Two new satellites are now in orbit around the moon, and they could reveal whether our moon ate a sibling many moons ago.
The , which launched together in September, separately went into orbit on 31 December and 1 January.
They are designed to produce the most detailed map ever made of the lunar gravitational field, which is lumpy thanks to mountains, craters, lava flows, and larger irregularities ā the moonās far side is much more mountainous than its near side, for example.
Advertisement
āWe donāt actually know why the near side and far side are different,ā says mission principal scientist of the Massachusetts Institute of Technology in Cambridge.
One theory is that Earth once had two moons, and the second one wrapped itself around the lunar far side in a low-velocity collision that created the highlands. GRAIL will look for signs of such a crash.
Surviving eclipse
Orbiting at a height of 55 kilometres, the twin satellites will use microwave signals to measure the distance between them, which varies according to the pull of the underlying terrain, to within the width of a human hair.
The resulting gravity map is expected to be 100 times more accurate than our existing knowledge of the lunar near side, and 1000 times more accurate on the far side. āWhen we can improve by a factor of two, we can learn a lot, and improving by a factor of 1000 is transformative,ā says Zuber.
Both the probesā batteries and solar panels are generating more power than expected. Zuber thinks they will have enough power to survive a lunar eclipse in June ā when the Earth blocks sunlight from falling on them. That should allow the probes to keep operating for six more months.
If so, the team will lower the spacecraft to an adventurous ātreetop-skimmingā orbit only 25Ā km above the surface. This will enable them to study the structure of craters spanning just 15Ā km ā āthe most common landform on the surfaces of terrestrial planetsā, Zuber says.
