There’s a well-established paradigm in planetary body exploration. It begins with a flyby, then later an orbiter, and then, if possible, a lander. Previous spacecraft have performed single flybys of Europa, and the Europa Clipper orbiter is on its way to Jupiter’s moon Europa for a more detailed orbital study of the frozen moon. Hopefully, a lander will follow. A presentation at the recent Lunar and Planetary Science Conference showed how the Europa Clipper can help find the best landing sites on the icy ocean moon for a future Europa lander.
We’re accustomed to Mars orbiters and enjoy their frequent images of the planet’s surface. NASA’s Mars Reconnaissance Orbiter (MRO) has been orbiting Mars for nearly 20 years. It follows a relatively simple, near-circular polar orbit, which is fairly straightforward and has no particular hazards.
The Europa Clipper faces a much more daunting environment. It can’t orbit its target, the icy ocean moon Europa. If it did, it would spend all of its time in Jupiter’s extremely powerful radiation environment, which the spacecraft wouldn’t be able to withstand. Instead, it will follow an orbital paradigm similar to Juno. That means it will follow long looping orbits that take it well out of the radiation environment and only approach Europa during intricately designed flybys at different angles and altitudes.
New research presented at the 2025 Lunar and Planetary Science Conference showed how, during certain of its orbits, the Europa Clipper can identify potential landing sites for a future Europa lander. It’s titled “POTENTIAL LANDING SITES: A COMPREHENSIVE RECONNAISSANCE ASSESSMENT OF THE EUROPA CLIPPER TRAJECTORY.” The first author is Jennifer Scully, a planetary geologist at NASA’s Jet Propulsion Laboratory.
The Europa Clipper will reach the Jovian system in April 2030. It will follow an elliptical orbit around Jupiter and perform 49 close flybys of Europa. Scientists took a long time to develop the Europa Clipper’s tour design, but they finally settled on one named 21F31v7.
This figure illustrates the complexity of Europa’s tour. There are multiple different types of orbits, including Crank Over the Top (COT) and Transfer Europa Campaign (TEC). The tour design ensures that the Europa Clipper’s different instruments can achieve the overall coverage necessary to meet the mission’s goals. Only some of these orbits can be used to detect landing sites for a future lander. Image Credit: Campagnola et al. 2024.
In their presentation, they assess “…which of the 49 currently planned Europa Clipper flybys (based on tour option ‘21F31v7’ are suitable to use for future reconnaissance and landing site selection.”
A future Europa lander will use Terrain Relative Navigation (TRN) to guide itself to the moon’s surface. TRN relies on previously acquired quality images of the surface combined with real-time camera data from the lander’s navigation cameras. NASA’s Perseverance rover used TRN to guide itself down to the Jezero Crater. The Mars Reconnaissance Orbiter provided the images with its HiRISE camera.
“The appropriate dataset to use for TRN will come from the narrow- and wide-angle cameras of the Europa Imaging System (EIS),” the authors explain. “Therefore, it is important to assess during which flybys the EIS data to be collected by Europa Clipper would be suitable for use in creating a TRN onboard map, i.e., making it a ‘reconable’ flyby.”
In order for a flyby to be reconable, it must meet three requirements:
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The right time of day so that the surface is in sunlight.
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Incidence angles of about 30° through 60° are required for the TRN process to work successfully for Europa.
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Altitude of about 50-100 km for appropriate image resolution and footprint size with minimal smearing.
This figure shows the global view of the groundtracks of the 49 prime mission flybys, colour- and symbol-coded with respect to reconnaissance. The actual reconable portion of each flyby is shown by the thicker line toward the center of each groundtrack. Solid green lines show flybys that cover regions of particular scientific interest. Image Credit: Scully et al. 2025.
Scully and her colleagues then ranked the reconable flybys according to the points of scientific interest they cover.
“Rank 1* is reserved for reconable flybys with particular scientific interest based on current knowledge, i.e., where there are unique and/or particularly interesting characteristics that could be investigated by an in-situ mission, for example, potential regions of recent activity and/or relatively pristine endogenic materials,” they write.
After ranking all 49 flybys, they determined that 12 are reconable and 13 are supporting. They also determined that one flyby, named E19, is the most desirable for determining a landing site.
It’s more than 700 km long and covers a transition between ridged plains and a Chaos Terrain named Powys Regio. Chaos Terrains are regions where the surface is jumbled and disrupted that hold clues to the moon’s interior. The Tegid crater is also nearby.
This figure shows the groundtrack of flyby E19, which has the top-ranked ground track for identifying landing sites for a future Europa lander. Image Credit: Scully et al. 2025.
The researchers point out that their groundtracks and rankings are based on data from the Galileo mission. “The rankings are thus highly likely to change when we observe the reconable areas with Europa Clipper,” they explain. They also point out that some of their reconable areas were not covered by Galileo’s high-resolution images.
“While the rankings will be updated, this work provides an important guidebook to the reconable and supporting Europa Clipper flybys, which can be used by the team during operations at Europa in the 2030s,” they conclude.
LPSC 2025 Conference Abstract: POTENTIAL LANDING SITES: A COMPREHENSIVE RECONNAISSANCE ASSESSMENT OF THE EUROPA CLIPPER TRAJECTORY