What is Consuming Hydrogen and Acetylene on Titan?

PASADENA, Calif. - Two new papers based on data from NASA's Cassini spacecraft scrutinize the complex chemical activity on the surface of Saturn's moon Titan. While non-biological chemistry offers one possible explanation, some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan's surface. According to one theory put forth by astrobiologists, the signatures fulfill two important conditions necessary for a hypothesized "methane-based life."

One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan's atmosphere and disappearing at the surface. Another paper online now in the Journal of Geophysical Research maps hydrocarbons on the Titan surface and finds a lack of acetylene.

This lack of acetylene is important because that chemical would likely be the best energy source for a methane-based life on Titan, said Chris McKay, an astrobiologist at NASA Ames Research Center, Moffett Field, Calif., who proposed a set of conditions necessary for this kind of methane-based life on Titan in 2005. One interpretation of the acetylene data is that the hydrocarbon is being consumed as food. But McKay said the flow of hydrogen is even more critical because all of their proposed mechanisms involved the consumption of hydrogen.

"We suggested hydrogen consumption because it's the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth," McKay said. "If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth."

To date, methane-based life forms are only hypothetical. Scientists have not yet detected this form of life anywhere, though there are liquid-water-based microbes on Earth that thrive on methane or produce it as a waste product. On Titan, where temperatures are around 90 Kelvin (minus 290 degrees Fahrenheit), a methane-based organism would have to use a substance that is liquid as its medium for living processes, but not water itself. Water is frozen solid on Titan's surface and much too cold to support life as we know it.

The list of liquid candidates is very short: liquid methane and related molecules like ethane. While liquid water is widely regarded as necessary for life, there has been extensive speculation published in the scientific literature that this is not a strict requirement.

The new hydrogen findings are consistent with conditions that could produce an exotic, methane-based life form, but do not definitively prove its existence, said Darrell Strobel, a Cassini interdisciplinary scientist based at Johns Hopkins University in Baltimore, Md., who authored the paper on hydrogen.

Strobel, who studies the upper atmospheres of Saturn and Titan, analyzed data from Cassini's composite infrared spectrometer and ion and neutral mass spectrometer in his new paper. The paper describes densities of hydrogen in different parts of the atmosphere and the surface. Previous models had predicted that hydrogen molecules, a byproduct of ultraviolet sunlight breaking apart acetylene and methane molecules in the upper atmosphere, should be distributed fairly evenly throughout the atmospheric layers.

Strobel found a disparity in the hydrogen densities that lead to a flow down to the surface at a rate of about 10,000 trillion trillion hydrogen molecules per second. This is about the same rate at which the molecules escape out of the upper atmosphere.

"It's as if you have a hose and you're squirting hydrogen onto the ground, but it's disappearing," Strobel said. "I didn't expect this result, because molecular hydrogen is extremely chemically inert in the atmosphere, very light and buoyant. It should 'float' to the top of the atmosphere and escape."

Strobel said it is not likely that hydrogen is being stored in a cave or underground space on Titan. The Titan surface is also so cold that a chemical process that involved a catalyst would be needed to convert hydrogen molecules and acetylene back to methane, even though overall there would be a net release of energy. The energy barrier could be overcome if there were an unknown mineral acting as the catalyst on Titan's surface.

The hydrocarbon mapping research, led by Roger Clark, a Cassini team scientist based at the U.S. Geological Survey in Denver, examines data from Cassini's visual and infrared mapping spectrometer. Scientists had expected the sun's interactions with chemicals in the atmosphere to produce acetylene that falls down to coat the Titan surface. But Cassini detected no acetylene on the surface.

In addition Cassini's spectrometer detected an absence of water ice on the Titan surface, but loads of benzene and another material, which appears to be an organic compound that scientists have not yet been able to identify. The findings lead scientists to believe that the organic compounds are shellacking over the water ice that makes up Titan's bedrock with a film of hydrocarbons at least a few millimeters to centimeters thick, but possibly much deeper in some places. The ice remains covered up even as liquid methane and ethane flow all over Titan's surface and fill up lakes and seas much as liquid water does on Earth.

"Titan's atmospheric chemistry is cranking out organic compounds that rain down on the surface so fast that even as streams of liquid methane and ethane at the surface wash the organics off, the ice gets quickly covered again," Clark said. "All that implies Titan is a dynamic place where organic chemistry is happening now."

The absence of detectable acetylene on the Titan surface can very well have a non-biological explanation, said Mark Allen, principal investigator with the NASA Astrobiology Institute Titan team. Allen is based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Allen said one possibility is that sunlight or cosmic rays are transforming the acetylene in icy aerosols in the atmosphere into more complex molecules that would fall to the ground with no acetylene signature.

"Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed," Allen said. "We have a lot of work to do to rule out possible non-biological explanations. It is more likely that a chemical process, without biology, can explain these results - for example, reactions involving mineral catalysts."

"These new results are surprising and exciting," said Linda Spilker, Cassini project scientist at JPL. "Cassini has many more flybys of Titan that might help us sort out just what is happening at the surface."

NASA Rover Finds Clue to Mars' Past and Environment for Life

PASADENA, Calif. -- Rocks examined by NASA's Spirit Mars Rover hold evidence of a wet, non-acidic ancient environment that may have been favorable for life. Confirming this mineral clue took four years of analysis by several scientists.

An outcrop that Spirit examined in late 2005 revealed high concentrations of carbonate, which originates in wet, near-neutral conditions, but dissolves in acid. The ancient water indicated by this find was not acidic.

NASA's rovers have found other evidence of formerly wet Martian environments. However, the data for those environments indicate conditions that may have been acidic. In other cases, the conditions were definitely acidic, and therefore less favorable as habitats for life.

Laboratory tests helped confirm the carbonate identification. The findings were published online Thursday, June 3 by the journal Science.

"This is one of the most significant findings by the rovers," said Steve Squyres of Cornell University in Ithaca, N.Y. Squyres is principal investigator for the Mars twin rovers, Spirit and Opportunity, and a co-author of the new report. "A substantial carbonate deposit in a Mars outcrop tells us that conditions that could have been quite favorable for life were present at one time in that place."

Spirit inspected rock outcrops, including one scientists called Comanche, along the rover's route from the top of Husband Hill to the vicinity of the Home Plate plateau that Spirit has studied since 2006. Magnesium iron carbonate makes up about one-fourth of the measured volume in Comanche. That is a tenfold higher concentration than any previously identified for carbonate in a Martian rock.

"We used detective work combining results from three spectrometers to lock this down," said Dick Morris, lead author of the report and a member of a rover science team at NASA's Johnson Space Center in Houston."The instruments gave us multiple, interlocking ways of confirming the magnesium iron carbonate, with a good handle on how much there is."

Massive carbonate deposits on Mars have been sought for years without much success. Numerous channels apparently carved by flows of liquid water on ancient Mars suggest the planet was formerly warmer, thanks to greenhouse warming from a thicker atmosphere than exists now. The ancient, dense Martian atmosphere was probably rich in carbon dioxide, because that gas makes up nearly all the modern, very thin atmosphere.

It is important to determine where most of the carbon dioxide went. Some theorize it departed to space. Others hypothesize that it left the atmosphere by the mixing of carbon dioxide with water under conditions that led to forming carbonate minerals. That possibility, plus finding small amounts of carbonate in meteorites that originated from Mars, led to expectations in the 1990s that carbonate would be abundant on Mars. However, mineral-mapping spectrometers on orbiters since then have found evidence of localized carbonate deposits in only one area, plus small amounts distributed globally in Martian dust.

Morris suspected iron-bearing carbonate at Comanche years ago from inspection of the rock with Spirit's Moessbauer Spectrometer, which provides information about iron-containing minerals. Confirming evidence from other instruments emerged slowly. The instrument with the best capability for detecting carbonates, the Miniature Thermal Emission Spectrometer, had its mirror contaminated with dust earlier in 2005, during a wind event that also cleaned Spirit's solar panels.

"It was like looking through dirty glasses," said Steve Ruff of Arizona State University in Tempe, Ariz., another co-author of the report. "We could tell there was something very different about Comanche compared with other outcrops we had seen, but we couldn't tell what it was until we developed a correction method to account for the dust on the mirror."

Spirit's Alpha Particle X-ray Spectrometer instrument detected a high concentration of light elements, a group including carbon and oxygen, that helped quantify the carbonate content.

The rovers landed on Mars in January 2004 for missions originally planned to last three months. Spirit has been out of communication since March 22 and is in a low-power hibernation status during Martian winter. Opportunity is making steady progress toward a large crater, Endeavour, which is about 11 kilometers (7 miles) away.

NASA Spacecraft Penetrates Mysteries of Martian Ice Cap

PASADENA, Calif. -- Data from NASA's Mars Reconnaissance Orbiter have helped scientists solve a pair of mysteries dating back four decades and provided new information about climate change on the Red Planet.

The Shallow Radar, or SHARAD, instrument aboard the Mars Reconnaissance Orbiter revealed subsurface geology allowing scientists to reconstruct the formation of a large chasm and a series of spiral troughs on the northern ice cap of Mars. The findings appear in two papers in the May 27 issue of the journal Nature.

"SHARAD is giving us a beautifully detailed view of ice deposits, whether at the poles or buried in mid-latitudes, as they changed on Mars over the last few million years," said Rich Zurek, Mars Reconnaissance Orbiter project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

On Earth, large ice sheets are shaped mainly by ice flow. According to this latest research, other forces have shaped, and continue to shape, polar ice caps on Mars. The northern ice cap is a stack of ice and dust layers up to two miles deep, covering an area slightly larger than Texas. Analyzing radar data on a computer, scientists can peel back the layers like an onion to reveal how the ice cap evolved over time.

One of the most distinctive features of the northern ice cap is Chasma Boreale, a canyon about as long as Earth's Grand Canyon but deeper and wider. Some scientists believe Chasma Boreale was created when volcanic heat melted the bottom of the ice sheet and triggered a catastrophic flood. Others suggest strong polar winds carved the canyon out of a dome of ice.

Other enigmatic features of the ice cap are troughs that spiral outward from the center like a gigantic pinwheel. Since the troughs were discovered in 1972, scientists have proposed several hypotheses about how they formed. Perhaps as Mars spins, ice closer to the poles moves slower than ice farther away, causing the semi-fluid ice to crack. Perhaps, as one mathematical model suggests, increased solar heating in certain areas and lateral heat conduction could cause the troughs to assemble.

Data from Mars now points to both the canyon and spiral troughs being created and shaped primarily by wind. Rather than being cut into existing ice very recently, the features formed over millions of years as the ice sheet grew. By influencing wind patterns, the shape of underlying, older ice controlled where and how the features grew.

"Nobody realized that there would be such complex structures in the layers," said Jack Holt, of the University of Texas at Austin's Institute for Geophysics. Holt is the lead author of the paper focusing on Chasma Boreale. "The layers record a history of ice accumulation, erosion and wind transport. From that, we can recover a history of climate that's much more detailed than anybody expected."

The Mars Reconnaissance Orbiter was launched on Aug. 12, 2005. SHARAD and the spacecraft's five other instruments began science operations in November 2006.

"These anomalous features have gone unexplained for 40 years because we have not been able to see what lies beneath the surface," said Roberto Seu, Shallow Radar team leader at the University of Rome. "It is gratifying to me that with this new instrument we can finally explain them."

Cassini - Nice images of Enceladus & Titan

On the left, Saturn's moon Enceladus is backlit by the sun, showing the fountain-like sources of the fine spray of material that towers over the south polar region. On the right, is a composite image of Titan. Image credit: NASA/JPL/SSI and NASA/JPL/University of Arizona

Ancient Galaxies Imaged

Astronomers are a bit like archeologists as they dig back through space and time searching for remnants of the early universe. In a recent deep excavation, courtesy of NASA's Spitzer Space Telescope, astronomers unearthed what may be the most distant, primitive cluster of galaxies ever found.

In a twist, however, this apparent ancestor to today's "big cities" of grouped galaxies looks shockingly modern. Called CLG J02182-05102, the ancient cluster is dominated by old, red and massive galaxies, typical of present-day clusters. For example, it is similar to a young version of the Coma Cluster of today, which has had billions of more years to develop.

"We are seeing something already aged and red like a younger version of the Coma Cluster from a distant, bygone era," said Casey Papovich, lead author of a new study and an assistant professor of physics and astronomy at Texas A&M University in College Station.

Papovich added, "it is as though we dug an archeological site in Rome and found pieces of modern Rome in amongst the ruins."

ClG J02182-05102 might have indeed been ahead of its time. Just as Rome was the world's biggest city more than 2,000 years ago with a population of about a million residents - a figure not again matched until the early 1800s in London - so too was this galactic grouping an advanced civilization for so early an era in the developing universe.

Galaxy clusters are the largest gravitationally bound structures in the universe and are thought to have formed piecemeal over cosmic time. For now, ClG J02182-05102 is the only known galactic grouping so far away in the past, and studying it will help researchers understand the overall history of how galaxies congregate and evolve.

A Cosmic Archeological Expedition

In their hunt for rare ancient cities in the early universe, Papovich and his team started with the largest extragalactic survey ever made. Called the Spitzer Wide-area InfraRed Extragalactic (SWIRE) survey, it observed a huge portion of the sky that could contain 250 full moons.

Because more light gathered means more information, the researchers looked at a cosmic region within this giant starscape that had also been studied by other instruments. These additional observations came from a survey combining light from Japan's Subaru telescope - housed atop Mauna Kea, Hawaii - and the European Space Agency's orbiting XMM-Newton telescope. The United Kingdom Infra-Red Telescope, also in Hawaii, provided infrared data along with another set of Spitzer observations called the Public Ultra Deep Sky survey.

When all these data were compiled, Spitzer's infrared observations made dozens of distant galaxies jump out. "We would not have found this object without Spitzer because there is very little optical light coming from this group of galaxies," said Papovich.

His team then obtained time on the Magellan telescope in Chile to study the faint light coming from ClG J02182-05102's least-dim galaxies. This light allowed the astronomers to archeologically date the candidate cluster to 9.6 billion years ago.

With these observations, Papovich and his team confirmed that seven of ClG J02182-05102's galaxies have nearly the same distance, suggesting they are part of a grouping of about 60 galaxies. Whether or not this association of galaxies fully qualifies as a gravitationally bound cluster will rely on further observations. Furthermore, the definition of a "cluster" itself remains unsettled, somewhat like the blurry distinctions between a city and a town, made trickier still given the limited light that makes it to our telescopes from these relics.

The Rise and Fall of CLG J02182-05102

For now, ClG J02182-05102 stands out as a greatly over-dense region of galaxies - a metropolis in a land of isolated villages. At its center regions loom red, monster galaxies containing about 10 times as many stars as our Milky Way galaxy. This puts them on par with the most mammoth galaxies in the nearby universe, which have grown fat through repeated mergers with other galaxies. These big galaxies are so uncharacteristic of those in the early universe that in some sense it is like finding modern skyscrapers in ancient Rome.

Rock and Roll: Titan's Gem Tumbler

It appears flash flooding has paved streambeds in the Xanadu region of Saturn's moon Titan with thousands of sparkling crystal balls of ice, according to scientists with NASA's Cassini spacecraft. By analyzing the way the terrain has scattered radar beams, scientists deduce the spheres measure at least a few centimeters (inches) and maybe up to a couple of meters (yards) in diameter. The spheres likely originated as part of water-ice bedrock in higher terrain in Xanadu.

"What we believe happened in this area is a lot like what creates polished river rocks on Earth," said Alice Le Gall, a postdoctoral fellow at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and the lead author of the study, which used the Cassini radar instrument. "Bouncing downstream smoothes out the edges of rocks."

As foothill residents know in southern California and other areas, sudden rains can trigger mudslides and flooding at the mountainous fringes of desert areas. Those flows can pick up boulders and debris and tumble them downstream. On Titan, the flows appear to have occurred periodically for eons, on a catastrophic scale. The process on Titan, however, involves rain made of liquid methane and ethane, rather than Earth's water rain. Titan's rocks are believed to be made primarily of water ice frozen into a hard mass about minus 180 degrees Celsius (minus 290 degrees Fahrenheit), rather than Earth's mineral rocks.

Earth-like river rocks have already been observed on Titan at the landing site of the European Space Agency's Huygens probe, near the equator in the borderland between the Adiri and Shangri-la regions. The landing site also showed signs of flash flooding that deposited cobblestones about 2 to 20 centimeters (1 to 8 inches) in diameter.

But the spidery channels in this southern lowland part of Xanadu looked brighter to Cassini's radar instrument than the Huygens landing area. In fact, the channels, which were scanned by Cassini in May 2008, are among the brightest features ever seen on Titan by the radar instrument.

In a paper now available online in the journal Icarus, Le Gall and colleagues concluded that the most plausible explanation for the extreme brightness of the Xanadu channels was a collection of transparent spherical sediments, packed more tightly together than the cobblestones at the Huygens landing site. The effect would be similar to bejeweling an area with light-catching rhinestones.

The spheres appear to be made of water ice - possibly doped with ammonia - that would look bright to the microwaves used by Cassini's radar. Spheres are good at sending light back in the direction it came from. This property has actually led manufacturers to use plastic spheres in reflective paints and tape, Le Gall said.

Xanadu may be an especially good gem grinder because of its broad expanse and gentle southward slope. Flows could have traveled long distances there and tumbled the chunks for hundreds of kilometers (miles). The subtle work to shape them into spheres could have come from fine grit rubbing against the rocks in the flowing methane. Or, ice may be malleable in Titan's cold temperatures, deforming plastically during the collisions rather than fracturing. The flows that transported these icy spheres probably traveled around 1 meter per second (2 mph).

"It's been really hard for a long time for people to understand why Xanadu is so bright," said Steve Wall, a radar team member at JPL. "You might not expect these kinds of geometries in a natural setting, but we believe this can explain the enigma."

The radar team plans to continue looking for other instances of small, smooth spheres in nature to increase their confidence about the explanation. They also said more study is needed on the mechanical properties of water ice at such cold temperatures.

"Here is yet another example of Titan as a world with Earth-like processes," said Linda Spilker, Cassini project scientist at JPL. "As the seasons change on Titan, maybe we'll get a chance to see methane flow through some of the river channels."

Herschel Finds a Hole in Space

The Herschel Space Observatory has made an unexpected discovery: a gaping hole in the clouds surrounding a batch of young stars. The hole has provided astronomers with a surprising glimpse into the end of the star-forming process.

Stars are born hidden in dense clouds of dust and gas, which can now be studied in remarkable detail with Herschel, a European Space Agency mission with important NASA participation. Although jets and winds of gas have been seen streaming from young stars in the past, it has always been a mystery exactly how a star uses the jets to blow away its surroundings and emerge from its birth cloud. For the first time, Herschel may be seeing an unexpected step in this process.

A cloud of bright reflective gas known to astronomers as NGC 1999 sits next to a black patch of sky. For most of the 20th century, such black patches were known to be dense clouds of dust and gas that block light from passing through.

When Herschel looked in its direction to study nearby young stars, astronomers were surprised to see the cloud continued to look black, which shouldn't have been the case. Herschel's infrared eyes are designed to see into such clouds. Either the cloud was immensely dense or something was wrong.

Investigating further using ground-based telescopes, astronomers found the same story no matter how they looked: this patch looks black not because it is a dense pocket of gas but because it is truly empty. Something has blown a hole right through the cloud.

"No one has ever seen a hole like this," says Tom Megeath of the University of Toledo, Ohio, the principal investigator of the research. "It's as surprising as knowing you have worms tunneling under your lawn, but finding one morning that they have created a huge, yawning pit."

The astronomers think that the hole must have been opened when the narrow jets of gas from some of the young stars in the region punctured the sheet of dust and gas that forms NGC 1999. The powerful radiation from a nearby adolescent star may also have helped to clear the hole. Whatever the precise chain of events, it could be an important glimpse into the way newborn stars rip apart their birth clouds.

Some Black Holes Can Kill Entire Galaxies

Black holes might kill entire galaxies with blazing energy, dooming embryonic stars before they can get born and condemning the remaining stars to a slow death, scientists have found.

Although nothing can escape from a black hole, before matter falls into one, it swirls around to form a disk that heats up as it packs together, radiating energy.

Supermassive black holes are thought to reside at the center of almost every galaxy, with some growing to billions of times the mass of our sun. To see what impact these monsters might have, researchers relied on data from the Hubble Space Telescope and the Chandra X-ray Observatory, looking for galaxies with very high X-ray emissions, a classic signature of black holes devouring gas and dust.

All this radiation can drive away the gas and dust that serve as the raw ingredients of new stars, permanently shutting down star formation in the surrounding galaxy. The remaining stars age, redden, die and are never replaced.

"We are left with a startling picture of the formation history of massive galaxies, where dramatic violence in the form of the torrent of radiation from matter falling into black holes leads to the death of galaxies they inhabit," said researcher Asa Bluck, an astrophysicist at the University of Nottingham in England.

"Black holes form inside their host galaxies and grow in proportion to them, forming an accretion disc which will eventually destroy the host," he added. "In this sense they can be described as viral in nature."

Still, "massive galaxies are in the minority in our visible universe," Bluck noted. "About one in a 1,000 galaxies is thought to be massive, but it may be much less."

Many other galaxies "would be too small to harbor really massive super-massive black holes, so would be unlikely to have really dramatic outpourings of radiation leading to the death of galaxies like we see in many very massive galaxies," Bluck told SPACE.com. "However, there is still likely to be some effect from this even in small systems."

When it comes to our own galaxy, "this is actually quite a big galaxy, but has an abnormally diminutive central black hole," Bluck noted. "Currently it is in a quiescent stage — not outputting much energy — but this could change in the future."

For instance, "we expect our own galaxy and Andromeda to merge in about 4 billion years or so," Bluck explained. "If this ends up providing new gas reserves and channeling this gas to the center of our galaxy — all big ifs — then there is a real chance of triggering our dormant black hole at some point in the distant future."

"But don't worry," he added, "our sun will have sputtered out by then anyway."