Launching a flagship-class mission like the Roman Space Telescope is always exciting, but with Roman in space, let’s also keep an eye on Pandora, a smaller though fascinating NASA mission (through its Astrophysics Pioneers program) that is now beginning its own work in exoplanet science. 20 exoplanets are targeted here, the idea being to work with data from transits to characterize their atmospheres via transmission spectroscopy, but with an additional twist. Elisa Quintana,(NASA GSFC) is principal investigator:

“Pandora’s data will help close a major gap in our knowledge about planets and their host stars because, right now, we can’t be entirely sure how the star’s light affects measurements of what makes up exoplanet atmospheres. We designed the Pandora spacecraft and its in-depth observing program to better understand this vexing issue.”

Launched January 11 of this year, Pandora is now beginning observations of its target stars. It’s in that category of smallsats that fascinate me because their low cost also gives them the option of higher tolerance of failure, making it possible to push the limits without great financial risk (the cost cap on this class of mission is $20 million). A tool like this can be tightly focused on specific targets without compromising larger instruments that are already besieged with obligations to existing observing programs. Word from the Pandora team is that science work begins with all instruments performing as expected.

Image: Artist’s concept of NASA’s Pandora mission, which will help scientists untangle the signals from exoplanets’ atmospheres and their stars. Credit: NASA GSFC/Conceptual Image Lab.

What makes Pandora so interesting is that it’s a multi-wavelength mission. Pandora’s telescope, an aluminum Cassegrain instrument 45 centimeters in diameter, feeds detectors that work in both visible light for long-baseline photometry as well as near-infrared (NIR) wavelengths. Starspots or other stellar activity can be separated from the near-infrared spectroscopy data on the planet’s clouds and atmospheric hazes. This is information that will inform subsequent work with telescopes like JWST and Roman as we refine our tools for removing noise in the data. A recent paper on Pandora makes the case:

Alongside the opportunities explored throughout this work, Pandora provides a unique opportunity to help overcome many hurdles inherent in observations with current instruments. Namely, multi-epoch observations of exoplanet atmospheres with JWST are often observed at different points in the stellar rotation, making them difficult to fit jointly (e.g., E. M. May et al. 2023). By providing information about the stellar activity and allowing for corrections at the data level, joint Pandora–JWST programs will unlock new insights into planets around active hosts. Additionally, these same insights will inform the presence of offsets between different instruments and epochs, which have been difficult to constrain thus far with JWST alone (e.g., A. L. Carter et al. 2024).

Pandora is going to give us useful data on stellar contamination in our transmission spectroscopy work. That means a clearer and more reliable look at the composition of exoplanet atmospheres. Stellar contamination should stand out, with a minimum of 10 transit observing sessions per target, each lasting about 24 hours. The plan is to accumulate, for each target, roughly 240 hours of pointing time, which should yield more than 120 hours of science data once Earth occultations and unavoidable gaps for downlinks, etc. are taken into account. An instrument like JWST can collect transmission spectroscopic data for exoplanets but only with relatively short observing sessions involving one or a small number of transits. The combined datasets of the two observatories will cleanly excise star signals from the data on planetary ones.

The finalized target list was published last January and contains 19 host stars, one of which is orbited by two of the target worlds. The stars range from M-dwarfs to K-class. 16 of these planets have been observed previously by JWST, which will allow the retrofitting of the Pandora measurements onto the JWST spectra. As far as I can tell, earlier provisional target lists included planets that didn’t make the final list, with the emphasis shifting toward larger warm Neptunes and Saturns. That makes sense given that these offer higher signal-to-noise ratios as we put these techniques to work together for the first time.

Image: This is Figure 1 from the paper. Caption: The absorption cross sections of common absorbers in exoplanet atmospheres considered in this work, shown at a pressure and temperature of 0.1 mbar and 1000 K. The wavelength coverage of Pandora’s NIR detector (NIRDA), JWST’s NIRCam F322W2 and F444W filters, and HST’s WFC3 instrument (for the G141 grism) are shown. Pandora/NIRDA covers absorption bands of H2O, CH4, NH3 and the wing of the K doublet, making it most sensitive to these absorbers. Credit: Rotman et al.

Using these methods, Pandora’s science observations should be more accurate and reliable than any planetary atmosphere readings ever taken before. The paper is Rotman et al., “NASA’s Pandora SmallSat Mission: Simulated Modeling and Retrieval of Near-Infrared Exoplanet Transmission Spectra,” accepted at The Astronomical Journal/em> (preprint).