Why ANDES @ ELT will redefine atmospheric characterization, and where the Kp wall waits for us

The atmospheric characterization of Neptune-mass exoplanets serves as a crucial stepping stone toward understanding smaller, potentially habitable worlds. This study presents a comprehensive multi-resolution analysis of WASP-107b, a warm super-Neptune with an extended atmosphere ideal for transmission spectroscopy, using the novel GUIBRUSHR framework that combines high-resolution ground-based observations (GIANO-B, IGRINS) with low-resolution space-based data (HST/WFC3, JWST/NIRCam, JWST/MIRI). Our analysis successfully detected seven molecular species (H₂O, CO₂, CO, CH₄, NH₃, SO₂, H₂S) through low-resolution spectroscopy while revealing significant challenges in high-resolution observations, particularly regarding telluric and stellar contamination that limited reliable detections to H₂O and CO. A critical finding is that when planetary and telluric signals overlap in velocity space, disentangling atmospheric absorption features becomes significantly more challenging, particularly for planets with low Kp values. This velocity overlap analysis serves as a critical planning step to optimize observational strategies and ensure the detectability of planetary atmospheric signatures. While the upcoming Extremely Large Telescopes (ELTs) will improve high-resolution exoplanet spectroscopy by providing increased collecting power and better signal-to-noise ratios, this fundamental disentangling challenge will persist for Earth and super-Earth planets. Despite enhanced sensitivity from ELTs, the velocity overlap between planetary and telluric features represents a systematic limitation that will require sophisticated mitigation strategies for reliable atmospheric characterization of terrestrial exoplanets.