by Joe Palca
This is the south polar cap of Mars
appeared to the Mars Orbiter Camera
Mars Global Surveyor on April 17, 2000.
underground lake was found near here.
An Italian team of scientists says it has strong evidence of a
subsurface lake of liquid water on Mars.
It's a discovery that
adds to the speculation that there could once have been life on Mars
- and raises the possibility that it might be there still today,
since liquid water is an essential ingredient for life.
The evidence comes from an instrument called
MARSIS aboard the European Space
Mars Express spacecraft in orbit
around the Red Planet.
MARSIS is a special kind
of radar called ground-penetrating radar.
radars use radio signals that are capable of penetrating into
the ground and then get reflections from the material under the
surface," says Roberto Orosei, principal investigator on MARSIS
and a planetary scientist at the Italian National Institute for
Such radars are useful
when searching for liquid water,
"because water is a
very strong radar reflector," he says.
From May 2012 through
December 2015, the Mars Express radar mapped an area near the south
pole of Mars.
When Roberto Orosei and his colleagues analyzed the data,
they saw what looked like a lake of water about 12 miles in diameter
and a mile below a surface layer made up of water ice and dust.
There are hundreds of
these subglacial lakes on Earth, mostly
But Orosei and his colleagues knew better than to run right out and
announce to the world they'd found liquid water on Mars. Remarkable
claims that seem too good to be true frequently are.
Instead, they tried to come up with as many other explanations as
possible for what they were seeing.
literally a couple of years of... discussion, debate and let's
say general head-scratching," Orosei says, "we really felt
confident that any other explanation would fail."
Or, he adds, paraphrasing
"Once you exclude
everything that is impossible, what remains necessarily has to
be the truth."
A report on the discovery
Evidence of Bubglacial Liquid Water on Mars) of the
underground lake appears in the journal Science.
Water detection under the south pole of Mars.
Credit: Context map: NASA/Viking;
THEMIS background: NASA/JPL-Caltech/Arizona State University;
MARSIS data: ESA/NASA/JPL/ASI/Univ. Rome;
R. Orosei et al 2018
Other scientists are impressed.
"I think this is
extremely strong evidence that there is liquid water beneath the
poles in this south polar layered terrain on Mars, which is
extremely exciting," says Ellen Stofan, the John and Adrienne
Mars Director at the Smithsonian's National Air and Space
Before joining the
museum, she was a member of the MARSIS science team.
Ellen Stofan says finding
liquid water is something scientists are extremely interested in
"because life here on
Earth evolved in liquid water. It stayed in the oceans for over
a billion years. And so as we go outward from the Earth, looking
for evidence of life beyond Earth, we're always looking for
The water in the Martian
underground lake is probably salty, otherwise it would freeze solid,
even deep in the ground, Stofan says.
And the salts are mostly
likely made up of something called
"which are very toxic
to life here on Earth. But on Mars, who knows?"
It's not clear where the
water the Italian team found is coming from, and it's not certain
there are any other underground lakes to be found.
But you can bet the new results will encourage others to look...