The Ten Most Significant Science Stories of 2025, From Medical Breakthroughs to an Interstellar Visitor
Every December, Smithsonian magazine’s science team picks which stories were the year’s most significant. We look for a broad set of topics that captured the public’s imagination or that fit in with trends that will affect us far into the future—and overall shape how we remember the year.
And when people look back on 2025, the stories below will loom large—but the year will also stand out as one that brought new challenges for scientists across disciplines. Researchers saw cuts in federal funding to universities, including the termination or freezing of more than 3,800 grants awarded by the National Science Foundation (NSF) and the National Institutes of Health. A New York Times investigation reported increased competition among scientists for the limited grants that were available. NASA, the National Oceanic and Atmospheric Administration, and the Environmental Protection Agency, among other agencies, also saw cuts to staff and budgets.
These policies represented a departure from how science was funded by presidential administrations since World War II, as Laura Dattaro reports for Chemical & Engineering News. “I personally know many scientists in my field leaving the United States altogether,” Kevin Johnson, a former program director at the NSF’s geosciences directorate, told the New York Times.
Scientific discoveries this year demonstrated the importance of continuing to examine the world that surrounds us, from cosmic objects to the human body to prehistoric remains.
This year, people shared rare videos that captured a meteorite striking the ground and an earthquake fault in motion. Scientists drilled some of the oldest ice ever recovered, researched a cancer blood test and identified the pathogen behind a devastating decline of sea stars. Astronomers surpassed 6,000 confirmed exoplanets, and a new observatory unveiled its first space photos. Rock fragments offered tantalizing evidence that humans set the first deliberate fires roughly 350,000 years earlier than thought.
Distilling 12 months of ingenuity, journal publications and aha moments into a list of ten blurbs is never an easy task. This year, we selected stories that span outer space, health, genetics, conservation, technology, paleontology and human origins—and each one of them grabbed our attention.
Here are Smithsonian magazine’s top ten most significant science stories of 2025.
Doctors extended patients’ lives with organ transplants from animals
More than 100,000 patients in the U.S. are on the waiting list for an organ transplant, and 13 people die each day without having received the needed surgery. The vast majority—about 90,000 Americans—are waiting for a kidney. Now, with a shortage of human organ donors, doctors are starting to look at pigs, which have metabolisms, immune systems and organ sizes that resemble our own.
In January, surgeons performed the fourth transplant of a gene-edited pig kidney in the U.S. The patient, Tim Andrews, lived with the pig organ for a record-breaking 271 days, before it failed and was removed in October. While taking strong drugs to prevent organ rejection, Andrews got a reprieve from dialysis for much of this year—and, as a living symbol of hope for other patients in need of kidney transplants, he threw the first pitch at a Boston Red Sox game.
The U.S. Food and Drug Administration recently approved trials of pig kidney transplants from two biotechnology companies, giving the green light for these procedures under “compassionate use.” This allows patients with life-threatening conditions to access experimental treatments when they don’t have other options. Separately, in October, scientists in China reported a successful transplant of a portion of a pig liver, which they removed after 38 days.
Human bodies try to reject transplanted pig organs, because the immune system targets the foreign sugar molecules in the animal tissue, ultimately leading to blood clots and death of the organ. That’s why scientists make gene edits to the organs before transplanting them—and why transplant recipients take immunosuppressant medicines.
However, in a November study conducted with a brain-dead patient whose body had been donated to science, researchers successfully prevented pig kidney rejection twice, administering medicine to restore the kidney’s function each time. The team chose to end the experiment after 61 days. But these recent steps forward promise to open new avenues for treatment that improve the quality of—and ultimately extend—patients’ lives. —Carlyn Kranking
Our third known interstellar visitor, comet 3I/ATLAS, made a rare dash through the solar system
3I/ATLAS made its debut on July 1, when a NASA-funded telescope in Chile, part of the Asteroid Terrestrial-impact Last Alert System (ATLAS), spied the comet in the night sky.
Because of its high speed of about 137,000 miles per hour—too fast to be following a closed orbit around the sun—astronomers immediately suspected the object had come from beyond the solar system.
That makes 3I/ATLAS our third known interstellar visitor, after 1I/‘Oumuamua, discovered in 2017, and comet 2I/Borisov, found in 2019. Over the past six months, researchers have uncovered fascinating details about the solar system’s current guest.
The Hubble Space Telescope revealed that the comet’s solid, icy core—called a nucleus—might be between roughly 1,400 feet and 3.5 miles wide. Surrounding that nucleus is a glowing cloud of gas and dust, or coma, with unusual chemistry.
The teardrop-shaped coma contains nickel, but no iron, according to observations by the Very Large Telescope in Chile. The two metals are usually intertwined, so the findings hint that nickel can come from some unknown chemical process. Additionally, data from the James Webb Space Telescope suggests the coma contains a lot of carbon dioxide relative to its water vapor content. The odd chemical composition of 3I/ATLAS could give clues about where it was born and the elusive conditions of interstellar space.
NASA spacecraft on or near Mars—including the Perseverance rover—captured the closest images to date of 3I/ATLAS, when it passed the Red Planet at a distance of about 19 million miles in early October.
The comet made its closest approach to us on December 19, when it was roughly 170 million miles from Earth, almost twice the distance between our home planet and the sun. In March 2026, 3I/ATLAS will zip by Jupiter before bidding adieu to the solar system forever. —McKenzie Prillaman
Scientists created genetically engineered “dire wolf” pups in de-extinction stunt
For more than 10,000 years, Earth has been devoid of the dire wolf—a long-extinct canid that chased down prey during the Pleistocene. But in April, a biotech company claimed it had created the first modern dire wolves: two males named Romulus and Remus, born in October 2024, and a female, Khaleesi, born in January of this year.
The startup, called Colossal Biosciences, aims to “bring back” extinct species by editing key genes of a close living relative. In this case, they sequenced the dire wolf genome from a 13,000-year-old dire wolf tooth and a 72,000-year-old dire wolf skull, then identified 14 genes that differ between the extinct animal and canids of today. They made 20 changes to the DNA of a gray wolf to create some physical traits of a dire wolf: bigger teeth, larger size, a wider head and white fur. Scientists placed the edited genes into domestic dog eggs, then implanted them into surrogate dog mothers.
Still, no matter how you look at them, the adorable animals in the viral video are not true dire wolves. Scientists pointed out that their genetic code is still that of a gray wolf with a handful of tweaks. And although Colossal notes the gray wolf is the dire wolf’s closest modern relative, the two aren’t that similar—a 2021 study found that the dire wolf isn’t technically a wolf at all and suggested the creature should belong to a different genus than the wolves and dogs of today.
“De-extinction” research, including Colossal’s parallel efforts for the dodo, the woolly mammoth and the thylacine, has drawn ethical criticisms as well, with some conservationists suggesting funding should go toward protecting existing species. But at an international convention in October, conservation leaders discussed how editing the genes of organisms—a field known as synthetic biology, which includes much more than just de-extinction work—might be used to save today’s species or improve human health. They voted to allow this type of research to move forward. —C.K.
Once thought to be a teenage T. rex, a “Dueling Dinosaur” is named Nanotyrannus
Though the prefix “nano” doesn’t sound like it should describe something anywhere near as large as many dinosaurs, research this year suggested a fossil of a small tyrannosaur might belong to a proposed species called Nanotyrannus lancensis.
The fossil in question, found in 2006 in Montana, is part of an assemblage known as the “Dueling Dinosaurs” that also contains the bones of a Triceratops, and the two creatures appear to be fighting. It may help settle a decades-long debate about whether N. lancensis is a unique species or simply a misclassification of juvenile Tyrannosaurus rex fossils.
A close examination of the tyrannosaur, published in Nature in October, unveiled key features that distinguish the skeleton from a T. rex.The fossil had fewer tail vertebrae and more teeth than T. rex did and was lacking the short arms T. rex was known for, instead featuring long, powerful forearms.
The researchers measured the growth rings found in the skeleton’s leg bones, revealing the animal was about 20 years old when it died and that it had finished growing—casting doubt that it could be a juvenile.
This year’s Nanotyrannus news is the latest chapter in a long debate about the smaller skeletons. In the 1980s, researchers examined a previously studied fossil and reclassified it as the first potential Nanotyrannus lancensis. Some scientists pushed back on the claims, saying it was a teenage T. rex instead.
But a December study in Science took a closer look at a neck bone from that original fossil and found more evidence in favor of Nanotyrannus. The team examined the microscopic anatomy of the bone to show that the skeleton was fully grown when it died—and yet, it didn’t rise close to the size of T. rex.
Together, these findings could mean that paleontologists don’t have a clear picture of what a juvenile T. rex looks like, potentially upending research on the growth and biology of the species. —Marta Hill
Canada lost its measles elimination status, and the U.S. could be next
On November 10, Canada was stripped of its measles-free designation—and, as a result, the Pan American Health Organization declared that the Americas, as a region, had lost its measles elimination status. (Individual countries retain their own designations.)
For more than 12 months, the highly contagious measles virus has been spreading between people in Canada. The outbreak began in October 2024 after the virus jumped from an infected international traveler, and this year, more than 5,300 confirmed or probable measles cases cropped up in the country.
Measles is caused by an airborne virus that spreads when an infected person breathes, coughs or sneezes. It can remain in the air for two hours, and up to nine out of ten unvaccinated people who are exposed to the virus will catch it.
While no measles-specific treatments exist, the measles, mumps and rubella vaccine—typically given to kids—is extremely effective and protects against measles for life. But vaccine hesitancy has been growing, especially since Covid-19 emerged, and in a sign of the trend, U.S. government health advisers suggested rolling back a longstanding recommendation for childhood vaccination against hepatitis B in December, despite strong objections from the medical community.
When it comes to measles, experts warn the U.S. could soon follow in Canada’s footsteps. Measles has been running rampant in the country since January, largely because of an outbreak that began in West Texas. As of December 16, nearly 2,000 confirmed measles cases have been reported across 43 states in 2025. And although the West Texas outbreak was declared over in August, outbreaks in neighboring states could be connected. If they are, the country has until late January 2026 to stop the spread to avoid being stripped of its own measles elimination status, which it has held since 2000. —M.P.
Fossil skulls might have finally revealed what Denisovans looked like
Denisovans, early humans first discovered in 2010, share a common ancestor with both Neanderthals and modern humans. But scientists have come to know them primarily from genetic data, because their intact fossils are mostly just bone fragments and teeth.
This year, analyses suggested two ancient skulls might have belonged to Denisovans, shifting our understanding of how we evolved from our ancestors—and what some of those ancestors looked like.
In June, two studies, one in Science and one in Cell, analyzed a well-known 146,000-year-old skull called the Dragon Man, with flat cheeks and prominent facial features, and suggested the fossil belonged to a Denisovan. To make this connection, researchers extracted proteins from a bone in the skull’s inner ear and DNA from plaque on its teeth. They suggested the ancient material matched samples from previously identified Denisovan fossils.
If scientists can link the Dragon Man to Denisovans, it will allow researchers to compare other specimens with an almost complete skull, instead of mere fragments, potentially helping them identify more Denisovans in the fossil record.
Then, a September study in Science reconstructed a million-year-old skull that might also be linked to Denisovans. Called Yunxian 2, the skull was found 35 years ago, badly crushed in a riverbank in central China. The reconstruction revealed a large and long cranium, with a wide upper face and nasal opening. By comparing the reconstruction with more than 100 fossils from the human record, the research tied the skull to Homo longi, a species that has been linked to Denisovans, challenging the skull’s previous classification of Homo erectus.
This shift suggests humans may have split from Neanderthals much earlier than previous work had indicated. It’s widely agreed upon that Homo sapiens, Denisovans and Neanderthals split from a common ancestor between 500,000 and 700,000 years ago, but if Yunxian 2 is a Denisovan, that would push the split back to more than a million years ago. —M.H.
Devastating wildfires burned across Los Angeles
In the early weeks of 2025, one story dominated U.S. news: Wildfires were ravaging the Los Angeles area. From January 7 through 31, intense fires blazed, claiming 31 lives, burning more than 16,000 homes and buildings, and thoroughly scorching the landscape.
Fires burned across the Los Angeles and San Diego areas, but the two largest—the Palisades Fire at the west of Los Angeles and the Eaton Fire in Altadena—together torched more than 38,000 acres.
The flames spread so fast and burned so aggressively because of the dry state California was in. At the start of the fires, the Los Angeles area hadn’t had significant rainfall for months. Combined with record-breaking heat in parts of the prior year, this dried out vegetation, creating a tinderbox for flames. The blazes were urged on by the powerful Santa Ana winds, with gusts surpassing 80 miles per hour.
Though officials declared the fires contained at the end of January, the longer-term impacts of the disaster—on humans, animals and soils—are still becoming clear. In August, a research letter published in JAMAestimated another 440 deaths were attributable to the fires. They point to a combination of factors as potential causes, including poor air quality and health care delays.
As the fires burned through homes and buildings, they released toxic gases into the air and leached lead, arsenic and PFAS chemicals into the soil. Alongside official soil remediation efforts, some Altadena residents have been exploring native plants as a solution.
The fires also had a disruptive effect on wildlife: Some fled, others hunkered down, and many faced longer-term effects of contamination. Though the blazes have stopped, rebuilding efforts are far from over, and further scientific work will continue to unpack the fires’ long-term consequences. —M.H.
“Strongest evidence yet” of life on an exoplanet raised astronomers’ hopes—and highlighted the need for more data
Astronomers have long been searching—and hoping—for a sign of extraterrestrial life, and every so often, tantalizing hints of habitability appear. But this year, a team identified what they called the “strongest evidence yet” of life on another planet: two chemical compounds that, on Earth, are only produced by living things.
The discovery, reported in April in Astrophysical Journal Letters, came from James Webb Space Telescope data about the world K2-18b. The exoplanet, orbiting a star 124 light-years away, had already seemed like a candidate for hosting life.
Importantly, scientists did not find actual life-forms on the exoplanet. But by examining light that had filtered through the planet’s atmosphere, the telescope spotted signatures of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS)—sulfur-based gases that we also have on Earth, where they are produced by living things like algae. But in space, it’s possible DMS and DMDS can be made in a way that doesn’t require any organisms, so they’re not a definite sign of life.
Still, the detection paints a picture of a world where algae-like life might dwell in oceans—especially because the team suggests K2-18b is a watery planet with an atmosphere rich in hydrogen.
While several researchers applauded the work, others were skeptical. About one week later, astrophysicist Jake Taylor at the University of Oxford in England published a preprint analysis, which had not been peer-reviewed, that cast doubt on the original findings. Using a basic statistical test, he looked again at the space telescope’s data and did not find detections of DMS and DMDS.
The scientists from the original paper stood by their research, saying Taylor’s model was not complex enough to match the exoplanet’s data. Astronomers will need much more information to truly understand what may—or may not—reside on this faraway world. —C.K.
People formed new, sometimes concerning, relationships with A.I. chatbots
Chatbots powered by artificial intelligence have been getting better at mimicking human conversations. But the pervasive bots are seeping into people’s lives in new—and sometimes alarming—ways.
Some people, for instance, found romantic partnerships in chatbots, often saying their A.I. companions helped them through emotional hardship. In September, MIT researchers posted a large-scale analysis of the Reddit community r/MyBoyfriendIsAI on arXiv.org. The preprint study, which has not been peer-reviewed, highlights themes from the group, including reported benefits such as reduced loneliness, around-the-clock support and improvements in mental health—though some people displayed unhealthy emotional dependency on the bots. At the time of the research, the Reddit group had roughly 27,000 members. Now, it has around 39,000.
Users turned to chatbots for other things, too, including medical advice and therapy. But the benefits remain unclear, as some cases demonstrate how A.I. can also harm mental health.
After 16-year-old Adam Raine died by suicide in April, his parents found logs of his conversations with ChatGPT. The bot had presented itself as a “confidant,” encouraged the teenager to isolate himself and guided him toward suicide, according to his father’s testimony at a Senate hearing. ChatGPT even offered to write a suicide note. Raine’s parents are now suing the bot’s maker, OpenAI.
When people begin to mistake a bot for a conscious being, it can drive them to hallucinate, have delusions or confuse reality in other ways. This year, the experience has earned a nonclinical name: “A.I. psychosis.” Writing for BusinessInsider, psychiatrist Keith Sakata of the University of California, San Francisco, says he has seen 12 patients hospitalized with the condition in 2025, mostly younger men.
We’re now seeing the same concerning pattern that emerged around 60 years ago, when MIT computer scientist Joseph Weizenbaum developed what is widely considered the first chatbot, a “psychotherapist” called ELIZA. “Some subjects have been very hard to convince that ELIZA … is not human,” he wrote in a 1966 paper describing the bot. Policy makers are now working to tighten regulations around chatbots, particularly to protect children. —M.P.
If you or someone you know is having thoughts of self-harm or suicide, you can reach the Suicide & Crisis Lifeline 24/7 by calling or texting 988.
Researchers recovered the oldest proteins from animal remains, pushing back the record by roughly 20 million years
Ancient DNA has opened a window to the past, revealing information about the genetics and ancestry of people and animals from long ago. But scientists think archaic proteins might be able to extend that record even deeper in history, since proteins break down more slowly than DNA does. These preserved fragments, if recovered, can offer clues to evolutionary relationships between ancient and modern lineages.
This year, in a promising sign of that potential, scientists extracted the oldest known proteins, setting a record by millions of years. A study published in July looked at the enamel of fossilized animal teeth found in Canada’s high Arctic, an environment that helped preserve the proteins due to its extreme cold. In a new record, they recovered proteins from a tooth belonging to an extinct rhinoceros, dating the remains to between 21 million and 24 million years old.
Previously, the oldest widely accepted proteins dated to 3.5 million years ago, and the oldest known DNA was just two million years old.
From the newly examined tooth, researchers gained new insights about the rhinoceros family tree, uncovering that two subfamilies had diverged earlier than thought. The breakthrough hints that in the future, scientists working in cold environments might reliably identify proteins from even older remains—maybe even from the time of the dinosaurs. —C.K.
