Any mention of Pluto among astronomy buffs, around water coolers and in comments sections, is enough to spark controversy. When the diminutive world officially became known as a dwarf planet in 2006, many took the “demotion” personally. But an announcement today from the SETI Institute might just be cool enough to bring everyone together.
The discoverers of Pluto’s two smallest moons are reaching out to the world for help in naming them. Currently designated P4 and P5, these tiny satellites were discovered in 2011 and 2012, respectively, using Hubble Space Telescope data. These were always temporary labels, though, and the time has come to select their official names. There might be even more moons lurking around the former planet, but the thing about Pluto is it’s really, really far, and even for Hubble the entire system registers as little more than dots. Plus, these moons are really small, only about 20 miles across max, making others like them extra hard to spot.
Cassini image of a landslide on Iapetus
Landslides can wreak enormous destruction, especially when they travel farther than expected. When an avalanche occurs, dirt both falls vertically and spreads horizontally, with the horizontal distance usually no more than twice the vertical drop. But in a sturzstrom, some unknown factor decreases the coefficient of friction, allowing the earth to slide much farther; it acts more like a glacier or a lava flow than a regular avalanche. Theories about that friction-reducing factor abound—trapped air, water, or mud, pressure, rubbed and heated rock becoming more slippery, rock nanoparticles, sound waves, changes in local gravity—but its true nature is still unknown. By examining sturzstroms that occur on distant planets and moons—whose forces of gravity, atmospheres, fluids, and soil differ from those on Earth—researchers hope to unravel the factors that contribute to a landslide’s length. This information could help us predict landslides’ shapes and alleviate the damage they cause.
What’s the News: Jupiter’s moon Io is more volcanically active than any other object in our solar system, releasing 30 times more heat than Earth through volcanism. It’s thought that Jupiter’s gravity pulls so hard on the moon and causes so much friction that the resulting thermal energy melts a huge amount of underground rock, feeding Io’s 400 active volcanoes.
For years, astronomers have debated whether Io’s spewing lava comes from isolated pockets of magma or a layer that spans the entire moon. Astronomers have now peered into Io’s interior for the first time, discovering that it has a global sea of magma roughly 30 miles thick. “It turns out Io was continually giving off a ‘sounding signal’ in Jupiter’s … magnetic field that matched what would be expected from molten or partially molten rocks deep beneath the surface,” lead researcher Krishan Khurana told Wired. Read More
What’s the News: Astronomers have known for many years that Saturn’s moon Titan sports lakes of liquid methane. And in the past couple years, scientists have suggested that it also has an underground ocean composed of water and ammonia. Now, based on past observations by NASA’s Cassini spacecraft, astronomers are saying that Titan’s rotation indeed points to an underground sea—and where there’s water, there may also be life. “Our analysis strengthens the possibility that Titan has a subsurface ocean, but it does not prove it undoubtedly,” researcher Rose-Marie Baland told Astrobiology Magazine. “So there is still work to do.”
Saturn and its moons may owe their distinctive looks to a legacy of destruction.
First, the magnificent rings of the sixth planet: Although astronomers have gazed at the rings for centuries, experts are still debating exactly how these loops formed. Now a new study in the journal Nature proposes that the rings are the leftovers of a large moon that was torn asunder when Saturn’s gravity reeled it in four and a half billion years ago. Lead researcher Robin Canup says this theory explains both how the rings got there, and why they’re made of nearly solid ice.
In the new study, Canup calculated that a moon the size of Titan — Saturn’s largest at some 5,000 kilometers across — would begin to separate into layers as it migrated inward. Saturn’s tidal pull would cause much of the moon’s ice to melt and then refreeze as an outer mantle. As the moon spiraled into the planet, Canup’s calculations show, the icy layer would be stripped off to form the rings. [Science News]
That layered removal is the key to Canup’s explanation, which we covered briefly when she first presented the idea at a meeting in October. Other explanations for the rings’ formation include a comet crashing into a moon, or Saturn pulling in a moon and causing it to shatter all at once. Those events would create a cascade of small objects that Saturn’s gravity could have coalesced into rings, but it would seem that they would have created much rockier rings. In reality, Saturn’s are 95 percent ice.
When the news comes from Saturn’s moons, the source is typically Titan—with its hazy atmosphere and frigid surface lakes of methane—or Enceladus—with its plumes of water ice. Last week, however, word came that Rhea, the second-largest Saturnian satellite, has some surprises of its own.
In Friday’s edition of Science, a study by Ben Teolis and colleagues confirmed that during a pass of the moon in March, when the ever-reliable Cassini spacecraft cruised over Rhea’s pole at an altitude of just 60 miles, it directly sampled tiny amounts of oxygen and carbon dioxide there.
“This really is the first time that we’ve seen oxygen directly in the atmosphere of another world,” said Andrew Coates, at UCL’s Mullard Space Science Laboratory, a co-author of the study. [The Guardian]
Carbonated oceans, moons torn apart, ring tsunamis—there’s a flurry of cool news about Saturn coming out of the American Astronomical Society’s Division for Planetary Science meeting in Pasadena, California.
The fizzy ocean of Enceladus
Saturn’s moon Enceladus is one of the prime candidates for some kind of life elsewhere in the solar system, thanks the the possibility that a large subsurface ocean feeds the plumes of ice and vapor that the Cassini spacecraft has spied blasting forth from the moon. At the AAS meeting in California, Cassini scientists Dennis Matson proposed something new about this extraterrestrial ocean: It could be carbonated.
Noncarbonated seawater circulating from the moon’s solid core to the surface would stall rather than seep though cracks in the ice because seawater is denser than the icy carapace. If the seawater were fizzy, however, gas bubbles would form in the liquid, reducing the ocean’s density. Once the seawater became less dense than the ice, the water could rise to within 10 to 15 meters of the frigid surface. That’s close enough to fill chambers in the icy crust with water that feeds the south polar plumes. [Science News]
Our own moon, the thinking goes, formed when a huge rock slammed into the Earth billions of years ago. Is the same true of one of Mars’ dual moons?
The Martian moon Phobos hides an unknown history. One idea has been that the 12-mile by 17-mile rock came from the nearby asteroid belt, and Mars’ gravity captured it. However, new evidence from the European Space Agency’s explorer Mars Express suggests that the stuff of Phobos is more Mars-like than asteroid-like, and therefore its origin goes back to a violent collision that knocked material from Mars into its own orbit. That material would have eventually coalesced into Phobos.
They’re new, they’re small, and they didn’t make sense.
That’s what could be said for five of the littlest members of Saturn’s expansive satellite family. The largest of this group, Janus, measures barely more than 100 miles in diameter, but it’s the age of these little moons that’s the odd bit. Their clean, crater-free surfaces help reveal that they’re only 10 million years old, meaning they didn’t form the way the planet’s other moons did—from the accretion disk that formed mighty Saturn itself billions of years ago. This week in Nature, astronomers published evidence to support an explanation for that oddity: Those moons formed from Saturn’s rings.
Sailing past Saturn’s outer rings, it found lumps of ice up to 100 metres across, ten times bigger than the rings’ other icy particles. For some researchers, the discovery called to mind another intriguing fact: that the moons and the rings share a composition of the purest ice in the Solar System. “When you put all this together, you had the strange feeling that something is going on in the rings’ outer edge,” says Sébastien Charnoz at Paris Diderot University, who was involved in the latest research [Nature].
While Jupiter’s two largest moons, Ganymede and Callisto, are nearly the same size, they’re far from identical twins. Now, in a Nature Geoscience study, Amy Barr and her team might have figured out this tale of two similar moons with very different histories.
Voyager and Galileo mission images showed Ganymede, seen here on the right, to be a geologically active place, with a surface that scientists think changes through tectonic processes like those that we have here on the Earth. Callisto, seen on the left, looks totally different: Its rock and ice have not mixed in the same way, and it doesn’t seem to have such active geology, despite being approximately the same size as Ganymede. For 30 years, researchers have wondered what process could have got enough heat into Ganymede to drive its geological evolution without setting off Callisto as well [ScienceNOW Daily News].