The researchers made the discovery using an instrument called the Nadir and Occultation for Mars Discovery (NOMAD), which is aboard the ExoMars Trace Gas Orbiter jointly operated by the European Space Agency (ESA) and Russia's Roscosmos.
By analyzing light passing through the Martian atmosphere, the team detected water vapor in the form of hydrogen chloride – a substance that had never been observed there prior to the detection. This finding could offer valuable insights into the Martian water cycle and how it changed over time.
"Measuring water isotopes (water variants with different molecular masses) is a crucial element of understanding how Mars as a planet has lost its water over time, and therefore how the habitability of Mars has changed throughout its history," said Manish Patel, a planetary scientist at the Open University in the U.K. and the co-principal investigator of NOMAD.
The presence of dried ancient valleys on the planet suggests that water once flowed on the surface of Mars. But much of Martian water is now locked up on the polar caps and underground. (Related: Geological curiosity: Mars "blueberries" reveal what ancient Mars may have looked like.)
The finding could also provide clues to some of the greatest mysteries of the Red Planet, including whether it is still geologically active. As the researchers wrote in a paper, which was published on Feb. 10 in the journal Science Advances, hydrogen chloride has been suggested as an indicator of active magmatic processes.
'This research is a key component in our quest to unearth the mysteries of the Red Planet," said Sue Horne, head of space exploration at the U.K. Space Agency.
Ultimately, the study might help answer the question of habitability. "Understanding water vapor on Mars would help answer the all-important question, was there life on Mars?" Horne said.
The study comes as the United Arab Emirates Space Agency's spacecraft Hope and the China National Space Administration's spacecraft Tianwen 1 entered orbit around Mars.
Hope reached the Red Planet on Tuesday and would stay in its current position for a few months before moving into its planned science orbit. This orbit would see Hope circling high over the planet's equator every 55 hours and hopefully allow scientists to study large-scale atmospheric phenomena on the planet.
Following this successful orbit insertion, the UAE became the fifth entity to reach Mars, joining the United States, Russia, ESA and India. Its Hope mission is scheduled to last for a full Martian year (687 days).
A day later, Tianwen 1 also pulled into orbit after nearly a yearlong trip into space, marking the first time that China reached Mars after a failed attempt almost a decade ago. The space probe Yinghuo-1 got stranded in Earth orbit when the rocket it was on failed in flight. The rocket eventually lost altitude and the spacecraft burned up in Earth's atmosphere.
China would attempt to place a lander and a robotic rover on the planet sometime in May. If successful, the China's machines would join the trio of rovers from the National Aeronautics and Space Administration's (NASA) that are now mapping the Martian surface.
China's lander would be dropped on Utopia Planitia, an enormous basin in the northern hemisphere that is believed to have been created by a meteorite impact and which NASA's Viking 2 lander visited in 1976. One goal of the Tianwen-1 mission is to gain a better understanding of the distribution of ice in the region, which future human colonists can use to sustain themselves.
Next week, NASA would also attempt to land its Perseverance rover on Mars. Launched during the summer last year, Perseverance would seek signs of ancient life and collect soil samples for possible return to Earth.
Learn more about Mars missions and studies about the planet at Space.news.