This column first ran in The Tablet in August, 2008; we first ran it here in 2016
A friend has a home on the western shore of Lake Huron, with a glorious view of the lake from her living room window. She tells how once she showed the sunrise over the lake through that window to her visiting four year old grandson. The boy took in the colorful display with rapt amazement. The next morning, she heard a shout from the living room. “Come quick, grandma!” cried the little boy. “It’s doing it again!”
The  discovery by the Phoenix spacecraft of ice in the Martian soil had all the inevitability of the sun rising yet again. But the scientists who found it were just as thrilled as that four year old boy.
For thirty [now going on 40!] years we’ve known there must have been water on Mars. The spacecraft that orbited the planet in the 1970s sent back images of dried up river beds. (But were we being fooled by mere appearances?) By the 1990s, drops of water had actually been extracted from meteorites we believe came from Mars. (But were those meteorites really from Mars?) In 1997, the first little rover, Pathfinder, showed us rocks that looked like they had been eroded by running water. (But could they have been eroded by wind?) And so it went. Every new bit of evidence added to the belief in water; but, at best, it was all circumstantial.
The water in the meteorite gave us an important clue, however. Water, of course, is made of hydrogen and oxygen. Hydrogen is the simplest atom in the universe: a proton surrounded by an electron. But there’s a variety of hydrogen atom, called deuterium, where the proton is joined to a neutron, a particle with the same mass as a proton, but no charge. Since it’s the charges that control the chemical behavior, these atoms can make water just like hydrogen can. The fact that the water from the meteorite was slightly heavier than Earth water was good evidence that the meteorite’s water came from someplace else.
How do you make heavy water on Mars? Water can escape from Mars’ atmosphere, since Mars has a weaker gravity. But the lighter water would go first, and leave the heavier water behind. Maybe that explained where the Mars water went.
In 2001, the Mars Odyssey orbiter was dispatched to look for evidence of hydrogen escaping from Mars’ atmosphere. They found it. In particular, though, they found that the atmosphere over different parts of the planet had more hydrogen flowing away. Thus the Phoenix lander was sent to one of those regions, to see if maybe the water was hiding as a layer of ice just below the red dust.
And, finally, that’s what they found. Digging two inches down, into a hard (and surprisingly sticky) layer, the lander fetched a sample of the soil and dumped it into a chemical analyzer. It was “the first time Martian water has been touched and tasted,” to quote a mission scientist. Like doubting Thomas, they knew that the more blessed person is the one who not only believes, but who can also see for themselves.
The importance of water as a substance that can sustain life is obvious. That life might be Martian; or it might be future colonists from Earth. A private company in the US is testing rockets that they hope will be able to send people to Mars, ten at a time, for a mere two million dollars a head. That’s for a one-way trip. When you get there, you’ll be expected to set up a new home. It’s nice to know you’ll be able to get a drink when you arrive.
And maybe, once we warm things up there, we’ll make lakes with some incredible sunrises.