A large underground lake has been discovered on Mars, offering an exciting new target in the search for life on the red planet.
Italian scientists working on the European Space Agency’s Mars Express mission announced on Wednesday that for the first time, a large body of liquid water — not just the momentary damp spots seen in the past — had been detected by radar measurements beneath the ice cap near the Martian south pole.
Because water is a critical building block for life, the discovery has generated considerable speculation that some form of life could have existed or may still exist underground.
“Water is there,” said Enrico Flamini, the former chief scientist of the Italian Space Agency who oversaw the research during a news conference.
“It is liquid, and it’s salty, and it’s in contact with rocks,” he added. “There are all the ingredients for thinking that life can be there, or can be maintained there if life once existed on Mars.”
The body of water appears similar to underground lakes found on Earth in Greenland and Antarctica. On Earth, microbial life persists down in those dark, frigid waters. The ice on Mars would also shield the Martian lake from the damaging radiation that bombards the planet’s surface.
For decades, planetary scientists have pored over the puzzling surface of Mars. Gargantuan canyons, possible shorelines and hints of lakebeds can be seen, but few signs of liquid water exist today on a planet that is cold and dry. The watery features appear to have been carved several billion years ago when Mars was warmer and wetter, leading to the notion that life could have arisen during the early cozy conditions.
If life did arise, it could have moved underground as the surface cooled and dried.
The current findings, however, “cannot say anything more,” Dr. Flamini said. “We may guess about what are the conditions and if the conditions are favorable.”
Roberto Orosei, a co-investigator on the radar instrument and lead author of the paper published on Wednesday in the journal Science, said they could not measure the thickness of the lake, but that it had to be at least a yard or so thick for the radar pulses to bounce back. A back-of-the-envelope calculation indicated billions of gallons of liquid water.
Mars Express entered orbit around Mars in 2003. Taking care not to damage the rest of the spacecraft, the team in charge of the instrument — Mars Advanced Radar for Subsurface and Ionosphere Sounding, or Marsis — took two years to deploy the radar’s 130-foot-long booms.
Once the instrument was working, it sent back uncertain, inconsistent findings over this polar region. In essence, the onboard computer was averaging 100 of more of the radar pulses, washing out the results. The scientists were able to modify the procedure and send back the raw data to Earth. That revealed bright reflections in a triangular region as the spacecraft passed multiple times. Intense pressure of the overlying ice could have melted some of the ice into a liquid.
The region corresponded to a basin, adding to speculation that liquid water had flowed into this spot.
“Water tends to collect in lower topography,” Dr. Orosei said.
Dr. Orosei said the scientists checked other possible explanations, like carbon dioxide ice, for the bright reflections, but those did not match the radar observations.
“We came thus to the conclusion that the only possible explanation for the bright reflection was the presence of liquid water,” he said.