The European Space Agency’s (ESA) Juice spacecraft, currently en route to explore Jupiter’s icy moons, has made an intriguing discovery much closer to home.
During its August 2024 flyby of Earth, Juice detected crucial life-signaling molecules in our planet's atmosphere. This achievement not only verifies that the spacecraft's instruments are fully operational but also sets the stage for the next phase of the mission, which aims to determine if Jupiter’s moons could support life.
Instruments Validate Detection of Life on Earth
During the flyby, two of Juice’s key scientific instruments—the Moons and Jupiter Imaging Spectrometer (MAJIS) and the Submillimetre Wave Instrument (SWI)—were put through rigorous tests. The SWI "listened" for signals from hundreds of molecules in Earth's atmosphere, detecting vital life elements like water and the so-called CHNOPS elements: carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur. These elements are the fundamental building blocks of all known life forms.
According to ESA, “MAJIS also measured the composition of the atmosphere, detecting important molecules such as oxygen, ozone, carbon dioxide, and water.” These molecules are critical indicators of habitability, demonstrating that the instruments aboard Juice can successfully identify life-associated compounds. In addition, MAJIS provided detailed temperature maps of Earth’s surface, allowing the team to analyze conditions vital to sustaining life.
This success is an essential step for the mission, confirming that Juice’s instruments can detect life in environments where it is abundant—like Earth. Olivier Witasse, ESA’s Juice project scientist, remarked on the positive results, saying, “We are obviously not surprised by these results… it would have been extremely concerning to find out that Earth was not habitable! But they indicate that MAJIS and SWI will work very successfully at Jupiter, where they will help us investigate whether the icy moons could be potential habitats for past or present life.”
A Critical Step Toward Investigating Jupiter’s Icy Moons
This Earth flyby marks an essential milestone for Juice, as it prepares for the long journey to Jupiter and its moons. Scientists are particularly excited about Europa, Ganymede, and Callisto due to their potential to harbor life-sustaining environments beneath their thick icy shells. Subsurface oceans on these moons could have the right conditions for life to develop, particularly if heat from tidal forces or chemical interactions in the oceans can create habitable niches.
Juice’s instruments will play a key role in assessing the moons’ habitability. By analyzing their atmospheres, icy surfaces, and subsurface oceans, the mission aims to uncover whether life could exist—or have existed—on these distant worlds. As ESA explained, “SWI will study the composition of the planet and its icy moons, telling us more about their current climates, their origin, and their history.” The information gathered by Juice will provide critical insights into the moons’ potential for biological activity, both in the past and present.
Once Juice reaches Jupiter in 2031, it will begin an extensive study of the gas giant and its moons. The spacecraft will orbit Ganymede, the largest moon in the solar system, which is thought to contain more water than all of Earth’s oceans combined. Juice will analyze Ganymede’s ice-covered oceans, thin atmosphere, and magnetic field, looking for signs of habitability and possibly even life itself.
The Road Ahead: Flybys and Long-Term Exploration
While the detection of life-signaling molecules on Earth is an exciting achievement, Juice’s mission is far from over. The spacecraft is still in the early stages of its journey, with two more Earth flybys and one flyby of Venus scheduled before it reaches Jupiter. These flybys will provide crucial gravitational boosts to help the spacecraft cover the immense distance between Earth and Jupiter.
The flyby of Venus, scheduled for 2025, will offer another opportunity to test Juice’s instruments in a different planetary environment. Venus’s thick atmosphere, with its extreme temperatures and pressure, will provide a contrast to the more life-friendly conditions detected on Earth. Once the spacecraft completes its journey to Jupiter, its instruments will be fully calibrated and ready for the mission's primary objective: investigating the habitability of Jupiter’s moons.
Upon arrival at Jupiter, Juice will focus on both the gas giant and its moons. The SWI will study the composition of Jupiter’s atmosphere, revealing details about the planet’s weather patterns and chemical makeup. Simultaneously, MAJIS will examine the icy surfaces of the moons, looking for clues about their geologic history and current conditions. These analyses will help scientists determine whether the moons have the ingredients necessary to support life.
Searching for Signs of Extraterrestrial Life
Juice’s mission is part of a broader scientific effort to search for extraterrestrial life within our solar system. Jupiter’s icy moons, with their hidden oceans, are considered some of the most promising locations to find life beyond Earth. The discovery of life on these moons—whether in microbial form or something more complex—would revolutionize our understanding of the universe and the conditions necessary for life to arise.
The successful detection of life-signaling molecules on Earth gives scientists confidence that Juice will be able to detect similar signs on Jupiter’s moons. As ESA noted, “The instruments are fully operational and capable of detecting telltale signatures of life, at least where it is abundant.” This validation means that the scientific community can look forward to exciting results as Juice moves closer to its target.