What NASA’s Discovery of Liquid Water on Mars Really Means—in the Words of NASA Scientists

This week’s announcement by NASA might make it seem like there is liquid water flowing on the surface of Mars right now. But when the agency’s scientists answered questions from the public via Reddit, they revealed a more nuanced picture. Quartz has edited and condensed a selection of their comments for clarity.

Do we really have flowing water on Mars? What quantity of water are we talking about?

We have not seen flowing water on the surface. If there is liquid water, think of this as a “seep” not a flow. We see something that darkens the soil, which may be just a wetting action but still involves (briny) liquid.

We think this is a very small amount of water—maybe just enough to wet the top layer of the surface of Mars. The streaks are about 5 meters wide and between 200 and 300 meters long.

Why should the person on the street care about this?

Liquid water, even if very salty, is still a good place to look for life forms. We think liquid water is essential for life (at least as we know it). Also, water in any form is a resource that future missions could exploit.

If it exists, what might happen to Martian life when the water disappears?

We don’t know how robust Martian life (if it exists) could be. We know of forms of life that hibernate during dry seasons on Earth. The water that we’re seeing within the RSL (the seasonal dark streaks that we’re seeing on slopes on Mars) is salty. Salty water could be harmful to life.

Where does the water come from?

We don’t know where the water in these hydrated salts come from. That is the next mystery to solve! The leading hypotheses are that (1) the salts are sucking up the water from the atmosphere, but you are correct, there isn’t much water in the atmosphere, and (2) that the water is coming from the subsurface.

Mars had liquid water on its surface billions of years ago. Where that water went is the subject of our current investigations. Was it lost to space? Or is it frozen in the crust today? Mars seems to have ice ages when water at the poles is sublimated and redistributed to the rest of the planet. Ice in the crust today may have been formed during one of those ice age cycles.

Can a rover approach specific areas (including where these salty streaks are located)?

These features are on steep slopes, so our present rovers would not be able to climb up to them. Because liquid water appears to be present, these regions are considered special regions where we have to take extra precautions to prevent contamination by earth life. [See Quartz’s explanation of this policy.] We don’t know what Earth life could do to any potential life on other worlds. That’s why we try to clean our spacecraft very carefully. But our current rovers have not been sterilized to the degree needed to go to an area where liquid water may be present.

How long into the future do you think it will be before we can realistically think about sending humans to Mars?

Presently, NASA is looking into the possibility of sending humans to the vicinity of Mars in the early 2030s. In this scenario, the earliest humans to the surface would be in the late 2030s.

What was your initial reaction to the data? What’s the next step?

This is all very exciting! The closer we look at Mars, the more interesting it gets.

The next step is to look for more locations where brine flows may occur. The Mars Reconnaissance Orbiter has been collecting data since March 2006, but we have covered only 3% of Mars at resolutions high enough to see these features.