Target Selection for the Pandora SmallSat: A NASA Mission to Disentangle Stellar and Exoplanet Atmosphere Signals

The Pandora SmallSat mission was selected for implementation in 2021 as part of NASA’s Astrophysics Pioneers Program. Pandora is designed to monitor stellar variability while studying the atmospheres of transiting exoplanets via transmission spectroscopy. The transmission spectroscopy technique is one of the best methods to identify the makeup of exoplanetary atmospheres now and in the coming decade. However, stellar variations that occur from the presence of, for example, cool star spots, have been shown to contaminate the exoplanet atmosphere spectra obtained with high-precision transmission spectroscopy measurements. This stellar contamination leads to ambiguous interpretations when attempting to distinguish features like potential water vapor absorption signatures in the exoplanet atmosphere from the presence of water vapor in the host star atmosphere. Pandora will address the problem of stellar contamination by collecting long-duration photometric observations with a visible-light channel and simultaneous spectra with a near-infrared channel. These simultaneous multiwavelength observations will constrain star spot covering fractions of exoplanet host stars, enabling star and planet signals to be disentangled in transmission spectra to then reliably determine exoplanet atmosphere compositions. The Pandora science team employs a systematic process to optimize the selection of 20 transiting exoplanet targets for Pandora to observe in its prime mission, with the exoplanet sizes ranging from Earth- to Jupiter-size and host stars spanning primarily K and M spectral types. Transiting exoplanet targets are chosen strategically in order to meet science requirements for the prime mission while also enabling synergies with science from other ground- and space-based facilities. With Pandora’s observational capabilities, auxiliary science observations of non-exoplanet targets are also feasible. Pandora is on track for launch readiness in Fall 2025. Following launch on a SpaceX Falcon 9 rocket and a month-long commissioning period, Pandora will have a prime mission of one year.