Hydrogen-breathing aliens? Study suggests new approach to finding extraterrestrial life

An exoplanet and its atmosphere pass in front of its star (artist’s impression, from an imaginary point near to the planet). NASA Goddard Space Flight Center

David Rothery, The Open University

The first time we find evidence of life on a planet orbiting another star (an exoplanet), it is probably going to be by analysing the gases in its atmosphere. With the number of known Earth-like planets growing, we could soon discover gases in an exoplanet’s atmosphere that are associated with life on Earth.

But what if alien life uses somewhat different chemistry to ours? A new study, published in Nature Astronomy, argues that our best chances of using atmospheres to find evidence of life is to broaden our search from focusing on planets like our own to include those with a hydrogen atmosphere.

We can probe the atmosphere of an exoplanet when it passes in front of its star. When such a transit happens, the star’s light has to pass through the planet’s atmosphere to reach us and some of it is absorbed as it goes. Looking at the star’s spectrum – its light broken down according to its wavelength – and working out what light is missing because of the transit reveals which gases the atmosphere consists of. Documenting exoplanet atmospheres is one of the goals of the much-delayed James Webb Space Telescope.

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Read more: Exoplanets: how we used chemistry to identify the worlds most likely to host life

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If we were to find an atmosphere that has a different chemical mix to what we would expect, one of the simplest explanations would be that it is maintained that way by living processes. That is the case on Earth. Our planet’s atmosphere contains methane (CH₄), which naturally reacts with oxygen to make carbon dioxide. But the methane is kept topped up by biological processes.

Another way to look at this is that the oxygen wouldn’t be there at all had it not been liberated from carbon dioxide by photosynthetic microbes during the so-called great oxygenation event that began about 2.4 billion years ago.

Look beyond oxygen atmospheres

The authors of the new study argue that we should start investigating worlds larger than the Earth whose atmospheres are dominated by hydrogen. These may not have any free oxygen, because hydrogen and oxygen make a highly flammable mixture.

The hydrogen-filled Hindenberg airship destroyed by fire in 1937. Such a fire could not happen on a world with an oxygen-free hydrogen atmosphere. Murray Becker/Associated Press

Hydrogen is the lightest of all molecules and escapes to space easily. For a rocky planet to have gravity strong enough to hang on to a hydrogen atmosphere, it needs to be a “super-Earth” with a mass between about two and ten times the Earth’s. The hydrogen could either have been captured directly from the gas cloud where the planet grew, or have been released later by a chemical reaction between iron and water.

The density of a hydrogen-dominated atmosphere decreases about 14 times less rapidly the higher up you go than in an atmosphere dominated by nitrogen like the Earth’s. This makes for a 14-times greater envelope of atmosphere surrounding the planet, making it easy to spot in the spectra data. The greater dimensions would also improve our chances of observing such an atmosphere by direct imaging with an optical telescope.

Hydrogen-breathing in the lab

The authors carried out laboratory experiments in which they demonstrated that the bacterium E. coli (billions of which live in your intestines) can survive and multiply under a hydrogen atmosphere in the total absence of any oxygen. They demonstrated the same for a variety of yeast.

Although this is interesting, it does not add much weight to the argument that life could flourish under a hydrogen atmosphere. We already know of many microbes within the Earth’s crust that survive by metabolising hydrogen, and there is even a multicellular organism that spends all its life in an oxygen-free zone on the floor of the Mediterranean.

Spinoloricus, a tiny but multicellular organism that apparently requires no oxygen to live. Scale bar is 50 micrometres. Roberto Danovaro, Antonio Dell'Anno, Antonio Pusceddu, Cristina Gambi, Iben Heiner & Reinhardt Mobjerg Kristensen

Earth’s atmosphere, which started out without oxygen, is unlikely ever to have had more than 1% hydrogen. But early life may have had to metabolise by reacting hydrogen with carbon to form methane, rather than by reacting oxygen with carbon to form carbon dioxide, as humans do.

Biosignature gases

The study did make an important discovery though. The researchers demonstrated that there is an “astonishing diversity” of dozens of gases produced by products in E. coli living under hydrogen. Many of these, such as dimethylsilfide, carbonyl sulfide and isoprene, could be detectable “biosignatures” in a hydrogen atmosphere. This boosts our chances of recognising life signs at an exoplanet – you have to know what to look for.

That said, metabolic processes that use hydrogen are less efficient than those using oxygen. However, hydrogen breathing life is already an established concept so far as astrobiologists are concerned. Sentient hydrogen breathers have even made appearances in some rationally-based science fiction, such as the Uplift novels of David Brin.

The authors of the new study also point out that molecular hydrogen in sufficient concentration can act as a greenhouse gas. This could keep a planet’s surface warm enough for liquid water, and hence surface life, further from its star than would otherwise be the case.

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Read more: Twin civilisations? How life on an exoplanet could spread to its neighbour

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The authors shy away from considering the chances of finding life in giant gas planets like Jupiter. Even so, by expanding the pool of habitable worlds to include super-Earths with hydrogen-rich atmospheres, they have potentially doubled the number of bodies we could probe to find those first elusive signs of extraterrestrial life.

David Rothery, Professor of Planetary Geosciences, The Open University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Space dust fossils are providing a new window onto Earth's past.

Space dust fossils are providing a new window onto Earth’s past

Finding fossil meteorites is a whole new level of difficulty because these rocks are not spread thinly on the surface but, like dinosaur fossils, entombed in ancient rocks. But geologist Professor Birger Schmitz at Lund University in Sweden has discovered a way to find them – and not just the odd rock, but sizeable quantities of fossilised space dust.

It turns out that this can paint a unique picture of how the course of ancient life on Earth was influenced by goings on in space – and has already revealed how space dust from an asteroid collision 466 million years ago could have triggered an ice age. 

Rocks

Meteorites are rocks from space that have fallen on Earth, mostly fragments of the asteroids jostling between Mars and Jupiter.

We know that one huge rock smashed into Earth 66 million years ago, killing off the dinosaurs and most other life. This was first hypothesised by Nobel Prize winner Luis Alvarez and his son Walter, both then based at universities in Berkeley, the US. They led the team that discovered a thin iridium-rich ash layer in sediments globally which formed when the dinosaurs became extinct. Iridium is extremely rare in our planet’s crust and so the team concluded that this element had been delivered by a huge asteroid. The implication was that this cataclysm wiped out the dinosaurs, along with three-quarters of all other living things. 

Prof. Schmitz did his postdoc with the Alvarez team and it’s fair to say it shaped his career. ‘Until their discovery, the evolution of life and the history of Earth was almost always thought of like a closed system,’ said Prof. Schmitz. ‘I became fascinated by trying to connect what goes on in space with what happens on Earth.’

Returning home to Sweden in 1990, Prof. Schmitz read some newspaper reports saying that an amateur geologist named Mario Tassinari had found a few fossil meteorites in the Thorsberg quarry on the southern shore of Lake Vänern. At this time, there were only a handful of fossil meteorites known to science. Was this a chance to study what meteorites had been like millions of years ago and piece together the effects they had on Earth? Prof. Schmitz called Tassinari and they agreed to collaborate on a systematic study of the quarry.

‘(Many of) these meteorites are as different from the meteorites that fall today as some of the animals that were living in that time are compared to today’s animals.’

Prof. Birger Schmitz, Lund University, Sweden

Quarry

The quarry workers carve out sheets of limestone for use as floor tiles. When they find a piece that looks like it might hold a space rock, they call Prof. Schmitz. Each year, they get four or five fossil meteorites. They mostly look like little more than black smudges embedded in the rock, a few centimetres across.

Prof. Schmitz wondered if other quarries might hold similar delights. He also went hunting for meteorites in places with the right kind of floor tiles, such as Paddington station in London.

But it turns out Thorsberg is, as far as we know, a one-off. Special conditions are required to preserve sizeable fossil meteorites in reasonable numbers. You need sediments at the bottom of a body of water that turn to rock very gradually. Slowness is crucial, because that allows more meteorites to accumulate on a small area.

Around 2000, Prof. Schmitz began to think he was finding rather a lot of stones – by this time he had nearly 50 in total. He worked out the amount of rock the quarry workers had carved out each year and divided it by the number of meteorites they found. That told him that back when the rock was formed the flux of meteorites, the number falling on a given area in a given time, was about 100 times greater than it is today. An area the size of Wales would have been getting not two meteorites a year, but 200.

‘I still remember the day I thought of this,’ said Prof. Schmitz. ‘I went immediately to the quarry. “Can I see your logbooks? Are you sure you’ve found such a large number of meteorites in such a small area?”’

There was no mistake. And Prof. Schmitz quickly came up with an explanation. ‘There is one very likely scenario: that if something explodes in space and breaks up into billions and billions of small pieces – well, what we saw in the quarry, that's exactly what would happen.’

In 2004, Prof. Schmitz and researchers at ETH-Zürich, Switzerland, published a paper detailing analyses of the fossil meteorites found. This showed that the meteorites had been in space for relatively short stretches of time – about a million years – by looking at the effect of cosmic rays on their mineralogy. He concluded that a violent collision had exploded them onto an Earth-bound trajectory. Still, these stones were small fry in the grand scheme of things; nowhere near large enough to cause an impact that would significantly affect Earth’s history.

You might think that Prof. Schmitz would have wanted to find something bigger. But it doesn’t work like that. It turns out that hefty meteorites are rare, but smaller ones are more common.

Space dust

Micrometeorites, otherwise known as space dust, are the most common of all: it’s estimated that today we get showered with 100 tonnes of this stuff each day. Prof. Schmitz reasoned that it must be strewn throughout the limestone in Thorsberg quarry too – if only there was a way to find it.

One mineral, chromite, in micrometeorites is incredibly hardy: ‘It’s extremely resistant, it survives everything,’ said Prof. Schmitz.

That gave him an idea, which he investigated through a project called Astrogeobiosphere. ‘I told my poor student the time, “Niklas, take 5 kilograms of rock and dissolve it in hydrochloric acid.”’

Doing so resulted in 10 tiny fragments of extraterrestrial chromite, each a tenth of a millimetre long. And repeating this at intervals in the limestone revealed there was a huge uptick in space dust in 466 million year old rock, results that Prof. Schmitz published in 2019.

The space dust arrival coincides with a cold period known as the mid-Ordovician ice age. Prof. Schmitz concluded that a massive collision in the asteroid belt spewed out both large meteorites and a gargantuan cloud of dust, which blocked lots of sunlight from reaching Earth, leading to an ice age. After the asteroid that killed the dinosaurs, it would be the second example of an event in the wider cosmos profoundly influencing Earth’s story.

‘I think this is a hugely exciting story,’ said Dr Katie Joy, a planetary scientist at the University of Manchester, UK. ‘It’s a massive amount of work and I don’t envy them, having to crush up tonnes and tonnes and rock and passing it through acid.’

She adds that there is still work to be done to understand the biases in the sample. The minerals Prof. Schmitz is studying are not found in every sort of asteroid and comet, which means they do not represent all the rock types that have fallen from space to Earth. ‘This record is a partial record,’ she said.

Through Astrogeobiosphere, Prof. Schmitz has taken this work even further by dissolving 20 tonnes of rock from different quarries, with samples from each representing different periods in Earth’s deep history. The idea was to provide the first sketch of how incoming space dust has varied over time.

He says this work is done and he and his team have a collection of different meteorites that fell on Earth in the distant past – but it won’t be published for a few months. However, fossil meteorites continue to reveal new information about Earth's past.

‘(Many of) these meteorites are as different from the meteorites that fall today as some of the animals that were living in that time are compared to today’s animals,’ he said.

The research in this article was funded by the European Research Council. If you liked this article, please consider sharing it on social media.

This post Space dust fossils are providing a new window onto Earth’s past was originally published on Horizon: the EU Research & Innovation magazine | European Commission.

How astronomers are piecing together the mysterious origins of superluminous supernovae

Known as superluminous supernovae, these events are typically 10 to 100 times brighter than a regular supernova but much more rare. We’ve spotted about 100 so far, but many aspects of these events remain elusive.

Why are they so much brighter than regular supernovae, for example, and what stars cause them? Astronomers are hoping to answer these and more questions in the coming years, with various studies underway to understand these events like never before.

Formation

Dr Ragnhild Lunnan from Stockholm University, Sweden, is one of the co-investigators on the SUPERS project, which is attempting to work out what stars lead to the formation of superluminous supernovae. With dozens found already, the team are building the largest collection of these events in an effort to learn more about them.

‘By following the evolution of these supernovae into a very late phase, you can decode their (structure),’ she said. ‘This tells you things about the star that exploded, and possibly how it exploded.’

To find these explosions, Dr Lunnan and her team are making use of a camera called the Zwicky Transient Facility (ZTF), part of the Palomar Observatory in California, US, to survey the sky. Only one supernova is expected per galaxy per century, with only one in 1,000 or even one in 10,000 of those being superluminous. But by looking at many galaxies simultaneously with the ZTF, it’s possible to spot these events.

Superluminous supernovae are found more often in star-forming galaxies than older galaxies, which means they are likely explosions of young stars, notes Dr Lunnan.

‘Additionally, you very often find them in galaxies that are kind of chemically primitive, called low-metallicity, and we think this is also a clue,’ she said. ‘We think they’re associated with very massive and metal-poor stars. But beyond that, we really don’t know.’

In 2018, Dr Lunnan and her team discovered a superluminous supernova with a giant shell of material around it, which it must have ejected in the final years of its short life. ‘That discovery (of the shell) is another clue that the stars must be very massive,’ said Dr Lunnan.

‘You very often find them in galaxies that are kind of chemically primitive, called low-metallicity, and we think this is also a clue.’

Dr Ragnhild Lunnan, Stockholm University, Sweden

Going supernova

The exact process that causes a superluminous supernova is another question. Typically, stars can go supernova either by independently collapsing, or sharing material with a small dense star known as a white dwarf before an explosion takes place, known as a Type 1a supernova. But what happens in a superluminous event?

Dr Avishay Gal-Yam from the Weizmann Institute of Science in Israel, project coordinator on the Fireworks project, has been trying to answer this question. The project has been using observations of the night sky from cameras like the ZTF that have a rapid cadence, meaning they show an event shortly after it occurred, to study cosmic explosions.

Previously we would only see supernovae about two weeks after they happened, but ZTF’s constant observations of the sky allows us to see them within about one or two days. And that’s particularly useful for superluminous supernovae. A regular supernova can brighten and fade over a period of weeks, but a superluminous supernovae can last several times longer, while also reaching its peak brightness slower.

‘They are relatively slowly evolving,’ he said. ‘The time for the explosion to reach its peak could be a couple of months, sometimes even longer. So studies of these objects are not focused on rapid observations, but rather a continuous follow-up campaign which takes months and sometimes years.’

So far Dr Gal-Yam and his team have published several studies, examining some of the theories for how these events happen. One idea is that a regular supernova leaves behind a rapidly spinning and highly magnetised neutron star, called a magnetar, which acts as a giant magnet and pumps energy into the supernova explosion.

But Dr Gal-Yam’s more favoured theory is the same advocated by Dr Lunnan – that collapsing massive stars are the cause. ‘What can generate so much energy that can power such a luminous emissions, both in terms of the amount of energy and the very long amount of time the emission continues to happen?’ he said. ‘The most intriguing (theory) is an explosion from a very massive star 100 times more massive than the sun.’

Distance

While many questions about superluminous supernovae remain unanswered, they are already proving useful as distance markers in the universe. Called ‘standard candles’, bright events like supernovae can tell us how far away a particular galaxy is as we know how bright they should be.

‘The idea here is a standard candle, an object of known luminosity,’ said Dr Mark Sullivan, project coordinator on the SPCND project that looked at how explosive events like this might be useful for cosmological studies. ‘If you can find it in the sky and measure how bright it appears to be to us on Earth, you can tell how far away it is.’

The brightness of superluminous supernovae makes them particularly useful. Using the Dark Energy Survey (DES), a survey of the night sky using the Cerro Tololo Inter-American Observatory in Chile, Dr Sullivan and his team found more than 20 superluminous supernovae in galaxies up to eight billion light-years from Earth, giving us a new cosmic distance ladder. ‘We got a new data set of these objects in the distant universe,’ said Sullivan.

With a growing sample size of these events, astronomers will now be hoping to answer once and for all what causes them. Upcoming telescopes like the Vera C. Rubin Observatory in Chile could prove vital, performing new sweeping surveys of the night sky, and finding more of these objects than ever before.

‘We really are in this era where we’re finding so many objects – even things that are rare,’ said Dr Lunnan. ‘It’s a lot of fun.’

The research in this article was funded by the EU. If you liked this article, please consider sharing it on social media.

This post How astronomers are piecing together the mysterious origins of superluminous supernovae was originally published on Horizon: the EU Research & Innovation magazine | European Commission.

Earth's magnetic field may change faster than we thought.

 

Earth’s magnetic field may change faster than we thought – new research

It’s long been a mystery how fast the Earth’s magnetic field changes. Andrey VP/Shutterstock

Christopher Davies, University of Leeds

The Earth’s magnetic field, generated 3,000km below our feet in the liquid iron core, is crucially important to life on our planet. It extends out into space, wrapping us in an electromagnetic blanket that shields the atmosphere and satellites from solar radiation.

Yet the magnetic field is constantly changing in both its strength and direction and has undergone some dramatic shifts in the past. This includes enigmatic reversals of the magnetic poles, with the south pole becoming the north pole and vice versa.

A long-standing question has been how fast the field can change. Our new study, published in Nature Communications, has uncovered some answers.

Rapid changes of the magnetic field are of great interest because they represent the most extreme behaviour of the ocean of molten iron in the liquid core. By tying the observed changes to core processes, we can learn important information about an otherwise inaccessible region of our planet.

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Read more: Why the Earth's magnetic poles could be about to swap places – and how it would affect us

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Historically, the fastest changes in Earth’s magnetic field have been associated with reversals, which occur at irregular intervals a few times every million years. But we discovered field changes that are much faster and more recent than any of the data associated with actual reversals.

Magnetic reversal. NASA.

Nowadays satellites help monitor changes in the field in both space and time, complemented by navigational records and ground-based observatories. This information reveals that changes in the modern field are rather ponderous, around a tenth of a degree per year. But, while we know that the field has existed for at least 3.5 billion years, we don’t know much about its behaviour prior to 400 years ago.

To track the ancient field, scientists analyse the magnetism recorded by sediments, lava flows and human-made artefacts. That’s because these materials contain microscopic magnetic grains that record the signature of Earth’s field at the time they cooled (for lavas) or were added to the landmass (for sediments). Sediment records from central Italy around the time of the last polarity reversal almost 800,000 years ago suggest relatively rapid field changes reaching one degree per year.

Such measurements, however, are extremely challenging, with results still being debated. For example, there are uncertainties in the process by which sediments acquire their magnetism.

Improved measurements

Our research takes a different approach by using computer models based on the physics of the field generation process. This is combined with a recently published reconstruction of global variations in Earth’s magnetic field spanning the last 100,000 years, based on a compilation of measurements from sediments, lavas and artefacts.

This shows that changes in the direction of Earth’s magnetic field reached rates that are up to ten degrees per year – ten times larger than the fastest currently reported variations.

The fastest observed changes in the geomagnetic field direction occurred around 39,000 years ago. This shift was associated with a locally weak field in a confined region just off the west coast of central America. The event followed the global “Laschamp excursion” – a “failed reversal” of the Earth’s magnetic field around 41,000 years ago in which the magnetic poles briefly moved far from the geographic poles before returning.

The fastest changes appear to be associated with local weakening of the magnetic field. Our model suggests this is caused by movement of patches of intense magnetic field across the surface of the liquid core. These patches are more prevalent at lower latitudes, suggesting that future searches for rapid changes in direction should focus on these areas.

The impact on society

Changes in the magnetic field, such as reversals, probably don’t pose a threat to life. Humans did manage to live through the dramatic Laschamp excursion. Today, the threat is mainly down to our reliance on electronic infrastructure. Space weather events such as geomagnetic storms, arising from the interaction between the magnetic field and incoming solar radiation, could disrupt satellite communications, GPS and power grids.

Satellites are at risk from space weather. Andrey Armyagov/Shutterstock

This is troubling – the economic cost of a collapse of the US power grid due to a space-weather event has been estimated at around one trillion dollars. The threat is serious enough for space weather to appear as a high priority on the UK national risk register.

Space weather events tend to be more prevalent in regions where the magnetic field is weak – something we know can happen when the field is changing rapidly. Unfortunately, computer simulations suggest that directional changes arise after the field strength begins to weaken, meaning we cannot predict dips in field strength by just monitoring the field direction. Future work using more advanced simulations can shed more light on this issue.

Is another rapid change in the magnetic field on its way? This is very hard to answer. The fastest changes are also the rarest events: for example, the changes identified around the Laschamp excursion are over two times faster than any other changes occurring over the last 100,000 years.

This makes it difficult for scientists to predict rapid changes – they are “black swan events” that come as a surprise and have a big impact. One possible route forward is to use physics-based models of how the field behaves as part of the forecast.

We still have a lot to learn about the “speed limit” of Earth’s magnetic field. Rapid changes have not yet been directly observed during a polarity reversal, but they should be expected since the field is thought to become globally weak at these times.

Christopher Davies, Associate professor, University of Leeds

This article is republished from The Conversation under a Creative Commons license. Read the original article.