nitrogen

Your Friendly Neighbourhood Insect, the Black Soldier Fly

‘I began composting my kitchen waste three years ago. Having experienced the process at such close quarters, I have learnt to live with the black soldier fly, and admire them.’

As home composting is becoming increasingly popular as a way to decentralise and resolve the growing problem of waste in cities, more and more of us are likely to come across the black soldier fly. We have long been educated to disapprove of flies due to their status as disease vectors, but the BSF is an exception to this rule.

In 2017, after resolving to reduce my waste footprint, I set up a pair of terracotta composters on my terrace plus all the tools I would need to manage them. It was rough at first. Within a week into the process of composting my kitchen waste, I opened the lid of the pot to see how things were going – and gagged in horror at the writhing nightmare inside: white larvae (also called maggots) covered the entire surface of the waste; on a quiet evening, I could hear the rustle of their movement and nearly sank to the floor in horror. No one had warned me about this.

Until this moment, I had been harbouring a sanitised idea of composting. In our house, we had pits dug in the ground to manage our leaf waste. The process here was simpler: we had to fill the pits and layer them with a sheet of soil. Then, once they were covered up, we ignored them for a couple weeks. By the time the pits were opened again, the leaves inside had turned into compost. Apart from the organic matter having been ‘out of sight, out of mind’, the fact that it was a leaf pit also made for less hassle because the dead leaves didn’t attract too many critters. But now, faced with the larvae, I wondered if composting my kitchen waste was such a good idea. Did I really want my terrace overrun by these creatures? Thankfully, my better sense prevailed quickly enough. After a few hours spent among books and articles, I was changed and, more importantly, humbled.

Flies are insects of the order Diptera (Latin for ‘two wings’) and include an estimated one million species, many of which humans haven’t studied in as great detail as the rest. In this order, the family of soldier flies alone contain over 2,700 species. The larvae in the composting pot were one kind of soldier fly: the black soldier fly, Hermetia illucens (BSF). It’s unfortunate that the relationship between humans and flies has for the most part been mediated by disease. The more I read about the BSF, the more reason I had to reconsider my view of this little creature. As it happens, BSFs could potentially redefine the future of many industries and, hopefully, our cities.

The many virtues of the black soldier fly

A black soldier fly. Photo: Arpita Joshi

The life-cycle of a BSF is similar to that of a typical fly: it starts off as an egg, becomes a larva, then a pupa and finally emerges as an adult fly.

An adult female lays her eggs on the surface of or around decaying organic matter because BSFs are detritivores, or detritus feeders: they obtain their food by consuming decomposing plant and animal parts. Detritivores, which also includes earthworms, are valued for their ability to break down decaying or dead materials and thus help recycle nutrients. They are essential for Earth’s biogeochemical and energy flow cycles. The way bees find their way to flowers, the BSFs are specialised in finding their way to waste.

I hadn’t encountered a BSF before lifting the lid of the composter, but there they were the minute it was filled with kitchen waste. In a few days, the larvae would emerge from the eggs and feed on the waste. They have a voracious appetite and are omnivorous; rotting kitchen waste, coffee grounds, dairy waste, fish offal and manure are all equally edible. As they grow, each BSF larva can consume 25-500 mg of organic matter per day; as a result, they are able to swiftly reduce the amount of waste.

YouTubers have captured this feeding frenzy in many videos (here’s how 5,000 larvae consume two large rainbow trout in only 10 hours). The larvae are also quite hardy and versatile relative to the more sensitive earthworms and other insects, and can survive between 0º and 45º C and a variety of chemical conditions within the compost pile. In this time, the larvae also secrete a compound that repels other species of flies, thus keeping away potential insect pests and disease vectors and rendering the waste safer for humans.

(This said, it is always a good idea to handle organic waste during the composting phases with protection for your hands ensuring you have no open wounds.)

The larval phase lasts about 14 days. After this, the larvae transform into pupae: they stop eating and their bodies get rid of their digestive tracts. They also begin migrating away from their food source in search of a dry and protected place to pupate. It is these crawling mature brown-black pupae that often deter many people from composting at home: the assumption is that these dirty, dangerous disease-carrying insects must not be encouraged around the house. While this is true for the common flies, blow flies and their larvae, the BSF through all stages of its life-cycle, is harmless to humans.

An adult BSF that appears in the final stage of its life-cycle is about 15-20 mm long and has a shiny black body with metallic green-blue membranous wings. Its lifespan is only a few days, in which time its principal goal is to reproduce. In this time, it survives on the fat deposits leftover from its larval phase and does not feed. As a result, the adult BSF is rarely found inside human homes. Timid and rather gentle, I sometimes find them in the garden resting on leaves or flowers through hot days. On the off chance you spot an adult BSF inside your house, please know that it doesn’t carry any diseases, can’t bite. You could softly scoop it up and release it in the garden.

The future of BSFs

A female black soldier fly depositing eggs in corrugated cardboard. Caption and photo: blacksoldierflyblog.com/Wikimedia Commons, CC BY-SA 3.0

I began composting my kitchen waste three years ago. Having experienced the process at such close quarters, I have learnt to live with the BSF as well as have come to admire and respect them – and I’m not the only one.

BSFs are increasingly garnering international attention because they are the perfect candidates for large-scale ‘waste valourisation‘: the process by which organic and manure waste treated by BSFs is converted to something of greater value. They are financially viable, clean, efficient and fast; BSF larvae’s droppings, called frass, is a potential fertiliser thanks to its high nitrogen content. Finally, the nutritious larvae and pupae could make for protein feed for domesticated livestock.

Producing food rich in proteins for animal husbandry has traditionally had a big ecological footprint. For example, fish meal is harvested from the ocean or requires farmers to invest in water, energy and land in order to raise the fish. Insects like BSF on the other hand provide a less resource-intensive option. They’re also valuable to the farming sector because their offspring subsequently feed on the waste generated by these farms. People in the UK, France, China and the US have already established BSF farms for commercial, agricultural and research use.

BSF larvae and pupae are also rich in nutrients, proteins and fat, in addition to being safe for human consumption, and have caught the attention of scientists who support entomophagy – the consumption of insects by humans; there are even larvae recipes available online! Inventors have also been toying with bug farms, finding new ways to incorporate them in our daily lives.

In 1881, Charles Darwin published his last scientific book, with a name as long as its subject: The Formation of Vegetable Mould through the Action of Worms. It was a thesis Darwin had put together based on observations and experiments he had undertaken over four decades on the behaviour and ecology of earthworms. In his conclusion, he proclaimed, “It may be doubted whether there are many other animals which have played so important a part in the history of the world as have these lowly organised creatures.” These words capture the great arc of Darwin’s journey through his years of study, beginning with ‘lowly creatures’ and culminating, through the rigours of research, with recognising their virtues.

Through the last decade, the BSF’s identity has undergone a similar transformation. It is increasingly becoming an important part of our solution to the mess we have created. As the climate crisis calls us to rethink and rebuild our relationship with the natural world, reacquainting ourselves with the little black soldier fly, and learning to live and work with it seems like a good first step.

Arpita Joshi is co-founder of The Curio-city Collective and co-host of their podcast on cities and well-being. Her interests lie in climate and intergenerational justice.

‘Magic Islands’ of Titan’s Lakes Could Be Streams of Nitrogen Bubbles

The results are relevant for future lander-probes to Titan – and to understand the surface chemistry of the only other body in the Solar System known to have liquids on its surface.

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

Titan is one of the more fascinating bodies in the Solar System. It is Saturn’s largest moon – larger than Mercury – and is the only body other than Earth in the system to have liquids on its surface. Now, 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.

Multiple Cassini flybys over Titan have thrown up some transient features around the moon’s Ligeia Mare lake (see left panels). Credit: NASA/JPL

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.

Why Titan’s ‘Long’ Dunes Could Be the Work of a Sand That Sticks

New studies of Saturn’s moon Titan should’ve made it more familiar – but the more we learn about it, the more outlandish Titan gets.

New studies of Saturn’s moon Titan should make it more familiar – but the more we learn about it, the more outlandish Titan gets.

Saturn and Titan, its largest moon. Credit: gsfc/Flickr, CC BY 2.0

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

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.

Astronomers Catch Star Just Six Hours After it Goes Supernova

They also found the dying star had begun to spew large amounts of material in the year or so before it blew up – something astronomers didn’t think would have happened.

They found the dying star had begun to spew large amounts of material in the year or so before it blew up – something astronomers didn’t expect.

The supernova 2013fs located in a blue, star-forming area (the red point sources in the vicinity are foreground stars), which is apparently a part of one of the major arms of the spiral host NGC 7610. Caption and credit: doi:10.1038/nphys4025

On the night of October 6, 2013, Dan Perley, then from the University of Copenhagen, was using one of the twin Keck Telescopes in Hawaii when he received a message. It was to follow up after a bright fleck in the sky that hadn’t been visible in images of the same patch taken only the night before, in the galaxy NGC 7610 166 million lightyears away. Perley had been informed by his colleagues, who in turn had been tipped off about the fleck by the intermediate Palomar Transient Factory (iPTF) survey, a fully automated survey of the night sky underway at the Palomar Observatory, California.

To be sure, Perley made four spectroscopic observations of the fleck instead of just the one. He was using the Keck-I telescope, the largest of its kind in the world. After further analysis, he and his colleagues would realise that they had been looking at a really young supernova – a star that had begun to die barely six hours earlier. No one has yet caught a supernova this quickly into its act; previous records were in the order of a week. Astronomers believe the new data could hold clues about what exactly happens to a star in its death throes.

“Such observations provide theorists and modellers of stellar evolution with crucial inputs and constraints to ultimately understand the exact mechanisms that effect the latest stages in the evolution of a star and also to understand the supernova explosion itself,” Ofer Yaron, an astrophysicist at the Weizmann Institute, Israel, told The Wire in an email. “Both of them are still not understood and are the topics of major ongoing research.” The Weizmann Institute is part of the international iPTF collaboration and Yaron was one of the scientists involved in analysing the data obtained of the young supernova.

For example, in supernova explosions that happen as a result of a star’s core having collapsed due its own mass, scientists don’t know how big the star is or what its innards look like at the moment of the explosion itself. “We actually don’t even know the exact mechanism” behind it, Yaron said. Is it driven by neutrinos speeding out of the core? Are nuclear fusion reactions kicked off in the intermediate layers of the star?

The red supergiant and its shell

The collaboration was able to study the star, designated SN 2013fs, in visible, radio and ultraviolet frequencies as well as collect X-ray data using the NASA Swift satellite. The cloud of ionised gas surrounding the star had been imaged by Perley using the Low Resolution Imaging Spectrometer on Keck-I. All together, they helped uncover an interesting medley of events signalling the beginning of the end.

Before the supernova explosion, SN 2013fs had been a red supergiant, a very voluminous star that had run out of hydrogen to fuse in its core. In such stars, helium accumulates in the core even as hydrogen fusion begins to occur in the outer layers. SN 2013fs began to expand to cool itself down, ballooning to 50-175-times as wide as our Sun and turning an orangish red (cooler than the usual white-hot). If our Sun itself became that big, it would swallow the orbits of Mercury or Mars depending on the range. Astronomers, however, note that SN 2013fs could have become even bigger. And now that they know it did not, they will have to think about why not.

Moreover, “the emission lines observed in the early spectra point to the fact that there was this nearby dense shell of circumstellar material” (CSM), Yaron said. It was a cloud of highly ionised gas surrounding the dying star at a distance of around 10 billion km and weighing about as much as Jupiter. The iPTF collaboration found that the CSM had also completely disappeared two or three months after the explosion because it stopped showing up in radio-frequency data. High-energy radiation from the star had excited the material, which then lost the extra energy in certain ways that gave away its identity: helium, oxygen, nitrogen, all starstuff. But exactly how was it lost?

The data favours multiple explanations; the iPTF collaboration prefers one in particular, and it is surprising. Their paper suggests “that this material was ejected by the star during the few hundred days prior to its explosion”. According to Yaron, “In recent years, we began accumulating observational evidence that massive stars experienced elevated mass-loss before the supernova explosion.” With the new study, “we have proved that normal red supergiants also experience this, so [it appears to be] a common phenomenon among massive stars in general.”

Their paper was published in the journal Nature Physics on February 14, 2017.

The data also makes room – but less so – for the possibility that, instead of a sustained ‘blowout’ over late-2012 and early-2013, SN 2013fs could have lost the material by sighing out a weaker wind over a longer span of time. Unfortunately, the iPTF group could not measure the velocity of the gas within the CMS: the slower the gas is moving away, slower the rate at which it would have been lost by the star.

Then again, similar uncertainty over the various properties of a star at the precise moment of its demise makes these observations all the more important. For example, once the red supergiant runs out of helium to fuse in its core and moves on to carbon, oxygen, neon and finally silicon, the core’s composition changes dramatically. Previous explorations of this process propose it would send shockwaves reverberating through the star all the way to its surface, where it would displace and throw off material.

Norbert Langer, a theoretical astrophysicist at the University of Bonn, explained in an accompanying article for Nature: “For example, for red supergiant wind velocities of only 5 [km/s], the high mass loss period could also have lasted hundreds of years, perhaps induced by violent pulsations. The gas shell could even be static, like the one recently discovered in Betelgeuse, our closest red supergiant, which is thought to be the result of the confinement of Betelgeuse’s wind due to external ionising photons.”

Catching supernovae a minute old

The radiation emitted by the star’s core during fusion creates an outward pressure that pushes against the weight of the star’s outer layers. Because the core is also successively attempting to fuse heavier elements, it has to become hotter to kickstart the necessary reactions, so it contracts. But at some point, nuclear fusion as well as radioactive decay of other isotopes begin to produce iron-56, the heaviest element the fusion of which produces more energy than it consumes. And once it is exhausted and the core no longer supports the necessary radiation pressure, the outer layers of the core collapse inwards, bounce violently off the inner core, shoot off into the star’s outer layers and send them reeling into space.

Thus, the star itself blows up. When this happened to SN 2013fs, the CSM became heated to over 60,000º C and was possibly dematerialised within a week.

If the progenitor star was once 8-40-times as heavy as our Sun, like SN 2013fs was, the ensuing explosion is called a type II supernova, the more common end for a star in the cosmos than a type I. There are many kinds of type II supernovae depending on how their brightness declines over time – gradually, rapidly, steadily, etc. SN 2013fs was thought to be a IIn but later turned out to be a IIP, which means its brightness falls slowly over time before normalising.

The star’s eventual disintegration releases the elements it produced into the interstellar medium (the space between stars) – this is how the universe’s heavier elements are created. The pieces of metal embedded in the device on which you are reading this? They were once inside a star. Star-born hardware is why humankind even has a digital age.

The work of the iPTF collaboration and others like it is key to understanding when, where and how supernovae occur and to validate what is still a mostly theoretical body of knowledge of how stars die. Catching it early in the act can be very useful because the violence of a supernova, after it occurs, usually destroys any evidence of what might have come before.

Later in 2017, iPTF will be replaced by the Zwicky Transient Factory, an upgraded version of the 48-inch telescope at Palomar Observatory plus a better camera that will enable a “full scan of the visible sky every night”, according to Yaron. “The meaning of this is that the number of transients in general, and supernovae in particular, discovered each night will grow tremendously, with many more events that will be detected young, not only within one day from explosion but even within very few hours or around one hour.”

There are also plans for a space-borne instrument called ULTRASAT to be launched before 2021. The Israeli Space Agency and NASA have announced that they will collaborate on it. ULTRASAT is set to have a camera that can scan a 30-times larger patch of the sky at once than the one in iPTF can, and will be able to pick up on early ultraviolet emissions from pre-supernova stars and alert astronomers within one minute.