Unravelling Martian Methane Mysteries in the Canadian Arctic

An image of our ABB methane detector deployed at Gypsum Hill on Axel-Heiberg Island in Nunavut. Alex's work here showed that the variability in a measured methane signal might be able to tell us more about our distance from the source than the total amount of methane does. This is important for how we might prospect for methane seeps on Mars. 

Oh, and look at that view!
Sometimes it's not just the results of our investigations that take our breath away.

by Alex Innanen

Almost three years ago now (and wow, time really flies) I spent three weeks in Nunavut, which you can read all about here. I talked a little in that post about why I went up and what sort of work I was doing there. But the work did not end when I landed back in Ottawa (or got back to Toronto after an extended weekend at the cottage). No, I then spent the next several months going “I guess I need to write this up in a paper somehow.” This was complicated by a few things – the fact I hadn’t ever written a paper based on fieldwork (nor read many), the fact that the results were not super clear cut, and some good old fashioned procrastination. But I ended up presenting the work a few times, including at my yearly research evaluation meetings and at a couple conferences, and it started to come together into some kind of story.
 
When I took methane measurements, I let the instrument ingest the air passing over for ten minutes, and the instrument took a measurement every second over this time period. This meant I ended up with what I took to calling a ‘spiky plot’ of hundreds of methane measurements over that ten-minute period. I noticed two things in these ‘spiky plots’. The first was that I could find the average methane concentration over that period, and that the average methane concentration tended to be highest right next to the source of the methane and drop off as I moved away downwind – typically the way you expect methane (or any gas) to work, which if nothing else meant the instrument was working. The other thing I noticed was that the variation in how spiky the spiky plot was was also higher right next to the methane source. That is to say, the methane signal varied over a much larger range when I was closest to the source, and had a much smaller range further away or upwind of the source. You can see this in the three graphs below which I took at one of the springs.

Three spiky plots. You can see that the upwind measurement has not only a lower average concentration (dashed line) but also is much, much less spiky (solid line) than the other two. Note that the y-axis is much larger on the 'Inside Wolf Spring' measurement because I saw such huge spikes of methane!

I saw this same phenomenon with the variability getting higher closer to the source even when I wasn’t moving in the exact same direction as the wind. At Wolf Spring I only moved in a (mostly) straight line in the wind direction, but at Gypsum Hill I took two sets of measurements – one along the wind direction, and one at a diagonal to the wind direction. This second set of measurements suggested that getting more data at various locations around the methane source could give us a clearer understanding of how methane behaves in a two-dimensional grid around such a source.

To that end, I sent the instrument back up to the arctic last summer in the company of an MSc student from McMaster with detailed instructions to get me a grid of measurements around Wolf Spring. My procrastination had achieved one thing – I was able to add this new dataset into my paper. And I’m glad I was! From the 2024 measurements I was able to see to impact both distance from the source and the angular distance I was from the wind direction had on the methane signal. (I’ve visualised the geometry simply below in case it’s not clear what I mean, where θ is that angular distance from the wind direction.)

Now, in 2022 I did not have any way of accurately measuring the wind direction. Instead I used a technique which is actually similar to how the Phoenix Lander did it, wherein I held up a roll of flagging tape and watched which way the wind blew it. In 2024 we were a bit more high-tech: the master’s student had access to a small weather station which gave me actual numbers for my wind direction. Knowing the position of the instrument at each measurement and the wind direction at the time of the measurement, I was able to get the distance from the source (d) and the angle of the instrument to the wind direction (θ) and combine these (d/cos(θ)) and compare this value to the average methane concentration and the variability in the measurements. I found that both fell off with increasing d/cos(θ) (or distance from the center of the methane plume), but that the variability actually fell off in a slightly more predictable way.  

Okay, you may be thinking, this is all mildly interesting but what does this have to do with planetary science? Well, as has been discussed on this blog before, there’s a lot we don’t know about martian methane. One of the unanswered questions is where it’s coming from – both in the sense of what is producing it, but of more interest to this work, the actual location from which it is being emitted. We know that we see methane plumes on Mars, but we don’t know how long they last, how the behave or, again, where they’re coming from. If we did send an instrument to Mars to investigate this, we could use what I learned in the arctic to determine what that instrument should look like and also how we should use it to find the source of these methane plumes.

I learned that the variability is a better indicator of how close we are to a methane source. The variability I saw in my spiky plots is over very short timescales, thus our hypothetical instrument should be able to make high frequency measurements to capture changes over these short timescales. I also learned that knowing the wind direction is pretty important, so our instrument should be combined with some kind of wind sensor. My measurements were taken from various locations around the methane source, so having our instrument on something that can move like a rover (or even a drone!) may be more useful than if the instrument just stands still.

There’s more I could say about this, but I don’t entirely want to spoil my paper (coming soon to an Acta Astronautica near you!). Even though it took nearly three years, it turns out there was quite a bit to learn from a few slap-dash methane measurements in the very distant north. 

To read the paper, visit: https://www.sciencedirect.com/science/article/pii/S0094576525003212

De-mystifying Martian Clouds

 Two of the lab's PhD students have just published analysis on how Martian clouds interact with sunlight in companion papers over in the Planetary Science Journal! The results represent work on thousands of images of the sky taken by the Curiosity Rover over more than ten (Earth) years and describe the thickness of the clouds we saw and give information on the crystals that make up those clouds. How can you use pictures of clouds to figure out what they are like on the scale of less than a thousandth of a cm? Read on to learn more!

by Alex Innanen & Conor Hayes

Here at PVL, we’re a big fan of Martian clouds. For over eleven (Earth) years, we’ve tasked our favourite PVL-er, the Mars Science Laboratory (MSL) Curiosity rover, with staring up at the sky for a handful of minutes every few sols to capture the clouds drifting over its home in Gale Crater. Recently, we had two papers accepted that discuss some of these cloud observations. Our papers are very similar – both look at how light interacts with water-ice clouds during the same time of year (the Aphelion Cloud Belt, or ACB, season) using the same cameras (Curiosity’s Navigation Cameras, or Navcams). Between our papers we have 33 figures and over 15 000 words. Reading through that much material can be a daunting proposition! So, presented below for the cloud-curious is a brief and hopefully engaging summary.

Over the years, clouds have made frequent appearances on this blog, but as a quick refresher, yes, there are clouds on Mars! Some are made of dust, some are made of carbon dioxide, and some are made of water-ice. The water-ice ones are the ones we’re interested in, particularly those that form as part of the ACB. Every year, when Mars approaches its furthest point from the sun, it sees an increase in water-ice cloud formation around the equator. Gale Crater, where Curiosity lives, is just five degrees south of the equator, so it sees the southern edge of this belt of clouds. This is really great for those of us on the environmental science team – we get an opportunity every year to study these clouds and look for patterns in their behaviour from year-to-year. 

ACB clouds above Gale crater tend to be fairly tenuous – think of those wispy cirrus clouds you might see on Earth (shown above). Like cirrus clouds, they’re made of tiny crystals of water ice. (On Earth we don’t tend to specify what kind of ice, but on Mars the atmosphere can be cold enough for both water and carbon dioxide to freeze, so it’s helpful to differentiate between the two.) These crystals form when water vapour in the atmosphere condenses on some kind of nucleus – usually dust particles.

On Earth, atmospheric water vapour tends to freeze into a certain set of shapes depending on the specific conditions present when the ice crystals are forming.  These shapes have been catalogued thanks to the fact that we can actually fly into and directly sample our clouds taking close-up pictures of the ice crystals. While it may be possible that the ice crystals in Martian clouds have similar shapes to those in terrestrial clouds, we unfortunately cannot (yet) directly image them like we can here on Earth. Instead, we have to rely on some physics tricks. One of these tricks is looking at how light interacts with the clouds. These light interactions can produce a myriad of cool optical effects, but more importantly can give us information about the size and shape of these particles. This information is captured by what’s called a ‘phase function’. The phase function is a mathematical description of how much light is scattered by some particle at different angles from 0 to 180°, visually represented by a curve. The exact shape of that curve depends on the shape and size of the ice crystals in the clouds, so we can attempt to determine the nature of martian ice crystals by comparing our phase function measurements to those that have been made for ice crystals on Earth.

To see how light is scattered by the clouds across different angles, former PVL member Brittney Cooper came up with the phase function sky survey: Curiosity takes a series of 9 small cloud movies looking in different directions all around the rover, like you can see in the gif below.

From this we get information about how sunlight is scattered by the clouds at different locations around the rover and put together an average phase function for the clouds we observe throughout the cloudy season at Gale Crater. We’ve been doing this observation through four Mars years so far, which means that we can compare different Mars years to see if there’s any change in the phase function. The ACB is a very stable feature – it doesn’t change much from year to year. Likewise, the average phase function at Gale doesn’t change much either. Nor does it show much difference between morning and afternoon observations. So, what does that tell us? Mostly it’s just that – the phase function doesn’t change much from year to year, or from morning to afternoon. But this could also suggest that the water-ice crystals that make up the clouds aren’t changing.

Which brings us back to the question of what those crystals look like. This problem has been tackled a number of ways in the past, often by comparing an observed phase function with one for a known ice crystal shape. Brittney took this approach, as did Alex in their Master’s work. However, we found that none of the modeled ice crystal shapes fit our curves very well. This could be for a couple reasons – the particles Brittney looked at were much bigger than the water-ice particles that we tend to see on Mars. It’s also likely that the water-ice crystals are not forming the same shapes they do on earth.

In the phase function paper, instead of forging along directly comparing our curves to known water-ice crystal shapes, we took a slightly different approach. It turns out you can make a simple approximation of a phase function mathematically using what’s called a Henyey-Greenstein (or HG) function. There are two values that go into making an HG function – the creatively named ‘b’ and ‘c’.  Helpfully for our purposes, the b and c values also give information about the particle shape. If we look at the b and c values we see in the Gale Crater phase functions, they’re close to b and c values for rough, irregularly shaped particles – not those relatively simpler geometries we see in Earth clouds. It’s not as exciting as actually having a picture of what a martian water-ice crystal looks like, but it is still a solid starting point.

The phase function is important not just because it gives us information about the shapes and sizes of the ice crystals in the clouds, but also because it is a critical input into various models. These include Martian global climate models (GCMs), which must include the effects of clouds on the amount of light that is transmitted through the atmosphere. It is also important for the topic of our second paper: the opacity of the ACB.

A cloud’s opacity basically describes how thick it is. An opacity (or “tau”) of zero means that there are no clouds and all light passes through.  As tau increases, more and more light is blocked, either through absorption or reflection into new directions (also called elastic scattering). In theory, tau can be arbitrarily high, but at a certain point so much light is blocked that it can barely be measured. During the Mars Year 34 global dust storm in 2018, Curiosity measured a tau as high as 8.5, meaning that about 99.98% of the Sun’s light was blocked by atmospheric dust (hence why the solar-powered Opportunity rover did not survive the storm).

We use a fairly simple model to determine the opacity of water-ice clouds. The math is not particularly exciting, but in essence it takes the amount of sunlight reaching Mars at the top of its atmosphere and determines how much “stuff” there has to be between the top of the atmosphere and the ground to explain the amount of light that Curiosity measures. The phase function is important here because it tells us how much of that light is being indirectly scattered towards the rover by the clouds.

The opacity of ACB clouds has been the topic of a number of PVL papers before this one, most recently by former member Jake Kloos in 2018. That paper covered the first two Mars Years of measurements. When we began writing this paper, we had just passed five Mars Years at Gale, so we were very much due for an update! We had initially hoped that this would be a fairly straightforward paper to put together. Because our model had already been well-established in our previous papers, we thought it would just be a matter of running the new data through the old model. Unfortunately, once we did so, the results pretty obviously made no sense. As previously noted, the ACB doesn’t change much from one year to the next, so we’d expect that the opacities would stay pretty much the same from year-to-year. Instead, the opacities output by our model for the new data were all over the place! They were neither consistent with each other nor with the old data, so we had to go hunting for a reason why.

It didn’t take much digging to find the cause. When we plotted the opacities as a function of each measurement’s distance from the Sun on the sky, there was a sharp increase as we got closer to the Sun. There’s no physical reason why clouds near the Sun should be thicker than those elsewhere, so our model was clearly breaking down in this area. The culprit, as it turned out, was the phase function. All of our previous opacity papers had assumed that the phase function was flat, taking on a single value of 1/15 at all angles. The results from the phase function sky survey have shown that this is very much not the case near the Sun, where the value of the phase function rapidly increases.

By assuming that the cloud opacities shouldn’t change very much over the ACB season, we were able to derive another phase function for ACB clouds, one that is reasonably similar to the one found using the phase function sky survey (which is good since we're all looking at the same clouds using the same cameras on the same rover!). After adding this new phase function into our opacity model, we were finally able to take a proper look at how ACB opacities have changed over five Mars Years.

In short, much like the phase function itself, they don’t really change at all, which makes sense given the consistency of the ACB between years. Notably, these new results invalidated one of the findings of Jake’s 2018 paper: that ACB clouds in the morning tend to be thicker than those in the afternoon. Although thicker clouds do appear more frequently in the morning in our new data, it doesn’t seem that this is the case generally. In fact, we found that observations in the morning tend to be taken closer to the Sun than those in the afternoon, which was artificially increasing their opacity values when using a flat phase function. Why didn't Jake include this in his paper? Without access to as much data as we have now, he simply didn't know that martian clouds behaved this way! (no one did) Therefore, while it can feel a little awkward calling out a former labmate’s paper as incomplete, science ultimately moves forward through incremental methodological improvements.

Just for fun, we also compared our opacity measurements with those taken by two cameras orbiting Mars: the MARs Colour Imager (MARCI) onboard the Mars Reconnaissance Orbiter (MRO), and the Emirates Exploration Imager (EXI) onboard the Emirates Mars Mission (EMM) Hope probe. Our methods did feel a little cyclical (assume the opacities don’t change much to derive a phase function, then use that phase function to conclude that the opacities don’t change much), so if we can match our ground-based measurements with those taken from orbit, we can have more confidence in our results.

Happily, the agreement between the MSL and MARCI/EXI measurements ended up being excellent, matching almost exactly with a few differences that can generally be explained by regional dust storm events that aren’t accounted for in the orbital data’s models. Thus, we can confidently say that our results reflect reality and probably aren’t a consequence of any assumptions that we made.

And don't forget to check out the papers themselves, available open-access at

Hayes et al. (2024)
Five Mars Years of Cloud Observations at Gale Crater: Opacities, Variability, and Ice Crystal Habits
&
Innanen et al. (2024)
Three Years of ACB Phase Function Observations from the Mars Science Laboratory: Interannual and Diurnal Variability and Constraints on Ice Crystal Habit

My Summer Trip to MARS

This past summer, PVL PhD student Alex Innanen traveled up to the high arctic (on an expedition led by Prof. Haley Sapers) to test an instrument called MAGE which may someday fly to Mars. Ironically, the name of the research base at which they were stationed is itself named MARS! Given the harsh conditions, the name is perhaps merited and many space agencies use this area to test out technologies they hope to use in exploration activities. (Image above: MARS as seen from up on Gypsum Hill. You can see the edge of Colour Lake below, and Wolf Mountain rising above the ridge, with Crown Glacier beside it.)

by Alex Innanen

As part of my PhD work, I have been working with an instrument called MAGE (the Mars Atmospheric Gas Evolution experiment), which is intended to study trace gases in the martian atmosphere (including methane). The instrument is an off-axis spectrometer, which I won’t get into detail about here, but it is able to measure very small amounts of and changes in methane and other trace gases.

In July, I was lucky enough to be able to take a version of the instrument up to Nunavut for testing – specifically to Umingmat Nunaat (ᐅᒥᖕᒪᑦ ᓄᓈᑦ), or Axel Heiberg Island, where the McGill Arctic Research Station (MARS) is located. MARS is at 79° N and change, which is not quite as far north as you can go in Canada but is pretty darn close. There were three of us going up: myself, Haley, and Calvin, a grad student from CalTech. Up north, we were joined by two grad students from McGill, whose group was then amalgamated with ours.

The reason for going so far away to test the instrument is because of two sites near MARS that are potential martian analogues – Lost Hammer and Gypsum Hill. Both are hypersaline (very salty) cold springs, which are home to methane seeps. The polar desert also has lots of polygonal terrain, which is formed from the freeze-thaw cycle in the ground and has also been seen on Mars. Polygonal terrain can also show interesting methane dynamics, with the troughs acting as a source of methane and the centre of the polygon acting as a sink. 

Polygonal terrain on Umingmat Nunaat seen from the air. 

But before we could get to taking measurements and making sure the instrument worked in such a remote location, we had to get there. The first leg of our journey was from Toronto to Ottawa, from where our flight would leave. We spent a couple days in Ottawa doing last minute shopping and packing and repacking out many coolers and bags of equipment and food. We had to bring not only the personal things we would need for around three weeks in the north, but also all the scientific equipment for the MAGE experiment and biological sampling that would also be done, and food to last us for our time at MARS. Altogether we had nine pieces of luggage, most of which was oversized by the airline’s standards, as well as a 40-50 L backpack apiece.

From Ottawa, we took the Canadian North airline up to Iqaluit. Iqaluit is already above the tree line and, having never been in the arctic, as soon as we set down I was blown away by the landscape, which is absolutely unlike any other place I’ve ever been. We had three hours in Iqaluit, so we left the airport to do a little looking around before it was time to get on a (smaller) plane to our next stop,
Mittimatalik (ᒥᑦᑎᒪᑕᓕᒃ, Pond Inlet). We had a brief stop there, then a quick hop to Ikpiarjuk (ᐃᒃᐱᐊᕐᔪᒃ, Arctic Bay), and then finally on to Qausuittuq (ᖃᐅᓱᐃᑦᑐᖅ, Resolute). This is where the Polar Continental Shelf Program (PCSP) has a base, and from where we would be flying out to MARS. 

The plan was to spend a few days at PCSP before flying to MARS. However, this plan was quickly derailed by the weather. It was a very wet year, and aside from us, many other teams had not been able to get to their field sites because of a combination of fog, thunderstorms, and, at MARS, an inability to land the small twin otter planes because the ground was too wet. Being stuck at PCSP was not the worst thing in the world. We got to meet lots of other scientists and learn about what they were up to, go for many hikes and appreciate the beautiful arctic landscape, and pack and repack and prepare for when we eventually were able to go to MARS.

Our field team in front of the Twin Otter that took us to and from MARS. From left to right: Calvin, Haley, Louis-Jaques, Scott and Me. 

On July 13, 10 days after we got to PCSP, it finally happened. The fog had finally lifted enough for us to get out, and while the ground was still too soggy to land right at MARS, we were able to land a few kilometers down Expedition Fjord. From there, us and our piles of equipment were ferried up to MARS by helicopter. The helicopters were a very special part of our time at MARS. We had originally planned to have only one helicopter day to take us to Lost Hammer, which is one Fjord south of Expedition. However due to the problems with the twin otter flights and other factors, we ended up having a helicopter at MARS nearly the entirety of our trip. Between us and another group we also had plenty of pilot hours, so we were able to make not only multiple trips to Lost Hammer but also to Crown Glacier and the much nearer Gypsum Hill springs (which are within walking distance, but when you’re bringing a bunch of equipment with you it’s nice to get a lift).

MAGE near the foot of Crown Glacier.

MARS is on one side of Gypsum Hill, overlooking Colour Lake and a view down Expedition Fjord. Once again I was absolutely blown away by the beauty, especially since when we landed the sun had peaked out of the clouds on its way around the sky. Like Qausuittuq, Umingmat Nunaat is a type of region known as a ‘polar desert’, but it didn’t seem like it. Not only was the tundra soggy from so much unseasonal rain, but it was carpeted with all kinds of artic plants – saxifrage, arctic poppies and even a kind of tree, the arctic willow, which instead of growing upwards sends its branches along the ground. As I was taking measurements with the MAGE instrument in the camp, a bee buzzed past me, and I was surprised to see something that looked like a butterfly. It was a butterfly! One of the great parts of staying somewhere with so many scientists is you get to learn about their areas of expertise, and there was an entomologist at MARS who told us all about the kinds of insects we might see. 

The major goal for the MAGE instrument was to be able to bring it up to almost 80° N and turn it on – success! More success followed, and I managed to get readings at MARS, the two spring sites, the polygonal terrain near MARS and at the foot of Crown Glacier. I had a lot of fun figuring out where to put the instrument, how to best run it with its power limitations, and what might make an interesting set of readings. Not only did the instrument successfully collect data on methane abundance, but we also figured out how we might be able to improve the instrument and the data we collected. For instance, I was measuring wind direction by holding up a roll of flagging tape and seeing which way the dangling end blew. An anemometer would let us get much more detailed information about how the wind effects our methane measurements.

The MAGE instrument taking measurements with Lost Hammer spring in the background. The white cone-like mound is made of Gypsum, with the spring hiding inside.

Before I left for the trip, I was extremely nervous, not only because I had never undertaken field work like this before, but also because I’d be spending nearly three weeks in one of the most remote parts of the world and had no idea what to expect. But from the moment I set foot in Nunavut I knew I’d made the right choice to go. There were still difficulties, like when it seemed like we might never make it to MARS, or getting frustrated with the limitations of the instrument, but taken altogether not only did MAGE preform admirably but doing fieldwork helped me discover and strengthen skills I didn’t know I had. I’m so grateful to have had this experience.

What is the geocorona, and how can modelling it help us find habitable exoplanets?

 

As a planet passes in front of a star, the size of the shadow it casts is different at different wavelengths. Typically the solid surface of the planet blocks all light. Above that, the wavelength variation of the absorption in the thin sliver of atmosphere seen against the star is used to help us understand the environment of that planet. But if you go to lyman-alpha (121.6 nm) wavelengths, the greatest absorber is hydrogen escaping from the top of the atmosphere. This sparse hydrogen region, called the geocorona, can be many times larger than the radius of the solid surface, blocking a much larger fraction of the star's light. The image above shows Earth's geocorona as seen from the moon, taken by Apollo 16 astronauts in 1972. https://www.esa.int/Science_Exploration/Space_Science/Earth_s_atmosphere_stretches_out_to_the_Moon_and_beyond

by Justin Kerr

For today’s PVL blog post, I am going to be giving you a brief introduction to my main research project with the team and eventual Master’s thesis. My research is focused on developing a better understanding of the hydrogen coronae that we expect to surround exoplanets in order to direct future searches for life with UV telescopes. 

But just what is a hydrogen corona? 

It may surprise you to hear that a small portion of the Earth's atmosphere extends past the orbit of the moon – this very outermost portion of Earth’s atmosphere consists of atomic hydrogen (so not the gas H2 that we are familiar with on the surface) which has yet to fully escape the gravity of the planet and is known as the geocorona. The geocorona is the hydrogen portion of the exosphere, which itself is defined as the region of the atmosphere where densities of atmospheric particles are so low that they can be described as collision-less. At the orbit of the moon, recent studies have shown that the density is so low that you would only find about one single atom of hydrogen per cubic meter. The geocorona extends past the moon to a radius of at least 100 times that of the Earth before eventually merging with empty space as the influence of the solar wind makes it impossible for the Earth to keep its grip on the atoms.
    
Now that we know what the geocorona is, how can we actually detect it? A single atom per cubic meter of empty space isn’t exactly something you could count visually or easily collect for sampling, after all. Luckily for us, hydrogen happens to be an exceptionally well studied element and we can borrow one of the most famous ways astronomers detect it throughout our galaxy. From quantum mechanics we know that the electrons in atoms can only occupy specific energy levels, and when they move between these levels they will either release or absorb light of a specific wavelength related to the energy difference between the two levels. 

For hydrogen, we know that when an electron moves between the first and second energy levels it will absorb or release light with a wavelength of 121.6nm. This specific line of light in the spectrum is known as the Lyman-alpha line. Since this wavelength falls within the ultraviolet (UV) portion of the electromagnetic spectrum of light, we can then detect it with UV telescopes. In the case of the geocorona, we can see this Lyman-alpha light around the Earth when 121.6nm light from the sun is absorbed by the geocoronal hydrogen and re-emitted in different directions. It is this light that the picture taken by the Apollo 16 astronauts shown above is seeing. This works slightly differently for exoplanets since the Lyman-alpha light produced by the planet’s hydrogen corona won’t make it all the way to Earth. Instead of looking for emissions from them, we look for drops in the Lyman-alpha light that should normally be produced by the star as some of it will have been absorbed by the corona and re-emitted in random directions.

So, we can see a hydrogen corona floating around an exoplanet. How does this relate to finding habitable worlds? It comes down to how a hydrogen corona is actually produced around a planet. From studying the geocorona, we know that it’s size is directly linked to the amount of water vapour located at the base of the exosphere. This is because the atomic hydrogen making up the geocorona is produced by the photo-dissociation (breaking apart of the molecule by light) of water. The size of the hydrogen corona around an exoplanet with an Earth-like atmosphere should also be linked to the amount of water vapour in the same location. While we can currently detect the hydrogen corona of gas giants with hydrogen-dominated atmospheres using the Hubble space telescope, we will need to wait for more powerful instruments such as the proposed LUVOIR telescope to see them around potentially habitable exoplanets.

The goal of my research is to use computer models of exoplanet atmospheres to understand how the size of the hydrogen corona changes with different atmospheric characteristics below the exobase. While telescopes such as LUVOIR which could be used to confirm our models are still a long way from launching, this work will help develop analysis plans and proposals for research so that we are ready when the necessary data becomes available for study. Even though it is just one potential piece of the massive effort put into the attempt to find alien life, I hope that my efforts here with PVL will one day play a role in this grand undertaking to better understand our place in the universe.

Update on K2-141b

Above, some art commissioned by NASA to commemorate the mission of the Kepler Space Telescope. Even as the mission encountered technical issues with its reaction wheels near the end of its journey, good science was extracted. The K2 mission allowed the telescope some drift from its original pointing near the constellation of Cygnus. This permitted the telescope to examine a wider range of stars, though each could not be observed for as long as the original set. Still, close-in short orbital period planets like K2-141b could be detected. This week, Giang updates us on his work to model this lava planet.

By Giang Nguyen

As 2021 marches on, I, along with everyone else in the lab, are also chugging along amidst a global pandemic. However, I’m more fortunate than most as my work solely lies in virtual space. As long as I have access to a computer and some internet, my work on K2-141b progresses. Although the internet isn’t necessary to run my models, I always need to have 5 tabs of Google searches on how to python open.

As a refresher, K2-141b is a planet about 200 light years away located in the Aquarius constellation. Its orbit is so close to the star it orbits that its surface temperature can be hot enough to melt and vapourize rocks, creating a thin atmosphere. K2-141b is also tidally locked which means there is a permanent dayside and nightside on the planet. Almost half of the planet is covered by giant magma oceans that can be over 100 km deep.

My work, previously published in the Monthly Notices of the Royal Astronomical Society, assumed an optically thin atmosphere such that all of the star’s light will reach to K2-141b’s surface unhindered. But now, we are restricting that assumption to account for the radiative transfer that occurs in the atmosphere. This involves calculating how much infrared and UV radiation is absorbed by the atmosphere and the subsequent feedback on the surface’s energy budget.

Infrared, or long-wave radiation, accounts for almost half of the stellar radiation but UV accounts for less that 1%. Although IR radiates much more than UV, an SiO atmosphere is better at absorbing UV than IR, 10,000,000 times better. As the atmosphere and the surface themselves also radiate infrared waves, they can warm each other up which complicates things further. Nonetheless, I pressed on with what I had and crunched the numbers.

If you neglect UV absorption, our results wouldn’t differ much from the results of our MNRAS paper. The atmosphere would be a bit warmer for a larger area but eventually drops down to near absolute zero when approaching the night-side; the winds would be about 33% faster. This makes sense as more energy is absorbed initially but, through sensible heat and radiative cooling, the system finds an equilibrium and temperature drops. Next step, add UV radiation.

Although UV absorption is minuscule initially, the atmosphere's thick optical depth at UV wavelengths ensures that 100% of UV stellar radiation is absorbed almost everywhere. While IR absorption and emission drops exponentially, UV absorption stays steady. Just like the tortoise and the hare, slow and steady wins the race. There comes a point when UV heating becomes the dominant radiative term and IR emission is not strong enough to cool the atmosphere. From there on out, the winds get faster and the temperature gets even hotter.

As you approach the night-side, the temperature gets hotter and hotter, upward of over 13,000 K. The winds go up to 7 km/s (400% increase from the classic no radiative transfer scenario). Unlike every other simulation, the results with UV absorption stayed subsonic throughout the entire atmosphere since the temperature rises faster than the wind’s acceleration. These strange results seem counterintuitive physically…but within the mathematical axioms we’ve built for our model everything checks out.

For now, I am further analyzing these results. Atmospheres like the one we have on Earth are also very good at absorbing UV radiation. However, our stratified atmosphere relegates that job to the top, far away from the surface. This leaves Earth with a temperature inversion, and K2-141b should have one too. The adiabatic profile may no longer be accurate when we introduce complex radiative transfer schemes. But if the results are true, then K2-141b’s atmosphere becomes plasma and flies across the surface at 7 km/s speed, like exhaust from a rocket. That’s pretty metal but I don’t know what the results are yet. I’ll keep you updated when I do. Until next time.

Characterizing the atmosphere of exoplanet K2-141b

 

The image above (Credit: ESO/L. Calçada) shows CoRoT-7b, an exoplanet located so close to its parent star that the input of radiation causes the surface to melt. It is for this reason that these strange worlds are called "Lava Planets" and they have unique atmospheres that are made up of rocky vapours. PVL PhD student Giang Nguyen has been working on understanding how a similar world, K2-141b, operates in collaboration with Prof. Nick Cowan at McGill University. There will be a paper out soon, but Giang provides a preview of the work below.

by Giang Nguyen

K2-141b belongs to a subset of rocky planets that orbit very closely to their star and are tidally locked. The dayside of the planet is hot enough to not only melt rocks (about half the planet is one giant magma ocean, hence the name lava planet) but to vapourize them as well. This vapourization process ultimately creates a thin atmosphere that may be detectable from hundreds of light year away with the right space telescopes.

For my work, I have been using computer models to simulate the atmosphere of K2-141b. I considered two cases: a sodium atmosphere and a silica atmosphere. Sodium is chosen as it is the most volatile component in minerals while silica is chosen as it is expected to be the most abundant for rocky planets. The atmospheric model is based on the shallow-wave equations with steady-state flow driven mainly by the temperature contrast between the planet’s permanent dayside and nightside hemispheres. As expected, since sodium is much more volatile, the pressure of the sodium atmosphere is more than 50 times that of the silica atmosphere. This also allows the sodium atmosphere to exist beyond the day-night terminator while the silica atmosphere collapses just before this point. However, as sodium has a lower heat capacity than silica, the sodium atmosphere cools off much faster which has implications for observations. In either case, the wind exceeds 1.5 km/s which is useful for high-dispersion spectroscopy.

The strength of Ancient Mars’ Greenhouse Effect

Over the past couple of years, Paul Godin has been leading an effort in my group to understand the warming potential of the ancient martian atmosphere, above he shows experimentally-derived values for CO2-CH4 CIA as measured using the Canadian Light Source. He just submitted a paper on this topic which is now under review.
 

By Dr. Paul Godin

We’ve discussed in previous blogposts about our group’s effort to better constrain the early Mars atmosphere by taking measurements at the Canadian Light Source (http://york-pvl.blogspot.com/2018/11/searching-for-liquid-water-on-mars-at.html and http://york-pvl.blogspot.com/2019/04/the-continuing-adventures-at-canadian.html). As a quick summary, geological features on the surface of present-day Mars imply that there was once liquid water on the surface. To have liquid water on the surface, a sufficiently strongly absorbing atmosphere is required to produce enough of a greenhouse effect to warm the surface above freezing temperatures. Since most ancient Mars modeling suggest that Mars did not have a dense atmosphere, the remaining possibility is that the gas composition of an ancient Mars atmosphere could be strongly absorbing. One idea was collision induced absorption (CIA) between CO2 and H2 molecules, and CO2 and CH4 molecules, could provide enough absorption to warm ancient Mars. The goal of the CLS trips was to experimentally measure this CIA effect to determine if it was as strong as predicted.

Life within Ice

A beautiful shot of micro-penitentes on Mt Rainier near Seattle, WA as photographed by Mark Sanderson in 2006 ( CC3.0, license and original file and description here ). What I love about this image is the lack of anything familiar that could indicate the scale of the features - aside from the notes from the photographer. They could be cm across or km! This is a familiar feeling from looking at images that come back from spacecraft that challenge our preconceptions. Today, PhD student Giang reflects on his recently published work trying to understand whether such textures could arise on Mars and if so, how big would they be and in what directions would they be orientated? Such models are needed to help us interpret what we see.

By Giang Nguyen

Perhaps it’s a mental coping mechanism from the summer heat, but I’ve been thinking a lot about ice. The behaviour of water ice across the solar system is studied by many people in the PVL group, and I am no exception. I’ve been looking at how water affects the atmosphere since my undergrad where I studied terrestrial weather systems. Later, the work for my Master’s consisted of surveying the icy conditions of the Martian north polar cap to look for surface-atmosphere interaction. Finally, with my PhD well on its way, I’ve been tasked with studying the atmospheric conditions of possible icy worlds beyond our solar system.

As you might guess, water is somewhat an important volatile for the propagation of life on Earth. Since there isn’t another planetary body within the solar system that is like Earth, it is helpful to look at the most extreme conditions Earth has to offer for clues. From my introductory paragraph, you’re probably thinking that I’m going to talk about Earth’s arctic polar conditions but that won’t be the case. The geography of interest here is actually high-altitude deserts, chiefly the Atacama desert located within South America’s Andes mountains.

Seasonally Shadowed Regions on the Moon: Adding Greater Intrigue to the Lunar Poles

This week, Jacob Kloos, a PhD Student here at PVL discusses exciting new research he has just published in the Journal of Geophysical Research, Planets. In his work, Jake found that the famous permanently shadowed regions (PSRs) are surrounded by seasonally shadowed regions (SSRs) which turn out to have important implications for the lunar water exosphere and the amount of water available in different locations at different times of the year - they're not what you would expect! Above, one of the key findings of the research: maps of the lunar poles showing these SSRs.

By Jacob Kloos

Over the past few decades, the north and south polar regions of Earth’s moon have garnered much attention within the field of planetary science. In addition to becoming prime targets for robotic and human exploration, the lunar poles have also been the subject of an increasing number of scientific studies. What makes these areas so intriguing for science and exploration? The answer lies in their unique illumination environments.

Unlike the Earth which rotates on an axis tilted 23.5 degrees from the ecliptic normal, the spin axis of the Moon is tilted only 1.5 degrees, ensuring that the Sun is always near the horizon for an observer at one of the poles. The low axial tilt of the Moon, coupled with its heavily heavily cratered surface, produce complex illumination patterns at high latitudes, giving rise to extremes in both sunlight and shadow: areas that are high in elevation may experience near-continuous sunlight, while some low-lying basins are in permanent shadow. Although no regions on the Moon (or indeed in the solar system) have yet been discovered which can claim the ethereal title of “peaks of eternal light,” some regions, like the rim of Shackleton crater near the South Pole, remain bathed in sunlight for 80-90% of the year. Such areas are attractive sites to send a solar-powered rover.

The permanently shadowed regions (PSRs), which are in many cases directly adjacent to the near-continuously illuminated regions, are not only interesting from an exploration perspective, but also from a scientific perspective. As a direct consequence of not receiving direct sunlight, and because the Moon lacks a substantial atmosphere to sequester and transport heat, permanently shadowed regions are among the coldest places in the solar system, enabling them to trap and store volatiles such as water across geologic periods of time. These volatile deposits constitute a valuable resource for scientific study as they would be well preserved and largely protected from chemical weathering; as such they could provide valuable insight into the delivery of water to the inner solar system - in particular to the Earth-Moon system. As for exploration, water could be extracted in-situ by future explorers, and could provide a source of potable drinking water, breathable air or perhaps even rocket fuel if broken down into its constituent components.