New analysis of Mars meteorite could change theory of how planets in our solar system formed

Findings raise questions about the origin and composition of Mars’ early atmosphere

A new analysis of an old meteorite from Mars’ interior contradicts a common assumption about how rocky planets like the Earth, Venus, and Mars acquire elements such as hydrogen, carbon, oxygen, and nitrogen.

Until now, the basic belief was that planets acquired these elements, as well as noble gases like helium, from the nebula around a young star, Sandrine Péron from the University of California (UC) - Davis, said in a statement.

In the early stages of the formation of these planets, when they were balls of molten rock, scientists believed elements like hydrogen, carbon, oxygen, nitrogen as well as inert gasses dissolved into the magma ocean and then degass back into the atmosphere.

They thought chondritic meteorites then crashed into these young planets delivering more volatile materials.

Researchers believed the volatile elements in the interior of the planet reflected the composition of the solar nebula, or a mixture of solar and meteoritic volatiles, while the gasses in the atmosphere were thought to mostly come from meteorites.

The two sources – solar and chondritic – they say can be distinguished by the ratios of isotopes of noble gases, in particular that of krypton.

However, the new study, published in the journal Science on Thursday, found that meteorites were delivering volatile elements to these forming planets much earlier than previously thought, and in the presence of the nebula.

In the research, scientists specifically assessed meteorite samples from Mars, which they say is of “special interest” as the planet formed relatively quickly – solidifying in about 4 million years after the birth of the solar system compared to the Earth that took 50 to 100 million years to form.

They assessed parts of the Chassigny meteorite, which fell to Earth in north-eastern France in 1815 – a rare and unusual sample since it is thought to represent the interior of the Red Planet.

By analysing very small quantities of the element krypton and its variant forms in the meteorite samples, researchers could deduce the origin of elements in the rock.

They found that the element’s various forms in the meteorite matched those from chondritic meteorites, not the solar nebula.

Based on the results, scientists say Mars’ atmosphere cannot have formed purely by outgassing from the mantle, as that would have given it a chondritic composition.

Instead they say, meteorites were delivering volatile elements to the forming planet much earlier than previously thought, and in the presence of the nebula, “reversing conventional thinking.”

Researchers say the planet must have acquired atmosphere from the solar nebula, after the magma ocean cooled, to prevent substantial mixing between interior chondritic gases and atmospheric solar gases.

The results also suggest that Mars’ growth was completed before the solar nebula was dissipated and the atmospheric krypton must have been preserved likely trapped underground or in polar ice caps.

“The Martian interior composition for krypton is nearly purely chondritic, but the atmosphere is solar. It’s very distinct,” Dr Peron explained.

“While our study clearly points to the chondritic gases in the Martian interior, it also raises some interesting questions about the origin and composition of Mars’ early atmosphere,” Sujoy Mukhopadhyay, another co-author of the study, said.