̽��ֱ�� of Cambridge - Oliver Shorttle

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?

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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No signs (yet) of life on Venus

sc604 — Tue, 14 Jun 2022 15:00:00 +0000

Researchers from the ̽��ֱ�� of Cambridge used a combination of biochemistry and atmospheric chemistry to test the ‘life in the clouds’ hypothesis, which astronomers have speculated about for decades, and found that life cannot explain the composition of the Venusian atmosphere.

Any life form in sufficient abundance is expected to leave chemical fingerprints on a planet’s atmosphere as it consumes food and expels waste. However, the Cambridge researchers found no evidence of these fingerprints on Venus.

Even if Venus is devoid of life, the researchers say their results, reported in the journal Nature Communications, could be useful for studying the atmospheres of similar planets throughout the galaxy, and the eventual detection of life outside our Solar System.

“We’ve spent the past two years trying to explain the weird sulphur chemistry we see in the clouds of Venus,” said co-author Dr Paul Rimmer from Cambridge’s Department of Earth Sciences. “Life is pretty good at weird chemistry, so we’ve been studying whether there’s a way to make life a potential explanation for what we see.”

̽��ֱ��researchers used a combination of atmospheric and biochemical models to study the chemical reactions that are expected to occur, given the known sources of chemical energy in Venus’s atmosphere.

“We looked at the sulphur-based ‘food’ available in the Venusian atmosphere – it’s not anything you or I would want to eat, but it is the main available energy source,” said Sean Jordan from Cambridge’s Institute of Astronomy, the paper’s first author. “If that food is being consumed by life, we should see evidence of that through specific chemicals being lost and gained in the atmosphere.”

̽��ֱ��models looked at a particular feature of the Venusian atmosphere – the abundance of sulphur dioxide (SO2). On Earth, most SO2 in the atmosphere comes from volcanic emissions. On Venus, there are high levels of SO2 lower in the clouds, but it somehow gets ‘sucked out’ of the atmosphere at higher altitudes.

“If life is present, it must be affecting the atmospheric chemistry,” said co-author Dr Oliver Shorttle from Cambridge’s Department of Earth Sciences and Institute of Astronomy. “Could life be the reason that SO2 levels on Venus get reduced so much?”

̽��ֱ��models, developed by Jordan, include a list of metabolic reactions that the life forms would carry out in order to get their ‘food’, and the waste by-products. ̽��ֱ��researchers ran the model to see if the reduction in SO2 levels could be explained by these metabolic reactions.

They found that the metabolic reactions can result in a drop in SO2 levels, but only by producing other molecules in very large amounts that aren’t seen. ̽��ֱ��results set a hard limit on how much life could exist on Venus without blowing apart our understanding of how chemical reactions work in planetary atmospheres.

“If life was responsible for the SO2 levels we see on Venus, it would also break everything we know about Venus’s atmospheric chemistry,” said Jordan. “We wanted life to be a potential explanation, but when we ran the models, it isn’t a viable solution. But if life isn’t responsible for what we see on Venus, it’s still a problem to be solved – there’s lots of strange chemistry to follow up on.”

Although there’s no evidence of sulphur-eating life hiding in the clouds of Venus, the researchers say their method of analysing atmospheric signatures will be valuable when JWST, the successor to the Hubble Telescope, begins returning images of other planetary systems later this year. Some of the sulphur molecules in the current study are easy to see with JWST, so learning more about the chemical behaviour of our next-door neighbour could help scientists figure out similar planets across the galaxy.

“To understand why some planets are alive, we need to understand why other planets are dead,” said Shorttle. “If life somehow managed to sneak into the Venusian clouds, it would totally change how we search for chemical signs of life on other planets.”

“Even if ‘our’ Venus is dead, it’s possible that Venus-like planets in other systems could host life,” said Rimmer, who is also affiliated with Cambridge’s Cavendish Laboratory. “We can take what we’ve learned here and apply it to exoplanetary systems – this is just the beginning.”

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

Reference:
Sean Jordan, Oliver Shorttle and Paul B Rimmer. ‘Proposed energy-metabolisms cannot explain the atmospheric chemistry of Venus.’ Nature Communications (2022). DOI: 10.1038/s41467-022-30804-8

̽��ֱ��unusual behaviour of sulphur in Venus’ atmosphere cannot be explained by an ‘aerial’ form of extra-terrestrial life, according to a new study.

Even if ‘our’ Venus is dead, it’s possible that Venus-like planets in other systems could host life

Paul Rimmer

NASA/JPL-Caltech

Venus from Mariner 10

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Microscopic view on asteroid collisions could help us understand planet formation

cmm201 — Thu, 24 Feb 2022 10:00:43 +0000

A team of researchers, led by the ̽��ֱ�� of Cambridge, combined dating and microscopic analysis of the Chelyabinsk meteorite — which fell to Earth and hit the headlines in 2013 — to get more accurate constraints on the timing of ancient impact events.

Their study, published in Communications Earth & Environment, looked at how minerals within the meteorite were damaged by different impacts over time, meaning they could identify the biggest and oldest events that may have been involved in planetary formation.

“Meteorite impact ages are often controversial: our work shows that we need to draw on multiple lines of evidence to be more certain about impact histories – almost like investigating an ancient crime scene,” said Craig Walton, who led the research and is based at Cambridge’s Department of Earth Sciences.

Early in our Solar System’s history, planets including the Earth formed from massive collisions between asteroids and even bigger bodies, called proto-planets.

“Evidence of these impacts is so old that it has been lost on the planets — Earth, in particular, has a short memory because surface rocks are continually recycled by plate tectonics,” said co-author Dr Oli Shorttle, who is based jointly at Cambridge’s Department of Earth Sciences and Institute of Astronomy.

Asteroids, and their fragments that fall to Earth as meteorites, are in contrast inert, cold and much older— making them faithful timekeepers of collisions.

̽��ֱ��new research, which was a collaboration with researchers from the Chinese Academy of Sciences and the Open ̽��ֱ��, recorded how phosphate minerals inside the Chelyabinsk meteorite were shattered to varying degrees in order to piece together a collision history.

Their aim was to corroborate uranium-lead dating of the meteorite, which looks at the time elapsed for one isotope to decay to another.

“ ̽��ֱ��phosphates in most primitive meteorites are fantastic targets for dating the shock events experienced by the meteorites on their parent bodies,” said Dr Sen Hu, who carried out the uranium-lead dating at Beijing’s Institute of Geology and Geophysics, Chinese Academy of Sciences.

Previous dating of this meteorite has revealed two impact ages, one older, roughly 4.5-billion-year-old collision and another which occurred within the last 50 million years.

But these ages aren’t so clear-cut. Much like a painting fading over time, successive collisions can obscure a once clear picture, leading to uncertainty among the scientific community over the age and even the number of impacts recorded.

̽��ֱ��new study put the collisions recorded by the Chelyabinsk meteorite in time order by linking new uranium-lead ages on the meteorite to microscopic evidence for collision-induced heating seen inside their crystal structures. These microscopic clues build up in the minerals with each successive impact, meaning the collisions can be distinguished, put in time order and dated.

Their findings show that minerals containing the imprint of the oldest collision were either shattered into many smaller crystals at high temperatures or strongly deformed at high pressures.

̽��ֱ��team also described some mineral grains in the meteorite that were fractured by a lesser impact, at lower pressures and temperatures, and which record a much more recent age of less than 50 million years. They suggest this impact probably chipped the Chelyabinsk meteorite off its host asteroid and sent it hurtling to Earth.

Taken together, this supports a two-stage collision history. “ ̽��ֱ��question for us was whether these dates could be trusted, could we tie these impacts to evidence of superheating from an impact?” said Walton. “What we’ve shown is that the mineralogical context for dating is really important.”

Scientists are particularly interested in the date of the 4.5-billion-year-old impact because this is about the time we think the Earth-Moon system came to being, probably as a result of two planetary bodies colliding.

̽��ֱ��Chelyabinsk meteorite belongs to a group of so-called stony meteorites, all of which contain highly shattered and remelted material roughly coincident with this colossal impact.

̽��ֱ��newly acquired dates support previous suggestions that many asteroids experienced high energy collisions between 4.48 – 4.44 billion years ago. “ ̽��ֱ��fact that all of these asteroids record intense melting at this time might indicate Solar System re-organisation, either resulting from the Earth-Moon formation or perhaps the orbital movements of giant planets.”

Walton now plans to refine dating over the window of the Moon-forming impact, which could tell us how our own planet came to being.

Reference:
Walton, C.R. et al. ‘Ancient and recent collisions revealed by phosphate minerals in the Chelyabinsk meteorite.’ Communications Earth & Environment (2022). DOI: 10.1038/s43247-022-00373-1

A new way of dating collisions between asteroids and planetary bodies throughout our Solar System’s history could help scientists reconstruct how and when planets were born.

Our work shows that we need to draw on multiple lines of evidence to be more certain about impact histories – almost like investigating an ancient crime scene

Craig Walton

False-colour image of impact recrystallised phosphate mineral in Chelyabinsk meteorite

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Traces of Earth’s early magma ocean identified in Greenland rocks

cmm201 — Fri, 12 Mar 2021 19:00:00 +0000

̽��ֱ��study, published in the journal Science Advances, yields information on an important period in our planet’s formation, when a deep sea of incandescent magma stretched across Earth’s surface and extended hundreds of kilometres into its interior.

It is the gradual cooling and crystallisation of this ‘magma ocean’ that set the chemistry of Earth’s interior – a defining stage in the assembly of our planet’s structure and the formation of our early atmosphere.

Scientists know that catastrophic impacts during the formation of the Earth and Moon would have generated enough energy to melt our planet's interior. But we don’t know much about this distant and fiery phase of Earth’s history because tectonic processes have recycled almost all rocks older than 4 billion years.

Now researchers have found the chemical remnants of the magma ocean in 3.6-billion-year-old rocks from southwestern Greenland.

̽��ֱ��findings support the long-held theory that Earth was once almost entirely molten and provide a window into a time when the planet started to solidify and develop the chemistry that now governs its internal structure. ̽��ֱ��research suggests that other rocks on Earth’s surface may also preserve evidence of ancient magma oceans.

“There are few opportunities to get geological constraints on the events in the first billion years of Earth’s history. It’s astonishing that we can even hold these rocks in our hands – let alone get so much detail about the early history of our planet,” said lead author Dr Helen Williams, from Cambridge’s Department of Earth Sciences.

̽��ֱ��study brings forensic chemical analysis together with thermodynamic modelling in search of the primeval origins of the Greenland rocks, and how they got to the surface.

At first glance, the rocks that makeup Greenland’s Isua supracrustal belt look just like any modern basalt you’d find on the seafloor. But this outcrop, which was first described in the 1960s, is the oldest exposure of rocks on Earth. It is known to contain the earliest evidence of microbial life and plate tectonics.

̽��ֱ��new research shows that the Isua rocks also preserve rare evidence which even predates plate tectonics – the residues of some of the crystals left behind as that magma ocean cooled.

“It was a combination of some new chemical analyses we did and the previously published data that flagged to us that the Isua rocks might contain traces of ancient material. ̽��ֱ��hafnium and neodymium isotopes were really tantalizing, because those isotope systems are very hard to modify – so we had to look at their chemistry in more detail,” said co-author Dr Hanika Rizo, from Carleton ̽��ֱ��.

Iron isotopic systematics confirmed to Williams and the team that the Isua rocks were derived from parts of the Earth’s interior that formed as a consequence of magma ocean crystallisation.

Most of this primeval rock has been mixed up by convection in the mantle, but scientists think that some isolated zones deep at the mantle-core boundary – ancient crystal graveyards – may have remained undisturbed for billions of years.

It’s the relics of these crystal graveyards that Williams and her colleagues observed in the Isua rock chemistry. “Those samples with the iron fingerprint also have a tungsten anomaly – a signature of Earth’s formation – which makes us think that their origin can be traced back to these primeval crystals,” said Williams.

But how did these signals from the deep mantle find their way up to the surface? Their isotopic makeup shows they were not just funnelled up from melting at the core-mantle boundary. Their journey was more circuitous, involving several stages of crystallization and remelting – a kind of distillation process. ̽��ֱ��mix of ancient crystals and magma would have first migrated to the upper mantle, where it was churned up to create a ‘marble cake’ of rocks from different depths. Later melting of that hybrid of rocks is what produced the magma which fed this part of Greenland.

̽��ֱ��team’s findings suggest that modern hotspot volcanoes, which are thought to have formed relatively recently, may actually be influenced by ancient processes. “ ̽��ֱ��geochemical signals we report in the Greenland rocks bear similarities to rocks erupted from hotspot volcanoes like Hawaii – something we are interested in is whether they might also be tapping into the depths and accessing regions of the interior usually beyond our reach,” said Dr Oliver Shorttle who is jointly based at Cambridge’s Department of Earth Sciences and Institute of Astronomy.

̽��ֱ��team’s findings came out of a project funded by Deep Volatiles, a NERC-funded 5-year research programme. They now plan to continue their quest to understand the magma ocean by widening their search for clues in ancient rocks and experimentally modelling isotopic fractionation in the lower mantle.

“We’ve been able to unpick what one part of our planet’s interior was doing billions of years ago, but to fill in the picture further we must keep searching for more chemical clues in ancient rocks,” said co-author Dr Simon Matthews from the ̽��ֱ�� of Iceland.

Scientists have often been reluctant to look for chemical evidence of these ancient events. “ ̽��ֱ��evidence is often altered by the course of time. But the fact we found what we did suggests that the chemistry of other ancient rocks may yield further insights into the Earth’s formation and evolution - and that’s immensely exciting,” said Williams.

Reference:
Helen M. Williams et al. ‘Iron isotopes trace primordial magma ocean cumulates melting in Earth’s upper mantle.’ Science Advances (2021). DOI: 10.1126/sciadv.abc7394

New research led by the ̽��ֱ�� of Cambridge has found rare evidence – preserved in the chemistry of ancient rocks from Greenland - which tells of a time when Earth was almost entirely molten.

It’s astonishing that we can even hold these rocks in our hands – let alone get so much detail about the early history of our planet

Helen Williams

Hanika Rizo

Isua in Greenland

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