OrbitalHub

For most of the history of exoplanet science, planets that orbit their host stars in the wrong direction were curiosities reserved for the rare hot-Jupiter systems where gravitational chaos had clearly been at work. A team led by doctoral student Yann Carteret at the University of Geneva has now reported the first retrograde planet ever found around a small, cool red dwarf star, and the result has no obvious explanation. The planet, GJ 3090 b, is a sub-Neptune 73 light-years away in the southern constellation Phoenix, and it traces an orbit that runs opposite to the rotation of its host. For an M-dwarf system, that is new ground.

Why this matters comes down to a single number. The angle between a planet’s orbital plane and the equator of its star, called Psi by the people who measure these things, sits at roughly 136 degrees for GJ 3090 b. Anything over 90 degrees counts as retrograde. In our own Solar System, that angle is between three and seven degrees for every planet, and Mercury nudges a little higher but stays comfortably prograde. The handful of other misaligned systems spotted over the last fifteen years each had a massive companion on hand, another giant planet or a stellar partner whose gravity could tilt or flip a smaller neighbor’s orbit after the fact. GJ 3090 does not. The second planet in the system is too small to do that kind of work, and there is no sign of a stellar companion. Whatever put this world on its current path had to do so without the usual accomplices, which means the textbook explanations of misaligned hot Jupiters do not apply. The find, published in Astronomy & Astrophysics, forces the field to consider mechanisms that would otherwise be filed under unlikely.

The story begins with TESS, NASA’s Transiting Exoplanet Survey Satellite, which flagged GJ 3090 b’s shadow back in one of its southern-sector campaigns. A transit is the easy part. The hard part is figuring out which way the planet is moving when it crosses the star, because that is what tells you whether the orbit is prograde or retrograde. The team watched five separate transits with the NIRPS infrared spectrograph, an instrument built in Geneva and installed on ESO’s 3.6-metre telescope at La Silla Observatory in Chile. NIRPS is tuned to the near-infrared, which is exactly the part of the spectrum where a cool, dim red dwarf like GJ 3090 puts out most of its light, and where telluric absorption from Earth’s own atmosphere is least annoying.

What the team was after is a phenomenon called the Rossiter-McLaughlin effect. As a star rotates, the hemisphere spinning toward Earth is slightly blueshifted, and the hemisphere spinning away is slightly redshifted, from the regular Doppler motion of the stellar surface. When a planet transits, it blocks a small patch of that rotating surface. If the planet moves across the star in the same direction as the star’s spin, the planet first covers a blue patch and the star appears briefly redder, then it covers a red patch and the star appears bluer, leaving a characteristic bump-dip pattern in the radial-velocity curve during the transit. For GJ 3090 b, the team saw the order reversed on every one of the five transits, with the red patch covered first. The orbital obliquity they derived is 136 degrees, in line with the inverted transit shape, and consistent across nights. There is no ambiguity left in the geometry, and that is what makes the result clean.

The science and engineering of the result sit at the same intersection that has made red dwarfs the most-studied stellar hosts over the past decade. M dwarfs are smaller and cooler than the Sun, so a sub-Neptune-sized planet produces a deeper transit signal and a larger radial-velocity wobble per unit mass than the same planet would around a Sun-like star, but the wobble from a 2.2-Earth-radius, 4.5-Earth-mass world with a 2.9-day period is still small and the transit still short. NIRPS’s design wavelength range of roughly 0.95 to 1.8 micrometres lines up with the infrared peak of a cool red dwarf, and its stability across a single transit, and across five transits taken on different nights, is what allowed the team to distinguish a genuine 136-degree obliquity from a smaller angle buried in noise. Carteret and his co-authors, including Léna Parc and Vincent Bourrier at UNIGE, point out that GJ 3090 b is now the smallest exoplanet to have its orbital obliquity mapped around any M dwarf. The technical milestone is as important as the discovery itself, because it means the technique works on the kinds of planets that are most common in the galaxy.

What remains genuinely puzzling is the missing companion. In every previously known misaligned multiplanet system, the configuration can be traced to gravitational interactions with a much larger body, either a second giant planet in the same system or a binary star whose orbital plane pulled things off course over hundreds of millions of years. GJ 3090 has a second planet, but it is not massive enough to do that kind of work, and there is no sign of a stellar companion. The team’s favoured hypothesis is a primordial disk flip, the idea that after the original protoplanetary disk dissipated, a second, misaligned disk of gas and dust fell onto the star from the surrounding interstellar medium. If that second disk arrived at the right angle, the planets that formed inside it would inherit its orientation rather than the star’s. There is precedent in so-called Peter Pan disks, which survive far longer than standard disk-evolution models predict, around other young stars. GJ 3090 b might be a snapshot of what happens when one of those long-lived disks finally does form planets, and the planets turn out to be running around the wrong way, in the wrong direction.

The takeaway is that this is the kind of measurement that quietly resets how a discovery category gets built. Until now, retrograde exoplanets were a hot-Jupiter phenomenon with a tidy dynamical explanation. Now there is a sub-Neptune on a 2.9-day orbit around a small red dwarf, and the dynamical explanation has fallen away. NIRPS will keep taking data, and the same technique can be applied to any of the dozens of transiting M-dwarf planets already on the books. Carteret’s team plans to extend the survey, and at least one follow-up is already in the queue. Whether GJ 3090 b turns out to be a one-off oddity or the first example of a new population of backwards travelers around small stars is the question that the next year or two of observations will answer.

Roughly 300 light-years from Earth, in a part of the Milky Way that no catalogue has bothered to name, two objects circle each other every 86 minutes and 39 seconds. One is a small star, a red dwarf about 85 times the mass of Jupiter. The other is a brown dwarf about 25 times Jupiter’s mass, an object too heavy to be a planet yet too light to fuse hydrogen the way stars do. They orbit so close together that the entire configuration would fit inside the diameter of the Sun. And the smaller one has been quietly leaking material onto the larger one, at a rate slow enough that the larger object will be feeding on its neighbour for billions of years. The system, named ZTF J0440+2325, is described in a paper appearing today in Nature Astronomy by Aaron Householder, Kevin Burdge, and collaborators at MIT and partner institutions, and reported in a parallel MIT News feature by Jennifer Chu. It is the first confirmed case of stable, long-lived mass transfer from a substellar object onto a main-sequence star, and it pulls a tidy assumption about what happens to planets and brown dwarfs that end up too close to a star.

The tidy assumption is the swallow-engulfment model. When a planet, a brown dwarf, or any other substellar object drifts close enough to its host star, the standard picture is that the host tidally strips or disrupts it on a short timescale. The engulfed material gets swallowed and incorporated into the star, the companion disappears, and the binary turns into a single object with a slightly higher mass. This is the fate that astronomers have routinely inferred from observations of close white-dwarf and neutron-star binaries, and it is the fate that theory predicts for the Earth when the Sun leaves the main sequence in five billion years and expands into a red giant. The brown dwarf in ZTF J0440+2325 was supposed to be on the same conveyor belt, dragged inward by tidal friction and consumed on a timescale of thousands to millions of years. Instead, it is doing something much slower and stranger. It is leaking material onto its companion at a rate of about one hundred-thousandth of an Earth mass per year, a number the team works out in the Nature Astronomy paper using the photometric wobble of the binary and the assumption that the donor is overflowing its Roche lobe along the L1 Lagrange point. That is about 40 million dump trucks of material per year by the team’s own analogy, a quantity that sounds large but is a tiny fraction of the brown dwarf itself. The star will not run out of food before the Galaxy ages out from under it.

What the team saw first was the triangular waveform. The Zwicky Transient Facility, a wide-field optical time-domain survey that uses a camera on the 48-inch Samuel Oschin Telescope at Palomar Observatory in California, had been picking up a strange light curve from a star in Taurus for several years. Supernova light curves are bell-shaped: gradual rise, peak, gradual fade. Buried in the ZTF archive was a signal that did not look like a bell at all. It looked like a triangle, repeating on a period of about 87 minutes, with no counterpart at other wavelengths and no obvious explanation. Burdge, an assistant professor of physics at MIT who had been searching the ZTF data for periodic variables, noticed it during a search for a different kind of system. He originally suspected a “black widow binary,” the colloquial name for a millisecond pulsar that is slowly eroding a low-mass stellar companion with its particle wind and radiation. In a black widow, the optical light curve wobbles because the companion is being whipped around the much heavier neutron star, and the orbit usually shows a clean Doppler signature of that motion. The ZTF light curve did not wobble in the same way, which is what tipped the team off that the two objects were not a David-and-Goliath pair but a more balanced system in which neither dominates. Householder, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences, reanalysed the ZTF photometry and combined it with follow-up time-series spectroscopy. The wobble was small, the spectrum showed hydrogen and helium emission lines characteristic of an M dwarf, and the orbital fit locked the masses at roughly 85 and 25 Jupiter masses. The orbit fit inside the Sun.

The simulation work clinched the picture. Once the team had a mass, a radius, and an orbital geometry, the next question was whether the brown dwarf was overflowing its Roche lobe, the teardrop-shaped region of space around a body in a binary inside which material is bound to that body. If the brown dwarf were inside its Roche lobe, no mass transfer would be possible; the two objects would simply orbit forever without exchanging material. If the brown dwarf were overfilling the lobe, material would spill through the L1 point and rain down on the companion’s surface. The team ran a set of smoothed-particle hydrodynamics simulations with the measured masses, the measured orbital separation, and a brown-dwarf radius tuned to match the photometric brightness. The simulated test particles do not orbit the brown dwarf indefinitely; they stream across the L1 point and pummel the surface of the red dwarf at high speed. The team describes the geometry as more like an asteroid hitting the Moon than the usual accretion disk around a black hole or a neutron star, where material spirals inward through a flattened disk before settling onto the central object. In ZTF J0440+2325, the brown dwarf is too small for its own gravity to capture the inflowing material into a disk, so the stream lands directly on the surface and heats a roughly circular hot spot at the impact point. That hot spot is what produces the triangular waveform. As the brown dwarf orbits, the hot spot rotates in and out of view, and the system brightens when the hot spot faces Earth and dims when it faces away. The peak of the triangle is the moment of direct face-on view, when the impact fireball is brightest.

The mass-transfer rate is low enough that the system is genuinely stable on astrophysical timescales. Most binary mass transfer is unstable on some level: the donor shrinks as it loses mass, the orbit responds by widening or shrinking in ways that either accelerate or choke off the transfer, and the system either spirals toward a common-envelope merger or settles onto a longer-period detached configuration. What the simulations show for ZTF J0440+2325 is the rarer case in which the mass-loss timescale of the brown dwarf and the angular-momentum loss timescale of the orbit are tuned just right that the rate stays roughly constant for hundreds of thousands of years and may hold for the entire remaining lifetime of the brown dwarf, on the order of billions of years. The brown dwarf, as a substellar object, cannot fuse hydrogen and so does not have a main-sequence lifetime in the usual stellar sense, but it has a thermal-cooling timescale, and the team argues that the binary will outlive that timescale many times over. The brown dwarf will not be eaten quickly. It will be eaten slowly, continuously, and quietly, and the Galaxy will be a different place by the time the meal is finished.

What the team plans to look for next is more of the same. The triangle-shaped light curve is a distinctive signature, and the ZTF archive contains years of survey photometry that have not been systematically searched for it. The paper names a second candidate, ZTF J1444+4820, with an even shorter 67-minute period and a similar wobble signature. If that system confirms, the slow-eating configuration stops being a one-off and becomes a routine endpoint of binary evolution when the masses and separation land in roughly the right place. The triangular waveform, the small wobble, and the absence of a Doppler signature that would betray a heavy compact object are the three ingredients of the search. The same configuration, in principle, applies to small stars and giant planets, and the team plans to look for those as well. The conventional picture of close planetary companions has to share the page with a quieter alternative: a slow, steady meal that outlasts planets.

On 11 October 2026, NASA’s Perseverance rover rolled past a line nobody had crossed before. After 299.6 feet (91.31 meters) of driving on its 2,006th Martian day, the rover’s odometer read 28.10 miles (45.22 kilometers), nudging it 0.04 miles past the 28.06-mile (45.16-kilometer) total that Opportunity, its predecessor, had built up across nearly fifteen years of service on Mars. The new figure makes Perseverance the farthest-driven vehicle ever operated on the surface of another world, with margin enough that the gap will only widen as the rover keeps climbing the western rim of Jezero Crater. The number is small in absolute terms, a Sunday stroll in a city park would cover more ground, but on Mars the steps add up slowly, and the record has stood since 2018.

The reason this matters has less to do with the odometer than with what the odometer is measuring. Setting a distance record on another planet is not a vanity project. It is a budget statement: how much ground a mission can cover in a fixed number of sols, how many distinct outcrops the science team can visit, and how many rock and regolith samples the rover can collect before its hardware gives out. Perseverance has collected twenty-nine samples already, from an ancient lakebed at the bottom of Jezero, from a delta fan built by a long-vanished river, and now from the rim itself, where the geology changes character. Each new mile opens another valley, another ridge, another chance to find traces of ancient water chemistry that a stationary lander would never see. The original mission specification called for no more than 12.4 miles of driving. The team has now more than doubled the contract.

This is the fourth chapter in a thirty-year American experiment in mobile Mars geology, and each rover in the sequence has reset what counts as routine. Sojourner, the microwave-oven-sized cart that landed with Mars Pathfinder in 1997, rolled about 330 feet (100 meters) during an 83-sol mission before its solar panels gave up. Spirit and Opportunity arrived in 2004 with ninety-sol prime missions, and Opportunity, in particular, refused to stop. It crossed the first extraterrestrial marathon in 2015, logged 5,111 sols of operation, and racked up the 28.06-mile total that Perseverance just surpassed. Spirit covered 4.8 miles before getting stuck in soft soil and succumbing to a Martian winter in 2010. Curiosity, which landed in Gale Crater in 2012, is still working and has logged more than 23.65 miles (38.07 kilometers). The pattern is the same each time: longer missions, longer drives, and a better understanding of what the rovers can be trusted to do on their own. Perseverance also has the lunar record in its rear-view mirror, having already overtaken the 22.2 miles covered by the Apollo 17 astronauts in 1972 and the 24.2 miles racked up by the Soviet Union’s Lunokhod 2 rover in 1973.

The deeper reason Perseverance is pulling away is software. A navigation system called AutoNav lets the rover think while it drives, building a three-dimensional map of hazards on the fly and picking its own path between waypoints chosen by rover planners on Earth. The version flying on Perseverance is orders of magnitude sharper than the original AutoNav that flew on Spirit and Opportunity: where Sojourner evaluated the path ahead with twenty measurement points, Perseverance processes six hundred thousand of them each time it looks. Roughly ninety percent of Perseverance’s total driving distance has come under AutoNav, compared with about five percent for the earlier generation. The rover has covered as much as 1,351 feet (412 meters) in a single sol under AutoNav, a figure that would have been unthinkable during the Opportunity era. Steven Lee, the project manager for Curiosity and Perseverance at NASA’s Jet Propulsion Laboratory, called the milestone a privilege to be part of, noting that the original mission specification capped driving at 12.4 miles and that all mobility systems remain in good shape for many more years of record-setting. Mark Maimone, deputy team chief for robotic operations, said the team is not finished improving Perseverance’s driving: newer software teaches the rover to minimize steering, roll more, and cross-check its position against orbital maps mid-drive. The next engineering target is glare in the navigation cameras, which still forces the rover to stop driving by mid-afternoon whenever the Sun is ahead, and teaching it to look past those artifacts would give every future Mars rover a longer working day. NASA Science blog (12 Oct 2026), NASA JPL news (11 Oct 2026)

The science payoff from the extra mileage is already showing up. The record-breaking sol took place inside a strip of terrain nicknamed Lac de Charmes on the western rim of Jezero, an area of the crater wall the science team picked specifically because the rocks there are some of the oldest Perseverance will ever see, pieces of crust old enough that their Earthly equivalents have been erased by erosion and plate tectonics. Mars has no plate tectonics, so the equivalent record is still readable on the surface. The rover is heading toward an outcrop named Idubi, where it will look for evidence of ancient hydrothermal systems, the kind of mineral-rich, hot-water environments that on this planet often host the most interesting microbial communities. The earlier leg of the mission already produced one potential biosignature, at a rock called Cheyava Falls in the ancient river delta, and Lac de Charmes is a chance to test whether similar chemistry shows up in a completely different part of the crater. NASA approved Perseverance’s first mission extension this month, a commitment that will carry the rim work through roughly the end of 2028 and, after Lac de Charmes, toward Rainbow Falls, a 328-foot-wide (100-meter-wide) block of ancient crust that was shoved into place by the same impact that created Jezero in the first place. The image that the team released to mark the milestone is a navigation-camera frame from the record sol: a stretch of rocky Martian ground under a dusty sky, with fresh rover tracks curving off into the distance. It is a working picture, the kind of frame the navigation team uses to plot the next day’s drive, not a glamour shot from Mastcam-Z, and that feels right for what is being celebrated. As long as the wheels turn and the software holds up, the number on the dashboard will keep climbing, and the science team will keep pulling rocks out of rocks that have been sitting on the surface of Mars for four billion years. NASA Science blog (12 Oct 2026), NASA Mars 2020 mission page, NASA Photojournal PIA26812 (13 Oct 2026), Sci.News (Oct 2026)

In the last week of September, NASA’s X-59 Quesst flew six times in four days. Two flights on September 22, then two more on the 24th, then two more on the 25th. The previous best was four, so the team didn’t just break its own record; it lapped it. One of those flights also pushed the aircraft to Mach 1.53, roughly 1,010 miles per hour, the fastest the X-59 has gone in the year since Lockheed Martin’s Skunk Works rolled it out of the Palmdale paint shop (NASA Quesst blog, October 2 2026). The run brought the program’s total to 38 test flights, and the aircraft is now in a scheduled three-week maintenance stand-down before the next phase of envelope expansion.

The X-59 is, on paper, the most unassuming supersonic jet ever built. It has no forward windshield. It is shaped like a long black arrow with a 33-foot nose spike, the cockpit pushed so far back that the pilot flies by reference to an external vision system, a four-camera array feeding a single high-resolution display. The whole point of the thing is what it does not do: it is designed so that the shock waves it generates at cruise do not coalesce into a single audible boom when they reach the ground. NASA wants the on-the-ground signature to come in around 75 effective perceived noise decibels, a level the agency compares to a car door closing two houses down (NASA, Quesst: The Vehicle; Lockheed Martin X-59 product page).

The reason that number matters has very little to do with engineering aesthetics and everything to do with regulation. Civil supersonic flight over land is, with limited exceptions, banned in the United States under FAA rules that trace directly back to the sonic boom problem. The Concorde, which flew at Mach 2.02 over the ocean and on a few chosen overland corridors at subsonic speeds, retired in 2003 partly because its boom made overland expansion politically impossible. Twenty-three years later, no commercial airliner has flown faster than sound over the contiguous United States. The X-59 is NASA’s bet that a different shape can produce a different shock structure, and that if the shock structure is quiet enough, regulators will eventually rewrite the rule.

The hardware story begins in February 2016, when NASA awarded Lockheed Martin a preliminary design contract under the Low-Boom Flight Demonstrator program. In April 2018, the agency converted that study into a $247.5 million build contract, the largest single X-plane procurement in a generation. Skunk Works in Palmdale, California, did the structural work. NASA Langley ran an 8%-scale model through three weeks of wind-tunnel testing in late 2017, sweeping angle of attack out to 50° and 88° at low speed to map the static margin and dynamic response of the unusually long forebody. The critical design review closed in September 2019, construction crossed the halfway line in late 2020, and the aircraft was rolled out, fully painted, in January 2024 (Lockheed Martin X-59 Quesst, Wikipedia; NASA Quesst gallery).

The first flight came on October 28 2025, subsonic, out of Armstrong Flight Research Center at Edwards Air Force Base in the Mojave. The aircraft stayed subsonic through the early envelope, and on April 3 2026 the team flew wheels-up for the first time, reaching 20,000 feet and roughly 460 mph. The first supersonic run came on June 5 2026, and a week later, on June 12, the X-59 reached its design cruise point of Mach 1.4 at 55,000 feet. What the late-September record set adds on top of those milestones is volume: not a single new speed or altitude, but the demonstrated ability to turn an experimental one-off into something that flies like a working test article, twice a day, on back-to-back days.

The underlying physics the aircraft is built to exploit is called Mach cutoff shaping, and it is older than the X-59 by several decades. A supersonic aircraft generates two main shock waves, one from the nose, one from the tail, and in a conventional shape those shocks hit the ground as two closely spaced impulses that the ear fuses into a single boom. The trick is to design the airframe so that the upper-frequency components of the pressure signature are refracted upward by the natural temperature gradient of the lower atmosphere, never reaching the surface. The rule of thumb is that a ray of the shock will be turned away from the ground if the local sound speed increases faster than the local Mach number falls as the ray climbs. In practice, that means the X-59 has to be flown within a tight band of altitude and speed; outside that band, the rays bend back down and the boom returns.

The airframe itself encodes the same idea geometrically. The 33-foot nose is shaped to spread the nose shock over a longer distance, lowering its peak overpressure. The planform is built around a long, thin fuselage with a single low-sweep wing and a horizontal tail deliberately set high enough to keep the tail shock from merging with the wing shock. Wind-tunnel Schlieren imaging in 2018 confirmed the resulting pressure signature on the ground: a rise time of about 6 milliseconds and a peak overpressure of about 0.5 pounds per square foot, low enough that listeners describe the event as a thump rather than a bang (Sonic boom, Wikipedia, Mach cutoff references; CNN, August 6 2026).

The reason nobody has been able to demonstrate this in commercial service yet is the public response. A 75 EPNdB thump is in the same A-weighted decibel range as a dishwasher running in the next room, but supersonic cruise would put that thump over populated areas that have never heard anything louder than a turboprop. To find out what people actually think, NASA plans community overflight tests in 2026 and 2027, dropping F/A-18 Hornets into shallow dives from 50,000 feet to reproduce the X-59’s signature without the X-59, then asking residents to rate the noise. The agency needs that data to take to the International Civil Aviation Organization’s Committee on Aviation Environmental Protection, which sets the supersonic noise standard, and to the FAA, which would have to amend 14 CFR Part 91 to permit overland cruise. Without that amendment, an aircraft that thumps instead of booms is still illegal to fly over Denver.

The next three weeks of maintenance, after the record run, are scheduled around exactly that preparation. When the X-59 returns to the air, the team plans to expand the flight envelope further before the first community-response flights. Whether the data ultimately change ICAO and FAA rules is not a question the engineers can answer; they can only build the airframe that makes the question worth asking. The September record tells you how far that build has come: from a concept on a Lockheed whiteboard a decade ago, to an aircraft that can fly two missions a day for three days in a row, faster than any civil airplane has flown over the United States in a generation.

Two years after it left Cape Canaveral on a Falcon 9, the European Space Agency’s Hera spacecraft turned its main science camera toward the place it has been chasing across the inner solar system and saw, for the first time, what it came to see. Didymos appeared as a single bright pixel in a 1020-by-1020 image, surrounded by background stars that the camera was tracking to subtract out. The asteroid was 236,500 kilometers away at the time, far enough that the image looked almost like a software test pattern. The date was 7 October 2026, exactly two years after launch. The first braking maneuver, BRM-1, is scheduled for 15 October 2026, the mission’s 12 km/s relative velocity has been bleeding away in tiny burns, and full arrival at the binary system is planned for next month, almost a month earlier than the original timeline. The image, published by ESA in early October 2026, is the first resolved optical sighting of the asteroid whose small moonlet Dimorphos NASA hit with the DART impactor four years ago, and it is the start of the science campaign the whole mission was built around, covered in a fresh Universe Today feature by David Dickinson and in ESA’s own early-arrival announcement.

The reason Hera is going to Didymos is the question DART left open. In September 2022, NASA crashed a refrigerator-sized kinetic impactor into Dimorphos at roughly 6.6 kilometers per second, in the first deliberate attempt by any space agency to change the trajectory of a celestial body. The impact shortened Dimorphos’s 11 hour 55 minute orbit around its parent by about 32 minutes, a much larger change than the pre-impact models had predicted. The extras came from ejecta, the spray of rock and dust thrown off the surface at the moment of contact, which acted like an unpropelled rocket exhaust pushing the moonlet the other way. The pre-impact momentum budget was therefore incomplete, and the right number to plug into a future deflection plan depends on details that ground-based telescopes could not measure: the mass of Dimorphos before the hit, the size and depth of the crater DART carved, the porosity of the surface, the density of the interior. Hera’s job is to measure all of these, with enough precision that the next time the world considers deflecting a real asteroid, the engineers will know what the impact will do.

Hera almost did not happen. The original plan, in the early 2010s, was a joint ESA-NASA mission called AIDA, in which NASA would supply DART and ESA would supply an orbiter called AIM that would arrive at Didymos first and watch the impact happen in real time. ESA cancelled AIM in 2016 because the agency’s member states would not underwrite the cost, and for several years the only follow-up to DART was a network of ground-based observatories that the LICIACube flyby camera and Hubble time had to substitute for. ESA’s member states eventually funded a stripped-down replacement called Hera in 2019, and the agency awarded the prime contract to OHB in Bremen, with a launch contract to SpaceX. The spacecraft left Earth on 7 October 2024 from Cape Canaveral’s SLC-40, riding a Falcon 9 first stage, booster B1061-23, that had already flown 22 missions and was expended to give Hera enough energy for a direct transfer, as documented in the mission’s Wikipedia timeline.

The cruise was longer than a Mars transfer and shorter than a trip to a comet. Hera flew by Mars on 12 March 2025, using the planet’s gravity to bend its trajectory and align it for the Didymos encounter, and took the opportunity to image the smaller Martian moon Deimos from a few hundred to a thousand kilometers away, the closest observations of that body since Viking 2 in 1977. Those images later fed a Nature Astronomy study in 2026 arguing that Deimos is a rubble-pile body reshaped by an oblique impact of a 320-meter asteroid, useful as a sanity check on the radar instruments aboard the Juventas CubeSat. Through 2025 and the first half of 2026, the spacecraft’s flight dynamics team used Hera’s Asteroid Framing Camera, a pair of baffle-protected 1020-by-1020 monochrome sensors built by Jena-Optronik in Germany, to practice the eventual arrival on two main-belt asteroids, Otero and Kellyday, that happened to be near the spacecraft’s line of travel. Tracking Otero for three hours and the much fainter Kellyday in July 2025 taught the team how to keep a tiny, slowly-moving point of light centered in a camera designed to image objects thousands of times closer, in the camera test ESA reported in August 2025. In October 2025, with the cruise going smoothly, ESA announced that the arrival had been pulled forward by a month. In March 2026, Hera performed its largest single deep-space maneuver, burning 123 kilograms of hydrazine for a 367 m/s change in velocity. In June and July 2026 the flight software was upgraded, the asteroid phase began.

The arrival sequence itself starts with the first pixel and ends with a network of small spacecraft hovering above a pair of dark, fast-spinning rocks. On 2 October 2026, controllers executed a short test burn to verify the braking configuration. BRM-1, the first real braking maneuver, is set for 15 October 2026, two days after the publication of this post, and a series of further burns will put Hera into orbit around Didymos. From orbit, the spacecraft will map both bodies in detail. The Asteroid Framing Camera, working alongside the Thermal Infra-Red Imager TIRI and the Planetary Altimeter PALT, will return global shape models of Didymos at a few-meter resolution and a 10-centimeter view of the DART impact site, the first close-up of the crater NASA made. The HyperScout-H visible and near-infrared mapper will look for compositional fingerprints across the surface. A Radio Science Experiment will track Hera’s orbit closely enough to pin down the gravity field of the binary, which is the cleanest way to get the mass of Dimorphos and therefore the cleanest measurement of the momentum DART actually transferred.

The CubeSats will do the part of the science Hera cannot do from a safe orbit. Juventas, built by GomSpace in Luxembourg, carries a low-frequency radar called JuRa, a laser altimeter, and a gravimeter, the first radar sounder ever aimed at an asteroid’s interior, and the data it returns will tell the team whether Dimorphos is a uniform rubble pile, a fractured monolith, or a coherent body with a deep layer of regolith over a denser core. If conditions allow, Juventas will also touch down on the surface and use its accelerometers to measure the mechanical response of the regolith, the first in-situ measurement of asteroid surface stiffness. Milani, built by Tyvak International in Italy, is a hyperspectral imager that will survey the surface mineralogy of both bodies and characterize the dust around the binary. Both CubeSats will be released after Hera is in a stable orbit and will operate on their own for a few months before their trajectories carry them away. Once the science is done, the plan is to repurpose the mission as a software laboratory for autonomous deep-space operations, running new code on the spare core of the spacecraft’s LEON3 processor and using the binary system as a long-duration test bench.

The reason the planetary defense community is watching this closely is that the DART impact was a real-world test of a method that only existed in textbooks before 2022, and the textbooks are being rewritten. If Hera measures a momentum transfer close to the simple mass-times-velocity prediction, the kinetic-impactor method works about as well as the engineers hoped, and a future asteroid on an Earth-crossing orbit could be pushed off course with a single heavy spacecraft launched a few years in advance. If the momentum transfer is much larger, the ejecta boost is doing more of the work than the impactor itself, and the design of a real deflection mission should emphasize surface coupling rather than impactor mass. The point of Hera is to give the answer in numbers that can be written into a flight plan. Didymos, a 780-meter rock discovered by the Spacewatch survey in 1996 with a 151-meter moonlet found seven years later, is the laboratory. The first photograph of it from the spacecraft built to study it is, on its own, just a single bright pixel. The work begins now.

Two days after the UK Space Agency signed a contract worth around eighty million US dollars with the in-orbit services company ClearSpace, the post is still drawing puzzled responses from engineers who have watched ClearSpace miss one launch deadline after another. The October 15 award puts ClearSpace’s UK subsidiary in charge of the country’s first nationally commissioned active debris removal mission, called UK ADR, with the goal of capturing two defunct British satellites in low Earth orbit and pulling them down to burn up on a single flight. The contract is the largest piece of business yet for a company whose European Space Agency mission to grab a single space debris target has slipped from 2025 to 2029, and it lands on a small spacecraft stack whose design is still being finalised.

What the UK Space Agency has bought is a service, not a satellite. The agency will hand ClearSpace a list of two retired UK-licensed payloads, then wait while the company flies a robotic servicer to meet them, grapples each in turn, and drops them into the atmosphere in sequence. The contract covers everything from the design and build of the servicer, through ground test and qualification, to the launch, the rendezvous in orbit, and the final disposal burns. Space Minister Liz Lloyd described the mission as the first time any spacecraft will dispose of more than one satellite in this way, and UK Space Agency officials were careful to frame the work as a building block for a broader in-orbit servicing economy rather than a one-off clean-up job (GOV.UK, October 15 2026).

The deal matters because the amount of junk in low Earth orbit has been climbing faster than any country has been willing to clean up. Hundreds of thousands of tracked objects now whiz around the planet at closing speeds that can exceed seventeen thousand miles per hour, and every newly launched mega-constellation adds more mass to a regime that already bristles with abandoned rocket bodies, dead payloads, and fragments from past collisions. The standard response so far has been passivation, the practice of venting leftover fuel and disconnecting power on a dying spacecraft so it does not explode later, combined with rules that ask operators to remove their own hardware within five years of mission end. Passivation reduces future debris, but it does nothing about the cloud of derelicts already up there. Active debris removal, in which a separate spacecraft goes out and grabs the offending object, has been on every space agency’s wish list since the 1980s and on none of their budgets until very recently. A 2025 update to the UK National Space Strategy named in-orbit servicing, assembly, and manufacturing, abbreviated ISAM, as one of four priority areas, and the ADR mission is the first concrete contract to come out of that policy.

ClearSpace did not win the work uncontested. The UK Space Agency ran a competitive procurement in which three bidders responded: ClearSpace UK, Japan’s Astroscale, and the US-based Starfish Space. Astroscale has already completed a commercial active debris removal demonstration, the ADRAS-J mission that flew up to a Japanese rocket stage in 2024 and is still working through rendezvous operations. Starfish Space has flown the Otter pup-sized servicing vehicle on a 2024 orbital transfer test and is now building a larger vehicle called Bluebonnet. ClearSpace itself has not yet reached orbit on its own propulsion stage, having lost its original 2025 launch slot when the ESA payload it was sent to remove was struck by a fragment in 2023 and had to be swapped out for a different target (Behind the Black, October 16 2026, SatNews, October 15 2026). ClearSpace was nonetheless judged the strongest offer, in part because the capture architecture it has been building for the European Space Agency’s Proba-1 retrieval mission is the closest existing match to what UK ADR needs. The two retired UK satellites that UK ADR will go after have not been identified publicly, but both are non-cooperative, meaning they were never built with a grapple fixture or docking adapter, so the servicer has to deal with whatever geometry it finds.

The price tag, around sixty-one million British pounds, lands at the high end of what an active debris removal demonstration has ever cost. The contract is structured so that the money stretches from the present through a launch window that closes in August 2029, with the bulk of the spending sitting on integration, qualification, and operations rather than on the bus itself. ClearSpace UK’s Managing Director, Rob Atchison, framed the next phase in unusually direct terms, telling reporters that the program would hire engineers across several spacecraft disciplines, and that the team would design, build, and qualify a spacecraft capable of safely approaching an object never meant to be captured and bringing it under control. ClearSpace UK will manage industrial delivery and mission operations, targeting a 2029 launch from Saxavord Spaceport on Unst, a Shetland launch site that received thirty million pounds of UK government money in 2024 to keep Britain’s sovereign launch capability alive (GOV.UK, October 15 2026). If the schedule works, the servicer will share its ride to orbit with other payloads heading to low Earth orbit.

The way the servicer is meant to work is the part that has drawn the most attention from debris-removal engineers. After separating from its launch vehicle, the spacecraft will use autonomous rendezvous and proximity operations, the choreography of thruster firings, sensor reads, and trajectory corrections that brings one spacecraft safely next to another, to match orbits with the first derelict target. Once in close formation, a multi-arm robotic manipulator will reach out and clamp onto whatever structural feature the dead satellite offers, since neither target has a standard grapple point. With the first satellite locked in its arms, the servicer will fire its thrusters in the direction that lowers the combined stack’s perigee, the low point of its orbit, into the upper reaches of the atmosphere. The first derelict is then released onto a decaying trajectory that brings it down within months. The servicer, now lighter and carrying a full tank of propellant by design, raises its orbit back up, repeats the rendezvous with the second target, captures it, and brings it down the same way. The sequence is what makes this mission a world first rather than a duplicate of ClearSpace-1, which is only designed to retrieve one object.

The technologies the mission leans on have been in development for nearly a decade. The capture architecture descends from the design ClearSpace built under an ESA contract first awarded in 2019, which uses four robotic arms that wrap around the target like fingers closing around a pen. The rendezvous and proximity operations software draws on Phase 2 of the UK’s Clearing the LEO Environment with Active Removal study, abbreviated CLEAR, in which ClearSpace partnered with Orbit Fab to study in-space refueling and ran a long autonomous approach sequence in simulation. The refueling capability is what makes the spacecraft useful beyond one mission. UK ADR will fly with a refuellable propellant system the company intends to top up between flights, which is the only way a single bus can plausibly clean up more than a handful of derelicts over its lifetime. The wider ISAM sector the mission anchors includes satellite inspection, life extension through on-orbit refueling, and eventually on-orbit assembly of larger structures, with analysts at the UK Space Agency estimating that the segment could grow into a billion-dollar annual market by the mid-2030s (GOV.UK, October 15 2026, Via Satellite, October 15 2026).

Two years is not a long time to design, build, qualify, and launch a brand-new spacecraft, and the skeptics in the debris-removal community are easy to find. ClearSpace’s earlier deadline slippage, the 2024 management shake-up that pushed OHB into a majority role, and the parallel pressure of an ESA contract for a 2027 proximity-operations demonstration all have to resolve before the UK ADR launch window closes. If the company meets its 2029 target, the mission will hand the UK Space Agency the first operational data set on multi-target active debris removal in orbit and give ClearSpace the flight heritage its future servicing business depends on. If it slips, the contract is structured in phases that protect the UK taxpayer from paying for a bus that never flies, and the second target does not get removed.