Date: January 8, 2010

Title: Lakes on Mars


Podcaster: Bob Hirshon

Organization: American Association for the Advancement of Science (AAAS)

Description: In a paper published this week in the journal Geology, scientists report new evidence that there were large lakes and rivers on the Martian surface during a period of history when the planet was thought to be cold and dry. In today’s podcast, we learn how the discovery will help researchers better understand planetary climate change and also why the finding increases the odds that life might have arisen on the planet.

Bio: Bob Hirshon is Senior Project Director at the American Association for the Advancement of Science (AAAS) and host of the daily radio show and podcast Science Update. Now in its 23rd year, Science Update is heard on over 300 commercial stations nationwide. Hirshon also heads up Kinetic City, including the Peabody Award winning children’s radio drama, McGraw-Hill book series and Codie Award winning website and education program. He oversees the Science NetLinks project for K-12 science teachers, part of the Verizon Foundation Thinkfinity partnership. Hirshon is a Computerworld/Smithsonian Hero for a New Millenium laureate.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by The Education and Outreach team for the MESSENGER mission to planet Mercury. Follow the mission as the spacecraft helps to unlock the secrets of the inner solar system at

Transcript: Welcome to today’s edition of the 365 Days of Astronomy podcast. I’m Bob Hirshon, host of AAAS Science Update radio and its companion podcasts.

Ever since Percival Lowell looked up at Mars and imagined that was a bit like Venice, Mars and water have been inextricably linked. Today, we’ll be looking at new evidence that while Mars has no canals, it once had lakes and rivers. And, according to a study just published in the journal Geology, it had them more recently than scientists had thought.

Nick Warner is lead author of the study, and Research Associate at Imperial College London. He and his colleagues, including a group at UCL, have been poring over detailed images of the Martian surface.


We use these images called the Context Camera images from the Mars Reconnaissance Orbiter and they’re about a resolution of six meters per pixel, so it’s pretty high resolution stuff, and what we noticed was that you have these flat-floored depressions, but the key observations is that there are little channels, little sinuous channel features that connect each of the depressions. And they look almost identical to what we see right now forming in the permafrost terrains in Alaska and in Siberia in the polar regions. So our understanding of that morphology and the fact that we have the channel features suggests is that these were actual lakebeds that actualformed interconnected networks. So they’re actually formed from the melting, most likely, of the near surface ice layer. So it’s very similar to the permafrost melt lakes that we see.

He said the lakebeds range from 2 km to 20 km long, and were up to 300 meters deep. The rivers connecting them range in length from a few km to tens of kms.

Warner says that lakes and rivers have been discovered on Mars before—but they date back some 4 billion years, to a time when Mars was warm and wet and altogether much more earthlike.


There are these beautiful branching stream networks on the oldest surfaces of Mars, and they look very similar to streambed that formed from rainfall. And they form on these ancient areas, they’re 3.8 to 4 billion years old, it’s the southern part of the planet Mars that has these. And the idea here is that ancient Mars was somewhat Earth like, maybe warmer and wetter and actually had rainfall.


The features Warner and his colleagues describe are nearly a billion years newer, having formed about 3 billion years ago.


They formed during what is called Hesperian Epoch. And that’s actually considered, based on the morphologies on Mars, to have been a cold and dry period. There are no large branching channels that could have formed from rainfall during that period, there’s very little evidence for water-rich minerals during this period, but here we have these lake beds with channels connecting them. So certainly there were at least temporary periods of stability and water later in history here.


Okay, so you’re probably thinking “three billion years, four billion years” what difference does it make? They’re both really old.” But the discovery of these lakes tells us at least two things: one is that Mars didn’t just start out warm and wet and gradually get colder and colder and drier and drier. Like earth, it went through cycles.


We’re coming to the realization that Mars, like Earth, goes through climate change, with periods of warming and cooling and warming and cooling. And during this time, there must have been some effect that possibly thickened the atmosphere or just created a warmer surface environment, cause this does suggest that there was ice here initially, so it was cold, probably dry, and then it melted, so there’s a couple of possibilities of how it would do that: you can have volcanic eruptions, perhaps, creating temporary thick atmospheres, and you could have large impacts on the surface creating temporary thick atmospheres or even atmospheres created by these huge, catastrophic floods that are created. So there are a couple of models – they’re not well constrained at this point. There may have also orbital changes like we see on Earth, as well.


The finding also tells us that Mars may have had longer and more frequent stretches where it had liquid water. In fact, in addition to lake beds formed from melted surface ice, Warner and his colleagues are exploring other features that suggest there may have been a large network of groundwater, too. And liquid water occurring in large quantities over more periods and for longer durations leads to one tantalizing question, which Warner has apparently been asked before:

Hirshon (on tape):

And, finally, this may be a stretch (Warner laughs) but does this have implications… I’m sorry?

Warner: No, I’m just laughing—I know what you’re going to say: the “life” issue…

Hirshon: YES! How did you know that? Whether there’s any implications for astrobiology or the evolution of life or anything like that. You read my mind…


Yeah, well that’s the big question. I think that anytime that you find evidence for water on Mars that has to be the question. You know, so now you have to figure out how long was the water there, when did it happen, so we’ve sort of constrained the “when”—we’re not sure the “how long.” Certainly more than a few days; it may have been there for years, or hundreds of years, it may have been locked up as liquid water in the sub-surface—so there may have been the potential for life in the subsurface there. So I guess the real key question is just trying to relate when this warming happened to when life evolved on earth and trying to figure how long this actually could have happened. Cause you really need water there for a substantial period of time to evolve life.

Now it certainly could have been an environment that could have sustained life that was already there—that had evolved earlier in the history of mars. I mean, this 3 billion year time period is a key time on earth. On earth, life evolved around 3.8 to 3.5 b years ago so its really a time period that we need to target, to focus on more, to see if these environments had water.


In other words, if Mars started out warm and wet like Earth, but dried out long before life arose on Earth, Mars probably remained barren. But if it managed to maintain at least some pockets of liquid water over the period that life arose on Earth, just maybe life arose on Mars, too.

That at least is the idea that teases and intrigues these scientists as they pore over these high resolution images. Of course, all they can reveal is whether such a thing is possible. It will take future missions—perhaps the planned Mars Science Laboratory mission scheduled for 2012—to see if life really did exist there or even if it still does.

For the 365 Days of Astronomy podcast, I’m Bob Hirshon.

End of podcast:

365 Days of Astronomy
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