The next decade is expected to bring real wealth to planetary science: space missions are set to bring rock samples from the Moon, Mars, Phobos and a primordial asteroid. Scientists say a new technique for determining the age of rocks, meteorites and even artifacts, could help open 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 nicknamed “Black Beauty” and was able to quickly and accurately date it by examining it with a small laser. Beam – A significant improvement over previous techniques, which included more work and destruction of parts of the sample. Their research has been published in Analytical Atomic Spectrum Journal.
“We are very excited about this demonstration study, as we believe we will be able to use the same approach to date rocks that will be returned by multiple space missions in the future,” said Nicholas Duvas, professor of geophysical sciences at Louis Block. at the University of Chicago and first author on a study explaining the findings. “The next decade will be amazing in terms of planetary exploration.”
rock of ages
Scientists use isotopes to estimate the ages of samples for more than a century. This method takes advantage of the fact that certain types of elements are unstable and will slowly transform into other types at a slow, predictable rate. In this case, scientists take advantage of the fact that rubidium-87 will turn into strontium-87 – so the older the rock, the more strontium-87 increases.
Rubidium dating can be used to determine the ages of rocks and objects that are billions of years old; It is widely used to understand how the Moon, Earth and the solar system formed, to understand the plumbing system of magma under volcanoes, and to trace human migration and trade in archaeology.
Previously, however, this method of making this measurement would have taken weeks – and would damage part of the sample.
To do those tests the traditional way, “you take your piece of rock, break it down with a hammer, melt the minerals with chemicals and use a super-clean lab to process it, and then you take it to a mass spectrometer for its “isotope” measurements,” explained study co-author Maria Valdez, a post-researcher. Ph.D. is in the Robert A. Pritzker Center for Meteorology and Polar Studies at the Field Museum of Natural History.
But Thermo Fisher Scientific developed a new machine that promised to dramatically reduce the time, toxicity and amount of sample destroyed in the process. It uses a laser to vaporize a small portion of the sample – the hole created the size of a human hair – and then analyzes the rubidium and strontium atoms with a mass spectrometer that uses new technological advances to cleanly measure strontium isotopes.
Dauphas, Valdes, and several other collaborators wanted to test the new technology—and they had a perfect candidate: a piece of meteorite that had landed on Earth from Mars.
This black beauty meteorite is nicknamed for its brilliant dark color. It is speckled with lighter fragments representing older rocks embedded in the rock.
However, these fragments were wrapped into another rock later during the history of Mars. It’s a bit like when you bake cookies, Valdes explained. Chocolate chips and nuts have been made at different times and places, but all the ingredients come together when the cookie is baked.
Scientists want to know the ages of all of these steps along the way, because the composition of each group tells them what conditions were like on Mars at the time, including the composition of the atmosphere and volcanic activity at the surface. They can use this information to compile a timeline of Mars.
However, so far, parts of the story have been disputed. Different studies have given different answers about the era when all the ingredients of Black Beauty came together and formed one rock – so scientists thought a meteorite would be an ideal candidate to test the capabilities of the new technology. They took a sample of Black Beauty to Germany to try it out.
In a matter of hours instead of weeks, the tool brought back its answer: 2.2 billion years. The team believes this marks the time they were united into their final form.
Furthermore, to perform the test, the scientists were able to put the entire piece of the meteorite into the device and then precisely locate a small site for age testing. “This was a particularly good tool for resolving this disagreement,” Duvas said. “When you cut a piece of rock to test the old method, it is possible that other fragments have mixed in, which could affect your results. We don’t have that problem with the new device.”
This technology could be very useful in many areas, but Duvas and Valdez are particularly interested in it for understanding everything from the history of water on Mars to how the solar system itself formed.
In the next decade, scientists expect an abundance of new samples from places other than Earth. The United States and China are planning new missions to the Moon. Missions to intercept an asteroid called Bennu will land in 2023 with loads of dust swept from its surface; Another mission will return samples from Mars’ moon Phobos in 2027; By the early 1930s, NASA hopes to return the samples the now persistent rover collects to the surface of Mars.
With all these samples, scientists expect to learn more about the planets and asteroids around us.
“That’s a lot of progress,” Duvas said. “There are many precious meteorites and artifacts that you don’t want to destroy. This allows you to significantly reduce the impact they have during your analysis.”
Mars rock turns back the clock
Nicolas Dauphas et al., In situ 87Rb-87Sr analyzes of ground and off-site samples by LA-MC-ICP-MS/MS with dual Wien filter and impingement cell techniques, Analytical Atomic Spectrum Journal (2022). DOI: 10.1039 / D2JA00135G
Presented by the University of Chicago
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