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Water detected on distant super-Earth planet with potential

Scientists Detect Water On A Faraway Planet

12 September 2019 International News News

Scientists announced another exciting discovery yesterday (September 11, 2019) regarding potentially habitable exoplanets.

For the first time, they’ve detected water vapor in the atmosphere of a distant super-Earth – called K2-18b – orbiting its star in the habitable zone. The word “habitable” in this context doesn’t mean humans could live there.

A star’s habitable zone is the zone where liquid water might exist, and water is essential for life as we know it. This particular exoplanet also has relatively moderate temperatures, by earthly standards. With confirmed water vapor and habitable temperatures, K2-18b has just become a very intriguing target in the search for life.

The peer-reviewed discovery was published in a paper today (September 11, 2019) in Nature Astronomy, by researchers from University College London (UCL). Another paper (draft version) was also published on ArXiv on September 10, 2019.

The new work stems from observations made with the Hubble Space Telescope. It marks the first overall successful atmospheric analysis of an exoplanet in the habitable zone of its star. Such studies have proven difficult due to the distances of these worlds and their smaller sizes as compared to gas giants like Jupiter.

Water has been discovered in the atmosphere of a “super-Earth” exoplanet orbiting its star within the habitable zone. While the exoplanet’s atmosphere isn’t expected to be “habitable” by human standards, this is a remarkable discovery:

According to Angelos Tsiaras at the UCL’s Centre for Space Exochemistry Data (CSED) and first author of the new paper:

Finding water in a potentially habitable world other than Earth is incredibly exciting. K2-18b is not ‘Earth 2.0’ as it is significantly heavier and has a different atmospheric composition. However, it brings us closer to answering the fundamental question: Is the Earth unique?

The analysis of K2-18b’s atmosphere was based on data from the Hubble Space Telescope. In this analysis, the scientists also found atmospheric hydrogen and helium.

Diagram of habitable zones for different size stars.

They believe nitrogen and methane might also be present, but further studies are needed to confirm that, or not. Scientists also need to figure out how cloudy the atmosphere is and how much water vapor there is, percentage-wise.

They also think it’s likely that there are water clouds in K2-18b’s atmosphere as well, and possibly even rain. From the second paper:

Given the relatively low irradiation by the star, K2-18b’s temperature is low enough that the detected water vapor can plausibly condense to form liquid droplets. It is therefore possible that liquid water rain precipitates in the mid-atmosphere of K2-18b.

Co-author Giovanna Tinetti said:

Our discovery makes K2-18b one of the most interesting targets for future study. Over 4,000 exoplanets have been detected but we don’t know much about their composition and nature. By observing a large sample of planets, we hope to reveal secrets about their chemistry, formation and evolution.

As Tsiaras added:

This study contributes to our understanding of habitable worlds beyond our solar system and marks a new era in exoplanet research, crucial to ultimately place the Earth, our only home, into the greater picture of the cosmos.


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