Science on the Moon
The American Institute of Aeronautics and Astronautics Space 2007 meeting was held last week in Long Beach, Califonria. Thursday a tag team of NASA personnel made a long presentation on lunar science. Laurie Leshin of GSFC spoke about "Science Capability on the Moon." Her opening points:
The Moon Presents Compelling Science Opportunities!
* Bombardment of the Earth-Moon system: Consequences for the emergence of life
* Lunar surface and interior processes and history
* Scientific treasure in the permanently shadowed lunar polar environment
* Regolith as recorder of the Sun's history
Expanding on the last point, scientists have been clueless whether the Sun's luminosity has been constant. Theories of astrophysics say that life should not exist on Earth at all! According to models when the Solar System was forming the Sun was only 75% as luminous. Earth's average temperature was 15 degrees below zero centigrade, frozen solid. This can't be correct, because geology shows signs of sedimentation and liquid water 4 billion years ago. Paleontology dates the earliest organisms at least 3.4 and possibly 4 billion years. Clearly liquid water and life existed when the model says Earth was an ice cube.
While Earth's surface has been churned by erosion, the lunar surface has rocks nearly as old as the Solar System. By examining a large enough sample of regolith, we can determine the lunar temperature history. Since the Moon has no atmosphere, its temperature is unaffected by greenhouse gases. The Moon can therefore help determine how brightly the Sun has shone over billions of years.
As readers of this blog know, speed of light c is related to age t of the Universe by GM = tc^3. The Sun turns its fuel to energy according to E = mc^2. Because c in the past was higher, instead of 75% the Sun was nearly as bright as today. Calculated over Solar System history, the upward curve of solar luminosity becomes a nearly level line. If c had not changed in precisely the amounts predicted, life would not have evolved on Earth.
The Lunar Laser Ranging Experiment left by Apollo revealed an anomaly in the Moon's orbit. According to LLRE the Moon is receding at 3.82 cm/yr. Geology and the fossil record tell more precisely how the Moon's orbit has changed. These markers say that recession is only 2.9 cm/yr. Small discrepancies in planetary orbits can be very significant. Mercury's orbit precesses at 5600 arcsec per century, yet a difference of only 43 arcsec per century was enough to verify General Relativity. If the Moon appears to recede 1/3 faster than geology says, it is a serious anomaly.
If the speed of light is slowly changing, that will increase the time for light to return, making the Moon appear to recede faster. The amount of yearly change is 0.935 cm/yr, precisely accounting for the anomaly. Solar luminosity and the lunar orbit are truly independent verifications of a changing speed of light.
The Moon offers many, many opportunities for science. These relate to the conditions for life and other important questions. By exploring the Moon, we can truly determine whether the solar constant is really constant. Discovery of a Lunar Orbit Anomaly indicates a changing speed of light. Many more surprises await those going where none has dared go before.