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A new study of an old meteorite contradicts current thinking about how rocky planets like Earth and Mars acquire volatile elements such as hydrogen, carbon, oxygen, nitrogen, and noble gases as they form. The play is published on June 16 Science.
A basic hypothesis about the formation of planets is that the planets first collect these nebulae volatiles around a young star, said Sandrine Péron, a postdoctoral researcher working with Professor Sujoy Mukhopadhyay in the Department of Earth Sciences. University of California Planetarium, Davis.
Because the planet is a ball of molten rock at this point, these elements initially dissolve in the ocean of magma and then degassed back into the atmosphere. Later, chondritic meteorites colliding with the young planet provide more volatile materials.
Thus, scientists expect the volatile elements inside the planet to reflect the composition of the solar nebula, or a mixture of solar and meteoritic volatiles, while the volatiles in the atmosphere would come mostly from meteorites. These two sources, solar and chondritic, can be distinguished by the proportions of isotopes of noble gases, in particular krypton.
Mars has a special interest because it formed relatively quickly, solidifying in about 4 million years after the birth of the Solar System, while the Earth took between 50 and 100 million years to form.
“We can reconstruct the history of volatile delivery in the first million years of the Solar System,” Péron said.
Meteorite from the interior of Mars
Some meteorites that fall to Earth come from Mars. Most come from surface rocks that have been exposed to Mars’ atmosphere. The Chassigny meteorite, which fell to Earth in northeastern France in 1815, is rare and unusual because it is believed to represent the interior of the planet.
Using extremely accurate measurements of small amounts of krypton isotopes in meteorite samples using a new method established at the UC Davis Noble Gas Laboratory, the researchers were able to deduce the origin of the elements in the rock.
“Because of their low abundance, krypton isotopes are difficult to measure,” Péron said.
Surprisingly, the krypton isotopes of the meteorite correspond to those of the chondritic meteorites, not to the solar nebula. This means that meteorites were delivering volatile elements to the planet in formation much earlier than previously thought, and in the presence of the nebula, reversing conventional thinking.
“The Martian interior composition for krypton is almost purely chondritic, but the atmosphere is solar,” Peron said. “It’s very different.”
The results show that the atmosphere of Mars would not have formed only by degassing the mantle, as this would have given it a chondritic composition. The planet must have acquired the atmosphere of the solar nebula, after the ocean of magma cooled, to avoid a substantial mixture between the inner chondritic gases and the atmospheric solar gases.
The new results suggest that Mars’ growth was completed before the solar nebula was dissipated by the Sun’s radiation. But the irradiation should also have expelled the nebular atmosphere from Mars, suggesting that the atmospheric krypton must have been preserved in some way, possibly trapped underground or in polar caps.
“However, this would require Mars to be cold immediately after its accretion,” Mukhopadhyay said. “While our study clearly points to chondritic gases inside Mars, it also raises some interesting questions about the origin and composition of Mars’ early atmosphere.”
Péron and Mukhopadhyay hope that their study will stimulate more work on the subject.
The krypton of the deep mantle reveals the ancestry of the Earth’s outer solar system. More information: Sandrine Péron, Krypton in the Chassigny meteorite shows that Mars accumulated chondritic volatiles before nebulae, Science (2022). DOI: 10.1126 / science.abk1175. www.science.org/doi/10.1126/science.abk1175
Citation: The Martian meteorite alters the theory of the formation of the planet (2022, June 16) recovered on June 17, 2022
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