Astronomers reveal a new link between water and planet formation

Researchers have found water vapour in the disc around a young star exactly where planets may be forming. Water is a key ingredient for life on Earth, and is also thought to play a significant role in planet formation. Yet, until now, we had never been able to map how water is distributed in a stable, cool disc -- the type of disc that offers the most favourable conditions for planets to form around stars. The new findings were made possible thanks to the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner.

"I had never imagined that we could capture an image of oceans of water vapour in the same region where a planet is likely forming," says Stefano Facchini, an astronomer at the University of Milan, Italy, who led the study published today in Nature Astronomy. The observations reveal at least three times as much water as in all of Earth's oceans in the inner disc of the young Sun-like star HL Tauri, located 450 light-years away from Earth in the constellation Taurus.

"It is truly remarkable that we can not only detect but also capture detailed images and spatially resolve water vapour at a distance of 450 light-years from us ," adds co-author Leonardo Testi, an astronomer at the University of Bologna, Italy. The 'spatially resolved' observations with ALMA allow astronomers to determine the distribution of water in different regions of the disc. "Taking part in such an important discovery in the iconic HL Tauri disc was beyond what I had ever expected for my first research experience in astronomy," adds Mathieu Vander Donckt from the University of Liege, Belgium, who was a master's student when he participated in the research.

A significant amount of water was found in the region where a known gap in the HL Tauri disc exists. Ring-shaped gaps are carved out in gas- and dust-rich discs by orbiting young planet-like bodies as they gather up material and grow. "Our recent images reveal a substantial quantity of water vapour at a range of distances from the star that include a gap where a planet could potentially be forming at the present time," says Facchini. This suggests that this water vapour could affect the chemical composition of planets forming in those regions.

Observing water with a ground-based telescope is no mean feat as the abundant water vapour in Earth's atmosphere degrades the astronomical signals. ALMA, operated by ESO together with its international partners, is an array of telescopes in the Chilean Atacama Desert at about 5000 metres elevation that was built in a high and dry environment specifically to minimise this degradation, providing exceptional observing conditions. "To date, ALMA is the only facility able to spatially resolve water in a cool planet-forming disc," says co-author Wouter Vlemmings, a professor at the Chalmers University of Technology in Sweden.*

"It is truly exciting to directly witness, in a picture, water molecules being released from icy dust particles," says Elizabeth Humphreys, an astronomer at ESO who also participated in the study. The dust grains that make up a disc are the seeds of planet formation, colliding and clumping into ever larger bodies orbiting the star. Astronomers believe that where it is cold enough for water to freeze onto dust particles, things stick together more efficiently -- an ideal spot for planet formation. "Our results show how the presence of water may influence the development of a planetary system, just like it did some 4.5 billion years ago in our own Solar System," Facchini adds.

With upgrades happening at ALMA and ESO's Extremely Large Telescope (ELT) coming online within the decade, planet formation and the role water plays in it will become clearer than ever. In particular METIS, the Mid-infrared ELT Imager and Spectrograph, will give astronomers unrivalled views of the inner regions of planet-forming discs, where planets like Earth form.

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James Webb Space Telescope detects water vapor, sulfur dioxide and sand clouds in the atmosphere of a nearby exoplanet

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European astronomers, co-led by researchers from the Institute of Astronomy, KU Leuven, used recent observations made with the James Webb Space Telescope to study the atmosphere of the nearby exoplanet WASP-107b. Peering deep into the fluffy atmosphere of WASP-107b they discovered not only water vapour and sulfur dioxide, but even silicate sand clouds. These particles reside within a dynamic atmosphere that exhibits vigorous transport of material.

Astronomers worldwide are harnessing the advanced capabilities of the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST) to conduct groundbreaking observations of exoplanets – planets orbiting stars other than our own Sun. One of these fascinating worlds is WASP-107b, a unique gaseous exoplanet that orbits a star slightly cooler and less massive than our Sun. The mass of the planet is similar to that of Neptune but its size is much larger than that of Neptune, almost approaching the size of Jupiter. This characteristic renders WASP-107b rather ‘fluffy’ when compared to the gas giant planets within our solar system. The fluffiness of this exoplanet enables astronomers to look roughly 50 times deeper into its atmosphere compared to the depth of exploration achieved for a solar-system giant like Jupiter.

The team of European astronomers took full advantage of the remarkable fluffiness of this exoplanet, enabling them to look deep into its atmosphere. This opportunity opened a window into unravelling the complex chemical composition of its atmosphere. The reason behind this is quite straightforward: the signals, or spectral features, are far more prominent in a less dense atmosphere compared to a more compact one. Their recent study, now published in Nature, reveals the presence of water vapour, sulfur dioxide (SO2), and silicate clouds, but notably, there is no trace of the greenhouse gas methane (CH4).

A dynamic atmosphere

These detections provide crucial insights into the dynamics and chemistry of this captivating exoplanet. First, the absence of methane hints at a potentially warm interior, offering a tantalising glimpse into the movement of heat energy in the planet’s atmosphere. Secondly, the discovery of sulfur dioxide (known for the odour of burnt matches), was a major surprise. Previous models had predicted its absence, but novel climate models of WASP-107b’s atmosphere now show that the very fluffiness of WASP-107b accommodates the formation of sulfur dioxide in its atmosphere. Even though its host star emits a relatively small fraction of high-energy photons due to its cooler nature, these photons can reach deep into the planet’s atmosphere thanks to its fluffy nature. This enables the chemical reactions required to produce sulfur dioxide to occur.

But that's not all they've observed. Both the spectral features of sulfur dioxide and water vapour are significantly diminished compared to what they would be in a cloudless scenario. High-altitude clouds partially obscure the water vapour and sulfur dioxide in the atmosphere. While clouds have been inferred on other exoplanets, this marks the first instance where astronomers can definitively identify the chemical composition of these clouds. In this case, the clouds consist of small silicate particles, a familiar substance for humans found in many parts of the world as the primary constituent of sand.

"JWST is revolutionising exoplanet characterisation, providing unprecedented insights at remarkable speed," says lead author Prof. Leen Decin of KU Leuven. "The discovery of clouds of sand, water, and sulfur dioxide on this fluffy exoplanet by JWST's MIRI instrument is a pivotal milestone. It reshapes our understanding of planetary formation and evolution, shedding new light on our own Solar System."

In contrast to Earth’s atmosphere, where water freezes at low temperatures, in gaseous planets reaching temperatures around 1000 degrees Celsius, silicate particles can freeze out to form clouds. However, in the case of WASP-107b, with a temperature of around 500 degrees Celsius in the outer atmosphere, traditional models predicted that these silicate clouds should be forming deeper within the atmosphere, where temperatures are substantially higher. In addition, sand clouds high up in the atmosphere rain out. How is it then possible that these sand clouds exist at high altitudes and continue to endure?

According to lead author Dr. Michiel Min: "The fact that we see these sand clouds high up in the atmosphere must mean that the sand rain droplets evaporate in deeper, very hot layers and the resulting silicate vapour is efficiently moved back up, where they recondense to form silicate clouds once more. This is very similar to the water vapour and cloud cycle on our own Earth but with droplets made of sand." This continuous cycle of sublimation and condensation through vertical transport is responsible for the enduring presence of sand clouds in WASP-107b's atmosphere.

This pioneering research not only sheds light on the exotic world of WASP-107b but also pushes the boundaries of our understanding of exoplanetary atmospheres. It marks a significant milestone in exoplanetary exploration, revealing the intricate interplay of chemicals and climatic conditions on these distant worlds.

“JWST enables a deep atmospheric characterisation of an exoplanet that does not have any counterpart in our Solar System, we are unravelling new worlds!”, says lead author Dr. Achrène Dyrek at CEA Paris.

Design and development of the MIRI instrument

Thanks to funding by the Belgian federal science policy office BELSPO via the ESA PRODEX programme, Belgian engineers and scientists played a key role in the design and development of the MIRI instrument, including the Centre Spatial de Liege (CSL), Thales Alenia Space (Charleroi) and OIP Sensor Systems (Oudenaarde). At the Institute of Astronomy at KU Leuven, instrument scientists tested the MIRI instrument extensively in special test chambers simulating the space environment in laboratories in the UK, at NASA Goddard and NASA Johnson Space centres.

“With colleagues across Europe and the United States we have been building and testing the MIRI instrument for almost 20 years. It is rewarding to see our instrument unravel the atmosphere of this intriguing exoplanet,” says instrument specialist Dr. Bart Vandenbussche of KU Leuven.

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Researcher finds inspiration from spider webs and beetles to harvest fresh water from thin air

A team of researchers is designing novel systems to capture water vapour in the air and turn it into liquid.

University of Waterloo professor Michael Tam and his PhD students Yi Wang and Weinan Zhao have developed sponges or membranes with a large surface area that continually capture moisture from their surrounding environment.

Traditionally, fresh water for consumption is collected from rivers, lakes, groundwater, and oceans (with treatment). The current technologies Dr. Tam is developing are inspired by nature to harvest water from alternative sources as the world is facing a serious challenge with freshwater scarcity.

"A spider's web is an engineering marvel," said Tam, a University Research Chair in the field of functional colloids and sustainable nanomaterials. "Water is efficiently captured by the web. The spider doesn't need to go to the river to drink, as it traps moisture from the air."

Similarly, Namib desert beetles have no easy access to water but acquire water from thin air by leaning into the wind to capture droplets of water from the fog with their textured body armour. This allows the moisture to accumulate and drip into their mouths.

Tam and his research group are engaged in biomimetic surface engineering for sustainable water harvesting. One technology Tam is designing is called atmospheric water harvesting. To mimic the beetle's unique surface structure, Tam's research group is designing a similar surface structure using a cellulose-stabilized wax emulsion to fabricate surfaces that attract tiny water droplets while swiftly releasing larger ones.

Tam is working with net zero carbon materials, such as natural and plant-based materials, to develop sustainable technologies. His research group is developing technologies that capture and repel water droplets by harnessing the power of interfacial science and nanotechnology. He has successfully developed superhydrophobic and waterproof paper. He is also engineering a smart and tunable surface that captures water from the air and dehumidifies it with minimal energy consumption.

The next step is to develop a scalable process to engineer such surfaces.

Solar evaporation systems directly harvest solar energy, absorbing water and generating fresh collectible vapour through evaporation. Unique mushroom structures inspired the smart biomimetic structural designs for solar evaporation.

The proposed freshwater generation systems are inexpensive, energy-efficient, and environmentally friendly.

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Webb finds water vapor, but from a rocky planet or its star?

The most common stars in the universe are red dwarf stars, which means that rocky exoplanets are most likely to be found orbiting such a star. Red dwarf stars are cool, so a planet has to hug it in a tight orbit to stay warm enough to potentially host liquid water (meaning it lies in the habitable zone). Such stars are also active, particularly when they are young, releasing ultraviolet and X-ray radiation that could destroy planetary atmospheres. As a result, one important open question in astronomy is whether a rocky planet could maintain, or reestablish, an atmosphere in such a harsh environment.

To help answer that question, astronomers used NASA's James Webb Space Telescope to study a rocky exoplanet known as GJ 486 b. It is too close to its star to be within the habitable zone, with a surface temperature of about 800 degrees Fahrenheit (430 degrees Celsius). And yet, their observations using Webb's Near-Infrared Spectrograph (NIRSpec) show hints of water vapor. If the water vapor is associated with the planet, that would indicate that it has an atmosphere despite its scorching temperature and close proximity to its star. Water vapor has been seen on gaseous exoplanets before, but to date no atmosphere has been definitely detected around a rocky exoplanet. However, the team cautions that the water vapor could be on the star itself -- specifically, in cool starspots -- and not from the planet at all.

"We see a signal, and it's almost certainly due to water. But we can't tell yet if that water is part of the planet's atmosphere, meaning the planet has an atmosphere, or if we're just seeing a water signature coming from the star," said Sarah Moran of the University of Arizona in Tucson, lead author of the study.

"Water vapor in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science. But we must be careful and make sure that the star is not the culprit," added Kevin Stevenson of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, principal investigator on the program.

GJ 486 b is about 30% larger than Earth and three times as massive, which means it is a rocky world with stronger gravity than Earth. It orbits a red dwarf star in just under 1.5 Earth days. It is expected to be tidally locked, with a permanent day side and a permanent night side.

GJ 486 b transits its star, crossing in front of the star from our point of view. If it has an atmosphere, then when it transits starlight would filter through those gasses, imprinting fingerprints in the light that allow astronomers to decode its composition through a technique called transmission spectroscopy.

The team observed two transits, each lasting about an hour. They then used three different methods to analyze the resulting data. The results from all three are consistent in that they show a mostly flat spectrum with an intriguing rise at the shortest infrared wavelengths. The team ran computer models considering a number of different molecules, and concluded that the most likely source of the signal was water vapor.

While the water vapor could potentially indicate the presence of an atmosphere on GJ 486 b, an equally plausible explanation is water vapor from the star. Surprisingly, even in our own Sun, water vapor can sometimes exist in sunspots because these spots are very cool compared to the surrounding surface of the star. GJ 486 b's host star is much cooler than the Sun, so even more water vapor would concentrate within its starspots. As a result, it could create a signal that mimics a planetary atmosphere.

"We didn't observe evidence of the planet crossing any starspots during the transits. But that doesn't mean that there aren't spots elsewhere on the star. And that's exactly the physical scenario that would imprint this water signal into the data and could wind up looking like a planetary atmosphere," explained Ryan MacDonald of the University of Michigan in Ann Arbor, one of the study's co-authors.

A water vapor atmosphere would be expected to gradually erode due to stellar heating and irradiation. As a result, if an atmosphere is present, it would likely have to be constantly replenished by volcanoes ejecting steam from the planet's interior. If the water is indeed in the planet's atmosphere, additional observations are needed to narrow down how much water is present.

Future Webb observations may shed more light on this system. An upcoming Webb program will use the Mid-Infrared Instrument (MIRI) to observe the planet's day side. If the planet has no atmosphere, or only a thin atmosphere, then the hottest part of the day side is expected to be directly under the star. However, if the hottest point is shifted, that would indicate an atmosphere that can circulate heat.

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