A sanitised fuel

I debated myself for ten minutes as to whether I should criticise an article that appeared on the DD News website on this blog. The article is flawed in the way many science articles on the internet are, but at the same time it appeared on DD News – a news outlet that has a longstanding reputation for playing it safe, so to speak, despite being a state-run entity. But what ultimately changed my mind was that the Department of Science and Technology (DST) quote-tweeted the article on Twitter, writing that the findings were the product of a study the department had funded. The article goes:

As the world runs out of fossil fuels and looks out for alternate sources of clean energy, there is good news from the Krishna-Godavari (KG) basin. The methane hydrate deposit in this basin is a rich source that will ensure adequate supplies of methane, a natural gas. Methane is a clean and economical fuel. It is estimated that one cubic meter of methane hydrate contains 160-180 cubic meters of methane. Even the lowest estimate of methane present in the methane hydrates in KG Basin is twice that of all fossil fuel reserves available worldwide.

Methane is known as a clean fuel – but the label is a bit of a misnomer. When it is combusted, it produces carbon dioxide and water, as opposed to a host of other compounds as well. So as a fuel, it is cleaner than fossil fuels like crude oil and coal. However, it still releases carbon dioxide, and even if this is in quantities appreciably lower than the combustion of coal or crude oil emits, we don’t need more of that in the atmosphere. One report has found the planet’s surface could breach the 1.5º C warming mark, if only temporarily, as soon as 2024. We don’t need more methane in the atmosphere, such as through fugitive emissions, more so: a kilogram of methane has the same greenhouse potential as a little over 80 kilograms of carbon dioxide. Ultimately, what we need is to lower consumption.

This said, the cleanliness of a fuel is to my mind context-specific. The advantages methane offers relative to other fuels in common use today would almost entirely be offset in India by the government’s persistent weakening of environmental protections, pollution-control regulations and indigenous peoples’ rights. (The Krishna-Godavari basin has already been reeling under the impact of the ONGC’s hydrocarbon extraction activities since the 1970s.) Even if we possessed technologies that allowed us to obtain and use methane with 100% efficiency, the Centre will still only resort to the non-democratic methods it has adopted in the last half-decade or so, bulldozing ecosystems and rural livelihoods alike to get what it wants – which is ultimately the same thing: economic growth. This is at least the path it has been carving out for itself. Methane extracted from a large river-basin is not worth this.

The DST’s involvement is important for these two reasons, considering the questionable claims they advance, as well as a third.

At the broadest level, no energy source is completely clean. Even solar and wind power generation and consumption require access to land and to infrastructure whose design and production is by no stretch of the imagination ‘green’. Similarly, and setting aside methane’s substantial greenhouse potential for a moment, extracting methane from the Krishna-Godavari river basin is bound to exact a steep price – directly as well as indirectly in the form of a damaged river basin that will no longer be able to provide the ecosystem services it currently does. In addition, storing and transporting methane is painful because it is a low-density gas, so engineers prefer converting it into liquefied natural gas or methanol first, and doing so is at present an energy-intensive process.

The DST’s endorsement of the prospect of using this methane as fuel is worrying because it suggests the department is content to believe a study it funded led to a supposedly positive finding – and is not concerned with its wider, deadlier implications. At any other time, this anarchy of aspirations, whereby one department doesn’t have to be concerned with the goals of another, would be siloisation of the worst sort – as if mining for hydrocarbons in a river-basin is cleanly separable from water pollution, shortage and the cascade of ecological imbalances brought on by the local endangerment of various plant, animal and bird species.

However, it would be delusional to accuse the current Government of India of being anarchic. This government has displayed a breathtaking fetish for centralising authority and power. Instead, the DST’s seemingly harmless tweet and DD News’s insular article are symptoms of a problem that rests at the other extreme: where all departments are pressed to the common cause of plundering India’s natural resources and destroying its ecological security, even at risk of undermining their own respective mandates.

The singularity of purpose here may or may not have rendered methane an absolutely ‘clean’ fuel – but it may be a glimpse of a DST simply reflecting what the government would like to reduce the country’s scientific enterprise to: a deeply clinical affair, in which scientists should submit to the national interest and not be concerned about other things.

Why Titan is awesome #11

Titaaaaan!

Here we go again. 😄 As has been reported, NASA has been interested in sending a robotic submarine to Saturn’s moon Titan to explore the hydrocarbon lakes near its north pole. Various dates have been mentioned and in all it seems likely the mission will be able to take off around 2040. In the 22 years we have left, we’ve got to build the submarine and make sure it can run autonomously on Titan, where the sea-surface temperature is about 95 K, whose waterbodies liquid-hydrocarbon-bodies are made of methane, ethane and nitrogen, and with density variations of up to 30%.

So researchers at Washington State University (WSU) tried to recreate the conditions of benthic Titan – specifically as they would be inside Kraken and Ligeia Mare – by working with the values of four variables: pressure, temperature, density and composition. Their apparatus consisted of a small, cylindrical cartridge heater submerged inside a cell containing methane, ethane and nitrogen, with controls to measure the values of the variables as well as modify conditions if needed. The scientists took a dozen readings as they varied the concentration of methane, ethane and nitrogen, the pressure, sea temperature, the heater surface temperature and the heat flux at bubble incipience.

The experimental setup used by WSU researchers to recreate the conditions inside one of Titan's liquid-hydrocarbon lakes. Source: WSU/NASA
The experimental setup used by WSU researchers to recreate the conditions inside one of Titan’s liquid-hydrocarbon lakes. Source: WSU/NASA

The data logged by WSU researchers pertaining to the conditions inside one of Titan's liquid-hydrocarbon lakes. Source: WSU/NASA
The data logged by WSU researchers pertaining to the conditions inside one of Titan’s liquid-hydrocarbon lakes. Source: Hartwig and Leachman, 2017/WSU

Based on them, they were able to conclude:

  • The moon’s lakes don’t freeze over even though their surface temperature is proximate to the freezing temperature of methane and ethane because of the dissolved nitrogen. The gas lowers the mixture’s freezing point (by about 16 K below the triple point), thus preventing the formation of icebergs that the robotic submarine would then have had to be designed to avoid (there’s a Titanic joke in here somewhere).
  • However, more nitrogen isn’t necessarily a good thing. It dissolves better in its liquid-hydrocarbon surroundings as the pressure increases and the temperature decreases – both of which will happen at lower depths. And the more nitrogen there is, the more the liquids surrounding the submarine are going to effervesce (i.e. release gas).

What issues would this pose to the vehicle? According to a conference paper authored among others by Jason Hartwig, a member of the WSU team, and presented earlier this year,

Effervescence of nitrogen gas may cause issues in two operational scenarios for any submersible on Titan. In the quiescent case, bubbles that form may interfere with sensitive science measurements, such as composition measurements, in acoustic transmission for depth sounding, and sidescan sonar imaging. In the moving case, bubbles that form along the submarine may coalesce at the aft end of the craft and cause cavitation in the propellers, impacting propulsive performance.

  • The quantity of effervescence and the number of sites on the submarine’s surface along which bubbles formed was observed to increase the warmer the machine’s outer surface got.

The planned design of the submarine NASA plans to use to explore Titan's cold hydrocarbon lakes. Source: Hartwig and Leachman, 2017/WSU
The planned design of the submarine NASA plans to use to explore Titan’s cold hydrocarbon lakes. Source: Hartwig and Leachman, 2017/WSU

If NASA engineers get all these details right, then their submarine will work. But making sure the instruments onboard will be able to make the observations they’ll need to make and the log the data they’ll need to log presents its own challenges. When one of the members of the WSU team decided to look into the experimental cell using a borescope (which is what an endoscope is called outside a hospital) and a video recorder, this is what he got:

(Source)

Oh, Titan.

(Obligatory crib: the university press release‘s headline goes ‘WSU researchers build -300ºF alien ocean to test NASA outer space submarine’. But in the diagram of the apparatus above, note that the cartridge heater standing in for the submarine is 5 cm long. So the researchers haven’t built an alien ocean; they’ve simply reconstructed a few thimblefuls.)

  1. Why Titan is awesome #1
  2. Why Titan is awesome #2
  3. Why Titan is awesome #3
  4. Why Titan is awesome #4
  5. Why Titan is awesome #5
  6. Why Titan is awesome #6
  7. Why Titan is awesome #7
  8. Why Titan is awesome #8
  9. Why Titan is awesome #9
  10. Why Titan is awesome #10

Featured image: A radar image obtained by Cassini during a near-polar flyby on February 22, 2007, showing a big island in the middle of Kraken Mare on Saturn’s moon Titan. Caption and credit: NASA.

Note: This post was republished from late February 15 to the morning of February 16 because it was published too late in the night and received little traffic.

A shot by Cassini of the lakes Kraken Mare and Ligeia Mare near Titan’s north pole. Credit: NASA

Titan's lakes might be fizzing with nitrogen bubbles

Featured image: A shot by Cassini of the lakes Kraken Mare and Ligeia Mare near Titan’s north pole. Credit: NASA.

TITAAAAAAAAAAN!

One more study reporting cool things about my favourite moon this week. Researchers from Mexico and France have found that the conditions exist in which the lakes of nitrogen, ethane and methane around Titan’s poles could be fizzy with nitrogen bubbles. In technical terms, that’s nitrogen exsolution: when one component of a solution of multiple substances separates out. In this case, the nitrogen forms bubbles and floats to the surface of the lakes, becoming spottable by the Cassini probe. The results were published in the journal Nature Astronomy on April 18.

The Cassini probe has been studying Saturn and its moons since 2004. In 2013, its RADAR instrument – which makes observations using radio-waves – found small, bright features on some of Titan’s lakes that winked out over time. These features have been whimsically called ‘magic islands’ and there has been speculation that they could be bubbles. The Mexican-French study provides one scientific form for this speculation.

The researchers used a numerical model to determine how and why the nitrogen could be degassing out of the lakes. Specifically, they extracted estimates of the temperature and pressure on the surface and interiors of the Ligeia Mare lake from past studies and then plugged them into simulations used to predict the properties of Earth’s oil and gas fields. They found that the bubbles could form if the solution of methane, ethane and nitrogen was forced to split up at certain temperatures and pressures. So, the researchers had to figure out the simplest way in which this could happen and then the likelihood of finding it happening in a Titanic lake.

When the lake’s innards are not forced to split up, they’re thought to exist in a liquid-liquid-vapour equilibrium (LLVE). In an LLVE, two liquids and a vapour can coexist without shifting phases (i.e. from liquid to vapour, vapour to liquid, etc.). The researchers write in their paper, “In the laboratory, LLVEs have been observed under cryogenic conditions for systems comparable to Titan’s liquid phases: nitrogen + methane + (ethane, propane or n-butane).” While cryogenic conditions may be hard to create on Earth’s surface, they’re the natural state of affairs on Titan because the latter is so far from the Sun. The surfaces of its lakes are thought to be at 80-90 K (-190º to -180º C), with the lower reaches being a few degrees colder.

For an LLVE-like condition to be disrupted, the researchers figured the lake itself couldn’t be homogenous. The reasons: “A sea with a homogeneous composition that matches that required for the occurrence of an LLVE at a specific depth is an improbable scenario. In addition, such a case would imply nitrogen degassing through the whole extent of the system.” So in a simple workaround, they suggested that the lake’s upper layers could be rich in methane and the lower layers, in ethane. This way, there’s more nitrogen available near the surface because the gas dissolves better in methane – and also because it could be dissolving into the top more from the moon’s nitrogen-rich atmosphere.

Over time, the lake’s top layers could be forced to move downward by weather conditions prevailing above the lake, and push the material at the bottom to the top. But during the downward journey, the rising pressure breaks the LLVE and forces the nitrogen to split off as bubbles. Given the size and depth of Ligeia Mare, the researchers have estimated that nitrogen exsolution can occur at depths of 100-200 m. The bubbles that rise to the top can be a few centimetres wide – not too small for Cassini’s RADAR instrument to spot them, as well as in keeping with what previous studies have recorded.

Of course, this isn’t the only way nitrogen bubbles could be forming on Ligeia Mare. According to another study published in March, when an ultra-cold slush of ethane settling at the bottom of the lake freezes, its crystals release the nitrogen trapped between their atoms. Michael Malaska, of NASA’s Jet Propulsion Lab, California, had said at the time:

In effect, it’s as though the lakes of Titan breathe nitrogen. As they cool, they can absorb more of the gas, ‘inhaling’. And as they warm, the liquid’s capacity is reduced, so they ‘exhale’.

The Mexican-French researchers are careful to note that their analysis can’t say anything about the quantities of nitrogen involved or how exactly it might be moving around Ligeia Mare – but only that it pinpoints the conditions in which the bubbles might be able to form. NASA has been tentative about sending a submarine to plumb the depths of another Titanic lake, Kraken Mare, in the 2040s. If it does undertake the mission, it could speak the final word on the ‘magic islands’. Ironically, however, NASA scientists will have to design the sub keeping in mind the formation of LLVEs and nitrogen exsolution.

But won’t the issue be settled by then? Maybe, maybe not. Come April 22, Cassini will fly by Titan’s surface at a distance of 980 km, at 21,000 km/hr. It will be the probe’s last close encounter with the moon, as mission scientists have planned to take a look at some of the smaller lakes. After this, the probe will fly a path that will take it successively through Saturn’s inner rings. Finally, on September 15, NASA will perform the probe’s ‘Grand Finale’ manoeuvre, sending it plunging into Saturn’s gassy atmosphere and unto its death, bringing the curtains down on a glorious 13-year mission that has changed the way we think about the ringed planet and its neighbourhood.

Published in The Wire on April 20, 2017.

 

A shot by Cassini of the lakes Kraken Mare and Ligeia Mare near Titan’s north pole. Credit: NASA

Titan’s lakes might be fizzing with nitrogen bubbles

Featured image: A shot by Cassini of the lakes Kraken Mare and Ligeia Mare near Titan’s north pole. Credit: NASA.

TITAAAAAAAAAAN!

One more study reporting cool things about my favourite moon this week. Researchers from Mexico and France have found that the conditions exist in which the lakes of nitrogen, ethane and methane around Titan’s poles could be fizzy with nitrogen bubbles. In technical terms, that’s nitrogen exsolution: when one component of a solution of multiple substances separates out. In this case, the nitrogen forms bubbles and floats to the surface of the lakes, becoming spottable by the Cassini probe. The results were published in the journal Nature Astronomy on April 18.

The Cassini probe has been studying Saturn and its moons since 2004. In 2013, its RADAR instrument – which makes observations using radio-waves – found small, bright features on some of Titan’s lakes that winked out over time. These features have been whimsically called ‘magic islands’ and there has been speculation that they could be bubbles. The Mexican-French study provides one scientific form for this speculation.

The researchers used a numerical model to determine how and why the nitrogen could be degassing out of the lakes. Specifically, they extracted estimates of the temperature and pressure on the surface and interiors of the Ligeia Mare lake from past studies and then plugged them into simulations used to predict the properties of Earth’s oil and gas fields. They found that the bubbles could form if the solution of methane, ethane and nitrogen was forced to split up at certain temperatures and pressures. So, the researchers had to figure out the simplest way in which this could happen and then the likelihood of finding it happening in a Titanic lake.

When the lake’s innards are not forced to split up, they’re thought to exist in a liquid-liquid-vapour equilibrium (LLVE). In an LLVE, two liquids and a vapour can coexist without shifting phases (i.e. from liquid to vapour, vapour to liquid, etc.). The researchers write in their paper, “In the laboratory, LLVEs have been observed under cryogenic conditions for systems comparable to Titan’s liquid phases: nitrogen + methane + (ethane, propane or n-butane).” While cryogenic conditions may be hard to create on Earth’s surface, they’re the natural state of affairs on Titan because the latter is so far from the Sun. The surfaces of its lakes are thought to be at 80-90 K (-190º to -180º C), with the lower reaches being a few degrees colder.

For an LLVE-like condition to be disrupted, the researchers figured the lake itself couldn’t be homogenous. The reasons: “A sea with a homogeneous composition that matches that required for the occurrence of an LLVE at a specific depth is an improbable scenario. In addition, such a case would imply nitrogen degassing through the whole extent of the system.” So in a simple workaround, they suggested that the lake’s upper layers could be rich in methane and the lower layers, in ethane. This way, there’s more nitrogen available near the surface because the gas dissolves better in methane – and also because it could be dissolving into the top more from the moon’s nitrogen-rich atmosphere.

Over time, the lake’s top layers could be forced to move downward by weather conditions prevailing above the lake, and push the material at the bottom to the top. But during the downward journey, the rising pressure breaks the LLVE and forces the nitrogen to split off as bubbles. Given the size and depth of Ligeia Mare, the researchers have estimated that nitrogen exsolution can occur at depths of 100-200 m. The bubbles that rise to the top can be a few centimetres wide – not too small for Cassini’s RADAR instrument to spot them, as well as in keeping with what previous studies have recorded.

Of course, this isn’t the only way nitrogen bubbles could be forming on Ligeia Mare. According to another study published in March, when an ultra-cold slush of ethane settling at the bottom of the lake freezes, its crystals release the nitrogen trapped between their atoms. Michael Malaska, of NASA’s Jet Propulsion Lab, California, had said at the time:

In effect, it’s as though the lakes of Titan breathe nitrogen. As they cool, they can absorb more of the gas, ‘inhaling’. And as they warm, the liquid’s capacity is reduced, so they ‘exhale’.

The Mexican-French researchers are careful to note that their analysis can’t say anything about the quantities of nitrogen involved or how exactly it might be moving around Ligeia Mare – but only that it pinpoints the conditions in which the bubbles might be able to form. NASA has been tentative about sending a submarine to plumb the depths of another Titanic lake, Kraken Mare, in the 2040s. If it does undertake the mission, it could speak the final word on the ‘magic islands’. Ironically, however, NASA scientists will have to design the sub keeping in mind the formation of LLVEs and nitrogen exsolution.

But won’t the issue be settled by then? Maybe, maybe not. Come April 22, Cassini will fly by Titan’s surface at a distance of 980 km, at 21,000 km/hr. It will be the probe’s last close encounter with the moon, as mission scientists have planned to take a look at some of the smaller lakes. After this, the probe will fly a path that will take it successively through Saturn’s inner rings. Finally, on September 15, NASA will perform the probe’s ‘Grand Finale’ manoeuvre, sending it plunging into Saturn’s gassy atmosphere and unto its death, bringing the curtains down on a glorious 13-year mission that has changed the way we think about the ringed planet and its neighbourhood.

Published in The Wire on April 20, 2017.

 

Saturn in the background of Titan, its largest moon. Credit: gsfc/Flickr, CC BY 2.0

Titan's chemical orgies

Titan probably smells weird. It looks like a ball of dirt. It has ponds and streams of liquid ethane and methane and lakes of the two ethanes, with nitrogen bubbling up in large patches, near its poles. It has clouds of hydrocarbons raining down more methane. And like the water cycle on Earth, Titan has a methane cycle. Its atmosphere is a stifling billow of (mostly) nitrogen. Its surface temperature often dips below -180º C, and the Sun is as bright in its sky as our moon is in ours. In all, Titan is a dank orgy of organic chemistries playing out at the size of a small planet. And it smells weird – like gasoline. All the time.

But it is also beautiful. Titan is the only other object in the Solar System known to have bodies of liquid something flowing on its surface. It has a thick atmosphere and seasons. Its methane cycle signifies a mature and stable resource recycling system, just the way a functional household allows you to have routines. Yes, it’s cold and apparently desolate, but Titan can’t help these things. Water would freeze on its surface but the Saturnian moon has made do with what wouldn’t, and it has a singularly fascinating surface chemistry to show for it. Titan has been one of the more unique moons ever found.

And new observations and studies of the moon only make it more unique. This week, scientists from the Georgia Institute of Technology reported Titan possibly has dunes of tar that, once formed, stay in formation because their ionised particles cling together. The scientists stuck naphthalene and biphenyl – two organic compounds thought to exist on Titan’s surface – into a tumbler, tumbled it around for about 20 minutes in a nitrogen chamber and then emptied it. According to a Georgia Tech press release, 2-5% of the mixture lumped up.

The idea of tarry sands is not new. The Cassini probe studying the Saturn system found strange, parallel dunes near Titan’s equator in 2006, over a hundred metres tall. Soon after, scientists were thinking about ‘sediment cohesiveness’, the tendency of certain particles to stick together because of weak but persistent static charges, to explain the dunes. These charges are much weaker among sand particles and volcanic ash on Earth. Then again, in a 2009 paper in Nature Geoscience – the same journal the Georgia Tech study was published in – planetary geologists showed that longitudinal dunes, as they were called, were known to form in the Qaidam Basin in China. A note accompanying the paper explained:

More recent models for linear dune formation are centred on two main scenarios for formation and perpetuation. Winds from two alternating directions, separated by a wide angle, result in the formation of dunes whose long axis falls somewhere between the two wind directions. Alternatively, winds blowing from a single direction along a dune surface that has been stabilized in some way, for example by vegetation, an obstacle or sediment cohesiveness, can produce the same dune form.

That the Georgia Tech study affirmed the latter possibility doesn’t mean the former has been ruled out. Scientists have shown that bi-directional winds are possible on Titan, where wind blows in one direction over a desert and then shifts by 120º and blows over the same patch, forming a longitudinal dune. One of the Georgia Tech study’s novelties is in finding a way for the dune’s particles to stick together. Previous studies couldn’t confirm this was possible because the dunes mostly occur near Titan’s equator, where the weather is relatively much drier than at the poles, where mud-like clumps can form and hold their shape.

The other novelty is in using their naphthalene-biphenyl model to explain why the longitudinal dunes are also facing away from the wind. As one of the study’s authors told New Scientist, “The winds are moving one way and the sediments are moving the other way.” This is because the longitudinal dunes accrue on existing dunes and elongate themselves backwards. And once they do form, more naphthalene and biphenyl grains stick on them thanks to the static produced by them rubbing against each other. Only storms can budge them then.

The Georgia Tech group also writes in its paper that infrared and microwave observations suggest the dune’s constituent particles don’t become available through the erosion of nearby features. Instead, the particles become available out of Titan’s atmosphere, in the form of ‘haze particles’. They write: “[Frictional] charging provides an efficient process for the aggregation of simple aromatic hydrocarbons, and may serve as a mechanism for the formation of dune grains with diameters of several hundred micrometers from micrometer-sized haze particles.”

A big-picture implication is that Titan’s surface features are shaped by agents that are almost powerless on Earth. In other words, Titan doesn’t just smell weird; it’s also sticky. Despite the moon’s being similar to Earth in many ways, there are still drastic differences arising from small mismatches, mismatches we’d think wouldn’t make a difference. They remind us of the conditions we take for granted at home that are friendly to life – and of the conditions in which we can still dream of the possibility of life. Again, studies (described here and here) have shown this is possible. One has even warned us that Titanic lifeforms, if they exist, would smell nowhere as good as their name at all.

Understanding the dunes is a way to understand Titan’s winds. This is important because future missions to the moon envisage wind-blown balloons and cruising gliders.

Featured image: Saturn in the background of Titan, its largest moon. Credit: gsfc/Flickr, CC BY 2.0.

I’d written this post originally for Gaplogs but it got published in The Wire first.

Saturn in the background of Titan, its largest moon. Credit: gsfc/Flickr, CC BY 2.0

Titan’s chemical orgies

Titan probably smells weird. It looks like a ball of dirt. It has ponds and streams of liquid ethane and methane and lakes of the two ethanes, with nitrogen bubbling up in large patches, near its poles. It has clouds of hydrocarbons raining down more methane. And like the water cycle on Earth, Titan has a methane cycle. Its atmosphere is a stifling billow of (mostly) nitrogen. Its surface temperature often dips below -180º C, and the Sun is as bright in its sky as our moon is in ours. In all, Titan is a dank orgy of organic chemistries playing out at the size of a small planet. And it smells weird – like gasoline. All the time.

But it is also beautiful. Titan is the only other object in the Solar System known to have bodies of liquid something flowing on its surface. It has a thick atmosphere and seasons. Its methane cycle signifies a mature and stable resource recycling system, just the way a functional household allows you to have routines. Yes, it’s cold and apparently desolate, but Titan can’t help these things. Water would freeze on its surface but the Saturnian moon has made do with what wouldn’t, and it has a singularly fascinating surface chemistry to show for it. Titan has been one of the more unique moons ever found.

And new observations and studies of the moon only make it more unique. This week, scientists from the Georgia Institute of Technology reported Titan possibly has dunes of tar that, once formed, stay in formation because their ionised particles cling together. The scientists stuck naphthalene and biphenyl – two organic compounds thought to exist on Titan’s surface – into a tumbler, tumbled it around for about 20 minutes in a nitrogen chamber and then emptied it. According to a Georgia Tech press release, 2-5% of the mixture lumped up.

The idea of tarry sands is not new. The Cassini probe studying the Saturn system found strange, parallel dunes near Titan’s equator in 2006, over a hundred metres tall. Soon after, scientists were thinking about ‘sediment cohesiveness’, the tendency of certain particles to stick together because of weak but persistent static charges, to explain the dunes. These charges are much weaker among sand particles and volcanic ash on Earth. Then again, in a 2009 paper in Nature Geoscience – the same journal the Georgia Tech study was published in – planetary geologists showed that longitudinal dunes, as they were called, were known to form in the Qaidam Basin in China. A note accompanying the paper explained:

More recent models for linear dune formation are centred on two main scenarios for formation and perpetuation. Winds from two alternating directions, separated by a wide angle, result in the formation of dunes whose long axis falls somewhere between the two wind directions. Alternatively, winds blowing from a single direction along a dune surface that has been stabilized in some way, for example by vegetation, an obstacle or sediment cohesiveness, can produce the same dune form.

That the Georgia Tech study affirmed the latter possibility doesn’t mean the former has been ruled out. Scientists have shown that bi-directional winds are possible on Titan, where wind blows in one direction over a desert and then shifts by 120º and blows over the same patch, forming a longitudinal dune. One of the Georgia Tech study’s novelties is in finding a way for the dune’s particles to stick together. Previous studies couldn’t confirm this was possible because the dunes mostly occur near Titan’s equator, where the weather is relatively much drier than at the poles, where mud-like clumps can form and hold their shape.

The other novelty is in using their naphthalene-biphenyl model to explain why the longitudinal dunes are also facing away from the wind. As one of the study’s authors told New Scientist, “The winds are moving one way and the sediments are moving the other way.” This is because the longitudinal dunes accrue on existing dunes and elongate themselves backwards. And once they do form, more naphthalene and biphenyl grains stick on them thanks to the static produced by them rubbing against each other. Only storms can budge them then.

The Georgia Tech group also writes in its paper that infrared and microwave observations suggest the dune’s constituent particles don’t become available through the erosion of nearby features. Instead, the particles become available out of Titan’s atmosphere, in the form of ‘haze particles’. They write: “[Frictional] charging provides an efficient process for the aggregation of simple aromatic hydrocarbons, and may serve as a mechanism for the formation of dune grains with diameters of several hundred micrometers from micrometer-sized haze particles.”

A big-picture implication is that Titan’s surface features are shaped by agents that are almost powerless on Earth. In other words, Titan doesn’t just smell weird; it’s also sticky. Despite the moon’s being similar to Earth in many ways, there are still drastic differences arising from small mismatches, mismatches we’d think wouldn’t make a difference. They remind us of the conditions we take for granted at home that are friendly to life – and of the conditions in which we can still dream of the possibility of life. Again, studies (described here and here) have shown this is possible. One has even warned us that Titanic lifeforms, if they exist, would smell nowhere as good as their name at all.

Understanding the dunes is a way to understand Titan’s winds. This is important because future missions to the moon envisage wind-blown balloons and cruising gliders.

Featured image: Saturn in the background of Titan, its largest moon. Credit: gsfc/Flickr, CC BY 2.0.

I’d written this post originally for Gaplogs but it got published in The Wire first.

A submarine on Titan in 2040

An artist's conception of the proposed Titan Submarine, which NASA could land on Titan around 2040 to explore the depths of Kraken Mare, the moon's largest hydrocarbon lake.
An artist’s conception of the proposed Titan Submarine (conceived before the latest design was released), which NASA could land on Titan around 2040 to explore the depths of Kraken Mare, the moon’s largest hydrocarbon lake. Image: NASA

Nothing bespeaks humankind’s potential more than the following statement: Around 2040, NASA plans to splash down a submarine to explore a liquid hydrocarbon lake on Titan.

Fore more than a decade now, Titan has captivated astronomers not simply by being Saturn’s largest moon by far but also with its vast seas of liquid methane and ethane. NASA has its eyes on the largest such lake, called Kraken Mare, located near the moon’s north pole. The Cassini mission helped map the lake in great detail since it reached the Saturnian system in 2004, accompanied by the Huygens probe that landed on the moon’s surface in 2005. Thanks to them, we know Kraken Mare has an intricate shoreline and deposits of water-soluble minerals around it. According to the scientists who authored the article describing the submarine, these features “hint at a rich chemistry and climate history”.

They continue: “The proposed ~1-tonne vehicle, with a radioisotope Stirling generator power source, would be delivered to splashdown circa 2040, to make a ~90-day, ~2,000 km voyage of exploration around the perimeter, and across the central depths of Kraken.” While its design is by no means final (it’s described as a “first cut”), that NASA is considering exploring Titan in great detail belies its interest in the moon as well as continued commitment to studying the Saturnian system in general. Note that the agency cancelled the development of the proposed Titan Mare Explorer – a nautical surface probe – soon after 2013 to channel the funds into developing Stirling radioisotope generators, which we now find could be used to power the submarine.

Notwithstanding future budgetary cuts, delivering such a vehicle to the surface of a faraway moon might just signify the next leap in astronautical engineering. As the scientists remark,

Even with its planetary application aside, this exercise has forced us to look at submarine vehicle design drivers in a whole new way.

The current design has been developed by scientists from the JHU Applied Physics Laboratory, the NASA Glenn Research Center, and the Penn State Applied Research Lab. It will be presented at the 46th Lunar and Planetary Science Conference in Texas, during March 16-20.

1970s Space Shuttle ditching tests at Langley show lifting bodies can make safe landing on liquid.
1970s Space Shuttle ditching tests at Langley show lifting bodies can make safe landing on liquid. Image: ‘Titan Submarine: Vehicle Design and Operations Concept for the Exploration of the Hydrocarbon Seas of Saturn’s Giant Moon’ by Lorenz et al

Around 2040, they expect to be able to deliver it to Titan on board a ‘spaceplane carrier’, essentially a repurposed US Air Force DARPA X-37. According to them, Titan’s thick atmosphere could allow the carrier to descend to the surface at hypersonic speeds, following which attempt a soft-landing on the Kraken Mare. Finally, “the backshell covering the submarine would be jettisoned and the lifting body would sink, leaving the submarine floating to begin operations. (Alternatively, the submersible could be extracted in low level flight by parachute).”

Once inside, it will explore tidal currents in Kraken Mare, use a camera mounted on the mast to explore the shoreline landscape, make meteorological observations, analyze sediments from the seabed, and study trace organic compounds to learn how they evolved.

The slender low-drag hull has propulsors at rear, and a large dorsal antenna at the front of which is a surface camera is mounted in a streamlined cowl. A sidescan sonar, seafloor camera, and seafloor sampling system are visible on ventral surfaces.
The slender low-drag hull has propulsors at rear, and a large dorsal antenna at the front of which is a surface camera is mounted in a streamlined cowl. A sidescan sonar, seafloor camera, and seafloor sampling system are visible on ventral surfaces. Image: ‘Titan Submarine: Vehicle Design and Operations Concept for the Exploration of the Hydrocarbon Seas of Saturn’s Giant Moon’ by Lorenz et al

The submarine itself looks conventional apart from a large dorsal antenna and two cylindrical buoyancy tanks that jut out of the upper surface. According to its designers, the antenna was shaped so to be able to send data across billions of kilometers to Earth. And such large buoyancy tanks are necessary because the lake the submarine will explore is composed of methane and ethane, whose densities range from 450 kg/m3 to 670 kg/m3, as well as to counter the unique drag effects arising due to the dorsal antenna.

Another complication is thermodynamics. Titan has a frigid surface, cold enough to keep methane, whose boiling point is -161.5 degrees Celsius, in its liquid form. As a result, extra heat rejected from the submarine’s radioisotope power source could cause the surrounding methane and ethane to bubble. As the scientists explain, this results in “heat transfer uncertainties” as well as the potential to interfere with sonar observations. At the same time, the vessel must also be heavily insulated to allow the power source to warm its insides.

NASA first announced its intention to explore Kraken Mare with a submarine in June 2014, elaborating that the mission would help scientists learn more about the history and evolution of organic compounds in the Solar System, in turn a “critical step” along the path to understanding the formation of life. Earth and Titan are the only two objects in the System to host liquid lakes on their surfaces, albeit of different compositions.

Life on Titan’s world of goo

In the August 8 issue of Science, an international team of scientists has a paper that submits evidence of life in an asphalt lake in Trinidad. Despite having a low water content of 13.5%, it still possesses methane-digesting microbes huddled up in tiny water droplets. One of the authors, Dirk Schulze-Makuch, speculates in an Air & Space Magazine article that the find could have important implications for Saturn’s moon Titan, which is wrapped in chemistries similar to what was found in the lake minus the presence of liquid water.

In fact, its atmosphere is mainly nitrogen, with lakes of liquid methane and ethane on its surface. So, that there are extremophiles living in a world of goo means not all hope is lost for alien life to form on Titan, no matter that such hopes are still too far beyond the ambit of scientific conservatism inspired by how little we know about life’s origins. Nevertheless, the Science paper isn’t the first to demonstrate that life can exist in such extreme conditions similar to those spotted on planetary bodies in the Solar System; in fact, going by previous reports, it isn’t likely to be the last either.

In a 2011 study published in Microbial Biotechnology, South American researchers reported the presence of a fungus, Neosartorya fischeri, that could metabolize asphaltene, “which is considered the most recalcitrant petroleum fraction”. Their work in turn draws from a 1993 study that proved asphalt is susceptible to reacting with certain extracellular enzymes.

However, Schulze-Makuch’s article makes many assumptions. For example, Titan is much colder than Trinidad’s Pitch Lake, a tropical deposition of oil rising up from a tectonic fault at its bed. For another, it is not known if Titan harbors liquid water, which – at least on Earth – is known to decisively encourage the formation of life, just as it did in the lake.

Two pairs of moons make a rare joint appearance. The F ring's shepherd moons, Prometheus and Pandora, appear just inside and outside of the F ring. Meanwhile, farther from Saturn the co-orbital moons Janus (near the bottom) and Epimetheus (near the top) also are captured. This view looks toward the sunlit side of the rings from about 47 degrees above the ringplane. Credit: NASA/JPL-Caltech/Space Science Institute
Two pairs of moons make a rare joint appearance. The F ring’s shepherd moons, Prometheus and Pandora, appear just inside and outside of the F ring. Meanwhile, farther from Saturn the co-orbital moons Janus (near the bottom) and Epimetheus (near the top) also are captured. This view looks toward the sunlit side of the rings from about 47 degrees above the ringplane. Credit: NASA/JPL-Caltech/Space Science Institute

 

Fortunately – rather, optimistically – astrobiologists have been able to rationalize how life could form on Titan. In 2005, Chris McKay and Heather Smith, both astrobiologists at NASA Ames Research Center, were able to come up with a mechanism by which methanogenic microbes in Titan’s troposphere could be metabolizing acetylene, ethane and some other organic compounds – of which the moon has plenty – to release 54-334 kJ/mol, an amount of energy that similar extremophile critters on Earth have been known to get by on.

They also think it’s possible that the microbes could be catalyzing biochemical reactions despite the low temperature, around -180 degrees Celsius. In either case, their calculations are dependent on the microbes consuming hydrocarbons along with atmospheric hydrogen – an adjustment for convenience. Being a gas with no other sources or sinks in Titan’s atmosphere, any dip in its concentration could be a sign of life, albeit a distant one. McKay had said in a NASA press release in 2010 that “We suggested hydrogen consumption because it’s the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth.”

His and Smith’s hypothesis found some validation in that year – 2010 – when the Cassini space probe found anomalous deficiencies of hydrogen and acetylene, which should be evenly distributed around the moon but weren’t, meaning they were disappearing into somewhere or something, like being consumed. “If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth,” McKay had said.

Just as well, some other astrobiolgists think the cosmic rays bombarding Titan’s atmosphere could be transforming acetylene into more complex hydrocarbons, constituting the non-biological explanation that scientists would like to have out of the way first. Even today, this attitude hasn’t changed because the basis of methanogenic life is still very theoretical, a possibility hinged on chemical reactions worked out by supercomputers. Yet, it’s a tantalizing possibility.

In a 2004 paper by Steven Benner, University of Florida, et al, the authors discuss how life could form without liquid water if only a few other conditions are met: a thermodynamic disequilibrium (a natural mechanism to maintain periodically varying temperatures), “temperatures consistent with chemical bonding” and the presence of a solvent system. The paper itself begins by questioning not how life originated but, in deference to its great adaptability, why life on Earth is what it is.

I reproduce a paragraph from it that I find provides a fitting explanation to why the search for life on Titan (and perhaps also Io and Enceladus) is worth keeping up:

The universe of chemical possibilities is huge. For example, the number of different proteins 100 amino acids long, built from combinations of the natural 20 amino acids, is larger than the number of atoms in the cosmos. Life on Earth certainly did not have time to sample all possible sequences to find the best. What exists in modern Terran [i.e. Earth-bound] life must therefore reflect some contingencies, chance events in history that led to one choice over another, whether or not the choice was optimal.

It’s also after 2004 – in 2013, actually – that we also discovered that Titan might be running out of methane soon. Studies conducted since around 2005 showed that the moon’s source of methane could be less from photochemical reactions in its atmosphere and more from subsurface pockets where the gas could have been trapped. According to a NASA statement, “the current load of methane at Titan may have come from some kind of gigantic outburst from the interior eons ago possibly after a huge impact,” and could run out in tens of millions of years, a short span on the geological timescale.

If so, then, if methanogenic life hasn’t already formed but is likely to, it better do so quickly. If our models have an as yet undetected or undetectable flaw, then, as always, time will tell. If, ultimately, life is already present on Solar System’s second-largest moon, then one can only hope it’s as versatile as the world that hosts it.

~

References

  1. Scientists Find Life in a Lake of Oil, Air & Space Magazine. Accessed August 10, 2014.
  2. Meckenstock, R.U. et al, Water droplets in oil are microhabitats for microbial life. Science, 8 August 2014: 345 (6197), 673-676. doi: 10.1126/science.1252215
  3. Uribe-Alvarez, C., Ayala, M., Perezgasga, L., Naranjo, L., Urbina, H. and Vazquez-Duhalt, R. (2011), First evidence of mineralization of petroleum asphaltenes by a strain of Neosartorya fischeri. Microbial Biotechnology, 4: 663–672. doi: 10.1111/j.1751-7915.2011.00269.x
  4. Fedorak, P.M, Semple, K.M., Vazquez-Duhalt, R., Westlake, D.W.S., Chloroperoxidase-mediated modifications of petroporphyrins and asphaltenes. Enzyme and Microbial Technology, Volume 15, Issue 5, May 1993, Pages 429–437. doi: 10.1016/0141-0229(93)90131-K
  5. Tobie, G., Lunine, J.I. and Sotin, C., Episodic outgassing as the origin of atmospheric methane on Titan. 28 November 2005, Nature 440, 61-64. doi:10.1038/nature04497
  6. Benner, S.A., Alonso Ricardo, A. and Carrigan, M.A., Is there a common chemical model for life in the universe?. Current Opinion in Chemical Biology, 2004, 8:672–689. doi: 10.1016/j.cbpa.2004.10.003

After less than 100 days, Curiosity renews interest in Martian methane

A version of this story, as written by me, appeared in The Hindu on November 15, 2012.

In the last week of October, the Mars rover Curiosity announced that there was no methane on Mars. The rover’s conclusion is only a preliminary verdict, although it is already controversial because of the implications of the gas’s discovery (or non-discovery).

The presence of methane is one of the most important prerequisites for life to have existed in the planet’s past. The interest in the notion was increased when Curiosity found signs that water may have flowed in the past through Gale Crater, the immediate neighbourhood of its landing spot, after finding sedimentary settlements.

The rover’s Tunable Laser Spectrometer (TLS), which analysed a small sample of Martian air to come to the conclusion, had actually detected a few parts per billion of methane. However, recognising that the reading was too low to be significant, it sounded a “No”.

In an email to this Correspondent, Adam Stevens, a member of the science team of the NOMAD instrument on the ExoMars Trace Gas Orbiter due to be launched in January 2016, stressed: “No orbital or ground-based detections have ever suggested atmospheric levels anywhere above 10-30 parts per billion, so we are not expecting to see anything above this level.”

At the same time, he also noted that the 10-30 parts per billion (ppb) is not a global average. The previous detections of methane found the gas localised in the Tharsis volcanic plateau, the Syrtis Major volcano, and the polar caps, locations the rover is not going to visit. What continues to keep the scientists hopeful is that methane on Mars seems to get replenished by some geochemical or biological source.

The TLS will also have an important role to play in the future. At some point, the instrument will go into a higher sensitivity-operating mode and make measurements of higher significance by reducing errors.

It is pertinent to note that scientists still have an incomplete understanding of Mars’s natural history. As Mr. Stevens noted, “While not finding methane would not rule out extinct or extant life, finding it would not necessarily imply that life exists or existed.”

Apart from methane, there are very few “bulk” signatures of life that the Martian geography and atmosphere have to offer. Scientists are looking for small fossils, complex carbon compounds and other hydrocarbon gases, amino acids, and specific minerals that could be suggestive of biological processes.

While Curiosity has some fixed long-term objectives, they are constantly adapted according to what the rover finds. Commenting on its plans, Mr. Stevens said, “Curiosity will definitely move up Aeolis Mons, the mountain in the middle of Gale Crater, taking samples and analyses as it goes.”

Curiosity is not the last chance to look more closely for methane in the near future, however.

On the other side of the Atlantic, development of the ExoMars Trace Gas Orbiter (TGO), with which Mr. Stevens is working, is underway. A collaboration between the European Space Agency and the Russian Federal Space Agency, the TGO is planned to deploy a stationary Lander that will map the sources of methane and other gases on Mars.

Its observations will contribute to selecting a landing site for the ExoMars rover due to be launched in 2018.

Even as Curiosity completed 100 days on Mars on November 14, it still has 590 days to go. However, it has also already attracted attention from diverse fields of study. There is no doubt that from the short trip from the rim of Gale Crater, where it is now, to the peak of Aeolis Mons, Curiosity will definitely change our understanding of the enigmatic red planet.