In October 2024, the Europa Clipper soared into space atop a SpaceX Falcon Heavy rocket, destined for a moon of Jupiter believed to harbor a vast ocean beneath its icy crust. Equipped with MASPEX (MAss Spectrometer for Planetary EXploration), the mission will analyze Europa’s thin atmosphere and hidden waters, searching for chemical clues that could answer the existential question—does life exist beyond Earth?
"This is NASA’s first mission dedicated to an ocean world," says Kelly Miller, a lead scientist at the Southwest Research Institute in San Antonio, Texas. "Where there is liquid water, the chance for habitability—and life—increases. MASPEX will be a critical tool for detecting and characterizing organic compounds and volatiles in Europa’s exosphere."
To meet these ambitious goals, MASPEX’s design features advanced elements to improve mass resolution and protective shielding to withstand one of the harshest environments imaginable. Separation Science spoke with Miller about the innovations that could set new benchmarks for analytical exploration.
Journey to Jupiter
The Europa Clipper mission emerged from decades of scientific intrigue surrounding Europa’s icy shell and hidden ocean. Miller, who honed her expertise as a postdoc with the Cassini Ion Neutral Mass Spectrometer (INMS) team, joined the Clipper project as Calibration Lead in 2019. “While we call our pre-flight testing ‘calibration,’ it differs from typical laboratory calibration—it focuses more on evaluating and verifying instrument performance metrics,” she explains.
The spacecraft faces a five-year journey to reach Jupiter. While much of this time involves transit, the team will conduct health checks, maintenance, calibration, and other preparations. Once at Jupiter, Europa Clipper must contend with intense radiation that can disrupt data and degrade sensitive components. For MASPEX, this requires operating with extensive shielding while capturing precise data during brief, high-speed flybys of Europa’s exosphere.
Miller explains that MASPEX remains sealed behind a protective door early in the mission to avoid exposure to spacecraft outgassing. As time passes and conditions stabilize, calibration activities can begin. “We’re planning to open the door around 2027 to start fully operating and characterizing the instrument,” she says. “Our first flyby of Europa is scheduled for 2031, so we have a long journey ahead.”
MASPEX: Advanced Instrumentation in Action
MASPEX uses multi-bounce time-of-flight (MBTOF) technology to achieve high mass resolution by reflecting ions between electrically charged mirrors, extending their path length to nearly a kilometer. This design enhances MASPEX’s ability to separate ions with exceptional precision, distinguishing tiny differences between complex molecules—capabilities critical for analyzing Europa’s volatile chemical environment.
“We’ll conduct around 50 flybys, each with a different closest approach altitude,” Miller says. “As we get closer to Europa, the density of the gas shell increases, giving us more opportunities to capture and analyze its composition.”
To help perform precise measurements of Europa’s exosphere—analyzing atoms and molecules such as water vapor, carbon dioxide, and potentially complex organic compounds—the team also incorporated a cryocooler into the probe. This system traps incoming gas by cooling it to extremely low temperatures, allowing MASPEX to concentrate and analyze volatile compounds with greater sensitivity and accuracy after each flyby.
During each flyby, MASPEX collects spatially resolved data in real time, with spatial resolution determined by the closest approach altitude, sometimes as low as 25 kilometers. “As we ‘sniff’ this gas, we’ll detect differences in its composition that might correlate with varying surface features,” explains Miller. During these passes, the cryocooler cools to about 70 Kelvin, measuring and ionizing some incoming gas while trapping another portion on its cold head.
Once the spatially resolved measurements are complete, a valve closes, and the cryocooler warms to ambient temperature, releasing the trapped gas sample into the instrument’s housing. This process allows MASPEX to make longer, more stable measurements in lower-radiation regions farther from Europa, enhancing its ability to detect trace compounds with greater accuracy.
Another innovation of MASPEX is its ‘ice grain mode,’ designed to analyze tiny frozen particles striking a plate in its entry chamber. Traveling at about 5 kilometers per second, these grains produce a flash of gas upon impact, a phenomenon first observed with Cassini INMS. MASPEX’s software monitors hydrogen levels, and when a spike indicates water, it adjusts to target heavier compounds in the ice grains rather than gas-phase molecules in the exosphere.
Habitability and the Hunt for Life
While atmospheric measurements of Europa are well planned, the search for habitability is enhanced by the potential presence of plumes—jets of water vapor and other materials possibly erupting from cracks in the icy surface. Observed by the Hubble Space Telescope and previous Galileo missions, these plumes offer rare access to Europa’s subsurface waters, locked beneath 15 to 25 kilometers of ice.
MASPEX is designed to detect biosignatures in Europa’s plumes, including organic molecules such as amino acids, lipids, and hydrocarbons, as well as volatile compounds such as methane, nitrogen species, and sulfur compounds. In Europa’s dark subsurface, life would likely be chemotrophic, relying on chemical reactions rather than sunlight for energy. MASPEX will analyze chemical imbalances, such as hydrogen-to-methane and nitrogen oxide ratios, which may indicate either biological activity or abiotic reactions similar to hydrothermal processes on Earth.
To address the fundamental question of extraterrestrial life, Miller explains that NASA has divided the process into smaller, manageable steps, beginning with habitability. “We know there is likely a subsurface ocean, but we need to evaluate whether it contains solutes and has the right pH, redox conditions, and temperature to support life,” she says. “This mission offers a fantastic opportunity to learn more about our solar system and the habitability of ocean worlds.”
About the Expert
Kelly Miller
Lead Scientist, Southwest Research Institute
Dr. Kelly Miller researches volatile cosmochemistry, especially with applications to planetary origins and habitability.She enjoys synthesizing ideas from different sub-disciplines, and has a broad range of past research experience. Current project areas include compositional analysis of chondritic samples, geochemistry of icy satellite interiors via modeling and experimentation, origin and evolution of Saturn's rings via analysis of flight data, and spaceflight mass spectrometry. Dr. Miller is the Calibration Lead for the Europa Clipper MASPEX instrument.
