Radar data collected by ESA’s Mars Express point to a pond of liquid water buried under layers of ice and dust in the south polar region of Mars.
Evidence for the Red Planet’s watery past is prevalent across its surface in the form of vast dried-out river valley networks and gigantic outflow channels clearly imaged by orbiting spacecraft. Orbiters, together with landers and rovers exploring the martian surface, also discovered minerals that can only form in the presence of liquid water.
ut the climate has changed significantly over the course of the planet’s 4.6 billion year history and liquid water cannot exist on the surface today, so scientists are looking underground. Early results from the 15-year old Mars Express spacecraft already found that water-ice exists at the planet’s poles and is also buried in layers interspersed with dust.
The presence of liquid water at the base of the polar ice caps has long been suspected; after all, from studies on Earth, it is well known that the melting point of water decreases under the pressure of an overlying glacier. Moreover, the presence of salts on Mars could further reduce the melting point of water and keep the water liquid even at below-freezing temperatures.
But until now evidence from the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument, MARSIS, the first radar sounder ever to orbit another planet, remained inconclusive.
It has taken the persistence of scientists working with this subsurface-probing instrument to develop new techniques in order to collect as much high-resolution data as possible to confirm their exciting conclusion.
Ground-penetrating radar uses the method of sending radar pulses towards the surface and timing how long it takes for them to be reflected back to the spacecraft, and with what strength. The properties of the material that lies between influences the returned signal, which can be used to map the subsurface topography.
The radar investigation shows that south polar region of Mars is made of many layers of ice and dust down to a depth of about 1.5 km in the 200 km-wide area analysed in this study. A particularly bright radar reflection underneath the layered deposits is identified within a 20 km-wide zone.
Analysing the properties of the reflected radar signals and considering the composition of the layered deposits and expected temperature profile below the surface, the scientists interpret the bright feature as an interface between the ice and a stable body of liquid water, which could be laden with salty, saturated sediments. For MARSIS to be able to detect such a patch of water, it would need to be at least several tens of centimetres thick.
“This subsurface anomaly on Mars has radar properties matching water or water-rich sediments,” says Roberto Orosei, principal investigator of the MARSIS experiment and lead author of the paper published in the journal Science today.
“This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered.”
“We’d seen hints of interesting subsurface features for years but we couldn’t reproduce the result from orbit to orbit, because the sampling rates and resolution of our data was previously too low,” adds Andrea Cicchetti, MARSIS operations manager and a co-author on the new paper.
“We had to come up with a new operating mode to bypass some onboard processing and trigger a higher sampling rate and thus improve the resolution of the footprint of our dataset: now we see things that simply were not possible before.”
The finding is somewhat reminiscent of Lake Vostok, discovered some 4 km below the ice in Antarctica on Earth. Some forms of microbial life are known to thrive in Earth’s subglacial environments, but could underground pockets of salty, sediment-rich liquid water on Mars also provide a suitable habitat, either now or in the past? Whether life has ever existed on Mars remains an open question, and is one that Mars missions, including the current European-Russian ExoMars orbiter and future rover, will continue to explore.
“The long duration of Mars Express, and the exhausting effort made by the radar team to overcome many analytical challenges, enabled this much-awaited result, demonstrating that the mission and its payload still have a great science potential,” says Dmitri Titov, ESA’s Mars Express project scientist.
“This thrilling discovery is a highlight for planetary science and will contribute to our understanding of the evolution of Mars, the history of water on our neighbour planet and its habitability.”
Mars Express launched 2 June 2003 and celebrates 15 years in orbit on 25 December this year.
Full study “Lake spied deep below polar ice cap on Mars”
Far beneath the deeply frozen ice cap at Mars’s south pole lies a lake of liquid water—the first to be found on the Red Planet. Detected from orbit using ice-penetrating radar, the lake is probably frigid and full of salts—an unlikely habitat for life. The lake resembles one of the interconnected pools that sits under several kilometers of ice in Greenland and Antarctica, but the processes that gave rise to a deep lake on Mars are likely to be very different. The discovery is sure to intensify the hunt for other buried layers of water that might be more hospitable.
Water detected on Mars, raising the possibility of finding life on Red Planet
There’s water on Mars.
For the first time, scientists have detected a lake of salty water under the Martian ice, a study released Wednesday said. The lake is about a mile under the surface and stretches 12 miles across.
The presence of water under the Martian polar ice caps has long been suspected but not seen until now, the study said.
The discovery raises the possibility of finding life on the Red Planet. “Without water, no form of life as we know it could exist,” said Anja Diez of the Norwegian Polar Institute.
Astronomers used radar data from the orbiting European spacecraft Mars Express to find the water. They spent at least two years checking over the data to make sure they had detected water and not ice or another substance.
“I really have no other explanation,” said study lead author Roberto Orosei of Italy’s National Institute of Astrophysics in Bologna. “This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered.”
Although evidence of water was obvious on the planet’s surface in the form of vast dried-out river valley networks from eons ago, Mars’ climate does not allow for water on the surface today.
The discovery could offer fresh clues about how Earth’s neighbor so profoundly transformed billions of years ago from a warmer, wetter world to its freeze-dried state today, according to Scientific American.
Cassie Stuurman, a geophysicist at the University of Texas, said that “if these researchers are right, this is the first time we’ve found evidence of a large water body on Mars.”
The area is similar to that of lakes found beneath the Antarctic and Greenland ice sheets on Earth, which also were detected using radar scans.
“This thrilling discovery is a highlight for planetary science and will contribute to our understanding of the evolution of Mars, the history of water on our neighbor planet and its habitability,” said Dmitri Titov of the European Space Agency.
The study was published Wednesday in the peer-reviewed journal Science.
In USA Today
Evidence detected of lake beneath the surface of Mars
A lake of liquid water has been detected by radar beneath the southern polar ice cap of Mars, according to a new study by Italian researchers from the Italian Space Agency, published Wednesday in the journal Science.
Evidence was gathered by the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument, also known as MARSIS, on the European Space Agency’s Mars Express spacecraft.
Between May 2012 and December 2015, MARSIS was used to survey the Planum Australe region, which is in the southern ice cap of Mars. It sent radar pulses through the surface and polar ice caps and measured how the radio waves reflected back to Mars Express.
Those pulses reflected 29 sets of radar samples that created a map of drastic change in signal almost a mile below the surface. It stretched about 12.5 miles across and looked very similar to lakes that are found beneath Greenland and Antarctic ice sheets on Earth. The radar reflected the feature’s brightness, signaling that it’s water.
“We interpret this feature as a stable body of liquid water on Mars,” the authors wrote in the study.
The study authors ruled out any other causes for this brightness, apart from water-rich sediments.
“This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered,” said Roberto Orosei in a statement. Orosei is the lead study author and principal investigator of the MARSIS experiment.
Previously, there has been some suggestions about water on Mars, like droplets of water condensing on the Phoenix lander or as the possible cause of recurring slope lineae, which are seasonal dark streaks on Martian slopes. But there hasn’t been evidence of stable bodies of water until now, the researchers said. However, the presence of liquid water at the base of Martian polar caps was first hypothesized in a study 31 years ago.
Given its location beneath the polar ice cap, the water is expected to be below the freezing point of water. But salts like magnesium, calcium and sodium already found on Mars could help the water to form a brine, which would lower the melting point to allow the lake to remain liquid.
On Earth, lakes exist below the Antarctic ice sheet even though the mean annual temperature is around negative 76 degrees Fahrenheit. Brine lakes on Earth can remain liquid at 8.6 degrees Fahrenheit, according to the study. In comparison, salty ocean water freezes at 28.4 degrees Fahrenheit, according to the National Oceanic and Atmospheric Administration.
Much like our own ice sheets, the polar ice caps change depending on the climate and act as archives for what has happened in the past. Learning more about these caps can reveal Mars’ climate history.
“The long duration of Mars Express, and the exhausting effort made by the radar team to overcome many analytical challenges, enabled this much-awaited result, demonstrating that the mission and its payload still have a great science potential,” said Dmitri Titov in a statement, Mars Express project scientist. “This thrilling discovery is a highlight for planetary science and will contribute to our understanding of the evolution of Mars, the history of water on our neighbor planet and its habitability.”
But how reliable are these detections?
Outside experts have not been able to confirm these findings with other radar detections, like SHARAD, the Shallow Radar sounder onboard the Mars Reconnaissance Orbiter.
“We don’t see the same reflector with SHARAD, not even when we recently summed together [thousands] of observations to create CATSCAN-like 3-D views of both polar caps,” Nathaniel Putzig, Mars Reconnaissance Orbiter SHARAD deputy team leader and senior scientist at the Planetary Science Institute, said in an email.
“We’re hoping to carry out that same imaging process with the MARSIS data next. I’m excited to see how the 3-D imaging will clarify the view of this detection and whether we will find similar ones elsewhere beneath the polar caps.”
ESA’s Mars Express Finds Evidence For Salty Lake Under Mars’ South Pole
The European Space Agency’s (ESA) Mars Express orbiter spacecraft has found radar evidence for a very ancient salty lake underneath the ice at the Martian south pole.
Although the results published today in the journal Science are preliminary at best, radar data collected by ESA’s Mars Express point to a pond of liquid water buried under layers of ice and dust in Mars’ south polar region.
“If this is right, then the liquid must be maintained by a high salt content—a hypersaline solution. So it is liquid water, but very saline,” Cornell University planetary scientist Jonathan Lunine, who wasn’t involved in the study, told me. “A dry lake would not provide the radar return they describe.”
The orbiter reveals that Mars’ south polar region is composed of layers of dust and ice down to a depth of some 1.5 km over a 200-km-wide area analyzed in this study, notes ESA. The space agency reports that a particularly bright radar reflection underneath the layered deposits is identified within a 20-km-wide zone.
“We’d seen hints of interesting subsurface features for years but we couldn’t reproduce the result from orbit to orbit, because the sampling rates and resolution of our data was previously too low,” adds Andrea Cicchetti, MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument operations manager and a co-author on the paper. “We had to come up with a new operating mode to bypass some onboard processing and trigger a higher sampling rate and thus improve the resolution of the footprint of our dataset. Now we see things that simply were not possible before.”
The best guess is that this subsurface anomaly has radar properties matching water or water-rich sediments, Roberto Orosei, MARSIS’s principal investigator and lead author of the paper, said in a statement. “This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered,” he said.
ESA notes that the finding is somewhat reminiscent of Lake Vostok, discovered some 4-km below the ice in Antarctica. Some forms of microbial life are known to thrive in Earth’s subglacial environments, but could underground pockets of salty, sediment-rich liquid water on Mars also provide a suitable habitat, either now or in the past?
The possibility of an ocean under the ice cap — combined with the discovery of organic molecules at Gale Crater by NASA’s Curiosity rover — raises the possibility of microbial life existing on Mars at the present time, Lunine says in a statement.
Underground Lake of Liquid Water Detected on Mars
Just a mile or so beneath the surface, near the south pole of Mars, there is a reservoir of briny water sloshing and churning below layers of ice and rock.
This subglacial lake, discovered by a ground-penetrating radar on the Mars Express spacecraft, is about 20 kilometers (12.4 miles) wide and perhaps no more than a meter deep. Its discovery is the latest piece of evidence that suggests water was not only present on Mars in the past but is still flowing in some capacity today. The findings, if confirmed by future observations, would be the most significant discovery of liquid water on Mars to date.
Scientists already had little doubt that there was, at one point, liquid water on Mars, thanks to tiny spherical deposits discovered by the Opportunity rover in 2004 and the comprehensive mineralogy studies conducted by the Curiosity rover. The evidence suggests that vast lakes and rivers dominated the surface of Mars billions of years ago. What’s more, tantalizing clues have continued to imply the existence of liquid water on Mars today. Condensation was measured on the Phoenix lander in 2009, and dark streaks spotted on Martian dunes may be evidence of briny water (although more recent examination suggests they could be avalanches of dry sand).
This new discovery of a subterranean water deposit, outlined in a new paper in Science,suggests water is indeed underneath the red sands of Mars. Perhaps the Red Planet even has entire subsurface lake systems like those beneath Antarctica.
A Breakthrough 15 Years in the Making
Mars Express is a European Space Agency probe that has been orbiting the fourth planet from the sun since December 2003. A year and a half after it arrived, the craft deployed two 20-meter radar booms, forming a 40-meter antenna. The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument came online. Since then, MARSIS has been studying Mars with radar signals to learn more about the planet’s interior structure and composition.
In 2007, the instrument detected something interesting. Near the Mars southern polar ice cap, it found strong reflections of radar signals—differences between two layers known as echoes. Strong echoes imply a big difference in what’s called dielectric permittivity.
“In the case of Mars, and also in the case of Earth, liquid water is the material that certainly would produce the strongest reflections,” says Roberto Orosei, a co-investigator of the MARSIS instrument at the University of Bologna in Italy and lead author of the new study.
The strong radar echoes in 2007 wound up being the result of a layer of icy carbon dioxide on the surface of Mars rather than liquid water beneath. “CO2 ice is very transparent and is able to let the radar pulse penetrate into the ice much better than pure water ice,” Orosei says, which is why it mimicked the signal one would expect from underground liquid water. However, he says, many believed the CO2 conclusions “were not the end of the story.”
Liquid Water Discovered on Mars
Continued observations proved difficult. “The real problem was that observations over the same place in different moments would reveal different results,” Orosei says. “So we would see a bright reflection on a certain area one day, and then we would fly over the same area maybe a week later, a month later… and we would not see the same strong reflection we would see ordinarily.”
Finally, the MARSIS engineers figured out what was thwarting their observations. It was the way their own spacecraft processed the data. “The radar by itself will produce a very high amount of data… [so] it’s necessary to sum together many pulses, more than 100 at a time,” Orosei says. This method of averaging the information meant that sometimes the data contained a small, high reflectivity area, while other times it had mysteriously disappeared.
“It was something that would really be frustrating in hindsight because we were of course spending years and years debating the possible causes, when in fact the solution really was to change the processing scheme of the spacecraft,” Orosei says
Even after this breakthrough, the team spent years taking more observations of the south pole region. Mars Express does not repeat the exact same orbit of Mars, meaning long gaps of time can separate flights over the same area. In addition, the team could gather useful observations only at low altitudes and when the spacecraft was on the night side of Mars because the sun excites the ionosphere of the planet, which blocks radar signals. In total, it took three and a half years to obtain 29 observations of the target location.
The scientist who designed MARSIS and who remained most adamant that the signals pointed to a subglacial lake, Giovanni Picardi, passed away during those years. “Professor Picardi… died in 2015, just a few months away from the completion of the data acquisition above the area. So it was really tragic that he could not live to see the end of this work,” Orosei says.
Even if Picardi wasn’t there to see, the MARSIS team realized his dream and revealed a frigid reservoir of liquid water beneath the southern polar ice cap of Mars. The implications for complex systems of subsurface lakes could revitalize the debate about whether microorganisms could exist beneath the surface of Mars to this very day.
“It was a long march, a sort of long march through the desert, and we are finally out of it,” Orosei says. “It’s like a dark cloud has gone away.”
Lakes Upon Lakes?
The study says the subglacial lake on Mars is cold indeed, and rather salty. Water ice that is near the melting point is opaque to radio waves, and so the ice above the lake must be well below freezing. Accordingly, the subglacial water must be at least negative 10 degrees Celsius.
For this to be possible, the reservoir must be saturated with salts—likely salts of sodium, magnesium, and calcium, which have been discovered on the Martian surface. These salts can reduce the melting point of water to negative 74 degrees C, so the subglacial lake is likely between this temperature and around negative 10 or 20 degrees.
“From what I think we have learned about this subglacial lake, the most likely analogue for this environment is the subglacial lake that was recently discovered in Canada… in which the lake itself is in contact with a deposit of salt, and so it is very very salty,” Orosei says.
Such subglacial lakes on Earth have been shown to support life in some cases. “There are microorganisms that are capable of surviving well below zero even without being in contact with water, and there are microorganisms that can use the salt, presumably the salt in the water on Mars… for their metabolism.”
The most intriguing possibility is that this Martian lake is not alone, but rather part of an extensive network expanding across the south polar region of Mars. “Data provide some hints that this single lake is not a unique finding,” Orosei says. “We do see bright spots in other areas.” MARSIS, however, does not have the technological capability to look for channels or rivers connecting a system of lakes.
“It would be a very different story if this was just an isolated patch of water produced by some thermal anomaly in the crust, let’s say, or if indeed the conditions under the polar caps are such that you have a fully connected hydraulic system like you have in Antarctica, in which most of the subglacial lakes are connected to each other so that material, and even life, potentially, could move from place to place,” Orosei says.
But before we envision such a thing, follow-up observations must confirm that this one lake really does exist. Because for all the exciting data that has been obtained by MARSIS, there is one major problem: Another radar orbiting Mars, the Shallow Radar (SHARAD) on NASA’s Mars Reconnaissance Orbiter (MRO), has not been able to detect the underground reservoir at all.
“The problem is SHARAD is operating at a much higher frequency, and we were almost shocked to discovered that SHARAD was seeing absolutely nothing on the areas in which we were seeing the bright reflections with MARSIS,” Orosei says. The MARSIS team believes that irregularities on the surface of the southern polar ice cap could scatter the radar signals of SHARAD, which operate at 20 megahertz compared to four or five megahertz for MARSIS, preventing it from seeing the reservoir of water.
Daniel Nunes, the Instrument Scientist for SHARAD with NASA’s Jet Propulsion Laboratory who did not participate in the new study, confirms that SHARAD has had trouble mapping the southern polar ice cap of Mars.
“There’s something intrinsic in the southern polar cap that causes the SHARAD signal to see not as deeply as it does in the northern polar cap,” Nunes told Popular Mechanics. “And as a result, we don’t see with SHARAD that interface between the ice and the underlying surface. So if there is a lake there, SHARAD wouldn’t see it.”
However, Nunes also cautions that scrutiny of the MARSIS team’s findings is required before we can make any hard and fast conclusions.
“I think there’s going to be a healthy debate on whether this interpretation is correct,” Nunes says. “One thing that we need to be also cautious about is that there are different kinds of materials that can produce large reflections as well… [and] I think the new processing has to withstand verification by the community,” he says, referring to the MARSIS team’s new data processing to remove errors from averaging.
Regardless, Nunes says that the MARSIS team’s findings are “a very exciting development.”
A new Mars orbiter in the works might be able to solve the mystery. The 2020 Chinese Mars Mission will carry a radar sounding instrument that will operate in between the frequencies of MARSIS and SHARAD. If this Chinese mission also spots radar reflections that indicate a subglacial lake in the same location as MARSIS, the implications for possible water ecosystems beneath the surface of Mars will be profound.
“I can only say that there is a new open door we have to go through and explore what’s behind that, and from the results we get, we will learn if Mars really is connected to the Earth somehow in terms of the persistence of a habitat for life,” Orosei says.
In Popular Mechanics