Free Astronomy Magazine January-February 2016

SPACE CHRONICLES 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. “Like the theft of a few coins from a cash register every day, the loss becomes significant over time,” said Bruce Jakosky, MAVEN principal in- vestigator at the University of Colo- rado, Boulder. “We’ve seen that the atmospheric erosion increases signif- icantly 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’ atmo- sphere in March 2015, and MAVEN found that the loss was acceler- ated. 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 chang- ing the Martian cli- mate. The solar wind is a stream of particles, mainly pro- tons and electrons, flowing from the sun’s atmosphere at a speed of about one million miles per hour. The magnetic field carried by the solar wind as it flows past Mars can generate an electric field, much as a turbine on Earth can be used to generate electricity. This electric field accelerates electrically charged gas atoms, called ions, in Mars’ up- per atmosphere and shoots them into space. MAVEN has been examining how the solar wind and ultraviolet light strip gas from of the top of the plan- et’s atmosphere. New results indi- cate that the loss is experienced in three different regions of the Red Planet: down the “tail” where the solar wind flows behind Mars, above the Martian poles in a “po- lar plume,” and from an extended cloud of gas surrounding Mars. The science team determined that al- most 75 percent of the escaping ions come from the tail region, and near- ly 25 percent are from the plume re- gion, with just a minor contribution from the extended cloud. Ancient regions on Mars bear signs of abundant water – such as fea- tures resembling valleys carved by rivers and mineral deposits that only form in the presence of liquid water. These features have led sci- n I n this simulation, we see how the solar wind accelerates ions from the Mars upper atmo- sphere into space. [NASA/GSFC] entists 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 observ- ed the seasonal appearance of hy- drated salts indicating briny liquid water on Mars. However, the cur- rent Martian atmosphere is far too cold and thin to support long-lived or extensive amounts of liquid wa- ter on the planet’s surface. “Solar- wind erosion is an important mech- anism for atmospheric loss, and was important enough to account for significant change in the Martian climate,” said Joe Grebowsky, MA- VEN project scientist from NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “MAVEN also is studying other loss processes— such as loss due to impact of ions or escape of hydrogen atoms—and these will only increase the impor- tance of atmospheric escape.” The goal of NASA’s MAVEN mis- sion, launched to Mars in November 2013, is to determine how much of the planet’s atmosphere and water have been lost to space. It is the first such mission devoted to understand- ing how the Sun might have influ- enced atmospheric changes on the Red Planet.