When studying rocky worlds outside the solar system, researchers use Mars as a laboratory on a planetary scale.
How long could a rocky planet, similar to Mars, remain habitable if it orbited a red dwarf? NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission, which has been studying our neighbor since November 2014, will help answer this difficult question.
“The observations of the MAVEN mission indicate that the Red Planet has gradually lost a significant part of its atmosphere, and this has changed the conditions on it,” says David Brain, a scientist for the MAVEN mission at the University of Colorado (USA).
Planetary laboratory
When studying rocky worlds outside the solar system, researchers use Mars as a laboratory on a planetary scale. At the fall meeting of the American Geophysical Union on December 13, 2017 in New Orleans, USA, David Brain shared with colleagues how the MAVEN data will affect the determination of the habitability of rocky planets orbiting distant stars.
Spacecraft MAVEN. Credit: NASA.
MAVEN has a suite of instruments on board that measure the loss of the Martian atmosphere. Studies show that much of it has escaped into space "thanks to" a combination of chemical and physical processes, and the data from the instruments provide clues as to what role each of them played.
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Over the past three years, the Sun has experienced periods of increasing and decreasing activity, while Mars has experienced solar storms, solar flares and coronal mass ejections. These changes have provided MAVEN with a unique opportunity to observe the behavior of the atmosphere under various conditions.
Red dwarf and hypothetical Mars
David Brain and his colleagues applied this knowledge to a hypothetical Mars-like planet orbiting a red dwarf star (the most common class of stars in our Galaxy). They suggested that the exoplanet, like Mars, is located at the edge of the habitable zone. But, since red dwarfs are weaker than the Sun, their habitable zone is much closer. It turned out that due to the extreme ultraviolet radiation of the star and the close orbit, the planet will receive 5-10 times more UV than Mars receives. This increases the amount of energy available for the processes responsible for the escape of the atmosphere.
The location of a hypothetical Mars in the habitable zone orbiting a red dwarf compared to the location of real Mars in the solar system. Credit: NASA's Goddard Space Flight Center.
Based on data from MAVEN, the researchers calculated that the exomars atmosphere could lose 3-5 times more charged particles in a process called ion leakage and 5-10 times more neutral particles as a result of photochemical escape. In addition, since there will be many charged particles in the atmosphere, it will begin to "spray". The spraying process is similar to a game of billiards: charged particles crash into molecules, pushing some of them into space and pushing others against their neighbors. This chain reaction significantly increases the rate of atmospheric loss. Finally, the hypothetical planet will face the loss of light molecules like hydrogen.
In general, finding a hypothetical Mars on the edge of the habitable zone of a calm red dwarf could shorten the life span of about 5-20 times. If the planet is placed in an active red dwarf system, this period will be reduced by about 1000 times.
Extenuating circumstances
Nonetheless, David Brain considered the worst-case scenario by placing Mars in the middle of a red dwarf. Another planet may have some mitigating factors, such as active geological processes, a magnetic field, or a larger size. All this allows you to replenish, protect and retain the atmosphere for a longer period.
“The habitability of distant worlds is one of the most important topics in astronomy, and these estimates demonstrate one way to use knowledge about Mars and the Sun in the search for life in the Universe,” concluded Bruce Yakoski, Principal Investigator for MAVEN at the University of Colorado (USA).
Roman Zakharov