The exoplanet count continues to increase. Currently, 5,819 exoplanets have been confirmed in 4,346 star systems, while thousands more await confirmation. The vast majority of these planets have been discovered in the last twenty years, thanks 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 others. Thousands more are expected as the James Webb Space Telescope continues its mission and is joined by the Nancy Grace Roman Space Telescope (RST).
Meanwhile, astronomers will soon have another modern observatory to help search for potentially habitable exoplanets. Called Pandora, it is a small satellite selected in 2021 as part of NASA's call for Pioneer mission concepts. This observatory is designed to study planets discovered by other missions by studying the atmospheres of these exoplanet planets and the activity of their host stars with long-term observations at multiple wavelengths. With the completion of the spacecraft bus, which provides the structure, power and other systems, the mission moves one step closer to launch.
Funded by NASA's Astrophysics Pioneers, Pandora is a joint initiative of Lawrence Livermore National Laboratory in California and NASA's Goddard Space Flight Center. The mission will study planets discovered by other observatories based on transit photometry (also known as the transit method), in which 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.
This method allows scientists to determine the chemical composition of exoplanets' atmospheres and look for evidence of biological activity (also known as “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 expects that Pandora will observe at least 20 exoplanets 10 times over 24 hours, during which transits will occur and the satellite will obtain spectra from the exoplanets' atmospheres.
In particular, Pandora will attempt to detect the presence of haze, clouds and water. The data obtained will provide a solid basis for interpreting Webb's measurements and future missions to search for habitable worlds. Daniel Apai, a mission co-investigator, is a professor of astronomy and planetary science at the U of A Steward Observatory and Lunar and Planetary Laboratory and leads the mission's Exoplanet Science Working Group. As he said in a U of A press release:
“Although Pandora is smaller and less sensitive than Webb, it will be able to stare longer at the host stars of extrasolar planets, allowing for deeper study. A better understanding of stars will help Pandora and its “big brother,” the James Webb Space Telescope, untangle signals from stars and their planets.”
The concept for the telescope arose to address a specific problem in transit spectroscopy. During transits, telescopes capture much more than just the passage through the planet's atmosphere. They also capture the light from the star itself. In addition, star surfaces are not uniform, having hotter, brighter regions (faculae) and cooler, dimmer regions (starspots), which change size and position as the star rotates. This creates “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 provide constraints on the variations in the star's light that can be used to separate the star's spectrum from the exoplanet's spectrum. 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 critical to the mission.
The bus's completion was announced Jan. 16 during a press conference 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 fall launch,” said Elisa Quintana, Pandora's principal investigator at NASA's Goddard Space Flight Center. “The bus houses our instruments and handles navigation, data collection and communication with Earth – it is the brains of the spacecraft.” Ben Hord, a NASA postdoctoral program fellow who discussed the mission at 245 AAS, said:
“We view 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 the atmosphere of exoplanets is that fluctuations in the host star's light can mask or mimic the signal from water. Separating these sources is where Pandora will shine.”
“Pandora's near-infrared detector is actually a replacement part designed for the Webb Telescope, which is currently the observatory most sensitive to the atmospheres of exoplanets. In turn, our observations will improve Webb's ability to separate the star's signals from those of the planet's atmosphere, allowing Webb to make more precise atmospheric measurements.”
Unlike Webb and other flagship missions, Pandora can conduct continuous observations over extended periods of time because the observation time requirement is comparatively small. Therefore, the Pandora satellite will bridge a critical gap between exoplanet discovery through flagship missions and exoplanet characterization. The mission is also a boon for the University of Arizona, as Pandora's scientific working group will be 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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