London, Feb 16 (ANI): The first detailed map of the gravity fields on the Moon's far side has shown that craters there are different than those on the near side, which could reveal more about the Moon as it was billions of years ago, when magma flowed across its surface.
According to a report in New Scientist, the new gravity map was collected by the Japanese lunar satellite Kaguya, which released two small probes into orbit around the Moon in 2007.
The motions of the three spacecraft, which are sensitive to variations in the Moon's gravity field, were measured by tracking their radio signals.
Crucially, while the main Kaguya spacecraft was on the far side of the Moon and therefore out of direct contact with Earth, one of the small probes relayed its signals to Earth.
The resulting map, which is the first detailed one completed of the Moon's far side, shows that craters on the far side have a markedly different gravity signature from those on the side that always faces Earth.
That suggests that billions of years ago, there might have been large differences in the temperature or thickness of the Moon's two halves.
"It's fabulous new data," said Walter Kiefer, a planetary geophysicist with the Lunar and Planetary Institute in Houston, Texas, who was not part of the study. "We haven't been able to get a good look at the far side until now," he added.
Most of the large craters on the Moon formed more than 3.8 billion years ago. These were partly filled in by magma that flowed on the surface before the Moon cooled and its geological activity died down.
But, a number of craters also seem to have been filled in from below.
Researchers believe material from the mantle also rose up in craters, since these are sites where impacts had thinned the Moon's crust.
The new Kaguya measurements reveal some craters on the far side that seem to have been filled only with mantle.
These craters have higher-than-normal gravity at the centre, surrounded by a thick ring of low gravity that closely matches the original low elevation of the crater.
It is not yet clear what these new crater measurements suggest about the early Moon.
In order for these structures to survive, the lunar far side must have been too cool and stiff to allow the mantle at the craters' centres to smooth out much over time, according to team leader Noriyuki Namiki, of Japan's Kyushu University.
"The surface had to be very rigid to support these structures," Namiki said. (ANI)