NASA spies tantalizing clue beneath Martian desert
Starting out in the nether reaches of our galaxy (and perhaps beyond), accelerated (we think) by interstellar magnetic fields, bits and pieces of atoms – protons, electrons, whole nuclei – slam into our solar system at close to the speed of light.
When these “cosmic rays” (which are actually particles) smash into something – Earth’s atmosphere, or the surface of a planet lacking a thick atmospheric blanket – they wreak havoc, breaking up atoms left and right.
Atoms are made of electrons surrounding a nucleus. The nucleus, in turn, is made of protons and neutrons. Struck with sufficient force, a nucleus spews its protons and neutrons like popcorn. These particles then slam like billiard balls into other nuclei. What happens next depends on the mass – the “heaviness” – of the nucleus they hit.
Imagine throwing a rock at a boulder. Rocks are elastic – they bounce when they collide. If the projectile stone is small compared to the boulder, it bounces off with pretty much the same energy it had before the collision.
If you hit a small rock instead, however, it’ll move, absorbing some of the energy of the projectile, which now bounces back slowly.
When a neutron blasted out of its nucleus by a cosmic ray slams into a heavy nucleus – a nucleus of iron or nickel, let’s say – it bounces off hard. But if the neutron should hit a lightweight nucleus, the light nucleus itself takes off and takes some of the neutron’s energy with it. The neutron bounces back slowly; its energy has been “moderated.”
Two-hundred forty miles above the surface of Mars, instruments aboard the spacecraft 2001 Mars Odyssey are collecting neutrons bouncing off the planet’s surface. Neutrons moving at high speed have likely collided with heavy nuclei. But those moving slowly have been moderated, likely by colliding with lighter nuclei.
The accompanying map of Mars shows the results of Odyssey’s first investigations. The fastest neutrons are bouncing off the regions shaded red; the slowest neutrons, off regions shaded blue. Two large regions, one of them at the south pole, show as an especially deep blue.
The lightest nucleus in the universe (and the most effective nucleus at moderating neutrons) is that of hydrogen. Because it is so light, hydrogen is a difficult atom for a planet to hold onto. Earth loses tons of hydrogen each day as the light gas wafts up to the edge of the atmosphere and then into space.
It’s easier for a planet to hang onto its hydrogen if the atom is combined with other atoms … atoms of oxygen, for instance. Scientists presume – and hope – that the neutron signal that Odyssey is seeing is an indication of subsurface dihydrogen oxide.
Unlike most aircraft, in which the pilot controls the motions of the vehicle directly, the space shuttle is flown “by wire.” By moving the controls, the pilot tells the craft’s computers what to do, and the computers then control the spaceplane.
Excess heat can send a computer’s transistors into “thermal runaway.” Rather than switching on and off to perform their calculations, they switch on … permanently.
Upon launch of the shuttle Columbia last week, a glitch was found in one of the spaceplane’s cooling circuits.
The end of a shuttle mission is a complex problem in “energy management” – managing the energy of a multi-ton glider as it falls back to Earth. The flight computers are vital to this phase of the mission.
As the craft and its crew complete their work on the Hubble next week, may they carry with them our prayers for a safe and successful planetfall.
Trained as a biologist, Alan Stahler is also an amateur astronomer. He teaches biology and geology at Bitney Springs Charter High School. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).
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