We all have a lot of questions about Mars. Recently, at a National Geographic Live event in Seattle, we collected quite a few. Luckily for us, Dr. Ray Arvidson, planetary geologist and professor at Washington University in St. Louis, has answers! Dr. Arvidson directs the Earth and Planetary Remote Sensing Laboratory, and has worked on the Mars Exploration Rover (Spirit and Opportunity) and the Mars Science Laboratory (Curiosity Rover). 

If Mars is farther from the sun than Earth, why is water still on Earth? Patrick, age 10

H₂O exists as gas, liquid (water), and ice on Earth because our planet is warm relative to Mars. It is closer to the sun than Mars and has a warming atmosphere. On Mars, H₂O today can only exist as gas and ice because the atmosphere is very thin and Mars is 1.54 times farther from the sun as compared to Earth. It makes Mars very cold. In the past when Mars had a dense atmosphere it was warmer and water could exist on the surface.

 

Have there been any signs of life on Mars? Tim, age 9

We have not seen any definitive signs of life on Mars yet. On the other hand, we have not had the right kinds of equipment on landers and rovers to test directly for life. Some of the rocks we have been examining with the Curiosity and Opportunity rovers prove that Mars was warm and wet in the past and likely was habitable. Next, we will seek for signs of ancient life directly, probably using rovers in the 2020s.

 

I’m 14. I’m a freshman at Ballard High School. I want to be in the control room. I want to be there, engineering, solving problems. I’ve wanted to do this for some time. What do I have to do to get there? Olivia, age 14

Pursue your passions for studies, do well, and you will get where you want to go. Most of the control room workers are engineers and scientists, so you might pursue these directions for study.

 

How does a planet lose its atmosphere? Is it possible to recreate or force one once lost? How is it different than what we’ve done to Earth as a species?

Mars lost some of its atmosphere when its internal magnetic field died as the internal liquid iron-nickel core froze. With no magnetic field, the solar wind started stripping away the atmosphere. Also, the atmosphere was converted into rocks by weathering—for example, perhaps making limestones (calcium carbonate). And very light elements, like hydrogen, can just escape from the gravitational pull of the planet. Earth is not losing much of its atmosphere to space because our planet still has an outer core of liquid iron and nickel. This makes a strong magnetic field that keeps the solar wind from stripping away our atmosphere. Also, volcanoes keep replenishing some atmospheric gases.

 

What’s the warmest place on Mars? If/when we colonize Mars, why wouldn’t we colonize at that warm place? Gracie, age 14

The equator in low regions would be warmest, particularly if the places are dark and absorb a lot of sunlight. These might be good places for a human expedition.

 

What’s the chance of an asteroid hitting a base? Milo, age 10

Asteroids and comets and debris from them are hitting all of the planets and moons all the time—mainly very small particles that burn up in the atmospheres of planets and moons that have atmospheres. Larger objects hitting Mars and other planets are really very rare events and very unlikely that one will hit a base.

 

What makes the North Pole on Mars white? Snow, ice, or something else? Charles, age 5

The winter poles on Mars are covered by ice made of frozen carbon dioxide. Very bright indeed.

 

Do you think there is life on Mars right now? Oliver, age 7

I think it is much more likely that low forms of life, like microbes, existed early on Mars, when it was warm and wet as compared to the very cold, dry planet we know today.

 

If we were to sublimate both polar ice caps on MARS (via nukes or any means) would we create an atmosphere? Would Mars be more habitable? Jimmy, age 22

Making the poles of Mars sublimate (go from ice to vapor) by heating them would put both carbon dioxide and water vapor into the atmosphere. However, it is likely that these gases would then react with rocks and be consumed over time. For example, carbon dioxide dissolved in liquid water makes carbonic acid, which is a main reason that rocks are Earth are chemically weathered. The carbon is converted into limestone and taken out of the atmosphere.

 

How would you terraform Venus? Sam, age 6

Yikes, the Venusian surface is hotter than your oven! I do not think it is possible to terraform Venus. Mars would be hard enough, maybe even impossible.

 

What is the most likely place for life on Mars? Nessa, age 11

Warm, wet areas like subsurface water deposits.

 

What is the easiest way to get around on Mars? Nathan, age 12

I like rovers to get along on the surface. Like cars on Mars!

 

Can you really change Mars? William, age 7

Mars is huge. It has the surface area of Earth’s continents. I doubt we could change it much in terms of terraforming.

 

Why was Mars able to sustain lakes and rivers ages ago, but cannot now? Isn’t it too cold, and wasn’t it always?

Warm wet areas today on Mars are likely to be subsurface deposits of liquid water and ice. In the past, Mars had active volcanoes. These emitted gases that kept the atmosphere warm and wet by greenhouse warming. Also, it had long ago a magnetic field that kept the solar wind from stripping away the protective atmosphere.

 

How about the peroxide in Mars soil? What about the lack of N2?

Chlorine has been found in all soils examined by landers and rovers on Mars. And there are strong indications that at least some of the chlorine exists in hydrated perchlorates. These compounds can be reactive and may explain the odd behavior of soils when wet, perhaps more likely than peroxides. There is clear evidence from landed and orbital measurements that a lot of nitrogen has been stripped away from the atmosphere by the solar wind.

 

Could you talk about the time and speed it would take to go 140 million miles?

You go into orbit about the sun to get to Mars and travel at a few miles/second, and even then it takes months to get to the Red Planet.

 

With its lower gravity, will Mars ever be able to have the atmospheric air pressure for liquid water?

Mars had a higher atmospheric pressure in the past, and greenhouse gases that kept the surface warm enough to be warm and wet. Lower gravity was not the reason this changed, although some lighter molecules were lost to space. Rather, with the demise of the magnetic field, the solar wind started stripping away the atmosphere. Also as volcanism slowed down, less gas was emitted into the atmosphere. All in all these changes put the Red Planet into the deep freeze.

 

I have heard planets such as Io and Europa could potentially be inhabited. Why do we not strive to colonize those planets?

We are intending to robotically explore Europa, one of the Galilean moons of Jupiter. The reason is that we have evidence from the Galileo orbiter around Europa that this moon has an ocean beneath a water ice crust. Maybe subsurface life exists. Currently, NASA is planning the Europa Clipper mission to fly close by Europa to make detailed measurements. And there is discussion of a Europa lander to sample the crust, where water and maybe some salts have recently come up through the subsurface oceans through fractures. Io is interesting but has lots of noxious gases and lots of active volcanoes.

 

Other than Mars and Earth, Venus and our moon have evidence of water. Should we make the journey to these entities?

Venus has water in its atmosphere and also sulfuric acid. The moon has permanent water ice deposits at its poles. There are plans to pursue measurements from orbiters and landers for both objects. Some measurements have also been done in the past.

 

Are there rovers from other countries currently on Mars, or will that be in the near future?

NASA has the only rovers on Mars. The European Space Agency ( a consortium of western European countries) is building the ExoMars rover, which will launch to Mars in 2020.

 

No oxygen or water on Mars—is that easily solved?

There are both oxygen and water on Mars, as ices and vapor and bound in rocks. Processing to refine oxygen and water is the issue. How will it be done? The process is called in situ resource utilization and it is under intense study.

 

Given the importance of selecting a single optimum landing site for human exploration, is a robotic mission planned to confirm the site’s suitability for advancing science?

Humans will not go to a landing site until it has been explored robotically. In fact, robots will likely construct the habitats humans will live in, preparing the shelters and other infrastructure needed before a human mission to the red planet.

 

Would it be best to focus on Mars as “moon, then Mars” since there are a lot of similarities with moon and Mars and the moon is just three days away? Would the moon be a good training ground?

Moon first or direct to Mars? Both have fierce advocates and detailed architectures. Time and money will guide the best path to the Red Planet.

 

Is Curiosity an international program, and is the info from Curiosity shared?

Curiosity is a NASA mission with international participation for instruments, including Spain, France, and Russia.

 

Can we use nuclear power to overcome some of our energy needs for rockets and Mars colonies?

Yes indeed, nuclear propulsion will speed up the transit time to Mars and nuclear energy will

provide power on the surface.

 

Do you know why water on Mars went away? Jack, age 9

Some was lost to space and some froze as ice on and beneath the surface.

 

Have you heard to the idea to add greenhouse gases to Mars’ atmosphere to warm it up? Henry, age 12

This is called terraforming and may work, but the planet is so big and so complicated that I suspect it is not possible. And we do not understand the consequences associated with making it warm.

 

Does Mars have tectonic plates?

Mars never seems to have had plate tectonics. In fact Earth seems to be the odd planet in that it definitely has tectonic plates and sheds a lot of its internal heat through plate tectonics, whereas our other planets do not seem to follow this path. They seem to be mainly one plate planets.

 

Why is Mars considered a better prospect for habitability than Earth’s moon?

Because Mars was warm and wet in the past and water is the elixir of life. Earth’s moon was always dry and cold, with just a bit of water ice trapped permanently in shadowed areas in the polar regions.

 

To learn more about how humans will travel to and live on Mars, please check out the new Nat Geo book MARS: Our Future on the Red Planet and our interactive Mars globe and downloadable educator guide!