An interview with Matt Golombek

Coordinated by: Satinder Chopra | Photos courtesy: Penny Colton
Matt Golombek

Matt Golombek is the Jet Propulsion Laboratory (JPL) Project Scientist for the Mars Exploration Rover and working on the NASA’s InSight discovery program mission. InSight is an acronym for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport. He is best known for his role as Project Scientist for NASA’s 1997 Mars Pathfinder mission to Mars and has spent the past 20 years heavily involved in the selection of all successful Mars landing sites. On November 18th, Matt was in town to deliver the Annual Honorary Address on Exploring Mars, which was sponsored by the CSPG. We availed of this opportunity and sat down with Matt for a very interesting interview. The following are excerpts from that interview.

Matt, let us begin by asking you about your educational qualifications and your work experience.

I am a traditional geologist, with an undergraduate degree in geology and geophysics from Rutgers University in New Jersey, as well as graduate degrees, i.e. Masters and Ph.D., in geology and geophysics from the University of Massachusetts in Amherst.

How did you end up with a job at NASA?

Totally by accident. I was originally trained as a structural geologist and when I was in graduate school my advisors suggested that rather than getting a Ph.D. in planetary science, which was in the doldrums back then, there wasn’t a whole lot going on and there might not be employment. They recommended that I do a Ph.D. on the Earth. So I worked on extensional tectonics in the Rio Grande Rift and just about when I was graduating – the year before, the oil business stopped hiring. So as I had no options there, I ended up getting a post-doc at the Lunar Planetary Institute in Houston where I worked for two years. I was then offered a job at JPL as a research scientist, initially half-time in Planetary and half-time in Terrestrial and with time, became more of a Martian and now I am a Martian all the time. That’s all I do – just Mars.

That brings me to the next question – why this fascination with Mars? You know it cannot be just because it has a reddish tint – that could not be the reason. There are other planets, like we have Mercury, we have Venus and beyond Mars there is Jupiter, so why this fascination specifically with Mars?

The real fascination is that it is the most Earth-like of all the terrestrial planets. It’s got a hard surface, animals can stand on it and structures can be built on it, which can’t be done on Jupiter and it has a rotation rate sort of like the Earth so its day, or we call it a sol, is 36 minutes longer than an Earth day. Its axis is tilted with respect to the ecliptic, similar to Earth’s, so it has seasons just like the Earth. Mars has summers, winters and fall and so on. Also, there is strong evidence that liquid water existed on the surface, actually ponded in either lakes or even potentially in an ocean about the same time when life got started here on Earth. We know on Earth that all life requires liquid water. It can’t be frozen, it can’t be gaseous, it’s got to be liquid. So – are we an accident of the highest order or will life form anywhere that liquid water is stable or does it take something more special? So you can address a question of profound importance by going to Mars with robots.

Recently, we heard news about water being discovered on Mars and that was followed by news about the solar wind which has robbed the planet of its atmosphere. Probably there was a thicker atmosphere at some point billions of years ago and then it has probably vanished now. Do you think the same reasoning would apply for the Earth also at some point because Earth is in an inner orbit?

There is a habitable zone around a star in which liquid water is stable and right now in our solar system, the Earth is the only planet in which that is the case. There may be habitable conditions in the sub-surface on Mars today but you would have to go down to a level where the temperature is higher. The surface on Mars today is not habitable. It’s cold and it’s dry and in fact, the temperature and pressure conditions are below the triple point of water, so ice may exist or water vapor but there is no liquid on the surface. And yet in the geologic past on Mars there is clear evidence that water existed on the surface and may have done so for a substantial period of time. It suggests that the atmosphere was denser in the past because at present it is too thin; i.e. the pressure must be much higher, enough for liquid water to exist. Thus the presumption is that the atmosphere was thicker earlier on and that it has in fact lost its atmosphere or thinned out and when that happened the water went somewhere else. The water was either stripped away by the solar wind or is now frozen or is underground. There is evidence for both that suggest water has been stripped away but we think there are substantial reservoirs beneath the ground in the form of ground ice as well as ice at the polar caps similar to those found on Earth. So the question is “what was different early on, why was there a thicker atmosphere than what exists now?” A variety of suggestions have been proposed and although there is no definitive answer to this question, there are certainly possibilities. One scenario might be that Mars initially had a magnetic field and that would suggest that the outer core was liquid and it was convecting because that’s how the Earth’s magnetic field is produced and that it stopped fairly early, sometime around four billion years ago. Without that magnetic field to protect Mars’ atmosphere, the solar wind would impinge directly on the atmosphere and it could be stripped away. In addition the geologic activity was much more active earlier on around four billion years ago and volcanism could have emitted enough gas to form a transient atmosphere. However, as the volcanic activity waned, the atmosphere could be lost by the solar wind leading to the current cold and dry climate.

The Earth is different; it is a special planet. The Earth has a geologic process called plate tectonics that over geologic time has renewed our atmosphere. So although volatiles are captured as weathering products into rocks in the creation of sedimentary rocks, plate tectonics subducts them down into the interior in subduction zones and the volatiles are liberated. Without that process the Earth probably could have dried up its oceans in a relatively short period of time. And so, the Earth has this geologic process (plate tectonics) that has maintained clement conditions (liquid water stable on the surface) throughout its history and has been critical for the evolution of life.

Matt Golombek and Mars Rover

But all this evidence of water on Mars is indirect evidence, right? All on the basis of images that you have received from different missions?

Not completely indirect. One of the landers landed in the high northern latitudes where ground ice was expected beneath several centimeters of dirt and that’s what was found and the ice is fairly pure. That’s direct evidence. So there is strong evidence that there is ice throughout most of the higher latitudes on Mars. In addition ice certainly makes up the polar caps. These are dominantly water/ice caps, and they are not carbon dioxide.

Based on available information that we have, would you say the planet Mars is dry arid land now?

Yes, super dry, super cold, super arid. The surface pressure and temperature are below the triple point of water. The surface temperature is extremely cold and the amount of water vapor in the atmosphere is very small. It is not warm enough or wet enough for liquid water to be stable. However, at a depth of a kilometer or more the geothermal gradient would increase the temperature and the overburden would increase the pressure such that, if there is enough water to occupy the pore space, a ground water table could exist and it is possible that conditions could be habitable. What’s interesting about this is most of the Earth’s biomass is beneath the surface and most of the organisms are not photosynthetic, but are living off the heat or chemical reactions. Thus it is possible that life in the subsurface exists on Mars today. There is intriguing information that could be interpreted as evidence for subsurface life on Mars today. Methane has been measured in the atmosphere and methane gas is completely unstable in Mars’ atmosphere today. So if it is being measured, it must be in the process of being produced today. There are a number of different ways to produce methane and living organisms are not the only way but nonetheless, that is one possible way.

Matt, you have been associated with the Mars Pathfinder mission, you are best known for that.

Yes, I was Project Scientist.

Pathfinder was launched back in December 1996 and it reached Mars in July of 1997. Tell us something about that because we know that it is not a crow’s flight distance from here to Mars that is followed; rather a specific path is followed. How do you decide that and how does that work in missions to Mars?

It is completely controlled by the orbital velocities of Earth and Mars. The minimum energy to get a spacecraft from Earth to Mars occurs once every 26 months when Earth and Mars are just about aligned on the same side of the sun. So the spacecraft is launched towards a location where Mars will be in once the spacecraft reaches that radial distance and this occurs once every 26 months. This makes Mars a difficult destination. Spacecraft can only be launched to Mars at a very specific time, which adds a significant schedule burden when the spacecraft is being designed and built. Either the spacecraft is ready to launch to Mars within a 3 week window or the project may get cancelled rather than fund another 26 months to try again. So it is imperative to have the spacecraft put together and ready to go. It must be thoroughly tested and loaded on top of a rocket at that time, which creates an engineering system challenge. All these pieces have to come together at the right time and in the right order and placed on top of an erected rocket that is only going to be there for a short time as well. As the rockets are not kept fueled, this creates an extra schedule incentive. In addition, there is significant risk to launching spacecraft as even the most reliable rockets sometimes blow up around four to five times out of a hundred. So how many times would a person get in a car and turn the key if they knew that four times out of a hundred it was going to blow up? Maybe no one would ever get into a car in that situation. But that is the only way to get to Mars. Spacecraft have incredible mass constraints, cost a lot of money – hundreds of millions to billions of dollars – and they are being placed on top of a rocket that is apt to explode. And it takes 3-10 years working on a spacecraft and there is absolutely nothing anyone can do whilst watching the rocket launch, rather than pray. No one has control over what is going to happen other than to say ‘please don’t let this be the one that is going to blow up’.

And for reference, the Pathfinder spacecraft was launched on a Delta II rocket which is, in fact, one of the most reliable rockets produced. And the very next rocket that was on a Delta II on the same launch pad carrying a GPS satellite exploded wiping out most of the pad and that could very well have been Pathfinder.

So there is definitely an element of risk there.

Yes, there is definitely an element of risk in this business.

How are landing sites for the lander decided upon? I imagine it this way – suppose, we have to land a rocket here on Earth from a different planet; will it be the U.S., will it be Canada, will it be Asia, will it be Europe and if not at any of those places then it will probably end up in the ocean waters. So how do you decide on that landing point and how do you select the site?

There are two main aspects to landing site selection, the first and without question the most important – is it safe for the spacecraft being sent there? Every spacecraft lands in a different way and for this we scientists have to talk to the engineers. I would guess it’s kind of like the oil business, where scientists talk to the engineers a lot. For landing sites, engineers want to know what makes a spacecraft fail? What sequence of events have to happen during entry, descent and landing in order to survive? What could be on the surface or in the atmosphere that’s going to make it not work? For example, winds in the atmosphere could affect the parachute descent, creating additional horizontal velocity. But as the spacecraft is coming down, it is trying to get rid of as much velocity as possible. The landing system designed to accommodate some winds, some slopes and some rocks but high winds, steep slopes and large rocks could damage the lander at touchdown. It is the scientists’ job to map these constraints onto the surface of Mars. If the lander uses solar power, it probably wants to be near the equator. A certain amount of atmosphere is necessary to slow the lander down; so it needs to land at lower elevations so there is more atmosphere in which to land. All of these factors need to be considered for spacecraft safety. And safety is absolutely the most important aspect, because if the spacecraft doesn’t land safely, it doesn’t matter what science it is designed to accomplish, it will not discover any of it. Furthermore, several hundred million to a billion dollars are invested on these projects, so safety is absolutely the most important factor in landing site selection.

The other factor is “what is the purpose of the lander – what is it going to do”? So, what is the lander designed to look for, what do we want to learn? For example, if we were looking for oil, we would want to land at a certain place where there are sedimentary rocks and we are going to have to drill. Thus if the main goal of a mission is to understand the aqueous history of Mars and what happened with the water, the lander would target aqueously deposited sedimentary rocks including clays or sandstones. Note that every spacecraft has different science objectives and can measure different things and so the science that it does or the materials it is going to investigate has to be evaluated in as much detail as possible. Site selection is then the marriage of science and safety in the end. Imagine a wonderful location but it has a 10% chance of failing versus a place that is almost as good but it has a 1% chance of failure and is that worth the higher rate of the failure? There is always this risk/ reward trade-off.

Matt Golombek speaking

The Pathfinder was a robotic spacecraft, and it landed on the planet with parachutes and air cushions or something like that and then a wheeled robotic Mars rover moved on the Martian surface and conducted some experiments. Tell us about the experiments that were done on that mission.

That is a great example that can put the landing site into perspective. So the spacecraft landed in giant air bags and the air bags could accommodate rocks around 0.5 m high. It was designed to land in places that were rocky because the airbags would protect the spacecraft structure. At that time, there was little information on what kind of rocks made up Mars. It was known that there are basaltic shield volcanoes on Mars and thus basalt was likely. But little was known of what other rocks could be on Mars. So where on Mars would allow the rover to visit the greatest number of different rocks? Suppose there is a geologic environment with a wide diversity of rocks all in one place and a small rover could sample them? So the Pathfinder landing site was sited just downstream from the mouth of a giant catastrophic outflow channel called Ares Vallis. By analogy with catastrophic outflow channels on Earth, the amount of water that welled up out of the ground exceeded that of the Great Lakes and in about a two-week period coursed across the surface and carved this channel that is a hundred kilometers wide and two kilometers deep. When the water got to the Northern Plains the gradient shallowed out, and created a depositional plain composed of material carried by the catastrophic flood. So all these rocks carried from all these different environments would have been deposited in a small enough area that could be examined by the Sojourner rover, which is as big as your microwave. It was designed to go tens of meters and examine the different rocks.

So is landing at the mouth of a catastrophic flood safe? The channeled scabland in eastern Washington State was used as an Earth analog that was formed by the same process. The lander, had a color camera and on the rover was a chemical analysis instrument, alpha proton X-ray spectrometer that could be placed against rocks or soils and measure the chemical composition. Geologists really want minerology, but chemical composition was sufficient to distinguish some rock types (for example granite from a basalt). So that was the science side of landing at a place where there might be a variety of rock types. And the safety side was all about how many rocks there were and whether the air bags could accommodate them.

What types of rocks did it detect?

Sojourner found a variety of rocks. The chemical composition of the first one measured looked like andesite. Of course on Earth andesites are produced by fractional crystallization and on Earth most are produced at subduction zones. But there is little evidence for plate tectonics on Mars. The rover also saw what looked like a pillow basalt – in which liquid lava formed in water and what very much looked like a conglomerate with spheres of rounded clasts in a matrix and that suggested liquid water flowed on the surface in the past. At that time it was hard to tell for sure whether it was warmer or wetter but that gave scientists more evidence that Mars was more of a habitable place in the past than what was thought previously.

Okay, tell us about some of the missions that are lined up for Mars in the near future and what are their exploration objectives?

The past 20 years has been what some call the renaissance of Mars exploration. There have been a wide variety of orbiters with different remote sensing instruments. There have been five successful landed mission in that past 20 years that have led to an explosion of information about Mars and generally the missions that come along after the ones that have been done are trying to build upon what has been learned. So there are two missions that are being built right now. One is InSight, which is the first attempt to learn what comprises the interior structure of Mars. It will place an immobile lander on the surface that carries a precision tracking station and will place a seismometer, and a heat flow probe on the surface. The heat flow probe will hammer a percussive drill to go 3-5 meters below the surface, and measure the temperature of and the heat flow of Mars.

And the seismometer will do two things. It will measure for marsquakes and the available evidence indicates there should be lots of them. It would also measure the impacts that are near enough to it and by measuring the impacts the crater time scale can be calibrated. The number of craters in a given area provides a proxy for its age. The seismometer will record the rates of impact. From the seismic waves produced by impacts and marsquakes, the thickness of the crust, mantle, and the size of the core can be determined; in addition, the precision tracking station carefully measures the location of the lander. The small circle produced by tracking the lander will wobble as the axis nutates and precesses and this will determine if the core is liquid or not. InSight should determine the internal structure of Mars. However, it is even more important because Mars is the key to understanding how the terrestrial planets differentiate. The Earth and Venus are so active that they have overprinted most of their geologic history. It is really hard to find rocks that are older than 4 billion years on either planet. Most of that history is destroyed. In contrast, the Earth’s Moon and Mercury have had rather abbreviated histories with little activity in the past 2-3 billion years. However, Mars is the Goldilocks Planet. It’s just the right size for it to have had geologic activity throughout the history of the solar system and those rocks are preserved on the surface. What were the main processes that led to differentiation of the terrestrial planets and how important were subsidiary processes that may have further divided the mantle into additional layers that have formed on Earth? InSight can address such fundamental questions about the accretion and the early differentiation of the terrestrial planet. That is very exciting.

The other mission that is being developed is the Mars 2020 Rover. It is similar to the Curiosity rover, only instead of carrying laboratory instruments to measure the mineralogy and chemistry of rocks and soils, it carries a sample collection and caching system. The Rover will collect a suite of samples (encase them separately) and will leave them on the surface to be picked up by a subsequent mission for eventual return to Earth. This would be the first step in a sample return from Mars.

Obviously these missions are robotic, unmanned, but there has been some talk about a manned mission to Mars IN THE FUTURE. Is this just speculation or something that may become a reality one day?

NASA talks about sending people to Mars. It is an incredibly expensive proposition, but robotic missions could help pave the way for human exploration. Landing site selection for human missions would have a whole new list of attributes that would become important. For example, if humans would be staying on the surface for an extended period of time and not just planting a flag and leaving, then resources to support humans are important and the most critical resource is water. So human landing site selection would include safety aspects, science objectives, and the presence and ability to extract the water. Initial thoughts are to go to subsurface ice deposits near 45 degree latitude. These ice deposits are frozen solid, so mining or extracting it is required along with making it liquid.

The other possibility is phyllosilicates or sulfates deposits on Mars. Sulfates and polyhydrated sulphites probably have up to 6% water, so maybe these deposits can be mined and heated up to liberate the water.

Very interesting! Mars gets it color from iron oxide that is found in abundance on the planet.

Hematite or rust.

Where did the iron oxide on the planet come from?

It is not completely understood, but it appears the red color is produced by extremely fine grain dust, less than a few microns that pervades the atmosphere and most of the surface. It appears to be semi amorphous, almost like a palagonite dust. It is present everywhere on Mars, it is in the atmosphere, and it slowly settles out. It settles down on the solar panels of the Rovers at a constant rate and there are places on Mars where it is meters to even tens of meters thick and there are other places on Mars that are relatively dust free. So there must be a dust cycle. Somehow a lot of this dust was made by some weathering process at some time and it gets in the atmosphere and moves around. So it does point to an active atmosphere surface interaction, just like what happens here on Earth.

It sounds very interesting, Matt. The largest mountain on Mars is about 25 km high, which is three times the height of Mt. Everest, and similarly there is a giant gash that we see on one of the pictures that is sort of a huge canyon stretching about 4,000 km. What does this suggest about the geology of Mars?

This giant volcano is a giant shield volcano and it’s about the size of Texas. It has very low slopes, so it is almost certainly made of basalt. Think of a hot spot – take all of the Hawaiian Islands chain of volcanoes and put them all in one place, that would be Olympus Mons. So that indicates there are no plates moving around on Mars. It also indicates that the lithosphere is strong enough to support this giant volcano. Mars has Northern Lowlands that is lightly cratered, and are at a lower elevation and it has Southern Highlands, with many of the craters standing at a higher elevation. Sitting on the edge of the highland-lowland boundary is the Tharsis bulge, which contains Olympus Mons, three other giant volcanoes and Valles Marineris, a giant radiating rift. Tharsis is a huge load sitting on the surface of the planet and the radius of that load is large relative to the radius of the planet. This produces completely different stresses than expected for small loads on thin lithospheres, whereas a volcano on the Earth’s thin lithosphere produces extensional concentric structures due to bending stresses at the edge of the load. However, if the load is large relative to the radius of the planet the stresses reverse and you get radial extensional structures and concentric compressional structures. On Mars, Tharsis structures cover the entire western hemisphere of Mars. So Mars likely has a thick, strong lithosphere that is holding up this load in contrast to the relatively thin lithosphere plates on Earth.

Matt Golombek speaking

The planet’s surface has a number of pock marks suggesting that it has been hit by asteroids or something like that?


I saw a picture on your website that shows a lot of these craters, tons of them. So the question that flashes in my mind is, why are there so many craters on Mars and so few on the Earth? Is it because some of these asteroids just burn up in the Earth’s atmosphere or is it something else?

There are two reasons. One is, Earth has a much thicker atmosphere and that destroys many of the small bolides that are coming in. That is what happened at Tungusta, and the recent impact in Russia, in which the bolide never made it to the ground. Instead it broke up and fragmented and created shockwaves in the atmosphere that struck down trees, but there was no crater. But the atmosphere only filters out the smaller bolides and most of the big ones that you see on Mars that are tens of kilometers or even a thousand kilometers in diameter will not be filtered by the Earth’s atmosphere. So where are all of the large craters on Earth? And the answer lies in how rapidly the Earth’s surface erodes. We have such an active hydrologic cycle and our erosion rates are so high here on the Earth that most of the craters are eroded and lost. So that is the main difference.

Apart from NASA leading the space exploration efforts, tell us about space exploration efforts in some of the other countries in the world. Are they doing something?

They certainly are. The Chinese had a rover on the Moon, and it traversed a few tens of meters and imaged the surrounding area. The Indian Space Agency has had an orbiter around Mars. The European Space Agency (ESA) has a variety of missions. There is an orbiter around Mars right now and they are designing a rover as well for the future. So there are other countries that are also engaging in Mars exploration.

So much for the work part, let me ask you about your other interests apart from Mars.

I work way too much. That is probably my biggest problem, but I do like what I do.

You don’t take out time for yourself, e.g. to go for long walks…?

I do walk. I like to walk and I like hiking. I have a dog who very much appreciates those walks. I certainly like to travel and explore new places.

One last question. What would be your message to young geoscientists who would like to become like you?

Think better of it and make sure you are prepared. I usually warn anybody that thinks that they want to become a research scientist and the possibility that they would not be successful. First of all, think of the number of Ph.D.s granted each year and the number of Professor or research jobs available. There are very few positions so most Ph.D.s will not get to do research. So I tell them that firstly, they better really want to do this and they better be committed. Secondly, they should have a Plan B if they are not able to be research scientists. So as long as they realize what they are getting into and the possibility that they won’t get the research or teaching position, then they should follow their hearts, and go for it.

Thank you very much for giving us this opportunity to sit down with you and ask you all these interesting questions. We appreciate it.


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