Mars was once an Earthlike planet but was stripped of most of its atmosphere by violent storms on the Sun, NASA revealed today. The bombardment of “space weather” turned the Martian climate from a warm and wet one that could support life to a cold and dry desert.

Today, Mars has a thin atmosphere made up largely of carbon dioxide, and any water that comes to the surface immediately evaporates – or more correctly sublimates – into space.

Storms continue to erupt on the Sun, and a NASA satellite in orbit around Mars has been able to observe their effect on the Red Planet.

The MAVEN mission – short for Mars Atmosphere and Volatile Evolution – allowed scientists to tell how quickly the planet’s atmosphere is currently being lost due to the solar wind, a constant flow of particles from the Sun’s own atmosphere.

It showed that this solar buffeting generally strips away about 100g (4oz) every second. But during a stormy time on the Sun in March 2015, MAVEN detected that the rate of loss was accelerated.

Mars lacks a protective magnetic field, which on Earth steers the solar wind around our planet. The findings suggest that storms on the Sun have been the major process in turning Mars from a planet friendly to life into one that is hostile.

NASA associate administrator John Grunsfeld, a former astronaut, said yesterday: “Mars appears to have had a thick atmosphere warm enough to support liquid water which is a key ingredient and medium for life as we currently know it.

“Understanding what happened to the Mars atmosphere will inform our knowledge of the dynamics and evolution of any planetary atmosphere. Learning what can cause changes to a planet’s environment from one that could host microbes at the surface to one that doesn’t is important to know, and is a key question that is being addressed in NASA’s journey to Mars.”

Close studies of Mars from orbiting satellites and rovers on the ground have revealed conclusive evidence that Mars was once awash with water. An ocean is believed to have covered much of the northern hemisphere a few billion years ago, and the planet is covered with dried up lakebeds and river beds.

Water on Mars today is mainly locked into ice below the surface. But a month ago, evidence was revealed that during warmer seasons, flows of salty water might still occur on the slopes of craters.

Bruce Jakosky, MAVEN’s principal investigator, from the University of Colorado, said: “We’ve seen that the atmospheric erosion increases significantly during solar storms, so we think the loss rate was much higher billions of years ago when the Sun was young and more active.”

Mars is easy to observe with a small telescope. For more about the Red Planet, see Skymania’s special pages about Mars.

 
A NASA animation shows how the atmosphere of Mars was stripped away by the solar wind