Category Archives: The Moon
That’s here; that’s home; that’s us—the two bright objects in this picture are Earth and the Moon, imaged by NASA’s OSIRIS-REx spacecraft on January 17, 2018 from a distance of 39.5 million miles (63.5 million km).
This is about the distance between Earth and Mars at their closest points to each other (give or take about 6 million miles) or about 165 times farther away from us than the Moon.
“We came all this way to explore the Moon, and the most important thing is that we discovered the Earth.”
– William Anders, Apollo 8 Commander
On Christmas Eve, December 24, 1968, the Apollo 8 CSM entered orbit around the Moon and, after completing 4 full orbits, provided the three astronauts on board with an amazing sight: a blue Earth rising* beyond the Moon’s cratered limb. Commander Frank Borman spotted the scene first and, after taking a 70mm black-and-white photograph, was able to rotate the Command Module so Earth remained in view through the small windows while CM pilot Jim Lovell captured this famous image on color film. It was the first time any humans saw the Earth from the vicinity of the Moon…and it was also the first Christmas that astronauts spent in space.
“The vast loneliness is awe-inspiring and it makes you realize just what you have back there on Earth,” Jim Lovell said.
On September 22 NASA’s OSIRIS-REx spacecraft made a “slingshot” gravity-assist pass by Earth in order to adjust the angle of its flight toward Bennu. Mission scientists took the opportunity to test out the spacecraft’s cameras with planned observations of Earth and the Moon, and I’m happy to report that everything worked out perfectly! Some of the first images shared with the public were of Earth from a distance of 106,000 miles; this one shows the Moon imaged from 746,000 miles away three days later on Sept. 25. It’s literally a view of the Moon we can’t ever get from Earth!
There are a lot of moons in our solar system—175 major planet satellites, and three times that if you count every natural satellite of every known object (like asteroids)—but among them our own capital-M Moon is in many ways unique. At a full quarter the size of Earth, only Pluto has a moon so near in size to itself, and unlike the swarms of icy worlds orbiting the gas giants the Moon is oddly very similar in composition to Earth…so similar, in fact, that it’s been casting increased doubt on the accuracy of the best-accepted model of the Moon’s formation, namely the Giant Impact Hypothesis.
Suggested in 1975 by planetary scientists William K. Hartmann and Don Davis, the model claims that the Moon was created 4.5 billion years ago when a Mars-sized world that’s been named Theia impacted the newly-formed Earth, blasting a chunk of molten material out into orbit that solidified to form the Moon. The model is based on a lot of science and answers a lot of questions, but not all—including a key issue of why the Moon today appears compositionally identical to Earth and not a mixture of Earth and a completely different planet.
As advanced computer measurement and modeling capabilities have increased a new wave of researchers are tackling the conundrum of the Moon’s origins, and a few new scenarios are coming to light. While ancient impacts are still involved, the question is now how many? With what kind of world(s)? And what exactly happened after the event?
“In the past five years, a bombardment of studies has exposed a problem: The canonical giant-impact hypothesis rests on assumptions that do not match the evidence. If Theia hit Earth and later formed the moon, the moon should be made of Theia-type material. But the moon does not look like Theia—or like Mars, for that matter. Down to its atoms, it looks almost exactly like Earth.”
Read the full story by Rebecca Boyle in The Atlantic here: The Moon’s Origin Story Is in Crisis
It’s been known for a while (especially since the 2009 LCROSS impact experiment) that there is water on the Moon. But so far the largest volume has been found as ice inside the shadowed walls of craters on the Moon’s south pole, likely originating from ancient comet impacts. Now, using data collected by India’s Chandrayaan-1 lunar satellite, researchers from Brown University in Providence, Rhode Island have identified water inside ancient pyroclastic flows located across the Moon’s surface—water that must have come from inside the Moon itself.
“We observe the water in deposits that are at the surface today, but these deposits are the result of magma that originally comes from deep within the lunar interior,” said Ralph Milliken, a geologist at Brown and lead author of the study. “Therefore, because the products of the magma have water, the deep interior of the Moon must also contain water.”
While the age and origin of this indigenous interior water aren’t yet known, its availability near the surface would be a valuable asset for any future human settlements on the Moon.
Read the rest of this article by Samantha Mathewson on Space.com here: The Moon’s Interior Could Contain Lots of Water, Study Shows