• First of all, in case you missed it, we live in the future. Proof? This actual photograph from Virgin Galactic’s successful supersonic rocketplane flight:

Awesome view of Space Ship 2's rocket firing during a successful supersonic test flight.

The plane in question is Space Ship 2, eventually intended to be a suborbital passenger plane for space tourists. Dear NASA: this is proof that sexy spaceships can also be functional. Take note!

• Speaking of exciting news in commercial spaceflight, check out this video of SpaceX’s “Grasshopper”:

Grasshopper is a proof-of-concept for SpaceX’s plan to return rocket stages under their own power. I’d say it’s looking pretty good! There’s a reason I’m more optimistic about SpaceX launch vehicles than anything from NASA.

• Next, I need to share my latest obsession. It’s a webcomics reality show called Strip Search, run by the guys who do Penny Arcade. It is extremely entertaining and unlike most reality shows all the contestants seem super nice and cool. Why mention it on this blog? Because one of the Contestants is Maki Naro who does the amazing Sci-ence webcomic. I think I linked to his awesome comics about Curiosity’s landing before, but now I need to share this brilliant one about Carl Sagan, brought to my attention on twitter by Emily Lakdawalla, who convinced Maki to make a T-shirtof the last panel. Needless to say, though I like all the contestants on the show, I’m rooting for Maki to win.

Click to see the full comic and the best punchline ever.

• And finally, I wanted to point you to this excellent New Yorker piece on the Curiosity mission. Callan shared it with me and I have to say I had very few nitpicks, it’s overall very well done. My only real complaint is that it makes it sound like we didn’t figure out that the landing ellipse was interesting until after we decided to go there and started the detailed mapping. Many people (myself included) showed that the ellipse itself was fascinating. But I’ll forgive the writer for mixing up the timeline for landing site selection to make it a bit more dramatic. I still highly recommend the piece.

Howard et al. point out that in the Noachian period (~4.1 to 3.7 billion years ago) there was enough erosion to fill craters 10s of kilometeres across with sediment, and they estimate that on average 100s of meters of erosion happened in the highlands (with variations according to local climate, slope, etc.). Some drainage networks in ancient Noachian terrain are 100s of kilometers long, suggesting that there was enough flowing water in some places to make relatively “mature” networks. You can think of the “maturity” of a drainage network as how long the water has been flowing. If you go outside and dump a bucket of water on a pile of dirt, you’ll end up with some erosion and a little channel carved into the dirt, but it isn’t connected with any other channels – it is “immature”. But if you pour water on a landscape for thousands or millions of years, the channels eventually connect up with each other to form a dense branching network or tributarys – a “mature” system.

But at the same time, it doesn’t look like early Mars was particularly wet by Earth standards. Howard et al. point out that not many Noachian-aged craters have breached rims, which is what you would get if the crater filled with water and overflowed. The authors estimate that the long-term erosion rate in the Noachian period was comparable to the erosion rate in the driest deserts on earth, like the Atacama in Chile or the dry valleys of Antarctica.

The central puzzle that is considered in this paper is that there are some valley networks on Mars that are much less degraded than others. Howard et al. consider these fresher-looking valleys on the border of the Isidis basin, south of the crater Schiaparelli, and in Margaritifer Sinus, and try to come to some conclusion about where the fresher valleys came from.

In the Isidis basin margin, the fresh-looking valleys stretch up to 800 km, and can be multiple kilometers wide at their thickest points. These valleys tend to cut several hundreds of meters into plains of material that appears to be sediment from erosion that occurred in the Noachian era. By carefully studying the topography of the area, the authors found that the valleys are deepest where the local slope is greatest, exactly where you would expect the most erosion to occur. But in a river system that is allowed to flow for a long time, this effect tends to smooth out the river’s profile (if you get the most erosion where it is steepest, pretty soon those areas become less steep!).

Over in Evros Valles south of Schiaparelli, the authors point out a drainage system that consists of a well-defined main valley with lots of faint tributaries. Again, the deepest parts of the valley are also the steepest parts. The same is true for the Parana  Valles in Margaritifer Sinus. In this area there is also an interesting example of erosion that occurred in multiple stages: early erosion created a gently sloping surface composed of fans or “pediments” (ramps of eroded bedrock), but then a later round of erosion carved channels into that, which then widened to create a new fan surface which was incised again! The details of this are not as important as the fact that clearly there was more than one round of erosion.

Fig 16 in the paper shows evidence for multiple stages of erosion. Age from oldest to youngest in panel C is red-blue-green-yellow.

Howard et al. also take a look at alluvial fans and possible deltas on Mars, and find that large alluvial fans are found in craters >50 km in diameter. Crater counts on the fans give them an age that falls near the boundary between the Noachian and Hesperian eras, and the fans don’t have drainage networks on them (something that is common on Earth when it rains after a fan has been formed). In terms of deltas, of course Eberswalde (a former candidate landing site for Curiosity) is the best example but the authors point out a couple of other possible deltas too. They note that the deltas often show inversion of relief which occurs when river beds are more resistant to erosion than their surroundings, and so they end up standing above the surrounding plains when erosion occurs. They also note that the volume of the Eberswalde delta is not far off from the volume of the valleys that feed into it, suggesting that they formed at the same time.

At this point, the authors take a step back and start looking for common characteristics of the “fresh” valleys. They note that the main valleys tend to carve sharply into plains in the highlands, and tend to have steep side walls. Most of the valley networks mapped from Viking-era data behave like this, and the authors interpret them to be valleys carving the sediment that was generated in the Noachian era when the highlands eroded.

The fact that there are some deltas of an age comparable with the Noachian-Hesperian boundary suggests that there was enough water flowing for long enough to create lakes, and the large alluvial fans are also about this age. The authors say that the fans “imply appreciable,  probably repeated flows extending  over a time interval of many hundreds or thousands of years”. Also, since the deltas and fans are not incised by later channels, the authors believe that the flows that formed them shut off pretty abruptly.

Based on the width of some channels, the authors estimate the amount of water that was flowing, and it is pretty large, suggesting that rain or snow was involved. It’s harder to get sudden large amounts of water from groundwater sources – those tend to be more of a steady trickle. And with groundwater there is the problem of refilling the aquifer, which would require precipitation anyway. Plus many of the valleys occur at high elevations where you wouldn’t expect groundwater to be discharged. Of course, the authors point out that it’s impossible to know how often the discharge occurred or how long it lasted, but making some assumptions based on rates on Earth, they estimate that the delta in Eberswalde would take thousands to 100s of thousands of years to form. If the water was flowing non-stop, it could form in tens of years.

Fig. 18 from the paper: A drainage system and possible delta in a crater northeast of Hellas. The fact that most deltas and fans are not incised by later flows suggests that the water shut off abruptly.

So what explains the fact that these valleys carve into sediment deposited from erosion in the Noachian, why didn’t the sediment just keep piling up? Basically you can switch from accumulating sediment to eroding it by either increasing the flow of water or decreasing the supply of new sediment. The authors list three scenarios:

1. To increase the flow of water, you could have the climate warm up (possibly related to volcanic eruptions, changes in the planet’s tilt, or big impacts), driving an increase in rain and snow.
2. You can also get big discharges by switching from mostly rain to mostly snow: snowmelt tends to lead to big pulses of water flowing through the system, but relatively low amounds of new sediment, so that can cause incision of new channels.
3. You can also do it by cutting into soft rocks below a resistant cap, such as a duricrust, which is a hard layer that forms at the surface of a soil.

Of course, you can have combinations of these scenarios, and there are lots of unresolved questions, but the bottom line is, there is good evidence that something changed toward the end of the Noachian period causing new valleys to be carved into the sediment accumulated earlier in the Noachian, and leading to the formation of alluvial fans and deltas.

Howard, A., Moore, J., & Irwin, R. (2005). An intense terminal epoch of widespread fluvial activity on early Mars: 1. Valley network incision and associated deposits Journal of Geophysical Research, 110 (E12) DOI: 10.1029/2005JE002459

The fireball lights up the pre-dawn sky over Chelyabinsk, Russia. The image is a screen grab from the video below.

I woke up this morning to find all of my social media feeds bursting with news of a huge meteor over Chelyabinsk, Russia. Reports are coming in from all over the place that the sonic boom(s) from the meteor have shattered windows, blown out doors, and injured hundreds of people (mostly from falling glass). Here are some videos that show the fireball and some of the damage:

There are also reports of a factory being damaged, but it’s not clear whether this is unrelated, or if the sonic boom caused it, or if a fragment of the actual meteorite hit the factory. I suspect it is probably not an actual fragment, but we’ll see.

Factory which may have been damaged by fragments of the meteorite. Click to go to the image source.

There are also unconfirmed reports that some fragments impacted in a nearby lake.

Also, be warned: the following image has been circulating with claims that it is the crater formed by this meteor. This is NOT a meteor crater, it is a natural gas fire in Derweze. A meteor of this size would probably not cause a flaming hole in the ground: counterintuitively, the rock itself can be quite cold, it’s just the outer layers that heat up as the meteorite streaks through the atmosphere. Once the meteorite is on the ground, the thin outer layer cools down and you end up with an icy-cold rock, not a red-hot fireball.

This is NOT a meteor crater, it is a natural gas fire.

There are inevitable parallels between this event and the famous Tunguska Event, when a huge swath of Russian forest was leveled by an exploding meteor in 1908. But compared to Tunguska, this fireball and its accompanying sonic boom were tiny. There is also rampant speculation that this fireball is related to the asteroid 2012 DA14 that is currently making a close approach to Earth. Everything I have read so far indicates that this is a coincidence. There are a lot of rocks out in space, we just happen to be noticing two of them today! And if DA14, weighing in at around 190,000 metric tons, were to impact the earth, it would do a lot more damage than a few broken windows and doors. It would be enough to obliterate a city. Speaking of which, I’d like to share this public service announcement shared by Neil de Grasse Tyson on Facebook:

For other summaries of events, check out Bad Astronomy, and this Russian Livejournal site has a good compilation of pictures and videos.

Figure from Orloff et al., 2011

How did the boulders in the picture above end up in clumps and arcs instead of randomly distributed across the surface? That’s the focus of the paper “Possible Mechanism of Boulder Clustering on Mars” by Travis Orloff, Mikhail Kreslavsky, and Eric Asphaug that is currently In Press in the journal Icarus.

The picture above is from their previous paper from 2011 about evidence for boulder movement at high-latitudes on Mars. They noticed that in many locations with “patterned ground” – a generic term for polygons and other shapes that form in permafrost areas – large boulders seem to have been moved into clumps and clusters that are decidedly non-random. How do they explain these boulder clumps without invoking little green men with a penchant for rock gardens? The secret is ice. Or rather, ices.
But let’s back up. We have patterned ground here on Earth, and Orloff et al. point out that there are several different mechanisms that explain why clusters of stones form in patterned ground. So why invent a new mechanism for Mars? Well for one thing, many of the mechanisms at work on Earth require at least a little bit of liquid water. But more importantly, the boulders that they have found clustered on Mars are huge – several meters across instead of the 1 cm to 25 cm sized stones seen in patterned ground on Earth. Mars has lower gravity, but that’s not enough to explain the clustering of these very large rocks.

Orloff and his co-authors aren’t the first people to tackle this problem, and they run through several other hypotheses that have been proposed to explain the boulder clumps. The first is called gravitational slumping. But this occurs on steep slopes that are not relevant to the clumps discussed in this paper.

A related process is called gravitational creep, and can occur on shallower slopes. But it requires something in the environment to give the rocks a bit of a nudge. On earth, this is generally living things, wind, or water. Orloff et al. argue that these factors are non-existant or very weak in the areas that they are studying, so gravitational creep is probably not a good explanation. Some authors have pointed out that sublimating ice could provide the nudge necessary for gravitational creep, but Orloff et al. point out that to move boulders, you would need to remove meters worth of ice.

Another idea is “dry cryoturbation”, a process where particles of soil are cycled from the edges of polygons in the patterned ground, down the cracks, and then pushed back up to the surface in the center of the polygon. Orloff et al. rule out this hypothesis because they don’t see evidence of boulders being buried by the circulating soil at the edges of the polygons, and they don’t see boulders being uncovered in the center of the frost polygons.

Orloff et al. do grant that “frost heave” is a possible explanation for the boulder clumping. This is a process where ice forms in porous soil, and since ice takes up more space than liquid water, it causes the soil to expand or “heave”. The process requires freezing and thawing, so it is probably not active on Mars today, but it could have occurred in the last few million years, which would be consistent with the age of the clustered boulder terrain. But, the clustered boulders are seen around craters of varying ages, so if frost heave is the culprit, it would require freeze and thaw over long period of Mars history, so Orloff et al. suspect another process may be at work. Also, the problem of the boulders’ size remains: how do you cluster such big rocks?

Figure 2 from Orloff et al., 2013: "Cartoon of mechanism for boulder clustering. (a) Boulders sitting on the ground at different radial positions on polygons. We describe these boulders as: one very large boulder near the edge, one boulder already in a polygon crack, one boulder in the center of the polygon, one boulder near a crack, and two boulders close to each other near another crack. (b) Seasonal CO2 frost forms a layer. (c) The frost layer solidifies into a slab locking in all small boulders (but not the large boulder) while the near surface ice continues to contract beneath the isothermal frost slab. (d) The frost slab sublimates away and the ground starts to heat up. (e) The boulders are free to move with the expansion of the near surface ice. The boulder already in a crack remains in the crack. The boulder in the center of the polygon stays in the center. The one boulder near a crack falls into the crack. The two boulders close to each other both move towards the crack but separation between them increases."

Enter, Orloff et al.’s new idea, illustrated in the figure above. The idea hinges on the fact that on Mars, during the winter at high latitudes, a layer of CO2 frost forms. This CO2 frost seems to form a slab-like layer rather than fluffy snow, and in doing so it locks any boulders on the surface into place. Once the CO2 slab has formed in early winter, the H2O-ice-saturated soil underneath it will cool down and contract, opening up the polygonal cracks of the patterned ground. Then, as spring arrives, the CO2 slab sublimates away and the underlying ground expands again. As it expands, it moves the boulders toward the cracks in the surface. Once the boulders are sitting on the cracks, they are trapped there for all subsequent seasonal cycles.

Orloff et al. calculate that, with this process, it would take a few hundred thousand years to move boulders from the center of the polygons to the edges, which is like the blink of an eye compared to the estimated age of the clumped boulder terrains.
They wrap up the paper with three ways to test this hypothesis: first, their idea would mean that there is a certain size threshold where boulders can’t be moved, so a careful study of the size of clustered boulders could test the prediction. In particular, as you go toward the pole, thicker CO2 ice slabs would form, allowing bigger boulders to be clustered. Second, big boulders should be the first ones to break free from the CO2 slab in the spring, so vents of CO2 gas from beneath the ice should coincide with big boulders. And third, of course, boulders (and the Phoenix lander) should move toward the edges of polygons. Orloff et al. rightly point out that this would be impossible to measure without extremely high resolution orbital images or a dedicated lander mission. To me, this last one is not really a testable part of the hypothesis since the movements are so small, but the other two tests are certainly do-able.

I chose to summarize this paper because it is a good example of how, despite apparent similarities with Earth, when you are dealing with another planet, you always have to be thinking of processes that could be at work there that have no analog here. Maybe frost heaving can explain everything given enough time to work, but Orloff’s frost slab hypothesis seems plausible too, and they propose two practical tests, so I say it is certainly worth keeping in mind as we continue to try to understand patterned ground on Mars.

Orloff, T., Kreslavsky, M., & Asphaug, E. (2013). Possible Mechanism of Boulder Clustering on Mars Icarus DOI: 10.1016/j.icarus.2013.01.002

Image credit: Discovery Enterprise

The other day I got a message asking about where the earth gets its heat. It brings up a number of misconceptions that I thought would be worth spending a post discussing, so here goes:

Many people assume the earth to be millions if not billions of years old. Lava is molten, but the earth being only 8,000 miles in diameter has no internal heat source. It is almost like a thermos bottle that will lose heat over time. Many suppose that extreme pressure causes heat, but at the deepest depths of the ocean where the pressure is very high, it is also very cold.

Image source: www.kidsgeo.com

This bit about pressure is correct: pressure does not cause heat if the thing you’re pressing on doesn’t change volume. However, compressing a gas can cause it to heat up. It’s called the “adiabatic lapse rate” and it explains why higher elevations see colder temperatures, and lower elevations are warmer. As air rises, it expands and cools so mountaintops are chilly. As air moves downward, it is compressed and warms up, which is why descending into the grand canyon or death valley in summer is a bad idea. But this effect can’t explain why the interior of the earth is hot, so let’s press on.

Others assume that radioactive decay causes the heat, but with the advent of nuclear plants and control rods, it would take some very precise levels to control the heating process. Also, with radioactive decay, there would naturally be some radiation that would be present in many different ways and in all probability, would be exposed with any volcanic eruption.

Here’s where we go wrong. About half of the earth’s interior energy does come from the radioactive decay of naturally occurring isotopes. In particular, potassium, uranium, and thorium. The confusion arises with the analogy to nuclear reactors. It’s true that a nuclear reactor needs to be maintained at a precise temperature to continue the fission reaction without going critical and melting down, but that has nothing to do with the radioactivity that heats the earth. Radioactivity is not the same thing as a fission chain reaction. Radioactive isotopes of potassium, uranium, and thorium spontaneously decay into more stable daughter elements no matter what temperature they are at. You could have a single atom of uranium, floating alone in frigid deep space, and it would still eventually decay and release some energy.

All of these people are getting an above-average dose of radiation from the granite used to construct Grand Central Station. Image Credit: Natalie Mikaels

The second point here, that there would be naturally occurring radiation exposed by volcanic eruptions is absolutely right. Any rocks erupted that contain significant amounts of potassium, thorium, and uranium will have measurable amounts of radioactivity. Take a geiger counter into Grand Central Station or the Vatican if you don’t believe me. Their granite walls contain above-average concentrations of radioactive elements. There are lots of other sources of radioactivity all around us. For example, bananas are rich in potassium, and so that are slightly radioactive.

Even with any explanation that would hold some degree of credibility, you would need a source of fuel to provide the necessary heat source so that it could operate and release the required energy. This heat source would require precision controls to avoid catastrophic results. Do you see my dillema? Given the size of our planet, no internal fuel or heat source could possibly sustain itself for millions of years, let alone billions of years given the mass and quantity required.

Radioactivity is a long-lasting source of heat for our planet that doesn’t require any “fuel” other than the naturally occurring unstable isotopes. I see the point about the need for precision controls on the Earth’s temperature, but a planet is a complicated thing, especially the earth with its active plate tectonics, huge oceans, and active water cycle. The Earth climate system is made of countless interacting feedback loops that serve to moderate the planet’s temperature. It’s possible to perturb the system with dire consequences (see anthropogenic climate change) but all in all it’s a pretty stable system.

The question goes on to suggest that since there is no way that the Earth could maintain its internal heat, it must be young and therefore creationists are right. Well, not really. As I explained above, simple decay of radioactive isotopes provides about half of the Earth’s heat, and will continue to provide heat for billions of years. The rest of the heat is left over from the planet’s formation. When a planet forms, the material falling in to form it has to release its gravitational potential energy, and much of that energy is released as heat. Likewise, once you have a protoplanet, as the iron begins to sink through the molten bulk of the planet and settles in the core, it again releases gravitational potential energy and heats the planet. The only way to get rid of heat from the planet is thermal radiation, which is actually a pretty inefficient way to transfer energy, so planets can remain warm for a long time even without radioactive heating. In fact, Jupiter and Saturn are still giving off significantly more heat than they receive from the sun: they are really massive so there was a lot of gravitational energy involved in their formation, and their inner layers are actually still contracting and producing additional heat!

I study the number four rock that goes around the sun. I use a car that drives around on that big rock and uses a very strong light to tell what it is made of. I also look at pictures of the number four rock as seen from space and try to say if it was nice to live there a long time ago.

I strongly encourage you to take a look at this compilation of other research descriptions, or try to explain your own work. All of this was, of course, inspired by the Up-Goer Five comic at xkcd.

I am always a sucker for research that uses very simple observations to come to profound conclusions, and that is definitely the case with “The dual nature of the martian crust: Young lavas and old clastic materials” by Josh Bandfield, Chris Edwards, David Montgomery, and Brittany Brand. This paper suggests that the martian crust has a dual nature, where the oldest rocks are actually softer and easier to erode, while more recently lava flows have led to much more durable terrain.

But before we get too far, we need to back up and look at past theories about the martian crust. For a long time, the thought was that Mars was not that different from the moon, and so its crust was composed of what’s called a “mega-regolith” which is just jargon for “a giant jumble of blocks broken up by impacts”. Older crust = more busted up = easier to erode. But then along came new orbiters with higher-resolution cameras, which revealed that Mars has outcrops of layered rocks, implying that it’s not just mega-regolith all the way down.

Given this background, Bandfield et al. took a look at some of the most prominent exposures of the martian crust: the walls of Valles Marineris, the canyon system that cuts across the face of Mars like a scar thousands of miles long. For the most part, the walls of the canyon are not sheer vertical cliffs, they have shallow slopes, which tend to indicate weak materials. Thermal inertia measurements tend to agree. Thermal inertia is a measure of how quickly something heats up or cools down. Generally, solid rock has a high thermal inertia, but fine sand or dust has a very low thermal inertia. The walls of Vallis Marineris have a low-ish thermal inertia that is more consistent with sand-sized particles than big solid blocks of lava rock.

Valles Marineris as seen by THEMIS on Mars Odyssey.

Another clever way of telling how strong the rocks in the walls of a canyon are is to look for boulders. Strong rocks break up into strong boulders that can tumble down for a long way before breaking up into pieces that are too small to see. Also, strong boulders can sit out exposed to erosion by the wind for much longer than boulders made of weak rock. Back in 2000, when Malin and Edgett were studying the first high-resolution images of the walls of Vallis Marineris, they noted that the boulders tend to survive only a few hundred meters down the slope, pointing to weak rocks that erode easily. There are some places in the canyon walls with strong rocks interpreted to be the result of big lava flows, but for the most mart the rocks appear to be weak.

Bandfield et al. also looked elsewhere on Mars, including in the giant outflow channels carved by ancient catastrophic floods. These channels tend to lack strong, blocky rocks in their walls, but have high thermal inertia on their floors. Bandfield et al. suggest that the floods may have carved through weaker materials until reaching stronger layers, which then ended up being the final floor of the channel. Also, they don’t mention it, but I know that at least some of the outflow channels are thought to have been flooded with lava flows after the water outflow was long-gone.

They also note that in the craters of the ancient southern highlands, most signs point to weak rocks. The craters tend to be heavily eroded and have low thermal inertia and few boulders, and the shape of the craters themselves (the ratio of their depth to their diameter) are more consistent with weak rocks.

The authors spend some more time comparing Mars craters to those on the Moon, which tend to be blocky (consistent with a megaregolith) and the surface of Venus, which shows in our very limited set of images from the surface shows particles ranging from gravel to blocks, consistent with a lava-covered planet. On Earth, Mt. St. Helens provides a good example of a soft-ashy material, in contrast to very strong blocky rocks on the nearby Columbia River basalt flow.

Figure 14 from the paper: An aerial view of the Columbia River basalts on Earth. These strong rocks erode to form sharp cliffs.

Figure 15: Mt.St. Helens ash is weak and erodes with much shallower slopes.

So what does it all mean? Well, Bandfield et al. suggest that “volcaniclastics” – that is, fine-grained ash and other small particles from volcanoes – can explain the weak early crust. There are lots of studies that have identified possible ash deposits on Mars, and one of the more prominent deposits, the “Medusae Fossae Formation” clearly has lava flows that lapped up against it, supporting the idea that early explosive ash-producing eruptions transitioned to “effusive” lava flow-producing eruptions later in martian history. This sort of makes sense: early on, the planet was wetter and the erupting magma itself may have contained more gases like water and CO2 that lead to explosive eruptions. As the climate dried and the gas-rich magmas were exhausted, you would end up with eruptions in the form of lava flows.

So, bottom line, the authors suggest that early Mars was probably dominated by explosive eruptions and ash deposits, leading to a soft, easy-to-erode ancient crust. As the planet dried out and the magma chambers for the major volcanoes ran out of gases, the eruptions switched over to lava flows. The end result is a planet with a weird dual nature to its crust, something to keep in mind when interpreting erosion on Mars, especially in the most ancient rocks.

 
Bandfield, J., Edwards, C., Montgomery, D., & Brand, B. (2013). The dual nature of the martian crust: Young lavas and old clastic materials Icarus, 222 (1), 188-199 DOI: 10.1016/j.icarus.2012.10.023
 

Image Credit: Unknown (Google Image Search)

Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.

-Robert Frost

Well folks, this is it. As of tomorrow, December 21, 2012, we will reach the end of the current b’aktun of the Mayan Long Count calendar. And then, well, you know what will happen.

That’s right, we’ll start the next b’aktun! And also, the world will not end. That said, I thought it might be instructive to take a look at our neighboring planets, Venus and Mars, which have actually met their apocalyptic fates. One ended in fire, the other ice.

Let’s start with Mars, which ended in ice. By now, with all of the various orbiters, landers and rovers that have been sent to the red planet, we know that once upon a time, Mars was a place where water flowed on the surface, and pooled to form lakes or perhaps oceans. The problem is, that couldn’t happen on Mars today. The average surface temperature on Mars these days is around -81 degrees Fahrenheit (-61 C), and on a hot day near the equator the temperature might barely creep above freezing. Not only that, but Mars has lost its atmosphere. The current pressure is about 1% the atmospheric pressure here on Earth. With such frigid temperatures and low pressures, any liquid water on the surface would exist only briefly, boiling away even as it froze solid. The only water left on Mars today is in the form of ice. Some is stored in the polar ice caps, some is stored in glaciers, and some is buried under the surface. What happened to make Mars so cold and inhospitable, if it once had lakes and rivers? Well, first I should clarify: nobody ever said Mars was a nice place to live. It’s entirely possible that it has always been quite colds and dry, with only intermittent periods of liquid water, lakes, and all the rest. Still, it’s hard to argue with the geomorphology: there used to be liquid water, at least occasionally,and now there isn’t.

That’s because Mars lost its magnetic field. It’s a smaller planet than the Earth, so it cools more quickly, and a planet’s magnetic field depends on convection from the hot core to the cool surface. If the core gets too cold, convection stops. Without a magnetic field, Mars has been exposed to the full force of the solar wind, which strips away atoms in the upper atmosphere, and over billions of years has reduced the atmospheric pressure to a fraction of what it once was. Without an atmosphere, not only is water unstable, but the surface is bathed in UV radiation from the sun, making it even less hospitable for life. Any life that got its start on Mars likely had to flee underground, following the remaining liquid water water and residual warmth of the dying planet.

Staying warm is hardly a problem on Venus though! Our sister planet is just slightly smaller than the Earth, and is closer to the sun, so you might expect it to be warmer. You would be very, very right. The average surface temperature on Venus is about 860 degrees Fahrenheit (460 C), thanks to monstrous carbon dioxide atmosphere with a surface pressure 93 times that on Earth. All that CO2 causes a runaway greenhouse effect that traps the sun’s energy and gives Venus the highest average surface temperature in the solar system.

Venus wasn’t always so hellishly hot. Based on measurements from Venus Express, we know that Venus once had water. Venus Express has detected an excess of heavy hydrogen atoms called deuterium in the upper atmosphere. Since all the planets formed out of the same original star stuff, they should all start with the same fraction of heavy and normal hydrogen isotopes. The excess heavy hydrogen on Venus means that some process has selectively been removing lighter atoms from the atmosphere. Enter, the solar wind. Venus also lacks a protective magnetic field, and just like Mars, the solar wind has worked diligently at stripping away its atmosphere. But Venus is a bigger planet than Mars, so it can hang onto atoms like carbon and oxygen, keeping it swaddled in its thick cozy carbon dioxide blanket. Light atoms like hydrogen can get stripped away by the solar wind though, and since regular hydrogen is twice as light as heavy hydrogen, it gets stripped away much faster.

Without hydrogen, you can’t have water. Once, long ago, Venus might have had liquid water and temperatures that were pleasantly warm. But as the early Sun got brighter, any liquid water evaporated and joined the CO2 in the atmosphere to act as a greenhouse gas. The warmer the planet got, the more water evaporated, leading to more warming and a runaway greenhouse effect. To top it all off, after Venus reached a certain temperature, it because too hot for carbonate rocks to form, preventing any CO2 in the atmosphere from being trapped as rocks and removed from the system. So Venus ended up as a planetary oven, its scorching, volcanic surface hidden from view by beautiful sulfuric acid clouds.

Any life that arose in the early lakes or seas on Venus would have had to adapt to live in those caustic clouds to find a pleasant temperature and pressure, and the loss of almost all of the water from the planet makes even the clouds an unlikely haven for venusian microbes.

Robert Frost might have been amused to learn that our neighboring planets ended in fire and ice, respectively. As for the end to our own planet? Well, it certainly has nothing to do with the Mayan calendar. Our planet hit the cosmic jackpot and exists in a sweet spot that allows it to have large oceans. These oceans buffer the climate and help to keep it pleasant for life, although our climate has been known to change significantly as continental drift changes the ocean currents. Our planet is large enough that the core hasn’t cooled, and so our magnetic field protects us from the ravages of the solar wind. These factors make Earth a decidedly nicer place to live than our neighbors. The biggest immediate question about how our world will end is what we humans choose to do with the finely-tuned planet that we have been given. We are already seeing the climate effects of human-made greenhouse emissions, but whether these effects last for just a few hundred years, or whether they trigger larger changes in the planet’s climate is yet to be seen.

As disastrous as climate change could be for humans and many other species, it will take more than that to wipe out all life on the planet. Barring a massive impact, or a nearby supernova, it is likely that some form of life will survive on the Earth for billions of years, until the sun swells into a red giant and consumes the planet. Ultimately, the world will end in fire. But that’s a long way off. Maybe before then, some form of life from Earth will find a way to become a multi-planet species, so that the loss of a single planet, even one as nice as the Earth, won’t mean the end of all life.

At the very least, I expect those future spacefarers won’t get so worked up when they need to get a new calendar.

Monday morning was my poster presentation, so that prevented me from seeing very many talks. I did stop by the Mars talks long enough to hear ChemCam team member Darby Dyar give a talk summarizing the many challenges involved in getting quantitative numbers out of LIBS data, especially for hydrogen. Nothing new to me, but a good primer for those in the audience who might wonder why we use strange multivariate methods to analyze LIBS spectra.

After the morning session, I went to hear Ira Flatow from NPR talk about how “Science is Sexy”. Many people enjoyed his talk but I was a bit disappointed. It was basically “Ira Flatow’s favorite science-related YouTube videos”. From Flatow’s talk, I rushed over and crammed into the standing-room-only MSL session, where it was fun to see some of my plots make an appearance in the ChemCam talk.

After the MSL-fest was over, I went and camped out in the “Planetary Habitability” session. My favorite talk of the session was by David Grinspoon, who discussed how some people are saying that humans have had such an influence on our planet that we are in a new geologic era dubbed the “Anthropocene”. Grinspoon suggested 4 categories of global change: Natural disasters, biologically induced change, inadvertent changes, and intentional changes. Natural disasters are things that would happen regardless of whether there is life on the planet (e.g. impacts). Biologically induced change would be something like the transition to an oxygen-rich atmosphere on Earth. “Inadvertent” changes occur as an intelligent species becomes more advanced and gains control over its surroundings. The examples that he gave of an inadvertent change are rising CO2 levels or the formation of the hole in the ozone layer. And finally, Intentional changes would be things like fixing the hole in the ozone layer, halting global warming, terraforming Mars, etc.

Grinspoon suggested that humans are reaching a “21st century bottleneck” where we are reaching the point where we have to face lots of problems and challenges that are the result of our own success and advances (e.g. global warming, overpopulation, finite resources, etc.). He said that it might be possible that once a civilization gets beyond roughly where we are now and deals with all of our current challenges, then the civilizations’s likelihood of living for a very long time increases dramatically. He said that if this is the case and that civilizations that pass this bottleneck become effectively immortal, then we need to rethink the Drake equation. It’s entirely possible that the vast majority of civilizations (maybe including ours) don’t survive the bottleneck, but those who do, go on to live forever, so the total number of civilizations in the universe would constantly increase instead of staying constant as suggested by the Drake equation.

Grinspoon ended his talk with this quote from Franz Kafka: “Is there hope? Oh yes, lots of hope. But not for us.”

James Cameron after his solo dive to the bottom of the ocean which tied the record for deepest dive ever.

Today’s highlight for me was going to see the special presentation by James Cameron about his ultra-deep dive in the Challenger deep. I almost didn’t go, but I am very glad I did. He was a good speaker, and clearly had a good technical knowledge about what he was talking about. And of course, his talk was accompanied by spectacular video that will eventually be assembled into the documentary that he is making about the dive. The strange life forms that he showed were truly alien-looking, and the engineering that went into designing the submersible was very impressive. Cameron’s talk was followed by scientific talks by scientists involved in the dive, which covered the strange biology, geology, and chemistry observed.

During this session, my twitter feed suddenly exploded as the NASA press conference announced that NASA will be sending a new MSL-like rover to Mars to land in 2020. I have to say, I have mixed feelings about this announcement. It is great news for me in terms of career prospects, but as I sat in the deep-sea session and heard Kevin Hand talking about how lessons from Earth’s deep ocean might carry over to astrobiology on Europa, I couldn’t help but wonder why a Mars mission was selected over a Europa mission.

Of course I know the answers: NASA currently is really good at landing on Mars. Money can be saved by using as much as possible from MSL. The orbital geometry for a Mars landing in 2020 is favorable. The public is clearly pretty interested in Mars these days. A Europa mission would be really expensive, etc., etc.

But it’s really a shame that NASA can’t do both a new Mars rover and a Europa mission. To paraphrase what Kevin Hand said today while on stage and oblivious to the big NASA announcement that had just been made in a different room at this conference: What Curiosity is doing on Mars is great, but the next stop should be Europa. We’ve got the tools and technology for a Europa mission. We just don’t have the will.

Still frame from the movie 2010. Borrowed from twitter account @BadPhysics who tweeted this image and said: "Pro-tip: it wasn't a documentary."

Red rocks somewhere near Sedona.

The view out my hotel room window here in San Francisco is somewhat less scenic. It overlooks the loading dock of a Bloomingdale’s. BUT I’m not here for scenery. I’m here for the AGU “fall” meeting, and I am armed with a new smart phone (It took the picture above) so I am hoping to tweet more than I have done in the past at other meetings. You can follow me at @marschronicler. Or just follow the #AGU12 hashtag and drink from the firehose of sciencey tweets. If time in the evening allows, I also plan to blog about the highlights that I see each day, so check in here.

I am presenting my poster first thing tomorrow morning, which is a pretty sweet deal since it means the rest of the week I don’t have to worry about it. If you happen to be among the 10,000 or so scientists at the meeting and you’d like to hear about mapping inverted channels in Terby and Runanga craters on Mars, stop by my poster: “A Survey of Sinuous Ridges and Inferred Fluvial Discharge Rates in Northwest Hellas, Mars (P11B-1832).