A Martian mystery that sparked years of debate \u2014 an alleged lake buried beneath miles of ice \u2014 now looks far less watery than scientists hoped.<\/p>\n
A new radar study from NASA\u2019s Mars Reconnaissance Orbiter (MRO) revisits the strange signal detected in 2018 by the European Space Agency\u2019s Mars Express (MARSIS), and the result isn\u2019t what anyone expected. With a sharper, more powerful radar technique, scientists at last got a clean look beneath the planet\u2019s south polar ice cap \u2014 and the evidence for an underground lake is slipping away.<\/p>\n
A stronger radar, a weaker signal<\/p>\n
The fuss began seven years ago, when the MARSIS instrument picked up an unusually bright radar reflection under 1,500 meters of polar ice. The signature resembled liquid water \u2014 or at least a briny lake, the only type that could remain unfrozen under Martian conditions.<\/p>\n
To test whether the 2018 signal was really liquid water, scientists needed to check it with NASA\u2019s SHARAD, MRO\u2019s onboard radar. But SHARAD\u2019s equipment couldn\u2019t see deep enough to pick up the signal\u2026 until now.<\/p>\n
In a recent study published in a peer-reviewed journal, Geophysical Research Letters, SHARAD scientists Gareth Morgan and Than Putzig describe how a newly developed maneuver \u2014 a \u201cvery large roll,\u201d rotating the spacecraft 120 degrees mid-orbit \u2014 finally gave the radar enough power to probe the depths.<\/p>\n
\u201cWe\u2019ve been observing this area with SHARAD for almost 20 years without seeing anything from those depths,\u201d Putzig said. But once the roll maneuver aimed the antenna directly at the ice, the radar dug in deeper than ever before.<\/p>\n
What the equipment found was the opposite of the 2018 claim: a faint return, not a bright one. And when MRO repeated the experiment over the adjacent region, the supposed signal disappeared entirely.<\/p>\n
\u201cThe lake hypothesis generated lots of creative work, which is exactly what exciting scientific discoveries are supposed to do,\u201d Morgan said. \u201cAnd while this new data won\u2019t settle the debate, it makes it very hard to support the idea of a liquid water lake.\u201d<\/p>\n
If not water, then what?<\/p>\n
Observations so far have shown Mars\u2019 south pole to be geologically messy: craters, buried terrain, and odd patches that reflect radar differently depending on their composition. Morgan and Putzig suggest a simple possibility \u2014 the spot where MARSIS saw the \u201clake\u201d might just be an unusually smooth slab under the ice, perhaps even an ancient lava flow.<\/p>\n
This would still explain the bright signal without requiring a reservoir of liquid water in one of the coldest, harshest regions of the planet.<\/p>\n
The technique itself might be the real breakthrough<\/p>\n
Even if the lake evaporates under closer scientific scrutiny, the new radar method is a win for future Mars exploration. The very large roll maneuver gives MRO a way to hunt for buried ice, rock layers, and subsurface resources that could support future human explorers.<\/p>\n
One target is already on the wishlist: Medusae Fossae, a massive equatorial formation that barely reflects radar at all. Some scientists say it\u2019s ash. Others think there might be deep, ancient ice hiding inside.<\/p>\n
\u201cIf it\u2019s ice, that means there\u2019s lots of water resources near the Martian equator, where you\u2019d want to send humans,\u201d Putzig said. \u201cBecause the equator is exposed to more sunlight, it\u2019s warmer and ideal for astronauts to live and work.\u201d<\/p>\n
What comes next<\/p>\n
MRO has been circling Mars since 2006, and with this new capability to see deeper beneath the surface, it may start re-examining old mysteries across the planet. Mars Express\u2019 original signal isn\u2019t entirely explained yet \u2014 the faint SHARAD return confirms something unusual is down there, just not liquid water.<\/p>\n
For now, a once-promising Martian lake has likely turned into dust and rock. But the method that disproved it might end up being the tool that uncovers something even better.<\/p>\n
Sources: NASA<\/a>, Geophysical Research Letters<\/a>, Science<\/a><\/p>\n