Cannon acknowledged that his theory does not explain the presence of minerals such as hematite on the surface, at least not yet. An iron oxide mineral, hematite is usually formed in moist environments with water, such as groundwater. It has been found at the landing sites for the Opportunity and Curiosity explorers.
"That could be a different story," Cannon said. "We do not really address that in the document."
The genesis of the research came from the previous work of Lindy Elkins-Tanton, a planetary scientist at Arizona State University who was specializes in planetary formation and evolution. (Elkins-Tanton is also the principal investigator of NASA's recently selected Psyche mission.) After launch in 2022, the spacecraft will explore the metallic asteroid 16 Psyche to learn more about planetary cores.)
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The Elkins-Tanton papers showed that most rocky planets had a completely global layer of molten rock when they formed. As the rock cooled, degassing of the surface interacted with the crust. Cannon's team connected their theories with the clays observed on Mars, he said.
"We believe that this process may have occurred on other planets such as Earth and Venus," he added, noting that other researchers suggested that the Earth also had an early vapor atmosphere. The ancient surfaces of Earth and Venus, however, have been almost completely annihilated by geological processes such as plate tectonics, erosion and volcanism.  Mars is an environment where ancient surfaces are conserved, allowing scientists to extrapolate for planets in our own solar system, or even exoplanets. But Cannon warned that it would be a while before telescopes could search for clay minerals in small rocky exoplanets.
"With James Webb Space Telescope" – which launches in 2019 – "we can see degassed atmospheres," he said.
Other evidence could come from the Mars 2020 mission, an explorer who has the task of collecting and storing samples on the Martian surface to a possible mission to return samples. If the clays were formed from a humid atmosphere, the researchers would expect to see noble gases such as krypton or xenon. But given the Mars 2020 instruments, which are not necessarily designed to search for these gases, Cannon suggested that the samples may need to return to Earth to provide definitive answers.