{"id":53011,"date":"2024-01-07T10:27:23","date_gmt":"2024-01-07T10:27:23","guid":{"rendered":"http:\/\/125b3ec5-3eb5-4cd1-b736-f7e351fbf8d7"},"modified":"2024-01-07T11:32:34","modified_gmt":"2024-01-07T11:32:34","slug":"biosignatures-could-point-to-life-on-distant-planets","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/biosignatures-could-point-to-life-on-distant-planets\/","title":{"rendered":"Biosignatures could point to life on distant planets"},"content":{"rendered":"

Oxygen, ammonia and other gases in exoplanet atmospheres could be an indicator of biological processes. <\/p>

By Lewis Dartnell\n <\/p>

Published: Sunday, 07 January 2024 at 10:27 AM<\/p>

\n\n

Over the coming years, as astronomers use spectroscopy<\/a> to read the atmospheres of Earth-sized, habitable exoplanets<\/a>, detecting the presence of one gas will be an important discovery: oxygen.<\/p>

On Earth, oxygen is released by life \u2013 specifically, by organisms using sunlight for energy.<\/p>

Oxygen is a very reactive gas. Early in Earth\u2019s history any oxygen released into the atmosphere was rapidly removed.<\/p>

It reacted with rocks, or was destroyed by photochemical reactions driven by ultraviolet rays in sunlight.<\/p>

What if a hot Jupiter existed in our Solar System?<\/strong><\/em><\/a><\/li>
How James Webb Space Telescope will study exoplanets<\/strong><\/em><\/a><\/li>
Why are there so many different kinds of planet?<\/strong><\/em><\/a><\/li><\/ul>Credit: NASA \/ restored by Toby Ord<\/figcaption><\/figure>
Such processes are known as \u2018sinks\u2019, and oxygen only started to accumulate in Earth\u2019s atmosphere once its production had overwhelmed these sinks.<\/p>
An oxygen-rich atmosphere is thought to be a sign of flourishing life on a world, which is why astronomers would be so excited about discovering one on an exoplanet.<\/p>
But is oxygen the only \u2018biosignature\u2019 gas that would indicate the presence of life on an exoplanet?<\/p>
Might other gases produced by biochemistry also be able to overwhelm the sinks on their exoplanets and accumulate to detectable levels?<\/p>
Sukrit Ranjan, at Northwestern University, and his colleagues have been investigating this.<\/p>
$\"\"$
Artist\u2019s impression of exoplanet LHS 1140b, which orbits a red dwarf star 40 light-years from Earth.<\/figcaption><\/figure>
The best candidate worlds for detecting such biosignature gases, they argue, are exoplanets orbiting small, cool M-class red dwarf stars.<\/p>
Such stars emit less ultraviolet radiation than larger, hotter stars like the Sun<\/a>, and so the sinks on those planets are much weaker.<\/p>
Exoplanets orbiting M-class red dwarfs offer favourable conditions for the accumulation of reactive gases to levels that we could hopefully detect with space telescopes.<\/p>
This is one of the reasons why the James Webb Space Telescope<\/a> (JWST) is targeting these stars.<\/p>
$\"The$
The Webb Telescope is helping discover biosignatures on distant planets. Credit: ESA, NASA, S. Beckwith (STScI) and the HUDF Team, Northrop Grumman Aerospace Systems \/ STScI \/ ATG medialab<\/figcaption><\/figure>
Ranjan\u2019s team considered an exoplanet with a hydrogen\/nitrogen atmosphere in orbit around a M-class red dwarf.<\/p>
The biochemistry of life on such a world might produce ammonia (like on Earth, where Rhizobacteria help nitrogen-fixing plants to draw nitrogen gas from the air).<\/p>
This scenario has been nicknamed a \u2018Cold Haber World\u2019, after the process that uses heat, pressure and a catalyst to convert atmospheric nitrogen into ammonia for fertilisers.<\/p>
The research team simulated a Cold Haber World with a climate suitable for oceans of liquid water, Earth-like volcanism and an atmosphere with the same surface pressure as Earth, but made up of 90% hydrogen and 10% nitrogen.<\/p>
$\"Ammonia$
Ammonia in the atmosphere of a rocky exoplanet could be one of the most important biosignatures in the search for signs of life beyond the Solar System. Credits: NASA\/JPL-Caltech<\/figcaption><\/figure>
They simulated how quickly life on such a planet would release ammonia and the rate at which atmospheric ammonia would be destroyed by the dwarf star\u2019s sunlight.<\/p>
They found that for realistic biological ammonia production rates, the gas can overwhelm the sinks on the planet and accumulate to notable levels in the atmosphere.<\/p>
They claim the JWST could detect such an atmospheric biosignature with two transits over two months.<\/p>
Such a world would be different to Earth, but this result gives astronomers hope that we\u2019ll be able to remotely detect atmospheric biosignatures on more diverse exoplanets.<\/p>
Lewis Dartnell was reading <\/strong><\/em>Photochemical Runaway in Exoplanet Atmospheres: Implications for Biosignatures<\/strong> by Sukrit Ranjan et al. Read it online at: arxiv.org\/abs\/2201.08359<\/a>.<\/strong><\/em><\/p>
This article originally appeared in the April 2022 issue of <\/strong><\/em>BBC Sky at Night Magazine<\/strong>.<\/strong><\/em><\/p> <\/body><\/html>\n
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