Scientists Investigate Exoplanet Atmospheres in Search for Extraterrestrial Life

January 29, 2024

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New research suggests that the subsequent generation of advanced telescopes may enhance the search for potential extraterrestrial life by closely examining the atmospheres of proximate exoplanets.

A recent paper published in The Astronomical Journal explains how a team of astronomers from the Ohio State University assessed the ability of forthcoming telescopes to detect oxygen, carbon dioxide, methane, and water, the biosignatures found in Earth's atmosphere that can provide essential scientific proof of life, on 10 rocky exoplanets.

The research found that for two nearby planets, namely Proxima Centauri b and GJ 887 b, the telescopes are highly proficient at detecting potential biosignatures. Among them, only Proxima Centauri b could detect the presence of carbon dioxide if it exists. Although no exoplanet has been found to perfectly twin Earth's early conditions for life, this work infers that if examined in more depth, super Earths—planets larger than Earth but smaller than Neptune—could potentially be promising targets for future research missions

Huihao Zhang, the study's lead author and a senior in astronomy at Ohio State, and his team also aimed to assess how well specialized imaging instruments like the James Webb Space Telescope (JWST) and other Extremely Large Telescopes (ELTs) including the European Extremely Large Telescope, the Thirty-Meter-Telescope and the Giant Magellan Telescope, could directly image exoplanets in the quest for habitable planets.

'Not all planets are compatible for direct imaging, but simulations can give us a general idea of what the ELTs would have delivered and their future potential,' commented Zhang.

Direct imaging of exoplanets involves using a coronagraph or starshade to inhibit a host star's light, allowing scientists to capture a dim image of the new planet in orbit. Due to the challenges and time consumption in locating them in this manner, the researchers set out to see how the ELT telescopes would fare against the task.

They tested each telescope's instruments' capacity to differentiate universal background noise from the planetary noise they sought to capture while detecting biosignatures - a signal-to-noise ratio; the greater it is, the easier it is to detect and analyze a planet's wavelength.

The Mid-infrared ELT Imager and Spectrograph, a European ELT instrument, showed better results in detecting methane, carbon dioxide and water on three planets (GJ 887 b, Proxima b and Wolf 1061 c) when used for direct imaging. Moreover, its High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph instrument was capable of detecting methane, carbon dioxide, oxygen, and water, though it required a considerably higher exposure time.

These results were compared with JWST's current outer space capabilities as they need to look through Earth's atmospheric chemical fog to continue the search for extraterrestrial life, said Zhang.

'Comparing space telescopes and ground-based ones is tricky because of their different settings, locations, and observation influences,' he added.

The study's findings showed that while GJ 887 b is a particularly suitable target for ELT direct imaging due to its location and size resulting in a high signal-to-noise ratio, JWST's techniques for studying planetary atmospheres are better suited for detecting some transiting planets, such as the TRAPPIST-1 system, than direct imaging from the ELTs on Earth.

However, Zhang mentioned that the study used a more cautious approach, and the actual effectiveness of future astronomical tools might exceed expectations. Despite minor differences in performance, these powerful tools serve to broaden our understanding of the universe and are meant to complement each other, stated Ji Wang, co-author of the study and an assistant professor in astronomy at Ohio State. Therefore, it is necessary to conduct studies like this one that assess these technologies' limitations, he added.

'The importance of simulation, especially for missions that cost billions of dollars, cannot be stressed enough,' said Wang. 'Not only do people have to build the hardware, they also try really hard to simulate the performance and be prepared to achieve those glorious results.'

In all likelihood, as the ELTs won't be completed until the tail end of the decade, researchers' next steps will settle around simulating how well future ELT instruments will take to investigating the intricacies of our own planet's rampant proofs of life.

'We want to see to what extent we can study our atmosphere to exquisite detail and how much information we can extract from it,' said Wang. 'Because if we cannot answer habitability questions with Earth's atmosphere, then there's no way we can start to answer these questions around other planets.'

Journal information: Astronomical Journal

Provided by The Ohio State University