AUTHOR=Cucho-Padin Gonzalo , Bhattacharyya Dolon , Sibeck David G. , Connor Hyunju , Youngblood Allison , Ardila David 

TITLE=EXOSpy: A python package to investigate the terrestrial exosphere and its FUV emission

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2023.1082150

DOI=10.3389/fspas.2023.1082150

ISSN=2296-987X

ABSTRACT=The exosphere is the uppermost layer of the terrestrial atmosphere, mainly composed of atomic hydrogen (H) that resonantly scatters solar far-ultraviolet (FUV) photons at 121.56 nm, also referred to as Lyman-Alpha (Ly-$\alpha$) emission. Analysis of this emission has been used to determine the global, three-dimensional, and time-dependent exospheric H density structure, which is essential to assess the permanent escape of H to space as well as to determine their role in governing the transient response of terrestrial plasma environment to space weather. Thus, Ly-$\alpha$ emission and its by-product, the H density, are highly desirable to the magnetospheric community. On the other hand, this emission can also be regarded as a significant source of contamination during studies of FUV targets such as O/B-type stars, planetary and exoplanetary atmospheres, and the circumgalactic medium, especially when observations are acquired from Earth-orbiting instruments. In this case, accurate specification of exospheric Ly-$\alpha$ photon flux and its subsequent removal is required by the planetary and astrophysics community studying solar/extra-solar system objects. This work introduces $\texttt{EXOSpy}$, an open-source python-based package that provides several models of terrestrial exospheric H density and calculates exospheric Ly-$\alpha$ emission with a high potential to contribute to investigations in both communities. We present several examples to demonstrate how \texttt{EXOSpy} can be used to (i) validate current and new exospheric models based on actual Ly-$\alpha$ radiance data, (ii) estimate exospheric contamination for a given instrument's line-of-sight and spatial location, and (iii) provide support for new space-based FUV instrument design.