Scientists have identified a large crater on the near side of the moon—the first detection of its kind in at least a century. The structure has been provisionally named after aviation pioneer Amelia Earhart. (BBC)
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- The exciting news that there’s a previously unidentified crater on the moon is even more remarkable because the crater is on the “near” side of the moon. What does this mean?
- The near side of the moon is simply the Earth-facing side. The moon, Earth’s only natural satellite, is in gravitational lock with the Earth: It takes the moon just as long to rotate around its own axis as it does to revolve around the Earth. This means the Earth and the moon are in synchronous rotation, and the same side of the moon always faces the Earth.
- Astronomers didn’t see the far side of the moon (sometimes called the “dark side”) until satellite imagery made it possible in 1959.
- How do scientists think the newly identified crater was formed? Read the third paragraph in our short encyclopedic entry on “crater” for some help.
- Our encyclopedic entry says “Because the moon has almost no atmosphere, there is hardly any wind, erosion, or weathering. Craters and debris, called ejecta, from millions of years ago are still crystal-clear on the moon’s surface.” So, how was a 200-kilometer-wide (124-mile-wide) crater “hiding in plain sight”?
- The Earhart crater was mostly buried by ejecta from a bigger, more recent impact. (That impact created the Mare Serenitatis, or “Sea of Serenity.”) So, the older crater isn’t really visible, much less “in plain sight.” It’s barely “in plain gravity.” (See next question.)
- How did scientists discover the Earhart crater?
- They examined data from NASA’s GRAIL mission. (NASA loves acronyms: This one stands for Gravity Recovery And Interior Laboratory.)
- The GRAIL data tracked tiny gravitational anomalies on the moon. The mission did this through the use of two probes—Ebb and Flow. (Tidal swelling of love for NASA nomenclature!) As Ebb and Flow orbited the moon, instruments kept track of minute changes in the gravitational pull of the moon on each probe. Differences in gravity directly relate to differences in the density of the interior lunar crust. The circular outline of the Earhart crater only became apparent when scientists evaluated the density of the subsurface lunar crust, not the surface topography of the moon. (Whew.) (FYI: Ebb and Flow are now a permanent part of the lunar landscape.)
- Why have scientists named the new crater Earhart?
- Well, they haven’t, officially. All new astronomical objects and features need to be approved by the folks at the International Astronomical Union. (They’ll probably go for it, though.)
- Legendary pilot Amelia Earhart was a visiting faculty member at Purdue University College of Technology. (She advised women on careers in aviation. What a great guidance counselor to have!) Earhart was flying a Purdue-funded Lockheed Model 10 Electra at the time of her disappearance. And . . . the new crater was identified by H Jay Melosh (an earth, atmospheric, and planetary science professor), Rohan Sood, and Loic Chappaz—a trio of researchers from Purdue. Nice.
- Do we need a reason to honor Amelia Earhart? Says Dr. Melosh: “Craters are named after explorers or scientists, and Amelia Earhart had not yet received this honor. She attempted a flight around the world, and we thought she deserved to make it all the way to the moon for inspiring so many future explorers and astronauts.”
Nat Geo: What is a moon?
Nat Geo: What is a crater?
NASA: GRAIL mission overview