Latest news with #Mars-size
National Geographic
27-06-2025
- Science
- National Geographic
Moons
With volcanoes, frozen oceans, and methane seas, moons are often much more than balls of rock circling a body other than the sun. In fact, the only definitive thing that separates many moons from planets like the Earth and Mars is what they revolve around. Planets circle the sun; moons circle the things that circle the sun—planets, dwarf planets, and other so-called small solar system bodies. Otherwise, moons are diverse and fascinating worlds unto their own. Earth's Moon and Europa One of four planet-size moons in orbit around the planet Jupiter, Europa has an almost glassy surface of ice that scientists say may cover an ocean that is 31 miles (50 kilometers) deep. Tidal forces between Jupiter and Europa are believed to generate enough heat to keep the ocean liquid. Observations with the Hubble Space Telescope also indicate Europa has a tenuous atmosphere of oxygen. The combination of water, a heat source, and an atmosphere raises the possibility that Europa harbors life. The best known moon is the one in orbit around planet Earth. It is Earth's only natural satellite and the only extraterrestrial body that humans have visited. Gravity on the moon is one-sixth of Earth's gravity, allowing astronauts to take giant leaps on its surface. The moon lacks an atmosphere, but spacecraft have found water ice at both poles, deposited from impacting comets. According to a leading theory, a Mars-size body smacked Earth about 4.5 billion years ago and the debris from the collision accumulated to form its moon. But unlike Earth's moon, many moons formed from the same material that glommed together and gave rise to the body they orbit. Other moons are asteroids captured into orbit by a larger body's gravity. Only the dwarf planet Pluto's moon Charon is thought to have formed from a collision like the one that gave rise to Earth's moon. No matter how they form, the moons are many. Only Mercury and Venus are moonless. Earth has one, Mars two. Neptune has 13 and Uranus 27. The gas giant Jupiter has 63 known moons. Saturn has at least 60—and 42 of those have been discovered since 1997. The dwarf planet Pluto has three moons. Eris, another dwarf planet, has one moon. Dozens more moons orbit small solar system bodies.
Yahoo
09-04-2025
- Science
- Yahoo
China's Chang'e 6 lunar samples suggest our moon is debris from an ancient Earth impact
When you buy through links on our articles, Future and its syndication partners may earn a commission. There's less water in the mantle beneath the farside of the moon than in the mantle on the nearside, according to studies of the precious lunar samples brought back to Earth by China's Chang'e 6 mission. Furthermore, the findings bolster the theory that the moon formed when a giant, Mars-size protoplanet slammed into the young Earth about 4.5 billion years ago and sent a cascade of debris into orbit that coalesced into the powdery gray orb we see today. "We believe the new result is in line with the giant impact hypothesis of the moon," HU Sen, a professor at the Institute of Geology and Geophysics at the Chinese Academy of Sciences, told Chang'e 6 arrived at the South Pole–Aitken (SPA) basin, located on the farside of the moon, in June 2024. The lander's robotic drill and scoop collected 4.27 lbs (1.935 kilograms) of basaltic regolith from the SPA basin before returning it to Earth. Chang'e 6's treasure trove of lunar material is the first sample to be collected from the moon's farside. As such, it has some questions to answer. Among them is whether its water content is compatible with the giant impact theory of the moon's formation. Modeling of the giant impact scenario suggests the mantle on the farside of the moon should have less water than the nearside does. One line of evidence for this comes from the relative abundances of thorium on the lunar surface. Magma is formed from melt within the mantle, and the areas of the mantle that produce such melt are referred to as the "mantle source." When magma is formed in the mantle source, thorium, like water, remains in the melt rather than producing crystalline minerals. Therefore, the abundance of thorium on the surface can act as a proxy for water. The nearside, covered in ancient deep impacts and volcanic flows, has regions that are rich in thorium, as we would expect. Few areas on the farside, with its dearth of volcanism, have a high abundance of thorium. However, the SPA basin is an exception: as a giant impact basin, its floor is flooded by now-solid lava that welled up through the wound in the moon's surface from the mantle below, like blood oozing from a cut. As one of the few impact basins on the farside, the SPA basin is one of the few farside locations with thorium on the surface, where the impact that formed the basin dug deep enough into the mantle to bring the melt to the surface. So, the logic goes, if the SPA basin has less thorium, then perhaps it means the mantle source has less water too. Analysis of the basaltic (volcanic) rock brought back from the SPA basin by Chang'e 6 yields a mantle source water content of between just 1 and 1.5 μg.g⁻¹ (micrograms — millionths of a gram — per gram of sample). "The modeling results suggest that the lunar mantle would have a maximum water content of less than 10 μg.g⁻¹ This estimate is substantially lower than the average water content in the nearside mantle, based upon the study of Apollo-mission samples that suggest a value of up to 200 μg.g⁻¹, depending upon the location on the nearside. "If the lunar interior on the farside is drier than the nearside, it means the water in the lunar mantle may exhibit dichotomic distribution," said Hu. This difference, or dichotomy, between the water abundance in the mantle on the farside compared to the nearside of the moon is just one more thing to add to the list of differences between the two hemispheres. Topology, volcanism, surface ages, rock types and the aforementioned thorium difference are just some of the differences that any hypothesis attempting to model the formation and subsequent evolution of the moon have to explain. Related Stories: — The far side of the moon was once a vast magma ocean, Chinese lunar lander confirms — China returns samples from the moon's far side in historic 1st (video) — Ancient impact that formed Earth's moon was likely a one-two punch "We infer that such a dichotomic distribution of water in the moon may be the result of the massive impact event forming the SPA basin," said Hu. The SPA basin is huge, spanning 1,600 miles (2,500 kilometers ) and is one of the very largest examples of its kind in the solar system — its effects on the rest of the moon, particularly the farside, would have been enormous. "Another possibility is the water in the lunar mantle may exhibit secular distribution," said Hu. "For instance, the deeper and earlier-formed lunar mantle may have relatively lower water content than the shallower and later-formed mantle source." One thing is for sure: Despite being as dry as a bone, the moon's farside continues to be one of endless fascination. The analysis of the Chang'e 6 samples was reported on April 9 in the journal Nature.
Yahoo
17-03-2025
- Science
- Yahoo
How did Earth get such a strange moon? Exploring the giant impact theory
When you buy through links on our articles, Future and its syndication partners may earn a commission. The moon is weird. It's completely unlike anything else in the solar system. So how did our planet end up with such a special moon? The answer is that, surprisingly enough, the moon is a piece of our planet. There's a lot going on with the moon. For starters, it exists, which is weird in its own way. Mercury has no moons, and neither does Venus. Mars does have two moons, but they're really just captured asteroids. Earth is the only rocky planet in the solar system with a significant moon. And the moon really is significant: It's roughly 1.2% the mass of Earth. That may not be big in an absolute sense, but for the solar system, that's huge. No other moon is that large relative to its parent planet. The oddities don't stop there. The total angular momentum of Earth's spin, the moon's spin and the moon's orbit is very large — far higher than for any other terrestrial planet. So how did we get so much momentum? Plus, the moon is full of "KREEPs" – that is, potassium (K), rare-Earth elements (REE) and phosphorus (P). These elements don't usually like to hang out together, but lunar samples show that they are often mixed. That requires the moon to have been molten at some point, which takes a lot of energy. And the real icing on the cake is that the moon has many of the same abundances of stable isotopes as Earth does, which indicates that Earth and the moon evolved from the same clump of material. The leading explanation for all of these mysteries is known as the giant impact hypothesis. According to this story, when the solar system was just getting started, a Mars-size protoplanet named Theia slammed into the proto-Earth. With an impact velocity of somewhere around 20,000 mph (32,000 km/h) — relatively slow as impacts go — what happened next was nothing short of catastrophic. The heavy core of Theia sank deep into Earth, enlarging our planet's core. The two bodies' mantles mixed and thus bulked up our planet. And the crusts were scattered far into space. What happened next is a little hard to follow and depends a lot on exactly how the impact unfolded and what Theia was made of. But the general picture is that some stuff went flying away, never to return. Other stuff rained onto Earth's surface. And a big chunk remained in orbit. In as little as a few hours — or perhaps up to a century or more — that material coalesced into its own solid object: the moon. Some models suggest that a second moon, just a few hundred kilometers across, formed past the far side and then slowly approached the moon and pancaked itself. This would explain why the far side of the moon is lumpier than the near side. There's also the possibility that this wasn't a low-energy, glancing blow at all — that instead, the proto-Earth was spinning really quickly and then got nailed by Theia. This would have delivered more than enough energy to vaporize everything and create a doughnut-shaped ring of plasma known as a synestia. No matter what, this impact released a lot of energy — more than enough to turn the moon into a molten ball, more than enough to bring the KREEP elements together, and more than enough to mix Earth's original material and Theia's to create a set of common features between Earth's crust and the moon. Related stories: —Massive space rock impact could have 'instantly' created the moon —A chunk of the 'protoplanet' that made the moon may be stuck near Earth's core —Ancient impact that formed Earth's moon was likely a one-two punch As with all hypotheses, it's not perfect. For example, if there's enough energy to liquefy the moon, there's enough energy to liquefy Earth's surface. But there is no evidence for large-scale magma seas in Earth's history. Also, the moon does have some volatile elements, like water, trapped in rock — but a giant-impact, giant-energy event should have gotten rid of those. Despite those caveats, the giant impact hypothesis is the most compelling story we have for how the moon formed. And without a time machine into our distant past, we'll never be able to prove it. But it still fits almost all of the evidence we have so far, so it's a story worth keeping around.
