American astronomers from the University of Colorado in Boulder have achieved a clearer view of atmospheric processes on hot Jupiter planets for the first time, thanks to the compact CUTE spacecraft launched in 2021. The findings were published in The Astronomical Journal, highlighting a milestone in ultraviolet observations of distant worlds.
The CUTE mission, short for Colorado Ultraviolet Transition Experiment, was specifically designed to probe the harsh environments of the most extreme exoplanets known to science. By focusing on ultraviolet light, the mission captures how these giant worlds interact with their blazing host stars, revealing the dynamics of their upper atmospheres and how they respond to intense stellar radiation. The study emphasizes how even subtle changes in UV starlight can betray the presence of atmospheric escape and other high-energy processes in action.
The CUTE probe is a compact instrument about 35 centimeters in length. It carries an ultraviolet telescope capable of monitoring many stars as their planets cross in front of them, causing a dip in the received UV radiation. In some observations, the instrument is sensitive enough to detect a dimming of starlight by as little as 1%, enabling the team to infer the density and distribution of escaping gas from the planet’s atmosphere. This precision opens a window into how heat and radiation sculpt these alien atmospheres, offering clues about planetary evolution under extreme conditions.
Hot Jupiters are gas giants akin to Jupiter but orbit very close to their stars, often enduring temperatures far higher than those found on gas giants in our own solar system. Their close-in orbits make them natural laboratories for studying atmospheric loss, chemical composition, and heat redistribution on a planetary scale. The CUTE observations shed light on how these planets manage energy input and how atmospheric layers respond to it, contributing to broader theories about planet formation and survivability in harsh stellar neighborhoods.
As a prime example, the CUTE team examined WASP-189b, a world located about 300 light-years away in the Libra constellation. Its surface temperatures exceed 8,300 °C, surpassing the host star’s effective temperature by a notable margin and illustrating the extreme heating these planets endure. The data indicate that gas is escaping from WASP-189b’s depths at an estimated rate of roughly 400 thousand tons per second, a rate that informs models of atmospheric replenishment and loss over time. These insights demonstrate the power of ultraviolet transit spectroscopy to quantify atmospheric escape in real time and to test competing theories about how such planets evolve under relentless stellar assault.
Over the course of the mission, the CUTE team has observed seven hot Jupiters, with several additional targets identified for future study. The researchers anticipate that ongoing observations will help address fundamental questions about why some planets shed substantial portions of their atmospheres while others retain their gaseous envelopes quite stably. Such findings have implications beyond exoplanets, potentially enriching our understanding of atmospheric evolution within the solar system itself. For instance, scientists continue to explore how Mars might have once possessed a denser atmosphere and how solar activity contributed to its gradual loss over billions of years. These comparative studies link distant worlds to familiar planetary history, reinforcing the relevance of ultraviolet observations for planetary science as a whole.
Alongside these results, there were prior announcements from Russia about plans to launch a satellite constellation intended to provide global internet coverage. This broader context underscores the ongoing expansion of space-based technologies and their capacity to deepen our knowledge of both distant planets and Earth.