'Star Trek'-like device for Mars mission

UA tool peeks inside rocks

Renee Sauer / Staff
The laser of the spectrometer Robert Downs, left, and M. Bonner Denton are building will divulge a rock's composition within seconds.

Renee Sauer / Staff The external cavity diode laser is part of the Mars-bound spectrometer being developed by two UA scientists.

'Star Trek" explorers who analyzed objects with a miraculous hand-held device had nothing on a pair of UA scientists designing their own version of a "tricorder" for a Mars mission.

Chemist M. Bonner Denton and geoscientist Robert Downs of the University of Arizona are principal investigators on a $1.5 million, NASA-funded project to develop a Raman spectrometer slated for a 2009 mission.

Back the rover up to the rock of your choice and the instrument will bounce a laser beam off it and seconds later tell you the rock's chemical composition, not unlike the instruments used in the "Star Trek" TV series.

"We're building a tricorder, that's pretty much what we're doing," Downs said. "And we've got the dream of someday making it into a hand-held instrument that could be used for a variety of applications."

Lots of different methods are used to figure out what a solid or liquid actually is, but most of them involve destroying the sample or placing it in certain containers, Denton said.

A Raman spectrometer can analyze most samples by merely pointing at them without preparing samples or modifying their form, he said.

The prototype Denton and Downs have been working on has already been used to test the legitimacy of diamonds in rings worn by people in the chemistry and geosciences departments. Two of the "diamonds" in the geosciences department turned out to be cubic zirconia, Downs said.

The Raman spectrometer could eventually be used by anyone who wants to test the legitimacy of a solid or liquid.

Gemologists buying gems, pharmacists who want to know the purity of a drug, and environmental workers who want to figure out what is in a 55-gallon drum are just a few of the people who could benefit from the technology, Denton said.

"We were working with the Environmental Protection Agency on this because they could take it into the field for rogue dumpsites," Denton said. "If someone dumps a bunch of barrels containing toxic waste in the desert, this is a device you could stick into those barrels to find out what's in them."

The spectrometer works by shooting a laser beam at an
object and collecting the different rays of light that bounce back. The vast majority of light gathered has a similar energy to that which the laser sent out, but about one out of a million photons, or particles of light, have a shifted frequency or color. These shifted photons act as a fingerprint for the object they're emitted from.

"It's almost like tapping a rock and listening to it ring," Denton said. "Each different mineral has a whole series of complicated bands that are unique, and that's how we identify it."

Downs' task in the process is to catalog the unique signatures of more than 4,000 minerals into a database. He does this by comparing Raman spectrometer signatures to another method called powder diffraction X-ray analysis.

"Bob happens to be a world expert in the field of powder diffraction, which today is the current gold standard for mineral identification," Denton said.

One of the biggest problems Downs has faced has been that many minerals he analyzed were initially misidentified, forcing him to run backup tests to figure out what they really are, he said.

Eventually, Downs' database will be worked onto a silicon chip for the Mars rover so that it can not only test a rock but also autonomously compare it to the list of known minerals. For the Mars mission that will save precious bandwidth, the amount of information that needs to be sent back and forth between the craft and mission control.

"The minerals you're really interested in are those that differ from that on Earth, so this instrument will be able to kind of cancel out all the minerals that aren't interesting," Downs said.

Bandwidth on space missions is rapidly consumed by sending things like high-resolution images and other data to mission control, and sending instructions to the rover, Denton said.

"That's why we felt a novel aspect of our program was to minimize that bandwidth," he said. "It'll only take it up when it finds something that doesn't compare to minerals on Earth, and that's information you definitely want to have."

In addition to bandwidth, other limiting factors on instruments include weight, volume and power consumption. Working a prototype instrument that takes up the surface of a dining table down to one smaller than a toaster will not be easy, but shouldn't require a leap of technology, Denton said.

Getting the spectrometer to meet those parameters will mean that the technology is not that far away from being worked into an instrument that could fit in your hand.

"Right now, it would cost about $130,000 to build one for somebody, but that's eventually going to come down," Denton said.

Sir C.V. Raman invented the Raman spectrometer and won the Nobel Prize for it in 1930. Denton's team has greatly increased the sensitivity of the technology, allowing the detection of samples as small as a few parts per million.

The Raman spectrometer aboard the 2009 rover would go a long way toward NASA's Mars mantra of "following the water" for evidence of past or present life on the red planet.

"Is there limestone on Mars, which would mean there were oceans?" Downs said. "And if there is still water, it could be stored in certain minerals called zeolites, so we could look for those."

* Contact reporter Thomas Stauffer at 573-4197 or at stauffer@azstarnet.com.

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