The Ammonia Trail: Unlocking Cosmic Mysteries of Distant Worlds With Webb

The Ammonia Trail: Unveiling Cosmic Enigmas of Distant Worlds with the James Webb Space Telescope

Recent scientific breakthroughs have led to the identification of ammonia isotopologues within the atmosphere of a brown dwarf, marking a significant milestone in the field of astronomy. This discovery, made possible by the James Webb Space Telescope (JWST), offers fresh insights into the formation of gas giants and exoplanets, challenging prevailing theories and shedding light on alternative mechanisms such as gravitational collapse.

The detection of ammonia isotopologues in a brown dwarf by the JWST represents a groundbreaking revelation, unveiling potential alternative pathways for the formation of gas giants and exoplanets.

Isotopes and isotopologues, molecules that vary only in the composition of their isotopes, play an increasingly pivotal role in the realm of astronomy. For instance, the ratio of carbon-12 (12C) to carbon-13 (13C) isotopes within the atmosphere of an exoplanet allows scientists to deduce the distance at which the exoplanet orbits its central star.

Advancements in Isotopologue Detection

Up until now, scientists could only measure the isotopologues of 12C and 13C bound in carbon monoxide within the atmosphere of an exoplanet. However, a recent breakthrough by a team of researchers has enabled the detection of ammonia isotopologues within the atmosphere of a frigid brown dwarf. As reported in the journal Nature, this includes the measurement of ammonia in the form of 14NH3 and 15NH3. Astrophysicists Polychronis Patapis and Adrian Glauser, affiliated with the Department of Physics and the National Centre of Competence in Research (NCCR) PlanetS, were key contributors to this study, with Patapis serving as one of the primary authors.

Exploring Brown Dwarfs

Brown dwarfs inhabit a space between stars and planets, bearing resemblance to giant gas planets in several aspects. This characteristic makes them an ideal system for studying gas giants. In their research, Patapis and his colleagues observed a specific brown dwarf named WISE J1828, located 32.5 light years away from Earth in the constellation Lyra.

WISE J1828 remains invisible to the naked eye due to its exceptionally low effective temperature, only 100°C, rendering it too cold for hydrogen fusion to emit visible light. To observe this ultracold Y spectral class dwarf star, the mirrors of the James Webb Space Telescope (JWST) were oriented towards the lyre constellation during the previous summer.

The Role of the JWST

The Mid-InfraRed Instrument (MIRI), an infrared detector integrated into the JWST, played a pivotal role in the discovery of ammonia isotopologues on WISE J1828. Operating within the wavelength range of 4.9 to 27.9 μm, the Medium Resolution Spectrometer (MRS) of MIRI captured a spectrum of the brown dwarf, revealing not only ammonia but also water and methane molecules, each characterized by distinctive absorption patterns. Notably, ammonia led to signal attenuation within the 9 to 13 μm wavelength range.

Spectroscopic resolution also made it possible to differentiate between ammonia isotopologues. When ammonia molecules consist of the less common nitrogen isotope 15N in addition to three hydrogen atoms, the presence of 15NH3 results in a distinctive spectral kink, as opposed to the more prevalent 14NH3.

New Tools for Probing Exoplanets

The particularly exciting aspect of the observation lies in the ratio of the two ammonia isotopologues measured within the atmosphere of WISE J1828. According to Patapis and his colleagues, the 14NH3-to-15NH3 ratio serves as a tracer, a future indicator for studying the formation of stars and planets. This novel tool promises to facilitate the testing of various established mechanisms for gas giant formation.

Gas giants like Jupiter and Saturn are not unique to our solar system. They play a crucial role in exoplanet studies, appearing early in the process of star formation and influencing the development of smaller, lighter planets. The precise mechanism behind the formation of massive gas giants has remained a subject of debate, with different theories proposed. The question of whether these planets form through nuclear accretion or gravitational collapse within the protoplanetary disk surrounding the progenitor star has yet to receive a definitive answer.

Insights into Planet Formation

The isotopologue ratio recorded by Patapis and his team holds the potential to provide valuable clues. On Earth, there are 272 atoms of 14N for every 15N atom. However, the paper reports a 14NH3-to-15NH3 ratio of 670 within the atmosphere of WISE J1828, indicating that this brown dwarf accumulated less nitrogen-15 during its formation compared to Earth and other celestial bodies in our solar system. This scarcity of 15N on WISE J1828 suggests that the brown dwarf may have followed a different path to planet formation, possibly resembling a star-like formation involving gravitational collapse, rather than the more conventional nuclear accretion process.

Furthermore, the study highlights the significant variation in the 14NH3-to-15NH3 ratio based on the distance between a gas giant and its central star, as demonstrated by simulations of a developing planet between the ammonia and molecular nitrogen ice lines. In astronomy, ice lines denote the minimum distances from the central star where temperatures are low enough for specific volatile compounds to transition into solid form.

According to Patapis and his colleagues, an increased 14NH3-to-15NH3 ratio could signify the accretion of ices between the ammonia and nitrogen ice lines during planetary formation.

Implications and Future Endeavors

Astronomers have gained a valuable new tool for studying directly observable exoplanets, thanks to the discovery of the ammonia trail, made possible by the JWST. This achievement underscores the immense significance and unparalleled capabilities of this space telescope.

Reference: “15NH3 in the atmosphere of a cool brown dwarf” by David Barrado, Paul Mollière, Polychronis Patapis, Michiel Min, Pascal Tremblin, Francisco Ardevol Martinez, Niall Whiteford, Malavika Vasist, Ioannis Argyriou, Matthias Samland, Pierre-Olivier Lagage, Leen Decin, Rens Waters, Thomas Henning, María Morales-Calderón, Manuel Guedel, Bart Vandenbussche, Olivier Absil, Pierre Baudoz, Anthony Boccaletti, Jeroen Bouwman, Christophe Cossou, Alain Coulais, Nicolas Crouzet, René Gastaud, Alistair Glasse, Adrian M. Glauser, Inga Kamp, Sarah Kendrew, Oliver Krause, Fred Lahuis, Michael Mueller, Göran Olofsson, John Pye, Daniel Rouan, Pierre Royer, Silvia Scheithauer, Ingo Waldmann, Luis Colina, Ewine F. van Dishoeck, Tom Ray, Göran Östlin and Gillian Wright, 6 November 2023, Nature.
DOI: 10.1038/s41586-023-06813-y

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More about Exoplanet Formation

• James Webb Space Telescope (JWST)
• Nature Journal Article: “15NH3 in the atmosphere of a cool brown dwarf”
• Brown Dwarfs
• Exoplanet Formation
• Gas Giants