Moonlet Study Sheds Light on Origins of Saturn's Rings

A new study of Saturn's striking rings has found clusters of "moonlets," lending support to the theory that large icy moons were slowly pulverized to form the ring system.

The boulder-size chunks, spotted in a narrow belt, could only have been formed when something collided into an object at least as large as Pan, Saturn's innermost moon, which is about 15 miles (25 kilometers) wide, scientists say.

The origin of Saturn's ring system remains a mystery. Some experts say the rings are remnants of the same gas and dust that formed Saturn.

Others support the idea that the ring's icy chunks formed from moons that were battered by asteroid impacts or blasted apart by collisions with meteors.

Unraveling the mystery of the rings' formation will help scientists better understand how our solar system—and alien ones—form.

"The origin and evolution of planetary rings is one of the prominent unsolved problems of planetary sciences," write the study authors in this week's issue of the journal Nature.

Encircled in Mystery

At ten times Earth's diameter, Saturn is the second-largest planet in the solar system.

Its rings are among the most beautiful features in the solar system: wide, flat discs of ice crystals that seem to float serenely in space.

The ice pieces range from the size of dust to more than ten feet (three meters) across.

For years researchers have noticed strange, paired bright streaks within Saturn's outermost ring, which is dubbed the A ring. The narrow band lies about 80,000 miles (130,000 kilometers) from the planet's surface.

Scientists call the streaks "propeller features," because they resemble the propellers of airplanes. Scientists now know that the features form when a larger object pushes debris into a wake, as if the moonlets were boats in water.

"These moons are not massive enough to make too much havoc in the rings, but they are still big enough to create some disturbance," said study co-author Miodrag Sremčević, a postdoctoral researcher at the University of Colorado in Boulder. "It's like a mini-moon inside of the ring."

One prevailing theory has been that larger pieces formed when some of the smallest ice fragments came together over time. But the new study calls that into question.

Tumultuous Realm

Sremčević and his colleagues studied images captured by NASA's Cassini spacecraft in August 2005, when Saturn's rings were backlit by the sun.

The team found that eight of the moonlets in Saturn's A ring were concentrated in a narrow belt, not scattered throughout the ring like a peaceful origin would suggest.

All eight of the moonlets are between 160 and 500 feet (60 and 140 meters) across.

"I really did not expect that," Sremčević said. "I was thinking these moonlets are everywhere, and with more patience and observation we would find them throughout the rings."

The images instead suggest the rings are a tumultuous realm where massive collisions break apart football-field-sized ice chunks, and time grinds the pieces into ever smaller bits, kind of like how sand forms on Earth.

"Some bigger moon was orbiting within the ring and was struck by a larger meteorite or comet," Sremčević said. "What we see today are remnants of that larger moon."

Solar Clock

The boulders may be useful as a sort of clock to chronicle the rings' history, Sremčević said.

Particles larger than about 30 feet (10 meters) tend to get ground down over time by meteorite impacts and interactions with other particles in rings, he pointed out.

So it's possible that the larger the particle, the more recently it was formed, he added, though this idea needs to be tested a lot more.

Sremčević said a rough estimate for the timing of the collision that formed the eight moonlets is about a hundred million years ago.

Scientists have evidence that in 1984 a similarly catastrophic impact occurred when a three-foot (one meter) object slammed into an icy boulder of similar size in Saturn's inner D ring.

"We actually came up with one hypothesis that could match up everything," Sremčević said. "That was: the rings were created a long time ago. That's an old idea. These moonlets are younger than the rest of the rings."

Dozens of Propellers

Matthew S. Tiscareno, a researcher at Cornell University, originally revealed the A ring's propeller features in a 2006 Nature study but didn't have a wide enough view to say how widespread they were.

He said the discovery of discrete belts is indeed surprising—and it may soon become even more complicated.

Tiscareno recently submitted a paper to the Astronomical Journal in which he catalogues 158 propeller features.

"My paper clearly resolves the 'belt of moonlets' into three sub-belts, perhaps indicating that the population of moonlets was sculpted by other ring processes after the break-ups that originally formed them," he told National Geographic News by email.

Moonlight Triggers Mass Coral "Romance"

Australian and Israeli scientists have discovered the trigger for the planet's biggest group sex spectacle: the mass spawning of hard corals along Australia's Great Barrier Reef.

One week each year in spring, after a full moon, millions of corals release eggs and sperm in what Bill Leggat, a co-author of the new study, called "a slow symphony."

But until now how the primitive animals—which lack brains or eyes—synchronized the mass spawning was a mystery.

In today's issue of the journal Science, researchers reveal that they have isolated an ancient gene in the corals' DNA that can detect moonlight.

By exposing corals to different colors and intensities of light, the team found that the gene—known as Cry2—was most active in Acropora corals during a full moon.

Leggat, a lecturer at James Cook University in Cairns, Australia, said Cry2 encodes a type of protein known as a cryptochrome, which appears to trigger the corals' reproductive cycle.

"This particular gene allows the coral to sense blue light and to actually work out what phase the moon is in," he added.

The research also suggests that the basic ability to sense changes in light and adapt a 24-hour cycle appeared early in the evolution of animals.

Sophisticated Spawning

Cry2 prompts a series of biochemical reactions that is surprisingly sophisticated, Leggat said.

Some 400 or 500 species of corals all spawn simultaneously during the week, creating vast slicks across the ocean, he pointed out.

"It's just magical," Leggat said. "To just sit in front of an individual coral and watch the pink sperm bundles get slowly pushed out of the corals' mouth and float away—it's incredible to watch."

"It's one of the greatest sights in nature, but the amazing thing is that, after going on for millions of years, it wasn't witnessed until the 1980s," he added.

How the right sperm ends up with the right egg is a complicated process that may rely on refined chemical pathways, he said. But scientists are still working on unraveling the exact details.

"To me, the really exciting thing is this huge, well-orchestrated symphony [is] going on, yet we still don't know how it works," Leggat said.

"We're only really just starting to understand corals and reefs in general, and something that's both exciting and worrying is that these reefs are threatened, that they may not be around in 50 years."

Night and Day

The new research also offers insights into the development of vision and the evolution of daily rhythms in animals.

Ove Hoegh-Guldberg, director of marine science at the University of Queensland, said cryptochromes are closely linked to primitive proteins known as photolyases—which harness blue light to repair DNA damaged by ultraviolet radiation.

"[In the Precambrian era] there were very high doses of ultraviolet reaching the planet surface, so organisms probably had to retreat out of range of the UV" in addition, said Hoegh-Guldberg, who was also a co-author on the new research.

"One way to do that would be to go into the deeper layers of the ocean during the day and to rise during the night as levels dropped" by adapting the light-sensing properties of the photolyases, he added.

From there, it was "a very simple step to evolve cryptochromes to set your clock to do the right things at the right time," he said.

"The first creatures wouldn't have had eyes," Hoegh-Guldberg continued. "They would have been depending on cellular biochemistry to detect changes in light. So cryptochromes are, in a sense, the functional forerunners of eyes."

Cryptochromes are still present in humans and other mammals, as well as insects, he said. They play an important role in regulating the circadian system, a "body clock" attuned to Earth's 24-hour rhythms that regulates things like cycles of metabolism and alertness.

"[These proteins] are the Swiss timing mechanism of biology," Hoegh-Guldberg said.

Surprising Complexity

In addition, the work shows the surprising level of sophistication of even the earliest animals.

"We think of corals as being very simple, but they're not," Leggat, of James Cook University, said. "They're actually incredibly complex—they have almost the same number of genes and proteins as humans.

"Many of these genes developed in deep time, in the earliest phases of organized life on the planet," he added. "They were preserved for hundreds of millions of years before being inherited by corals when they developed about 240 million years ago, and are still found today in modern animals and humans."

They are an indicator that corals and humans are in fact distant relatives, sharing a common ancestor way back."

Hoegh-Guldberg said the team would head back to the reef this spring to delve deeper into the secrets of cryptochromes.

"We've got all the smoking guns of this mechanism," he said. "The next step is to track down the way they drive things like reproduction. We fully expect to uncover other behavior that they are controlling."

"Vibrating Mice" Develop Less Fat, Study Shows

A new study in mice could shake up the fight against fat.

Laboratory mice that spent 15 minutes a day on a vibrating platform developed 28 percent less fat than control mice during a recent experiment.

But forget the ads for waistband-jiggling vibration belts guaranteed to "burn away fat." These mice experienced very subtle, almost undetectable, tremors.

Scientists theorize that as the mice developed, the vibrations mimicked muscle activity and induced their stem cells to develop into bone or muscle cells rather than fat cells.

"We're not burning fat or taking fat mice and making them skinny," said lead author Clinton Rubin, a biomedical engineer at the State University of New York, Stony Brook.

"We're taking mice who are growing and ... influencing the decision of stem cells [so that they don't] become fat cells."

The finding came in part from research in human spaceflight. Rubin and colleagues are trying to induce stem cells to become bone cells in order to offset the bone loss that results in zero-gravity space environments.

Rubin has also co-founded a for-profit company, Juvent Medical, that is using a similar concept to treat osteoporosis.

The study will appear this week in the journal Proceedings of the National Academy of Science.

Fighting Fat Before it Appears

The human body needs fat cells, which store food energy for future use.

Most doctors believe that obesity is the result of consuming more calories than a body burns. Recent research suggests that genetics and other factors may also play a role.

Rubin cautions that the study is preliminary and raises as many questions as it answers.

But the possibilities for human weight control are intriguing, and they may include developmental as well as metabolic factors.

"Just imagine a way to keep people from getting fat that is not [only] about how many Oreos they eat or how much they exercise—but about keeping them from forming fat cells in the first place," he said.

No Guilt-Free Solutions

But if the prospect of consequence-free overeating and sloth sounds too good to be true, it probably is, experts say.

"The reason we have those cells is to take [in] excess fat," said Roger Unger, an obesity researcher at the University of Texas Southwestern Medical Center.

"If you inhibit [fat cells] and overeat, you haven't done that person a favor," said Unger, who was not involved in the new research.

"The surplus lipids would end up in organs where you don't want to have surplus lipids—like the heart and the liver."

"People that don't have [as many] fat cells, if they overeat, get very sick—[they get] sicker at a much earlier age than people who first get fat and then develop complications."

Rexford Ahima is a University of Pennsylvania endocrinologist.

"The idea that 'non-strenuous work' can reduce body fat is intriguing; however, the findings have to be interpreted with caution," he said.

Ahima noted that key information regarding the mice's energy expenditure, hormones, and metabolism remains unknown and may have impacted the results.

Mars Volcanoes May Re-Erupt, Hawaii Comparison Shows

A trio of volcanoes on Mars may have been created by a similar geologic process to the one that formed the Hawaiian Islands, a new study says.

The observations also suggest that the three Martian volcanoes might not be extinct.

If sufficiently large eruptions do eventually occur, they could spew enough heat-trapping carbon dioxide and water into the atmosphere to warm the red planet up from its current cold, dry state—at least for a little while.

Those are the findings of a research team led by Jacob Bleacher of Arizona State University and NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The researchers traced the flow of molten rock under three large Martian volcanoes in the Tharsis Montes mountain range, partly by comparing their surface features to those found on Hawaiian volcanoes.

They discovered that the same basic process formed the mountains but that it worked in very different ways because of each planet's unique geology.

"On Earth the Hawaiian Islands were built from volcanoes that erupted as the Earth's crust slid over a hot spot—a plume of rising magma," Bleacher said in a press release.

"Our research raises the possibility that the opposite happens on Mars—a plume might move beneath stationary crust."

The results appeared in the September 19 issue of the Journal of Geophysical Research, Planets.

Mysterious Mountains

Tharsis Montes contains three large shield volcanoes—Arsia Mons, Pavonis Mons, and Ascraeus Mons—in a northeast-trending chain across the Tharsis rise on Mars.

The rise spans about 2,800 miles (4,500 kilometers) of Mars' western hemisphere and includes seven partly buried shield volcanoes, lava plains with clusters fissure vents, and other features that intrigue geologists.

The same region contains the giant Olympus Mons volcano, the largest volcano in the solar system. At about 373 miles (600 kilometers) in diameter—about the size of the state of Arizona—Olympus Mons is twice the size of each of the Tharsis Montes volcanoes.

So far no volcanic activity has been observed at Tharsis Montes.

But the Mars Express, Mars Global Surveyer, and Mars Odyssey spacecraft have recently sent back high-resolution images of the region, providing insights into each volcano's explosive past.

Hawaii and Mars

Bleacher and his team compared the new images with information on Hawaii's volcanoes.

On the Big Island, the youngest volcanoes are on the southeastern end, directly over a magma hot spot.

As the Pacific crustal plate slowly moves to the northwest, the volcanoes are carried away from the hot spot. Over time the movement has created Hawaii's chain of volcanic islands.

Volcanoes over the hot spot have the hottest lava. As the mountains move away, though, only isolated pockets of rising magma remain.

The researchers found the Martian volcanoes had similar surface features and seemed to evolve in a similar way as the Hawaiian volcanoes.

But there is no evidence for such plate movement on Mars. So the researchers suggest that the mountain-creating plume instead moved beneath the stationary Martian crust.

Sleeping Giants?

The findings have some bizarre implications for the evolution of the red planet.

On Earth, cooling magma releases trapped gas, which creates short, explosive eruptions of cinders. Earlier flows become covered with piles of cinders, called cinder cones, which form around these eruptions.

The Tharsis Montes chain show no evidence of cinder cone eruptions—the final stage of hot spot volcanoes—suggesting the mountains might only be dormant, not extinct.

The mountains also erupted relatively recently in Martian history, judging from the lack of large impact craters near the chain.

Volcanic eruptions release large amounts of greenhouse gases, such as carbon dioxide, into the atmosphere.

If eruptions begin again on Mars—and the future eruptions are large enough—they could contribute significant amounts of water and carbon dioxide to the atmosphere.

That's unlikely to make the planet hospitable, though, scientists warn.

"The Martian environment becoming habitable in the future due to a volcanic eruption is extremely improbable," Bleacher told National Geographic News.

Mars once had a magnetic field, but currently lacks one strong enough to protect the atmosphere from solar wind, he pointed out.

"The current Martian surface environment is very hostile towards life as we know it to exist," he added.

"From a planet-wide perspective, a single volcanic eruption—if one was to occur on Mars—would not create an environment suitable for life to survive. Any erupted gases would quickly be stripped away by the solar wind."

Randy Kirk, a geophysicist at the U.S. Geological Survey in Flagstaff, Arizona, said the paper represents an interesting hypothesis that could explain why the three Tharsis volcanoes are equally spaced in a straight line, "which is something people have wondered about for a long time.

"At some level this explanation seems like it just resolves a matter of minor curiosity, why these three volcanoes happen to be in the places they are," he said.

But the work could have farther-reaching implications toward our understanding of magma circulation inside planets, he added—for "Mars definitely, and maybe this will also say something about Earth, eventually."