[Paper Review] The Pandora SmallSat: Multiwavelength Characterization of Exoplanets and their Host Stars

Elisa V. Quintana, Knicole D. Colón+25 more|arXiv (Cornell University)|Aug 14, 2021

Stellar, planetary, and galactic studies22 references5 citations

TL;DR

Pandora is a SmallSat mission designed to simultaneously observe exoplanets in visible and near-infrared wavelengths to disentangle stellar activity effects—such as spots and faculae—from planetary transmission spectra. By providing long-baseline, multiwavelength photometry and spectroscopy, it enables robust characterization of exoplanet atmospheres, including detection of hydrogen- and water-dominated envelopes and cloud/haze coverage, filling a critical gap in pre-JWST and JWST-era exoplanet science.

ABSTRACT

Pandora is a SmallSat mission designed to study the atmospheres of exoplanets, and was selected as part of NASA's Astrophysics Pioneers Program. Transmission spectroscopy of transiting exoplanets provides our best opportunity to identify the makeup of planetary atmospheres in the coming decade. Stellar brightness variations due to star spots, however, can impact these measurements and contaminate the observed spectra. Pandora's goal is to disentangle star and planet signals in transmission spectra to reliably determine exoplanet atmosphere compositions. Pandora will collect long-duration photometric observations with a visible-light channel and simultaneous spectra with a near-IR channel. The broad-wavelength coverage will provide constraints on the spot and faculae covering fractions of low-mass exoplanet host stars and the impact of these active regions on exoplanetary transmission spectra. Pandora will subsequently identify exoplanets with hydrogen- or water-dominated atmospheres, and robustly determine which planets are covered by clouds and hazes. Pandora will observe at least 20 exoplanets with sizes ranging from Earth-size to Jupiter-size and host stars spanning mid-K to late-M spectral types. The project is made possible by leveraging investments in other projects, including an all-aluminum 0.45-meter Cassegrain telescope design, and a NIR sensor chip assembly from the James Webb Space Telescope. The mission will last five years from initial formulation to closeout, with one-year of science operations. Launch is planned for the mid-2020s as a secondary payload in Sun-synchronous low-Earth orbit. By design, Pandora has a diverse team, with over half of the mission leadership roles filled by early career scientists and engineers, demonstrating the high value of SmallSats for developing the next generation of space mission leaders.

Motivation & Objective

• Address the challenge of stellar variability—particularly star spots and faculae—contaminating transmission spectroscopy of transiting exoplanets.
• Enable precise characterization of exoplanet atmospheres by disentangling planetary atmospheric signals from stellar spectral contamination.
• Identify which exoplanets have hydrogen- or water-dominated atmospheres and which are obscured by clouds or hazes.
• Provide long-baseline, simultaneous optical and near-infrared data to overcome limitations of current ground- and space-based facilities.
• Support and inform target selection and observing strategies for flagship missions like JWST and Ariel/CASE by delivering critical stellar activity constraints.

Proposed method

• Utilize a 0.45-meter all-aluminum Cassegrain telescope with a visible-light photometer and a near-IR spectrograph for simultaneous multiwavelength observations.
• Conduct long-duration photometric monitoring (≥1 year) in Sun-synchronous low-Earth orbit to capture stellar variability over multiple rotation periods.
• Leverage heritage hardware, including a NIR sensor chip assembly from the James Webb Space Telescope, to reduce mission cost and risk.
• Apply multiwavelength light curves to model and quantify spot and faculae covering fractions on low-mass host stars (mid-K to late-M spectral types).
• Use simultaneous visible and near-IR data to correct for stellar contamination in transmission spectra, improving atmospheric retrieval accuracy.
• Integrate data with ground- and space-based follow-up observations through a Science Working Group structure to maximize scientific output.

Experimental results

Research questions

• RQ1 To what extent do stellar spots and faculae contaminate transmission spectra of transiting exoplanets, particularly around low-mass stars?
• RQ2 Can simultaneous visible and near-infrared observations reliably disentangle planetary atmospheric signals from stellar variability?
• RQ3 Which exoplanets in the sample (20 planets, Earth- to Jupiter-sized) have hydrogen- or water-dominated atmospheres, and which are obscured by clouds or hazes?
• RQ4 How do stellar activity levels correlate with atmospheric retrieval uncertainties in transmission spectroscopy?
• RQ5 To what extent can Pandora’s data improve target selection and observing strategies for JWST and future missions like Ariel/CASE?

Key findings

• Pandora will observe at least 20 exoplanets with sizes ranging from Earth-size to Jupiter-size, primarily around mid-K to late-M type stars.
• The mission will provide long-baseline, simultaneous visible and near-infrared photometry, enabling precise quantification of stellar spot and faculae covering fractions.
• By combining visible and NIR data, Pandora will correct for stellar contamination in transmission spectra, significantly improving atmospheric composition retrieval accuracy.
• Pandora is expected to identify which planets have hydrogen- or water-dominated atmospheres and which are obscured by clouds or hazes with higher confidence than current facilities allow.
• The mission will operate concurrently with JWST, providing critical pre- and post-JWST context for transmission spectroscopy, including target selection and data interpretation.
• Pandora’s data will be archived and made publicly available, enhancing value for future exoplanet science and mission planning.