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Recent advances in astrophotography have made it possible to overcome previously unthinkable limits, both in capture distance and image resolution. At the 241st meeting of the American Astronomical Society (AAS) in Seattle (USA), researchers presented incredible images of the Moon captured from Earth. Amazingly detailed, some showing as far as the Apollo 15 landing site and the Tycho crater, these are believed to be the highest resolution images from our natural satellite ever obtained from Earth. A feat achieved thanks to a radar system barely more powerful than a microwave oven!
The Moon’s surface is littered with relatively isolated craters and valleys. Unlike the mountain ranges on Earth, those of the Moon are more composed of dunes, in particular due to the absence of atmosphere and surface water (no erosion or sedimentation). On the Moon, the shaping of the surface is carried out mainly through the large contrast of temperatures between day and night, as well as through the bombardment of meteorites (no atmosphere impeding their passage).
The Tycho crater is a trace left by a meteorite that impacted the lunar surface millions of years ago (about 200 million). Particularly famous, this crater is among the most remarkable elements of the surface of the Moon, because it can be easily distinguished during a full moon and with the help of good binoculars, or with a simple high resolution camera.
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On some of the best photos of the Moon Taken from Earth, you can easily make out its dark circular structure, as well as the bright rays emanating from the rim of the crater. The new images, shown at the Seattle press conference, were taken from Earth using the Green bank (GTB) radio telescope in West Virginia. With its 100 meters in diameter, it is currently the largest rotating radio telescope in the world.
A spectacular result
According to Patrick Taylor, head of the Radar Division at Green Bank Observatory and the US National Radio Astronomy Observatory (NRAO), the GTB projected waves toward the Moon to be bounced back toward a set of four radio telescopes 25 meters in diameter, located in Hawaii (the Very Long Baseline). To be able to capture the images, a prototype radar system was installed on the GTB, with a maximum power of 700 watts. It is “comparable to a microwave-type household appliance or a set of light bulbs”, noted Taylor.
Stunningly detailed images show the landforms around the Apollo 15 landing site with a resolution of just 1.5m. Details captured at Tycho Crater have a resolution of 5 meters. In addition, the researchers used the radar to be able to capture images and data of a 1 km long asteroid, located 5 times the Earth-Moon distance. The new instrument has made it possible to determine its exact size, its speed of revolution and rotation, its composition, and the way in which light is reflected on its surface. A feat achieved with an instrument “ less powerful than your microwaves,” Taylor said at the press conference.
According to the researchers who designed the radar, the size and orbit of this asteroid means that it could one day represent a potential danger for the Earth. However, its current position indicates that we are out of danger for the moment.
As a next step, the researchers plan to design an improved version of the radar, with 700 times more power (about 500 kilowatts). Such power could in particular make it possible to carry out geological studies of the Moon, as well as of small celestial bodies orbiting around the natural satellite. Better still, the future instrument would make it possible to detect and analyze asteroids likely to threaten our planet.
Eventually, the GTB could take over from the Arecibo radio telescope (located in Puerto Rico). It was indeed the largest radio telescope in the world used to detect asteroids, but it unfortunately collapsed on itself in 2020, causing great emotion within the community of astronomers.