嘿嘿视频

Martian Meteorite Upsets Planet Formation Theory

News
Red-brown planet with a small northern ice cap.
When our solar system formed, Mars formed earlier than Earth, and its composition gives clues about early steps in planet formation. A new 嘿嘿视频 study overturns previous ideas about how rocky planets form. (NASA image)

A new study of an old meteorite contradicts current thinking about how rocky planets like the Earth and Mars acquire volatile elements such as hydrogen, carbon, oxygen, nitrogen and noble gases as they form. The work is published June 16 in Science.

A basic assumption about planet formation is that planets first collect these volatiles from the nebula around a young star, said Sandrine P茅ron, a postdoctoral scholar working with Professor Sujoy Mukhopadhyay in the Department of Earth and Planetary Sciences, University of California, Davis.

Because the planet is a ball of molten rock at this point, these elements initially dissolve into the magma ocean and then degas back into the atmosphere. Later on, chondritic meteorites crashing into the young planet deliver more volatile materials.

So scientists expect that the volatile elements in the interior of the planet should 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 鈥 solar vs. meteoritic 鈥 can be distinguished by the ratios of isotopes of noble gases, in particular krypton.

Mars is of special interest because it formed relatively quickly 鈥 solidifying in about 4 million years after the birth of the solar system, while the Earth took 50 to 100 million years to form.

鈥淲e can reconstruct the history of volatile delivery in the first few million years of the solar system,鈥 P茅ron said.

Meteorite from Mars鈥 interior

Some meteorites that fall to Earth come from Mars. Most come from surface rocks that have been exposed to Mars鈥 atmosphere. The Chassigny meteorite, which fell to Earth in northeastern France in 1815, is rare and unusual because it is thought to represent the interior of the planet.

By making extremely careful measurements of minute quantities of krypton isotopes in samples of the meteorite using a new method set up at the 嘿嘿视频 Noble Gas Laboratory, the researchers could deduce the origin of elements in the rock.

鈥淏ecause of their low abundance, krypton isotopes are challenging to measure,鈥 P茅ron said.

Surprisingly, the krypton isotopes in the meteorite correspond to those originating from meteorites, not the solar nebula. That means that meteorites were delivering volatile elements to the forming planet much earlier than previously thought, and in the presence of the nebula, reversing conventional thinking.

鈥淭he Martian interior composition for krypton is nearly purely chondritic, but the atmosphere is solar,鈥 P茅ron said. 鈥淚t鈥檚 very distinct.鈥

The results show that Mars鈥 atmosphere does not contain meteoritic isotopes, which means that it cannot have formed purely by outgassing from the mantle. The planet must have acquired atmosphere from the solar nebula after the magma ocean cooled, to prevent substantial mixing between interior meteoritic gases and atmospheric solar gases.

The new results suggest that Mars鈥 growth was completed before the sun鈥檚 radiation dissipated the solar nebula. But the irradiation should also have blown off the nebular atmosphere on Mars, suggesting that atmospheric krypton must have somehow been preserved, possibly trapped underground or in polar ice caps.

鈥淗owever, that would require Mars to have been cold in the immediate aftermath of its accretion,鈥 Mukhopadhyay said. 鈥淲hile 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鈥 early atmosphere.鈥

P茅ron and Mukhopadhyay hope their study will stimulate further work on the topic.

P茅ron is now a postdoctoral fellow at ETH Z眉rich, Switzerland.

Media Resources

Media Contacts:

  • Sandrine P茅ron, ETH Z眉rich, sandrine.peron@erdw.ethz.ch
  • Sujoy Mukhopadhyay, 嘿嘿视频 Earth and Planetary Sciences, smuk@ucdavis.edu
  • Andy Fell, 嘿嘿视频 News and Media Relations, 530-304-8888, ahfell@ucdavis.edu

 

Primary Category

Secondary Categories

Science & Technology

Tags