Scientists studying Mars’ atmosphere say solar storms probably played a big role in transforming the Red Planet from the warm, hospitable place it was billions of years ago to the cold world it is today.
That’s just one of the many findings about Mars found in four dozen research papers published today by Science and Geophysical Research Letters. The source of the scientific cornucopia is NASA’s $671 million MAVEN mission, which put a bus-sized spacecraft into Martian orbit last year.
The mission’s name is an acronym that stands for Mars Atmosphere and Volatile EvolutioN. Its aim is to measure the current dynamics of the Martian atmosphere – and then factor those measurements into models to figure out how Mars lost much of its air billions of years ago.
Based on earlier observations, scientists surmised that because Mars’ magnetic field isn’t as strong as Earth’s, electrically charged particles from the sun are able to strip away molecules and ions from the top of the Martian atmosphere as they streamed by.
MAVEN’s scientists had a golden opportunity to gather data for analysis on March 8, when an unusually strong solar storm swept past Mars. In one of the Science papers, a research team led by the University of Colorado’s Bruce Jakosky, the MAVEN mission’s principal investigator, reports that the magnetic field accelerated ions to roughly 10 times their usual velocity. Oxygen ions were flung higher up into the atmosphere than expected.
When the scientists plugged the numbers into their computer models, they determined that under such conditions, atmospheric ions would be lost at around 10 or 20 times the normal rate.
The researchers note that solar storms are thought to have occurred frequently during the early days of the solar system. Also, Mars’ magnetic field is thought to have faded away very early in its history as its liquid metal core cooled down.
“As these early periods may have been the dominant times at which the Martian atmosphere experienced loss, the inferred climate change on Mars may have been driven to a large extent by these solar storms,” they wrote.
One of the study’s co-authors, Paul Mahaffy of NASA’s Goddard Space Flight Center, stressed that there aren’t yet enough measurements to produce a detailed scenario for atmospheric loss on Mars. “I think it’s still early in developing that story. … Long-term, we’ll probably need to do more mapping to understand this better,” he told GeekWire.
But the findings are generally consistent with what other Mars missions have found. For example, when atmospheric readings from NASA’s Curiosity rover were compared with samples taken from Mars meteorites, scientists concluded that most of the Red Planet’s atmosphere was stripped away more than 3 billion years ago. Mahaffy was the lead author of one of the resulting research papers.
“The big story is really the nuts and bolts of the physics and chemistry of the upper atmosphere of Mars,” Mahaffy said, referring to the research papers published today. “It’s a new window to understanding what’s going on up there.”
Another study reports an unexpected level of variability in atmospheric density. “At certain latitudes and times of day, there are these high-amplitude density waves, especially toward sunrise and sunset,” Mahaffy said. That suggests Mars’ atmospheric interactions are more complex than previously thought – with gravity wave interactions, wind patterns and the planet’s weak magnetic field all playing a role.
Still other papers document observations of Mars’ faint northern aurora, which dips to the surprisingly low level of 37 miles (60 kilometers); the distribution of dust in the atmosphere, which is found at the surprisingly high level of 620 miles (1,000 kilometers) and may come from interplanetary sources; and plumes of escaping ions that account for a significant proportion of Mars’ atmospheric loss.
“All of these measurements form the basis of our ability to model [atmospheric] escape,” Mahaffy said.
At the current rate of loss, Mars should retain an atmosphere for at least the next couple of billion years, Jakosky said, “but I can’t tell you exactly what it’s going to be like.”
MAVEN is still collecting scientific data for its primary mission, and it’s expected to continue operating for an extended mission that includes serving as a backup relay satellite for other Mars probes. Meanwhile, India’s Mars Orbiter Mission, also known as MOM or Mangalyaan, is studying the Red Planet’s atmosphere as well.
