Washington, Oct 16 : A sensitive laser instrument 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.
The researchers reported that they could detect biomolecules at concentrations as low as 3 parts per trillion.
According to INL scientist Jill Scott, high sensitivity is crucial for NASA's search for life on Mars. "The worst-case scenario is a false negative," he said. "If you're just missing stuff, that would be devastating," he added.
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.
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 INL study also could help determine which samples should be collected, based on how likely they are to show signs of life.
According to Nancy Hinman, a geochemist at the University of Montana-Missoula, "The wider the variety of minerals we test, the larger the suite we can target on Mars."