Scientists involved in NASA鈥檚 Mars Atmosphere and Volatile Evolution (MAVEN) mission, which is being led by the 精品SM在线影片, have identified the process that appears to have played a key role in the transition of the Martian climate from an early, warm and wet environment that might have supported surface life to the cold, arid planet Mars is today.
MAVEN data have enabled researchers to determine the rate at which the Martian atmosphere currently is losing gas to space via stripping听by the solar wind. The findings reveal that the erosion of Mars鈥� atmosphere increases significantly during solar storms. The scientific results from the mission appear in the Nov. 5 issues of the journals Science and Geophysical Research Letters.
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.
鈥淟ike the theft of a few coins from a cash register every day, the loss becomes significant over time,鈥� said Bruce Jakosky, MAVEN principal investigator at CU-Boulder鈥檚 Laboratory for Atmospheric and Space Physics (LASP) and a professor in geological sciences. 鈥淲e'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.鈥�
听鈥淢ars appears to have had a thick atmosphere warm enough to support liquid water which is a key ingredient and medium for life as we听currently know it,鈥� said John Grunsfeld, astronaut and associate administrator for the NASA Science Mission Directorate in Washington.
听鈥淯nderstanding what happened to the Mars听atmosphere听will inform our knowledge of the dynamics and evolution of any planetary atmosphere. Learning what can cause changes to a planet鈥檚 environment from one that could host microbes at the surface to one that doesn鈥檛 is important to know, and is a key question that is being addressed in NASA鈥檚 journey to Mars.鈥�
In addition, a series of dramatic solar storms hit Mars鈥� 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.
The solar wind is a stream of particles, mainly protons 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鈥� upper atmosphere and shoots them into space.
MAVEN has been examining how solar wind and ultraviolet light strip gas from the top of the planet's atmosphere. New results indicate that the loss is experienced in three different regions of the Red Planet: down the 鈥渢ail,鈥� where the solar wind flows behind Mars, above the Martian poles in a 鈥減olar plume,鈥� and from an extended cloud of gas surrounding Mars. The science team determined that almost 75 percent of the escaping ions come from the tail region, and nearly 25 percent are from the plume region, with just a minor contribution from the extended cloud.
Ancient regions on Mars bear signs of abundant water 鈥� 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.
MAVEN has been operating at Mars for just over a year and will complete its primary science mission on Nov. 16.
There are roughly 30 LASP scientists, graduate students and undergraduates who are on the science team and analyzing the MAVEN science results. CU-Boulder provided two science instruments and leads science operations as well as education and public outreach for the mission. LASP鈥檚 Nick Schneider, Frank Eparvier and Robert Ergun all head up instrument teams on NASA鈥檚 MAVEN project.
