EXCITE: Balloon Telescope to Map Exoplanet Atmospheres for Under JWST’s Cost
A high-altitude balloon carrying a specialized telescope took to the skies above Fort Sumner, New Mexico, in August 2024, marking a key test of a novel approach to studying the atmospheres of distant exoplanets. The mission, known as the EXoplanet Climate Infrared TElescope (EXCITE), aims to provide detailed atmospheric data at a fraction of the cost of larger observatories like the James Webb Space Telescope (JWST).
While JWST has revolutionized exoplanet research, including the detection of carbon dioxide and methane in the atmosphere of K2-18 b, and clear signs of water vapor in WASP-96 b, time on the telescope is limited. EXCITE offers a complementary strategy, focusing on capturing comprehensive “phase curves” of hot Jupiter exoplanets – gas giants orbiting incredibly close to their stars. These curves map a planet’s temperature and atmospheric composition as it orbits, providing a three-dimensional view unavailable through the brief snapshots offered by traditional transit and eclipse observations, according to researchers.
Most exoplanet atmospheric studies rely on observing transits, when a planet passes in front of its star, or secondary eclipses, when it passes behind. These methods provide limited, two-dimensional data. Hot Jupiters, yet, are often tidally locked, meaning one side perpetually faces their star. As these planets orbit, their “terminator line” – the boundary between day and night – rotates into view, allowing EXCITE to map temperature and composition changes over days, creating a longitudinal weather map.
The telescope’s spectroscopic capabilities will allow astronomers to determine atmospheric pressure by analyzing how different wavelengths of light are absorbed. This detailed analysis could reveal insights into a planet’s formation and atmospheric dynamics.
EXCITE’s design addresses some limitations of existing observatories. JWST’s sensitivity, while a strength, can be a drawback when observing the brightest stars, potentially overwhelming its sensors. The Hubble Space Telescope, orbiting in low Earth orbit, experiences thermal fluctuations as it passes in and out of Earth’s shadow, requiring lengthy stabilization periods that would interrupt the continuous observations needed for a complete phase curve. EXCITE, floating at approximately 40 kilometers above the Earth’s surface, avoids these issues, operating above 99.5% of the atmosphere and benefiting from the cold, stable conditions above Antarctica.
The August 2024 test flight demonstrated the gondola’s ability to stabilize with sub-arcsecond precision and confirmed the functionality of the cryogenic system that cools the infrared detectors. However, the flight also revealed challenges. The GPS system failed, and contraction of the aluminum housing surrounding the telescope’s bearings restricted its ability to tilt and observe. Engineers are currently addressing these issues in preparation for a long-duration flight planned for the 2026-2027 summer in Antarctica.
If successful, the Antarctic flight could double the number of known exoplanet phase curves, providing a significant leap forward in understanding these distant worlds. Researchers published their findings on the EXCITE mission in a paper titled “The EXoplanet Climate Infrared TElescope (EXCITE): A balloon-borne mission to measure spectroscopic phase curves of transiting hot Jupiters.”