Probing exoplanet atmospheres could reveal telltale signatures of life

Detecting these so-called biosignatures, compounds that are known to be produced by living organisms, would be strong evidence that worlds may contain life. But picking up chemicals from such distant worlds, and choosing the right compounds to look for, is complicated.

Professor Ignas Snellen at Leiden University in the Netherlands has been refining techniques that combine data from the largest ground-based telescopes with high-contrast imaging that can reveal faint objects like planets. The telescopes use high-precision spectroscopy to examine the different wavelengths of the light they detect from space.

‘You want to filter out the actual starlight as much as possible to make visible whatever information you can get from the exoplanet,’ Prof. Snellen said.

By examining the starlight that filters through a planet’s atmosphere and reaches us on Earth, it’s possible to derive the types of gases that are present.

While telescopes are not yet large enough to examine the spectra for Earth-size planets, scientists are honing their methods on larger exoplanets, so-called hot Jupiters, which are far too hot to support life as we know it. These are gas giant exoplanets that orbit very closely to their parent star. So closely, in fact, that they are tidally locked, like our moon, with the exoplanet rotating only once with every orbit around its star.

With one side of such planets always in light and the other always in darkness, the light side gets so hot that the atmosphere can boil off, creating a wind of matter flowing off the planet, a bit like a comet’s tail.

In the EXOPLANETBIO project, Prof. Snellen and his team used high-precision spectroscopy for the first time to confirm the amount of helium in a hot Jupiter’s atmosphere using ground-based telescopes, which can reveal how far gone this process is.

‘That was a breakthrough for these hot Jupiters,’ he said. ‘These kinds of exospheric tails were known, but they are very difficult to observe because the only way to see them was through detecting hydrogen, which can’t be detected through Earth’s atmosphere, using the Hubble space telescope.

‘Now, with the stronger helium line we can do this very well from the ground with telescopes.’

Understanding if a hot Jupiter may bleed off its atmosphere, and how long it may take, can explain how the atmospheres of all exoplanets change over time.

‘These kind of atmospheric escape processes are not very important now, but in the early solar system they were, because the sun was a lot more active,’ Prof. Snellen said.

Exoplanet climate

Using these new techniques, his team has also been able to achieve another first, detecting the spin rate – how fast a planet rotates – and orbital velocity of exoplanets.

‘The spin rates on hot Jupiters are generally quite low, as they are generally tidally locked,’ he said.

That can reveal something about the climate and related weather on the exoplanet.

‘When a planet rotates fast, it gets bands like Jupiter. The Earth rotates slower and has some bands, but it’s still mostly dominated by low pressure systems. Now, if you have a hot Jupiter which is rotating even slower, you wouldn’t get any banded structure. You get very different weather systems,’ he said.

He has been able to observe winds high up in the atmosphere of such planets, as energy from the hotter, eternal-day side is rotated to the cooler night side.

Prof. Snellen is confident that an upgrade to the CRIRES (CRyogenic high-resolution InfraRed Echelle Spectrograph) instrument, set to go online next year on the European Southern Observatory’s (ESO) Very Large Telescope, will let them find compounds such as methane on cooler planets. Methane can be a component in life if it is found in Earth-size planets.

‘I see this as a kind of a playing ground. We are learning the methods now that we can someday apply to Earth-like planets. The (ESO’s) Extremely Large Telescope should be ready in 2026, and with that we can start to probe Earth-like planets.’

Sign of life

Yet even if you have good samples from rocky, Earth-size planets, how do you know if a compound is truly a sign of life?

‘Geology is very good at producing things that look like life, such as methane. It could come from cows or it could come from rocks,’ said Professor Kevin Heng, a professor at the University of Bern in Switzerland.

‘If you think about biosignatures, they have to satisfy various conditions. They have to not be mimicked by geology, they have to exist in the atmosphere for long periods of time, meaning that they are very stable or are replenished somehow, and they have to be detectable.'

As part of the EXOKLEIN project, Prof. Heng is working on determining if such compounds, like methyl chloride and ammonia, can last long enough in exoplanetary atmospheres to study, by modelling small planets around dwarf stars. It’s a particular challenge for Earth-size planets, whose atmospheres can change over time.

'Geology is very good at producing things that look like life, such as methane. It could come from cows or it could come from rocks.'

Dr Kevin Heng, University of Bern, Switzerland

‘If you look at a planet like Jupiter … they kind of look like the sun. They are made of hydrogen, they have trace elements of metals and so on. Based on differences between the planet and the star I can figure out how it formed. It would keep a fossil record of how it formed,’ Prof. Heng said.

But for smaller planets, their atmospheres have changed significantly over time through processes like the carbon cycle.

‘We spent the last eight to 10 years figuring out how to use climate models designed for Earth (on exoplanets), and how to tweak and modify them.’

Those models will be used to provide potential explanations for data collected when instruments are capable of surveying smaller planets for life, to understand if compounds are really biosignatures or can be explained away as geological.

‘Extraordinary claims require extraordinary standards of proof, so if something is consistent with not requiring biology, I would say there’s no biology,’ said Prof. Heng.

He is also modelling planets that may have had more dramatic fates. For small planets around red stars to support life, they would need to have a very tight orbit, making them tidally locked like hot Jupiters.

‘This means that the night side is really cold, and maybe cold enough that the gases in the atmosphere would condense into ice. So, you get a runaway condensation and you have no atmosphere – atmospheric collapse,’ he said. Such collapse would leave planets cold and lifeless, like Mars.

While the work is just theoretical now, upcoming missions like the European Space Agency’s CHEOPS satellite and NASA’s James Webb Space Telescope should yield data that he can match up against his theories.

‘When Webb launches (in 2021), there is going to be a quantum leap in the quality of data. It may so happen that atmospheric collapse is so prevalent that half the small planets around red stars don’t have atmospheres.’

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

This post Probing exoplanet atmospheres could reveal telltale signatures of life was originally published on Horizon: the EU Research & Innovation magazine | European Commission.

How scientists are working together to solve one of the universe's mysteries

An artist’s impression of fast radio bursts in the sky above the Australian SKA precursor, ASKAP. OzGrav, Swinburne University of Technology

Emma Platts, University of Cape Town and Amanda Weltman, University of Cape Town

One of the most baffling puzzles of modern astrophysics is the nature of Fast Radio Bursts, which were discovered in 2007. These are seemingly rare, extremely bright flashes of light with radio wavelengths. They last only milliseconds; originate outside our galaxy, the Milky Way; come from regions with enormously strong magnetic fields; and pass through a significant amount of gas or dust before reaching Earth.

All of these facts may make it sound as though scientists know a lot about Fast Radio Bursts. In reality, we don’t. For instance, though we know they’re not from our galaxy, we don’t know where exactly they come from. We don’t know what causes them. And we’re not sure whether they might be useful as cosmological standards to measure the large scale properties of our universe.

Dozens of theories about Fast Radio Bursts have been proposed. Some conform to standard physics. Others are more exotic, including cosmic strings – hypothetical, one-dimensional structures formed in the early universe – or even rather bizarre: one theory suggests that aliens are responsible.

Now, in an attempt to discover the truth about Fast Radio Bursts, we have created a catalogue that lists each theory, along with its pros and cons. Scientists from around the world can weigh in, and new data and discoveries will be added throughout the process.

Some of this data will come from projects on the African continent, like the Hydrogen Intensity and Real-time Analysis eXperient (HIRAX), MeerKAT, and the Square Kilometre Array (SKA), which are expected to discover and localise thousands of Fast Radio Bursts.

---

Read more: Africa's MeerKAT 'first light' images have blown all expectations

---

This platform will produce a great deal of knowledge. It will also provide valuable insight into scientific sociology as international researchers work together and ultimately, we hope, identify the most acceptable model.

A range of theories

Perhaps precisely because they are so elusive, Fast Radio Bursts have received a lot of attention from astronomers, astrophysicists, cosmologists, and physicists in the years since their discovery.

These are the main theories that have emerged so far.

• Fast Radio Bursts involve types of neutron stars, such as pulsars (which rotate rapidly) or magnetars (which are highly magnetised). These are probably the most plausible theories, since neutron stars’ intrinsic and extremely large magnetic fields can naturally fulfil the energy requirements for Fast Radio Bursts.

• The merging of astronomical bodies (such as black holes, neutron stars and white dwarfs), and their collapse, has been proposed as a possible origin for Fast Radio Bursts.

In such processes, enormous amounts of energy are released over short timescales. This could possibly create radiation akin to Fast Radio Bursts.

• some of the more exotic models have a more theoretical basis. They involve hypothetical objects such as quark stars (quarks are the subatomic particles that constitute neutrons and protons), axion stars (axions are extremely light, hypothetical subatomic particles), and dark matter: the hypothetical, unobserved matter that is believed to account for 27% of the total matter content of the universe.

• Another fairly improbable theory is that Fast Radio Bursts are lightning striking on pulsars.

And then there’s the suggestion that Fast Radio Bursts are evidence of aliens. It’s certainly the most unusual of the proposed theories, but it cannot be ruled out as a possibility yet.

Although it’s unlikely, Fast Radio Bursts may be signals from a beacon set up by an extraterrestrial civilisation, or perhaps from light sails that harness photons to travel across the galaxy.

There’s a remarkable variation in these models, and it’s hard work to narrow down the options and reach consensus. Of the 50 theories or models proposed to date, only three have been eliminated. This is what prompted us to set up the catalogue and to invite engagement from the broader scientific community.

Platform for debate

It’s no easy task to get scientists talking to each other about Fast Radio Bursts. That’s because the scientists in question have different specialisations and are from all over the world.

The online catalogue provides a suitable and accessible platform for discussion, debate, and the sharing of knowledge. There is also a traceable history, which creates an opportunity for us to study how as humans we work together to solve scientific problems – and perhaps how this process can be optimised in the future.

Part of our motivation, as theoretical physicists, was to develop this engagement and to dive in ourselves. The problems are rich and the waters are deep.

Data about Fast Radio Bursts is starting to pour in now, thanks to such game-changers as MeerKAT and HIRAX. As it arrives, is examined and papers are published, we’ll be able to start ruling out theories and digging deeper into viable theories. Within five years, this mystery could be solved.

Emma Platts, PhD Student, University of Cape Town and Amanda Weltman, South African Research Chair in Physical Cosmology, Department of Mathematics and Applied Mathematics, University of Cape Town

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

In a rare sighting, astronomers observe burst of activity as a massive star forms

This artist’s impression shows the blast from a heatwave detected in a massive, forming star. Katharina Immer/JIVE

James Okwe Chibueze, North-West University

Here on Earth, we pay quite a lot of attention to the sun. It’s visible to us, after all, and central to our lives. But it is only one of the billions of stars in our galaxy, the Milky Way. It’s also quite small compared to other stars – most are at least eight times more massive.

These massive stars influence the structure, shape and chemical content of a galaxy. And when they have exhausted their hydrogen gas fuel and die, they do so in an explosive event called a supernova. This explosion is sometimes so strong that it triggers the formation of new stars out of materials in the dead star’s surroundings.

But there’s an important gap in our knowledge: astronomers don’t yet fully understand how those original massive stars themselves are initially formed. So far, observations have only yielded some pieces of the puzzle. This is because nearly all the known massive stars in our galaxy are located very far away from our solar system. They also form in close proximity to other massive stars, making it difficult to study the environment where they take shape.

One theory, though, is that a rotating disc of gas and dust funnels materials into the growing star.

Astronomers have recently found that the funnelling of matter into a forming star happens at different rates over time. Sometimes the forming star swallows up a huge amount of matter, resulting in a burst of activities in the massive star. This is called an accretion burst event. It is incredibly rare: only three such events have been observed, out of all the billions of massive stars in the Milky Way.

This is why astronomers are so excited about a recent observation of the phenomenon. I was part of the team that recorded this observation. Now, our team and other astronomers will be able to develop and test theories to explain how high-mass stars gain their mass.

A global collaboration

After the first detection of an accretion burst, in 2016, astronomers from around the world agreed in 2017 to coordinate their efforts to observe more. Reported bursts have to be validated and followed up with more observations, and this takes a joint, global effort – which led to the formation of the Maser Monitoring Organisation (M2O).

A maser is the microwave (radio frequency) equivalent of laser. The word stands for “microwave amplification by stimulated emission of radiation”. Masers are observed using radio telescopes and most of them are observed at centimetre wavelength: they are very compact.

A maser flare can be a sign of an extraordinary event such as the formation of a star. Since 2017 radio telescopes in Japan, Poland, Italy, China, Russia, Australia, New Zealand and South Africa (HartRAO, in the country’s Gauteng province) have been working together to detect a flare stimulated by a burst in the funnelling of materials into a massive star.

In January 2019, astronomers at Ibaraki University in Japan noticed that one such massive protostar, G358-MM1, showed signs of new activity. The masers associated with the object brightened significantly over a short period of time. The theory is that masers brighten when excited by an accretion burst.

Follow-up observations with the Australian Long Baseline Array revealed something astronomers are witnessing for the first time – a blast of heat-wave coming from the source and travelling through the surroundings of the forming big star. Blasts can last for about two weeks to a few months.

Burst of energy

Blasts like this were not observed in the previous two accretion bursts in massive stars. This may imply that it’s a different kind of accretion burst. There may even be a “zoo” of accretion burst types – a whole range of different types which act in different ways that may depend on the mass and evolutionary stage of the young star.

Although the burst activity has died down, the masers are still a lot brighter than they were before the burst. Astronomers are watching with interest to see whether a similar burst will occur again, and at what scale.

This experience shows how valuable it is to have lots of eyes on the sky, from different corners of the globe. Collaboration is astronomy is crucial for new, important discoveries.

James Okwe Chibueze, Associate Professor, North-West University

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