The solar system just got 100 new moons — and they rewrite a story we thought was finished

For four centuries, our map of the solar system was a map of the things that were easy to see. The big round moons. The bright planets. The famous rings. This week brought a reminder that the easy-to-see things were never the whole picture — and that the parts we missed may hold the more interesting story.

The moons that were hiding in plain sight

Beyond Jupiter, the solar system looks like a quiet backwater. The Sun is a cold white lamp; the planets are separated by gulfs of darkness so wide that light takes more than an hour to cross from Uranus to Neptune [18]. For a long time, that quiet seemed real.

It wasn’t. Astronomers now count more than 100 newly found moons that, until recently, were almost invisible — faint, fast-moving specks lost in their planets’ glare [18]. In 2025 alone, researchers announced 128 new moons around Saturn, pushing the solar system’s known total past 450 [18]. These aren’t worlds like ours. They are “irregular moons” — small, dark, misshapen lumps, often just a few kilometres wide, on tilted and sometimes backwards orbits [18].

The reason we missed them is simple and important: they were never bright enough for older telescopes to catch. An irregular moon is a small natural satellite captured from elsewhere, rather than one that formed alongside its planet — which is why its orbit is wild instead of neat. As cameras improved through the 2000s, astronomers started seeing smaller and smaller ones, and then last year the floodgates opened. “Everybody was surprised,” says Marina Brozovic at NASA’s Jet Propulsion Laboratory, the agency’s robotic-mission centre in California [18]. The expectation was a few dozen more; the reality may be thousands still waiting [18].

Here is why a pile of tiny moons matters. Their odd orbits and tendency to travel in loose family groups suggest they are fragments — the broken pieces of larger moons that smashed apart in collisions [18]. Read the fragments carefully and you can reconstruct the crash. And one new finding makes the crash recent. A team led by Edward Ashton at Academia Sinica in Taiwan modelled a cluster of about 100 small moons around Saturn, the Mundilfari group, and argued they formed in a collision just 100 million years ago — not in the solar system’s violent youth, but practically yesterday in cosmic terms [18]. “These collisional processes are still alive and well,” Brozovic said [18]. The outer solar system, it turns out, may still be reshaping itself.

There may even be a link to Saturn’s rings. Measurements from NASA’s Cassini probe, before it plunged into the planet in 2017, found the rings surprisingly clean and low-mass — too fresh to be billions of years old, perhaps only a few hundred million [18]. That age sits suspiciously close to the age of the new moon cluster, and researchers are now asking whether the same kind of recent smash-up that made the moons also made the rings [18]. None of this is settled. But it all comes from looking at objects nobody could see a generation ago.

A galaxy caught killing itself

A different kind of “what we couldn’t see” turned up in the early universe. Astronomers using the James Webb Space Telescope — NASA’s big infrared observatory — and ALMA, a giant radio array in Chile, found a galaxy in the act of strangling its own ability to make stars [8].

The puzzle is old: the early cosmos is full of massive galaxies that stopped forming stars far sooner than anyone expected, and nobody knew why [8]. The galaxy here, CRISTAL-02, seen as it was just a billion years after the Big Bang, is forming stars at twice the normal rate for its era — and pouring a vast wind of gas out into space at the same time, twice as fast as it builds stars [8]. “If this rapid blowout continues, the galaxy could be dead in less than 50 million years,” said lead author Rebecca Davies of Swinburne University in Australia [8]. The cause appears to be a galactic collision: gas funnels inward, stars form in a frenzy, the biggest ones explode as supernovas, and those explosions blast out the very gas needed for the next generation [8]. Roughly half of massive early galaxies were merging with neighbours, which means this self-destruct may have been common [8]. A long-standing mystery may have a natural answer — the galaxies lived fast and killed themselves young.

Routine, which is its own kind of news

Two stories this week are about reliability, not spectacle.

Japan’s space agency, JAXA, flew its H3 rocket successfully on Friday from the Tanegashima launch site, six months after a December failure [53]. That earlier flight lost a navigation satellite when a faulty payload adapter let it separate too early; the satellite burned up in the atmosphere [53]. This time the rocket — a new three-engine version — delivered all six of its small satellites to orbit cleanly [53]. A rocket that fails and then flies again is doing the hard, unglamorous work that turns a launcher into a dependable service.

In orbit, a quieter fix. Ten days ago, NASA briefly ordered its astronauts to shelter in a docked SpaceX Dragon capsule because of persistent cracks in a small section of the Russian part of the International Space Station [21]. According to sources cited by Ars Technica, the cracks have now been successfully sealed, ending a long behind-the-scenes dispute between NASA and Russia’s space agency over how serious the leaks were [21]. The station is more than 25 years old; keeping it airtight is becoming a steady job rather than an occasional one.

Meanwhile NASA named the four-person crew for Artemis 3 — a 2027 test flight that will stay in low Earth orbit and practise docking with prototype Moon landers, commanded by shuttle and station veteran Randy Bresnik [16]. Low Earth orbit is the band a few hundred kilometres up where the space station flies — high enough to circle the planet, far below the Moon. It is a step toward a landing, not the landing itself.

And one for the “we were astonished” file

Finally, the under-covered finding. A team studying how planets form ran the numbers on the chaotic regions around active supermassive black holes — the dense, turbulent discs of gas that feed the giant black holes at galaxies’ centres — and concluded that millions of planets could be born there [4]. “We were totally amazed when we noticed this mass and size range of planet formation,” one researcher said [4]. It is a model, not a sighting, and worlds orbiting a black hole would be strange places. But it is a reminder of the week’s theme: the universe keeps making things in corners we hadn’t thought to look.

• More than 100 newly found “irregular” moons — small, dark, easy to miss — have pushed the solar system’s known moon count past 450, and they hint the outer solar system is still being violently reshaped.
• A cluster of small moons around Saturn may have formed in a collision just 100 million years ago, and could be linked to the surprisingly young age of Saturn’s rings.
• JWST and ALMA caught an early galaxy blowing out gas twice as fast as it forms stars — a likely answer to why so many early galaxies died young.
• Japan’s H3 rocket flew successfully after a December failure, and the long-running cracks on the space station’s Russian section have reportedly been sealed.