At one time, Mars had a thick, protective atmosphere — possibly even cushier than Earth’s — but the bubble of gases mostly dissipated about 4 billion years ago and has never been replenished, new research shows.
The findings come from NASA’s Mars rover Curiosity, which has been moonlighting as an atmospheric probe as it scours planet’s surface for habitats that could have supported ancient microbial life. The rover landed inside a large impact basin called Gale Crater last August.
Two instruments aboard Curiosity are providing scientists with unprecedented details about Mars’ present-day atmosphere. The data is then run through computer models as well as compared to analysis of trapped gases in ancient Mars meteorites that have been recovered on Earth.
The scientists look for telltale isotopes, which are atoms of elements that have different numbers of neutrons. Normal carbon, for example, is known as carbon-12 and contains six neutrons. Some carbon stragglers may have seven, or even eight, neutrons. What’s key is how the isotopic concentrations change over time.
Across all the gases in Mars’ atmosphere — carbon dioxide, argon, nitrogen, oxygen and carbon monoxide — scientists found higher concentrations of isotopes, evidence that most of the atmospheric gas has escaped.
“The overarching conclusion is that the Mars atmosphere hasn’t really changed a lot in 4 billion years,” said Chris Webster, manager of the Planetary Sciences Instruments Office at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
Why the planet lost its atmosphere is a matter of debate, but scientists believe it stemmed from the loss of the planet’s magnetic field.
“On Earth, our magnetic field protects us, it shields us from the solar wind particles. Without Earth’s magnetic field, we would have no atmosphere and there would be no life on this planet. Everything would be wiped out — especially when you go back 4 billion years. The solar wind was at least 100 times stronger then than it is today. It was a young sun with a very intense radiation, ” Webster told Discovery News.
That might be exactly what happened on Mars, though whether life could have evolved and been preserved are key questions being addressed by Curiosity and the focus of follow-on missions now in the planning stages.
“The jury is out on how long an earlier, heavy atmosphere might have persisted after the late heavy bombardment, when things were flying around,” said NASA’s Paul Mahaffy, lead scientist for Curiosity’s Sample Analysis at Mars suite of instruments.
“Before that, the record is probably hard to find because things probably really got changed by all these impacts. But once things settled down a little bit, it’s a really important to understand what the climate conditions were,” Mahaffy told Discovery News.
“The isotopes in the atmosphere and the isotopes in very old materials that we might analyze as we proceed along with the Curiosity mission are solid data points that can go into theories. Hopefully, that will give us a better prediction, if there were friendly conditions, how long they really could have persisted on the surface,” he said.
The research is published in this week’s Science.