Scientists Use LRO Data to Create Moon Map

Scientists have used data sent back from NASA's  Lunar Reconnaissance Orbiter (LRO)  to create a detailed topographic map of the Moon.

 LRO has just finished its year-long mission of mapping the Moon in order to look for landing spots for future spacecraft and will spend the next two years providing information about the Moon's history.

It provides scientists with information on the lunar surface by sending laser pulses to the surface and then measuring the amount of time it takes for the pulses to bounce back to the craft. Scientists have used this information to form their map.

The data show that two distinct groups of asteroids bombarded the Moon's surface when the Moon was young. The first group bombarded the Moon about 4.1 billion years ago, and the other group about 3.8 billion years ago.

LRO studied over 5000 lunar crater. The oldest parts of the Moon's surface have both large and small craters. Younger regions, which have been affected by volcanic activity, have much smaller craters.

This disparity indicates that the earlier population of asteroids had more large fragments than the later population.

According to Brown University's James Head, the craters left by the impacts of the two populations can easily be distinguished from one another.

Robert Strom, a planetary surface geologist, believes that there was a shift in meteor types around 3.9 billion years ago, when Jupiter and Saturn repositioned. The change in gravitational pull caused many asteroids -both large and small - to become ejected from the asteroid belt. A large influx of comets could also have caused a change in the composition of the asteroid belt at the time.

This would have caused the Moon to be bombarded by large asteroids.

Once this shift in the asteroid belt took place, only small asteroids would have left the asteroid belt.

Caleb Fassett, a geologist at Brown University, says that the data from LRO suggest that the shift took place before the volcanic flow regions on the Moon, which are known as mare, were created 3.6 billion year ago.

The Moon can be divided between two different areas - the highlands, which are rich in calcium and aluminum, and the maria, which have large quantities of iron and magnesium. The highland crust is anorthositic while the maria crust is basaltic

Data from LRO has also revealed differences in the composition of the crust in the highlands as well as the presence of silica-rich material in five different regions of the Moon. Silica-rich materials such as these are only found in rocks that have been through a great deal of magmatic processing.

The lunar map been used to confirm that the Moon was volcanic until about 2 billion years ago, that the oldest parts of the Moon are the north-central far side and the southern near side and that the Aitken Basin at the South Pole is the Moon's oldest basin.

LRO's data has also revealed the existence of natural bridges on the Moon. These bridges resemble bridges that were created by water or wind erosion on Earth.

Scientists believe that these tunnels may have been created by lava tubes -deep holes under the surface of the Moon - that have collapsed.

Scientists hope to use the topographic map of the Moon to help them gain a better understanding of the history of the Earth. While the asteroids that bombarded the Moon have left permanent tracks in the form or craters, plate tectonics and the movement of wind and water are constantly changing the appearance of the Earth's surface, making it more difficult to get a clear picture of the Earth's history.

When the Moon was bombarded by asteroids 3.9 million years ago, the Earth would have been bombarded as well. Any water that was on Earth at the time would have evaporated.

LRO has also measured temperature and radiation levels on the Moon's surface.

The Lunar Reconnaissance orbiter has been orbiting the Moon since June 2009.