OrbitalHub

Valles Marineris runs nearly 3,900 kilometres across Mars, reaches 600 kilometres wide in places, and drops more than nine kilometres from rim to floor. NASA calls it the largest canyon system in the solar system, and by the numbers it is not a close call: nearly nine times longer than the Grand Canyon, more than twenty times wider, roughly five times deeper (NASA, NASA Science). For most of the last two decades it has been treated as scenery, a feature that formed in the first billion years of Martian history and has been sitting quietly ever since. A paper published in Nature Communications on 15 October makes that assumption harder to hold. Jung-Hun Song of Imperial College London and colleagues report direct seismic evidence that the ground deep beneath the canyon is still moving, and that the structure controlling where it moves was inherited from the canyon’s own formation billions of years ago (Nature Communications).

The evidence comes from a single earthquake. On sol 976 of the InSight mission, 25 August 2021, the lander recorded an event its catalogue calls S0976a. It was unusual in two ways that made it useful. It arrived from the far side of the planet, roughly 146 degrees away, more than any other well-located marsquake InSight had found, and it was the only event in the mission’s catalogue that could be pinned to Mars’s western hemisphere. It was also puzzling. A seismic signal on Mars does not automatically mean a fault broke. Meteoroid impacts, landslides, and mass wasting all send vibrations through the crust, and the earlier analysis of S0976a had placed it near western Valles Marineris without settling on a cause. Nobody had shown that it was a marsquake at all, rather than something falling over.

Song’s team went back to the raw seismograms and asked what kind of motion would produce that signature. The answer turned on a problem of geometry. Working out how a fault ruptured normally requires many seismometers spread around the source, sampling the radiation pattern from many directions. InSight was one station, sitting roughly 8,000 kilometres away on the opposite side of Mars, so it sampled the pattern once, badly. The trick the team used is that seismic waves bouncing off the planet’s surface arrive as echoes, and each echo corresponds to a different angle between the wave and the surface it left. By jointly inverting the first-arriving P and S echoes, called PP and SS, the team recovered the fault geometry from a single station, validated first against a terrestrial event recorded the same way.

The solution is a predominantly double-couple strike-slip mechanism: blocks of crust sliding horizontally past each other on a steep fault. Across the acceptable solutions, 82.2 percent fall in the strike-slip family, with nodal plane strikes clustering around 48 and 143 degrees and dips steep enough to be nearly vertical. The best-fitting mechanism gives fault strikes near 60 and 330 degrees. The pressure axis sits roughly parallel to the canyon trough, the tension axis roughly perpendicular to it, which reads as horizontal extension across the canyon combined with shear along its length. Depth is the other half of the answer. The source lies in the middle to lower crust, above a Moho estimated at 55 to 65 kilometres beneath western Valles Marineris, with the allowed depth range running from about 20 to 40 kilometres depending on which interior velocity model is used. That is intact crust, not the loose material at the surface.

Rejecting the alternatives took as much work as finding the mechanism. The team ran impact-like explosions, single-force landslide models, and combinations of double-couple and non-double-couple sources, comparing each against the observed waveforms. None of the impact or landslide models reproduced the PP and SS arrivals. A landslide of the size needed to generate an event this big on Mars would have required a failure volume of at least 10 million cubic metres, which should have left a fresh deposit hundreds of metres to a kilometre across. The team checked every available post-event Context Camera image from the source region and found no fresh crater and no new collapse. The seismic data and the orbital imagery pointed the same way, which is what makes the result convincing rather than merely interesting: two kinds of evidence converging on one answer.

The geology says something the seismology alone cannot. Western Valles Marineris is crisscrossed by long-lived fault systems, and the stress orientation from the focal mechanism matches what those structures would experience today. Song’s team mapped faults, grabens, wrinkle ridges, and boulder-fall sites from high-resolution imagery and found a bimodal population of grabens with dominant strikes near 15 and 115 degrees, defining an orthogonal fault set. The P and T axes from the earthquake line up with those dominant trends. The best interpretation is slip on inherited fabric, not the creation of something new: the fault that broke in 2021 was already there, and the present-day stress field is now favourable for it to slip again.

What supplies that stress is a more open question, and the honest answer is a combination. Three sources are invoked. Long-term planetary cooling supplies a background horizontal compression, which no amount of waiting makes go away. Tharsis, the enormous volcanic rise west of the canyon, loads the lithosphere and flexes it, modifying both the magnitude and the orientation of the horizontal principal stresses. And the canyon itself, having been deeply incised, has unloaded the crust vertically, which reduces vertical stress and produces horizontal compression. At the source depth the basaltic crust carries lithostatic pressures of several hundred megapascals, a confining pressure that suppresses tensile opening and favours brittle shear failure instead. The paper is explicit that the relative contributions of flexural loading and dynamic support cannot be separated uniquely from this event alone.

Two results change what the data means beyond this canyon. The first is the aftershock question, and the answer is that InSight would not have seen one. The authors modelled aftershock production and wave propagation and found that ground displacements from a marsquake in western Valles Marineris would rarely exceed the ambient noise level at the lander, a consequence of geometric limits on long-distance propagation across Mars, including core shadowing. The probability of detecting even a single sizeable aftershock within 50 sols is 0.1 percent, which is a strange thing to have calculated, and I am glad they ran the numbers. The absence of follow-up events in the catalogue therefore says nothing about whether the fault is quiet, which is a limit of the instrument rather than of the planet. The second is the comparison across three regions. InSight’s seismograms now resolve three distinct styles of present-day deformation on Mars: strike-slip faulting beneath Valles Marineris from S0976a, compressional faulting in southern Elysium Planitia from S1222a, and normal faulting beneath Cerberus Fossae. Three different mechanisms in three different places means deformation is partitioned across a mechanically heterogeneous shell rather than driven by one planet-wide stress pattern.

The broader implication is about stagnant-lid planets, which is most rocky worlds. Mars has no plate tectonics; its outer shell behaves more like a single lid that cools slowly rather than recycling. Whether faults formed early in a planet’s history can stay weak enough to matter billions of years later has been argued about theoretically and never directly confirmed, because the geological record alone cannot distinguish a fault that reactivated today from one that has been dead since the Hesperian. A dated, located seismic event with a fault mechanism is exactly the missing measurement. Fault zones in a stagnant lid heal slowly, and stress fields evolve slowly, so the two together can keep old structures marginally close to failure indefinitely. The motion at the bottom of Valles Marineris is happening on the same fault that was already there when the canyon opened, under a stress field that has drifted slowly since.

Song put it plainly: “faults deep beneath the canyon can still slip and generate marsquakes” (Lamont-Doherty Earth Observatory, Columbia Climate School). The InSight mission ended in 2022 and its seismometer is off, but the recordings it returned are still producing results five years on. This one is the clearest evidence yet that a planet’s oldest fractures are still part of its present.

The day the captain left the bridge

I heard the news today, and I’m still sitting with it. Sir Patrick Stewart has died at 86. To the world he was many things: a Shakespearean actor, a knight, Professor X. To me, he will always be Captain Jean-Luc Picard first.

I first met him on the bridge of the USS Enterprise. I was 14 when I first watched The Next Generation. He didn’t swagger the way TV heroes usually did. He sat down, tugged his uniform straight, listened to his crew, and then made a decision.

Something about that calm made the stars feel reachable. Picard is the reason I started reading about real space exploration: rockets, orbits, probes, the people who actually build the ships. I know I’m not the only one. Today is a loss for a whole generation who looked up because a quiet man in a red uniform told us there was something worth finding out there.

More than a captain

Patrick Stewart was born in 1940 in Mirfield, a small mill town in West Yorkshire. His childhood was difficult, and he spoke openly about it later in life. He turned that pain into decades of public campaigning against domestic violence.

He found the stage young and never really left it. In 1966 he joined the Royal Shakespeare Company, and he spent years playing kings, villains and fools in front of live audiences. That training shows in everything he did afterwards: the voice, the stillness, the way a single pause could carry a whole scene.

In 1987 he was cast as Jean-Luc Picard in Star Trek: The Next Generation. Plenty of people doubted that a bald, middle-aged British stage actor could lead an American TV franchise. He proved them wrong across seven seasons and four feature films, and the show became one of the most loved in television history.

In 2000 a new generation met him as Professor Charles Xavier in X-Men, the patient teacher who believed people who were different deserved a place in the world. He played the role for nearly two decades, ending with a heartbreaking turn in Logan in 2017. In 2010 he was knighted for services to drama.

Then, at nearly 80, he did something few actors ever get to do. He came back to Picard in Star Trek: Picard, which ran for three seasons from 2020 to 2023. We got to see our captain grow old, doubt himself, and still choose to do the right thing.

What Picard stood for

Picard was a different kind of captain. He reached for diplomacy before phasers, and he treated every new species as something to understand rather than defeat. He read Shakespeare, loved archaeology, and listened to the people around him before he gave an order.

A few moments stay with me:
• The Measure of a Man. Picard defends the android Data in a hearing over whether he is property or a person. It is a courtroom drama about what makes a mind worthy of rights, and it feels more relevant every year.
• The Inner Light. A probe lets Picard live an entire lifetime on a dying planet in what is only minutes on the Enterprise. He comes back carrying a family, a community and a flute. It may be the best hour Star Trek ever made.
• Chain of Command. Captured and tortured, Picard refuses to say he sees five lights when there are four. It is a lesson in holding on to the truth when everything pushes you to give it up.

Even his catchphrases said something about leadership. “Make it so” meant he trusted his crew to carry out the plan. “Engage” meant the thinking was done, and now we go.

Above all, Picard showed that exploration could be a mature, curious, peaceful act. The point of going out there was never conquest. It was to learn, to meet others, and to come back a little wiser.

From the bridge to the launch pad

Star Trek has always had a habit of turning viewers into scientists. Engineers, astronomers and astronauts have said for decades that the show is why they first looked up. Mae Jemison, the first African American woman in space, credited Star Trek as an early inspiration, and she later appeared in an episode of The Next Generation, sharing the screen with Picard’s crew.

That loop between fiction and reality is the part of his legacy I care about most. Picard made the future look like a place you’d want to live: a place where curiosity was a career and science was something you did together. For a lot of kids, and a lot of adults, that was enough to start asking real questions.

For me it started small. I wanted to know how a ship actually gets to orbit, why some missions take years to reach their target, and who decides where we go next. One question led to the next, and space exploration became a lasting interest rather than a TV backdrop.

The real version is slower and messier than warp drive, but it is happening. Space telescopes are looking back to the earliest galaxies, robots are roaming Mars, and crewed missions are aiming at the Moon again. None of it is the Enterprise. All of it carries a little of the spirit Picard stood for: go carefully, go together, and go to learn.

Engage

It’s strange to grieve someone you never met. But Patrick Stewart spent decades in our living rooms, and for many of us he helped shape who we became. He gave us a captain who led with his mind and his conscience, and he showed us what a decent person in charge could look like.

The best way I know to honour him is to keep doing what Picard taught me to do. Stay curious. Listen before deciding. Treat the unknown as something to understand, not something to fear. And keep looking up.

Thank you, Sir Patrick. The bridge is quieter tonight, but the course you set is still laid in.

Engage.

Image: Patrick Stewart at the 2019 San Diego Comic-Con International. Credit: Gage Skidmore, CC BY-SA 3.0, via Wikimedia Commons.

A moon usually has a simple job description: it goes around a planet. The candidate announced this week in the CD-35 2722 system breaks that shortcut. It appears to orbit a brown dwarf, while the brown dwarf itself circles a small star. The outer object has at least the mass of Jupiter. The middle object is about 37 times as massive as Jupiter, too heavy to fit the usual planet category but too light to sustain hydrogen fusion like a star, according to the European Southern Observatory’s release.

That makes the system a three-level orbiting arrangement, but “exomoon” is not quite the right label. The authors of the Nature study call it a planetary-mass exosatellite and describe the result as evidence, not a final, uncontested discovery. That caution matters. The object was not photographed as a separate dot. Researchers inferred its pull from the motion of its brown-dwarf host.

Artist’s impression of CD-35 2722. The star is at left, the brown dwarf is in the foreground, and the newly found object is near the centre. Credit: ESO/M. Kornmesser. ESO image page.

Astronomers have found more than 6,000 exoplanets, but no moon orbiting one of those planets has been confirmed without serious dispute. A planet’s moon is smaller and fainter than the planet, and the planet is already lost in the glare of its star. The geometry makes the signal hard to isolate. In CD-35 2722, the host is a brown dwarf, which is dimmer than an ordinary star and can be observed directly with instruments built for high-contrast infrared work. That changes the observing problem, even if it does not make the interpretation easy.

The result also tests how useful familiar categories are. A moon-like object is defined by the body it orbits, while a planet is often defined by its mass, formation history, or the way it dominates its orbit. Those definitions work tolerably well in the Solar System. They become awkward when a Jupiter-mass body circles a brown dwarf. Calling it a moon describes its orbit. Calling it a planet describes its scale. Calling it an exosatellite avoids pretending that one word settles the physics.

There is a practical reason to care about the label debate. If this detection holds up, it gives observers a new class of target. They can search for satellites around directly imaged brown dwarfs, where the host’s spectrum is accessible and the companion’s gravitational effect may be measurable. The sample will be small, but the method is concrete enough to test.

CD-35 2722 is a star roughly half the Sun’s mass, located about 73 light-years away in the constellation Columba. Its companion, CD-35 2722 B, was directly imaged years ago and is a brown dwarf. The ESO team describes the brown dwarf as orbiting the star on a timescale of about 5,000 years, which means that the star and brown dwarf barely move across a human observing campaign. The newly reported object is the fast-moving part of the system: it circles the brown dwarf.

The researchers used the Very Large Telescope’s CRIRES+ instrument, a high-resolution infrared spectrograph. The observing programme monitored the brown dwarf from October 2023 through January 2025, according to the open version of the paper. The aim was to measure tiny changes in the brown dwarf’s radial velocity, the component of its motion toward or away from Earth.

A satellite changes that velocity because the brown dwarf does not sit perfectly still. Both bodies orbit their common centre of mass. If the satellite is on one side of that balance point, the brown dwarf moves slightly toward us; half an orbit later it moves slightly away. The resulting pattern is periodic. In principle, it is the same basic idea used to discover the first exoplanets around Sun-like stars, applied one level down to a brown dwarf and its companion.

The analysis found a periodic signal consistent with at least one planetary-mass body orbiting CD-35 2722 B. The Nature paper reports a Jupiter-mass exosatellite candidate. “Candidate” is doing real work here. A radial-velocity curve can be distorted by instrumental systematics, activity in the brown dwarf’s atmosphere, or an incomplete model of the system. The team therefore presents the finding as strong evidence rather than an official first exomoon announcement.

The system’s arrangement is unusual even before the terminology begins. The star is the largest body. The brown dwarf is a companion that formed or evolved in a regime between planets and stars. The outer body has the mass of a gas giant but occupies the satellite role. In our Solar System, Jupiter’s moons are far less massive than Jupiter. Here, the supposed moon may be a substantial fraction of its host’s mass, so the two-body orbit is better understood as a binary pair nested inside a wider stellar orbit.

Follow-up observations will have to answer several questions. Does the signal repeat with the same period? Can independent instruments recover it? Does the inferred mass remain stable when the orbit and brown-dwarf properties are fitted together? And can the system’s long-term dynamics keep the outer body bound while the brown dwarf travels around the star? A few clean observing seasons could do more for the claim than a louder headline would.

Radial velocity does not measure an object’s mass directly. It measures the line-of-sight speed of the body being observed. The mass estimate comes from fitting an orbit to the velocity curve and combining that fit with the host mass and orbital geometry. If the orbit is viewed nearly face-on, the true companion mass can be larger than the minimum value inferred from the measured wobble. That is one reason the paper uses language such as “at least as massive as Jupiter.”

CRIRES+ helps by spreading infrared light into a detailed spectrum. Molecules in the brown dwarf’s atmosphere absorb particular wavelengths. As the dwarf moves, those absorption lines shift through the Doppler effect. The instrument tracks the shifts against a wavelength reference, while the analysis separates the brown dwarf’s motion from the Earth’s motion and from the instrument’s behaviour. The expected signal is small, so many individual spectral lines can be combined to improve the velocity estimate.

The nested orbit adds another layer. The brown dwarf’s broad, slow motion around the star is nearly constant over the observing window, while the satellite’s motion should be much faster. A useful model must account for both. It must also distinguish orbital motion from changing atmospheric patterns. Brown dwarfs are not quiet, featureless balls of gas: clouds and temperature variations can alter their spectra. A signal that survives those tests is much more persuasive than a visually pleasing curve.

Stability is a separate engineering-style constraint. The satellite must remain inside the brown dwarf’s gravitational sphere of influence, often approximated by its Hill sphere, while avoiding an orbit so close that tides or disruption become dominant. The star’s distant pull sets the outer boundary. A long-lived configuration needs room between those limits. The reported architecture remains useful even if the object is eventually reclassified: it gives dynamical modelers a real system to stress-test.

The CD-35 2722 result is best read as a careful detection claim, not as the end of the exomoon hunt. Researchers have found a periodic radial-velocity signal in the directly imaged brown dwarf CD-35 2722 B, and the signal is consistent with a companion at least as massive as Jupiter. That is enough to make the system worth following. It is not enough to erase every alternative explanation.

The interesting part is the mismatch between orbit and category. The object behaves like a moon because it circles a brown dwarf. Its mass makes it look like a planet. The brown dwarf itself occupies the middle ground between planet and star. Nature has supplied a system that forces the vocabulary to catch up with the observations.

For now, “planetary-mass exosatellite” is the honest name. More observations will decide whether it becomes the first broadly accepted exomoon-like detection, or a well-measured example of how messy planetary systems can be.

The drawing is the concept schematic from Jahnke et al., taken from the open-access manuscript held in DLR’s electronic library.

On 15 December, ministers from ESA’s member states will gather in Rome to settle how Europe stays in low Earth orbit once the International Space Station is retired. NASA’s part of that timetable is fixed rather than debated: the agency has committed to operating the station through 2030 and has already picked SpaceX to build the vehicle that brings the whole structure down in a controlled manner afterwards, under a contract with a potential value of $843 million (NASA on the US Deorbit Vehicle selection). What is still open is whether Europe buys seats on someone else’s station or builds hardware of its own.

Eight years ago the German Aerospace Center had already drawn that station. The Orbital Hub concept, published in 2018 by Jahnke and colleagues in the system analysis group at DLR’s Institute of Space Systems in Bremen, describes a small modular outpost made of two elements: a base platform holding a permanent crew of three, and a laboratory that flies free of the crew for months at a time (Jahnke et al., Orbital Hub, CEAS Space Journal). The timing makes it more than a museum piece. The paper notes that moving between two crewed orbital platforms has historically taken 10 to 15 years, so a direction chosen in December 2026 is already late for hardware aimed at the 2030s.

ESA put three scenarios to its member states ahead of the November 2025 ministerial. The first leans on commercial stations flown by others, the second buys a limited amount of European hardware for use on those stations, and the third proposes a European-led outpost that accepts contributions from partners outside Europe. In September 2026, ministers meeting at the International Space Summit in Paris endorsed a call to boost European space exploration, naming three priorities: keeping European access to low orbit after the station, a stronger presence on and around the Moon, and using both as staging posts for eventual Mars missions. The argument for the third scenario is that Europe stops being an occasional passenger in someone else’s vehicle and starts owning it and keeping the keys.

Cargo is the unglamorous half of the answer, and it is already under contract. At the same Paris summit, ESA signed a service deal with The Exploration Company worth €760 million for its Nyx capsule, with €310 million set aside for a demonstration flight to the ISS and two optional service missions worth €450 million still to be confirmed. The company covered 40 percent of the demonstration through private investors, with ESA taking the remaining 60 percent under the ALADDIN programme, whose name spells out autonomous docking to an ISS node (ESA on the ALADDIN contract). ESA framed the award as the first and largest capsule transport contract it has handed to a European company, and the agency is now preparing options for ministers to weigh in Rome (ESA media invitation for the December ministerial).

How the DLR concept was built matters as much as what it proposed. The system analysis group started from the science community rather than from hardware, running a workshop to collect research requirements and defining strawman payloads from the result. Those fed concurrent engineering studies in which industry engineers and flown astronauts sat alongside the analysts, refining a first draft design day by day until the requirement set and the layout were consistent. The character of the station comes straight out of that requirement list. One entry states that no spacewalk should be needed for assembly or operation, with EVA reserved for contingency cases alone. Another caps the free-flying element at under 5 metres in diameter, 15 metres long, and below 19,000 kg at launch, the mass a single Ariane 6 flight was assumed to lift.

The base platform carries the people: a service module supplying 30 kW of electrical power, a docking node with five ports, and an expandable habitat built on Bigelow Aerospace’s BA-330 for three crew. The second element, the Free Flyer, holds the more interesting decisions. It is a pressurised laboratory wrapped around an external platform, roughly the size of a Kibo module with its exposed facility, and it flies on its own for about three months before returning to dock for a fortnight of servicing and payload exchange. That separation is the point of the whole design. Crew activity generates vibration and air currents, and a laboratory that leaves the crew behind can hold microgravity quality near one millionth of a g while remaining serviceable by the same people who visit the station. The heritage behind it is deliberate and named in the paper: the pressurised section is based on Columbus with a shortened length, the rendezvous sensors and the reaction control thrusters come from the European ATV cargo ship, and the external truss borrows from Kibo and the ISS structure. A seven degree-of-freedom robotic arm with roots in DLR’s DEOS programme rides a circular rail around that truss to move payloads out of the airlock and onto the platform.

The engineering numbers are where the cost argument hides. Mass across all of the parts came to roughly 60,000 kg, launchable in three flights, with the base platform itself weighing 65 tonnes at 30 kW of power, a little over 15 percent of the station’s in-orbit mass and about a quarter of its electrical budget. The authors compare that to the ISS in 2000, when Zarya, Unity, Zvezda and the first truss element together reached about 60 tonnes with 17 kW, and argue the comparison holds for the functions that matter: crew living, life support, power, attitude control and docking. Propulsion is where the Free Flyer is both clever and awkward. It carries four 400 newton chemical engines and 24 thrusters of 220 newtons each for agility, with tanks for about 760 kg of bipropellant, enough for one complete free-flying phase including rendezvous and docking. The electric system uses RIT ion thrusters in the 10 to 130 millinewton range, and the paper estimates that 660 kg of xenon would cover the vehicle’s 15-year life. Refuelling those high-pressure tanks in orbit is not a solved problem, and the authors say so, offering exchangeable tanks handled by the robotic arm, on-orbit servicing, or shorter free-flying periods as the ways out.

The cost estimate came by analogy first, borrowing the ISS figure of 80 million dollars per tonne and landing on 5.1 billion dollars for the base platform, dropping to 3.5 billion if the habitat module is bought rather than developed. A bottom-up estimate for the first flight hardware put base platform development at about 2,220 million euros and the Free Flyer at 530 million euros, roughly 2.8 billion euros for the pair. The authors then draw the uncomfortable conclusion: that total is more than half of ESA’s entire budget for 2017, which is why they argue the concept cannot be built by Europe alone.

That is the question now in front of ministers. ESA selected Airbus Defence and Space and OHB in late September to run parallel feasibility studies on the third scenario, with six additional industrial and institutional partners the agency did not name (European Spaceflight on the study awards). ESA has asked both consortia to draw on European hardware heritage, including the Columbus module and the European Service Module built for Orion, and to deliver a minimum viable product rather than a full station. A SpaceNews report puts the ceiling at €1 billion for each three-year block of development funding, with development limited to two such periods. Whether the Orbital Hub drawing ever becomes hardware is doubtful: its three-launch layout predates the commercial stations now in the pipeline, and its price tag was set in 2016 euros. What survives is the requirement set it produced, and those are the requirements the current studies keep restating: a small crew, autonomous systems doing the servicing, no routine spacewalks, and hardware that separates crew time from payload quality. Europe has to pick between buying seats and owning a vehicle on 15 December. The blueprint for the vehicle has been sitting on a shelf for eight years.

A star that would look green if you stood on a planet beneath it sounds like the kind of object that should not exist. The colours a star shows in the night sky are set almost entirely by temperature. Cool stars glow red, stars like our Sun glow white, hot stars glow blue, and the hottest of all glow a faint violet at the edge of vision. Green sits in the middle of the visible spectrum, but stellar blackbody curves tend to slide through it on the way from orange to blue without ever pausing there. For more than a century, the quiet compact rule “stars are red, orange, white, or blue, and that is the list” has been a piece of astronomy no one had to defend, because no counterexample ever showed up.

On 15 October 2026, Mark Hollands at the University of Warwick and three collaborators broke the rule. In a paper titled “Any colour you like: the diverse chromaticities of white dwarfs,” Hollands and his co-authors report the first known star that would actually look green to a human standing underneath it, and at the same time identify what is probably the reddest star on record, a deep salmon-pink white dwarf only 48 light years from Earth that pushes the chromatic boundary in the other direction. A preprint of the paper has been on arXiv since the same day. The work turns on a method that sounds obvious in hindsight but had not been done at scale before: take a high-quality stellar spectrum, feed it through a model of human colour vision, and see what comes out.

The green object is a cool white dwarf called WD J1330+6435, sitting roughly 280 light years away in the constellation Draco. It is about 4,000 degrees Celsius at the surface, which on its own would make it look orange. Instead, in the team’s modelling, it glows a ghostly chartreuse. The reason is chemistry rather than physics in the usual sense. The atmosphere of a cool white dwarf can reach a density close to one gram per cubic centimetre, comparable to water and millions of times denser than the Sun’s photosphere. Under those conditions, trace metals behave very differently than they do in ordinary stellar atmospheres. Sodium, calcium and lithium pulled in from a long-disrupted planetary system absorb light across a much wider range of wavelengths than they would at lower densities. In WD J1330+6435, sodium draws a broad V-shaped valley centred near 600 nanometres that swallows yellow, orange and red. Calcium adds a deep notch at 400 nanometres that takes out some of the blue. Lithium adds a thin gap near 670 nanometres. What survives between those three absorptions is mostly green. Hollands told a University of Warwick press release that the experience of standing beneath such a star would feel like “something out of science fiction,” and that no other star, living or dead, has been credibly reported as green before.

To put that result on a solid footing, the team did not stop at one object. A white dwarf is the exposed core of a Sun-like star that has shed its outer layers. There is no fusion happening any more; the object is a cooling cinder, dense as a planet, slowly dimming over billions of years. The earliest examples astronomers found were the brightest and hottest of the population, glowing white or pale blue, and that is how the whole class got its name. Cooler white dwarfs are dimmer and harder to spot, so for most of the history of the field they have been undercounted. Hollands and his co-authors, Boris Gänsicke and Pier-Emmanuel Tremblay at Warwick plus Detlev Koester, set out to ask a simple question that turned out to have a complicated answer: what colours would white dwarfs actually show if we could see them up close? For the 151 white dwarfs within 20 parsecs, or roughly 65 light years, of the Sun, the team measured a median correlated colour temperature of about 6,800 Kelvin, which is exactly the white of a standard computer display. Most stars, Hollands noted, behave like “perfect radiators,” so their colour is set almost entirely by temperature, and the local sample of white dwarfs obeys that rule on average. The textbook picture that white dwarfs look bluish is, the team argues, a selection effect. Surveys that pick up the faintest sources in the sky are biased toward the hotter, brighter white dwarfs that can be seen from far away. The local sample is dominated by cooler, dimmer ones, and those look, on average, plain white.

Roughly five out of those 151, around three percent, looked nothing like a blackbody. Two glowed yellow and three glowed pink. When the team broadened the search to known white dwarfs across the rest of the sky, the outliers became more vivid. WD J1330+6435 is the chartreuse green star described above. A second star, WD J1011+2845, only 48 light years from Earth in Leo, is the reddest star ever recorded. Its atmosphere has a deep convection zone that has reached the helium-dominated core, lifted carbon up to the surface, and let it form C2 molecules. Those molecules absorb blue, green and yellow so heavily that almost everything that leaves the star is squeezed into wavelengths longer than 600 nanometres, the deep salmon end of the visible spectrum. A third star, WD J2356-2054, looks vivid blue even though its surface temperature is only about 4,000 Kelvin. The mechanism there is different again, hydrogen molecules colliding with helium atoms in the dense atmosphere, and the team flags it as one of the bluest cool stars known. The pattern that emerges is that white dwarfs split into a few colour families tied to what is in their atmospheres: carbon-rich ones lean pink or purple; stars that have swallowed rocky debris from old planetary systems lean yellow, orange or green depending on which metals dominate; mixed hydrogen-helium atmospheres with their own peculiar chemistry tend toward cyan or pale blue. The reason this matters for the rest of astronomy is that the colour is a reading of what the star has eaten. White dwarfs that show metal absorption lines in their atmospheres are, by definition, white dwarfs that have been pulling in the rocky leftovers of their former planetary systems. Polishing the colour, this new paper shows, can pinpoint which elements they have been consuming and how recently. WD J1330+6435 is a fossil of a planetary system that has been mostly devoured, and the green glow is the colour of those remnants, briefly visible in the atmosphere of the star that ate them. The same approach can in principle be extended to the cooler white dwarfs being catalogued by Gaia, which should turn up more coloured outliers in the years ahead. Across the Milky Way’s full census of several billion white dwarfs, the team’s estimate of one unusually coloured star in thirty is a small fraction per object but a very large absolute number. The day Gaia’s pipeline finishes classifying the nearest few hundred cool white dwarfs, several dozen more greens, pinks and blues are likely to come out of the noise. Standing on a planet in the WD J1330+6435 system, looking up at a green sun, would not be science fiction at all. It would simply be Tuesday.

A comet is a bad neighbour for a telescope built to stare at distant galaxies. Fixed light holds still inside an exposure. Comets do not. They smear a short streak across the detector, drag stray light into frames that were supposed to be empty, and complicate somebody’s photometry. Euclid was built to do the opposite. ESA’s dark Universe mapper sits at the second Sun-Earth Lagrange point and spends its nights holding position on patches of sky far beyond the Milky Way, measuring the shapes of galaxies with a precision the atmosphere never allows from the ground.

On 8 October 2026, the Minor Planet Center confirmed an object nobody had reported before, found by that telescope. C/2026 S1 (Euclid) is the first new comet Euclid has ever discovered, according to the agency’s announcement of the discovery.

There is a practical reason to care that a Solar System object turned up in a deep-space survey. Euclid’s science case rests on cleanly separating fixed sources from everything else. A comet trail crossing a galaxy image is a contaminating streak that has to be identified and masked, and a mask applied carelessly biases the weak lensing measurement the entire mission is built around. Every moving thing in the field gets accounted for, whether the team set out to look for it or not. There is also an older reason. Comets are leftovers from the Solar System’s formation, around 4.6 billion years old, arriving from the Kuiper Belt and the distant Oort Cloud. They have been altered very little since they formed, so the ices and dust they carry are a sample of the raw material that built the planets, including much of the water that ended up on Earth.

The detections came out of Euclid’s Deep Field North, in the constellation Draco, across a run of images taken between 16 and 24 September 2026. That field was chosen partly because it overlaps a region the now-retired Spitzer Space Telescope surveyed in infrared, a detail Universe Today reported on the discovery. Euclid caught the object in five separate fields of view, two to four exposures each, for 16 exposures in total.

Mikko Pöntinen, a PhD student at the University of Helsinki, wrote the software that caught it. He developed a moving-object detection tool to search Euclid images for small Solar System bodies, and it flagged a streak smeared across several frames. Predicting where the object ought to turn up next, he located it again in other image sets. Closer inspection turned up a fuzzy envelope around the point source, the signature of something actively shedding dust and gas rather than a solid rock. Pöntinen and the Solar System Objects Science Working Group of the Euclid Consortium checked the position against catalogues of known comets and asteroids. No match. He reported the observations to the Minor Planet Center, the global clearing house that collects reports from observers, confirms discoveries, computes orbits and assigns designations. Ground-based astronomers picked up the alert and contributed follow-up, and on 8 October the centre confirmed it as a comet. The designation C/2026 S1 follows standard convention, with the S marking a September discovery and the comet named for the telescope that found it.

At roughly 1.3 billion kilometres from Earth, the comet sits about where the Sun would be if you placed it halfway between the orbits of Jupiter and Saturn. Its orbit is the odd part. Most small bodies travel close to the plane the planets occupy. This one does not. It approaches from high above, and ESA describes the path as one that will take thousands of years to complete. The orbital period will be refined once more data has been collected. That geometry explains how the discovery happened at all, and it happened partly by luck. Euclid deliberately avoids the band of sky lying along the Solar System plane, where dust scatters sunlight into the optics and wrecks deep exposures. Finding new Solar System objects is harder for this telescope than for almost any other in service. Archive Scientist Bruno Altieri said very few comets are expected to turn up in Euclid data, and called the capture a happy coincidence of the comet’s orbit and the telescope’s scanning pattern across those particular days. Project Scientist Valeria Pettorino added that while this comet is not a suitable target for ESA’s planned Comet Interceptor mission, the discovery and the alert that followed give the two mission teams a real case study in how they would coordinate.

Two design decisions shaped what was possible. The first is Euclid’s observing strategy. It works step-and-stare: settle on a target, take the exposures, slew to the next position, do not come back. Each piece of sky gets visited once. For a fixed galaxy that is fine. For a moving comet it means a discovery has to be stitched together from unrelated snapshots taken at different points in the orbit, and confirmed by prediction rather than by simply looking again at the same spot. The five-field, 16-exposure recovery is a reconstruction from fragments. The second is scale. The visible imager is a mosaic of 36 CCDs, each with more than 4000 pixels a side, giving roughly 600 megapixels total, and it covers about half a square degree at a time, the area of two and a half full moons, across wavelengths from 550 to 900 nanometres, as ESA describes the instrument. The consortium specifies the field of view as 0.57 square degrees sampled at 0.1 arcseconds across a 609-megapixel array. Those numbers matter for the detection, because a comet at that distance is not a bright object. It registered as a faint smudge in a frame built to see galaxies looking back close to ten billion years. There is a third reason the find matters beyond curiosity. Comets and asteroids crossing Euclid’s fields are contaminating data as well as discoveries. The team’s job is to identify every moving object, work out where it should have been, and subtract it. Doing that well enough to also notice a fuzzy envelope around one of them is the same detection pipeline doing two different jobs at once.

Euclid has been working at L2 since 2023, partway through a planned six-year survey of roughly a third of the sky, and it is expected to measure more than a billion galaxies. It found a comet anyway. Not because it was hunting one, and not because dark Universe observatories are good comet hunters, but because a PhD student’s software was watching for streaks in the data as routine housekeeping. More finds like it are plausible. The consortium team already had to detect known comets in Euclid frames before this one turned up, and every streak lifted out of a galaxy image is a streak somebody examined closely. The orbital period of C/2026 S1 is still open pending more measurements, and there is a fair chance the follow-up community revises the initial description before the numbers settle.

The discovery will be archived under a name that will not change: C/2026 S1, the first comet Euclid found, in a survey pointed deliberately away from it.

Image: Comet C/2026 S1 (Euclid) in Euclid VIS data, 20 September 2026. Credit: ESA/Euclid/Euclid Consortium.