For forty years, Saturn’s north-pole hexagon was treated as a cosmic oddity without explanation — a six-sided jet-stream wave so geometrically perfect that scientists spent decades arguing over whether it could be natural. Now, researchers have confirmed that Saturn grew an equally massive polygon around its south pole while no spacecraft was watching, and the conclusion is unavoidable: the hexagon was never special. Saturn is simply a planet that makes geometric polygons.

That paradigm-shifting result — published in Science Advances on September 2, 2026, and this week presented at the 20th Europlanet Science Congress (EPSC2026) in The Hague, Netherlands — arrived alongside the first detailed chemical portrait of an interstellar comet observed by a fleet of 25 spacecraft, and with Europe and Japan’s first Mercury mission just ten weeks from its target orbit. For planetary scientists gathered this week in the hometown of Christiaan Huygens, the timing felt less like coincidence and more like a reckoning.

Saturn’s southern hemisphere dropped below the horizon of Earth-facing telescopes around 2012, the result of the planet’s axial tilt. It did not return to view until 2023. NASA’s Hubble Space Telescope, operating its Outer Planet Atmospheres Legacy (OPAL) program — an annual campaign that photographs the giant planets — captured the first images of the south pole when it reappeared.

Saturn Already Had Polygons We Couldn’t See

What the images showed stopped researchers cold. Embedded in a powerful southern jet stream at roughly 63 degrees south latitude was an undulating, dark band that, when processed into polar projections, resolved into ten vertices. A decagon. Citizen scientists Trevor Barry of Broken Hill Observatory in Australia and Jean-Paul Oger of the French Astronomy Association processed images from the Planetary Virtual Observatory Laboratory and spotted the signal in 2024 before high-resolution Hubble observations confirmed it fully in August–September 2025.

By then each side of the decagon already exceeded 16,700 km (10,376 miles) in length. For comparison, the entire continental United States measures roughly 4,500 km (2,800 miles) coast to coast.

“The discovery of the wave really did come as a surprise, as neither earlier images of Saturn taken by the Hubble Space Telescope nor those captured by the Cassini spacecraft, which orbited Saturn between 2004 and 2017, had shown it,” lead author Agustín Sánchez-Lavega of the University of the Basque Country said. The Cassini mission, which orbited Saturn for 13 years and ended in 2017 when it was deliberately crashed into the planet, had specifically searched for a southern counterpart to the northern hexagon. It found nothing — because the southern hemisphere was already tilting away from the sun when Cassini arrived, rendering the south-pole region poorly lit and difficult to observe.

The decagon is not a copy of the hexagon. The northern hexagon is essentially stationary, locked to Saturn’s interior rotation rate, with its center near the exact geographic pole. The decagon drifts eastward at approximately 10 km/h (6.2 mph), moves around the jet stream in which it sits, and is noticeably more asymmetric in brightness — more pronounced near a nearby anticyclone (a high-pressure vortex analogous to a smaller version of Jupiter’s Great Red Spot) and less distinct on the opposite side of the planet. Sánchez-Lavega’s team ran three distinct formation simulations. None could fully reproduce the observed decagon.

The significance, Sánchez-Lavega noted, is conceptual: the hexagon shows “the ‘unique’ hexagon is not as extraordinary as we thought.” What that means for planetary science is that Saturn’s jet streams apparently sustain large polygonal standing waves in both hemispheres, under different conditions, with different characteristics. The question has shifted from “why does Saturn have a bizarre six-sided anomaly?” to “what property of Saturn’s atmosphere generates this general behavior?” — a question that opens an entirely new line of atmospheric dynamics research.

What Is a Polar Polygon, and Why Does Saturn Make Them?

Planetary atmospheres routinely develop large-scale oscillations in their jet streams — a class called Rossby waves named for Rossby, a Norwegian-American meteorologist who described them in Earth’s atmosphere in the 1930s. On most planets, including Jupiter, these waves produce sinusoidal undulations rather than geometric shapes bounded by straight sides. Saturn appears to be uniquely capable of locking these oscillations into rigid polygonal forms, a phenomenon researchers believe is related to the extreme symmetry and stability of Saturn’s jet streams, though the precise mechanism remains unresolved.

The northern hexagon has been observed continuously since Voyager 1 and 2 imaged it in 1980 and 1981, and it has remained structurally stable for at least 45 years. The decagon, by contrast, appears to have formed sometime between 2017 and 2023, during the years the southern hemisphere was tilted away and unobservable. It may still be evolving. Its vertices were unevenly developed as recently as 2025. Whether it will persist, stabilize, or dissipate is unknown — and because Saturn currently has no orbiting spacecraft, that question will remain open until a future mission can watch the south pole directly.

A Fleet of Spacecraft Chased an Interstellar Visitor

The second headline result at EPSC2026 belongs to 3I/ATLAS — the third confirmed interstellar object to pass through the Solar System and the most extensively observed of the three.

Discovered on July 1, 2025, by the ATLAS (Asteroid Terrestrial-impact Last Alert System) telescope in Chile when the comet was still several AU from the Sun, 3I/ATLAS is a comet from another stellar system. Its hyperbolic excess velocity of approximately 57.9 km/s relative to escape — the speed at which it is traveling relative to the Solar System’s escape velocity — confirmed immediately that it originated outside our Sun’s gravitational sphere. Its two predecessors, the cigar-shaped 1I/’Oumuamua (2017) and the comet-like 2I/Borisov (2019), triggered global observing campaigns but were followed by handfuls of facilities. 3I/ATLAS mobilized 25 spacecraft.

That fleet included 11 interplanetary spacecraft, 8 solar probes and observatories, and 6 space telescopes. ESA’s JUICE spacecraft, en route to Jupiter, observed 3I/ATLAS in November 2025 as 3I/ATLAS departed the inner Solar System after its late-October 2025 perihelion. NASA’s Psyche spacecraft observed it in September and October. Five spacecraft orbiting Mars tracked it from the red planet’s vantage point. Europa Clipper, which launched toward Jupiter in 2024, joined the campaign during the mission.

On Monday at EPSC2026, Dominique Bockelée-Morvan of the Observatoire de Paris delivered the most comprehensive synthesis to date of those combined observations. Her central finding: 3I/ATLAS did not form around a star like our Sun. The comet’s isotopic signatures — particularly its deuterium-to-hydrogen (D/H) ratio and elevated carbon and nitrogen isotopic ratios — indicate it formed in a cold, distant, metal-poor galactic environment, consistent with an ancient planetary system that predates our Solar System. It appears to be a preserved relic, possibly billions of years old, from a planetary system orbiting one of the Milky Way’s earliest stars.

That conclusion builds on spectroscopic observations from the James Webb Space Telescope, which found 3I/ATLAS’s coma dominated by CO₂ before perihelion at heliocentric distances where water ice does not yet sublimate. Post-perihelion analysis has added detail: CO₂ enrichment approximately 4.5 standard deviations above what Solar System comets show, along with elevated carbon monoxide (CO) and organic molecule abundance. One prominent hypothesis holds that the comet’s outermost layers were chemically processed by galactic cosmic rays during its billions of years of travel through interstellar space, converting CO into CO₂ and synthesizing organic-rich surface material. If correct, current observations of 3I/ATLAS are sampling processed rind rather than the comet’s pristine primordial interior.

Early estimates of the comet’s nucleus diameter ranged as high as 20 km (12.4 miles), based on its brightness before detailed high-resolution imaging was possible. Later Hubble observations suggest the nucleus itself may be considerably smaller — a few kilometers or less — with the extended coma responsible for the object’s apparent size.

What Does 3I/ATLAS Tell Us About Other Stars?

The significance of a well-observed interstellar comet goes beyond the comet itself. Every atom and molecule in 3I/ATLAS’s coma arrived in our Solar System from another planetary system. Its chemical composition is a direct diagnostic of the environment in which its parent planetary system formed — the dust grain chemistry of a molecular cloud that collapsed into stars and planets around another star, possibly in the Milky Way’s thick disk, which is home to older stars formed when the galaxy was less enriched in heavy elements.

For context: ‘Oumuamua’s composition remained mysterious because it showed no coma — no gas or dust envelope — leaving astronomers with only its shape and anomalous acceleration to analyze. 2I/Borisov was compositionally closer to solar comets than expected. 3I/ATLAS is the first interstellar object large enough, active enough, and observed comprehensively enough to yield a genuine chemical fingerprint of another stellar environment.

How Quickly Life Arose on Earth: What That Means for Finding It Elsewhere

Friday — the congress’s closing day — will bring the week’s final major keynote from Stephen Mojzsis of Bayerisches Geoinstitut, whose talk addresses a different kind of discovery window: how quickly life emerged on Earth after the planet cooled, and what that window implies for finding life elsewhere.

Mojzsis’s framework draws on molecular clock analyses placing the Last Universal Common Ancestor (LUCA) — the ancestral organism from which all current life on Earth descends — at approximately 4.2 billion years ago, combined with isotopic biosignatures preserved in Hadean zircon crystals dating to 4.1 billion years ago and morphological microfossils at roughly 3.5 billion years. The RNA World — the era of life before DNA-based genetics, in which RNA molecules both stored genetic information and catalyzed chemical reactions — persisted for fewer than 130 million years between the emergence of LUCA and the transition to DNA-based life.

That is a narrow window by geological standards, suggesting that wherever the physical conditions for life exist — sustained liquid water, wet-dry cycling environments capable of concentrating organic molecules, crustal recycling to recirculate chemical energy — life may arise relatively quickly. The implications for the search for habitable exoplanets are direct: if 130 million years is sufficient for life to establish itself on a suitably equipped rocky world, then many of the candidate habitable-zone planets identified by current space telescopes may already harbor life at various stages of complexity.

Mercury in Ten Weeks: What BepiColombo Will Do There

BepiColombo — the joint ESA/JAXA mission that launched from Kourou, French Guiana in October 2018 — is now in the final weeks before becoming the second spacecraft in history to orbit Mercury.

On September 3, mission controllers confirmed that the spacecraft’s Mercury Transfer Module (MTM) successfully separated from the orbiter stack, beginning what ESA calls the “arrival phase.” The composite spacecraft is scheduled to enter Mercury orbit November 21, 2026, making it Europe’s first spacecraft ever to orbit the innermost planet.

The mission comprises two orbiters: ESA’s Mercury Planetary Orbiter (MPO), which will circle the planet in a 480 km × 1,500 km (298 × 932 mile) polar orbit with a 2.3-hour orbital period, and JAXA’s Mercury Magnetospheric Orbiter (Mio), which will occupy a broader 590 km × 11,640 km (367 × 7,231 mile) orbit to study the planet’s magnetosphere. The two spacecraft will separate from each other on December 9–10, 2026, and science operations will begin in April 2027 after instrument checkout.

Getting there required eight years and nine gravity assists — one flyby of Earth, two of Venus, and six of Mercury itself — plus sustained ion propulsion. Mercury’s proximity to the Sun creates extreme gravitational conditions that must be bled away slowly; a direct trajectory from Earth would require more fuel than any rocket can carry. The BepiColombo sessions at EPSC2026 this week represent the last major scientific community gathering before orbital insertion.

BepiColombo’s predecessor at Mercury, NASA’s MESSENGER spacecraft, operated from 2011 to 2015. BepiColombo’s two-spacecraft architecture will, for the first time, allow simultaneous measurements of Mercury’s surface, interior, and magnetosphere from different orbital geometries — data that MESSENGER could only approximate with a single instrument platform.

Venus and the Question That Won’t Let Go

Europe’s next major planetary destination after Mercury is Venus, and the EnVision mission received a significant status update at this week’s congress from ESA mission scientist Anne Grete Straume.

Adopted into ESA’s science program in January 2024, EnVision is under construction by Thales Alenia Space under a contract worth €367 million (approximately $423 million USD), signed in January 2025. The spacecraft is scheduled to launch in 2031, with science operations beginning in the mid-2030s after a 15-month cruise and an extended aerobraking phase to settle into a low polar orbit between 220 and 540 km (137 and 336 miles) above Venus’s surface.

EnVision’s instrument suite will map Venus from its inner core to its upper atmosphere simultaneously: VenSpec-U and VenSpec-H provide ultraviolet and infrared spectroscopy; VenSpec-M maps the near-infrared surface; and a Subsurface Radar Sounder (SRS) will probe several kilometers below the surface for evidence of subsurface structure, volcanic plumbing, and possible liquid reservoirs. A Radio Science Experiment will map Venus’s gravity field and probe atmospheric structure during radio occultations.

One significant update at EPSC2026: ESA announced this summer that it is opening a competitive Phase B1 process for a European Synthetic Aperture Radar (SAR) instrument. A NASA-provided SAR called VenSAR had been planned as a partnership contribution. The in-development European SAR would ensure EnVision retains its radar-imaging capability regardless of the status of that partnership. The ESA European SAR science team is being constituted in parallel.

The central question EnVision is designed to answer — why Venus and Earth, which formed at the same time from similar material in adjacent parts of the solar system, evolved so differently — has never had a mission capable of addressing it holistically. Venus Express (ESA, 2006–2014) studied the atmosphere. MESSENGER gave a passing look at the surface. EnVision will be the first mission to connect the planet’s interior structure, surface geology, atmospheric chemistry, and climate history in a single, multi-year observing program.

Oceans Under Ice, Life Under Ice

Alongside the headline results, EPSC2026 devoted sustained attention to the Solar System’s most promising habitats for extraterrestrial life: the subsurface oceans of the outer Solar System.

Enceladus, Saturn’s small moon, produces active plumes of water vapor, salt, silica nanoparticles, and complex organic molecules from a tiger-striped fracture system at its south pole — direct evidence of a subsurface liquid water ocean in contact with a rocky seafloor. Europa, Jupiter’s moon, is believed to harbor an ocean beneath a shell of water ice tens of kilometers thick; the depth and salinity of that ocean, and whether hydrothermal vents at its seafloor might sustain life, are key targets for NASA’s Europa Clipper, currently en route to Jupiter.

Flavio Petricca of JPL delivered Wednesday’s keynote surveying the state of knowledge on icy satellite interiors and what JUICE and Europa Clipper will reveal. Both missions are operating now. Their gravity, magnetic, and compositional measurements will yield unprecedented constraints on ice shell thickness, ocean depth, and water-rock chemistry at the ocean floors of Europa, Ganymede, and Callisto. A Wednesday session on JUICE-Europa Clipper scientific synergy examined how the two missions’ distinct orbital geometries can be leveraged together to extract information neither could provide alone.

A dedicated session also previewed NASA’s Dragonfly mission to Titan — a rotorcraft lander planned for launch in 2028 and arrival at Titan in 2034. Titan’s nitrogen-rich atmosphere, hydrocarbon lakes, and complex chemistry have long made it a candidate for prebiotic chemistry at low temperature. Dragonfly will move between landing sites, surveying the chemistry of Titan’s dunes, river plains, and impact craters in a search for molecular complexity relevant to the origins of life.

Community, Huygens, and the Next Generation

EPSC2026 is the first time the congress has been held in the Netherlands. That choice was deliberate. Christiaan Huygens was born in The Hague in 1629, and in 1655 he discovered Titan — Saturn’s largest moon — using telescopes of his own design, becoming the first astronomer to correctly describe the nature of Saturn’s rings. The week’s public program has placed his legacy at the center of the event: a self-guided Hague Planet Trail walks visitors to scale from the congress venue at Amare to the North Sea shoreline at Scheveningen, with the Sun at the front steps and Pluto at the beach.

“Hosting EPSC in The Hague provides a unique opportunity to connect the international community, but also to reflect on the history of planetary science,” said Dr. Sebastiaan de Vet and Prof. Dr. Inge Loes ten Kate, co-chairs of the local committee from TU Delft and Utrecht University respectively. “Christiaan Huygens’ discoveries fundamentally changed our understanding of the Solar System, which makes it an extra special meeting place to discuss the future of planetary exploration.”

“Around half of EPSC participants are students and early-career researchers, many of whom are attending their first international conference,” noted Anita Heward, Vice President of Europlanet. “So, in 2026, The Hague will play a vital role in ensuring Huygens’ legacy is passed to the next generation of planetary researchers.”

The congress closes Friday, September 11, with a morning keynote on abiogenesis kinetics and an afternoon session presenting the Saturn decagon results formally to the full congress.

(Exchange rate as of July 30, 2026; conversions are approximate.)

Frequently Asked Questions

What is the Saturn south-pole decagon, and how is it different from the hexagon?

The decagon is a ten-sided atmospheric wave embedded in a powerful jet stream at approximately 63 degrees south latitude on Saturn. Like the famous hexagon at Saturn’s north pole, it is a planetary-scale wave that gives the jet stream a polygonal shape rather than a smooth circular path. The key difference is behavior: the hexagon is nearly stationary and has persisted unchanged for at least 45 years; the decagon migrates eastward at roughly 10 km/h (6.2 mph) and is more asymmetric, possibly influenced by a nearby high-pressure vortex. Each side of the decagon already exceeds 16,700 km (10,376 miles). The decagon’s discovery proves that the hexagon was never a unique anomaly — Saturn apparently generates large polygonal structures in both hemispheres under the right jet-stream conditions. More detail is in the published study in Science Advances.

What did the fleet of spacecraft learn from 3I/ATLAS?

The 25-spacecraft campaign produced the most chemically detailed portrait of any interstellar object ever observed. Key findings include: the comet’s coma is unusually rich in carbon dioxide and organic molecules compared with Solar System comets; its isotopic ratios (particularly deuterium-to-hydrogen) indicate it formed in a cold, metal-poor galactic environment consistent with an ancient planetary system that predates the Sun; and its surface layers may have been chemically altered by galactic cosmic rays during billions of years of travel through interstellar space. Together, the data suggest 3I/ATLAS is a preserved sample of early planetary system chemistry from a part of the Milky Way more ancient than our own neighborhood. Full findings from the EPSC2026 conference program will be published in coming months.

When will BepiColombo reach Mercury, and what will it study there?

BepiColombo is scheduled to enter Mercury orbit November 21, 2026 — approximately ten weeks from the time of this article. Its Mercury Transfer Module successfully separated on September 3, 2026, beginning the arrival phase. Science operations will begin in April 2027 after the two spacecraft separate in December and complete instrument checks. The mission will study Mercury’s surface composition, geological history, interior structure, magnetic field, and magnetosphere — questions that MESSENGER (2011–2015) began but could not fully resolve with a single spacecraft.

What happens at the next Europlanet Science Congress?

EPSC 2027 will be held at the Pierre Baudis Congress Centre in Toulouse, France, September 19–24, 2027. Toulouse is home to CNES (the French space agency), Airbus Defence and Space, and major ESA facilities — giving the 2027 edition a particularly strong industrial and mission-development flavor. By that point, BepiColombo will have completed its first year of Mercury science operations, EnVision’s SAR instrument will be further into development, and Europa Clipper and JUICE will both be operating around Jupiter.