Posted: 01 Nov 2010 03:17 PM PDT

If life ever existed on Mars, then newly discovered mineral deposits on the flanks of a long-dead volcano would be a good place to dig for its remains.

Spotted by a high-powered orbital imager, they're not the first deposits found on Mars of silica, a mineral used by some simple forms of life, including single-celled algae that evolved early in Earth's volcanic past.

But the new deposits are the first from a locale with a definite volcanic pedigree, formerly rich in heat and water, as well as minerals — a locale formerly suited, by any earthly definition, for life.

Stand on the slopes of Nili Patera 3.7 billion years ago, and "you would see steam rising up out of the volcano. In the spots we see the deposits, that's where the highest concentration of steam would be," said geoscientist Jack Mustard of Brown University. "It'd be like standing on Hawaii, looking across a volcano, seeing the fumaroles where vapors are given off, or standing in Iceland where the hills are steaming."

Mustard's findings, co-authored with fellow Brown geoscientist J.R. Skok, were published October 31 in Nature Geoscience. His laboratory is among those that in recent years has processed an extraordinary flow of red planet data, returned by Mars-orbiting spacecraft and surface-exploring robots.

This data has moved researchers beyond looking for signs of water — the latest of which was reported just last week, by both the Spirit and Phoenix rovers — to evaluating potentially once-habitable environments in precise detail.

"It's the most definitive hydrothermal system we've found on Mars. You can see the source of the heat, the driving of the fluids that left the deposits," said Mustard. "In this deposit, you have the culprit right before you. In other deposits, they're either sedimentary, or in the center of an impact crater. You have no idea how they happened."

According to Mustard, traces of any organisms that existed could still be found in the silica, which is non-porous and ideal for preserving fossil remains from the ravages of time and weather. Even after 3.7 billion years, any degradation would come only from silica-penetrating cosmic rays, which break down biological compounds. Those would still leave telltale residues of carbon, and the ExoMars expedition robot, scheduled to launch in 2018, will be equipped with a six-foot-long drill perfect for digging beneath ray-damaged layers.

Mustard isn't yet prepared to say the rover Curiosity, successor to the Phoenix and Spirit rovers, should visit Nili Patera when it lands on Mars in 2012. Curiosity lacks ExoMars' planned drilling capacity, and already has a wealth of places to explore: the ancient lake deposits of Holden crater, a stack of sedimentary layers three miles thick in Gale crater, and the Mawrth Vallis river valley.

But Mustard couldn't help but speculate. "It would be pretty intriguing" if Curiosity found carbon amidst the silica, he said. "Or the rover, as it's going up the slopes, could dislodge some rocks and look underneath. That's where the good stuff is."

Images: The Nili Patera caldera./NASA, JPL-Caltech, MSSS, JHU-APL, Brown University.

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Citation: "Silica deposits in the Nili Patera caldera on the Syrtis Major volcanic complex on Mars." By J. R. Skok, J. F. Mustard, B. L. Ehlmann, R. E. Milliken and S. L. Murchie. Nature Geoscience, advance online publication, October 31, 2010.

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Giant Waves Solve Saturn Ring Mystery

Posted: 01 Nov 2010 11:57 AM PDT

Saturn's largest ring appears to behave like a mini spiral galaxy. NASA's Cassini spacecraft caught enormous waves sloshing back and forth across Saturn's B ring, similar to waves believed to give galaxies their spiral shapes.

"This is a major result," said Cassini imaging team leader Carolyn Porco of the Space Science Institute. "Saturn's rings are tiny tiny tiny compared to a galaxy, but we see the same physics."

The new observations also show two warped regions, including a tall arc of spiky peaks that rise almost two miles above the ring plane. These perturbations may have been sculpted by small moons that migrated across the ring disk, a process believed to be important in shaping planetary systems.

Saturn's most massive ring, the B ring, has baffled astronomers since the Voyager spacecraft flew by in 1980 and 1981. Those observations showed the B ring was sculpted into a flattened football shape with a sharp outer edge by the moon Mimas. But even in the Voyager images, it was clear the B ring was too complex and chaotic to be shaped by Mimas alone.

Now, in a new analysis published in the Astronomical Journal, thousands of Cassini images gathered over the course of four years have revealed three separate wave patterns that are not driven by any moons, but spring up spontaneously by drawing energy from the small, random motions of ring particles. The waves, which can be hundreds of miles long, keep themselves going by reflecting off the ring's edges.

"Think of it like waves in a pool," Porco said. If two kids are hopping up and down at either end of a pool, she says, the waves they send sloshing across the water will pass through each other and reflect off the edge of the pool.

In Saturn's rings, the waves are more like compressions in a Slinky than water waves, but the physics is similar. "These waves just go back and forth, and keep reflecting until they finally grow large enough so that we can actually see them," Porco said.

"Normally viscosity, or resistance to flow, damps waves — the way sound waves traveling through the air would die out," said planetary ring expert Peter Goldreich of Caltech and the Institute for Advanced Study in Princeton, who was not involved in the new study, in a press release. "But the new findings show that, in the densest parts of Saturn's rings, viscosity actually amplifies waves, explaining mysterious grooves first seen in images taken by the Voyager spacecraft."

Cassini has also observed similar waves on smaller scales, with wavelengths around 300 feet. Computer models of galaxies and protoplanetary disks around other stars have shown similar randomly generated waves with proportionally larger wavelengths. But because those waves would take hundreds of millions of years to complete one slosh, astronomers can't observe them directly.

"This is the first time we've seen these things in nature," Porco said. "It underscores the deep, physical connection between what we're studying at Saturn's rings, and disk systems across the universe at a very large range of spatial scales."

Cassini has also snapped pictures of sharp, stalagmite-like peaks at the edge of the B ring that made themselves known by throwing long spiky shadows (below).

The new study suggests this region of the rings contains small moons that compress the ring material like a soda can and force it upward. This idea is supported by the presence of at least one moonlet, caught during Saturn's summer equinox when it cast a shadow across the rings.

These moonlets may have migrated across Saturn's rings, and become trapped in a gravitational resonance with the larger moon Mimas. This process of migration and trapping is exactly how scientists believe the solar system achieved its current architecture.

In this way, Saturn serves as a nearby laboratory to study celestial structures on all scales, from planets to solar systems to galaxies.

"There are basically two shapes in the universe, there's disks and there's spheres," Porco said. "Saturn's rings allow us to understand one of the two main structures in the universe: a celestial disk system."

"This is not just a slight addition, it's something significantly new," Goldreich told Wired.com. Goldreich and colleagues predicted the presence of these waves in 1985, but the Cassini observations provide the first proof.

"A lot of times, you don't expect to be around to see whether you made a prediction that worked," Goldreich said. "I was quite pleased to see it."

Video and Image: NASA/JPL/Space Science Institute

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Video: Climate Model Suggests Where the Aliens Are

Posted: 01 Nov 2010 10:36 AM PDT

The jury is still out on whether nearby red dwarf star Gliese 581 hosts a planet in its habitable zone, as astronomers announced last month. But the controversy hasn't stopped the planet's co-discoverer from speculating about where the aliens are in a new study that lays out the first model of what the planet's atmosphere might look like.

The potentially habitable world, called Gliese 581g, is about three times the mass of Earth and orbits its star once every 36.6 Earth days, reported astronomer Steve Vogt of the University of California, Santa Cruz. That orbit plants it close enough to the star that it ought to be tidally locked, showing the same face to the star at all times.

This setup would likely leave one hemisphere a scorching desert and the other a frigid ice sheet. With the right amount of global warming, either or both sides could conceivably be habitable. But the most comfortable place for life to grab a toehold would probably be in the zone of permanent twilight, where the sun is always rising or setting.

Or so Vogt assumed. In a new paper submitted to the Monthly Notices of the Royal Astronomical Society, Vogt and atmosphere-modeling expert Kevin Heng of The Swiss Federal Institute of Technology Zurich find that the planet's most comfy spots probably lie along a sideways V-shaped curve, with two eddies of warmth at the tips.

"What we're finding basically is that the patterns of warmth and cold on these things is a little more complicated," Vogt said. "In fact, the most comfortable place is probably around the chevron, in the vortices."

The still-unconfirmed planet was detected through subtle gravitational tugs on its parent star, which had to be teased apart from the conflicting signals of five sibling planets that range from about two to 15 times the mass of Earth.

This planet-hunting method gives no data on what the planet looks like, however. Future telescopes may be able to snap fuzzy pictures of Gliese 581's planetary family. But until then, the alien atmospheres are up in the air.

To bring Gliese 581g's possible climate down to Earth, Vogt and Heng modified a simplified climate model often used to simulate Earth. In recent years, Heng and others have started using the modeling package to simulate atmospheres on gas giant exoplanets.

"As soon as I heard about this, I thought, let's turn it loose on Gliese 581g and tell me where the aliens are living," Vogt said.

The researchers scaled the model's temperature parameters to reflect the heat Gliese 581g would absorb from its parent star, which is dimmer but closer than ours. They set the temperature at the equator to about 40 degrees Fahrenheit, and assumed the temperature difference between the equator and the poles was similar to Earth's, about 60 degrees. The team also assumed certain properties of the atmosphere, like the amount of heat it can absorb and the surface pressure, were just like Earth's.

The team ran the model for 1,000 Earth days to see what long-term weather patterns showed up. They found a constant light wind, like a slow jet stream, developed around the planet, pulling warm air into a V-shape. That whole V would probably be habitable, Vogt suggests. Extra whorls of warmth in the north and south "might be nice vacationing spots," he said.

"It's a great start for understanding the patterns of flow on these super-Earth exoplanets," said exoplanet expert Sara Seager, who was not involved in the new study. "It's pretty cool that even under all these approximations and assumptions, he always finds spots that are habitable. That's reassuring."

But don't pack your bags yet. A separate group of astronomers announced Oct. 12 that the planet might not be there at all, and could just be a trick of the data.

"Personally, I have to admit that this debate on habitability seems a lot less relevant if Gliese 581g doesn't actually exist," said astronomer Heather Knutson of the University of California, Berkeley, who models the atmospheres of hot gas giant exoplanets. "Given all of the other transiting planets currently being discovered by the Kepler mission, I think we'll probably have an actual, confirmed planet in the habitable zone … in the next one to two years."

Vogt is undeterred. "Whether or not Gliese 581g is confirmed, there's going to be others like this," he said. "'What is life like there?' is becoming an interesting field in its own right. We have enough computing power now to make some interesting conclusions about where things might live."

Video: Heng & Vogt/MNRAS. Image: Heng & Vogt/MNRAS.

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