wookie

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