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Why tornadoes touched down near New York City
Twisters don’t touch down in New York City often, but they can when the conditions are just right
NASA’s Artemis II Crew Set to Receive Congressional Space Medal of Honor
President Donald J. Trump will award each of NASA’s Artemis II crew members the Congressional Space Medal of Honor at 11 a.m. EDT on Friday, Aug. 28, during a ceremony at the agency’s Johnson Space Center in Houston.
NASA astronauts Reid Wiseman, Victor Glover, and Christina Koch, and CSA (Canadian Space Agency) astronaut Jeremy Hansen, completed a 10-day mission around the Moon on April 10. During a historic test flight as the first astronauts to fly aboard NASA’s Orion spacecraft, these crew members were the first to travel beyond the Moon in more than 50 years and traveled farther in space than humans have ever before.
NASA Administrator Jared Isaacman will join the President and astronauts in the awards ceremony.
The event will stream live on a variety of platforms. Learn how to watch online:
In addition to pooled media, limited media credentialing is available for this event. To apply, please submit your request online by 5 p.m. CDT on Tuesday, Aug. 25.
Learn more about NASA’s Artemis program on the agency’s website.
-end-
Bethany Stevens / Cheryl Warner
Headquarters, Washington
202-358-1600
bethany.c.stevens@nasa.gov / cheryl.m.warner@nasa.gov
NASA’s Artemis II Crew Set to Receive Congressional Space Medal of Honor
President Donald J. Trump will award each of NASA’s Artemis II crew members the Congressional Space Medal of Honor at 11 a.m. EDT on Friday, Aug. 28, during a ceremony at the agency’s Johnson Space Center in Houston.
NASA astronauts Reid Wiseman, Victor Glover, and Christina Koch, and CSA (Canadian Space Agency) astronaut Jeremy Hansen, completed a 10-day mission around the Moon on April 10. During a historic test flight as the first astronauts to fly aboard NASA’s Orion spacecraft, these crew members were the first to travel beyond the Moon in more than 50 years and traveled farther in space than humans have ever before.
NASA Administrator Jared Isaacman will join the President and astronauts in the awards ceremony.
The event will stream live on a variety of platforms. Learn how to watch online:
In addition to pooled media, limited media credentialing is available for this event. To apply, please submit your request online by 5 p.m. CDT on Tuesday, Aug. 25.
Learn more about NASA’s Artemis program on the agency’s website.
-end-
Bethany Stevens / Cheryl Warner
Headquarters, Washington
202-358-1600
bethany.c.stevens@nasa.gov / cheryl.m.warner@nasa.gov
SpaceX fires up Starship ahead of megarocket’s 1st orbital flight (video)
SpaceX is picking up the pace of preparations for the next launch of its giant Starship rocket.
On Wednesday night (Aug. 19), the company completed a single-engine static fire test with its Ship 41 vehicle, the upper stage that's in line to fly Starship's upcoming Flight 14 mission. As its name suggests, Flight 14 will be Starship's 14th test flight, but it will be the rocket's first launch into orbit, if all goes according to plan.
The recent engine burn was designed to prepare for that jaunt. "Starship completed a single engine static fire demonstrating a deorbit burn for upcoming orbital missions," SpaceX wrote in an X post on Thursday (Aug. 20).
SpaceX conducts a static fire test with Ship 41, the upper-stage spacecraft slated to fly Starship's 14th test flight. (Image credit: SpaceX)Video included in the post shows Ship 41 standing at SpaceX's Massey's test site, near the company's Starbase facility in South Texas. The clip shows the moment of ignition of one of the spacecraft's six Raptor 3 engines, which burns for approximately 15 seconds.
SpaceX followed up Wednesday night's test with a full six-engine test on Thursday (Aug. 20). That burn lasted approximately 60 seconds, as seen in video posted by the company the next day.
With the completion of Ship 41's first static fires, SpaceX could be on track to launch Flight 14 sometime in early to mid-September. However, there are still a number of prelaunch activities for the ship and its Super Heavy first-stage booster to clear before SpaceX will declare them launch ready, and, with Flight 14 tasked with placing Starship in orbit for the first time, the company is likely to be extra cautious.
Flight 14 will be Starship's third launch of 2026, and the third to feature the upgraded "Version 3" (V3) of the vehicle, which SpaceX introduced in May. SpaceX is also modifying a Starship V3 to dock with NASA's Orion spacecraft as a part of the Artemis III mission to Earth orbit next year.
NASA contracted SpaceX as one of two commercial moon lander providers for the Artemis program. The agency plans to land astronauts on the surface of the moon aboard a Starship lunar landing vehicle on the Artemis IV mission in late 2028.
SpaceX had apparently originally intended to attempt a return-to-launch-site recovery for Ship 41, but company founder and CEO Elon Musk recently said that milestone will now likely happen "in a few months."
Ship 41 will instead likely attempt a soft ocean splashdown at the end of its flight, and its Super Heavy counterpart, Booster 21, is expected to do the same. SpaceX has returned three of its Super Heavy boosters to Starbase for successful catches using chopstick-like arms on the rocket's "Mechazilla" launch tower, and it has managed to refly two of those. But a V3 Super Heavy catch has not yet been attempted.
Returning and reflying both Starship stages is a key component in SpaceX's design for the giant rocket, which will be the largest, most powerful launch vehicle in history once the company works out all its kinks. If it can, Musk said on a recent earnings call that he expects the rocket to launch "at least one flight a day, possibly more." In an Aug. 20 X post, Musk said SpaceX aims to support 30 Starship launches per day, or more.
'Dark stars' could be the seeds of supermassive black holes, scientists say
A mysterious hum of gravitational waves that fills the cosmos may be the echo of "dark stars" that served as the seeds of the first supermassive black holes.
These low-frequency gravitational waves were detected back in 2023 using an array of cosmic lighthouses, or pulsars, in a so-called "pulsar timing array." Pulsars are neutron stars that spin rapidly and regularly while blasting out collimated beams of radiation from their poles that can be used to detect tiny fluctuations in space and time. Such fluctuations are caused by the gravitational waves, or ripples in spacetime.
For a long time, the source of this particular low-frequency gravitational wave background has been somewhat shrouded in mystery, but scientists have hoped that they may be encoded with the secrets of the universe as it was around 13 billion years ago. Indeed, the team behind this research believes this hum of spacetime ripples could help explain how supermassive black holes grew so rapidly before the universe was even a billion years old. They link this solution to hypothetical supermassive "dark stars" that may have collapsed and died in the early universe to birth massive black hole seeds, giving supermassive black hole growth a head start.
"Dark stars were originally proposed as objects that might be seen directly at cosmic dawn," Ilie said. "This work points to a completely different way of testing their possible role in cosmic history," team member Cosmin Ilie of Colgate University said in a statement. "Their descendants could leave a gravitational-wave imprint that persists all the way to the present-day universe."
Cosmic clocks and collapsing Dark StarsPulsar timing arrays detect gravitational waves when their passage squashes and stretches space as the waves ripple past them, causing tiny delays in the pulsars' beams of radiation reaching Earth.
Detecting a gravitational wave background, however, required monitoring pulsar timing arrays for many years.
"Pulsar timing arrays are usually thought of as probes of supermassive black-hole binaries in the relatively recent universe," Ilie said. "What our work shows is that the signal may also contain information about how the ancestors of those black holes formed at cosmic dawn.
"In that sense, gravitational waves observed today could provide a new window onto the birth of the first supermassive black holes."
The currently favored explanation for this background is a cosmic history of binary black holes spiraling together before merging, particularly pairings with combined masses of over 1 billion times the mass of the sun.
However, that doesn't explain where these supermassive black holes came from and how the James Webb Space Telescope (JWST) is routinely detecting them before the universe was even 1 billion years old — despite the fact that the feeding and merger chains proposed to create supermassive black holes should take over 1 billion years.
Ilie and his Colgate University colleague Sohan Ghodla questioned if supermassive balck hole growth began with heavy seeds, and if these heavy seeds were created by the collapse of dark stars.
Dark stars are hypothetical primordial stars that, rather than producing energy through nuclear fusion, are instead powered by self-annihilating dark matter within their cores. As dark matter fuels these primordial stars, they would remain cool compared to other stellar bodies, allowing them to continue to accrete matter throughout their lives.
This process would continue until Dark Stars reached masses millions of times that of the sun and collapsed under their own gravity, creating massive black holes; seeds that collide and merge to form supermassive black holes.
Ilie and Ghodla modeled the environment in which the resultant black hole seeds would exist and merge, calculating merger rates and the influence on the gravitational wave background.
They found supermassive dark star remnants could indeed provide a major, perhaps dominant, contribution to the gravitational wave background detected in 2023. That means the measurements provided by pulsar timing arrays could help determine how abundant heavy black hole seeds were in the early universe.
"Produce too many of these massive seeds, and you end up over-producing the pulsar timing array-detected signal," Ghodla said. "Produce too few, and you need other sources to efficiently assemble these supermassive black holes later in the life of the universe to match pulsar timing array observations."
An illustration of dark stars in a halo of dark matter. (Image credit: Robert Lea (created with Canva))The key determining factor here would be the masses of the dark matter haloes in which the dark stars live and in which the heavy black hole seeds form.
Determining if the researchers' theory is correct may have to wait for improvements in pulsar timing array measurements of the gravitational wave background, along with a better understanding of populations of black holes and their characteristics in the early universe.
The team's research was published on Monday (August 17) in the journal Physical Review D.
SpaceX launches 29 Starlink satellites, lands rocket on ship at sea (video, photos)
SpaceX launched yet another Starlink mission today (Aug. 21), sending 29 more of the broadband satellites to orbit from Florida's Space Coast.
The spacecraft flew aboard a Falcon 9 rocket, which lifted off from Florida's Cape Canaveral Space Force Station today at 11:14 a.m. EDT (1514 GMT). That was a day later than planned; SpaceX scrubbed a liftoff attempt on Thursday (Aug. 20) for reasons that were not immediately clear.
The Falcon 9's first stage came back to Earth as planned today, landing about 8.5 minutes after launch in the Atlantic Ocean atop the SpaceX droneship "A Shortfall of Gravitas." It was the 30th liftoff and touchdown for this particular booster, which is designated B1078.
A SpaceX Falcon 9 rocket launches 29 Starlink internet satellites from Florida’s Cape Canaveral Space Force Station on Aug. 21, 2026. (Image credit: SpaceX)The Falcon 9's upper stage, meanwhile, continued hauling the Starlink satellites skyward. It will deploy the new batch into low Earth orbit 61.5 minutes after liftoff, if all goes to plan.
There are already quite a few operational Starlink spacecraft up there —nearly 11,000, in fact, according to astronomer and satellite tracker Jonathan McDowell.
The Falcon 9's first stage rests on the deck of a drone ship shortly after its touchdown on Aug. 21, 2026. (Image credit: SpaceX)Previous Booster B1078 launchesCrew-6 | SES O3b mPOWER-B | USSF-124 | Bluebird 1-5 | Nusantara Lima (PSN N5) | Starfall Demo | 23 Starlink missions
Today's launch was the 98th Falcon 9 flight of the year already. Seventy-five of them have been dedicated Starlink missions.
SpaceX also has three other liftoffs under its belt in 2026 — one launch of its Falcon Heavy rocket and two test flights of its Starship megarocket, which is still in development.
Why this El Niño will be the largest in living memory
A strengthening El Niño may surpass any seen since the 19th century and will usher in another record hot year or two
What you need to know about West Nile virus
The mosquito-borne illness has sickened hundreds of people this year
On this day in space! Aug. 21, 1914: Total solar eclipse expedition crashed by WWI
On Aug. 21, 1914, a total solar eclipse temporarily darkened skies across Europe and Asia. A young German astronomer and friend of Albert Einstein's, Erwin Finlay-Freundlich, led an expedition to the Crimean Peninsula of Russia, where he hoped to record observations that would verify Albert Einstein's general relativity theory.
This theory predicted that the light from distant stars appearing very close to the sun's edge should shift due to the curvature of space. Those stars would only be visible during a total solar eclipse, when the moon blocks out the sun's bright light. Unfortunately, the start of World War I just 20 days before the eclipse foiled the expedition. After Germany declared war on Russia, Freundlich and his colleagues were captured by the Russian army and their equipment was confiscated.
After the war, a solar eclipse on May 29, 1919 was used to confirm Einstein's theory of general relativity, so the experiment was ultimately a success.
The 2026 total solar eclipse. (Image credit: NASA/Keegan Barber)Why it matteredToday, Einstein's general relativity theory is a given. This theory is firmly cemented in our modern understanding of how the universe works (not counting fringe conspiracists). But looking back just over 100 years, it is interesting to see how hard scientists had to work to gather evidence to validate this theory and consider the way war and geopolitics played a part in postponing this work.
Scientists continue to validate the theory to this day through a variety of methods and observations, though a modern trek to witness a total solar eclipse would be a lot easier than it would have been in 1914.
This expedition, or rather the planned expedition, took place well over 100 years ago. Whether for the purposes of trying to validate Einstein's general theory of relativity or just for fun, people have experienced eclipses for as long as we can date back.
It's fascinating to look at the parallels between this planned expedition over 100 years ago and the treks that people around the world (including Space.com reporters) take in modern times to see a total solar eclipse. For example, during the 2026 total solar eclipse, people flocked from all over to locations like Spain and Iceland to experience the eclipse far from home.
Ancient stars dazzle in a celestial chandelier | Space photo of the day for Aug. 21, 2026
Stars scattered across the cosmos sparkle in the appropriately named Chandelier Cluster.
What is it?The Hubble Space Telescope captured this twinkling image of NGC 6723, or the Chandelier Cluster, a globular star cluster located 27,000 light-years away in our Milky Way galaxy.
Every bright spot in this mesmerizing cosmic chandelier is an individual star in the cluster. Globular clusters typically contain older stars. In fact, they're known to hold some of the oldest stars in the galaxy, with some being 10 billion years old or older. Globular clusters are thought to contain some of the first stars, or the oldest stars in the universe.
As their name implies, globular star clusters are groups of stars. But this particular type of star cluster isn't just full of ancient stars; it's also giant. Globular star clusters can contain tens of thousands to millions of stars. And just in our Milky Way galaxy, there are about 150 known globular clusters.
Why is it incredible?While this incredible image was captured by an ultra-powerful space telescope, backyard astronomers could spot the far-off globular cluster with binoculars or a telescope.
This type of star cluster is so visible because they are so massive and contain so many stars. With all those stars clumped together, even fainter globular clusters will typically be easier to spot than the smaller variety.
In fact, the Chandelier Cluster was discovered long before space telescopes were even a remote possibility. The cluster was discovered in 1826 by British astronomer James Dunlop.
For night sky enthusiasts, astrophotographers or casual skywatchers looking for this cluster, you can find it nestled in the constellation Sagittarius near the constellation Corona Australis. Have you ever spotted the Chandelier Cluster? Will you try to spot it now?
Watch Sophie Adenot’s second spacewalk live
After a successful EVA-97 on Tuesday 18 August, watch ESA astronaut Sophie Adenot venture into the vacuum of space for the second time on Tuesday 25 August, during EVA-98.
Week in images: 17-21 August 2026
Week in images: 17-21 August 2026
Discover our week through the lens
My favorite thing in the night sky appears on Aug. 28 — and it proves Earth is a sphere
What's your favorite thing in the night sky? Maybe it's the Pleiades, that sparkling open cluster that dominates winter in the Northern Hemisphere. Perhaps it's a sight of the Milky Way arching across the summer sky. Or could it be Saturn, a close-up sight of which has many people reaching for their wallets to buy a bigger telescope.
My favorite sight? It's us or, rather, our shadow. It's something that's only observable during a partial lunar eclipse — and there's one coming up very soon. Overnight on Aug. 27-28, an unusually deep partial lunar eclipse will be visible across Europe and North America, during which I will be watching Earth's shadow do something spectacular for precisely 3 hours, 18 minutes and 5 seconds.
A lunar eclipse happens when the sun, Earth and a full moon — in this case, August's Sturgeon Moon — line up closely enough for the moon to pass through Earth's shadow, a vast cone of darkness stretching away into space. Because the sun is a disk rather than a point of light, Earth's shadow tapers as it travels, narrowing like the beam of a flashlight in reverse. It creates two distinct shadows:
- Umbra: its dark inner section, which extends roughly 870,000 miles (1.4 million kilometers) into space, four times farther than the moon. Earth passes through it during a partial and total lunar eclipse.
- Penumbra: a paler outer shadow where Earth blocks only part of the sun. During a penumbral eclipse, the moon merely brushes this outer zone and often appears only subtly dimmed.
Those shadows create, in turn, three phases — penumbral, partial and total — as the moon passes through Earth's shadow. What we'll get on Aug. 27-28 is a penumbral phase, followed by a partial phase, followed once again by a penumbral phase. No totality, no drama? Not quite. During a partial lunar eclipse, part of the moon enters the umbra, allowing us to see the curved edge of our planet's shadow projected onto the lunar surface. It is one of astronomy's most direct visual proofs that Earth is a sphere.
During the Aug. 27-28 event, just over 96% of the moon will pass into the umbra, which is why it will look almost, but not quite, total. It may even make the moon look pinkish close to that maximum eclipse, because the umbra is not completely black. Sunlight bent and filtered through Earth's atmosphere leaks into the shadow, carrying the red-orange glow of every sunrise and sunset around the world.
Total lunar eclipses get the "blood moon" nickname, leaving partial lunar eclipses sounding like leftovers. But a deep partial eclipse can be stranger because one bright sliver remains outside the darkest part of Earth's shadow while the rest of the moon turns dim and rusty. You also get more of an impression of the moon moving slowly through a circular shadow in space.
The key sight during a partial lunar eclipse is the curved edge of Earth's shadow. (Image credit: Phil Walter/Getty Images)What's happening and when to lookNorth and South America get the best view. In North America, maximum eclipse occurs late on Aug. 27 in the west and around or after midnight on Aug. 28 farther east. Europe sees the eclipse before dawn on Aug. 28, with the moon low and setting during the later stages in many places. A clear western horizon will matter there.
Knowing the schedule is key. Punch in your location to Time Date, and you'll get timings for the eclipse's phases, with the partial phase the one to watch. For example, the partial phase in New York will begin at 10:33 p.m. EDT on Aug. 27, peak at 96% at 00:12 a.m. EDT on Aug. 28, and end at 01:51 a.m. EDT. In Los Angeles, it will be 7:33 p.m. PDT, 9:12 p.m. PDT and 10:51 p.m. PDT on Aug. 27. From London, it will be 3:33 a.m. BST, 5:12 a.m. BST and end as the moon sets at 6:15 a.m. BST on Aug. 28.
Expect an odd-looking "crescent moon" once the eclipse reaches 96%. (Image credit: Seung-il Ryu/NurPhoto via Getty Images)How and when I'm watching itThe beginner's mistake is to look at the maximum eclipse once and call that the event. Seeing and appreciating the curved edge of the umbra that reveals Earth's shape, projecting onto — and moving across — the moon, is what I'll be watching for. Every lunar eclipse quietly repeats the evidence: Earth casts a round shadow because Earth is round.
The best way to watch is with a telescope tracking the moon, so you can easily see the edge of the shadow creep across craters and maria, then recede over the 3 hours, 18 minutes and 5 seconds of partiality. I'll probably use my image-stabilized binoculars to give me a close-up, but this is a sight anyone can see easily and safely with the naked eye. Besides, the naked eye gives a better sense of the moon as a whole object entering a larger object's shadow.
You obviously need a clear sky to see it at all, but gaps in the cloud are fine — you only really need glimpses every now and then to get the full effect. If you're in a dark-sky park or somewhere away from light pollution, you may also see the Milky Way appear as the light of the full moon is temporarily flattened, but my favorite sight in the night sky will be far closer — the full moon slowly being marked by the planet I'm standing on.
Stargazer's corner: Aug. 21-27The bright moon dominates this week, growing from a thickening gibbous toward full, which is bad news for faint deep-sky observing. I would also not plan a serious Milky Way-hunting session this week — though it may be wise to be somewhere as dark as possible for the eclipse (though the shadow moving across the moon can be seen from everywhere, even in the most light-polluted cities). While you moon-gaze, keep an eye out for Saturn late in the evening and into the night (it will be to the upper-left of the eclipsed full moon), and half an eye out for late Perseid stragglers — particularly during the eclipse. That said, this is a week largely for waiting for the full moon to do its one slow, peculiar thing.
Constellation of the week: AquariusThe constellation Aquarius. (Image credit: E. Slawik/NOIRLab/NSF/AURA/M. Zamani)Aquarius is not the easiest constellation to love from a bright suburban sky. It is large, faint and not especially helpful if you expect constellations to resemble their names. But it matters this week because the full moon sits within it during the eclipse. To find Aquarius, look south to southeast in the late evening from the northern hemisphere, below the Great Square of Pegasus and west of the Summer Triangle. The easiest time to find it this week is probably close to the peak of the partial lunar eclipse, when Aquarius will surround a darkened moon.
‘Earth-like’ exoplanets may exist—but we don’t know of any yet
Claiming an exoplanet to be “Earth-like” is a trend that needs to bite the dust
What happened when people with anorexia tried magic mushrooms
Researchers are exploring whether magic mushrooms could offer a new treatment for anorexia
The national debt is $40 trillion. What does that mean mathematically?
An investigation into the incomprehensibly, unfathomably large amount of money the U.S. owes
Could 'dark photons' explain dark matter?
New research suggests that if dark matter is composed of "dark photons," it would not have heated the early cosmos like scientists previously thought. If correct, this discovery could represent a paradigm shift in the hunt for the universe's most mysterious stuff.
Dark matter remains so elusive because, despite outweighing the everyday matter that composes stars, planets, moons and our bodies by a ratio of five to one, it is effectively invisible. That is because it doesn't interact with light. And the fact that electrons, protons, and neutrons do interact with light (or, more accurately, electromagnetic radiation) has inspired the search for particles beyond the Standard Model of particle physics, leading to lots of hypothetical candidates for dark matter.
One of these candidates is the dark photon, the dark universe's version of a photon carrying a force other than electromagnetism, which is the responsibility of standard photons.
When dark photons have been considered in the past, scientists have concluded that they would have transformed into ordinary photons while still embedded in the thick and dense soup that filled the early cosmos. This would have further heated this already blisteringly hot plasma and left detectable traces of dark photons.
This severely limits the search parameters in which dark photons could exist — so much so that many cosmological observations rule out the existence of dark photons.
Now, new computer simulations show that the dismissal of dark photons may have been a little hasty. The conversion of dark photons to photons would have shut off before significant heating could occur.
That brings previously excluded search parameters back into play.
"These exclusions were saying the strength of dark matter had to be 10^8 times weaker than it actually can be," team member Anson Hook at the University of Maryland said in a statement. "This paper opens up a lot of new possibilities to look for dark matter."
An illustration of a dark photon, a candidate for dark matter. (Image credit: Robert Lea (created with Canva))The team behind this research first saw hints that the transformation of dark photons to photons may not be as straightforward as scientists had assumed when they realized the amount of energy involved is suspiciously large. The problem, they began to suspect, was the fact that this process had been considered to be linear; in other words, the energy released gradually and steadily converts to plasma.
"The treatment for the last 15 years is a linear treatment. If you use that approximation, you can compute the amount of energy transfer, and it's very large," team member Junwu Huang of the Perimeter Institute said in the statement. "And I realized it's not possible."
Performing their first computer simulations, Huang and colleagues realized that the linear process fails to paint a complete picture.
"What we realized is that, as you are converting energy into the Standard Model plasma, the plasma actually goes crazy," Huang said. "There are a lot of nonlinearities in the system, and these nonlinearities basically shut off the energy conversion after a tiny amount of energy is converted."
Dark matter seen at the center of a galaxy. (Image credit: Mattia Di Mauro (ESO/Fermi-Lat))The research represents a major widening of the parameters in which dark photons could exist, expanding this metaphorical hunting ground considerably. In fact, it could also impact the hunt for hypothetical particles beyond the Standard Model of particle physics.
"By calculating the early universe plasma correctly, experiments will probe new parameter spaces and potentially actually see something," team member Mohamad Shalaby of the Perimeter Institute said in the statement.
The team's research was published on August 13 in the journal Physical Review Letters.
This Week's Sky at a Glance, August 21 – 30
The waxing Moon is on its way to a not-quite-total lunar eclipse Thursday the 27th. On Friday the 21st, it's still east of Antares in the evening sky.
The post This Week's Sky at a Glance, August 21 – 30 appeared first on Sky & Telescope.
Sentinel-1 captures major ice loss from Greenland glacier
Europe’s Copernicus Sentinel-1 mission has captured a dramatic change at Petermann Glacier in northwest Greenland, where a 76 sq km section of the glacier’s floating ice tongue broke away on 4 August 2026.
The event marks the glacier’s largest loss of floating ice since 2012 and the most significant calving event in the Arctic since 2020 – revealing once again how rapidly Earth’s polar landscapes can change.