by Alexander Bolshakov, Applied Spectra
Fremont CA (SPX) Dec 18, 2012
On August 6th, 2012 the automatic rover "Curiosity" landed on Mars. One of the scientific instruments on board is ChemCam, which has a pulsed laser capable of ablating a focused spot on a remote sample to create a glowing plasma plume of target's material. Light from plasma is collected by rover's telescope on a mast, and the optical spectra are then analyzed by an internal spectrometer.
ChemCam can take thousands spectra per day from a distance of about 7 meters, thus making chemical analyses on the surface of Mars with unprecedented speed. ChemCam has become the most frequently used instrument on the rover because of simplicity of its stand-off operation.
The NASA Tech Briefs recently published a feature article about possible adaptation of the ChemCam for a new task of measuring isotopes. The new technology is named Laser Ablation Molecular Isotopic Spectrometry (LAMIS) that has been developed in the joint research efforts between Applied Spectra (funded by NASA SBIR program) and the Lawrence Berkeley National Laboratory.
LAMIS shares all the same technical benefits of its predecessor Laser Induced Breakdown Spectroscopy (LIBS), including rapid analysis and the elimination of sample preparation.
LIBS measures atomic emission spectra during the first microsecond after an ablation pulse. LAMIS measurement follows later when the plasma cools down.
Then molecules form in the plasma and the intensity of molecular spectra increases and persists in the afterglow. Molecular spectra are useful for isotopic analysis because the isotopic shifts in molecular emission are significantly larger than in atomic spectra.
The difference in isotopic masses has only a small effect on electronic transitions (as in atoms) but appreciably affects the vibrational and rotational energy levels in molecules.
There is no need for a large high-resolution spectrometer; a compact spectrometer can resolve isotopic spectra. LIBS and LAMIS techniques can be accomplished on the same instrument, thus extending ChemCam with a new dimension of isotopic analysis.
LAMIS achieves rapid and direct chemical and isotopic characterization without any acidic dissolution or deep evacuation of samples as required in typical mass spectrometry. Furthermore, rasterizing surface scans and depth profiling are easily realized with high spatial definition (~10 nm in depth and ~10 m lateral). The ability to measure isotope abundance with a low-resolution spectrometer is a significant attribute of LAMIS.
Isotopic analyses have proved to be powerful tool of science. Isotopes formed at the origin of the Universe and are produced in stars including catastrophic events of supernovae. Studies of the sources and driving mechanisms of isotopic variations can provide answers to fundamental questions on the development and evolution of stars and planets, and our Solar System.
Large fractionation in stable isotopes of H, C, N, O can be particularly indicative of a range of diverse processes in the biosphere, hydrosphere and lithosphere. Life processes lead to distinctive isotope patterns thereby providing clues to the origin of life and evolution in a galactic context. Isotopic information in paleoclimatology plays a critical role for the reconstruction of variations in past climate conditions.
Consequently, isotopic records hold keys to the prediction of future climate changes that may influence global temperature, energy needs, availability of drinking water, and food supplies.
"Overarching issues that could have a significant impact on... strategies for Mars include the absolute chronology of the planet" - this assertion was strongly emphasized in the National Research Council review Assessment of NASA's Mars Architecture 2007-2016. Radioisotopic age dating is the primary method in which accurate geochronological ages can be established. Measurements of the
isotopic ratios of 87Rb/86Sr and 87Sr/86Sr isotopes using LAMIS can provide the age at which rocks solidified by applying the well-known radiometric isochron dating method.
Presently, the dissolution and chromatographic separation of strontium from rubidium is necessary prior to conventional mass spectrometric analysis because of non-resolvable isobaric interference between the 87Sr and 87Rb. The results of LAMIS measurements of 86Sr, 87Sr and 88Sr isotopes were recently published, while optical spectra of 85Rb and 87Rb in laser ablation plasmas were obtained earlier.
Accordingly, a ChemCam-like device can potentially be used for age determination. Until now, there was no means by which to make direct age dating measurements on other planets (indirect age estimates for Mars have uncertainties in billions of years, validity of which is unknown).
Applied Spectra has developed a prototype LIBS instrument for standoff measurements at a distance of 30 meters, and also has participated in 50-meter standoff measurements using LIBS in the field. NASA's ChemCam can measure LIBS spectra from 7 meters away. Similar standoff distances should be possible for isotopic analysis using LAMIS.
Applied Spectra, Inc.
Lawrence Berkeley National Lab
Space Technology News - Applications and Research
Mars News and Information at MarsDaily.com
Lunar Dreams and more
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