A new analysis of an ancient meteorite challenges conventional wisdom about how stony planets like the Earth and Mars acquire volatile components like hydrogen, carbon, oxygen, nitrogen, and noble gases as they develop. The study was published in Science on June 16th.
According to Sandrine Péron, a postdoctoral scholar working with Professor Sujoy Mukhopadhyay in the Department of Earth and Planetary Sciences at the University of California, Davis, “a basic assumption about planet formation is that planets first collect these volatiles from the nebula around a young star.”
These elements dissolve into the magma ocean and subsequently degass back into the atmosphere since the globe is a molten rock ball at this time. Later, additional volatile components are delivered to the newborn planet by chondritic meteorites slamming onto it.As a result, scientists predict the volatile elements in the planet’s core to resemble the solar nebula’s composition, or a combination of solar and meteoritic volatiles, while the volatiles in the atmosphere will primarily originate from meteorites. The ratios of noble gas isotopes, particularly krypton, can identify these two sources — solar vs. chondritic.
Mars is particularly interesting since it developed very fast after the origin of the Solar System, hardening in around 4 million years, whereas the Earth took 50 to 100 million years to form.”In the first few million years of the Solar System, we can recreate the history of volatile delivery,” Péron added.
Mars’s interior meteorite
Some of the meteorites that hit Earth are from Mars. The majority come from surface rocks exposed to Mars’ atmosphere. The Chassigny meteorite, which landed in north-eastern France in 1815, is unique in that it is supposed to depict the planet’s innards.The researchers were able to identify the origin of elements in the meteorite by taking highly precise measurements of minute amounts of krypton isotopes in samples of the meteorite using a novel approach developed at the UC Davis Noble Gas Laboratory.
“Krypton isotopes are difficult to test due to their low quantity,” Péron explained.
Surprisingly, the krypton isotopes in the meteorite match those found in chondritic meteorites rather than those found in the solar nebula. That suggests meteorites delivered volatile materials to the developing planet more sooner than previously anticipated, and in the presence of the nebula, inverting prior assumptions.
“The Martian interior is virtually totally chondritic for krypton, but the atmosphere is solar,” Péron added. “It has a particular flavor.”
The findings suggest that Mars’ atmosphere could not have originated only from mantle outgassing, as this would have resulted in a chondritic composition. To prevent significant mixing between inner chondritic gases and atmospheric solar gases, the planet must have received atmosphere from the solar nebula after the magma ocean cooled.According to the latest findings, Mars’ development was completed before the solar nebula was dispersed by solar radiation. However, the irradiation should have blown off the nebular atmosphere on Mars, implying that atmospheric krypton was maintained in some way, maybe underground or in the polar ice caps.
“However, that would need Mars becoming frigid shortly after its accumulation,” Mukhopadhyay explained. “While our research confirms the presence of chondritic gases in the Martian deep, it also raises some intriguing concerns concerning the origin and composition of Mars’ early atmosphere.”
Péron and Mukhopadhyay believe that their research will inspire more research on the subject.