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Solar wind likely stripped Martian atmosphere

Mars was once warm and wet, say scientists. But most of the water from its atmosphere was likely stripped away by solar winds.

Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet's upper atmosphere. Image credit: NASA/GSFC

Artist’s rendering of a solar storm hitting Mars and stripping ions from the planet’s upper atmosphere.
Image credit: NASA/GSFC

Data suggest that most of the water from the atmosphere on Mars was likely stripped away by solar winds, NASA scientists announced yesterday (November 5, 2015). For the first time, NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has observed this process in action – by measuring the speed and direction of ions escaping from Mars.

Although Mars is a cold and barren desert today, scientists think the planet was warm and wet in its ancient past. How did Mars lose its watery atmosphere? Scientists say a prime suspect is the solar wind – a stream of particles, mainly protons and electrons, flowing from the sun’s atmosphere at about a million miles per hour. Unlike Earth, Mars lacks a global magnetic field to deflect the stream of charged particles continuously blowing off the sun. Instead, the solar wind crashes into the Mars upper atmosphere and can accelerate ions into space.

This data visualization compares simulations of the solar wind and Mars atmospheric escape with new measurements taken by MAVEN.

Data from the MAVEN mission have enabled researchers to determine the rate at which the Martian atmosphere currently is losing gas to space via stripping by the solar wind. The findings reveal that the erosion of Mars’ atmosphere increases significantly during solar storms.

John Grunsfeld is an astronaut and associate administrator for the NASA Science Mission Directorate in Washington. Grunsfeld said:

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.

MAVEN measurements indicate that the solar wind strips away gas at a rate of about 100 grams (equivalent to roughly 1/4 pound) every second. MAVEN principal investigator Bruce Jakosky said:

Like the theft of a few coins from a cash register every day, the loss becomes significant over time. 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.

In addition, a series of dramatic solar storms hit Mars’ atmosphere in March 2015, and MAVEN found that the loss was accelerated. The combination of greater loss rates and increased solar storms in the past suggests that loss of atmosphere to space was likely a major process in changing the Martian climate.

Ancient regions on Mars bear signs of abundant water – such as features resembling valleys carved by rivers and mineral deposits that only form in the presence of liquid water. These features have led scientists to think that billions of years ago, the atmosphere of Mars was much denser and warm enough to form rivers, lakes and perhaps even oceans of liquid water.

Recently, researchers using NASA’s Mars Reconnaissance Orbiter observed the seasonal appearance of hydrated salts indicating briny liquid water on Mars. However, the current Martian atmosphere is far too cold and thin to support long-lived or extensive amounts of liquid water on the planet’s surface.

Joe Grebowsky is MAVEN project scientist from NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Grebowsky said:

Solar-wind erosion is an important mechanism for atmospheric loss, and was important enough to account for significant change in the Martian climate.

The scientific results from the mission appear in the November 5, 2015 issues of the journals Science and Geophysical Research Letters.

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Bottom line: On November 5, 2015 NASA scientists announced that data from from the MAVEN mission suggest that most of the water from the atmosphere on Mars was likely stripped away by solar winds.

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