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
Saturn’s largest moon Titan is often called an analogy to early Earth, with its thick, chemical-rich atmosphere and widespread system of flowing rivers and north polar lakes. But located almost a billion miles away from the Sun, everything on Titan is shifted into a completely different—and frigid—level of existence from that found on Earth. With surface temperatures of 300 degrees below zero F, the lakes are filled with liquid methane and what’s life-giving water here is literally solid rock there. Even the rain on Titan falls as oversized drops of ethane.
But even in this extreme cryo-environment it’s possible that life may right now exist…life relying on an entirely different chemistry than what’s possible on our planet.
Recently scientists have identified a molecule on Titan called vinyl cyanide, or acrylonitrile. To Earthly life acrylonitrile is toxic and carcinogenic; luckily for us it isn’t naturally-occurring here. But on Titan it is and apparently in quantity; it’s possible that vinyl cyanide, raining down from Titan’s atmosphere into its vast hydrocarbon lakes, could even help form methane-based cell structures in much the same way phospholipids do here.
The molecule (C2H3CN) has the ability to form membranes and, if found in liquid pools of hydrocarbons on Titan’s surface, it could form a kind of lipid-based cell membrane analog of living organisms on Earth. In other words, this molecule could stew in primordial pools of hydrocarbons and arrange itself in such a way to create a “protocell” that is “stable and flexible in liquid methane,” said Jonathan Lunine (Cornell University) who, in 2015, was a member of the team who modeled vinyl cyanide and found that it might form cell membranes.
Further evidence of life “not as we know it?” Read more on Ian O’Neill’s Astroengine blog here: Vinyl Cyanide Confirmed: Weird Form of Alien Life May Be Possible on Saturn’s Moon Titan and in a Gizmodo article by Maddie Stone here: Potential Building Block of Alien Life Spotted in Titan’s Atmosphere
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
On May 12, 2016, the Hubble Space Telescope captured a series of images of Mars and in them the planet’s moon Phobos can be seen appearing from behind the western limb. This was just 10 days before opposition which, in 2016, was the closest Mars had been to Earth since 2005, lending particularly good opportunity for picking out its largest—yet still quite small—moon.
Today is the the 52nd anniversary of America’s first spacewalk, performed by NASA astronaut Edward H. White II on the afternoon of June 3, 1965 during the four-day Gemini IV mission. In NASA terminology spacewalks are also referred to as extravehicular activities, or EVAs—basically anything done outside the protection of a spacecraft. The video above shows footage of the historic Gemini IV EVA with narration by White himself. (Sound begins about 30 seconds in.)
The photo below was captured on medium-format film by fellow astronaut Jim McDivitt from inside the Gemini IV craft. It shows White free-floating in orbit during his EVA, holding the Hand-held Maneuvering Unit (or “zip gun”) that used canisters of propellant to move the user around. (You can see scans of the original photos from the mission here on ASU’s “March to the Moon” gallery.)
White was tragically killed just two years later on Jan. 27, 1967 in the fire that claimed his life and those of fellow Apollo 1 astronauts Gus Grissom and Roger Chaffee. But his legacy lives on each and every time an American astronaut “suits up” and opens a hatch to venture out into an alien environment, whether it’s in Earth orbit, on the Moon, on Mars…or somewhere we haven’t even thought of visiting yet!