The James Webb Space Telescope is a marvel of modern engineering. This tennis court-sized beast is the only space telescope that can see the universe in infrared light, allowing it to see through cosmic dust and reveal what’s inside the atmospheres of distant exoplanets. But there’s one thing JWST lacks—time. During the last call for proposals, the science community requested 78,000 hours across 2,377 unique proposals. That’s a nine-to-one oversubscription rate.
JWST needs help—and that’s where NASA’s newest mission, Pandora, comes in. If you want to find clouds, haze and water—signs of potential habitability—in a planet’s atmosphere orbiting a distant star, you’d better be prepared to look carefully and repeatedly. Cue Pandora.
Water Worlds
Pandora, whose spacecraft bus (the “brains”) was completed by engineers this week and stands ready for launch in fall 2025, aims to conduct in-depth studies of at least 20 exoplanets. Its job will be to analyze their atmospheric compositions, focusing on detecting hazes, clouds and water.
“We see the presence of water as a critical aspect of habitability because water is essential to life as we know it,” said Ben Hord at NASA’s Goddard Space Flight Center in Greenbelt, at the 245th meeting of the American Astronomical Society in National Harbor, Maryland, earlier this month.
Small Satellite
Hosting an all-aluminum, 17.7-inch (45 centimeters) aperture Cassegrain telescope—not much bigger than a backyard telescope—Pandora is a small satellite, nothing like JWST. But the mission has a unique characteristic—patience. “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 Daniel Apai, Pandora co-investigator and 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.
It may be less impressive than JWST, but it’s directly related to its big brother—Pandora’s near-infrared detector is a spare developed for JWST.
Lucky Light
Astronomers use lucky light to study the atmospheres of distant exoplanets. If an exoplanet passes in front of its star from a telescope’s perspective—termed a transit—the star’s light passes through the planet’s atmosphere. A telescope captures that light, which has embedded within it a story—told in dips in brightness at specific wavelengths—of the substances that light has passed through. The result is a picture of what’s inside a planet’s atmosphere.
There are limitations to what can be done. For starters, only planets that happen to transit across their stars can be studied, or even seen. However, by now, astronomers know the exoplanets of interest that do so—and that’s what makes up Pandora’s to-do list.
Special Effects
Pandora is specifically designed to overcome a limitation of JWST that was only realized in 2018. A former student of Apai’s, Benjamin Rackham, now an MIT research scientist, identified an astrophysical effect where light from a star interferes with the signal of light passing through an exoplanet’s atmosphere. This effect was predicted to limit JWST’s ability to study habitable planets. “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,” said Hord. “Separating these sources is where Pandora will shine.”
Long Hours
After its launch, Pandora’s detectors will simultaneously capture data on a host star’s brightness and the near-infrared light from the star and its transiting planet. Although its initial mission will last only a year, its exquisitely-timed observations will have it study at least 20 exoplanets 10 times, each lasting 24 hours. “Better understanding of the stars will help Pandora and its ‘big brother,’ the James Webb Space Telescope, disentangle signals from stars and their planets,” said Apai.
Wishing you clear skies and wide eyes.
