The atmosphere of Mars might be extremely thin but that doesn’t mean it is not a complex system. There are giant dust storms that envelop the whole planet, along with dramatic seasonal and daily variations. Understanding it all has not been easy and new research suggests that the entire Martian atmospheric system behaves as one.
Researchers used 10 years' worth of data from the European Space Agency (ESA) orbiter Mars Express to understand movement in the atmosphere. They found compelling evidence that phenomena once thought to only affect the lower atmosphere can also be seen at higher altitudes. The study is published in the Journal of Geophysical Research: Planets.
“The lower and middle levels of Mars’ atmosphere appear to be coupled to the upper levels: there’s a clear link between them throughout the Martian year,” lead author Beatriz Sánchez-Cano of the University of Leicester said in a statement. “We discovered a surprising and significant increase in the amount of charged particles in the upper atmosphere during springtime in the Northern Hemisphere, which is when the mass in the lower atmosphere is growing as ice sublimates from the northern polar cap.”
The polar regions of Mars are a mix of water ice and frozen carbon dioxide. Planetary scientists know that the polar caps change in size over the course of the seasons, but they just assumed that the gases would stay in the lower altitudes of the atmosphere. The data showed that when the ice sublimates in spring it moves higher and higher.
“This sublimation process was thought to mostly only affect the lower atmosphere – we didn’t expect to see its effects clearly propagating upwards to higher levels,” said ESA's Olivier Witasse, former ESA Project Scientist for Mars Express. “It’s very interesting to find a connection like this.”
Seasons on Mars are slightly different from those on Earth, because of the Red Planet's orbital parameters and axial tilt. In the Northern Hemisphere, spring is by far the longest season, lasting about seven months. To properly understand what goes on, it is necessary to have years and years' worth of data. Luckily Mars Express has been there since 2003 and it won’t stop anytime soon.
“This wealth of comprehensive and complementary observations by different instruments on Mars Express makes studies like this one possible and, together with ESA’s Trace Gas Orbiter and NASA’s MAVEN mission, is helping us to unravel the secrets of the Martian atmosphere,” concluded ESA Mars Express Project Scientist Dmitri Titov.