image: An artist's concept of the Pandora mission, seen here without the thermal blanketing that will protect the spacecraft, observing a star and its transiting exoplanet.
Credit: NASA’s Goddard Space Flight Center/Conceptual Image Lab
Pandora, NASA's newest exoplanet mission, is one step closer to launch with the completion of the spacecraft bus, which provides the structure, power and other systems that will allow the mission to carry out its work. Pandora's exoplanet science working group is led by the University of Arizona, and Pandora will be the first mission to have its operations center at the U of A Space Institute.
The completion of the bus was announced during a press briefing at the 245th Meeting of the American Astronomical Society in National Harbor, Maryland, on Jan. 16.
"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 in Greenbelt, Maryland. "The bus holds our instruments and handles navigation, data acquisition and communication with Earth – it's the brains of the spacecraft."
Pandora is a small satellite poised to provide in-depth study of at least 20 known planets orbiting distant stars to determine the composition of their atmospheres – especially the presence of hazes, clouds and water. The data will establish a firm foundation for interpreting measurements by NASA's James Webb Space Telescope and future missions aimed at searching for habitable worlds.
"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," said Pandora co-investigator Daniel Apai, 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. "Better understanding of the stars will help Pandora and its 'big brother,' the James Webb Space Telescope, disentangle signals from stars and their planets."
Astronomers can sample an exoplanet's atmosphere when it passes in front of its star as seen from Earth's perspective, during an event known as a transit. Part of the star's light skims the planet's atmosphere before making its way to the observer. This interaction allows the light to interact with atmospheric substances, and their chemical fingerprints — dips in brightness at characteristic wavelengths — become imprinted in the light.
The concept of Pandora was born out of necessity to overcome a snag in observing starlight passing through the atmospheres of exoplanets, Apai said.
"In 2018, a doctoral student in my group, Benjamin Rackham – now an MIT research scientist – described an astrophysical effect by which light coming directly from the star muddies the signal of the light passing through the exoplanet's atmosphere," Apai explained. "We predicted that this effect would limit Webb's ability to study habitable planets."
Telescopes see light from the entire star, not just the small amount grazing the planet. Stellar surfaces aren't uniform. They sport hotter, unusually bright regions called faculae and cooler, darker regions similar to the spots on our sun, both of which grow, shrink and change position as the star rotates. As a result, these "mixed signals" in the observed light can make it difficult to distinguish between light that has passed through an exoplanet's atmosphere and light that varies based on a star's changing appearance. For example, variations in light from the host star can mask or mimic the signal of water, a likely key ingredient researchers look for when evaluating an exoplanet's potential for harboring life.
Using a novel all-aluminum, 45-centimeter-wide telescope, jointly developed by Lawrence Livermore National Laboratory and Corning Specialty Materials in Keene, New Hampshire, Pandora's detectors will capture each star's visible brightness and near-infrared spectrum at the same time, while also obtaining the transiting planet's near-infrared spectrum. This combined data will enable the science team to determine the properties of stellar surfaces and cleanly separate star and planetary signals.
The observing strategy takes advantage of the mission's ability to continuously observe its targets for extended periods, something flagship observatories like Webb, which offer limited observing time due to high demand, cannot regularly do.
Over the course of its yearlong mission, Pandora will observe at least 20 exoplanets 10 times, with each stare lasting a total of 24 hours. Each observation will include a transit, which is when the mission will capture the planet's spectrum.
Karl Harshman, who leads the Mission Operations Team at the U of A Space Institute that will support the spacecraft's operation once it launches later this year, said: "We have a very excited team that has been working hard to have our Mission Operations Center running at full speed at the time of launch and look forward to receiving science data. Just this week, we performed a communications test with our antenna system that will transmit commands to Pandora and receive the telemetry from the spacecraft."
Pandora is led by NASA's Goddard Space Flight Center. Lawrence Livermore National Laboratory provides the mission's project management and engineering. Pandora's telescope was manufactured by Corning and developed collaboratively with Livermore, which also developed the imaging detector assemblies, the mission's control electronics, and all supporting thermal and mechanical subsystems. The infrared sensor was provided by NASA Goddard. Blue Canyon Technologies provided the bus and is performing spacecraft assembly, integration and environmental testing. NASA's Ames Research Center in California's Silicon Valley will perform the mission's data processing. Pandora's mission operations center is located at the University of Arizona, and a host of additional universities support the science team.