The story of the lost Martian atmosphere

The Curiosity rover NASA has used the SAM tool to analyze xenon, a heavy noble gas that occurs naturally in nine isotopic forms, to better understand the story of the lost Martian atmosphere.
While the rover Curiosity NASA carried out in recent weeks the detailed examination of the rock layers of the outcrop “Pahrump Hills” in Gale Crater on Mars, some members of the team that oversees the operations of the laboratory were undertaken to analyze the walking in the Martian atmosphere in search of xenon, a heavy noble gas, with the instrument SAM (Sample Analysis at Mars).



Since the noble gases are chemically inert and do not react with other substances in the air or soil, they act as excellent markers of climatic history. Xenon (or Xe) is present in the atmosphere of Mars, but at a rate so low that its measurement is really a challenge and it can be done effectively only with instruments on site, such as SAM.
“That xenon is a key measure to be taken on planets like Mars or Venus, as it provides essential information for understanding the early history of these celestial bodies and prove why so drastically different than the Earth,” said Melissa Trainer, one of the scientists which analyzed data from SAM.
Located inside the rover, SAM is a laboratory to analyze the chemistry of the samples that are introduced through mass spectrometry, gas chromatography and laser spectrometry. SAM had previously measured the ratio of two isotopes of another noble gas, argon. The results showed a continuous loss in time of much of the original atmosphere of Mars.
A planetary atmosphere consists of different gases, which are in turn made up of variants of the same chemical element, called isotopes. When a planet loses its atmosphere, the relative amounts of the different isotopes will be affected. Measuring the xenon, rather than other gases, scientists can reconstruct the history that led to the loss of the Martian atmosphere. This thanks to the fact that the xenon occurs naturally in nine different isotopic forms, with atomic masses ranging from 124 (with 70 neutrons per atom) to 136 (with 82 neutrons per atom).


Credit: NASA

Before affecting the layers of gas that are higher, the process of loss of the atmosphere removes more easily isotopes lighter than heavy ones, leaving a higher ratio in the heavy isotopes than it was originally. The measure by SAM relations between nine isotopes of xenon recounts an early period in the history of Mars, when a vigorous process of escape Atmospheric tore away even the heavier isotopes of xenon, a rate only slightly lower than the lighter ones.
Today we can read in the Martian atmosphere the changing balance of power between different groups of isotopes as a trace of that ancestral exodus. One track remained to fluctuate for billions of years and the researchers had already guessed some decades ago from the measurements of the isotopes in tiny bubbles of Martian atmospheric gases trapped in the rocks of the red planet arrived on Earth as meteorites.
“We have seen a remarkable correspondence of data collected in situ with those of samples of atmosphere incorporated in some of the Martian meteorites,” said Pan Conrad, the deputy head of scientific SAM.
As you might guess, the experiment on the xenon has required a lot of preparation. In particular, extensive tests were carried out at the NASA Goddard Space Flight Center in Greenbelt, Maryland, using an exact copy of the instrument SAM, enclosed in an environmental chamber that simulates the environment of Mars.
“I’m really gratified by the success of this experiment and the fact that we were able to demonstrate this new feature for Curiosity,” said Charles Malespin of Goddard, who developed and optimized the entire sequence of instructions to be executed by SAM on Mars.

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