Probing Alien Worlds: NASA's Pandora Mission Builds on UArizona Research
This illustration captures an exoplanet as it is about to cross in front of – or transit – its star. By analyzing light from the star through the planet's atmosphere, scientists can gather clues about its composition.
NASA's Goddard Space Flight Center
In the quest for habitable planets beyond our own, NASA is studying a mission concept called Pandora, which could eventually help decode the atmospheric mysteries of distant worlds in our galaxy. One of four low-cost astrophysics missions selected for further concept development under NASA's new Pioneers program, Pandora would study approximately 20 stars and exoplanets – planets outside of our solar system – to provide precise measurements of exoplanetary atmospheres.
One of the co-investigators on the Pandora mission is Daniel Apai, an associate professor of astronomy and planetary science who heads a major NASA-funded research program called "Alien Earths," dedicated to finding which nearby planets are likely to host habitable worlds. His group has developed powerful tools and methods to create some of the first maps of the atmospheres of exoplanets and brown dwarfs.
"Equipped with the tools and methods we have developed, we will now use data from Pandora to build on advanced data analysis methods," said Apai, who leads Pandora's exoplanets science working group. "This will allow us to push the boundaries of high-precision atmospheric characterization of fascinating new worlds."
The Pandora mission concentrates on studying the atmospheres of stars and their planets by surveying planets as they cross in front of – or transit – their host stars. To accomplish this, Pandora would take advantage of a proven technique called transit spectroscopy, which involves measuring the amount of starlight filtering through a planet's atmosphere, and splitting it into bands of color known as a spectrum. These colors encode information that helps scientists identify gases present in the planet's atmosphere, and can help determine if a planet is rocky with a thin atmosphere like Earth or if it has a thick gas envelope like Neptune.
Pandora is designed to use a concept called transit spectroscopy to reliably identify an exoplanet’s atmospheric composition as it passes in front of its host star.
Lawrence Livermore National Laboratory and NASA’s Goddard Space Flight Center
The Pandora mission would seek to determine atmospheric compositions by observing planets and their host stars simultaneously in visible and infrared light over long periods. Most notably, Pandora would examine how variations in a host star’s light impacts measurements of exoplanet atmospheres. This so-called stellar contamination remains a substantial problem in identifying the atmospheric makeup of planets orbiting stars covered in starspots – the equivalent of the more familiar sunspots – which can cause brightness variations as a star rotates.
Stellar contamination is a sticking point that complicates precise observations of exoplanets, according to Pandora co-investigator Benjamin Rackham, who obtained his doctoral degree in Apai's research group and is now a 51 Pegasi b Postdoctoral Fellow at the Massachusetts Institute of Technology in Cambridge.
"Pandora would help build the necessary tools for disentangling stellar and planetary signals, allowing us to better study the properties of both starspots and exoplanetary atmospheres,” Rackham said.
"Understanding how to disentangle the signals from planetary atmospheres and from those of their host stars is a key step toward studying the atmospheres of potentially habitable worlds," Apai added.
Pandora is a small satellite mission known as a SmallSat, one of three such orbital missions receiving the green light from NASA to move into the next phase of development in the Pioneers program. SmallSats are low-cost spaceflight missions that allow the agency to advance scientific exploration and increase access to space. Pandora would operate in sun-synchronous low-Earth orbit, which always keeps the sun directly behind the satellite. This orbit minimizes light changes on the satellite and allows Pandora to obtain data over extended periods. The mission is focused on trying to understand how stellar activity affects measurements of exoplanet atmospheres, which will lay the groundwork for future exoplanet missions aiming to find planets with Earth-like atmospheres.
Synergy in Space
Joining forces with NASA's larger missions, Pandora would operate concurrently with the James Webb Space Telescope, slated for launch later this year. Webb will provide the ability to study the atmospheres of exoplanets as small as Earth with unprecedented precision, and Pandora would seek to expand the telescope's research and findings by observing the host stars of previously identified planets over longer periods.
Pandora’s orbital pattern in sun-synchronous low-Earth orbit enables the spacecraft to obtain multiple observations of exoplanets over long periods and the Earthshine exclusion zone helps avoid reflected light from Earth.
Lawrence Livermore National Laboratory and NASA’s Goddard Space Flight Center
Missions such as NASA's Transiting Exoplanet Survey Satellite, Hubble Space Telescope, and the retired Kepler and Spitzer spacecraft have given scientists astonishing glimpses at these distant worlds, and laid a strong foundation in exoplanetary knowledge. These missions, however, have yet to fully address the stellar contamination problem, the magnitude of which is uncertain in previous studies of exoplanetary atmospheres. Pandora seeks to fill these critical gaps in NASA's understanding of planetary atmospheres and increase the capabilities in exoplanet research.
"Pandora is the right mission at the right time because thousands of exoplanets have already been discovered, and we are aware of many that are amenable to atmospheric characterization that orbit small active stars," said Jessie Dotson, an astrophysicist at NASA's Ames Research Center in California's Silicon Valley and the deputy principal investigator for Pandora. "The next frontier is to understand the atmospheres of these planets, and Pandora would play a key role in uncovering how stellar activity impacts our ability to characterize atmospheres. It would be a great complement to Webb's mission."
A Launch Pad for Exploration
NASA's Pioneers program, which consists of SmallSats, payloads attached to the International Space Station, and scientific balloon experiments, fosters innovative space and suborbital experiments for early-to-mid-career researchers through low-cost, small hardware missions. Under this new program, Pandora would operate on a five-year timeline with a budget cap of $20 million.
