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Eyes on the Prize: JWST Detects a Unique Exoplanet

An Artist’s Interpretation of What K2-18b May Look Like Orbiting Its Cool Dwarf Star K2-18
Credit: NASA, CSA, ESA, J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)

In the atmosphere of an exoplanet 120 light years away from Earth, the James Webb Space Telescope (JWST) has detected carbon-bearing molecules, some of which have scientists questioning the possibility of life elsewhere in the universe. On September 11th, 2023, the international partnership overseeing the operation of JWST announced the discovery of gasses such as methane and carbon dioxide in the atmosphere of the exoplanet K2-18b. Furthermore, while it is yet to be confirmed, they also announced the potential detection of a gas which is only known to be produced by life here on Earth. That being said, the question of whether or not life exists in some form on a world other than our own is now being reconsidered. 

Clearing the trees of a tropical rainforest on an Ariane 5 rocket, the James Webb Space Telescope took to the skies on December 25th, 2021 from the Guiana Space Center of French Guiana. After a multi month coast phase filled with nail biting hardware and instrument deployments, JWST entered service on July 12th, 2022, residing around Lagrange Point 2 (L2) about a million miles away from the Earth. However, JWST’s journey didn’t begin here. Costing about $10 billion, Webb took multiple decades to be designed, built, and flown, and is considered to be the single most expensive payload ever sent into space. Luckily, the cost, wait, and tension were worth it. Over the past couple of years, JWST has shocked the world with its awe-inspiring images of nebulae, galaxies, and Earth’s neighboring planets and will continue to prove itself as a priceless piece of scientific innovation.

JWST’s First Deep Field Image of SMACS 0723, a Galaxy Cluster
 Located About Four Billion Light Years Away From Earth
Credit: NASA, ESA, CSA, and STScI

However, being named after former NASA administrator James Webb, a fair amount of controversy has been encountered throughout its development and operation. Throughout the 1950s and 1960s, Webb went along with the violation of LGBT rights as lesbian and gay employees were discriminated against and purged from government jobs. As detailed in a report issued by NASA, concerns regarding Webb’s involvement in the so-called “Lavender Scare” prompted NASA to conduct a thorough investigation into his background. Following this investigation, NASA concluded that “no available evidence directly links Webb to any actions or follow-up related to the firing of individuals for their sexual orientation”, and so the name stuck. 

To conduct its observations, JWST is equipped with four main instruments; The Mid-Infrared Instrument (MIRI), Near-Infrared Camera (NIRCam), Near-Infrared Imager and Slitless Spectrograph (NIRISS), and the Near-Infrared Spectrograph (NIRSpec). All four of these instruments are capable of spectroscopy to some extent, but MIRI, NIRISS, and NIRSpec are dedicated spectrographs while NIRCam is used primarily for imaging. Instruments such as NIRSpec operate by dispersing the light that enters it into its wavelengths. By analyzing the patterns of these wavelengths, astronomers back on Earth are able to determine the chemical compositions of the molecules producing the light being observed. In the case of JWST’s observations of K2-18b, NIRISS and NIRSpec were utilized.

One of NASA’s programs which will benefit greatly from observations of this nature is the “Habitable Worlds Observatory” (HWO). Still very early in its development phase, HWO was recommended as a flagship mission in 2020 and would be NASA’s first spacecraft dedicated to the mission of searching for signs of life on potentially habitable exoplanets. As NASA becomes more serious about the program, early estimates put the launch of HWO in the 2040s. HWO will be able to utilize data collected by current observational equipment, such as JWST, to narrow down planetary bodies which have the strong potential of harboring life. When in service, HWO will then expand on our current knowledge of exoplanets by conducting more detailed and accurate observations of what molecules are found on worlds other than our own. Considering the conditions we believe to be present on K2-18b, it is safe to assume this could potentially become a target for HWO.

K2-18b is an exoplanet orbiting the dwarf star known as K2-18, which sits at a distance of roughly 120 light years away from Earth. With a mass 8.6 times that of the Earth, planets such as these are simply unheard of in our own solar system. K2-18b immediately captured the interests of astronomers because it is located in what is known as its star’s habitable zone, the region surrounding a star in which temperatures allow for liquid water to be present. Not only does this suggest water is present, but prior observations which have now been supported by JWST indicate the surface of K2-18b is covered in ocean, making it what is known as a Hycean exoplanet. All of these factors made K2-18b an excellent target for researchers to study further.

Before JWST pointed its 6.5 meter (21.3 foot) primary mirror towards the K2-18 star system, astronomers already knew a fair amount about its orbital companion. Previous studies conducted with the Hubble Space Telescope (HST) indicated significant amounts of water on its surface and a hydrogen rich atmosphere. With the help of JWST’s instruments, NASA detected an abundance of carbon dioxide and methane along with a shortage of ammonia. This supported the prior hypothesis that K2-18b contained an immense ocean under a hydrogen rich atmosphere. More intriguingly, this initial observation by JWST detected possible traces of a molecule known as dimethyl sulfide (DMS). At least on Earth, DMS is only known to be produced by biological processes, primarily being emitted by phytoplankton in marine environments. With astronomers already confident that K2-18b is covered in a large ocean, it stands to reason that this possible discovery of DMS should be considered seriously until further observations are made.

Spectral Graph of K2-18b Showing an Abundance of Carbon-Rich Elements Such as Methane, Carbon Dioxide, 
and Possibly Dimethyl Sulfide, Obtained With JWST’s NIRISS and NIRSpec Instruments
Credit: Illustration: NASA, CSA, ESA, R. Crawford (STScI), J. Olmsted (STScI), Science: N. Madhusudhan (Cambridge University)

With the potential of microbial life on planets other than Earth back in the spotlight, it is important to approach this topic cautiously and emphasize the fact that the detection of DMS is yet to be confirmed by peer review. In 2020, what was thought to be a discovery of the molecule phosphine in the upper atmosphere of Venus made global headlines. Similar to DMS, phosphine is known to be produced by microbial life here on earth. While this announcement was exciting, it still had to be confirmed. Flying at an altitude of 45,000 feet, NASA pointed the Stratospheric Observatory for Infrared Astronomy (SOFIA) at Venus and ultimately refuted the discovery. While it may still be possible that microbial life exists in the atmosphere of Venus, SOFIA’s observation indicated that there is no current reason to believe that this is the case. However, this false discovery did impact the future of scientific analysis of Venus. In the wake of this discovery, three new missions tasked with exploring Venus were selected; the European Space Agency’s EnVision orbiter and NASA’s DAVINCI and VERITAS spacecrafts. The three of these missions will come equipped with equipment to analyze Venus’ atmosphere, surface, and internal structure to an extent never seen before. 

While it is exciting to consider the possibility of microbial life in the oceans of K2-18b, history proves that it is important that we continue to make observations and wait until astronomers are confident in this potential discovery. Considering the atmospheric and surface conditions of K2-18b that have been confirmed, the potential detection of DMS is still something to be seriously considered by JWST for future observations. Furthermore, it makes K2-18b a prime target for future space telescopes such as HWO, which will help astronomers make more confident conclusions using the data they collect. JWST has only been in service for just over two years and has already warped our prior interpretations of the universe around us. It is still far too early to draw conclusions as to what resides inside the oceans and atmosphere of K2-18b, however scientists and astronomy enthusiasts should certainly still be excited about what this detection could mean for the future of exoplanet analysis and planetary science.

2 thoughts on “Eyes on the Prize: JWST Detects a Unique Exoplanet

  • So cool! It’s amazing what the JWST has accomplished already!

  • Nicholas Piombino

    Great article Brandon!


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