Scientists have discovered a new history of Mars, written in the elusive element krypton, inside a unique Martian meteorite that crashed in France more than 200 years ago, reports a new study.
The results shed light on the origin of many important ingredients for life—such as hydrogen, carbon, oxygen, and nitrogen—on planets like Mars and Earth. Understanding how these “volatile” elements were seeded into rocky worlds can help unravel the mystery of how life emerged on Earth, and if it might exist elsewhere in the universe.
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Volatile elements, so named because they are easily vaporized, are present in the nebulas from which star systems are born. Most models suggest that gasses from these nebulas deliver an initial dose of volatiles to embryonic planets. Later, the thinking goes, primitive asteroids supply more volatiles by crashing into planets while they are still molten, a process that enriches the young worlds with distinctive meteorites known as chondrites.
Now, a pair of researchers have upended the conventional view of how Mars evolved with precise observations that “contradict the common hypothesis that, during planet formation, chondritic volatile delivery occurred after solar gas acquisition,” according to a study published on Thursday in Nature.
Led by Sadrine Péron, a postdoctoral scholar at ETH Zürich in Switzerland, the new research is built on unprecedented measurements of krypton, an inert noble gas, inside the Chassigny meteorite, an extremely unusual rock that represents the interior of Mars, opening a rare window into the initial stages of planetary formation in the solar system.
“We know that Mars formed very quickly,” said Péron in a call, noting that the planet took just four million years to form. “When we study Mars’ interior composition, we can have an idea of what processes form the terrestrial planets very early on during the solar system’s formation. We can’t have this kind of information for the Earth, because the Earth took much longer, between 50 to 100 million years, to form and so Mars’ composition really is an insight into what was happening in the solar system very early on.”
To extract the secrets of this ancient history, Péron and study co-author Sujoy Mukhopadhyay, a professor of Earth and planetary sciences at the University of California, Davis, used krypton as a tracer. Krypton was ideal because its isotopes, which are different atomic configurations of an element, are imprinted with information about the sources of volatiles.
“Krypton is very useful among the different noble gasses because the krypton isotope composition of different potential sources like the Sun or the interior of planets is very distinct,” said Péron. With this in mind, she and Mukhopadhyay obtained “the first precise measurements of krypton in this meteorite. Krypton is challenging to measure, so we developed a new protocol to be able to measure precisely those isotopes in the meteorite.”
“This particular meteorite, Chassigny, is the only one from the noble gas point-of-view that can give access to the Martian interior composition,” she added. “All the other Martian meteorites we have currently in the collection are totally or highly influenced by the Martian atmospheric composition. If we want these pure interior components, it’s the only meteorite we have so far.”
The krypton the team studied inside the meteorite upends the conventional view of how Mars evolved. Chassigny’s isotopes carry clear chondritic signatures, meaning that asteroids were pummeling Mars, and enriching it with volatiles, before the infant Sun evaporated the solar nebula, a timeline that is “opposite to most models of planet formation,” according to the study.
Indeed, those models suggest that rocky planets cool from their molten phase and release gasses from their magma oceans that feed nascent atmospheres. If this were true on Mars, one might expect the atmosphere to contain chondritic volatiles like those the new study identifies from its interior.
But puzzlingly, the Martian atmosphere today lines up with the composition of the solar nebula. Péron and Mukhopadhyay speculate that elements from the solar nebula might have been locked up in ice on the young Mars, which were later released to give it its current composition, but they note this explanation requires more research.
For now, the mystery of why direct evidence from early Mars seems at odds with traditional models of planetary formation remains unsolved. Finding the answer to this enigma would not only help us understand the red planet, it could inform our search for other potentially habitable worlds by focusing on their volatile elements, which are essential for life as we know it on Earth.
“There are so many questions that remain open,” Péron said. “I hope [the study] will have a broader impact for people that focus on modeling the formation of planetary atmospheres, which are crucial for the origin of life.”
