As early as the 1600s, observers suspected that the white blotches that cover Mars’ poles and the wispy patches which drift across its surface were signs of water. Those polar patches were later confirmed to be permanent CO2 ice glaciers with an underlying layer of water ice.
In 1963, water vapor was detected in the atmosphere. In 1965, that atmosphere was determined too thin to allow liquid water to exist without freezing or boiling instantly, and the lack of evident erosion showed that water had not existed on the surface in some time. Mars’ core is also dead, which means there is no geothermal heat from the planet to warm the surface. The Mars of today is no place for liquid water.
But this wasn’t always the case. By the 2000s, scientists determined from the Martian terrain that water had intermittently flowed over the surface. They confirmed what theorists had suspected since the 1980s: Mars potentially had enough atmosphere 3.8 billion years ago to host a liquid water ocean covering a third of the planet’s surface.
When the 2010s rolled around, a slew of observations from rovers, telescopes, and orbiting spacecrafts, revealed the motherload of Martian water data. More data collected on the surface revealed more definitive ancient riverbeds, gullies, lakebeds, and other water-related features. In 2015, geographical evidence hinted at low volumes of transient water on the surface. In 2016, a patch of underground ice the size of Lake Superior was added to the catalog of Martian water ice (which now totals 5 million cubic miles).
And finally, in 2018, the discovery that truly warranted the oft-used headline “Water on Mars!”: a lake of liquid water located 1 mile below the ice of the southern glacier provided the first evidence of stable liquid water on Mars.
Let’s pause here and take a big swig. Maybe siphon off some of that glacier water (and hope there aren’t any alien microorganisms making their home there!). We’re now heading out of our solar system to stars light years away.
Distance to next destination: 70 trillion – 15 quadrillion miles (12 – 2491 light years)
To stay hydrated, drink: 2.2 trillion – 460 trillion gallons (or, the total combined lifetime water consumption of every person living in the United States today – every person who has ever lived)