The coming decade should bring a real boon for planetary science: space missions are planned to bring back rock samples from the moon, Mars, the Martian moon of Phobos and an early asteroid. And scientists say there is a new technique for determining the age of rocks, meteorites and even artifacts that could help usher in a new era of discovery.
A group with the University of Chicago and the Field Museum of Natural History tested an instrument made by Thermo Fisher Scientific on a piece of a Martian meteorite dubbed “Black Beauty” and were able to quickly and accurately date it by probing it with a tiny beam laser – a significant improvement over earlier techniques, which involved much more work and destroyed parts of the sample.
“We are very excited about this demonstration study, as we believe we can use the same approach to date rocks that will be returned from multiple space missions in the future,” said Nicolas Dauphas, Louis Block Professor of Geophysical Sciences. at the University of Chicago and first author of a study presenting the results. “The next decade is going to be breathtaking in terms of planetary exploration.”
rock of ages
Scientists have been using isotopes to estimate the age of specimens for over a century. This method takes advantage of the fact that some element types are unstable and will slowly transform into other types at a slow, predictable rate. In this case, scientists are exploiting the fact that rubidium-87 will turn into strontium-87. Thus, the older the rock, the more strontium-87 it will contain.
Rubidium dating can be used to determine the age of rocks and objects that are billions of years old. it is widely used to understand how the moon, Earth, and solar system formed, to understand the magmatic plumbing system beneath volcanoes, and to trace human migration and archaeological trades.
Previously, however, the way to do this measurement took weeks and destroyed part of the sample.
To perform these tests with the conventional method, “you take your piece of rock, smash it with a hammer, dissolve the minerals with chemicals and use a special ultra-clean laboratory to process them, then take it to a spectrometer to measure isotopes,” explained study co-author Maria Valdes, a postdoctoral fellow at the Robert A. Pritzker Center for Meteoritics and Polar Studies at the Field Museum of Natural History.
But Thermo Fisher Scientific developed a new machine that promised to drastically reduce the time, toxicity and amount of samples destroyed in the process. It uses a laser to vaporize a tiny portion of the sample – the hole created is the size of a single human hair – then analyzes the rubidium and strontium atoms with a mass spectrometer that uses new technological advances to measure strictly the isotopes of strontium.
Dauphas, Valdes and several other collaborators wanted to test the new technique – and they had a perfect candidate: a piece of meteorite that landed on Earth from Mars.
This particular meteorite is nicknamed “Black Beauty” for its gorgeous dark color. It is dotted with lighter fragments that represent even older rocks embedded in rock.
However, these fragments were encased in another rock at some point much later in Mars’ history. It’s kind of like when you bake cookies, Valdes explained; chocolate chips and nuts were made at different times and places, but all the components come together when you bake the cookie.
Scientists want to know the age of everything of these stages along the way, as the composition of each set tells them what conditions on Mars were like at the time, including the composition of the atmosphere and volcanic activity on the surface. They can use this information to piece together a timeline of Mars.
However, so far parts of the story have been disputed; different studies had given different answers for when all the components of Black Beauty came together and formed a single rock – so scientists believed the meteorite would be a perfect candidate to test the new technique’s abilities. They took a sample of Black Beauty to Germany to try.
In a few hours rather than a few weeks, the instrument returned its answer: 2.2 billion years. The team believes this represents the moment he fused into his final form.
Additionally, to perform the test, the scientists were able to place the entire piece of meteorite into the machine and then precisely select a tiny site to test for age. “It was a particularly effective tool in resolving this controversy,” Dauphas said. “When you cut a piece of rock to test the old way, it is possible for other fragments to get mixed in, which can affect your results. We don’t have that problem with the new machine.
The technique could be extremely useful in many areas, but Dauphas and Valdes are particularly interested in understanding everything from the history of water on the surface of Mars to the formation of the solar system itself.
Over the next decade, scientists expect a bonanza of new samples from places other than Earth. The United States and China are planning new missions to the Moon; a mission to intercept an asteroid called Bennu will land in 2023 with earth payloads extracted from its surface; another mission will bring back samples from Mars’ moon Phobos in 2027; and by the early 2030s, NASA hopes to bring back samples that the Perseverance rover is currently collecting on Mars.
With all these samples, scientists expect to know a lot more about the planets and asteroids around us.
“It’s a huge step forward,” Dauphas said. “There are many precious meteorites and artifacts that you don’t want to destroy. This allows you to significantly minimize the impact you have during your analysis.
The meteorite was provided by the Robert A. Pritzker Center for Meteoritics and Polar Studies at the Field Museum of Natural History. Timo Hopp, Zhe Zhang, Phillip Heck, Bruce LA Charlier and Andrew Davis are among other scientists affiliated with UChicago. Other study co-authors included those from Thermo Fisher Scientific, Victoria University of Wellington in New Zealand, University of California, Los Angeles, and Washington University in St. Louis.
Quote : “In situ 87Rb–87Sr analyzes of terrestrial and extraterrestrial samples by LA-MC-ICP-MS/MS with double Wien filter and collision cell technologies.” Dauphas et al, Journal of Analytical Atomic Spectrometry, October 10, 2022.
Funding: NASA, National Science Foundation, US Department of Energy.
#technique #determining #age #usher #era #planetary #science #researchers