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Radar love – the Moon’s hidden surface shines in new images

Elizabeth Howell, News Writer
May 16, 2014, 14:51 UTC

Sen—Though the Moon is close enough to us for a small telescope to observe its features, there's much about its history that remains hidden to our eyes. This is because the Moon has a thick layer of dust on its surface, making it difficult to see its origins.

To peer through the grains, scientists sent out radar images from two observatories and examined the images when they came back. The goal is not only to figure out more about the Moon's history, but also to plan for future landing missions.

The hefty Arecibo Observatory sent out the radar from its location in Puerto Rico, allowing the signal to go through the Moon's dust. Once the radar reflected back, the National Radio Astronomy Observatory's Green Bank Telescope picked up the signal.

One of the resulting images showed new information about Apollo 17's landing site, penetrating about 10-15 metres (33-50ft) below the surface of Mare Serenitatis (Sea of Serenity). "The light and dark features are the result of compositional changes in the lunar dust and differences in the abundance of rocks buried within the soil," a spokesman for the NRAO said.

Sea of Serenity /moon

Mare Serenitatis (Sea of Serenity) on the Moon imaged using radar emanating from Earth. Credit: Bruce Campbell (Smithsonian Institution, National Air and Space Museum); Arecibo/NAIC; NRAO/AUI/NSF

A probe of Aristillus Crater, which is about 55km (34 miles) in diameter and 3.5km (2 miles) deep, found more information about the debris generated when a small body smacked into the surface a long time ago. "The dark 'halo' surrounding the crater is due to pulverized debris beyond the rugged, radar-bright rim deposits," NRAO stated.

"The image also shows traces of lava-like features produced when lunar rock melted from the heat of the impact."

There's much to learn about the properties of the dust that covers the Moon. For example, scientists are intrigued that the dust appears to hover at the sunrise/sunset line of the moon. This phenomenon was first observed by the Apollo astronauts and was one of the targets of research of the just-completed NASA LADEE mission.

Moon / Aristillus Crater

Aristillus Crater on the Moon imaged by radar emanating from Earth. Credit: Bruce Campbell (Smithsonian Institution, National Air and Space Museum); Arecibo/NAIC; NRAO/AUI/NSF

LADEE (which stands for Lunar Atmosphere and Dust Environment Explorer) launched September 2013 and impacted our closest neighbour as planned in April. Scientists are still examining the trove of data it sent back to Earth, but one of its early finds included finding changes in the Moon's sodium content in its "exosphere" (thin atmosphere) as the Moon orbits Earth.

Soft landings on the Moon itself have been rare since the Apollo era, but in December China's Chang'e-3, carrying the Yutu rover, successfully made it to Sinus Iridum. The Yutu rover, although facing mechanical difficulties, exceeded its three-month design lifetime.

Another active mission at the Moon is the Lunar Reconnaissance Orbiter. Scientists recently released the first interactive mosaic of the lunar north pole based on its images. LRO also obtained images of the Chang'e-3 landing site.