On Monday, Sept. 28, NASA confirmed evidence of liquid water on the surface of Mars. In an interview with News Bureau physical sciences editor Liz Ahlberg, astronomy professor Leslie Looney discusses the finding, what it means for our understanding of the red planet and the ever-present question of life on Mars.
What is the evidence that there is liquid water on Mars now, and not just in the past?
We have strong evidence of liquid water on Mars today. We have long known that there is water ice on Mars, but it is so cold and the atmosphere is so low pressured that we don’t expect liquid water on the Martian surface. Liquid water would either freeze or evaporate immediately. However, we just discovered salty water. Salt acts like an antifreeze and allows liquid water to flow on Mars.
Our wet and salty discovery was found with an orbiting spacecraft instrument that can identify molecules by the color of light they absorb. The salt in this case is not table salt, but rather a type called perchlorates that is common on Mars.
Where is the water? Why did it take us so long to find it?
The flowing water is marked by dark streaks that are found along the slopes of mountains, craters and canyons. These streaks were already interesting because they lengthen in the summer and shorten in the winter. One explanation for the seasonal change was the existence of liquid water darkening the salts, much like rain darkens the sidewalk. The big breakthrough was the use of a sensitive instrument when the dark streaks were at their longest to confirm the liquid water.
Why are scientists so excited about finding liquid water? What does it tell us about Mars’ geology and history?
This makes a total of two bodies in our solar system with liquid water on the surface – Earth and Mars. That is exciting by itself! Additionally, these dark streaks give us a clear location to explore further. It seems likely that we are seeing underground water emerging on the surface. Now, we can send new rovers or landers with missions to ascertain the properties of the water. We know that liquid water was common on Mars in its distant past, but is there still significant water underground?
What does this mean for the possibility of life on Mars?
The possibility of life on Mars is the most interesting to me. Life requires water. If water is common underground, is life common under the Martian surface? This is the outstanding question. Of course, when I say life, I mean Martian microbes, but finding those would still be transformative for our species. If life can exist on Mars under today’s conditions, then life is likely common in the universe.
One of the ironic aspects is that even though the Curiosity Mars Rover is only 1 to 2 miles away from some of the streaks (more than a couple of years of hard driving), we really don’t want the rover to explore them. The rover could still have microbial Earth life hitchhiking along waiting for a nice watery area to colonize, which may threaten any Martian life. It is expensive to sterilize a rover, so we compromise by not operating one near regions with possible liquid water.
What does having liquid water mean for a human mission to Mars – or even a future colony?
Again, life requires water. If we want to visit Mars or even colonize it in the future, any local source of water would make it much more practical. It is very expensive to bring anything from Earth. As an extra bonus, the perchlorates salts are also an important ingredient in rocket propellant.