As Phil Plait explains, there’s one big question the standard theory about how the Moon came to be still can’t answer.
OK, so the Moon is wetter, which is nifty. Mind you, we’re not talking about potential geysers or subsurface lakes here; the amount of water we’re seeing here means you’d need to grind up a couple of cubic meters of this glass just to get enough water to drink with lunch. So what’s the big deal?
The important part here is that this has a huge effect on how we think the Moon formed. The current thinking is that shortly after the Earth itself formed, maybe 50 – 100 million years or so later, something the size of Mars came careening in and smacked into our new planet. It was a glancing blow, so a vast amount of material blasted out, away from the Earth, and into orbit around us. This stuff formed the Moon. This idea has a lot going for it: for example, it explains why the Moon is less dense than the Earth on average (by the time of impact, a lot of heavier stuff had settled to the Earth’s core, leaving the lower density materials near the surface to become the Moon).
It was also thought to take care of why the Moon is so dry compared to Earth: all the water boiled away in the impact. In fact, a lot of the more delicate (technically called volatile) materials would have been destroyed, explaining why we see so few volatiles on the Moon.
Except now we see more water. Clearly something is amiss. To be honest, I think the Giant Impact Hypothesis is still the best thing going — it really does have a lot of explanatory power — but it looks like we missed something. Maybe water was protected somehow in the impact, able to survive the blow. Perhaps our understanding of the timing of the impact is off, or maybe it’s something else entirely. The first order of business is to figure out if there is some add-on to the hypothesis that can explain this water. If not, then it’s time to make some hard choices.
Enter GRAIL, twin spacecraft that have just assumed lunar orbit.
During GRAIL’s science mission, the two spacecraft will transmit radio signals precisely defining the distance between them. As they fly over areas of greater and lesser gravity caused by visible features such as mountains and craters, and masses hidden beneath the lunar surface, the distance between the two spacecraft will change slightly.
Scientists will translate this information into a high-resolution map of the moon’s gravitational field. The data will allow scientists to understand what goes on below the lunar surface. This information will increase knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today.
Each spacecraft carries a small camera called GRAIL MoonKAM (Moon Knowledge Acquired by Middle school students) with the sole purpose of education and public outreach. The MoonKAM program is led by Sally Ride, America’s first woman in space, and her team at Sally Ride Science in collaboration with undergraduate students at the University of California in San Diego.
GRAIL MoonKAM will engage middle schools across the country in the GRAIL mission and lunar exploration. Thousands of fifth- to eighth-grade students will select target areas on the lunar surface and send requests to the GRAIL MoonKAM Mission Operations Center in San Diego. Photos of the target areas will be sent back by the GRAIL satellites for students to study.
A student contest that began in October 2011 also will choose new names for the spacecraft. The new names are scheduled to be announced in January 2012. Ride and Maria Zuber, the mission’s principal investigator at the Massachusetts Institute of Technology in Cambridge, chaired the final round of judging.
Along with the Cassini Solstice Mission, the New Horizons program to Pluto, the Curiosity rover on Mars, and the Dawn project to the asteroid belt, 2012 looks set to be a seminal year for space exploration.