Nitrogen-fixing aliens

Scientists hope that Titan, a moon of Saturn, with its nitrogen-rich atmosphere, could act as a model system for terrestrial chemistry before life began on our planet. Now, another step towards that goal has emerged as researchers at the University of Arizona have incorporated atmospheric nitrogen into organic macromolecules under conditions resembling those on Titan.

“Titan is so interesting because its nitrogen-dominated atmosphere and organic chemistry might give us a clue to the origin of life on our Earth,” explains Hiroshi Imanaka, who is an assistant research scientist in the UA’s Lunar and Planetary Laboratory. “Nitrogen is an essential element of life.” Titan looks orange through a telescope because its atmosphere is a rich smog of organic molecules. Particles in the smog could settle on the surface and be exposed to conditions that might eventually create life, said Imanaka.

Saturn's A and F rings, the small moon Epimetheus and the smog-enshrouded Titan, Saturn’s largest moon. (Credit: NASA/JPL/Space Science Institute)
Saturn's A and F rings, the small moon Epimetheus and the smog-enshrouded Titan, Saturn’s largest moon. (Credit: NASA/JPL/Space Science Institute)

Of course, nitrogen alone is not enough, nitrogen molecules must be converted to a chemically active form that can drive the necessary biochemical reactions that underpin biological systems.

Imanaka and Mark Smith converted a nitrogen-methane gas mixture similar to Titan’s atmosphere into a collection of nitrogen-containing organic molecules by irradiating the gas with high-energy ultraviolet light. The laboratory set-up was designed to mimic how solar radiation affects Titan’s atmosphere.

Most of the nitrogen simply formed solid compounds directly, rather than gaseous ones, explains Smith, whereas previous theories suggested that nitrogen would move from gaseous compounds to solid ones in stepwise process. But, those settling particles may not contain nitrogen at all. If some of the particles are the same nitrogen-containing organic molecules created by the UA team in the laboratory then it would suggest that conditions conducive to life might just exist on Titan, Smith says.

These and other laboratory observations help scientists planning future space missions to decide on what to look for on other worlds that might hint at life and what instruments should be developed to help in the search.

Links

Proc Natl Acad Sci, 2010, online
Mark A. Smith homepage
UA lunar and planetary laboratory

Moon river?

The media was recently drenched with the idea that water had been found on the Moon, offering speculation as to our nearest neighbour offering an oasis-like site for a lunar base from which we could launch missions to Mars and beyond. The truth, if it is ever confirmed, is a little more subtle.

Is moisture on the Moon, simply wishing on a star? (Photo by David Bradley)
Is moisture on the Moon, simply wishing on a star? (Photo by David Bradley)

The Apollo missions of the 1970s had always hinted at the presence of water on the Moon, although its presence in samples brought back to earth was thought to be nothing more than contamination. In 1998, scientists announced that the Lunar Prospector spacecraft had detected 300 million tonnes of water on the moon and hinted that there may be as much as 6 billion tonnes. In July, an analysis of tiny beads of volcanic glass collected by two Apollo missions revealed water trapped inside, suggesting that the Moon’s water had not been entirely vaporized by the violent events that led to its formation. The discovery had implications for the volcanic origin of possible water reservoirs at the Moon’s poles.

However, new evidence released at the end of September based on data from India’s Chandrayaan-1 probe and the Deep Impact and Cassini missions suggests that there may well be some degree of hydration up there. Researchers in India and the US used data from NASA’s Moon Mineralogy Mapper, the M3, aboard the Chandrayyan-1 satellite, which was launched into orbit around the moon in October 2008 to reveal the presence of water on the moon. Chandrayaan’s mission ceased in August 2009.

M3 uses reflectance spectrometry to determine the content of minerals in the thin layer of upper soil on the surface of the moon. The data revealed the presence of chemical bonds between hydrogen and oxygen atoms, like those found between the oxygen atom and its attendant hydrogen atoms in H2O.

However, the next generation of lunar astronauts are not likely to sip from moon springs or splash their silvery boots in lunar puddles because revelations of chemical bonds between hydrogen and oxygen atoms is indicative of water molecules but is even more indicative of hydroxyl ions (OH). It could be that good, old-fashioned H2O forms only when the solar wind doth blow and brings with it hydrogen atoms that can combine with the hydroxyl radicals forming “H+OH” (H2O). It may be that less than a litre of actual water is present per tonne of rock spread across the surface to a depth of a few centimetres and present as water of hydration of the minerals from which the rock is composed.

The rocks and soils that comprise the lunar surface contain about 45 percent oxygen, mostly in the form of silicate minerals. The constant deluge of hydrogen atoms from the solar wind could readily pull oxygen and hydroxyl from the soil and form water molecules on the fly, especially given the hydrogen ions are moving at one third the speed of light when they hit.

Taylor and other M3 team members believe their findings will be of particular significance as mankind continues to plan for a return to the moon. The maps created by M3 could provide mission planners with locations prime for extraction of needed water from the lunar soil.

Following the lunar announcement, Jim Bell, President of The Planetary Society, said: “The possible presence of minor amounts of hydrated material on the Moon is intriguing, though the findings still need to be confirmed by other methods and other investigators. Chandrayaan is another great example of the power and value of international collaboration in space exploration, and The Planetary Society congratulates the entire Chandrayaan, Deep Impact and Cassini teams.”

Researchers still hope to find liquid water at the bottom of the deepest, darkest lunar craters at depths that never see sunlight nor feel the solar wind. Such, hopefully, icy depths are akin to the cold places on the planet Mars where evidence of water ice has been found.

LINKS
Science, 2009, in press
Chandrayaan-1 site

Double rubble

Our Solar System contains a vast belt of rocky asteroids sitting in an orbit roughly between the planets Mars and Jupiter, but astronomers have found a reason for us to be envious of other star systems. They have discovered that a single belt is not the only possible arrangement of the primordial debris that remains following planet formation around a star.

Dana Backman of the SETI Institute and colleagues have found that the nearby star Epsilon Eridani has two rocky asteroid belts and an outer icy ring, making it a triple-ring system. The inner asteroid belt is a virtual twin of the belt in our solar system, while the outer asteroid belt is much more massive, holding twenty times as much material. The astronomers explain that the existence of these three rings of material suggests that undiscovered planets in the Epsilon Eridani system confine and shape the rings.

Massimo Marengo

Massimo Marengo

Epsilon Eridani is a smaller, younger, cooler star than the Sun, nestling in the southern constellation of Eridanus, the river, about 10.5 light-years from Earth. It is a mere 850 million years old and astronomers consider the Epsilon Eridani planetary system to have some remarkable similarities with our solar system at a comparable age. Studying Epsilon Eridani is like having a time machine to look at our solar system when it was young, according to team member Massimo Marengo of the Harvard-Smithsonian Center for Astrophysics. Backman agree pointing out that, This system probably looks a lot like ours did when life first took root on Earth.

Using NASA’s Spitzer Space Telescope, the team identified an asteroid belt orbiting Epsilon Eridani at an equivalent distance as our own asteroid belt – 3 astronomical units. However, they also spotted a second asteroid belt at 20 astronomical units from Epsilon Eridani, the approximate distance Uranus is located in our solar system. The total mass of this second asteroid belt is about the same as Earth’s Moon.

Dr Dana Backman

Dr Dana Backman

The third, ring of icy material sits at about 35 to 100 astronomical units from Epsilon Eridani and is the equivalent of the Kuiper Belt in our solar system, but this previously discovered third ring has a mass one hundred times that of the Kuiper Belt.

Some star systems are more equal than others (Credit: NASA/JPL-Caltech)

Some star systems are more equal than others (Credit: NASA/JPL-Caltech)

Theorists have suggested that when our Sun was 850 million years old, the Kuiper Belt would have resembled more that seen in Epsilon Eridani, but in the intervening billions of years, much of its material has been swept away, hurled out of the solar system, or plunged into the inner planetary region in the Late Heavy Bombardment. The enormous craters on our Moon are evidence of this bombardment.

Running rings around a star system (Credit: NASA/JPL-Caltech)

Running rings around a star system (Credit: NASA/JPL-Caltech)

It is possible that Epsilon Eridani will undergo a similar dramatic clearing in the future, the astronomers say. Epsilon Eridani looks a lot like the young solar system, so it’s conceivable that it will evolve similarly, said Marengo. The team points out that the pattern of rings and their total masses suggest that three giant planets with masses between those of Neptune and Jupiter are also orbiting Epsilon Eridani. Further observations will soon reveal more about the character of our distant stellar cousin.

D. Backman, M. Marengo, K. Stapelfeldt, K. Su, D. Wilner, C. D. Dowell, D. Watson, J. Stansberry, G. Rieke, T. Megeath, G. Fazio, M. Werner (2009). Epsilon Eridani’s Planetary Debris Disk: Structure and Dynamics based on Spitzer and CSO Observations Astrophysical Journal

Further reading

Dr Dana Backman homepage
http://www.seti.org/Page.aspx?pid=390

Massimo Marengo homepage
http://www.cfa.harvard.edu/~mmarengo/me/home.html

Suggested searches

asteroids
Kuiper belt