The James Webb Space Telescope (JWST) has opened up new frontiers in exoplanet characterization with its excellent data quality allowing us to identify previous undetected spectral features in exoplanet atmospheres in the 3-5 micron range. Identifying signatures of molecules like sulfur dioxide, hydrogen sulfide, and ammonia in the atmospheres of exoplanets might allow us access to elemental ratios like C/S, O/S, and N/O, which in addition to C/O, could act as formation tracers, allowing us to decode planet formation. In addition, spectroscopic studies of giant exoplanets also provide insights into the interesting atmospheric physics and chemistry prevailing in their interiors.

First Direct Spectroscopy of GJ 504 b reveals Clouds and Possible Metal Enrichment

Link to paper: Baburaj et al. 2026b, Astronomical Journal

In this work, I use JWST/NIRSpec to obtain the first-ever spectrum of cold GJ 504 b (Teff ~ 550 K), a planetary mass companion (PMC) too faint for ground-based spectroscopy. Leveraging NIRSpec cross-correlation techniques, I detect the companion at S/N > 300. I also present the first successful PSF subtraction with angular differential imaging (ADI) in the high-contrast regime, detecting GJ 504 b at S/N > 10 in both NRS1 and NRS2, and reaching contrasts < \(10^{-4}\). This enables recovery of the 3-5-micron spectral continuum for GJ 504 b, which is lost with the aforementioned cross-correlation techniques. CCF analysis of the R~2,700 spectrum leads to detections of trace species \(\rm CO_2, NH_3, ^{13}CO, C^{18}O,\) and \(\rm H_2S\). Joint retrieval modeling of the JWST spectrum and previous photometry indicates Teff~564 K, [M/H]~0.67, and existence of disequilibrium chemistry. My efforts also provide strong evidence for salt clouds (chlorides/sulfides) in GJ 504 b. Comparison of abundances of GJ 504 b to the primary reveals stellar sulfur, super-stellar carbon, and possibly, oxygen, with the observed metal enrichment only tentatively supporting planet-like formation. My work highlighted the importance of clouds while modeling the spectrum of cold objects (Teff < 600 K). Furthermore, it demonstrates an imminent need for self-consistent atmospheric grids and evolutionary models accounting for clouds, disequilibrium chemistry, and super-solar metallicities in cold objects.​
This work had a press release by Northwestern University (Link to article).

ADI spectrum of GJ 504 b
Figure: ADI extracted NIRSpec G395H spectrum of GJ 504 b (cyan) with the dominant molecular opacity sources − H\(_2\)O, CO, CH\(_4\), CO\(_2\), and NH\(_3\) marked. The gray shaded region indicates the 1σ error on the extracted flux.

JWST/NIRSpec IFU Spectroscopy of HD 206893 B (GO 5485; PI Baburaj)

As a graduate student, I sucessfully conceived and executed a Cycle 3 JWST program (GO 5485; PI Baburaj) to observe the \(\sim20~M_{\rm Jup}\) companion HD 206893 B using the NIRSpec IFU. Measuring the detailed abundances of this companion will provide a window into the utility of formation diagnostic tools at the extreme upper end of the planet formation process. I successfully detect HD 206893 B at an angular separation \(\sim0^{\prime\prime}.19~\) despite the bright star saturating the detector at the companion position . Combined atmospheric modeling of the NIRSpec data and previous low-resolution data and photometry is ongoing (Baburaj et al., in prep).

JWST/NIRSpec IFU Spectroscopy of circumbinary planet HD 143811AB b (GO 10963; PI Baburaj)

I am the PI of an approved ~13 hr Cycle 5 JWST program (GO 10963) for direct spectroscopy of the recently discovered circumbinary planet HD 143811 AB b (Jones et al. 2025, ApJL), aiming to eluciate differences in planet formation between single-star and binary-star environments. The observations are scheduled for July 2027.