̽��ֱ�� of Cambridge - Cambridge Initiative for Planetary Science and Life in the Universe

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

̽��ֱ��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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New class of habitable exoplanets 'a big step forward' in search for life

sc604 — Wed, 25 Aug 2021 23:01:00 +0000

In the search for life elsewhere, astronomers have mostly looked for planets of a similar size, mass, temperature and atmospheric composition to Earth. However, astronomers from the ̽��ֱ�� of Cambridge believe there are more promising possibilities out there.

̽��ֱ��researchers have identified a new class of habitable planets, dubbed ‘Hycean’ planets – ocean-covered planets with hydrogen-rich atmospheres – which are more numerous and observable than Earth-like planets.

̽��ֱ��researchers say the results, reported in ̽��ֱ��Astrophysical Journal, could mean that finding biosignatures of life outside our Solar System within the next few years is a real possibility.

“Hycean planets open a whole new avenue in our search for life elsewhere,” said Dr Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who led the research.

Many of the prime Hycean candidates identified by the researchers are bigger and hotter than Earth, but still have the characteristics to host large oceans that could support microbial life similar to that found in some of Earth’s most extreme aquatic environments.

These planets also allow for a far wider habitable zone, or ‘Goldilocks zone’, compared to Earth-like planets. This means that they could still support life even though they lie outside the range where a planet similar to Earth would need to be in order to be habitable.

Thousands of planets outside our Solar System have been discovered since the first exoplanet was identified nearly 30 years ago. ̽��ֱ��vast majority are planets between the sizes of Earth and Neptune and are often referred to as ‘super-Earths’ or ‘mini-Neptunes’: they can be predominantly rocky or ice giants with hydrogen-rich atmospheres, or something in between.

Most mini-Neptunes are over 1.6 times the size of Earth: smaller than Neptune but too big to have rocky interiors like Earth. Earlier studies of such planets have found that the pressure and temperature beneath their hydrogen-rich atmospheres would be too high to support life.

However, a recent study on the mini-Neptune K2-18b by Madhusudhan’s team found that in certain conditions these planets could support life. ̽��ֱ��result led to a detailed investigation into the full range of planetary and stellar properties for which these conditions are possible, which known exoplanets may satisfy those conditions, and whether their biosignatures may be observable.

̽��ֱ��investigation led the researchers to identify a new class of planets, Hycean planets, with massive planet-wide oceans beneath hydrogen-rich atmospheres. Hycean planets can be up to 2.6 times larger than Earth and have atmospheric temperatures up to nearly 200 degrees Celsius, depending on their host stars, but their oceanic conditions could be similar to those conducive for microbial life in Earth’s oceans. Such planets also include tidally locked ‘dark’ Hycean worlds that may have habitable conditions only on their permanent night sides, and ‘cold’ Hycean worlds that receive little radiation from their stars.

Planets of this size dominate the known exoplanet population, although they have not been studied in nearly as much detail as super-Earths. Hycean worlds are likely quite common, meaning that the most promising places to look for life elsewhere in the Galaxy may have been hiding in plain sight.

However, size alone is not enough to confirm whether a planet is Hycean: other aspects such as mass, temperature and atmospheric properties are required for confirmation.

When trying to determine what the conditions are like on a planet many light years away, astronomers first need to determine whether the planet lies in the habitable zone of its star, and then look for molecular signatures to infer the planet’s atmospheric and internal structure, which govern the surface conditions, presence of oceans and potential for life.

Astronomers also look for certain biosignatures which could indicate the possibility of life. Most often, these are oxygen, ozone, methane and nitrous oxide, which are all present on Earth. There are also a number of other biomarkers, such as methyl chloride and dimethyl sulphide, that are less abundant on Earth but can be promising indicators of life on planets with hydrogen-rich atmospheres where oxygen or ozone may not be as abundant.

“Essentially, when we’ve been looking for these various molecular signatures, we have been focusing on planets similar to Earth, which is a reasonable place to start,” said Madhusudhan. “But we think Hycean planets offer a better chance of finding several trace biosignatures.”

“It's exciting that habitable conditions could exist on planets so different from Earth,” said co-author Anjali Piette, also from Cambridge.

Madhusudhan and his team found that a number of trace terrestrial biomarkers expected to be present in Hycean atmospheres would be readily detectable with spectroscopic observations in the near future. ̽��ֱ��larger sizes, higher temperatures and hydrogen-rich atmospheres of Hycean planets make their atmospheric signatures much more detectable than Earth-like planets.

̽��ֱ��Cambridge team identified a sizeable sample of potential Hycean worlds which are prime candidates for detailed study with next-generation telescopes, such as the James Webb Space Telescope (JWST), which is due to be launched later this year. These planets all orbit red dwarf stars between 35-150 light years away: close by astronomical standards. Already planned JWST observations of the most promising candidate, K2-18b, could lead to the detection of one or more biosignature molecules.

“A biosignature detection would transform our understanding of life in the universe,” said Madhusudhan. “We need to be open about where we expect to find life and what form that life could take, as nature continues to surprise us in often unimaginable ways.”

Reference:
Nikku Madhusudhan, Anjali A. A. Piette, and Savvas Constantinou. ‘Habitability and Biosignatures of Hycean Worlds.’ ̽��ֱ��Astrophysical Journal (2021). DOI: 10.3847/1538-4357/abfd9c

( ̽��ֱ��paper can also be viewed on arXiv.)

A new class of exoplanet very different to our own, but which could support life, has been identified by astronomers, which could greatly accelerate the search for life outside our Solar System.

Hycean planets open a whole new avenue in our search for life elsewhere

Nikku Madhusudhan

Amanda Smith

Artist's impression of a Hycean planet

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From extravagant to achievable - pushing the boundaries of research to find life beyond Earth

sc604 — Tue, 20 Apr 2021 11:27:07 +0000

Led by 2019 Physics Nobel Laureate Professor Didier Queloz, the Cambridge Initiative for Planetary Science and Life in the Universe will be the driving force for the development of a new Cambridge research community investigating life in the Universe, from understanding how it emerged on Earth to examining the processes that could make other planets suitable for life.

̽��ֱ��initiative comes at a crucial moment in science, as scientists are able to study exoplanets – planets orbiting stars other than our Sun – in ever-greater detail, and outstanding progress is being made in prebiotic chemistry: carefully-regulated laboratory experiments to recreate the conditions when life first formed on Earth.

In addition, the recent successful landing of the Mars 2020 Perseverance Rover set in motion one of the greatest international scientific endeavours of recent decades. Within the next ten years, samples returned from a four-billion-year-old lake deposit on Mars will offer a unique window on the Solar System as it was when life originated on Earth and could provide evidence of ancient life on the Red Planet.

“These recent revolutions and future perspectives offered by next-generation space missions mean that the planets are aligned for us to create a vibrant new field at the cutting edge of modern science,” said Queloz, from Cambridge’s Cavendish Laboratory and Director of the Initiative.

Building on the ̽��ֱ��’s research excellence and enhancing the multidisciplinary research conducted in various departments of the School of the Physical Sciences, the focus of the research within the new Initiative will be to understand the origins and physical properties of planets throughout the Universe, as well as the chemical and biological processes capable of starting and sustaining life.

“By bringing together chemists, geologists, biologists, and astrophysicists to work creatively together toward a common goal, the Initiative will ensure we truly exploit the full potential of this exciting new field of research, bringing us closer to understanding life in the Universe and finding life beyond Earth,” said Queloz.

̽��ֱ��School of the Physical Sciences and its various departments (Cavendish Laboratory, Chemistry, Applied Mathematics and Theoretical Physics, Earth Sciences and the Institute of Astronomy) recently committed to an initial funding package that will support the Initiative as it builds the foundations of its vision and will create the conditions for its research and educational ambitions to grow and develop.

Professor Nigel Peake, Head of the School of the Physical Sciences, said: “During the last decades our understanding of the microbiology of life has made spectacular progress, but knowledge on origins of life on Earth, and more generally in the Universe, are still nascent. This is about to change. I am proud that Cambridge is leading the way to a radically new approach based on a convergence of recent results in astrophysics, planetology and molecular chemistry.

“With the Cambridge Initiative for Planetary Science and Life in the Universe, we will provide the infrastructure that will allow scholars from various disciplines to combine their interests to address the fundamental question of our origins in the Universe. This sets the scene for a revolution to come.”

For more information, news and updates about the Cambridge Initiative for Planetary Science and Life in the Universe, visit www.iplu.phy.cam.ac.uk.

̽��ֱ�� ̽��ֱ�� of Cambridge is creating a new research initiative, bringing together physicists, chemists, biologists, mathematicians and earth scientists to answer fundamental questions on the origin and nature of life in the Universe.

By bringing together chemists, geologists, biologists, and astrophysicists to work toward a common goal, we can exploit the full potential of this exciting new field of research, bringing us closer to understanding life in the Universe and finding life beyond Earth

Didier Queloz

Prof. Didier Queloz introduces Cambridge IPLU

NASA, ESA, G Illingworth, D Magee, and P Oesch, R Bouwens and the HUDF09 Team

̽��ֱ��Hubble eXtreme Deep Field

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