If life did indeed exist on the surface of Mars at one time, NASA believes that the slowly depleting atmosphere - and the frigid temperatures in brought with it - would have gradually driven it to live primarily underground or in smaller habitable pockets tucked away around the planet.
Particles blasting out from the sun stripped away what was once a thick, Earth-like atmosphere on Mars, leaving behind a dry and cold world inhospitable to life, researchers said in a study released on Thursday. The loss of this carbon dioxide from the Red Planet may "tell us why the surface of Mars could have gone from habitable in ancient times to not being able to support life today", Jakosky told Space.com.
In sputtering, ions from the solar wind smash into the gas molecules at high speed, knocking them out of the atmosphere.
Yelle explained the main reason why Mars can't hold on to its atmosphere is its magnetic field, which is a feeble remnant of its former self.
It had previously been shown atmospheric gas had been lost to space, but NASA's new measurements from its MAVEN spacecraft show just how much. Each isotope of an element has different numbers of neutrons; for instance, argon-36 possesses 18 neutrons in its nucleus, while argon-38 has 20.
"We've determined that most of the gas ever present in the Mars atmosphere has been lost to space", said Bruce Jakosky, principal investigator for the Mars Atmosphere and Volatile Evolution Mission (MAVEN), University of Colorado in Boulder. More details of the study have been published as a paper in Science Magazine. Calculations show that Mars might have lost as much as 66% of its lightest argon isotope as well as large amounts of other gases over the last 4 billion years. Since the lighter of the two isotopes escapes to space more readily, it will leave the gas remaining behind enriched in the heavier isotope.
New research suggests that alien life on Mars may have been possible at some point in the planet's history.
Instruments on NASA's Curiosity rover assessed the composition of argon in the planet's atmosphere.
The orbiter, which is the most data-productive spacecraft yet at Mars, continues to compile the most sharp-eyed global coverage ever accomplished by a camera at the Red Planet.
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As a "noble gas" argon cannot react chemically, so it cannot be sequestered in rocks; the only process that can remove noble gases into space is a process called "sputtering" by the solar wind.
Then, they did the same for carbon dioxide and other gases, revealing that this, too, has largely been lost to space.
The data was collected by the Mars Atmosphere and Volatile Evolution, or MAVEN, spacecraft, one of eight satellites and rovers now operating around or on Mars.
CO2 is of interest because it is the major constituent of Mars' atmosphere and because it's an efficient greenhouse gas that can retain heat and warm the planet.
"The whole goal is to really understand all of the (atmospheric) loss processes, and how the sun influences loss, and using that to infer what the atmosphere was like billions of years ago", Slipski said.
"We determined that the majority of the planet's [carbon dioxide] was also lost to space by sputtering", said Jakosky.
Mahaffy is principal and lead investigator of the SAM and NGIMS instruments respectively - both were developed at NASA Goddard.
The discovery helps paint a clearer picture of the red planet's atmospheric history and how it evolved geologically from a wet, warm planet to today's cold, arid place.
"After 11 and a half years in flight, the spacecraft is healthy and remains fully functional", said MRO Project Manager Dan Johnston at NASA's Jet Propulsion Laboratory, Pasadena, California.
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