Sensitive Laser Instrument Could Aid Search for Life on Mars

Minuscule traces of cells can be detected in a mineral likely present on Mars, a new study shows. The results, obtained using a technique developed at the U.S. Department of Energy's Idaho National Laboratory (INL), could help mission scientists choose Martian surface samples with the most promise for yielding signs of life.

INL's instrument blasts off tiny bits of mineral and looks for chemical signatures of molecules commonly found in cells. While other methods require extensive sample handling, this analysis relies on a "point-and-shoot" laser technique that preserves more of the rock and reduces contamination risk. In the current online issue of the peer-reviewed Geomicrobiology Journal, the researchers report they could detect biomolecules at concentrations as low as 3 parts per trillion.

High sensitivity is crucial for NASA's search for life on Mars, says INL scientist Jill Scott, whose team collaborated with researchers at the University of Montana-Missoula on the study.

"The worst-case scenario is a false negative," Scott says. "If you're just missing stuff, that would be devastating."

While other techniques also have achieved parts-per-trillion sensitivity, they often require scientists to first extract the organic cell remnants from the mineral. This type of preparation can use up large amounts of sample and potentially introduce contamination.

INL's method is based on a technique called laser desorption mass spectroscopy. By focusing a laser beam on a spot less than one-hundredth the width of a pencil point, the researchers can knock microscopic fragments off the mineral. Those fragments react with organic molecules to form detectable charged particles called ions. The team can then study the ion patterns for signatures that might be specific to biomolecules.

Typically, this method would require the organic molecules to be embedded in a synthetic matrix that encourages ion formation. But the INL team simply relies on the rock to act as the matrix, eliminating the need for sample preparation.

"We thought, what can the rock do for you?" Scott says. "You don't want to damage the sample more than you have to. You'd like to just shoot it directly."

With funding from NASA's Astrobiology program, the researchers have done previous studies showing that minerals like halite and jarosite yield distinct ion patterns when organic molecules are present. This time, they tried thenardite, a compound thought to be part of the Martian surface. Because thenardite is left behind when lakes dry up, its presence could signify the past existence of water -- and hence life.

The team tested thenardite samples taken from the evaporated Searles Lake bed in California. They also created artificial thenardite samples that contained traces of stearic acid, which is left behind by dead cells, and glycine, the simplest amino acid used by organisms on Earth. In all cases, the researchers found a distinct ion pattern that did not appear for thenardite alone, suggesting they had detected a signature for the biomolecules.

The team also measured the sensitivity of its instrument for the first time. By testing more and more dilute artificial samples, they found they could detect the stearic acid signature at levels as low as 3 parts per trillion. In fact, the signatures became even more distinct as concentration dropped, presumably because more ion-producing matrix surrounded each biomolecule.

While the instrument is too big to send into space, it could potentially be used for analysis if NASA brings Martian samples back to Earth.

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Human Preference for Other Species Could Determine Whether They Survive

As humans exert ever-greater influence on the Earth, their preferences will play a substantial role in determining which other species survive. New research shows that, in some cases, those preferences could be governed by factors as subtle as small color highlights a creature displays.
In the case of penguins, mostly black-and-white flightless birds that live predominantly in the Southern Hemisphere, those most popular with humans appear to be the ones that display markings of warm colors such as red, orange or intense yellow, said David Stokes, a conservation biologist at the University of Washington, Bothell.

He and his undergraduate students calculated the popularity of various species by studying photographs in four large-format photograph books about penguins. Decisions about how many and which photographs to use and how large to make them presumably were made by the books' editors based on their own preferences or on their beliefs of what would appeal to the book-buying public.

"Penguins are lucky because they are popular with people, especially right now. But that's not true of 99.9 percent of the species out there," Stokes says. "Even the penguin species I found to be among the least appealing to people are tourist attractions."

Tops on the list are the Emperors, featured in the film March of the Penguins, and their close cousins the King penguins. Second are crested penguins, including Rockhoppers and Macaroni.
Species at the bottom of the list are Adelie, Yellow-eyed and Little Blue. Stokes was surprised by the relative lack of popularity of Adelie penguins because that species is probably the most familiar to the public.

There are 17 penguin species, and in the past some were hunted for food or boiled to extract their oil. Some species now struggle to survive climate change, changing food patterns and encounters with humans or human activity, such as oil drilling at sea.

The species are fairly similar, with some larger and some smaller, Stokes says. But the ones that appear to be most popular are the ones that display the warmest colors in the upper body, the neck and head. He likened the effect to that of a man in a tuxedo pinning on a red carnation.

No 'cuteness factor'

Unlike some other types of animals, human preference for particular penguin species does not seem to be driven by a "cuteness" factor.

The four books Stokes examined were published in the last decade and were aimed at the popular adult audience. He eliminated photographs from consideration when factors other than the penguins themselves -– the surrounding landscape, for example, or accompanying humans – could have played a role in their selection. He was left with 304 pictures that clearly showed specific penguin species, and he concluded that a species' popularity wasn't because it was easy to get to, or because it had the largest population, or because of similar factors.

"I went to great lengths to ensure that what I was looking at was a purposeful set of pictures and not one just based on logistics," he says. The popularity rankings were similar across all four books, he added, which suggests that human preferences could be widely shared.

The work has been published in the online edition of the journal Human Ecology, and will appear in an upcoming print edition.

Color is not the only factor that determines a species' attractiveness to humans. Characteristics such as size and neoteny – the retention of babyish physical traits such as large eyes and large head – also can play major roles for some animals. Pandas, zebras and elephants, for example, are black and white or gray but are highly preferred by humans. Millions of insects and the countless slimy invertebrates that occupy the oceans are likely not as lucky, Stokes says.

"The work pretty conclusively shows there is a large difference of appeal among organisms, even among closely related organisms," he says. "For different kinds of organisms, different qualities seem to cause differences of appeal."

The work is a signal to conservationists to be mindful of the role of public popularity, and what might cause it, when making decisions about how to deal with various species, even invasive species.

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