Scientists demonstrate speed, precision of planetary dating device in situ

Scientists at the Southwest Research Institute have increased the speed and precision of a laboratory-scale instrument to determine the age of planetary samples at the site. The team is progressively miniaturizing the Chemical, Organic and Dating Experiment (CODEX) instrument to reach a size suitable for space flight and landing missions.

“Aging in situ is an important scientific objective identified by the Decadal Study of the National Research Council for Mars and the Moon, as well as by the Analysis Groups of the Lunar and Mars Exploration Program, entities responsible for providing the necessary scientific contributions to plan and prioritize exploration activities. ” said SwRI staff scientist Dr. F. Scott Anderson, who is leading the development of CODEX. “Doing this on-site rather than trying to return samples to Earth for evaluation can solve the major dilemmas of planetary science, offers tremendous cost savings, and increases opportunities for eventual sample returns.”

CODEX will be slightly larger than a microwave and will include seven lasers and a mass spectrometer. On-site measurements will address fundamental questions in the history of the solar system, such as when Mars was potentially habitable. CODEX is accurate to ± 20-80 million years, significantly more accurate than the dating methods currently in use on Mars, which are accurate to ± 350 million years.

“CODEX uses an ablation laser to vaporize a series of small fragments of rock samples, such as those from the surface of the Moon or Mars,” said Anderson, who is the lead author of a CODEX article published in 2020. “We acknowledge some elements directly from that vapor plume, so we know what a rock is made of. Then the other CODEX lasers select and quantify the abundance of traces of radioactive rubidium (Rb) and strontium (Sr). A decomposition isotope Rb in Sr for known amounts of time, so by measuring both Rb and Sr we can determine how long it has been since the rock was formed. “

Although radioactivity is a standard technique for dating samples on Earth, few other places in the solar system have been dated in this way. Instead, scientists have greatly limited 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 team led by SwRI. “It’s kind of like saying that a person gets wet the longer they’ve been in the rain. It’s undoubtedly true. But just as with the falling rain, we really don’t know the rate at which meteorites have fallen from the sky.” This is why radioisotope dating is so important. Radioactive decay is a clock that runs 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 responsive than its previous incarnation. This precision was largely achieved by modifying the sample distance from the instrument to improve data quality. The instrument also includes an ultra-fast pulsed laser and better signal-to-noise ratios to better restrict the timing of events in the history of the solar system.

“We are miniaturizing CODEX components for use in the field on a landing mission to the Moon or Mars,” said Anderson. “Developing compact lasers with pulse energies comparable to what we currently require is a considerable challenge, although five of the seven have been successfully miniaturized. These lasers have a repetition rate of 10 kHz, which will allow the instrument to acquire 500 data times faster than today’s engineering design. “

The CODEX mass spectrometer, power supplies, and timing electronics are already small enough for space flight. Instrument components are being upgraded to improve robustness, thermal stability, radiation resistance, and energy efficiency to withstand launch and extended autonomous operations in strange environments.

Going to various 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 Advancement of Solar System Observations (PICASSO) programs and Instrument Maturation for Solar System Exploration (MatISSE) programs are funding the development of the instrument, with prior support for CODEX / CDEX of the Planetary Instruments Definition and Development Program (PIDDP)

The article entitled “Dating of a Martian meteorite with 20 Ma precision using a prototype in situ dating instrument” was published in Planetary and space science on June 15, 2020.