NASA: Sun has stolen Mars’ atmosphere

Thought to once have been habitable, planet lost its air over billions of years

NASA’s Mars-orbiting Maven spacecraft has discovered that the sun likely robbed the red planet of its once-thick atmosphere and water.

The air on Mars — what there is of it — is leaking away, about half a pound per second sputtering into space, scientists announced Thursday.

The planet’s early atmosphere is thought to have been as thick as or thicker than Earth’s today, and even over the 4.5-billionyear history of the solar system, that slow leak would not explain how it atrophied to its current wisps.

But new readings from NASA’s Mars Atmosphere and Volatile Evolution mission — MAVEN, for short — show that when Mars is pummeled by a solar storm, the ferocious bombardment of particles from the sun strips away the upper atmosphere at a rate 10 to 20 times as high, perhaps 10 pounds a second.

“What this tells us is loss through space has been an important process,” said Bruce M. Jakosky, a scientist at the Laboratory for Atmospheric and Space Physics at the University of Colorado and the principal investigator for the MAVEN mission.

The answer to what happened to the Martian air is key to understanding how Mars might have once been a warm, habitable planet with lakes and maybe an ocean covering the northern hemisphere. When the air disappeared, liquid water largely disappeared, too.

Jakosky and other scientists reported their findings from MAVEN in four scientific papers published on Thursday in the journal Science. Another 44 papers by the MAVEN team appear in the journal Geophysical Research Letters.

Jasper Halekas, a professor of physics and astronomy at the University of Iowa and a member of the MAVEN team, said the energy hitting the Martian atmosphere during the storm was equivalent to 1 million tons of TNT an hour. “That’s one large nuclear weapon per hour, if you like,” he said.

Such solar storms are not everyday events, but they are also not rare, happening a few times a year, Halekas said. He gave an analogy of a geologist studying beach erosion, wondering whether it was caused more by the steady, daily effects of waves and tides or by one or two big tsunamis.

The solar storm, Halekas said, “is the equivalent of the tsunami at Mars.”

A rendering depicts a solar storm hitting the red planet.

Goddard Space Flight Center / NASA via Associated Press An artist’s rendering shows a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere. NASA’s Mars-orbiting MAVEN craft has discovered that solar storms rob the red planet of about 10 pounds of atmosphere per second.