Evidence of rivers and lakes on Mars and what it means

NASA’s Mars rover Curiosity in action. (Inset) Dr Ashwin Vasavada

NASA’s Mars rover Curiosity in action. (Inset) Dr Ashwin Vasavada

I did the following interview for a well-known diaspora news site The Indian Diaspora.

By Mayank Chhaya

Mars was supportive of life much longer than thought so far even though whether life ever existed there remains unknown, Dr Ashwin Vasavada, Mars Science Laboratory deputy project scientist, says.

As NASA scientists study the findings produced by the Curiosity rover over the last 14 months, it is becoming increasingly apparent that Mars is probably the most habitable planet in the solar system apart from Earth. Moons of Jupiter and Saturn may also be habitable but no mission has landed there yet.

The mission has found evidence of the existence of lakes and rivers for a period longer than thought so far. That finding opens up possibilities of looking for organic life.

As someone involved in the geologic studies of Mars, Dr Vasavada is a key player as the $2.5 billion mission studies the planet’s geology with unprecedented precision.

There are expectations among Mars watchers that NASA may be preparing to make an important announcement about the presence of organics on December 16.

At the heart of whether life as we know it existed there is the discovery of the presence of water more widespread once than believed until now.

“I’d say the consensus is that liquid water was widespread and relatively long-lived. These conclusions are from the geology, whether evidence for lakes, deltas, or water-cut valleys,” Dr Vasavada told The Indian Diaspora in an email interview. Excerpts:

Do you now have a handle on how long the period during which all conditions were right for possible life on Mars might have lasted?

Last year Curiosity discovered evidence for an ancient lake within Gale Crater that contained fresh water, the key chemical elements required by life as we know it, and potential sources of energy for life.  This allowed us to conclude that a habitable environment existed on Mars at that place, and at that time.  Since then we’ve driven for 14 months in order to reach the foot of Mt Sharp, a five-km high mountain of layered rock at the center of Gale Crater. Along the way, we noticed patterns in the rocks that we interpret as a stacked set of river deltas. Deltas are distinctive features that form when sediments carried by a river empty into a standing body of water, such as a lake. The fact that we saw deltas stacked vertically in the ancient rock layers indicated that a series of rivers and lakes came and went over time. The rivers flowed downhill toward the center of the crater, indicating that Mt Sharp was not there, but instead, it was created as these lake sediments built up the mountain’s layers over time.

All this to say that Gale Crater was likely warm (above freezing) and wet for a span of perhaps tens of millions of years, either continually or intermittently. Either way, it extends the time that Mars was likely supportive of life, if it ever existed.

Cross-bedding seen in the layers of this Martian rock is evidence of movement of water recorded by the waves or ripples of loose sediment the water passed over, such as a current in a lake. This image was acquired by the Mastcam on NASA's Curiosity Mars rover on Nov 2, 2014

Cross-bedding seen in the layers of this Martian rock is evidence of movement of water recorded by the waves or ripples of loose sediment the water passed over, such as a current in a lake. This image was acquired by the Mastcam on NASA’s Curiosity Mars rover on Nov 2, 2014

How long ago did that period of great convergence exist in terms of standing water, enough energy and basic elements?

The geological evidence we see in Gale Crater probably dates from about 3.8 to 3.5 billion years ago.  This matches the time period when many other water-formed features are seen across Mars, including the networks of valleys in Mars’ southern hemisphere. It is not clear whether Mars had a stable, warm climate, or whether volcanoes or large asteroid impacts may have created temporary warm climates.

Do you think the latest conclusions make Mars as the likeliest habitable planet in our solar system apart from Earth?

Mars certainly appears to be the most habitable planet after Earth, based on our understanding of what conditions support life, as we know it. There are moons of Jupiter and Saturn that also may offer habitable environments, but we have not yet explored them enough to know.

Is it correct to say that the growing consensus now is that water was indeed present in various forms globally on Mars rather than just a few specific locations?

I’d say the consensus is that liquid water was widespread and relatively long-lived. These conclusions are from the geology, whether evidence for lakes, deltas, or water-cut valleys. There is less consensus on the nature of the climate required to support this liquid water. For example, were global temperatures above freezing?  Did wet and warm conditions come and go over some time span, or were they sustained?

If that is indeed the consensus, are we not talking several multiples of the possibility of life having existed on the planet?

I suppose this depends on how rare and difficult it is for life to originate or exist. We’re still struggling to understand this even for Earth.

Curiosity is not designed to detect organic compounds. What are NASA’s plans for the next mission to Mars, which would have this capability?

Curiosity is well-equipped to detect organic compounds, but so far has detected only traces of simple carbon-containing molecules. It’s tough because organics concentrate only in certain geologic settings.  Then, over the billions of years from their deposition to our study of them, they can be changed or destroyed by fluids that circulate through the rocks, chemicals in the atmosphere, or radiation from space or the sun. We’re not only looking for organics, but also trying to understand where best to look for them. This information will greatly help future missions that attempt to find materials that contain evidence for ancient life.

This simulation depicts a lake partially filling Mars' Gale Crater, receiving runoff from snow melting on the crater's rim. Evidence that NASA's Curiosity rover has found of ancient streams, deltas and lakes suggests the crater held a lake such as this more than three billion years ago (all photographs courtesy: NASA/JPL-Caltech/MSSS)

This simulation depicts a lake partially filling Mars’ Gale Crater, receiving runoff from snow melting on the crater’s rim. Evidence that NASA’s Curiosity rover has found of ancient streams, deltas and lakes suggests the crater held a lake such as this more than three billion years ago (all photographs courtesy: NASA/JPL-Caltech/MSSS)

Could Curiosity not have been equipped with some instruments that could detect life?

It could have, but at the time such instruments were in early stages of development due to the difficulty of detecting ancient signatures of life, even on Earth. It was thought that Curiosity’s mission should be to understand the conditions that support life, as well as those that preserve evidence of it.

What is the best guess about the presence of organics?

Curiosity will be releasing new results related to organics on December 16th.

Do you and your colleagues ever discuss deeper philosophical consequences of life having existed on Mars and how that might fundamentally change human certitudes?

We all know in the back of our minds that the question of life outside of Earth is one of the most profound questions we can ask as humans. However, we also know it is incredibly difficult to answer. So we’re using Curiosity to its best ability to answer the questions we can, which build toward this ultimate question.

Would it be fair to say that with the latest finding Curiosity has delivered on one of the most important aspects of its mission?

I believe that, thanks to a dedicated science and engineering team and a good bit of fortune from Mars, Curiosity has made an initial deposit on every promise it made. For example, we have found an ancient habitable environment, we are learning how Mt Sharp came to be, we have explored for organic materials and the conditions that allow their accumulation and preservation, and we have gathered an enormous amount of data on the modern environment. In all these areas, we still have more to do.  Climbing lower Mt Sharp will allow us to access the time dimension, with younger rocks the higher we go. That is one promise we have left to fulfill.

Purely as an aside, what is the power source of Curiosity? Is it entirely solar or there is more? What is it lifetime?

Curiosity is powered by a radioisotope thermoelectric generator. Naturally, radioactive material inside the device generates heat, which is turned into electricity, which charges a battery continuously. The benefit of this power source is that, unlike solar panels, it is unaffected by dust, weather, or seasons. One down side is that it decays over time according to basic physics. So we need to keep working hard for the next few years, knowing that each year will have less energy than the last.

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About chutiumsulfate

South Asians can infer from my name what I am. View all posts by chutiumsulfate

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