Mars loses water to space during warm, stormy seasons

All kinds of geological formations on Mars, alluvial fans, dry lake beds and eroded river valleys, suggest the Red Planet once hosted an abundance of water. Today, the water is mostly gone. What's left is largely locked up in the planet's polar ice caps. Scientists have been trying to figure out where all the water went and how fast it disappeared. New research, published this week in the journal Science, suggests Mars' seasonality may have dictated the rate at which water vapor was able to escape from the atmosphere and into space. In addition to the water trapped in the Red Planet's ice caps, trace amounts of water vapor persist in the Martian atmosphere. If these tiny water crystals rise high enough into the atmosphere, they can dissipate into space. To better understand this mechanism of water loss, scientists used data collected by the NASA spacecraft ExoMars Trace Gas Orbiter to produce vertical distribution of water in the Martian atmosphere. "TGO uses solar occultation method," researcher Anna Fedorova, an astrophysicist at the Space Research Institute in Moscow, told UPI in an email. "The presence of water vapor and their amount are determined using the spectroscopic signatures near 1.38 micrometer [infrared bands] by the NIR/ACS spectrometer." In other words, TGO studies how sunlight is absorbed as it passes through the Martian atmosphere in order to detect the presence of H2O. "The results were obtained using the analysis of absorption features of H2O and CO2 gases," Fedorova said. "For each occultation we have the vertical profiles of H2O density and temperature from CO2."

Scientists surveyed the data for links between temperature and water distribution and found the Martian atmosphere became supersaturated during the warmest portions of its orbit. Their findings suggest water is more likely to rise into the upper atmosphere and escape to space when Mars is warmer and wetter.

Authors of the new study suspect their findings will improve a variety of Martian climate models.

"Saturation is one of the key points in the water transport on Mars," Fedorova told UPI. "The climate models have to be updated to predict such levels of supersaturation and perform the necessary adjustments."

So far, TGO has only collected water vapor distribution data during Mars warm season, so there isn't enough data to understand the full picture of seasonal water distribution on Mars.

"We don't have information that the cold aphelion season is less supersaturated," Fedorova said.

That data will be available soon, and when it is, scientists will have more analysis to do.