Earlier this year, an astronaut on board the International Space Station (ISS) snapped some striking photos, and an eerily beautiful video, of a "fireball" streaking over Earth as chunks of space debris burned up in the nighttime sky.

NASA's Chris Williams, who lived and worked on the ISS between November 2025 and July 2026, captured the eye-catching images from the station's cupola — a large, roughly dome-shaped series of windows that constantly points down at our planet — and later shared them on the social media platform X.

"Just as we were passing over West Africa, I saw a bright object directly below us, streaking through the upper atmosphere," Williams wrote in the post. "I saw its tail grow and then split apart into a shower of smaller pieces," he added. "It was quite a light show!"

Williams initially peered down at Earth to catch a glimpse of the Russian cargo spacecraft Progress 95, which successfully delivered essential supplies and additional equipment to the ISS later the same day. Instead, he saw what he believed was "some piece of orbital debris or a satellite breaking up as it entered the atmosphere."

Live Science's sister site Space.com later revealed that Williams had actually witnessed the burning remains of the Russian Soyuz rocket that had carried Progress 95 into space, after it lifted off from a recently repaired launchpad at the Baikonur Cosmodrome in Kazakhstan.

Shortly after deploying the resupply shuttle into low Earth orbit, the rocket's fairings and booster fell back toward our planet as expected, breaking apart into smaller pieces that were superheated and later vaporized by intense friction as they hit the upper atmosphere, according to Space.com. A very similar fireball was seen above Australia in August 2023, when another Soyuz rocket reentered the atmosphere.

Russia's prior resupply mission, Progress 94, also made headlines earlier this year when one of its antennae failed to deploy after separation from its Soyuz rocket, forcing cosmonauts (Russian astronauts) to use a remote control "backup system" to dock the spacecraft to the ISS.

Historically, the only fireballs visible in Earth's skies have been those caused by meteors, which can similarly break apart in flames. We were recently reminded of this when fireballs were spotted above the U.S. this spring, including one space rock that exploded with a massive sonic boom over Ohio and another that crashed through the roof of a house in Houston. (A NASA statement said the fireball Williams witnessed also may have been caused by meteor activity but was more likely to be the Soyuz rocket.)

However, fireballs from human-made objects are becoming more common. The number of spacecraft orbiting Earth has skyrocketed (pun intended) in recent decades, and "what goes up must come down."

Most spacecraft and large pieces of space junk burn up around 50 miles (80 kilometers) above Earth's surface — just below the imaginary boundary with space, known as the Kármán line. While this may lead to visually stunning spectacles like the one Williams captured, scientists are starting to realize that these fireballs may be having a bigger impact on the upper atmosphere than they previously expected.

In recent years, researchers have detected a sharp increase in atmospheric metal pollution from vaporized spacecraft. And while they are still trying to figure out what effect this may have, some scientists have proposed that it could affect the ozone layer or potentially alter Earth's magnetic field.

Additionally, as the number of falling spacecraft rises, the chances that debris may fall to Earth's surface — after failing to properly burn up upon reentry — also increase. This came to the fore in March 2024, when the remains of a 3-ton battery pack that was discarded from the ISS crashed into a family home in Florida.

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'> 'Quite a light show': NASA astronaut snaps atmospheric fireball as Russian rocket explodes over West Africa

The research, published Sept. 30 in the journal PLOS One, found that rats exposed to levels of radiation similar to what an astronaut might experience on a long-term trip to Mars developed more scar tissue around the small blood vessels of their hearts than rats that were not exposed to this radiation. This scar tissue is indicative of a condition known as cardiac fibrosis, which is known to increase the risk of heart failure.

This scar tissue was observed nearly a year after the rats were first exposed to the radiation.

But since this study was in rats, it cannot definitively say whether this effect will play out in humans. For example, given that humans have a longer life expectancy than rats (80 years versus 2 to 4 years), the effects seen in rats may take around 30 years to show up in humans. However, the study authors say the research highlights the importance of following astronauts' health long after they return to Earth.

"The message that we try to convey … is that the follow-up time is really important," study co-author John Baker, a professor of surgery in the Radiation Bioscience Laboratory at the Medical College of Wisconsin, told Live Science. "When astronauts come back to the Earth, they expect ‪—‬ and we expect ‪—‬ that they're going to live for a long time. I think we have to be wary that they could well develop at least some type of cardiac disease."

How space radiation affects the heart

The link between exposure to radiation and cardiac issues has been well documented. However, "no astronaut has ever been exposed to galactic cosmic radiation for long periods of time," Baker said, which makes it difficult to determine exactly how space radiation affects the heart.

Although Baker and his team previously pinpointed cardiac issues among rats exposed to radiation, this new study utilized NASA's Simulated Galactic Cosmic Ray Simulation (SimGCRSim). This new simulator provides a more precise comparison of the levels of space radiation an astronaut might experience while exploring deep space for more than a year.

During the study, the researchers exposed rats to several minutes of radiation proportionate to their size, similar to what they might experience on a trip to Mars and back (a roughly 18-month round trip, with current technology). Some of the rats' hind legs were suspended, to "simulate conditions of weightlessness," Baker said.

After 360 days, the rats that were exposed to cosmic radiation developed twice as much scar tissue around the heart's small blood vessels than unexposed rats. This buildup of scar tissue means "the heart can't relax to the point when it needs to," thereby increasing the risk of heart failure, Baker said.

This effect was not seen in the rats who were exposed only to simulated weightlessness, confirming "it was only the radiation that produced the damaging effect on the heart," Baker said. However, long-term testing revealed that this group of rats had lower levels of key immune cells, suggesting that microgravity also may affect aspects of long-term health. (Numerous studies have shown various short-term health impacts related to microgravity.)

This study "is a very valuable contribution to space biology," Rupak Pathak, an associate professor of pharmaceutical science at the University of Arkansas for Medical Sciences who was not involved in the study but holds a doctorate in radiation biology, told Live Science. While rats and humans have clear differences, "they share more than 90% of genetic information," he said, as well as very similar cardiac systems.

Given that the study authors were able to expose the rats to radiation only once, Pathak would like to see further experiments exploring whether chronic radiation exposure affects the function of the heart and other vital organs.

Baker and his colleagues hope that future experiments can be used to help NASA implement safeguards for astronauts on long-term missions, such as providing astronauts heart medications or improving shielding for the spacecraft.

"The more we know before we start, then the better NASA is going to be at working out what types of countermeasures can be developed," said Baker.

'> Mars-bound astronauts could face years of heart scarring, rat study hints

"He lived with a chronic urogenital infection," study lead author Natalia Berezina, an anthropologist at Lomonosov Moscow State University in Russia, told Live Science in an email.

"It was not a brief episode," she said. "His last years were probably marked by considerable and more or less constant pain."

Berezina and colleagues investigated a small, stone-like object found in an Early Bronze Age burial in the Stavropol Upland region of southwestern Russia. They published their findings Sept. 30 in the journal Archaeological and Anthropological Sciences.

The burial was part of a kurgan cemetery, an ancient steppe funeral tradition that involved constructing a large mound of dirt over a grave. Archaeologists discovered a catacomb when they excavated the mound, and inside was the skeleton of a man who was in his 40s when he died around 5,300 years ago. The researchers found a flint arrowhead near the man's pelvis.

But during a laboratory analysis after the skeleton was excavated, researchers noticed an odd stone-like object in the collection of hand bones. The brownish object was round with several protrusions and measured about 0.8 inches (2.1 centimeters) in diameter, or roughly the size of a grape. A small crack in the object showed a crystal-like structure inside.

To learn more, the researchers used several analytical methods to determine what the tiny object was made of. First, X-ray fluorescence analysis revealed that the main components of the object were calcium and phosphorus. Then, they used X-ray powder diffraction analysis to identify the crystal structures.

In addition to common minerals, the researchers discovered the presence of whitlockite, a rare calcium salt that is known to occur in kidney, bladder and prostate stones. These "stones," collectively called calculi, are hard masses of minerals, such as calcium-containing salts. They differ in terms of the organ they form within, the exact mechanism of how they form, and their chemical makeup, although kidney and bladder stones tend to contain very similar compounds.

Whitlockite is strongly associated with bacterial infections in the human body, which suggests that the Bronze Age man had a chronic infection that resulted in the stone, the scientists concluded.

"On the balance of the available evidence, we regard a renal [kidney] stone secondary to chronic upper urinary tract infection as the most probable origin," the researchers wrote. That is, the man dealt with chronic or recurrent UTIs, which led to the formation of the stone and likely caused him considerable discomfort. UTIs can contribute to the formation of kidney stones by altering the acidity of urine and making minerals more likely to accumulate.

The researchers aren't sure why the man had urinary tract issues or whether it contributed to his death.

Notably, kidney stones can sometimes travel to the bladder, so it's unclear exactly where the stone was in the man's body when he died. If the stone had obstructed the man's ureter ‪—‬ one of the two long tubes that connect the kidneys to the bladder ‪—‬ it may have caused kidney swelling, a secondary infection or sepsis. These conditions were frequently fatal prior to the invention of antibiotics.

Other possibilities for what caused the stone include a bacterial infection of the man's prostate gland or even a sexually transmitted infection.

The man was likely on the move frequently within this Early Bronze Age steppe society, and other injuries to his skeleton suggested he had a physically demanding life, the researchers wrote. His bones showed that he was well muscled but was also dealing with degenerative joint disease in his spine, shoulders, hips, hands and feet. He had a series of healed fractures in his right shoulder, ribs and forearm.

"These were people who worked with cattle and heavy wagons on the open steppe," Berezina said, "and the injuries that follow from that are the injuries we find." In a previous study at a nearby cemetery, Berezina and colleagues found the skeleton of a man who was injured when a wagon ran over him, several years before his death. "Against that background, four healed fractures in our man look unremarkable," she said.

But the urinary tract stone would have made the man's life difficult, the researchers noted. "This individual suffered from a painful and debilitating chronic urogenital infection, a condition that would have significantly impacted his quality of life," they wrote.

What do you know about the bones in your body? Test your knowledge with our human skeleton quiz.

'> 5,300-year-old kidney stone the size of a grape found in Bronze Age man's burial near Black Sea

In the new research, published Monday (Nov. 2) in the journal PNAS, the scientists said they identified microscopic structures resembling red blood cells alongside chemical signatures of heme, the oxygen-carrying component of hemoglobin.

The new findings come from limb bones of a roughly 10-foot-long (3 meters) dinosaur called Aratasaurus museunacionali. While previous research has detected blood in dinosaur fossils, this is the first study to use chemical processes to identify heme-based signatures in dinosaur bones.

"Traditionally, fossils give us information through bones, teeth, shells and morphology. But exceptionally preserved fossils may contain another archive of information: microscopic structures and molecular traces of the original organism," study co-author Kliti Grice, a professor in the School of Earth and Planetary Sciences at Curtin University in Australia, told Live Science via email. "That opens the possibility of asking questions about ancient biology that skeletal anatomy alone cannot answer."

Deep in the bones

The team was not originally looking for traces of dinosaur blood, Grice said. Her research was driven by a broader question: How much of an ancient organism's original biology can survive fossilization?

To investigate, Grice and her team studied the limb bones of A. museunacionali, an extinct species of small theropod that lived during the Early Cretaceous period in Brazil. Theropods were a group of mostly meat-eating dinosaurs that walked on two legs. They included famous predators such as Tyrannosaurus rex and Velociraptor.

Using microscopic and chemical analysis on the theropod's limb bones, the researchers found numerous microscopic structures within vascular canals, channels that once carried blood vessels through the bone. Their shape, size and location were consistent with red blood cells, the team said.

"We combined microscopy, mineralogical analyses and molecular geochemistry," Grice said. "Critically, we investigated the chemistry in situ [in the bone itself], so we could relate the chemical signals to the microscopic structures in their physical context within the fossil. That is much stronger than simply extracting molecules from a piece of fossil and assuming where they originated."

The team's chemical analyses detected preserved heme-related compounds associated with these structures, providing more chemical evidence to support the idea that the finding could be traces of dinosaur blood, as heme is the iron-containing, ring-shaped molecule that forms a key part of the molecule hemoglobin in red blood cells.

A time capsule

Grice and the team think the conditions the theropod dinosaur was buried in could have helped preserve the vascular structures and the red blood cells within them. They suggested that the animal was rapidly covered by sediment in a low-oxygen environment containing microbial mats ‪—‬ thin biofilms made of microorganisms. These conditions may have altered the normal process of decomposition, helping to preserve the microscopic structures and associated chemical signatures.

"The red-blood-cell-like structures were mineralised with hausmannite, a manganese oxide mineral (Mn₃O₄)," Grice said. "We think early mineralisation helped stabilise or replicate microscopic biological structures before they were completely destroyed, while aspects of the associated chemistry also survived in altered form."

The fossil also contained preserved amino acids associated with collagen, the structural protein found in bone.

Not everyone is convinced

While blood has been found in dinosaur fossils before, not everyone agrees that these latest findings are truly red blood cells.

"I very much appreciate this team bringing rigor to the study of deep time fossils," said Mary Schweitzer, a molecular paleontologist at North Carolina State University who was not involved in the study but has previously studied soft tissues from the dinosaur age. "I am in agreement that endogenous [produced within the body] molecules can persist over geological time in some form, and that there is much these can teach us. However, I am not convinced that the images they figure are remnant RBCs [red blood cells] for several reasons."

For one, the structures do not convincingly match the expected appearance of red blood cells in nonmammalian animals, Schweitzer said. Unlike mammalian red blood cells, which lose their nuclei during development, those of birds and reptiles retain their nuclei. This typically produces a characteristic nuclear bulge in the shape of the cell.

According to Schweitzer, the latest findings show the microstructures having more of a concave shape with no nuclear bulge. The structures also were smaller than most non-mammalian red blood cells, "so morphological similarity is not met," Schweitzer said.

"I appreciate these authors bringing technological innovations to the study of dinosaur fossils," she said. "I am excited to see that this team and others are moving forward with a molecular approach to ancient fossil remains."

Editor's Note: This article was updated at 5:44 p.m. E.D.T. to remove an outside comment that suggested the study did not include resonance Raman spectroscopy. The team did perform that analysis.

'> Traces of ancient blood found in 115 million-year-old dinosaur fossil, new study claims