The MAVEN (Mars Atmosphere and Volatile Evolution) mission team is always conducting exciting, new scientific research. Many of these results are then published in leading academic journals. In our Publication Highlight series, we’ll be highlighting interesting papers in a jargon-free format. In this one, we looked at “Solar cycle and seasonal variability of H [hydrogen] in the upper atmosphere of Mars,” which Dr. Majd Mayyasi and colleagues published in the journal Icarus in September 2022.
This figure from Mayyasi et al. shows the seasonal change in how much Hydrogen there is in the upper atmosphere, demonstrating changes that peak in the Southern Summer/Northern Winter season at Mars. Each color represents a Martian year, and the dotted line at Ls 180 degrees indicates the seasonal transition from aphelion to perihelion in Mar’s orbit.
A saying that’s often heard on Earth, the only constant is change, is also true for space. Galaxies drift slowly together and apart. Earth and Mars change seasons because of the slight tilt of their axes. The Sun cycles through periods of more and less activity. Constant changes, no matter how small, can lead to some big discoveries. In a recent study by Mayyasi et al., new observations reveal that the rate at which hydrogen escapes from Mars to space, and the corresponding loss of water, depends on seasonal variability on the planet. This discovery can further explain the loss of the substantial amounts of water that over millions of years slowly changed Mars into the arid environment it is today.
Through various explorations of present-day Mars, scientists know that the planet used to have lots of water billions of years ago. As Mars was stripped of its atmosphere, water escaped from the planet into space. To understand why liquid water, made up of hydrogen and oxygen, is no longer present, multiple surface- and space-based missions, including MAVEN, are studying the rate of hydrogen escape—one of the main factors that control present-day water loss—from the Red Planet. The study by Mayyasi et al. took this research a step further by looking at whether the Martian seasons and the Sun’s solar cycle controls how much hydrogen is able to escape.
MAVEN went into orbit around Mars in 2014, just as the Sun was entering a phase of declining activity in its 11-year cycle. Thanks to the longevity of the MAVEN mission, which continues to orbit Mars, scientists have had the opportunity to make long-term observations of Mars during changing solar activity, to investigate how solar activity is related to hydrogen escape. The MAVEN mission has also been able to observe seasonal changes through multiple Martian years. MAVEN observations of solar ultraviolet light scattered by hydrogen atoms in the atmosphere of Mars demonstrate a consistent seasonal pattern. This allowed Mayyasi et al. to also looked at how hydrogen escape is affected by the change of seasons. These observations led the team’s conclusion that seasonal variability dominates the planet’s hydrogen escape rate.
In fact, the amount of hydrogen concentrated in the outer region of the atmosphere, where it is most likely to escape, can vary by more than a factor of 10 between the points when Mars is farthest and closest to the Sun in its orbit. The hydrogen escape rate from the planet’s seasonal variability determined in Mayyasi et al. is sufficient to explain the loss of a layer of water that is an average of 6.5 meters deep across the entire planet.
As the Sun approaches another peak in its activity cycle in 2025, MAVEN scientists are looking forward to observing how the increased activity will compare to the effects of Mars seasons. With each passing season and solar cycle, who knows what else we will discover about our neighboring planet?
To read the full Mayyasi et al. publication, visit: https://www.sciencedirect.com/science/article/pii/S0019103522003852
By Willow Reed – MAVEN Communications Lead
