{"id":14765,"date":"2017-03-28T01:24:34","date_gmt":"2017-03-27T17:24:34","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/scientists-say-thinning-atmosphere-drove-the-drying-and-cooling-of-mars\/"},"modified":"2017-03-28T01:24:34","modified_gmt":"2017-03-27T17:24:34","slug":"scientists-say-thinning-atmosphere-drove-the-drying-and-cooling-of-mars","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/scientists-say-thinning-atmosphere-drove-the-drying-and-cooling-of-mars\/","title":{"rendered":"Scientists say thinning atmosphere drove the drying and cooling of Mars"},"content":{"rendered":"
\"\"
Artist\u2019s concept of a solar storm hitting Mars and stripping ions from the upper atmosphere. Credit: NASA\/GSFC<\/figcaption><\/figure>\n

Data collected by NASA\u2019s MAVEN spacecraft in its first two years at Mars confirm suspicions that the solar wind is blasting away the planet\u2019s atmosphere and helped transform the world from a warmer, wetter and potentially habitable world into the barren landscape seen today, scientists said.<\/p>\n

The robotic orbiter has been looping around Mars since September 2014, skimming just above the Martian atmosphere at the low point of its elongated orbit and searching for particles streaming away from the planet.<\/p>\n

As Mars is bombarded by the solar wind, a stream of solar particles that flow out through the solar system at a million miles per hour, the red planet\u2019s atmosphere is buffeted and eroded, chipping away bit by bit, according to Bruce Jakosky, MAVEN\u2019s principal investigator at the University of Colorado, Boulder.<\/p>\n

Researchers examining data from MAVEN\u2019s instruments have identified multiple processes by which Mars loses parts of its atmosphere.<\/p>\n

In one scenario called photochemical loss, solar radiation can ionize oxygen, carbon dioxide and nitrogen molecules in the Martian upper atmosphere. The reactions can split the molecules, scientists said, sometimes giving the resulting atoms enough energy to permanently escape Martian gravity.<\/p>\n

\u201cWe have enough measurements that we can calculate the loss rate orbit-by-orbit,\u201d Jakosky said March 20 at the Lunar and Planetary Science Conference near Houston.<\/p>\n

Robert Lillis, a research physicist at the Space Sciences Laboratory at the University of California, Berkeley, said that MAVEN data show the photochemical loss rate has declined as solar radiation waned since the spacecraft arrived at Mars. The sun goes through an 11-year cycle of intense and quiet activity, and the cycle\u2019s effects are observable Mars\u2019s distance.<\/p>\n

\u201cMAVEN is making, in situ, most of the measurements necessary to calculate rates of photochemical escape,\u201d Lillis said March 20.<\/p>\n

The measurements collected by MAVEN so far are \u201cconsistent\u201d an amount of oxygen loss from Mars over the last 3.5 billion years equivalent to about one-fifth of Earth\u2019s present-day atmospheric pressure through the photochemical process alone, according to Lillis.<\/p>\n

But there are other ways for atmospheric gases to escape from the tug of Mars and thin its atmosphere, and the photochemical process is just part of the picture.<\/p>\n

\u201cThe next steps include cross-sections in modeling other species, and combining it with other escape processes to put this whole story together because it\u2019s not just one escape process in isolation,\u201d Lillis said. \u201cThey do feed into each other, so that\u2019s the next step that the MAVEN team is embarking on. It\u2019s a very complicated system, and this will take us a few more years.\u201d<\/p>\n

Scientists will also couple MAVEN\u2019s atmospheric observations with the solar wind conditions at Mars to link the two data points and begin constructing a timeline of how molecules could have been stripped away from planet over the last 4 billion years.<\/p>\n

Each time MAVEN dips into the upper atmosphere, the spacecraft\u2019s science instruments scoop up the flow of particles in its path, giving researchers an idea of the velocity and direction the material is moving.<\/p>\n

One of MAVEN\u2019s instruments, the Solar Wind Ion Analyzer, spotted a halo of hydrogen around Mars that Jakosky said apparently fluctuates with the dustiness of the Martian atmosphere.<\/p>\n

\u201cWhat we think we\u2019re seeing here is an increase that corresponds to the dusty season,\u201d Jakosky said. \u201cThe dust changes temperatures in the atmosphere. That allows water to go up to high altitudes \u2026 So we think we\u2019re putting water closer, or farther, from the vicinity of the corona.\u201d<\/p>\n

Jakosky said the escape rate of hydrogen, an indicator of water, can vary by a factor of 10 with the Martian seasons.<\/p>\n

Particles need to be accelerated to a speed of around 8,500 mph (3.8 kilometers per second) at the outer edge of the atmosphere to permanently escape Martian gravity, according to Jakosky.<\/p>\n

\u201cOxygen ions can be grabbed by the solar wind and stripped off,\u201d Jakosky said. \u201cThat\u2019s the primary mechanism.\u201d<\/p>\n

The oxygen streams away off the poles and down a tail down the side of Mars facing away from the sun.<\/p>\n

According to Jakosky, the MAVEN science team believes oxygen ions 3.5 to 4 billion years ago were escaping the Martian atmosphere at a rate several orders of magnitude faster than today.<\/p>\n

\u201cThe driver is the extreme ultraviolet (EUV) photons coming from the sun,\u201d Jakosky said. \u201cAlthough the sun itself \u2014 the total energy \u2014 has been getting brighter through time, the EUV radiation is getting dimmer through time.\u201d<\/p>\n

When solar radiation reaches Mars, it ionizes atoms and molecules in the atmosphere. Scientists say the ionization process is critical to propel particles away from the planet, which is not shielded from the solar wind by a magnetic field like Earth.<\/p>\n

Astronomical observations of other sun-like stars tell scientists how the sun likely behaved billions of years ago.<\/p>\n

At the rate of hydrogen escape today, Jakosky said Mars could have lost from 11.5 feet to 78 feet (3.5 meters to 24 meters) of water from its surface over the last 4 billion years.<\/p>\n

But there\u2019s an important caveat.<\/p>\n

Scientists have not calculated how much more hydrogen left the ancient Martian atmosphere than leaves it today. A more active sun would have driven off more hydrogen, but experts have not ruled out a slower escape rate, especially if the atmosphere was more Earth-like.<\/p>\n

\u201cIt\u2019s very hard to know which way it goes, and I\u2019m just going to leave it at a constant rate,\u201d Jakosky said.<\/p>\n

The MAVEN team is also examining how much carbon dioxide has disappeared from Mars.<\/p>\n

\u201cAt the oxygen loss rate we measure, it would take about 2 to 4 billion years to remove all the oxygen in the atmospheric carbon dioxide, just multiplying the rate times 4 billion years,\u201d Jakosky said.<\/p>\n

Using Earth as a metric, that would be equivalent to an amount of carbon dioxide around 40 percent the pressure of Earth\u2019s atmosphere at sea level.<\/p>\n

\"\"
Artist\u2019s concept of the MAVEN spacecraft. Credit: NASA\/GSFC<\/figcaption><\/figure>\n

Scientists have also identified \u201csputtering\u201d events, in which blasts of radiation knock oxygen out of the atmosphere. This process is \u201cnegligible\u201d today,\u201d Jakosky said, but could have been much more prominent in the past, responsible for removing another chunk of carbon dioxide.<\/p>\n

Individual solar storms also cause temporary spikes in atmospheric escape. One eruption in March 2015 triggered a 20-fold increase in the atmospheric loss rate, and the activity relaxed once the solar system was over, Jakosky said.<\/p>\n

Solar storms were likely stronger and more common in the ancient solar system, and scientists question whether such events were responsible for much of the Martian atmosphere\u2019s thinning over time.<\/p>\n

Scientists have a way of calculating how much of the ancient Martian atmosphere has been ripped away. By measuring two isotopes of argon \u2014 one slightly heavier than the other \u2014 MAVEN can tell researchers what fraction of the atmospheric gas has been lost to space.<\/p>\n

That allows scientists to complete the puzzle and determine whether the escaping oxygen came from carbon dioxide, which makes up about 95 percent of Mars\u2019s present-day atmosphere, or from water, which is primarily locked in polar ice caps.<\/p>\n

The lighter type of argon is more prone to escaping, while Martian gravity keeps a firmer hold on the heavier argon isotope.<\/p>\n

\u201cRelatively speaking, the larger isotope is more abundant because it doesn\u2019t escape as much,\u201d Jakosky said.<\/p>\n

\u201cEssentially, two-thirds of the argon that was ever in the atmosphere has been lost to space,\u201d Jakosky said. \u201cThat really tells us that the loss of oxygen is coming from both water and carbon dioxide.\u201d<\/p>\n

That tells Jakosky and his team that most of Mars\u2019s air and water has leaked away into space.<\/p>\n

\u201cThe bottom line is that loss to space was certainly a major player, if not the major process, for changing Mars from having an early warm, wet climate in ancient times to the cold, dry climate we see today,\u201d he said.<\/p>\n

MAVEN is in an extended mission after completing its primary science campaign last year, and scientists hope more data will yield insights into how the atmosphere behaves year-to-year.<\/p>\n

The prime mission phase covered one Martian year, and the extended mission\u2019s funding is approved by NASA through 2018.<\/p>\n

But the spacecraft has enough fuel to operate for up to another decade, Jakosky said, and MAVEN may eventually be used more often as a data relay satellite for landers and rovers on the Martian surface.<\/p>\n

Officials are searching for the right balance between MAVEN\u2019s scientific mission and its secondary function as a communications orbiter. NASA\u2019s other Mars orbiters are aging \u2014 they have been at the red planet since 2001 and 2006 \u2014 but the European Space Agency\u2019s ExoMars Trace Gas Orbiter, which arrived in October 2016, could take on much of the relay responsibilities.<\/p>\n

\u201cThe long-term role of MAVEN as a relay asset is currently under discussion,\u201d Jakosky said. \u201cWe are carrying out regular relay passes with the (the Opportunity and Curiosity) rovers, and we\u2019ll see what happens as we get into interactions with InSight after it lands (in November 2018), especially in its commissioning phase, as well as with the Mars 2020 rover.\u201d<\/p>\n

Email the author.<\/i><\/b><\/p>\n

Follow Stephen Clark on Twitter: @StephenClark1.<\/strong><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

Artist\u2019s concept of a solar storm hitting Mars and stripping ions from the upper atmosphere. Credit: NASA\/GSFC Data collected by NASA\u2019s MAVEN spacecraft in its first two years at Mars confirm suspicions that the solar wind is blasting away the planet\u2019s atmosphere and helped transform the world from a warmer, wetter and potentially habitable world […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[3369,1860,472,3368,367,3370,1561,2311],"class_list":["post-14765","post","type-post","status-publish","format-standard","hentry","category-news","tag-bruce-jakosky","tag-heliophysics","tag-lockheed-martin","tag-lpsc-2017","tag-mars","tag-maven","tag-planetary-science","tag-solar-wind"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/14765"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=14765"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/14765\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=14765"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=14765"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=14765"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}