SwRI scientists demonstrate speed, precision of in situ planetary dating device

Southwest Research Institute scientists have increased the speed and accuracy of a laboratory-scale instrument for determining the age of planetary specimens onsite. The team is progressively miniaturizing the Chemistry, Organics and Dating Experiment (CODEX) instrument to reach a size suitable for spaceflight and lander missions. "In situ aging is an important scientific goal identified by the National Research Council's Decadal Survey for Mars and the Moon as well as the Lunar and Mars Exploration Program Analysis Groups, entities responsible for providing the science input needed to plan and prioritize exploration activities," said SwRI Staff Scientist Dr. F. Scott Anderson, who is leading CODEX development. "Doing this onsite rather than trying to return samples back to Earth for evaluation can resolve major dilemmas in planetary science, offers tremendous cost savings and enhances the opportunities for eventual sample return." CODEX will be a little larger than a microwave and include seven lasers and a mass spectrometer. In situ measurements will address fundamental questions of solar system history, such as when Mars was potentially habitable. CODEX has a precision of ) +/-20-80 million years, significantly more accurate than dating methods currently in use on Mars, which have a precision of +/-350 million years. "CODEX uses an ablation laser to vaporize a series of tiny bits off of rock samples, such as those on the surface of the Moon or Mars," said Anderson, who is the lead author of a CODEX paper published in 2020.

"We recognize some elements directly from that vapor plume, so we know what a rock is made of. Then the other CODEX lasers selectively pick out and quantify the abundance of trace amounts of radioactive rubidium (Rb) and strontium (Sr). An isotope of Rb decays into Sr over known amounts of time, so by measuring both Rb and Sr, we can determine how much time has passed since the rock formed."

While radioactivity is a standard technique for dating samples on Earth, few other places in the solar system have been dated this way. Instead, scientists have largely constrained the chronology of the inner solar system by counting impact craters on planetary surfaces.

"The idea behind crater dating is simple; the more craters, the older the surface," says Dr. Jonathan Levine, a physicist at Colgate University, who is part of the SwRI-led team.

"It's a little like saying that a person gets wetter the longer they have been standing out in the rain. It's undoubtedly true. But as with the falling rain, we don't really know the rate at which meteorites have fallen from the sky. That's why radioisotope dating is so important. Radioactive decay is a clock that ticks at a known rate. These techniques accurately determine the ages of rocks and minerals, allowing scientists to date events such as crystallization, metamorphism and impacts."

The latest iteration of CODEX is five times more sensitive than its previous incarnation. This precision was largely accomplished by modifying the sample's distance from the instrument to improve the data quality. The instrument also includes an ultrafast pulsed laser and improved signal-to-noise ratios to better constrain the timing of events in solar system history.

"We are miniaturizing the CODEX components for field use on a lander mission to the Moon or Mars," Anderson said.

"Developing compact lasers with pulse energies comparable with what we currently require is a considerable challenge, though five out of the seven have been successfully miniaturized. These lasers have a repetition rate of 10 kHz, which will allow the instrument to acquire data 500 times faster than the current engineering design."

The CODEX mass spectrometer, power supplies and timing electronics are already small enough for spaceflight. Instrument components are being enhanced to improve ruggedness, thermal stability, radiation resistance and power efficiency to endure launch and extended autonomous operations in alien environments.

Targeting several future missions, SwRI is developing two versions of the instrument, CODEX, which is designed for Mars and can measure organics, and CDEX, which is designed for the Moon, and does not need to measure organics.

NASA's Planetary Instrument Concepts for the Advancement of Solar System Observations (PICASSO) and the Maturation of Instruments for Solar System Exploration (MatISSE) programs are funding the instrument development, with previous support for CODEX/CDEX from the Planetary Instrument Definition and Development Program (PIDDP).

NASA awards $3M to develop Lunar LASVEGAS

NASA has awarded Southwest Research Institute $3 million to develop a lunar version of its Laser Absorption Spectrometer for Volatiles and Evolved Gas (LASVEGAS) instrument. This spectrometer can precisely measure the volatile compounds present in planetary atmospheres and surfaces - critical information for space science and exploration. "LASVEGAS is about half the size of a paper towel roll. It's extremely compact, low mass, low volume and low power - all important characteristics for spaceflight," said SwRI's Dr. Scot Rafkin, principal investigator of the instrument. "It can be deployed on the smallest of rovers or landers as well as carried in a single hand by an astronaut sauntering across the lunar surface in search of water ice, methane and other useful resources." The instrument measures gases from planetary atmospheres such as Mars to understand their composition. It can also heat a sample of a planetary surface such as the icy surface of Jupiter's moon Europa or from lunar soil to determine the composition of released gases. NASA's Maturation of Instruments for Solar System Exploration (MatISSE) program provided $3M in 2019 to develop the LASVEGAS instrument for application to Europa and similar icy worlds. In 2020, SwRI received an additional $3 million from the agency's Development and Advancement of Lunar Instrumentation (DALI) program to adapt the design to operate on the Moon's surface. "Spectrometry is one of the key analytical tools used in space exploration," Rafkin said. "LASVEGAS heats a thimble-sized sample from a planetary surface to release water and other volatile gases like methane."

The gas flows into a small, cylindrical chamber where laser light of different wavelengths is bounced back and forth between mirrors on each end. As the light passes repeatedly through the gas in the sample, the different molecular species in the gas absorb the light differently depending on the wavelength.

Then the laser light is directed onto a detector that measures its intensity to determine the abundance of the volatile compounds. Each molecular species in the gas has a distinct "fingerprint" of absorption, revealing its overall abundance.

"The instrument is yet to be selected for flight on a mission, but the work funded under the MatISSE and DALI programs will allow the instrument to be credibly proposed for a variety of future opportunities, especially those related to the return of humans to the surface of the Moon," Rafkin said.

The LASVEGAS development team also includes Ball Aerospace, Southwest Sciences Inc. and Princeton University.

SwRI scientists study Saturn's rings to discover downpour

Using some of the Cassini spacecraft's final measurements, Southwest Research Institute scientists have discovered that complex organics rain down from Saturn's rings into its upper atmosphere. Cassini's final orbits allowed instruments to sample particles in the ring environment, discovering that the inflow of water and other material is much heavier than expected. "For its final adventure, Cassini dove into the unknown region between Saturn's rings and its atmosphere," said SwRI's Dr. Kelly Miller, who coauthored the paper "Chemical interactions between Saturn's atmosphere and its rings" published Oct. 4 in the journal Science. "Based on previous work, scientists expected water was raining from the rings into Saturn's atmosphere, so the spacecraft used its radio antenna as an umbrella to protect it from debris." After almost 20 years in space and 13 years in the Saturn system, the Cassini spacecraft was running out of fuel. NASA decided to use its last orbits to skim the upper atmosphere and skirt the edge of the inner rings before taking its final destructive dive into the planet's atmosphere in September 2017. Those final 22 orbits allowed instruments to measure the composition of Saturn's upper atmosphere and its chemical interactions with material originating in the rings.

"Turns out, ring rain is more like a ring downpour," said SwRI's Dr. Hunter Waite, the paper's lead author and principal investigator of Cassini's Ion and Neutral Mass Spectrometer (INMS). "While INMS was designed to investigate gases, we were able to measure the ring particles because they hit the spacecraft at such high velocities they vaporized. Water ice, along with the newly discovered organic compounds, is falling out of the rings way faster than anyone thought - as much as 10,000 kilograms of material per second."

"Molecular hydrogen was, as expected, the most abundant atmospheric constituent," Miller said. "But the downpour coming from the rings included plenty of water as well as molecules like butane and propane - the kind of chemicals you might use for a grill or camping stove."

The high speed of the Cassini spacecraft relative to Saturn's atmosphere allowed INMS to measure the ring particles, but it also complicated the interpretation of the data. Molecules and particles would likely shatter upon impact with the detector so the various organic compounds detected by INMS are likely fragments. The observations also show evidence for variations from one spacecraft orbit to the next in the relative abundances of infalling material, suggesting that regions in Saturn's innermost D ring are materially variable, either over time or by locality.

"While INMS was one of the last instruments collecting data to the mission's end, getting these results was not easy," said SwRI's Rebecca Perryman, INMS operations lead and the paper's second author. The team spent months processing, examining and reexamining the data.

"It was worth it. The large mass of infalling material has implications for ring evolution, hinting that material from the C ring repeatedly replenishes the neighboring D ring," Waite said. "This infalling material likely affects the atmospheric chemistry and the carbon content of Saturn's ionosphere and atmosphere."