The Webb Telescope won the hearts of the public with its beautiful pictures of space. Photographs are also of great importance to scientists, but perhaps even more important are spectral measurements, thanks to which we learn the chemical composition of distant worlds. Today’s topic is about such a case, which at first glance looks just like a graph. But as we will show, the content of this graph is very interesting. As part of this observation, the James Webb telescope turned its gaze to the exoplanet K2-18 b, which is 8.6 times more massive than Earth. Its spectral measurements confirmed the presence of carbonaceous molecules – for example, carbon dioxide and methane. The current discovery supports recent studies that suggest K2-18 may have a hydrogen-rich atmosphere and a surface covered by a watery ocean, referred to as the Hycean.
Artist’s impression of the exoplanet K2-18 b.
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The first glimpse into the atmosphere of this exoplanet, which orbits its star in the so-called habitable zone, came from the Hubble telescope, prompting further studies that have gradually changed our understanding of this system. Exoplanet K2-18 b orbits the cool dwarf star K2-18 in the constellation Leo, 120 light years from Earth. Exoplanets like K2-18 b, which are somewhere between Earth and Neptune in size, are unlike anything we know from the Solar System. The lack of similar nearby planets means that little is understood about these “sub-Neptunes,” and the nature of their atmospheres is the subject of active debate among astronomers.
The idea that “sub-Neptune” K2-18 b could be a Hycean-type exoplanet is tempting, as some astronomers believe these worlds could be a promising environment for searching for evidence of life on exoplanets. “Our findings underscore the importance of considering different habitable environments in the search for life,” explains Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the scientific paper reporting the discovery, adding: “The search for life on exoplanets has traditionally focused on smaller rocky planets, but larger Hycean-type worlds are much more suitable for observing atmospheres.“
Model molecular dimethyl sulfide.
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The abundance of methane and carbon dioxide, along with the lack of ammonia, supports the theory that exoplanet K2-18b could host a water ocean beneath a hydrogen-rich atmosphere. These initial observations from the Webb Telescope yielded another very interesting observation. Traces of a compound said to have been discovered in the spectral analysis dimetylsulfid (DMS). This molecule is very interesting because only living organisms produce it on Earth. Most of the DMS on Earth was created by ocean-dwelling phytoplankton. In one breath, it is necessary to add that the spectral trace of DMS in the measurement is less pronounced and requires further confirmation. “Upcoming observations by the Webb Telescope should confirm whether DMS is indeed present in significant quantities in the atmosphere of K2-18 b,” adds Madhusudhan.
Although K2-18 b lies in the habitable zone and its atmosphere contains carbon molecules, this does not necessarily mean that this world may be suitable for life. The large size of this planet (2.6 times the radius of Earth) means that the interior of the planet is probably a large mantle of high-pressure ice, like we know from Neptune, but with a thinner hydrogen-rich atmosphere and a watery surface. However, we cannot yet rule out the possibility that this ocean is too hot to host life. There is also a real possibility that the conditions here will not even allow the existence of liquid water.
Spectral measurements of the atmosphere of the exoplanet K2-18 b performed by the James Webb Telescope – specifically the NIRISS and NIRSpec instruments.
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„Although planets of this type do not exist in the Solar System, sub-Neptunes are the most abundant type of exoplanet known in our galaxy,” explains member of the scientific team, Subhajit Sarkar from Cardiff University, adding: “We obtained the most detailed spectrum of sub-Neptune in the habitable zone to date, allowing us to determine what molecules exist in the atmosphere there.The characteristics of the atmospheres of exoplanets such as K2-18 b, i.e. the identification of the chemical composition of the gases there and their physical properties, is a very active field in astronomy. But these planets are literally drowned in the glow of their parent stars, which greatly complicates the observation of the atmospheres of these exoplanets.
NIRSpec (Near-InfraRed Spectrograph) instrument
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The researchers therefore avoided this technological challenge by analyzing the light from the parent star at the time when the exoplanet K2-18 b was passing through the disc of its star from our view. During this transit, the exoplanet slightly eclipses its star, reducing its brightness. After all, this is how this exoplanet was discovered in 2015 using the Kepler telescope as part of its extension mission K2. But this also means that during the transit, some of the star’s light passes through the planet’s atmosphere before reaching the telescope’s detectors. It is the passage of light through the exoplanet’s atmosphere that leaves spectral traces on it – some wavelengths are absorbed by molecules in the atmosphere, and their absence in the measurement will thus allow astronomers to determine what gases are in the atmosphere.
NIRISS and FGS devices form one functional unit, but they can also work independently.
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„These results were only possible thanks to the extended wavelength range and unrivaled sensitivity of the Webb Telescope, which enabled the clear detection of spectral traces in just two transits,” states Madhusudhan, adding, “By comparison, data from a single transit taken by the Webb Telescope provided comparable accuracy to eight observations made over several years and over a relatively narrow range of wavelengths.The exceptionality of the observation is also confirmed by Savvas Constantinou from the University of Cambridge, who is the head of the scientific team: “The results are the product of just two K2-18 b transits, with many more to come. This means that our work is so far only a sample of what the Webb telescope can observe for exoplanets in the habitable zone.“
The results written by the scientific team have been accepted for publication in the Astrophysical Journal Letters. Experts from this team now want to carry out follow-up spectral measurements with the MIRI instrument, which they expect should provide a new insight into the conditions prevailing on the exoplanet K2-18 b.Our main goal is the discovery of life on a habitable planet, which would change our perception of our position in the universe,” concludes Madhusudhan, adding, “Our discoveries are a promising step towards a better understanding of Hycean-type worlds.“
Image Sources:
https://solarsystem.nasa.gov/…/JWST_Illustration-1280.jpg
sites/default/files/thumbnails/image/stsci-01h9r8aek6y7qr03mgn9v9p6zj.jpg
wikipedia/commons/7/7c/Dimethyl-sulfide-3D-vdW.png
sites/default/files/thumbnails/image/stsci-01h9rf3tqe6xa9x01kxxj351z6.png
/…/JWST_s_Near_InfraRed_Spectrograph_NIRSpec.jpg
wikipedia/commons/7/78/JWST_FGS_ETU_picture.jpg
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2023-09-12 22:14:24
#JWST #discovered #interesting #compounds #exoplanet
