̽��ֱ�� of Cambridge - exoplanets

Strongest hints yet of biological activity outside the solar system

sc604 — Thu, 17 Apr 2025 04:09:34 +0000

Astronomers have detected the most promising signs yet of a possible biosignature outside the solar system, although they remain cautious.

Scientists reveal structure of 74 exocomet belts orbiting nearby stars

Anonymous — Fri, 17 Jan 2025 08:00:00 +0000

̽��ֱ��crystal-clear images show light being emitted from these millimetre-sized pebbles within the belts that orbit 74 nearby stars of a wide variety of ages – from those that are just emerging to those in more mature systems like our own Solar System.

̽��ֱ��REASONS (REsolved ALMA and SMA Observations of Nearby Stars) study, led by Trinity College Dublin and involving researchers from the ̽��ֱ�� of Cambridge, is a milestone in the study of exocometary belts because its images and analyses reveal where the pebbles, and the exocomets, are located. They are typically tens to hundreds of astronomical units (the distance from Earth to the Sun) from their central star.

In these regions, it is so cold (-250 to -150 degrees Celsius) that most compounds are frozen as ice on the exocomets. What the researchers are therefore observing is where the ice reservoirs of planetary systems are located. REASONS is the first programme to unveil the structure of these belts for a large sample of 74 exoplanetary systems. ̽��ֱ��results are reported in the journal Astronomy & Astrophysics.

This study used both the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile and the Submillimeter Array (SMA) in Hawai‘i to produce the images that have provided more information on populations of exocomets than ever before. Both telescope arrays observe electromagnetic radiation at millimetre and submillimetre wavelengths.

“Exocomets are boulders of rock and ice, at least one kilometre in size, which smash together within these belts to produce the pebbles that we observe here with the ALMA and SMA arrays of telescopes,” said lead author Luca Matrà from Trinity College Dublin. “Exocometary belts are found in at least 20% of planetary systems, including our own Solar System.”

“ ̽��ֱ��images reveal a remarkable diversity in the structure of belts,” said co-author Dr Sebastián Marino from the ̽��ֱ�� of Exeter. “Some are narrow rings, as in the canonical picture of a ‘belt’ like our Solar System’s Edgeworth-Kuiper belt. But a larger number of them are wide, and probably better described as ‘disks’ rather than rings.”

Some systems have multiple rings/disks, some of which are eccentric, providing evidence that yet undetectable planets are present and their gravity affects the distribution of pebbles in these systems.

“ ̽��ֱ��power of a large study like REASONS is in revealing population-wide properties and trends,” said Matrà.

For example, the study confirmed that the number of pebbles decreases for older planetary systems as belts run out of larger exocomets smashing together, but showed for the first time that this decrease in pebbles is faster if the belt is closer to the central star. It also indirectly showed – through the belts’ vertical thickness – that objects as large as 140 km across and even Moon-size objects are likely present in these belts.

“We have been studying exocometary belts for decades, but until now only a handful had been imaged,” said co-author Professor Mark Wyatt from Cambridge’s Institute of Astronomy. “This is the largest collection of such images and demonstrates that we already have the capabilities to probe the structures of the planetary systems orbiting a large fraction of the stars near to the Sun.”

“Arrays like the ALMA and SMA used in this work are extraordinary tools that are continuing to give us incredible new insights into the universe and its workings,” said co-author Dr David Wilner from the Center for Astrophysics | Harvard & Smithsonian “ ̽��ֱ��REASONS survey required a large community effort and has an incredible legacy value, with multiple potential pathways for future investigation.”

Reference:
L. Matrà et al. ‘REsolved ALMA and SMA Observations of Nearby Stars. REASONS: A population of 74 resolved planetesimal belts at millimetre wavelengths.’ Astronomy & Astrophysics (2025). DOI: 10.1051/0004-6361/202451397

Adapted from a Trinity College Dublin media release.

An international team of astrophysicists has imaged a large number of exocomet belts around nearby stars, and the tiny pebbles within them.

Luca Matra, Trinity College Dublin, and colleagues

Millimetre continuum images for the REASONS resolved sample of 74 exocomet belts

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Researchers deal a blow to theory that Venus once had liquid water on its surface

sc604 — Mon, 02 Dec 2024 16:01:07 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, studied the chemical composition of the Venusian atmosphere and inferred that its interior is too dry today for there ever to have been enough water for oceans to exist at its surface. Instead, the planet has likely been a scorching, inhospitable world for its entire history.

̽��ֱ��results, reported in the journal Nature Astronomy, have implications for understanding Earth’s uniqueness, and for the search for life on planets outside our Solar System. While many exoplanets are Venus-like, the study suggests that astronomers should narrow their focus to exoplanets which are more like Earth.

From a distance, Venus and Earth look like siblings: it is almost identical in size and is a rocky planet like Earth. But up close, Venus is more like an evil twin: it is covered with thick clouds of sulfuric acid, and its surface has a mean temperature close to 500°C.

Despite these extreme conditions, for decades, astronomers have been investigating whether Venus once had liquid oceans capable of supporting life, or whether some mysterious form of ‘aerial’ life exists in its thick clouds now.

“We won’t know for sure whether Venus can or did support life until we send probes at the end of this decade,” said first author Tereza Constantinou, a PhD student at Cambridge’s Institute of Astronomy. “But given it likely never had oceans, it is hard to imagine Venus ever having supported Earth-like life, which requires liquid water.”

When searching for life elsewhere in our galaxy, astronomers focus on planets orbiting their host stars in the habitable zone, where temperatures are such that liquid water can exist on the planet’s surface. Venus provides a powerful limit on where this habitable zone lies around a star.

“Even though it’s the closest planet to us, Venus is important for exoplanet science, because it gives us a unique opportunity to explore a planet that evolved very differently to ours, right at the edge of the habitable zone,” said Constantinou.

There are two primary theories on how conditions on Venus may have evolved since its formation 4.6 billion years ago. ̽��ֱ��first is that conditions on the surface of Venus were once temperate enough to support liquid water, but a runaway greenhouse effect caused by widespread volcanic activity caused the planet to get hotter and hotter. ̽��ֱ��second theory is that Venus was born hot, and liquid water has never been able to condense at the surface.

“Both of those theories are based on climate models, but we wanted to take a different approach based on observations of Venus’ current atmospheric chemistry,” said Constantinou. “To keep the Venusian atmosphere stable, then any chemicals being removed from the atmosphere should also be getting restored to it, since the planet’s interior and exterior are in constant chemical communication with one another.”

̽��ֱ��researchers calculated the present destruction rate of water, carbon dioxide and carbonyl sulphide molecules in Venus’ atmosphere, which must be restored by volcanic gases to keep the atmosphere stable.

Volcanism, through its supply of gases to the atmosphere, provides a window into the interior of rocky planets like Venus. As magma rises from the mantle to the surface, it releases gases from the deeper portions of the planet.

On Earth, volcanic eruptions are mostly steam, due to our planet’s water-rich interior. But, based on the composition of the volcanic gases necessary to sustain the Venusian atmosphere, the researchers found that volcanic gases on Venus are at most six percent water. These dry eruptions suggest that Venus’s interior, the source of the magma that releases volcanic gases, is also dehydrated.

At the end of this decade, NASA’s DAVINCI mission will be able to test and confirm whether Venus has always been a dry, inhospitable planet, with a series of flybys and a probe sent to the surface. ̽��ֱ��results could help astronomers narrow their focus when searching for planets that can support life in orbit around other stars in the galaxy.

“If Venus was habitable in the past, it would mean other planets we have already found might also be habitable,” said Constantinou. “Instruments like the James Webb Space Telescope are best at studying the atmospheres of planets close to their host star, like Venus. But if Venus was never habitable, then it makes Venus-like planets elsewhere less likely candidates for habitable conditions or life.

“We would have loved to find that Venus was once a planet much closer to our own, so it’s kind of sad in a way to find out that it wasn’t, but ultimately it’s more useful to focus the search on planets that are mostly likely to be able to support life – at least life as we know it.”

̽��ֱ��research was supported in part by the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI).

Reference:
Tereza Constantinou, Oliver Shorttle, and Paul B Rimmer. ‘A dry Venusian interior constrained by atmospheric chemistry.’ Nature Astronomy (2024). DOI: 10.1038/s41550-024-02414-5

A team of astronomers has found that Venus has never been habitable, despite decades of speculation that our closest planetary neighbour was once much more like Earth than it is today.

NASA/Jet Propulsion Laboratory-Caltech

View of surface of Venus

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Astronomers uncover risks to planets that could host life

sc604 — Mon, 05 Aug 2024 14:10:39 +0000

̽��ֱ��discovery suggests that the intense UV radiation from these flares could significantly impact whether planets around red dwarf stars can be habitable.

“Few stars have been thought to generate enough UV radiation through flares to impact planet habitability. Our findings show that many more stars may have this capability,” said first author Vera Berger, who led the research while based at the ̽��ֱ�� of Hawai’i and who is now based at the ̽��ֱ�� of Cambridge.

Berger and her team used archival data from the GALEX space telescope to search for flares among 300,000 nearby stars. GALEX is a now-decommissioned NASA mission that simultaneously observed most of the sky at near-and far-UV wavelengths from 2003 to 2013. Using new computational techniques, the team mined insights from the data.

“Combining modern computer power with gigabytes of decades-old observations allowed us to search for flares on thousands and thousands of nearby stars,” said co-author Dr Michael Tucker from Ohio State ̽��ֱ��.

According to researchers, UV radiation from stellar flares can either erode planetary atmospheres, threatening their potential to support life, or contribute to the formation of RNA building blocks, which are essential for the creation of life.

̽��ֱ��study, published in the Monthly Notices of the Royal Astronomical Society, challenges existing models of stellar flares and exoplanet habitability, showing that far-UV emission from flares is on average three times more energetic than typically assumed, and can reach up to twelve times the expected energy levels.

“A change of three is the same as the difference in UV in the summer from Anchorage, Alaska to Honolulu, where unprotected skin can get a sunburn in less than 10 minutes,” said co-author Benjamin J. Shappee from the ̽��ֱ�� of Hawai’i.

̽��ֱ��exact cause of this stronger far-UV emission remains unclear. ̽��ֱ��team believes it might be that flare radiation is concentrated at specific wavelengths, indicating the presence of atoms like carbon and nitrogen.

“This study has changed the picture of the environments around stars less massive than our Sun, which emit very little UV light outside of flares,” said co-author Jason Hinkle.

According to Berger, now a Churchill Scholar at Cambridge, more data from space telescopes is needed to study the UV light from stars, which is crucial for understanding the source of this emission.

“Our work puts a spotlight on the need for further exploration into the effects of stellar flares on exoplanetary environments,” said Berger. “Using space telescopes to obtain UV spectra of stars will be crucial for better understanding the origins of this emission.”

Reference:
Vera L Berger et al. ‘Stellar flares are far-ultraviolet luminous.’ Monthly Notices of the Royal Astronomical Society (2024). DOI: 10.1093/mnras/stae1648

Adapted from a ̽��ֱ�� of Hawai’i media release.

Astronomers have discovered that red dwarf stars can produce stellar flares that carry far-ultraviolet (far-UV) radiation levels much higher than previously believed.

Scott Wiessinger/NASA

A red dwarf star unleashes a series of powerful flares.

Yes

‘Bouncing’ comets could deliver building blocks for life to exoplanets

sc604 — Wed, 15 Nov 2023 00:10:19 +0000

In order to deliver organic material, comets need to be travelling relatively slowly – at speeds below 15 kilometres per second. At higher speeds, the essential molecules would not survive – the speed and temperature of impact would cause them to break apart.

̽��ֱ��most likely place where comets can travel at the right speed are ‘peas in a pod’ systems, where a group of planets orbit closely together. In such a system, the comet could essentially be passed or ‘bounced’ from the orbit of one planet to another, slowing it down.

At slow enough speeds, the comet would crash on a planet’s surface, delivering the intact molecules that researchers believe are the precursors for life. ̽��ֱ��results, reported in the Proceedings of the Royal Society A, suggest that such systems would be promising places to search for life outside our Solar System if cometary delivery is important for the origins of life.

Comets are known to contain a range of the building blocks for life, known as prebiotic molecules. For example, samples from the Ryugu asteroid, analysed in 2022, showed that it carried intact amino acids and vitamin B3. Comets also contain large amounts of hydrogen cyanide (HCN), another important prebiotic molecule. ̽��ֱ��strong carbon-nitrogen bonds of HCN make it more durable to high temperatures, meaning it could potentially survive atmospheric entry and remain intact.

“We’re learning more about the atmospheres of exoplanets all the time, so we wanted to see if there are planets where complex molecules could also be delivered by comets,” said first author Richard Anslow from Cambridge’s Institute of Astronomy. “It’s possible that the molecules that led to life on Earth came from comets, so the same could be true for planets elsewhere in the galaxy.”

̽��ֱ��researchers do not claim that comets are necessary to the origin of life on Earth or any other planet, but instead they wanted to place some limits on the types of planets where complex molecules, such as HCN, could be successfully delivered by comets.

Most of the comets in our Solar System sit beyond the orbit of Neptune, in what is known as the Kuiper Belt. When comets or other Kuiper Belt objects (KBOs) collide, they can be pushed by Neptune’s gravity toward the Sun, eventually getting pulled in by Jupiter’s gravity. Some of these comets make their way past the Asteroid Belt and into the inner Solar System.

“We wanted to test our theories on planets that are similar to our own, as Earth is currently our only example of a planet that supports life,” said Anslow. “What kinds of comets, travelling at what kinds of speed, could deliver intact prebiotic molecules?”

Using a variety of mathematical modelling techniques, the researchers determined that it is possible for comets to deliver the precursor molecules for life, but only in certain scenarios. For planets orbiting a star similar to our own Sun, the planet needs to be low mass and it is helpful for the planet to be in close orbit to other planets in the system. ̽��ֱ��researchers found that nearby planets on close orbits are much more important for planets around lower-mass stars, where the typical speeds are much higher.

In such a system, a comet could be pulled in by the gravitational pull of one planet, then passed to another planet before impact. If this ‘comet-passing’ happened enough times, the comet would slow down enough so that some prebiotic molecules could survive atmospheric entry.

“In these tightly-packed systems, each planet has a chance to interact with and trap a comet,” said Anslow. “It’s possible that this mechanism could be how prebiotic molecules end up on planets.”

For planets in orbit around lower-mass stars, such as M-dwarfs, it would be more difficult for complex molecules to be delivered by comets, especially if the planets are loosely packed. Rocky planets in these systems also suffer significantly more high-velocity impacts, potentially posing unique challenges for life on these planets.

̽��ֱ��researchers say their results could be useful when determining where to look for life outside the Solar System.

“It’s exciting that we can start identifying the type of systems we can use to test different origin scenarios,” said Anslow. “It’s a different way to look at the great work that’s already been done on Earth. What molecular pathways led to the enormous variety of life we see around us? Are there other planets where the same pathways exist? It’s an exciting time, being able to combine advances in astronomy and chemistry to study some of the most fundamental questions of all.”

̽��ֱ��research was supported in part by the Royal Society and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI). Richard Anslow is a Member of Wolfson College, Cambridge.

Reference:
R J Anslow, A Bonsor and P B Rimmer. ‘Can comets deliver prebiotic molecules to rocky exoplanets?’ Proceedings of the Royal Society A (2023). DOI: 10.1098/rspa.2023.0434

How did the molecular building blocks for life end up on Earth? One long-standing theory is that they could have been delivered by comets. Now, researchers from the ̽��ֱ�� of Cambridge have shown how comets could deposit similar building blocks to other planets in the galaxy.

It’s possible that the molecules that led to life on Earth came from comets, so the same could be true for planets elsewhere in the galaxy

Richard Anslow

solarseven via Getty Images

Artist's impression of a meteor hitting Earth

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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Explore life in the Universe with new postgraduate programme

lw355 — Mon, 18 Sep 2023 10:00:19 +0000

A new postgraduate programme will train researchers to understand life's origins, search for habitable planets and consider the most profound question of all: are we alone?

Carbon-based molecules found in atmosphere of exoplanet K2-18b

sc604 — Mon, 11 Sep 2023 11:39:20 +0000

An international team of astronomers led by the ̽��ֱ�� of Cambridge has used data from the NASA/ESA/CSA James Webb Space Telescope to discover methane and carbon dioxide in the atmosphere of K2-18 b, an exoplanet in the ‘Goldilocks zone’. This is the first time that carbon-based molecules have been discovered in the atmosphere of an exoplanet in the habitable zone.

Scientists have new tool to estimate how much water might be hidden beneath a planet’s surface

cmm201 — Wed, 15 Mar 2023 12:25:33 +0000

Scientists from the ̽��ֱ�� of Cambridge now have a way to estimate how much water a rocky planet can store in its subterranean reservoirs. It is thought that this water, which is locked into the structure of minerals deep down, might help a planet recover from its initial fiery birth.

̽��ֱ��researchers developed a model that can predict the proportion of water-rich minerals inside a planet. These minerals act like a sponge, soaking up water which can later return to the surface and replenish oceans. Their results could help us understand how planets can become habitable following intense heat and radiation during their early years.

Planets orbiting M-type red dwarf stars — the most common star in the galaxy — are thought to be one of the best places to look for alien life. But these stars have particularly tempestuous adolescent years — releasing intense bursts of radiation that blast nearby planets and bake off their surface water.

Our Sun’s adolescent phase was relatively short, but red dwarf stars spend much longer in this angsty transitional period. As a result, the planets under their wing suffer a runaway greenhouse effect where their climate is thrown into chaos.

“We wanted to investigate whether these planets, after such a tumultuous upbringing, could rehabilitate themselves and go on to host surface water,” said lead author of the study, Claire Guimond, a PhD student in Cambridge’s Department of Earth Sciences.

̽��ֱ��new research, published in the Monthly Notices of the Royal Astronomical Society, shows that interior water could be a viable way to replenish liquid surface water once a planet’s host star has matured and dimmed. This water would likely have been brought up by volcanoes and gradually released as steam into the atmosphere, together with other life-giving elements.

Their new model allows them to calculate a planet’s interior water capacity based on its size and the chemistry of its host star. “ ̽��ֱ��model gives us an upper limit on how much water a planet could carry at depth, based on these minerals and their ability to take water into their structure,” said Guimond.

̽��ֱ��researchers found that the size of a planet plays a key role in deciding how much water it can hold. That’s because a planet’s size determines the proportion of water-carrying minerals it is made of.

Most of a planet’s interior water is contained within a rocky layer known as the upper mantle — which lies directly below the crust. Here, pressure and temperature conditions are just right for the formation of green-blue minerals called wadsleyite and ringwoodite that can soak up water. This rocky layer is also within reach of volcanoes, which could bring water back to the surface through eruptions.

̽��ֱ��new research showed that larger planets — around two to three times bigger than Earth — typically have drier rocky mantles because the water-rich upper mantle makes up a smaller proportion of their total mass.

̽��ֱ��results could provide scientists with guidelines to aid their search for exoplanets that might host life, “This could help refine our triaging of which planets to study first,” said Oliver Shorttle, who is jointly affiliated with Cambridge’s Department of Earth Sciences and Institute of Astronomy. “When we’re looking for the planets that can best hold water you probably do not want one significantly more massive or wildly smaller than Earth.”

̽��ֱ��findings could also add to our understanding of how planets, including those closer to home like Venus, can transition from barren hellscapes to a blue marble. Temperatures on the surface of Venus, which is of a similar size and bulk composition to Earth, hover around 450oC and its atmosphere is heavy with carbon dioxide and nitrogen. It remains an open question whether Venus hosted liquid water at its surface 4 billion years ago. “If that’s the case, then Venus must have found a way to cool itself and regain surface water after being born around a fiery sun,” said Shorttle, “It’s possible that it tapped into its interior water in order to do this.”

Reference:
Guimond, C. M., Shorttle, O., & Rudge, J. F. 'Mantle mineralogy limits to rocky planet water inventories'. Monthly Notices of the Royal Astronomical Society (2023). DOI: 10.1093/mnras/stad148

In the search for life elsewhere in the Universe, scientists have traditionally looked for planets with liquid water at their surface. But, rather than flowing as oceans and rivers, much of a planet’s water can be locked in rocks deep within its interior.

We wanted to investigate whether these planets, after such a tumultuous upbringing, could rehabilitate themselves and go on to host surface water

Claire Guimond

NASA

Water worlds

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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