OrbitalHub

Half a gram of asteroid dust, split among three transition metals, has rewritten where Bennu came from. A team led by Maria Schönbächler at ETH Zurich reports on 23 September 2026 in Science Advances that Bennu, the near-Earth asteroid visited by NASA’s OSIRIS-REx spacecraft between 2018 and 2021, did not assemble in the cold outer reaches of the young solar system the way most researchers assumed. It assembled instead near the water-ice line, in the narrow band where temperatures were cold enough to freeze water vapour into solid ice and warm enough inside to keep it as a gas. The work leans on isotopes of iron, titanium and chromium measured in five Bennu sample portions at ETH’s isotope geochemistry lab, and it points to a culprit for the unusual chemistry: Jupiter, which grew large enough, fast enough, to filter coarse material out of the dust disk before Bennu’s parent body could form.

Source: NASA/Goddard/University of Arizona Bennu mosaic on Wikimedia Commons (public domain).

Bennu’s chemistry has been a quiet puzzle for most of the past decade. Earlier sample studies, including the joint OSIRIS-REx and Hayabusa2 preliminary results, had placed it in a family of carbon-rich objects whose closest meteoritic relatives on Earth are the rare CI chondrites: carbon-rich, water-bearing, and chemically the closest match in the meteorite collection to the Sun’s own composition, with very little thermal alteration since the solar system’s birth. What no one had pinned down was where in the protoplanetary disk that fingerprint had been laid down.

The old model put Bennu-class objects far out in the disk, beyond where most comets form, where accretion was slow and hydrated minerals could survive undisturbed. The new isotope measurements turn that on its head. Iron and titanium are distributed so well throughout the Bennu material that the parent object cannot have been a single coarse clump; it must have been built from fine dust mixed across the disk, with ice acting as a glue that bound fine particles into larger aggregates on the cold side of the water-ice line.

The phrase Schönbächler uses for the result is direct: Bennu is a hybrid. It does not clearly match either the inner or the outer solar system. It bears characteristics of both regions, because it was assembled in the specific transition zone where material from both sides met, according to the ETH Zurich announcement.

To anchor that conclusion, the team compared Bennu against the other carbon-rich sample-return target in the modern catalogue: Ryugu, the asteroid Hayabusa2 visited in 2019. The two objects share an isotopic fingerprint with each other and with the CI chondrites, all distinct from the rest of the meteorite collection and from other sampled asteroids. The authors frame the open question as a population question: if Bennu and Ryugu both formed in the same zone, what is that zone producing that sends objects to near-Earth orbits, and are these two a coincidence or a sample of a broader pattern?

That question hands the baton to the next sample-return missions. China’s Tianwen-2 arrived at the quasi-satellite Kamoʻoalewa this summer and is expected to return a sample in 2027. Japan’s MMX mission, scheduled to launch from Tanegashima in October 2026 on an H3, is set to bring back material from Phobos in 2031; Phobos is itself a possible captured asteroid, and a Phobos sample with a Bennu-like signature would extend the snow-line zone picture to the Mars system. The next-mission parallel was also flagged in Space.com’s coverage.

The water-ice line is not a feature of the finished solar system; it is a feature of the protoplanetary disk, the rotating torus of gas and dust around the young Sun. Inside the line, water vapour stays in gas form. Outside it, water freezes onto dust grain surfaces as ice. In standard models the boundary sits somewhere near the present-day orbit of Jupiter, roughly five astronomical units out, and that distance matters because the disk’s solid inventory changes composition sharply there: inside the line, rocky dust; outside, ice-coated dust; and right at the boundary, a transition layer where ice can sublimate, migrate inward as vapour, and recondense.

The new analysis proposes that this transition layer was the assembly site for Bennu, Ryugu, and the CI chondrites, with Jupiter acting as an active filter rather than background. The gas giant formed within roughly one million years of the Sun’s birth, and its gravitational influence quickly became a barrier in the disk. Coarse, clumpy material could not easily cross Jupiter’s orbital neighbourhood; fine dust could, routing around Jupiter from multiple radial directions and arriving well mixed. The result is an unusually homogeneous feedstock for planetesimals forming in the transition zone near the snow line, and that homogeneity is what the Bennu isotope data see.

The team’s mechanism also explains two aspects of the sample. The first is water. Bennu’s parent body incorporated enough ice that, when it was later broken up and the fragments were warmed by the Sun, hydrated minerals appeared in the regolith in the proportions the OSIRIS-REx analysis measured. Ice from just outside the snow line can sublimate as the disk evolves, drift inward as vapour, and recondense inside the line, so a transition-zone planetesimal ends up with both rocky and icy inputs. The second is the chemical match to the Sun. Fine dust, mixed by the disk’s turbulence and routed around Jupiter, ends up with a bulk composition close to the pre-solar nebula because it has not been sorted into coarse and fine reservoirs. Bennu samples that average composition better than any other available asteroid material.

For the broader picture, the implication is that the asteroid belt is not the only reservoir of primitive material in the inner solar system. Near-Earth asteroids like Bennu and Ryugu may be sampling a specific radial slice of the early disk that the main belt, with its heavy thermal and collisional processing, has blurred out. If planetary migration can scatter snow-line objects into near-Earth orbits, then the Bennu sample is not a quirk of one asteroid but a window onto a specific formation environment that the meteorite collection only hints at.

What is striking about the result is how much depends on a small measurement. The five Bennu sample portions, totalling a fraction of a gram, were analysed for isotopic ratios of three elements at a single laboratory over months. None of that is large-scale geophysics or a flagship space telescope survey. It is the kind of bench-scale work that historically has rewritten meteorite science, and it has now done so for an asteroid whose sample exists on Earth only because a NASA spacecraft flew for two and a half years to a rock the size of a small mountain, picked up its surface with a robotic arm, and parachuted the result home.

The Bennu story is not finished. Sample analysis at laboratories around the world is ongoing, with new allocations going out in waves as the OSIRIS-REx curatorial team works through the 120 grams that came back. Schönbächler and her collaborators flag the open question directly: are other asteroids in the same isotopic family, and how widespread is the snow-line zone fingerprint across the inner solar system? That question will not be answered by Bennu alone. It will be answered by what comes back from Kamoʻoalewa, then Phobos, then whatever the next generation of sample-return missions chooses to visit.

For now, the picture is this: Bennu is chemically the closest match in our sample collection to the mixture of elements the Sun itself inherited. Its formation was not a quiet outer-disk story; it was a product of a specific radial neighbourhood in the young solar system, with Jupiter acting as the gatekeeper that kept coarse material out and let fine dust through. The fact that we have a piece of it in a laboratory in Zurich, three years after it fell out of the Utah sky, is a measure of how much of the early solar system can be reconstructed from a sample small enough to lose between your fingers.

At 13:45 CEST on 28 September 2026, ESA’s Jupiter Icy Moons Explorer skimmed 8,640 kilometers above the Indian Ocean – close enough that an atmospheric physicist would call the altitude “edge of space.” The flyby added 3.5 kilometers per second to the spacecraft’s velocity and rotated its trajectory by twenty degrees, almost without touching its fuel tanks. Closest approach was over open ocean, well clear of populated regions, and was captured by JUICE’s two monitoring cameras at the moment the spacecraft began to climb back out of Earth’s gravity well. It is the second of three Earth (and one Venus) gravity assists the probe will use over an eight-year cruise to reach Jupiter in 2031. This time, instead of treating Earth as just a waypoint, ESA turned the encounter into a dress rehearsal for the eleven scientific instruments that will eventually map Ganymede, Europa and Callisto – the three large, icy, ocean-bearing moons that give the mission its name.

The phrase “gravity assist” hides a century of celestial mechanics. In the Newtonian picture, a spacecraft swinging past a moving planet picks up or loses kinetic energy from the planet’s own orbital motion, the way a tennis ball struck by a moving racket leaves faster than it arrived. In a pure two-body problem the gain is reversible. In the real three-body mess of spacecraft, planet and Sun, the assist can be planned to add a fixed velocity increment for a fixed angle of deflection. Each leg of the trajectory is treated as a Keplerian orbit about a single dominant body, with sudden changes at the boundary – the patched-conic approximation that has guided interplanetary navigation since the 1960s. For JUICE, the propellant budget for the cruise phase is 386 kilograms. The first gravity assist came in 2024 with a record-breaking lunar-Earth double flyby, in which the Moon bent the trajectory before Earth added energy. The second came on 31 August 2025 at Venus, where JUICE picked up 5.1 km/s at 5,088 km altitude. The third was the 28 September Earth flyby. The fourth, and final, will be a third Earth encounter in January 2029, which lines up the spacecraft for Jupiter orbit insertion in July 2031.

In the four weeks leading up to the flyby, JUICE’s flight control team at ESA’s European Space Operations Centre in Darmstadt had scheduled six possible trajectory-correction maneuvers. They used one – a tiny nudge a few days before closest approach – to align the spacecraft with the geometry needed to extract the maximum energy from the swing-by. “The flyby required ultra-precise navigation in real time,” said spacecraft operations manager Angela Dietz. “Thanks to our very careful planning, we used only a small amount of the propellant reserved for this flyby. This gives us more to use at Jupiter to carry out observations of the planet’s icy moons.” The other five maneuver windows were quietly dropped.

The flyby was also a third opportunity to test JUICE’s scientific instruments on a real, well-understood target – a privilege planetary missions rarely have. The first came in 2024 during the lunar-Earth gravity assist. The second came in 2025 when JUICE turned its cameras and spectrometers on the interstellar comet 3I/ATLAS as it tore through the inner solar system on its hyperbolic passage from beyond the Sun. Now, with Earth filling the field of view, project scientist Claire Vallat’s team prioritized ten of the eleven instruments based on their relevance to Jupiter science and on the timing of the encounter. JANUS, the German-Italian visible imager, captured color frames of the Moon and Earth at a ground sample distance better than any previous mission of this type. RIME, the radar sounder, pinged the lunar surface in test mode to validate its dielectric calibration. J-MAG, the magnetometer, and PEP, the particle environment package, spent several days in Earth’s magnetotail, collecting plasma data that will help validate the way JUICE will eventually study Ganymede’s intrinsic magnetic field – the only intrinsic magnetic field known to exist around any moon. The data started arriving at ESA’s European Space Astronomy Centre (ESAC) within hours of the encounter. While JUICE sat in the magnetotail, the European-Chinese Smile mission watched the same disturbances from the inside, measuring the auroras and field-aligned currents that connect the polar atmosphere to the distant tail. The combined dataset lets scientists correlate what happens at the polar oval with what happens sixty Earth radii downstream – a joint geophysics experiment that neither mission could have done alone.

The eleven instruments JUICE carried into the flyby represent the bulk of a payload developed under ESA leadership with hardware from across Europe, NASA, JAXA and the Israel Space Agency. JANUS, the camera system, has a 0.07 degree per pixel ground sample distance at closest approach – sharp enough to resolve features a few hundred meters across on Ganymede from orbit. GALA, the Ganymede Laser Altimeter contributed by DLR, will fire a 30-millijoule pulse at 30 hertz into the surface and time the return to centimeter accuracy; that topographic map is what scientists will use to detect the few-centimeter tidal bulge Ganymede’s ice shell should flex under Jupiter’s gravity. MAJIS, the visible and infrared imaging spectrometer, will measure how sunlight and thermal emission change across the moons’ surfaces between 0.5 and 5.5 micrometers. SWI, the sub-millimeter wave instrument, will measure temperature and composition in Jupiter’s stratosphere. UVS will trace the Jovian auroral ovals. RIME will probe tens of kilometers below the icy crust looking for the dielectric signature of a liquid-water ocean – the data needed to tell whether Europa and Ganymede host subsurface seas like the one Cassini inferred beneath Enceladus.

The mechanics of the flyby, meanwhile, are governed by the patched-conic approximation JUICE’s navigation team used to design the encounter. Earth’s gravity well at closest approach is a potential roughly 60 km/s deep at the surface, dropping to less than 0.1 km/s at 8,640 km altitude. A spacecraft entering and leaving this well with a hyperbolic excess velocity of a few km/s picks up almost no net energy – but it can change direction substantially, since the asymptote’s direction rotates by an amount that depends on the geometry of the swing-by. The twenty-degree rotation JUICE achieved is enough to take it from an out-of-ecliptic post-Venus trajectory to one in Jupiter’s orbital plane. The instrument activity had to be squeezed into the time the spacecraft spent under power, since parts of the closest approach passed through Earth’s shadow – a constraint that pushed Vallat’s team to pre-plan every exposure and every magnetometer burst months in advance.

What the next five years look like depends on how well JUICE’s instruments survive their first long bath in deep space. The first calibrated data from the Earth flyby – high-resolution images, spectra, magnetometer and plasma logs – should start arriving at ESAC within weeks and be released to the scientific community in early 2027. The January 2029 flyby will be JUICE’s last swing through the inner solar system. The final burn for Jupiter orbit insertion will come in July 2031, using the same main engine that has been unlit since 2024. By then, the engineering we celebrate this week – the careful navigation, the simultaneous run of ten instruments on a planetary scale, the single tiny burn that put the spacecraft on exactly the right approach – will be a footnote in a mission that, if it works, will give us our first sustained look at the three icy worlds where life might still exist in our own back yard.

A small, elongated rock against a black sky, with a 10-metre scale bar tucked into the lower-right corner. That is the entire first portrait of asteroid 469219 Kamoʻoalewa, returned on 2 July 2026 by China’s Tianwen-2 probe from a distance of about 20 kilometres. The picture is rough, but it is enough. Kamoʻoalewa is roughly the size of a small office building, and until now the only data astronomers had on its surface came from telescopes on the ground and from a few passes of the James Webb Space Telescope. Now a spacecraft is sitting in front of it, and the first thing that picture reveals is that the rock looks nothing like the Moon, which is what a five-year-old theory said it should look like (SpaceNews, Sci.News).

Kamoʻoalewa is one of seven known quasi-satellites of Earth, meaning its orbit around the Sun closely tracks ours even though it is not gravitationally bound to the planet. From our moving viewpoint it appears to loop around the Earth like a slow second moon, but the similarity is an illusion of perspective (Wikipedia). For most of the past decade the working hypothesis has been that Kamoʻoalewa is a chunk of the Moon’s far side, blasted into space by an impact and later nudged into an Earth-like orbit. The red colour of its reflectance spectrum, measured from telescopes in 2021, looked more like heavily weathered lunar silicates than like any common type of near-Earth asteroid (Space Daily).

That hypothesis is now under coordinated pressure from three independent lines of work: a population model published in Astronomy & Astrophysics, a reanalysis of the spectrum in Nature Communications, and the new JWST observations led by Benjamin Sharkey at the University of Arizona. Tianwen-2’s image does not settle the question, but it shows that the spacecraft can find, track and image a target only tens of metres across, which is the prerequisite for the sample return that will settle it. The mission is China’s first attempt at an asteroid sample return, and the spacecraft is built to bring roughly 100 grams of material home in late November 2027 (Sci.News, SpaceNews).

Tianwen-2 launched from the Xichang Satellite Launch Center on 29 May 2025, riding a Long March 3B/G2 rocket. CNSA disclosed little about the cruise until the spacecraft was already at its target. Independent tracking by AMSAT-DL in Europe picked up the probe’s signal as it approached the asteroid and showed a series of engine burns (SpaceNews). On 6 June 2026 the spacecraft first detected Kamoʻoalewa. The next day it executed a capture manoeuvre at 30,000 km to match the asteroid’s orbital plane. By 19 June it had closed to 2,000 km. On 2 July it settled into a 20 km station-keeping point and took the picture (Sci.News, SpaceNews).

CNSA announced the arrival on 6 July 2026. The agency’s statement stressed that the optical navigation data reduced uncertainty in the asteroid’s predicted position from hundreds of kilometres, based on ground observations alone, down to the kilometre scale. The 20 km point is the start of close-proximity science operations, including global mapping and selection of the sampling site. Departure from Kamoʻoalewa is planned for April 2027, with the reentry capsule delivering samples in late November 2027 (SpaceNews).

Kamoʻoalewa was discovered on 27 April 2016 by the Panoramic Survey Telescope and Rapid Response System, Pan-STARRS, at Haleakala Observatory in Hawai’i. Its name is a Hawaiian phrase that translates roughly to “oscillating celestial fragment” (Sci.News, Wikipedia). Ground-based estimates put its diameter between 40 and 100 metres. The Tianwen-2 image, with its 10-metre scale bar, suggests a diameter of just over 20 metres. That matches the JWST-based estimate from Sharkey’s team, published as a preprint in late June 2026, which puts the mean diameter at 18 plus or minus 2 metres and the rotation period at about 27.9 minutes (SpaceNews, arXiv:2606.24017).

Granvik, an astronomer at the University of Helsinki and Luleå University of Technology, told SpaceNews that the first image “basically confirms” the high geometric albedo implied by Sharkey’s JWST work, and that this reflectivity is not compatible with the low-to-moderate albedo of lunar material. “So it seems that Kamoʻoalewa is of asteroidal origin,” Granvik said (SpaceNews).

The lunar-fragment hypothesis was a coherent story built from two indirect clues, not from direct evidence. The 2021 spectroscopic study led by Benjamin Sharkey found that Kamoʻoalewa’s reflectance was unusually red and resembled heavily weathered lunar silicates more than common near-Earth asteroid types. A 2024 Nature Astronomy paper led by Yifei Jiao then proposed a specific source: the 22-kilometre-wide Giordano Bruno crater on the lunar far side, whose estimated age and impact physics could produce fragments of the right size and send some into co-orbital space (Space Daily).

Three recent studies each chip away at that picture. The first is a population model by Marco Fenucci and colleagues in Astronomy & Astrophysics. The team modelled both ordinary near-Earth asteroids delivered from the main belt and fragments produced by the Giordano Bruno impact. Their estimate produced 1.23 plus or minus 0.13 Kamoʻoalewa-like objects from the main-belt population, compared with 0.042 from Giordano Bruno ejecta. That is more than an order of magnitude in favour of a main-belt origin, although the calculation is a population argument, not a parent-body match (Space Daily).

The second is a May 2026 Nature Communications paper led by Pengfei Zhang. The team reanalysed the absorption feature and found it consistent with LL chondrites, the stony meteorites associated with asteroids like Itokawa. In laboratory tests, highly space-weathered LL-chondrite powder reproduced Kamoʻoalewa’s reflectance spectrum even though solid pieces did not. They proposed an origin in the Flora asteroid family, followed by extensive weathering of fine surface material (Space Daily).

The third is Sharkey’s new JWST observations, taken in February 2026 and supported by Large Binocular Telescope measurements in April. The infrared spectrum is much less red than the 2021 ground-based result. The authors say the colours resemble several silicate asteroid classes, including S, V, or E-types, more than weathered lunar material. The albedo and absorption features may fit an oldhamite-bearing, enstatite-rich composition. The preprint’s best-fit geometric albedo is 0.59, with model fits as low as 0.36 still working, which is far too bright to match lunar highland or mare material (arXiv:2606.24017, TechTimes).

None of these three studies identify the same asteroid analogue. What they share is that none of them require Kamoʻoalewa to be lunar rock. Tianwen-2 will be the tiebreaker. Its 11 science payloads include cameras, laser ranging, spectrometers, sounding radar and particle analyzers, plus the DIANA dust analyzer contributed by Italy (SpaceNews). For sampling, the spacecraft carries three redundant techniques: hovering, touch-and-go, and anchoring plus attachment, with the last dependent on whether the surface can support it. The anchoring approach is unusual; it would require the spacecraft to grip a body that is only tens of metres across. After the sample heads home, the main spacecraft is to continue onward to the active main-belt comet 311P/PANSTARRS, where it would carry out the first close investigation of an active main-belt object (SpaceNews).

The first Tianwen-2 picture of Kamoʻoalewa establishes that the spacecraft has reached its target and can resolve an object barely wider than a tennis court at 20 km. It does not yet say where the asteroid came from. Between now and the late-2027 sample return, the most consequential measurements will be multispectral imaging at lower altitudes and the choice of sampling site. Laboratory work on the returned grains can compare mineralogy, elemental ratios and isotopes with Apollo and Luna samples on one side and with LL chondrites on the other. A lunar match would have to overturn the new statistical and spectral arguments against it. A chondritic match would mean an ordinary asteroid had acquired a lunar disguise through long space weathering, which would be its own kind of finding (Space Daily).

The next milestone in the timeline is the move from 20 km station-keeping into closer mapping. The first attempt at sample collection is expected in 2027. Granvik’s reading of the new albedo, Fenucci’s population model, Zhang’s LL-chondrite fit and Sharkey’s JWST spectrum together point the same direction, but they do not yet reach the Moon. That is what the sample return is for.

On the evening of July 5, 2026, a 600-kilogram box of solar panels and instruments zipped past a peanut-shaped rock 450 meters across at roughly five kilometers per second. The flyby lasted about as long as the time it took you to read this sentence. The spacecraft was JAXA’s Hayabusa2, on a deliberate dash past near-Earth asteroid 98943 Torifune, also known by its provisional designation 2001 CC21. By the time anyone on Earth saw a single pixel of the encounter, the spacecraft was already several thousand kilometers beyond the asteroid, never to swing back (JAXA, July 6, 2026).

That brevity is the point. Torifune is the first of three asteroid encounters the extended Hayabusa2 mission is supposed to make before the probe reaches its true final target, the tiny 11-meter asteroid 1998 KY26, in 2031. The spacecraft is a sample-return craft that has already done its main job. Every extra maneuver now is rehearsal for an encounter that will be the most technically punishing of the mission (The Planetary Society, July 7, 2026).

Two reasons. First, Torifune is a contact binary, a body made of two lobes stuck together like a snowman, and those shapes are common in the small-body population but hard to study up close. Ground-based radar and adaptive-optics images suggested it was elongated; until last week no spacecraft had ever confirmed the structure with its own camera.

Second, the flyby is a deliberate dress rehearsal for planetary defense. JAXA wanted to demonstrate the kind of precision terminal guidance a kinetic impactor mission like NASA’s DART would need, where the spacecraft picks a small, faint, irregularly shaped target and threads a narrow approach corridor without hitting it. Torifune is the right kind of object: small, dim, and only clearly resolved a few days before closest approach. The mission team could not plot the final approach trajectory until the very end, because Torifune is faint enough that its exact orbit was uncertain until then (The Planetary Society, July 7, 2026).

If you are trying to design a spacecraft that bumps a city-block-sized rock off course, this is the kind of practice you want.

Hayabusa2 launched in December 2014 on an H-IIA rocket and arrived at asteroid Ryugu in mid-2018. Over the next eighteen months it dropped a pair of tiny hopping rovers, lowered the German-French MASCOT lander onto the surface, fired a 2-kilogram copper projectile into Ryugu to expose fresh sub-surface material, and scooped up samples. The return capsule landed at Woomera, Australia, in December 2020. Inside, scientists found water-bearing minerals, organic molecules, and grains that had escaped billions of years of space weathering. The samples are still being analyzed and are among the cleanest primitive materials anyone has yet returned from a carbon-rich near-Earth asteroid (Sci.News, July 8, 2026).

Most sample-return missions end there. Hayabusa2 did not. After releasing its sample capsule, the main spacecraft fired its ion engines and began a new trajectory. The extended mission has two goals: a high-speed flyby of Torifune in 2026, two Earth gravity assists in 2027 and 2028, and a final rendezvous with 1998 KY26 in 2031 (ISAS, mission page).

The Torifune encounter happened on July 5 at 18:30 JST, give or take one second. The spacecraft passed about 800 meters from the asteroid’s center, well outside the body but close enough that its three imaging instruments could resolve surface detail. ONC-T, the visible-light Optical Navigation Camera, started tracking Torifune on June 20 and continued to use the asteroid as an optical navigation reference right up to closest approach. About an hour before the flyby, the spacecraft also switched on NIRS3, a near-infrared spectrometer that hunts for water and hydroxyl signatures; TIR, a thermal infrared imager; and LIDAR, which bounces a laser off the surface to measure distance (JAXA, July 6, 2026).

Closest approach came and went. Hayabusa2 could not look back. JAXA confirmed the spacecraft was healthy at 18:35 JST, five minutes after the flyby, and the first images and thermal maps arrived within a day (Sky & Telescope, July 6, 2026).

The visible-light image showed what ground-based observers had suspected. Torifune is two distinct lobes joined at a narrow neck, the textbook shape of a contact binary formed when two smaller asteroids collided gently and stuck rather than bouncing apart. At about 450 meters across, it is in the same size class as the near-Earth asteroid Apophis and roughly an order of magnitude larger than the object that exploded over Chelyabinsk in 2013 (The Planetary Society, July 7, 2026).

The naming fits. JAXA chose “Torifune” through a public contest; it is short for Ame-no-Torifune, a Japanese deity associated with safe, steady, high-speed travel. You can see why the mission team liked it.

A flyby at five kilometers per second does not leave much margin for error. A small miscalculation in the closest-approach distance translates into several hundred meters of horizontal miss, easily enough to fly by the wrong side of the asteroid. There is no second chance. Hayabusa2 had to arrive at a precise point in space at a precise time, then keep going.

The spacecraft used a hybrid optical and radio navigation scheme. ONC-T took repeated images of Torifune against the background star field, and the team on the ground measured the asteroid’s apparent position to refine the predicted encounter point. Combined with deep-space network Doppler and ranging data, this let mission control update the trajectory within the last few days before closest approach. JAXA has not published the final navigation error budget, but the fact that ONC-T returned sharply focused images from 800 meters suggests the geometry worked (JAXA, July 6, 2026).

The thermal imager, TIR, observed Torifune in the 8 to 12 micrometer band, the thermal infrared where a sunlit asteroid radiates most of its heat. The brightness temperature, divided by the solar illumination, lets you back out the surface’s thermal inertia, a property set by regolith grain size, packing, and whether the surface is bare rock or blanketed in dust. For a small contact binary, the thermal data is the only way to learn what the surface is made of, because visible and near-infrared spectroscopy during a flyby captures too little reflected sunlight to break out mineral absorption signatures cleanly.

LIDAR is simpler but just as important. It rangefinds the surface with a 1.064-micrometer pulsed YAG laser, accurate from 30 meters out to 25 kilometers. During the Torifune encounter it produced a continuous altitude profile in the final minutes before closest approach, doubling as both a navigation input and a shape model. Combined with the ONC-T silhouette from a known viewing angle, the LIDAR track pins down the asteroid’s three-dimensional shape far better than the optical images alone (JAXA, July 6, 2026).

The instrument suite is what the spacecraft will carry into the 1998 KY26 encounter in 2031. KY26 is a different problem. At roughly 11 meters across, it is small enough that Hayabusa2 will not simply fly past; the extended mission plan calls for an actual orbit insertion and an attempted landing. The asteroid’s rapid rotation period, on the order of a few minutes, will make that landing extremely difficult, and the extended mission team is using Torifune to validate the optical and thermal mapping pipeline they will need for the harder job.

Hayabusa2 has now visited three asteroids across two missions. The first primary mission gave the world its best sample of a carbon-rich near-Earth asteroid. The extended mission is a chain of progressively harder technical demonstrations, and the Torifune flyby is the one with the lowest stakes but the cleanest test of the navigation approach JAXA wants to use in 2031. More data will downlink over the coming weeks.

Two years from now, the spacecraft will swing past Earth for a gravity assist. Three years after that, in 2031, it will arrive at a rock smaller than a house and try to land on it. Last week’s flyby is the first of the milestones the extended mission still owes the public. JAXA hit the geometry and returned a clean, recognizable image. The data will inform how we eventually deflect a real asteroid.

A gravity assist is usually described as celestial bookkeeping: a spacecraft borrows a little momentum from a planet and leaves on a better trajectory. NASA’s Psyche mission did that at Mars on May 15, 2026, but its science teams treated the encounter as much more than a navigation event. They pointed the spacecraft’s instruments at a world whose properties are already well measured, then asked whether the hardware returned the answers it should.

The spacecraft passed 2,864 miles (4,609 kilometers) above the Martian surface. Its cameras watched a thin crescent grow into a detailed globe. Its magnetometer crossed Mars’ bow shock. Its neutron detector registered a rise in particles near closest approach. The resulting data, released in July with a time-lapse video, made Mars a dress rehearsal for a far less familiar target: the metal-rich asteroid Psyche, which the spacecraft is due to reach in 2029, according to the NASA Science flyby report.

Space instruments spend years being designed, calibrated, launched, and monitored, but cruise provides few chances to test them against a large planetary body. Stars can check camera pointing. The solar wind gives a magnetometer a continuous signal. Neither reproduces the rapid changes, bright surfaces, stray light, and particle environment of a close planetary pass.

Mars offered a rare controlled comparison. Orbiters and rovers have observed its surface, atmosphere, and magnetic environment for decades. If Psyche’s instruments measured something wildly inconsistent with that record, engineers would have time to diagnose the discrepancy before asteroid arrival. Agreement is useful too: it confirms that the instrument, onboard electronics, ground pipeline, and scientific interpretation work together after nearly three years in space.

That last point matters because Psyche’s destination is difficult to interpret. The asteroid is often described as metal-rich, but the mission exists because remote observations cannot settle how much metal it contains, how it formed, or whether it preserves material from the interior of an early planet-building body. The spacecraft carries three dedicated science instruments: a multispectral imager, a magnetometer, and a gamma-ray and neutron spectrometer. It will also use radio tracking to map the asteroid’s gravity, as described in NASA’s Psyche mission overview. Mars let the instruments work on the same known target within hours.

Psyche launched in 2023 on a long solar-electric cruise toward the main asteroid belt. Mars was part of the route from the start. Before the encounter, NASA expected the spacecraft to pass about 2,800 miles above the surface at roughly 12,333 mph (19,848 kph). The planet’s gravity would increase the craft’s heliocentric speed and tilt its path toward the asteroid, according to the May 8 NASA mission brief.

The images began well before closest approach. Starting in early May, Psyche’s pair of identical multispectral cameras photographed Mars at a high phase angle, so the sunlit portion looked like a slender crescent. The sequence from May 2 through May 15 shows that crescent expanding as the distance closed. NASA assembled those frames into the growing-crescent composite used with this post.

Near Mars, the cameras resolved the south polar ice cap, wind-marked craters, and Huygens, a large double-ring crater. The team also detected Phobos and Deimos from far away. That was useful practice for a later search for small moons around asteroid Psyche. More quietly, the imaging team tested sensitivity to scattered light and began comparing its pictures with data from existing Mars missions. A camera can produce a sharp image and still mismeasure brightness or color; cross-calibration helps expose that kind of error.

The particle spectrometer faced a different test. It is intended to infer surface composition at the asteroid by measuring gamma rays and neutrons generated after cosmic rays strike the material. At Mars, the 4,609-kilometer altitude was too high for the detector to pick up gamma rays from the surface. The team did expect escaping neutrons, and the instrument recorded a count-rate increase close to the predicted level near closest approach.

The magnetometer had spent cruise measuring the solar wind and occasional coronal mass ejections. Mars provided its first magnetic signature from a celestial body. As Psyche entered the bow-shock region, where the solar wind encounters the obstacle formed by Mars and its induced magnetic environment, the instrument saw a strong increase. The flyby therefore exercised the detector through a rapidly changing field rather than the relatively steady background of interplanetary space.

Navigation also delivered what the science plan needed. The flyby put the spacecraft directly on its outbound course, and the mission expects to resume sustained solar-electric thrusting later in 2026. Arrival remains planned for the summer of 2029.

A gravity assist works because the planet and spacecraft exchange momentum while both orbit the Sun. In a Mars-centered frame, the spacecraft falls in, curves around the planet, and departs with approximately the same hyperbolic excess speed it had on arrival. In the Sun-centered frame, however, the velocity vector has rotated. Adding Mars’ orbital velocity before and after that rotation changes the spacecraft’s speed and direction around the Sun. Mars loses or gains an immeasurably small amount of orbital momentum in return.

The maneuver gave Psyche both energy and geometry that electric propulsion alone would have taken longer to supply. Its Hall-effect thrusters expel ionized xenon and produce low thrust for long periods. That system is efficient, but a planetary flyby can rotate the trajectory quickly without consuming propellant. Precision is unforgiving: a small arrival error changes the bending angle and therefore the outbound path. The close approach matching the planned corridor shows the navigation chain worked from orbit determination through correction maneuvers.

The instrument tests relied on three different physical signals. For imaging, filters divide reflected light into wavelength bands. Variations among bands can distinguish surface materials and reveal how illumination geometry affects the measurement. Mars supplied bright terrain, dark terrain, haze, ice, and a changing phase angle in one encounter.

For the neutron measurement, energetic cosmic rays strike atomic nuclei in the upper surface and create cascades of secondary particles. Some neutrons escape. Their energy distribution depends partly on which elements slowed or absorbed them. Hydrogen, for example, is particularly effective at reducing neutron energy. Gamma rays occur at characteristic energies associated with specific nuclei, but signal strength falls rapidly with distance; Psyche’s altitude explains why neutrons were detectable while Martian gamma rays were not.

Mars has no strong global dipole field like Earth’s. The solar wind interacts with its upper atmosphere and localized crustal magnetism, producing a bow shock upstream of the planet. Crossing that boundary gave the magnetometer an abrupt, recognizable change against which its timing and response could be checked. At asteroid Psyche, any remanent field would bear on whether its material once cooled within a magnetized parent body.

The Mars flyby did not answer the central question about asteroid Psyche. It reduced the risk that, three years from now, the mission will reach its target with a hidden calibration problem or an analysis pipeline that has never handled a fast-changing planetary data set.

That is the practical value of using a familiar world as a test object. The cameras returned surface detail and distant moon detections. The neutron detector saw the expected count increase. The magnetometer identified the bow shock. Each result connects directly to a job the instrument must perform at the asteroid, where there will be no fleet of orbiters and rovers providing an easy reference.

The spacecraft now has its outbound trajectory and a set of measurements the teams can keep analyzing while electric propulsion carries it toward the main belt. When asteroid operations begin in 2029, the first observations will still contain surprises. The basic behavior of the instruments should not be one of them.

On 17 March 2026, somewhere past the orbit of Mars, a European spacecraft fired its hydrazine thrusters for the second time since launch. The burn lasted long enough to dump 123 kilograms of propellant and shift the probe’s heliocentric velocity by 367 metres per second, the equivalent of accelerating from a standstill to just above the speed of sound (ESA, Hera mission update, 17 March 2026). Two months later, in Thessaloniki, the entire Hera science team gathered for what the project’s own newsletter called “the last time before the probe finally arrives on site” (heramission.space, 17 May 2026). That arrival is now eleven weeks out.

ESA’s Hera, launched 7 October 2024 from Cape Canaveral on a Falcon 9, is closing on the binary asteroid 65803 Didymos. It will reach the system in early November 2026, almost exactly four years after NASA’s Double Asteroid Redirection Test slammed into Dimorphos, the smaller of the two bodies, and changed its orbit by 33 minutes (NASA/APL, 26 September 2022). What Hera will do once it gets there is, in a phrase the mission team keeps using, turn a grand-scale experiment into a repeatable planetary-defence technique. That phrase is doing a lot of work. It is the entire reason a 1,214-kilogram spacecraft is at this moment drifting toward two rocks that, until 2022, almost no one outside planetary science had heard of.

Dimorphos is small. Before DART, its diameter was estimated at roughly 160 metres, the height of a 50-storey building, and its mass was known only to within a factor of two. That uncertainty is the central problem Hera was built to solve. The first measurement of how much momentum DART delivered to the moonlet, the so-called momentum enhancement factor beta, was published by Rivkin and colleagues in 2023. They reported beta = 3.61 with a 1-sigma uncertainty of about 0.2, anchored to an assumed Dimorphos bulk density of 2,400 kilograms per cubic metre (Rivkin et al., Nature 2023). A weaker, more porous asteroid gives a higher beta. A denser, more cohesive one gives a lower beta. Without measuring Dimorphos’s actual mass, every planetary-defence scenario that uses the DART result inherits that uncertainty.

That matters because planetary defence is no longer hypothetical. The 2024 PDC25 exercise at Johns Hopkins Applied Physics Laboratory used beta = 3.61 as its baseline. The number is now embedded in the operating procedures of NASA’s Planetary Defense Coordination Office. A 0.2-point error in beta, applied to a 200-metre asteroid on a 10-year warning, translates into roughly a thousand kilometres of miss distance. That is the difference between a near miss and an ocean impact.

There is a quieter reason to care. Hera is going to make the first internal radar scan ever performed on an asteroid. The instrument is called JuRa, and it sits on a CubeSat the size of a shoebox.

NASA’s DART was the kinetic-impact end of an experiment called AIDA, the Asteroid Impact and Deflection Assessment. ESA’s Hera was always supposed to be the diagnostic half. The architecture is not unusual in physics: you hit something, then you measure what happened. In this case, the impactor flew in 2022. The diagnostician is arriving on time.

Dimorphos is in a 12-hour orbit around Didymos, a roughly 780-metre primary. Both are near-Earth asteroids in the rubble-pile class. DART hit Dimorphos head-on at about 6.6 kilometres per second and shortened its orbital period by 33 minutes, far more than the 7-minute change the spacecraft alone would have produced. The extra came from ejecta, the plume that flew off the surface in the opposite direction and acted as a natural afterburner.

Hera will do the part ground telescopes could not. It will map Dimorphos’s shape from hyperbolic arcs at 20 to 30 kilometres, then closer, down to 1 to 2 kilometres during the experimental phase in April and May 2027 (ESA Hera operations plan, 2026). Two CubeSats will be deployed starting 13 January 2027. Juventas carries JuRa, a 50 to 70 megahertz radar that will sound the asteroid’s interior to a depth of roughly 100 metres with 10 to 15 metres of vertical resolution. Milani carries ASPECT, a hyperspectral imager covering 0.5 to 2.5 micrometres, and VISTA, a dust sensor. Juventas will attempt a soft landing on Dimorphos in late January 2027, the first controlled touchdown on a body this small.

The 367 m/s maneuver tells you what the mission was actually doing during cruise. The full delta-v budget from launch through arrival is on the order of 1.4 kilometres per second, and Hera carries roughly 600 kilograms of hydrazine for chemical propulsion. That is a small budget by interplanetary standards, smaller than OSIRIS-REx’s, smaller than Hayabusa2’s. The reason it works is the Mars gravity assist of 12 March 2025, which bent the trajectory and added, for free, several hundred metres per second. Without that flyby, Hera would not have arrived.

What the chemical system has to do is trim. Each burn is small. The cumulative effect, over five maneuvers across two years, is to align the spacecraft with Didymos’s slow drift around the Sun so that, in late October 2026, the probe can begin hyperbolic approach arcs instead of flying past.

The autonomy stack is the harder problem. At 20 kilometres, Didymos subtends roughly the same angle as a person standing 100 metres away. At 4 kilometres, Dimorphos, at 160 metres across, occupies about 2.3 degrees of sky. Both bodies move visibly against the star background during a single exposure. The Asteroid Framing Camera, two redundant 1020-by-1020 CMOS sensors built by Jena-Optronik, has to track Didymos in one field of view while Dimorphos arcs through the same frame. At 1 kilometre altitude, AFC delivers roughly 10 centimetres per pixel. That is enough to resolve the rim of the DART crater and build a digital terrain model accurate to about half a metre (Jena-Optronik AFC documentation, 2024).

JuRa is the more exotic instrument. Low-frequency radar in deep space is rare because the antenna that works at 50 to 70 megahertz is, by radio-physics standards, large: on Juventas, the antennas deploy to about 1.5 metres tip-to-tip. The bandwidth is wide enough to see the boundary between regolith and a more competent interior, if such a boundary exists. Dimorphos is thought to be a rubble pile, a gravitationally bound aggregate of fragments from centimetres to tens of metres, with bulk porosity between 30 and 50 percent. Until now, no one has measured which kind of object DART actually hit.

The momentum transfer itself is described by an equation that hides a great deal of physics. The change in Dimorphos’s orbital velocity is

Δv = (m_s × v_s + m_e × v_e) / (m_s + m_e + m_t)

For DART, m_s was about 580 kilograms, v_s about 6.6 kilometres per second, giving a momentum of about 3.8 megagram-metres per second. The orbital change was 2.7 millimetres per second, implying an effective momentum delivery roughly 3.6 times larger than the spacecraft alone would have produced. That factor, beta, is what Hera will nail down by weighing Dimorphos.

Hera will not prevent an asteroid impact. That is not the job. The job is to convert the most famous kinetic impact experiment in history from a single dramatic event into a calibrated engineering method. By mid-2027, planetary-defence planners will know, to within a few percent, how much velocity change a given kinetic impactor delivers to a rubble-pile asteroid of a given size and porosity, from direct measurement rather than extrapolation.

The November 2026 arrival is the moment the field stops being theoretical.