Water on Mars

Where is the water on Mars?

Almost all of it is ice. NASA says there is water on Mars today, but the atmosphere is too thin for liquid water to exist for long on the surface.[1]

• At the poles. The layered ice at the south pole is at least 90% water ice, reaches 3.7 km (2.3 mi) deep and covers an area bigger than Texas. Melted, it would cover the whole planet about 11 m (36 ft) deep.[2] The bright cap on top at the south pole is mostly frozen carbon dioxide, about 85%, ESA says.[3]
• Just under the ground. NASA’s Phoenix lander dug up bright chunks of ice in the Martian arctic in June 2008 and watched them vanish into vapor over four days.[4] Orbiter radar has found a buried ice sheet in Utopia Planitia holding about as much water as Lake Superior.[5] A 2019 NASA map showed ice as little as 2.5 cm (1 inch) down in places; a scientist on the study said you could dig it up with a shovel.[6]

Is there liquid water on Mars?

Not on the surface. Water there freezes or turns to vapor quickly, because the air is so thin.[1] Whether liquid water hides deep underground is debated:

• Under the south pole? In 2018 a team led by Roberto Orosei, using the MARSIS radar on ESA’s Mars Express, reported a bright radar reflection about 1.5 km below the surface, under the layered ice, and interpreted it as a lake of salty water.[7] Later studies found that frozen clays can make the same reflection, and in 2025 NASA’s Mars Reconnaissance Orbiter radar picked up only a faint reflection there, more likely from a layer of rock and dust, NASA said.[8][9]
• Deep in the crust? A 2024 study of marsquakes recorded by NASA’s InSight lander found that rock 11.5 to 20 km (7 to 12 mi) down saturated with liquid water “best explains” the data.[10] Other scientists say the data don’t require water.[11]
• Dark streaks on slopes? In 2015 NASA said seasonal streaks on steep slopes pointed to flowing salty water.[12] A 2017 study found they behave like dry, flowing sand instead.[13]

Did Mars have oceans?

Mars had rivers and lakes: NASA lists ancient river valleys, deltas and lakebeds, and huge floods about 3.5 billion years ago.[1] Gale Crater held a lake more than 3 billion years ago, and Jezero Crater held one fed by a river delta.[21][22] NASA’s two working rovers have explored those old lakebeds; what they have found about life has its own page.

An ocean is less certain. A 2015 NASA study estimated that about 4.3 billion years ago Mars had enough water to cover the planet 137 m (450 ft) deep, more likely as an ocean covering almost half of its northern hemisphere.[14] In 2025 radar data from China’s Zhurong rover showed buried layers that look like beach deposits. The authors call the ocean idea controversial, but say their findings “provide support for the existence of an ancient Martian ocean in the northern plains.”[15]

Where did the water go?

Some escaped to space. NASA’s MAVEN orbiter found that Mars lost most of the gas its atmosphere ever had,[16] and the 2015 study estimated Mars has lost 87% of its early water.[14] A 2021 study found that much may never have left: between 30% and 99% of Mars’s early water could be locked in minerals in its crust.[17] Dust storms speed up the loss: during the 2018 global storm, Mars lost as much water in 45 days as it usually does in a whole Martian year, NASA said.[18]

Could astronauts use it?

NASA’s planning studies assume so. A 2015 NASA workshop on landing sites set a target of about 20 metric tons of local water per crew, mostly to make oxygen and methane propellant for the ascent vehicle that would lift the crew off Mars; a 2016 NASA study of ways to use local resources built on that figure.[19] NASA has since mapped buried ice in the mid-latitudes within about 1 m (3 ft) of the surface, which it says could provide drinking water and a key ingredient for rocket fuel.[20]

Sources

1. NASA Science — Mars: FactsPrimary · checked Oct 4, 2026
2. NASA JPL — Mars’ South Pole Ice Deep and WidePrimary · checked Oct 4, 2026
3. ESA — Mars Express science highlights #4: Probing the polar regionsPrimary · checked Oct 4, 2026
4. NASA JPL — NASA Phoenix Mars Lander Confirms Frozen WaterPrimary · checked Oct 4, 2026
5. NASA JPL — Mars Ice Deposit Holds as Much Water as Lake SuperiorPrimary · checked Oct 4, 2026
6. NASA JPL — NASA’s Treasure Map for Water Ice on MarsPrimary · checked Oct 4, 2026
7. ESA — Mars Express detects liquid water hidden under planet’s south polePrimary · checked Oct 4, 2026
8. NASA JPL — Clays, Not Water, Are Likely Source of Mars ‘Lakes’Primary · checked Oct 4, 2026
9. NASA JPL — NASA Orbiter Shines New Light on Long-Running Martian MysteryPrimary · checked Oct 6, 2026
10. PNAS — Liquid water in the Martian mid-crust (Wright, Morzfeld and Manga, PNAS, 2024)Primary · checked Oct 4, 2026
11. PNAS — Liquid water might not be the only answer (Xiao et al., PNAS letter, 2025)Primary · checked Oct 4, 2026
12. NASA JPL — NASA Confirms Evidence That Liquid Water Flows on Today’s MarsPrimary · checked Oct 4, 2026
13. NASA JPL — Recurring Martian Streaks: Flowing Sand, Not Water?Primary · checked Oct 4, 2026
14. NASA — NASA Research Suggests Mars Once Had More Water Than Earth’s Arctic OceanPrimary · checked Oct 4, 2026
15. PNAS — Ancient ocean coastal deposits imaged on Mars (Li et al., PNAS, 2025)Primary · checked Oct 4, 2026
16. NASA — NASA’s MAVEN Reveals Most of Mars’ Atmosphere Was Lost to SpacePrimary · checked Oct 4, 2026
17. NASA JPL — New Study Challenges Long-Held Theory of Fate of Mars’ WaterPrimary · checked Oct 4, 2026
18. NASA — Heat and Dust Help Launch Martian Water Into Space, Scientists FindPrimary · checked Oct 4, 2026
19. NASA Technical Reports Server — An Assessment of ISRU Options in Support of Future Human Missions (Hoffman, Andrews and Watts, 2016)Primary · checked Oct 4, 2026
20. NASA JPL — NASA Is Locating Ice on Mars With This New MapPrimary · checked Oct 4, 2026
21. NASA JPL — Curiosity Peels Back Layers on Ancient Martian LakePrimary · checked Oct 4, 2026
22. NASA JPL — NASA’s Perseverance Rover Deciphers Ancient History of Martian LakePrimary · checked Oct 4, 2026