Saturn and Jupiter are examples of gas giants—huge, uninhabitable planets
composed of gas rather than solid matter. Based on observations of these planets and models of their evolution, astronomers have long believed [pdf] that they form by guzzling gas from young stars. This week, courtesy of a telescope in the deserts of Chile, astronomers reported seeing the first direct evidence of gas giant formation.
Astronomers were observing a young star
called HD 142527, some 450 light years from Earth. Like most young stars, HD 142527 is surrounded by a disk of gas and dust—remnants of the star’s conception that continue to circle the star for millions of years . But there was something strange about this particular star’s disk. Astronomers observed a large gap in the gas and dust, which, as reported in Nature this week, they believe is caused by an up-and-coming gas giant.
An illustration of the descent
While the Cassini probe has been taking the gorgeous pictures of Saturn we know and love, its little buddy and traveling companion, the Huygens lander, has been on the surface of the moon Titan. A just-published reconstruction of what happened when Huygens hit Titan’s surface eight years ago gives insight into what the ground on the methane-soaked body is like: something like damp sand, or perhaps crusty snow.
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.
Artist’s rendering of AVIATR flying on Titan.
Saturn’s moon Titan is a lot like Earth: it has rain, seasons, volcanoes, and maybe even life. Well, it’s not exactly like Earth: the rain is liquid methane, the volcanoes spew ice, and any life would be based on methane. But still, it’s an interesting and relatively Earth-like place, considering the other planets and moons in our solar system. And University of Idaho physicist Jason Barnes says he has a perfect way to explore this moon: with a flying drone.
Why use a flying machine rather than the rovers that worked so well on Mars? With 1/7 the gravity but 4 times the atmospheric density of Earth, flying through Titan is 28 times easier than on our own planet. In fact, it’s the easiest place to fly in our entire solar system. Drones on Titan can be heavier while requiring less fuel. With these facts in hand, University of Idaho physicist Jason Barnes has proposed AVIATR, otherwise known as the Aerial Vehicle for In-situ and Airborne Titan Reconnaissance.
What’s the News: NASA’s considering launching a boat from Earth, hurling it 746 million miles through space, and plopping it onto one of the minus-290 degrees Fahrenheit methane oceans of Titan. This mission to Saturn’s largest moon would the first of its kind to probe an alien ocean and—depending on the weather conditions—could be the first spacecraft to witness extraterrestrial rain. If the proposed mission beats out two other finalists, it could launch within the next five years. “Titan is an endpoint [in] exploring … the limits to life in our solar system,” project leader Ellen Stofan told New Scientist. “We’re going to be looking for patterns in abundances of compounds to look for evidence for more complex or interesting reactions.”
What’s the News: Images sent back from NASA’s Cassini spacecraft depict storm clouds and methane rain puddles, the first solid evidence of modern rainfall on Titan, Saturn’s largest moon. “We’re pretty confident that it has just rained on Titan,” lead author Elizabeth Turtle, from Johns Hopkins University Applied Physics Laboratory, told Wired. Astronomers have previous evidence of sulfuric-acid precipitation on Venus, but it doesn’t count as rainfall because it never reaches the surface.
What’s the Olds:
Not So Fast: Don’t read too much into these showers: Methane rain doesn’t mean life. The search continues.
Reference: “Rapid and Extensive Surface Changes Near Titan’s Equator: Evidence of April Showers.” E.P. Turtle, J.E. Perry, A.G. Hayes, R.D. Lorenz, J.W. Barnes, A.S. McEwen, R.A. West, A.D. Del Genio, J.M. Barbara, J.I. Lunine, E.L. Schaller, T.L. Ray, R.M.C. Lopes, E.R. Stofan. Science, Vol 331, March 18, 2011. DOI: 10.1126/science.1201063
Image: NASA/JPL/Space Science Institute
A new sight appeared on Saturn earlier this month: A massive, swirling storm with a tail that cuts across the gas giant. Amateur astronomer Anthony Wesley, who was the first to spot the Earth-sized scar on Jupiter last summer, took the first pictures of this storm. And then on Christmas Eve the Cassini spacecraft beamed home its own ravishing images.
The spacecraft took images of the planet on December 24th, returning — as usual — jaw-dropping pictures of Saturn showing the storm. This image, taken with a blue filter, shows the storm clearly. The main spot is huge, about 6,000 km (3600 miles) across — half the size of Earth! Including the tail streaming off to the right, the whole system is over 60,000 km (36,000 miles) long.
There’s an added bonus in these images: the shadow of the rings on the planet’s clouds is obvious, but the rings are nearly invisible! You can just make out the rings as a thin line going horizontally across Saturn in the first image. These pictures were snapped when Cassini was almost directly above the rings, which are so thin they vanish when seen edge-on. Actually, that works out well as otherwise they might interfere with the view of the storm in these shots.
For more details, check out the rest of Phil’s post at Bad Astronomy.
80beats: By Demolishing a Moon, Saturn May Have Created Its Rings
80beats: Mysterious Smash on Jupiter Leaves an Earth-Sized Scar
Bad Astronomy: Saturn rages from a billion kilometers away
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]