Didymos and its small moon Dimorphos are household names in the space community for a dramatic reason. In September 2022, NASA’s DART spacecraft slammed into Dimorphos, shortening the moonlet’s orbital period and demonstrating, for the first time, that humanity can alter the trajectory of an asteroid. Hera’s job is to survey the aftermath in exquisite detail, and JuRa is central to that effort. The DART experiment proved that a kinetic impactor can move an asteroid, but how well it works depends entirely on what the asteroid is made of and how it is assembled. A monolithic boulder would respond very differently to a hit than a loose pile of gravel barely held together by its own gravity. Right now, nobody knows which description fits Dimorphos, and JuRa is designed to find out.

The physics behind the measurement is elegantly simple in principle and fiendishly complex in practice. Every radar measurement is governed by the complex dielectric permittivity of the materials the wave traverses. The real part of the permittivity controls wave velocity, while the imaginary part, expressed as the loss tangent, governs how quickly the wave dissipates. JuRa transmits at 60 MHz with a 20 MHz bandwidth, corresponding to a wavelength of five meters in free space. At that wavelength, sand grains and gravel simply do not scatter the signal, so the wave propagates as if through a continuous medium. But blocks of rock several meters across, separated by voids, scatter the wave in all directions, destroying its coherence. That scattering regime is exactly what scientists expect inside a rubble pile, and it is precisely what JuRa will map: the returned power, quantified as a backscatter coefficient, becomes a proxy for the size, contrast and arrangement of the constituent blocks and voids.

Turning raw echoes into a three-dimensional picture of the asteroid’s guts is where the engineering wizardry comes in. Because JuRa’s crossed-dipole antennas have almost no directivity, a single acquisition illuminates nearly the entire asteroid at once, mixing echoes from many locations that arrive simultaneously. Only the diversity of observing geometries along Juventas’ orbit allows image reconstruction, in a small-body analogue of Synthetic Aperture Radar processing. The formalism is described by the Ewald sphere: each measurement samples one shell of the three-dimensional spectrum of the asteroid’s permittivity-contrast map, and an inverse transform can, in principle, reconstruct the interior. In practice, the fast spin of Didymos, the tumbling of Dimorphos, surface refraction and severe undersampling of the orbit geometry mean that standard SAR shortcuts fail. The JuRa team has therefore built a brute-force, fully three-dimensional processor that evaluates the geometry separately for every point of the imaged body, together with advanced diffraction-tomography methods already validated on asteroid analogues in anechoic-chamber experiments in Marseille.

The observing campaign itself is a delicate dance. Juventas will be released by Hera in mid-January 2027, and after commissioning, including the high-stakes deployment of JuRa’s four antenna booms, the CubeSat will settle into a sun-synchronous terminator orbit. From the end of January to the end of March 2027 it will circle the binary system at a radius shrinking from about 3.3 kilometers to about 2 kilometers, sharing data with Hera through an inter-satellite link whose bandwidth imposes strict limits on telemetry. Scientists expect JuRa to penetrate 100 meters or more below the surface, deep enough to characterize the rubble-pile structure of both bodies. Then, in a fittingly audacious finale, Juventas will land on Dimorphos at the end of March 2027, and JuRa may operate during descent and possibly afterward, using the round-trip propagation time through the moonlet for an absolute measurement of its average permittivity.

What the team hopes to learn is specific and ambitious. For Dimorphos, JuRa aims to reveal the aggregate structure at scales from roughly 20 centimeters to 20 meters, the expected size range of constituent blocks and voids, and to detect whether fine dust or gravel fills the gaps, which would discriminate between macro- and micro-porosity. Dimorphos is thought to be more porous than Didymos, with a macro-porosity near 35 percent and an estimated mean density of 2400 kilograms per cubic meter, and its pre-impact surface showed an apparently uniform accumulation of boulders with no obvious fine debris. JuRa will test whether that homogeneity extends into the interior or whether layers, large blocks, sub-aggregates or compaction zones hide beneath. Such information will directly constrain models of the DART impact, though the team notes that the instrument’s expected 10 to 15 meter resolution will not resolve the local mass redistribution near the crater itself.

Didymos tells its own story. Likely a rubble pile assembled from the debris of a collisional disruption of the Baptistina family’s parent body some 140 to 320 million years ago, it spins once every 2.26 hours, dangerously close to its disruption spin barrier. Its top-shaped profile, with a smooth equatorial ridge and rough, boulder-strewn polar regions, suggests a cohesive interior of roughly 10 pascals covered by weakly cohesive regolith that is progressively shed to feed the moonlet. Comparing the radar textures returned from the primary and the moon will reveal whether segregation processes operated during Dimorphos’ formation, helping scientists distinguish between gradual mass shedding and catastrophic fission, and testing how binary asteroids are born and how stable they remain.

Building a radar that fits inside one unit of a six-unit CubeSat required an unconventional development philosophy. The payload, developed between July 2020 and its delivery to the platform in July 2024 by a consortium led by EmTroniX in Luxembourg, TU Dresden, IPAG in Grenoble and the Polish antenna specialist Astronika, embraces the ‘New Space’ approach: commercial automotive-grade electronics, carefully tested for radiation sensitivity, triple-modular redundancy for critical functions, and deliberately limited redundancy elsewhere. Instead of the classical chirp of planetary radars, JuRa transmits binary phase-shift-keyed codes, including a 13-symbol Barker code compressed by optimal filters, granting the versatility to operate at distances from tens of kilometers down to a ground-penetrating-radar mode on the asteroid’s surface. Full linear polarization, using two independent dipoles, two transmit and two receive channels, provides both partial redundancy and the radiometric accuracy needed for coherent tomographic processing. Cruise commissioning has already shown the instrument behaving well, with noise levels even lower than in laboratory tests.

JuRa’s success will matter far beyond one asteroid. The same team is already adapting the design into the Apophis Radar for ESA’s RAMSES mission, launching in April 2028 toward the near-Earth asteroid Apophis. And for planetary defense writ large, the stakes could hardly be higher: if a hazardous asteroid ever needs deflecting, emergency planners will need to know whether they are pushing a coherent rock or rearranging a cosmic gravel heap. In early 2027, a radar smaller than a cereal box will give humanity its first honest look inside the building blocks of the solar system, and possibly its best insurance policy yet.

Subject of Research: Radar sounding of the internal rubble-pile structure of the binary asteroid system Didymos and Dimorphos by the Juventas Radar on ESA's Hera mission.

Article Title: JuRa: The Juventas Radar on Hera Mission to Probe Internal Structure of Didymos and Dimorphos Asteroids

Article References: Herique, A., Plettemeier, D., Rogez, Y., Berquin, Y., Ciarletti, V., Fa, W., Eyraud, C., Haynes, M., Heggy, E., Kechouindi, A., Kobayashi, T., Kofman, W., Laabs, M., Nolbert, D., Pettinelli, E., Pursiainen, S., Rochat, S., Schmidt, C., Virkki, A., … Ulamec, S. (2026). JuRa: The Juventas Radar on Hera Mission to Probe Internal Structure of Didymos and Dimorphos Asteroids. Space Science Reviews, 222(7), Article 74. https://doi.org/10.1007/s11214-026-01324-4

Image Credits: AI Generated

DOI: 10.1007/s11214-026-01324-4

Keywords: Hera mission, Didymos, Dimorphos, JuRa, Juventas CubeSat, radar tomography, asteroid internal structure, rubble pile, DART impact, planetary defense, synthetic aperture radar, ESA

Hera launched on October 7, 2024, and will become the first mission ever to rendezvous with a binary asteroid system. It is also the first multi-satellite expedition devoted to deep-space asteroid exploration. The stakes are high because NASA’s DART spacecraft slammed into Dimorphos on September 26, 2022, deliberately altering the moonlet’s orbit as a test of planetary defense. Hera, together with Milani and its sibling CubeSat Juventas, will survey the impact site and characterize the system in unprecedented detail. Milani’s trajectory design is aggressive for a six-unit CubeSat, involving a cascade of maneuvers through three main phases: a roughly three-week Far-Range Operations Phase for global mapping, a four-week Close-Range Operations Phase for close-up observations of Dimorphos and the DART impact site, and an Experimental Phase in which the satellite descends along a self-stabilized terminator orbit and eventually attempts a landing on Dimorphos.

The NavCam itself is a study in pragmatic engineering. Its optical head, designed and coated by Optec SpA, uses three lenses that hold focus at infinity with distortion below one percent, delivering an average transmissivity above 90 percent across the visible spectrum and a focal length of 12.96 millimeters. A coating on the first lens blocks wavelengths beyond 700 nanometers, shielding the detector from near-infrared leakage. At its heart sits a 1/3-inch CMOS rolling-shutter sensor from Onsemi, fitted with an RGB Bayer filter and an array of 2048 by 1536 pixels, each 2.2 micrometers square. That fine pixel pitch yields an instantaneous field of view of 35 arcseconds and a field of view spanning 19.72 by 14.86 degrees. In practical terms, the camera resolves 1.7 meters per pixel at 10 kilometers and a remarkable 8.5 centimeters per pixel at 500 meters, comfortably covering observation distances from 30 kilometers down to 200 meters.

Before any of that can happen, the camera had to earn its flightworthiness on the ground. Calibration at the Budapest University of Technology and Economics, the same facility that calibrated Hera’s instruments, covered bias and dark frames, bad-pixel identification, flat fields, linearity, radiometric response and distortion. The results are striking for such a small instrument: dark and bias frames show a uniform noise pattern with a standard deviation of only about 0.6 digital numbers, with no significant drift across exposure times, thanks to on-chip black-level correction. Flat-field correction removes strong vignetting, a 50 percent intensity drop toward the frame edges, and achieves better than 1 percent uniformity, while absolute radiometric uncertainty comes in under 2.5 percent. Distortion near the edges can shift star positions by as much as 50 pixels, but radial correction handles most of it, and in-flight starfield imaging against the Hipparchos and Tycho catalogs is expected to tighten the residual uncertainty from about 1.5 pixels down to 0.1 pixels.

The operations plan turns those optics into science. Data acquisition profiles, generated from the latest operational SPICE kernels, show that Milani will enjoy viewing geometries unavailable to Hera or Juventas, sampling a wide spread of phase angles that is crucial for surface characterization. By the team’s cumulative accounting, the NavCam can operate for 37 days with ground sampling better than 2 meters per pixel on Dimorphos, compared with 20 days for Hera’s Asteroid Framing Camera over the same window and 61 days for Juventas’ camera along its terminator orbit. Roughly 200 megabytes of asteroid imagery, compressed losslessly onboard with JPEG2000, will be downlinked over the mission, amounting to about 540 images or one picture every four hours on average. Each frame serves triple duty: orbit determination, flight dynamics reconstruction, and science.

The scientific payoff begins with global properties. Pre-impact models pictured Didymos as a top-shaped body like Bennu or Ryugu, but DART’s own DRACO camera revealed a surprisingly different silhouette, with a pronounced equatorial bulge and a shorter polar axis. Because DART’s observations are biased toward one hemisphere, Milani’s NavCam will help fill in the far side, contributing to high-resolution shape models built through stereophotoclinometry, a technique that fuses limb observations with landmark-based surface maplets. Those shape models cascade into bigger questions: how binary asteroids form, how the thermally driven binary YORP effect slowly reshapes their spins and orbits, and how much the DART impact deformed Dimorphos itself, which carries direct implications for assessing the efficiency of kinetic deflection. Combined with the Juventas radar’s mass and interior measurements, NavCam-derived shapes will also let the team test whether Didymos and Dimorphos share a uniform density or hide internal heterogeneity.

Surface science is the second pillar. The NavCam’s RGB channels cover roughly 400 to 700 nanometers, complementing the ASPECT hyperspectral imager on the same CubeSat, which works from 650 to 2500 nanometers, and providing color where Hera’s panchromatic Asteroid Framing Cameras offer finer resolution but no spectral information. To test what the camera can detect, the team convolved known mineral spectra from the RELAB database with the measured RGB response curves and ran k-means clustering on simulated measurements of asteroid Bennu, using spectra recorded by OSIRIS-REx’s OVIRS instrument. The clustering recovered distinct surface groups that overlap with earlier spectroscopic mapping, suggesting the camera can discriminate materials on Didymos and Dimorphos. Simulations of shocked anorthosite and irradiated ordinary chondrite add nuance: shock darkening changes reflectance uniformly across wavelengths and will be nearly invisible in color ratios, but space weathering reddens surfaces enough to raise the red-to-blue ratio by roughly 12 percent, a signal well within the camera’s reach. Mapping that ratio across the two asteroids could reveal freshly exposed impact ejecta and trace the system’s exposure age.

The camera will also feed gravity science. The University of Bologna leads Hera’s Radio Science Experiment, which fuses Earth-based tracking, inter-satellite links and optical images to estimate the asteroids’ mass, gravity harmonics and moments of inertia. NavCam images, taken from orbital geometries that differ from Hera’s, add independent constraints on the spacecraft-asteroid relative state, and tracking data collected during the final descent and landing will pin down the local gravity field near Dimorphos. The team even quantified the detectability of orbiting debris: one- and ten-centimeter particles should be visible across a useful range of distances and phase angles, echoing OSIRIS-REx, where tracking Bennu’s natural ejecta sharpened that asteroid’s gravity estimate dramatically.

Finally, the NavCam fronts Milani’s headline technology demonstration, the Autonomous Optical Navigation experiment. Milani’s vision-based guidance, navigation and control system, developed at Politecnico di Milano, computes asteroid centroids onboard to steer the spacecraft without relying on Earth. A dedicated Navigation Experiment Operation Centre in Milan will opportunistically compare the onboard navigation solution against a more precise, landmark-based ground reconstruction, testing the image-processing algorithms, the onboard estimator’s covariance, and even the GNC state machine’s ability to switch modes autonomously. In a closing twist, fictitious maneuvers computed from the onboard knowledge will be propagated in simulation and scored against the mission’s official flight dynamics solution, effectively rehearsing a fully closed-loop autonomous guidance cycle. For a CubeSat priced at a fraction of a flagship mission, the NavCam’s blend of navigation muscle and legitimate science makes a compelling case that the future of asteroid exploration may be very small indeed.

Subject of Research: The scientific operations and calibration of the Milani CubeSat's navigation camera aboard ESA's Hera mission to the Didymos binary asteroid system.

Article Title: The Scientific Operations of Milani NavCam

Article References: Ferrari, F., Fodde, I., Piccolo, F., Giordano, C., Rizza, A., Cremasco, A., Panicucci, P., Civati, L. F., Califano, P., Pugliatti, M., Topputo, F., Cardi, M., Pavoni, M., Calvi, D., Zanotti, A., Corradino, F., Kovacs, G., Palomba, E., Dirri, F., … Michel, P. (2026). The Scientific Operations of Milani NavCam. Space Science Reviews, 222(6), Article 73. https://doi.org/10.1007/s11214-026-01327-1

Image Credits: AI Generated

DOI: 10.1007/s11214-026-01327-1

Keywords: Milani, NavCam, Hera mission, Didymos, Dimorphos, DART impact, CubeSat, planetary defense, autonomous navigation, asteroid science, Space Science Reviews, stereophotoclinometry

The scope of the meeting reflects the extraordinary breadth of modern planetary research. Sessions will span the full spectrum of the discipline: new results from the Solar System, the characterization of exoplanetary and interstellar bodies, updates on current and forthcoming space missions, ground-based observational campaigns, and the increasingly prominent role of artificial intelligence and machine learning in extracting insight from planetary data. Planetary defence, the emergence of life in our Solar System and beyond, and the Search for Extraterrestrial Intelligence — SETI — all feature prominently on the programme, a signal of how far the field has expanded from its geology-and-telescopes origins into a genuinely interdisciplinary enterprise that touches on astrobiology, engineering, data science and even public policy.

The choice of host city carries a poetic resonance for attendees. The Hague holds a singular place in the history of astronomy: it was the birthplace of Christiaan Huygens, the seventeenth-century polymath who pioneered the telescope and discovered Titan, Saturn’s largest moon. The city was also the site of the world’s first published written account of an astronomical observation made with a telescope — a milestone that effectively inaugurated the era of observational planetary science. Four centuries later, a Congress devoted to exploring Titan’s methane lakes, Saturn’s rings and the distant corners of the Solar System returning to Huygens’ hometown is more than a logistical coincidence; it is a deliberate act of historical continuity. Organizers have embraced this connection, planning an extensive public outreach programme in the run-up to and during the conference week, including a walking tour threading through the city’s astronomical heritage, concerts, arts installations, public lectures and events designed for local schools.

For media representatives, the Congress offers unusually rich material. Media registration is free, and bona fide journalists can register by contacting the Europlanet press office. Press briefings will be livestreamed for remote audiences, and the EPSC2026 Press Office will issue press notices throughout the week highlighting presentations of particular interest. Two briefings, in particular, are already generating considerable buzz among space scientists and space journalists alike — and both concern European missions arriving at pivotal moments in their operational lifetimes.

The first, scheduled for Monday 7 September at 11:00 CEST, will focus on the European Space Agency’s Hera mission as it counts down to its arrival at the Didymos binary asteroid system. Hera represents the follow-up act to one of the most dramatic planetary science experiments ever conducted: NASA’s Double Asteroid Redirection Test, or DART, which deliberately impacted the asteroid moonlet Dimorphos in September 2022 to test humanity’s ability to alter the trajectory of a near-Earth object. DART succeeded spectacularly, shortening Dimorphos’ orbital period around its parent asteroid and proving that the kinetic impactor technique is a viable planetary defence strategy. But the experiment left behind critical unanswered questions — most notably, the precise internal structure of Dimorphos and the detailed physics of how the impact crater formed and how momentum was transferred. Hera, arriving at the system in November 2026, will conduct a detailed post-impact survey of Dimorphos, transforming a one-off experiment into a fully characterized planetary defence benchmark.

The press briefing will provide updates on the status and plans for the mission post-arrival, but organizers have also promised something more: the Hera team will unveil what they describe as a revolutionary way for the public to engage with the mission and become part of its space adventure. The briefing will also cover the ESA/JAXA RAMSES mission, which will rendezvous with the asteroid (99942) Apophis and accompany it during its exceptionally close flyby of Earth on 13 April 2029 — a natural experiment in asteroid science that occurs only once every few thousand years for an object of this size. Speakers will include Michael Küppers, ESA Hera Project Scientist at ESA-ESAC in Spain; Patrick Michel, Hera Mission Principal Investigator, RAMSES ESA Project Scientist and Director of Research at CNRS, Observatoire de la Côte d’Azur in France; and Heli Greus of the Hera and RAMSES ESA project teams. Together, these missions represent Europe’s commitment to building a comprehensive, layered planetary defence capability — from impact prediction to impact response.

The second major briefing, on Wednesday 9 September at 12:45 CEST, concerns the long-awaited arrival of the ESA/JAXA BepiColombo mission at Mercury. After an eight-year journey through the inner Solar System, involving a series of gravity assists that have tested the patience of mission planners and the endurance of the spacecraft’s thermal systems, BepiColombo will finally reach its destination this autumn. The timeline is tightly choreographed: separation of the European and Japanese orbiters from the Mercury Transfer Module will take place on 3 September, orbit insertion follows on 21 November, and the ESA Mercury Planetary Orbiter and JAXA’s Mio spacecraft will separate from each other on 9–10 December. From that moment, BepiColombo will officially become the first two-spacecraft mission operating at Mercury, with the science phase beginning in April 2027.

The significance of this architecture cannot be overstated. Mercury remains the least explored of the terrestrial planets, a world of extremes where surface temperatures swing from searing daylight to frigid darkness and where a surprisingly strong magnetic field hints at a partially molten core. Operating two spacecraft simultaneously — one optimized by ESA, the other by JAXA with a complementary instrument suite — allows scientists to make coordinated, two-point measurements of the planet’s magnetic environment, exosphere and magnetospheric dynamics that no single spacecraft could achieve. The briefing will feature Santa Martinez, Mission Manager; Ignacio Tanco, Head of the Inner Solar System Missions Unit; Geraint Jones, Lead ESA Project Scientist; and Go Murakami, JAXA Project Scientist, offering an update on the spacecraft’s condition following the transfer module separation and an overview of the critical steps ahead.

Beyond the headline briefings, the Congress programme offers a window into the techniques reshaping planetary science itself. The dedicated sessions on artificial intelligence and machine learning reflect a discipline undergoing a methodological transformation: convolutional neural networks now classify craters and surface features across vast planetary image archives, while machine learning pipelines sift through the exponential growth of data returned by modern instrumentation. Sessions on interstellar bodies will revisit the paradigm shift that began with the detection of objects such as ‘Oumuamua and 2I/Borisov — visitors from other star systems whose compositions offer the only direct sampling of material formed around alien suns. Planetary defence sessions will build on the momentum of DART and the anticipation surrounding both Hera and RAMSES, while astrobiology and SETI sessions will tackle what many consider the deepest question in science: whether life is a cosmic inevitability or an improbable fluke.

The hybrid format, which proved its worth in recent editions of the Congress, ensures that scientists unable to travel — whether for financial, political or personal reasons — can still participate fully in sessions and discussions, a model that has measurably broadened participation across the more than 40 countries represented. Details of scientific sessions and presentation abstracts are available through the official EPSC2026 website, alongside a programme overview and information about the public walking trail and events in The Hague. The meeting hashtag, #EPSC2026, will aggregate real-time discussion throughout the week.

What emerges from the programme as a whole is a portrait of planetary science at an inflection point. Within a single year, Europe has missions arriving at Mercury and at a battered asteroid moonlet, a planetary defence mission to Apophis in development, and a community embracing computational tools that would have seemed like science fiction a generation ago. That all of this converges in the city where humanity first recorded what it saw through a telescope gives EPSC2026 a narrative arc that few scientific conferences can claim. From Huygens’ crude refractor to a two-spacecraft orbital mission at the innermost planet, the through-line is unbroken: an unrelenting curiosity about the worlds beyond our own, now armed with instruments and international cooperation that the Dutch master himself could scarcely have imagined. For the 1,200 scientists gathering in The Hague this September, the next chapter of that four-century-old story is about to be written.

News Publication Date: 6-Sep-2026

Web References: Not provided

References: Media reminder: Europlanet Science Congress (EPSC) 2026. EurekAlert! Not provided.

Keywords

Europlanet Science Congress, EPSC2026, planetary science, Hera mission, BepiColombo, Mercury, Dimorphos, asteroid deflection, planetary defence, RAMSES, Apophis, The Hague