Earth as a transiting exoplanet. SPIRou observation of Earth near-IR transmission spectrum during the November 19, 2021 lunar eclipse

Detecting and characterizing the atmosphere of rocky planets in the habitable zone is a key objective of exoplanet research in the era of JWST and the upcoming E-ELT. Spectroscopy of a planetary transit is the primary method of obtaining a transmission spectrum of an exoplanetary atmosphere. A lunar eclipse is a natural proxy for an Earth transit, offering a unique opportunity to study Earth’s atmosphere as if it were an exoplanet. This work aims to derive the empirical, wavelength-dependent effective height of Earth's atmosphere in the near-infrared, spanning the Y to K bands. During a lunar eclipse, the penumbra -- the region where the Sun is partially occulted by the Earth -- contains the signature of the transmission spectrum of the atmosphere along Earth's limb. The high-resolution (R=70, 000) SPIRou spectrograph at CFHT was used to collect spectra during and after the November 19, 2021 eclipse. Two distinct methods, using either one or two penumbral spectra, were employed to derive the effective height of the atmosphere. Each method was evaluated in the context of distinct astrometric and spectrophotometric approaches. The derived effective height spans 964 to 2498, nm and shows the absorption bands of H₂O, O₂, CH₄, and CO₂ peaking at up to 29. 6, km at a spectral resolution of R=70, 000, including a 12. 7, km offset defining a reference altitude taken from a transit model. The uncertainty assessed from individual penumbra observations and from uncertainties on telluric lines correction and Moon reflectance is found to be 3σ Heights are up to 25. 1, km at a convolved resolution of R=1000. The measured heights are in good agreement with theoretical predictions. The high-resolution wavelength-dependent effective heights are made publicly available to the community.