NASA is Building a Space Telescope to Observe Exoplanet Atmospheres

The exoplanet census continues to grow. Currently, 5,819 exoplanets have been confirmed in 4,346 star systems, while thousands more await confirmation. The vast majority of these planets were detected in the past twenty years, owing to missions like the Kepler Space Telescope, the Transiting Exoplanet Survey Satellite (TESS), the venerable Hubble, the Convection, Rotation and planetary Transits (CoRoT) mission, and more. Thousands more are expected as the James Webb Space Telescope continues its mission and is joined by the Nancy Grace Roman Space Telescope (RST).

In the meantime, astronomers will soon have another advanced observatory to help search for potentially habitable exoplanets. It’s called Pandora, a small satellite that was selected in 2021 as part of NASA’s call for Pioneer mission concepts. This observatory is designed to study planets detected by other missions by studying these planets’ atmospheres of exoplanets and the activity of their host stars with long-duration multiwavelength observations. The mission is one step closer to launch with the completion of the spacecraft bus, which provides the structure, power, and other systems.

Funded by NASA’s Astrophysics Pioneers, Pandora is a joint effort between Lawrence Livermore National Laboratory in California and NASA’s Goddard Space Flight Center. The mission will study planets detected by other observatories that rely on Transit Photometry (aka. the Transit Method), where astronomers monitor stars for periodic dips in brightness that indicate the presence of orbiting planets. Pandora will then monitor these planets for future transits and obtain spectra from their atmospheres – a process known as Transit Spectroscopy.

Using this method, scientists can determine the chemical composition of exoplanet atmospheres and search for indications of biological activity (aka. “biosignatures”). During its year-long primary mission, the SmallSat will study 20 stars and their 39 exoplanets in visible and infrared light. The mission team anticipates Pandora will observe at least 20 exoplanets 10 times for 24 hours, during which transits will occur, and the satellite will obtain spectra from the exoplanets’ atmospheres.

In particular, Pandora will be looking to determine the presence of hazes, clouds, and water. The data it obtains will establish a firm foundation for interpreting measurements by Webb and future missions to search for habitable worlds. Daniel Apai, a co-investigator of the mission, is a professor of astronomy and planetary sciences at the U of A Steward Observatory and Lunar and Planetary Laboratory, who leads the mission’s Exoplanets Science Working Group. As he said in a U of A News release:

“Although smaller and less sensitive than Webb, Pandora will be able to stare longer at the host stars of extrasolar planets, allowing for deeper study. Better understanding of the stars will help Pandora and its ‘big brother,’ the James Webb Space Telescope, disentangle signals from stars and their planets.” 

The concept for the telescope emerged to address a specific problem with Transit Spectroscopy. During transits, telescopes capture far more than just the passing through the planet’s atmosphere. They also capture light from the star itself. In addition, stellar surfaces are not uniform and have hotter, brighter regions (faculae) and cooler, darker regions (stellar spots) that change in size and position as the star rotates. This produces “mixed signals” that make it difficult to distinguish between light passing through the planet’s atmosphere and light from the star – which can mimic the signal produced by water.

Pandora will disentangle these signals by simultaneously monitoring the host star’s brightness in visible and infrared light. These observations will provide constraints on the variations in the star’s light, which can used to separate the star’s spectrum from the exoplanet’s. With the completion of the spacecraft bus, Pandora is one step closer to launch thanks to the completion of the spacecraft bus, which provides the structure, power, and other systems vital to the mission.

The completion of the bus was announced on January 16th during a press briefing at the 245th Meeting of the American Astronomical Society (AAS) in National Harbor, Maryland. “This is a huge milestone for us and keeps us on track for a launch in the fall,” said Elisa Quintana, Pandora’s principal investigator at NASA’s Goddard Space Flight Center. “The bus holds our instruments and handles navigation, data acquisition, and communication with Earth — it’s the brains of the spacecraft.” Said Ben Hord, a NASA Postdoctoral Program Fellow who discussed the mission at the 245 AAS:

“We see the presence of water as a critical aspect of habitability because water is essential to life as we know it. The problem with confirming its presence in exoplanet atmospheres is that variations in light from the host star can mask or mimic the signal of water. Separating these sources is where Pandora will shine.”

“Pandora’s near-infrared detector is actually a spare developed for the Webb telescope, which right now is the observatory most sensitive to exoplanet atmospheres. In turn, our observations will improve Webb’s ability to separate the star’s signals from those of the planet’s atmosphere, enabling Webb to make more precise atmospheric measurements.”

Unlike Webb and other flagship missions, Pandora can conduct continuous observations for extended periods because the demand for observation time will be low by comparison. Therefore, the Pandora satellite will fill a crucial gap between exoplanet discovery provided by flagship missions and exoplanet characterization. The mission is also a boon for the University of Arizona since Pandora’s science working group is led from there, and Pandora will be the first mission to have its operations center at the U of A Space Institute.

Further Reading: U of A News

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