Archive for the ‘Briony’s research’ category

AGU 2009 – Day 1

December 16, 2009

For those not familiar with the conference, the fall meeting of the American Geophysical Union is a terrifyingly, overwhelmingly large conference. Each year, something like 16,000 geoscientists descend on San Francisco to share their work. It is also one of the major planetary science conferences, so a lot of new results are first presented here.

Moscone Center in San Francisco. This building is filled with science at every fall AGU meeting.

This year, the first talks that I checked out on Monday were about radar observations of Mars. By sending radar waves from spacecraft to the surface and then recieving the reflected waves, we can learn a lot about Mars. In particular, since radar penetrates tens to hundreds of meters below the visible surface, it can reveal otherwise hidden structures. This has been especially successful at mapping the structure of the polar caps, because radar penetrates through ice quite well.

Roger Phillips gave a talk summarizing some of the results from the SHARAD radar instrument on MRO. Among other thers, SHARAD has found evidence that the spiral troughs in the north polar ice cap have migrated over time, as predicted many years ago by theoretical models. SHARAD has also found ancient buried canyons in the polar ice, which menas the ice caps have been around for quite a while. There are also some exiting new results implying that the material filling valleys in the Deuteronilus Mensae area is quite transparent to radar waves, and might in fact be something like glacier ice.

Image credits: NASA/ESA/JPL-Caltech/ASI/University of Rome/University of Washington St. Louis

After the radar talks, there were a whole bunch of presentations about aqueous alteration on Mars. One of the main lessons that I took away from those talks was that Mars is still a very confusing place. For example, Hap McSween used data from the Mars rovers and characterized typical soils at both landing sites. He found that the compositions of soils are roughly 70% unaltered material and 30% alteration products. He also showed that the soil compositions are quite similar between the two landing sites, which are on opposite sides of the planet, and that the unaltered portion of the soil is similar to the rocks at both sites.

However, the next talk by Josh Bandfield used orbital data and found that in general rocks on Mars have more of the mineral olivine than the soils. This is a somewhat different result than the rover data, and it might imply that rocks on Mars actually have more magnesium and iron than previously thought.

Other talks related to Mars alteration focused on “clay” and sulfate minerals detected on Mars. One that I found particularly interesting was by Paul Niles, who pointed out that Mars is an “obliquity-driven” planet. In other words, its tilt varies widely, and the Mars we see now is not typical. Niles suggested that during more typical periods, ice might have formed large layers at Mawrth Vallis, a location known for its strong hydrated mineral features. Melting at the base of that ice could have leached the rocks, explaining the presence of specific Al-bearing clay minerals.

Map of water-bearing minerals at Mawrth Vallis. Image credit: ESA/OMEGA team

Another interesting talk was by Itav Halevy, who took a look at how the presence of SO2 gas influences the formation of carbonate minerals. It turns out, even a tiny amount of SO2 gas (which is often released by volcanoes) can prefent the formation of CaCO3. If there is iron around, FeCO3 (the mineral siderite) forms instead. The implication is that sulfur minerals should form in different locations than clay minerals and siderite.

Continuing with the sulfur theme, Albert Yen talked about some results from the Spirit rover. He said that basically, if the rover had to get stuck, it picked a really fascinating place to do it! Based on the compositions measured, it turns out that there is too much sulfur in the soil to balance it out by assuming it is combined with other elements like Fe and Mg. That means there might be pure elemental sulfur mixed in with the soil, which would be consistent with hydrothermal activity!

My officemate and occasional contributor here at the Martian Chronicles, Briony Horgan, also gave a nice talk summarizing some of her recent work. For a long time there has been a question about the so-called “surface type 2” on mars. This surface type has higher than usual Si, but that could be due to a different type of lava, or alteration of the more common basalt seen elsewhere on Mars. Briony presented new evidence, based on the overall shape of the spectra of surface type 2 regions, that these areas might be due to a silica glass coating! This sort of coating could form when thin films of water from thawing ground ice altered the surface of sand grains, and would imply relatively recent alteration processes on mars.

Finally, the day ended with the Whipple prize lecture, which was unfortunately full of some misleading information about the history and status of Mars science. But that’s the topic for a future post.

Advertisements

Sand Dunes Quote

December 3, 2008

Briony has kindly updated my last Mars Art post, adding the sand dunes quote which I referred to. In case you don’t feel like going back to look at that post, here’s the quote:

In places vast accumulations of sand weighing millions of tons move inexorably, in regular formation, over the surface of the country, growing, retaining their shape, even breeding, in a manner which, by its grotesque imitation of life, is vaguely disturbing to an imaginative mind.
~ Bagnold (1941)

Phoenix Update: Pondering Perchlorates

August 7, 2008

Since we last checked in on Phoenix, the team has had made remarkable progress in investigating the lander’s local environment. The team has:

Finished the mission-success panorama
– Officially detected water ice in TEGA
Investigated the bizzarely clumpy and sticky nature of the landing site’s soil
Observed changes in the ice deposits under the lander
– Continued to monitor the summer polar weather
Received a mission extension from NASA through Sept. 30

And much more! But the discovery that I’d like to focus on today involves potential detection of an interesting chemical compound in a few select teaspoons of martian soil: Perchlorate salts.

The internet has been going batty over the past week or so, first with rumors that the Phoenix team had discovered “something really interesting” and “provocative”, then all of this week with confusion over the announcement of perchlorates. While there’s tons of information (and non-information) floating around about the discovery, I haven’t found any in-depth looks at perchlorates. So here’s mine.

What is a perchlorate?
A perchlorate is made of a chlorine atom bonded to four oxygen atoms (ClO4), making an anion. An anion is the negative half of a salt molecule, like the Cl in NaCl (table salt). So a perchlorate doesn’t exist on its own as a solid substance, only attached to a cation, like sodium (Na) or ammonium (NH3). Perchlorate can exist on its own when the solid salt has been dissolved in a liquid, which causes the cations and anions to split apart, making a solution.

Perchlorate is an oxidizer, which means that it tends to react with other compounds. This is especially bad when combined with organics, and the presence of such oxidizers on Mars may have implications for past or present life on Mars (see below).

How did Phoenix detect perchlorates?
Phoenix has 2 main instruments to investigate soil chemistry. The first is the wet chemistry lab on the Microscopy, Electrochemistry, and Conductivity Analyzer (MECA). MECA dissolves a sample of the soil in a water-based solution and does various tests to figure out what ions and anions are present. MECA detected perchlorate ions in 2 soil samples.

The second soil chemistry instrument is TEGA, or the Thermal and Evolved Gas Analyzer. TEGA bakes soil samples to high temperatures, and analyzes the gases that are released along the way. TEGA has also analyzed 2 soil samples. Interestingly, while TEGA did detect oxygen in one sample, but not the other, it did not detect chlorine in either. In other words, TEGA could not positively confirm the detection of perchlorates.

DID Phoenix detect perchlorates?
At this point, the results are too inconclusive for the team to make a concrete statement about the presence or abundance of perchlorates in martian soils. So, the answer is: we don’t know. All we can say is that some of the results are consistent with perchlorates.

How did perchlorates get into the martian soil?
The easiest way that perchlorates may have gotten into the soil samples is via Phoenix itself. Perchlorates are a common industrial compound on Earth, and, most notably, ammonium perchlorate is often used as a component of solid rocket fuel. While Phoenix’s retro rockets that landed it on the surface used a fuel that probably did not contain perchlorates, the vehicles used to launch Phoenix from Earth may have. Another wrench to throw in this cog is that the soil samples were taken from below the surface, and probably were not affected by the landing. Perhaps the scoop or MECA itself was contaminated earlier? These are all possibilities the Phoenix team is considering.

Alternatively, the perchlorates may have been formed on Mars. In the lab, perchlorates can be created by evaporating the right kind of acid. However, perchlorate salts also occur naturally in Earth in extremely arid environments, like the Atacama desert in Chile. One study has shown that these salts can form by exposing typical chloride salts (think NaCl) to sunlight or ultraviolet light for long periods of time (months). This is a pretty appealing case for Mars, since certain salts that often form with chloride salts have been detected all over the north polar region (ref: my thesis!), and the surface of Mars receives a ton of UV through the thin atmosphere.

What does this mean for life?
If perchlorates or other oxidizers are abundant in the surface soil layer on Mars, this is not a good sign for finding signs of past or present life on Mars near the surface. Prolonged exposure to oxidizing agents (not to mention ultraviolet and cosmic rays) would destroy almost all organic molecules, leaving little to no trace or organics for us to pick up.

However, if the primary oxidizing agent is perchlorate, the news might not be quite so dire. Perchlorate is one of the slightly more benign oxidizers, since it tends to react more slowly than most. Also, if it was formed by breakdown of chloride salts at the surface, it probably is only present near the surface. Lower soil layers may not be as much at risk, and the deeper subsurface might be free of oxidants all together.

So, we’ll have to wait and see what the Phoenix team learns from their results and future tests. We’ll keep you updated.

Phoenix hilarity

June 24, 2008

My old thesis title: “Composition and morphology of aeolian deposits in the north polar region of Mars and implications for sediment transport.”

alien life form?

My new thesis title: “Why the #$%#& are there polar bears at the north pole of Mars?”

Which is Earth?

June 14, 2008

We had another great day at Great Sand Dunes National Park and Preserve today, with lots of pictures, but it also involved a lot of hiking and I’m tired. So instead of a full post, I will refer you to my adviser’s post about our first day at the dunes, over at the Planetary Society blog. I’m also stealing the image that he posted over there, comparing granule ripples on mars to the ones that we saw at the dunes. Can you tell which one is Earth and which is Mars? Check Jim’s post to find out.

Sand Dunes!

June 13, 2008

Greetings folks! I’ve been silent for a few days because I am in the midst of a lot of traveling. On Monday, Tuesday and Wednesday this week I was at a team meeting for the Mars Color Imager (MARCI) and Context Camera (CTX). Rather than spend a lot of time explaining what that means, I will do what I always do and link to the planetary society blog. My adviser Jim Bell is guest blogging over there while Emily is on vacation, and he explains MARCI and CTX very nicely.

After that meeting, Jim and I flew down to Denver, Colorado and met up with Briony and Melissa. We then drove all night to get to Alamosa. After a few hours of sleep, we met up with a couple of colleagues who are sand dune experts and headed out to Great Sand Dunes National Park and Preserve.

The dunes are situated in a flat basin, surrounded by mountains on all sides, and you can see them from a long way off as a series of buff-colored rises. As you drive closer, the dunes loom larger and larger. From twenty miles away, they look like you’re almost there, because any other dunes you’ve ever seen are smaller. The dune field at the park is enormous: the tallest dune is 750 feet (229 m) tall! When we finally arrived at the base of the dunes, this was the view:

(Click for a larger version and try to spot the people climbing the dunes like ants on an oversized anthill)

As you can see, there is a stream to cross before reaching the dunes. This stream acts as a conveyor belt for sand: the wind blows sand from the dunes into the stream, which washes the sand back upwind so it can be lifted by the wind and become part of the dunes again.

There is no word for these dunes other than spectacular. I could wax poetic all night about them, but instead, I’ll let a few pictures do the work for me:

The beautiful, lighter-toned ripples in this view are made from coarser, more quartz-rich sand grains than the surrounding dunes.

Here we are setting up a GPS station. To goal of the day’s field work was to use GPS to measure the shape of several dunes very precisely.

Blue sky, mountains, dunes. What this beautiful view doesn’t convey is the sandblasting that we received as the afternoon winds picked up.

And finally a panorama of the dunes, as seen from the visitor’s center in the afternoon light. Click for a much bigger version! Can you find the people in this picture?

Stay tuned, I’ll have more dune pictures tomorrow, and then we’re all heading up to Winnipeg Canada to visit some Mars-analog locations.

Phoenix’s Neighborhood (Part I): The Basin

June 5, 2008

If you’re like us, you’ve been refreshing the Phoenix news page constantly, looking for the next update from Mars. If you need a little catching up on what’s going on in the mission, here are some recent posts with updates.

But with all the Phoenix coverage, there hasn’t been much talk about the context for the Phoenix landing site. What’s so cool about the north pole of Mars?

The north pole of Mars sits at the lowest elevation of the huge basin that takes up most of the northern hemisphere of Mars:


MOLA elevation map of Mars (credit: NASA)

Like any basin here on Earth, the northern basin acts as a trap for all kinds of materials from elsewhere on the planet: wind-blown sand, water and debris from outflows, groundwater, and maybe even precipitation. The idea that the northern basin may have once held water has made it the prime location for a possible ancient martian ocean.

While observations of features that look like shorelines and deltas support the concept of an ancient northern ocean on Mars, the evidence is not conclusive. Right now, the consensus in the scientific community is that the northern ocean may have never existed, and if it did, that it was pretty short-lived on geologic timescales.


Possible deltas and shorelines at the edge of the northern basin (Pablo and Pacifici, 2008).

Even if there never was an ocean, there has still been a huge amount of material deposited by wind and outflows in the northern basin. In the shaded elevation map above, did you notice how smooth the northern plains look compared to the southern highlands? This indicates that enough material has been added to the northern basin to smooth over and obscure the ancient cratered terrain – many, many kilometers of sediments.

The northern basin has gotten much more interesting in the past decade. Until high resolution images came back from Mars Global Surveyor in the late 90’s, it was thought that vast floods of lava had smoothed out the plains a few billion years ago, and not much had changed since. Our new picture of the northern plains is a vast stack of sediments that have been constantly reworked by erosion and permafrost processes for potentially billions of years.

In the next installment, we’ll look at the evidence for ice in the northern plains before Phoenix landed on it.