SPACE/COSMOS
New study finds no significant joint damage in astronauts after short-duration spaceflight, highlighting promise of ultrasound monitoring
DENVER - Researchers at National Jewish Health have published new findings demonstrating that short-duration spaceflight may not significantly impact lower extremity joint structures, while also identifying a promising, non-invasive tool to monitor astronaut musculoskeletal health on future long-duration missions.
The study, led by Richard Meehan, MD, and Smarika Sapkota, MD, evaluated three astronauts before and after Axiom Mission 4 (Ax-4), an 18-day mission onboard the International Space Station (ISS). Using advanced musculoskeletal ultrasound imaging, researchers assessed cartilage thickness, synovial fluid levels, and tendon and ligament integrity in the hips, knees and ankles. The results, published in the International Journal of Clinical Rheumatology(Opens in a new window), showed no statistically significant changes in joint structures or evidence of inflammation following the mission. Dr. Sapkota will present the results at the May 2026 Annual Scientific Meeting of the Aerospace Medical Association in Denver.
“This study provides encouraging early evidence that short-duration spaceflight, combined with exercise and medical countermeasures, may help preserve joint health,” said Dr. Meehan, senior author and rheumatologist at National Jewish Health. “Equally important, it demonstrates that ultrasound can serve as a powerful, real-time tool to monitor joint health in space.”
Astronauts in the study engaged in cycling exercise during the mission and used anti-inflammatory medications, both of which may have contributed to maintaining joint health. Researchers observed no significant differences in cartilage thickness across the hips, knees or ankles, no meaningful overall change in knee synovial fluid levels, and no evidence of inflammation using power Doppler imaging. Tendon and ligament thickness also remained stable before and after spaceflight.
While the findings are reassuring, researchers caution that the study’s short duration and small sample size limit broader conclusions, particularly for longer missions to the Moon or Mars, where astronauts may face extended exposure to microgravity.
“Although we did not observe measurable changes after 18 days, longer missions could present very different risks to cartilage and joint structures,” said Dr. Sapkota, co-author and rheumatologist at National Jewish Health. “Our findings highlight the importance of continued research and the potential of ultrasound to guide personalized countermeasures for astronaut health.”
The study is among the first to use quantitative ultrasound immediately following spaceflight to assess multiple joint structures in humans, capturing changes within hours of return to Earth. Researchers believe this approach could play a critical role in future missions by enabling real-time monitoring of joint health, informing personalized exercise protocols, and reducing the risk of injury during and after spaceflight. The implications may extend beyond space exploration, offering potential benefits for patients on Earth, including those recovering from prolonged immobility or facing the risk of joint degeneration.
“This technology has the potential to transform how we monitor and protect joint health, not only for astronauts, but for patients here on Earth,” Dr. Meehan added.
The observational pilot study analyzed pre- and post-flight ultrasound measurements from three astronauts participating in the Ax-4 mission. Imaging was conducted within hours of return to Earth, and the research was supported by National Jewish Health in collaboration with Axiom Space and other partners.
“Leveraging the unique environment of space provides a vital laboratory for developing the next generation of biomedical technologies and medicine for terrestrial use,” explained Emmanuel Hilaire, PhD, director of Technology Transfer at National Jewish Health. Dr. Hilaire oversees the commercialization of innovations developed at National Jewish Health and is spearheading a space research initiative to accelerate further biomedical advancements.
National Jewish Health is the leading respiratory hospital in the nation delivering excellence in multispecialty care and world class research. Founded in 1899 as a nonprofit hospital, National Jewish Health today is the only facility in the world dedicated exclusively to groundbreaking medical research and treatment of children and adults with respiratory, cardiac, immune and related disorders. Patients and families come to National Jewish Health from around the world to receive cutting-edge, comprehensive, coordinated care. To learn more, visit njhealth.org or the media resources page.
Journal
International Journal of Clinical Rheumatology
Article Title
Ultrasound assessments of lower extremity joint structures from astronauts after 18 days on board the International Space Station
Venus’ atmosphere jumps and waves
Vast atmospheric waves on Venus are caused by largest known “hydraulic jump”
image:
These images taken on Aug. 18 (left) and Aug. 27 (right), 2016, by the near-infrared camera on Japan’s Akatsuki Venus probe, show the clear line of denser (darker) clouds moving across the planet.
view moreCredit: T. Imamura, Y. Maejima, K. Sugiyama et al., 2026
The mysterious origin of an impressive cloud disturbance on Venus has now been revealed by a team including the University of Tokyo. Researchers used numerical models to show that an enormous 6,000-kilometer-wide atmospheric wave front, which circumnavigates the planet for days at a time, is caused by a large “hydraulic jump.” This is when a fluid abruptly slows down, changing from shallow and fast to deep and slow. On Venus, a sudden change in airflow in the lower cloud region is coupled with the creation of a strong updraft, forcing sulfuric acid vapor higher into the atmosphere where it condenses into a massive line of cloud. Future planetary studies can consider the potential impacts of this process, and what it might mean for any exploratory missions.
A grim, gray day may spoil weekend plans now and then, but on Venus, it’s cloudy all day every day with a chance of sulfuric acid showers. On the bright side, Venus’ constant thick cloud cover provides an excellent opportunity for us to study patterns and processes that would be difficult to spot on planets where clouds are more sparse or intermittent, like here on Earth.
A key feature of Venusian clouds is that they “superrotate,” moving about 60 times faster than the planet turns. We now know that superrotation also occurs elsewhere, including on Mars, our sun, and even Earth’s upper atmosphere. In 2016, images from Japan’s Akatsuki Venus orbiter also revealed that an enormous atmospheric wave — sometimes 6,000 km wide — repeatedly sweeps around the planet’s equator.
“We identified the phenomena, but for years we couldn’t understand it,” said Professor Takeshi Imamura from the Graduate School of Frontier Sciences at the University of Tokyo. “However, thanks to this research, we’re now able to show that this cloud disruption is caused by the largest known hydraulic jump in the solar system.”
We can see a hydraulic jump in action in the humble kitchen sink. As water from the tap hits the basin, it appears fast and shallow at first, but suddenly slows and becomes deeper as it spreads.
The hydraulic jump on Venus occurs when an eastward-moving atmospheric wave (called a Kelvin wave) in the lower to middle cloud region suddenly becomes unstable. Wind speed as seen from the atmospheric wave abruptly slows down and a strong localized updraft is created, which carries sulfuric acid vapor higher into the atmosphere. The droplets condense into clouds which trail behind, causing the massive wave front which can be seen sweeping around the planet.
“Venus has three distinct cloud layers, and the dynamics of the lower and middle layers are not so well understood,” said Imamura. “Our discovery of a hydraulic jump on Venus connecting a very large-scale horizontal process with a strong localized vertical wave is unexpected, as in fluid dynamics these are usually disconnected.”
The hydraulic jump was simulated using a fluid dynamic model (a numerical analysis which simulates how gas or liquids flow), and the cloud formation studied using a microphysical box model (which follows the behavior of an example section of air as it moves through the atmosphere). As well as simulating the same cloud disturbance, the team also found that this process helps to maintain the superrotation of Venus’ atmosphere.
“Up until now, we used a global circulation model (GCM) for Venus that is similar to Earth’s, but this model doesn’t include the hydraulic jump which we have now identified,” explained Imamura. “Our next step will be to test this discovery within a more inclusive climate model that includes other atmospheric processes. We will face some challenges due to the huge amount of processing power required to run such simulations. Even with modern supercomputers, it isn’t easy.”
Although this is the first observation of a hydraulic jump of this scale on another planet, the physics behind it may also occur on other celestial bodies. “Under some circumstances, Mars’ atmosphere may also have the right conditions for a hydraulic jump,” mentioned Imamura. Creating more accurate models of atmospheric conditions will aid in the success of future missions to Mars, as well as wider space exploration.
--- ---- --- Paper and Contact Details --- --- ---
Journal:
Takeshi Imamura, Yasumitsu Maejima, Ko-ichiro Sugiyama, Takehiko Satoh, Javier Peralta, Kevin McGouldrick, Takeshi Horinouchi, Kohei Ikeda, “A planetary-scale hydraulic jump driving Venus' cloud front”. Journal of Geophysical Research: Planets. April 24 2026. DOI: 10.1029/2026JE009672
Funding:
This work was funded by JSPS KAKENHI Grant Numbers 24H00021, 24K21565, and 23H01236. J.P. acknowledges project EMERGIA20_00414 funded by Junta de Andalucía in Spain, and project PID2023-149055NB-C33 funded by the Spanish MCIN.
Conflicts of Interest:
The authors declare there are no conflicts of interest for this manuscript.
Useful links:
Graduate School of Frontier Sciences: https://www.k.u-tokyo.ac.jp/en/
JAXA's Akatsuki website: https://akatsuki.isas.jaxa.jp/en/
About The University of Tokyo:
The University of Tokyo is Japan's leading university and one of the world's top research universities. The vast research output of some 6,000 researchers is published in the world's top journals across the arts and sciences. Our vibrant student body of around 15,000 undergraduate and 15,000 graduate students includes over 5,000 international students. Find out more at www.u-tokyo.ac.jp/en/ or follow us on X (formerly Twitter) at @UTokyo_News_en.
In this image, the clearly defined hydraulic jump can be seen in the difference between the smooth inner circle of shallow and fast water, and the ripples of deeper, slower water beyond.
Credit
Takeshi Imamura 2026
Hydraulic jump simulation [VIDEO] |
This cross section of the Venusian atmosphere shows a numerical simulation of a hydraulic jump in action. The color indicates the “potential temperature,” which represents the atmospheric material surface. The jump appears as a stepwise transition of the material surface.
Credit
T. Imamura, Y. Maejima, K. Sugiyama et al., 2026
Journal
Journal of Geophysical Research Planets
Method of Research
Computational simulation/modeling
Subject of Research
Not applicable
Article Title
A planetary-scale hydraulic jump driving Venus' cloud front
Lonely Jupiter-like planet tells us more about gas giants
Ohio astrophysicist is helping unlock secrets of exoplanets with James Webb Space Telescope
image:
University of Cincinnati astrophysics graduate and current geosciences student Paul Smith visits the Cincinnati Observatory's historic telescope in Mount Lookout. Smith spent a 20-year career at P&G and another 10 as a writer and speaker on business leadership before returning to UC to study physics and geosciences. He also is pursuing a master's degree in planetary science from the University of Aberdeen in Scotland.
view moreCredit: Connor Boyle
One evening last fall, University of Cincinnati astrophysics graduate Paul Smith waited anxiously for data to start rolling across his computer screen from the James Webb Space Telescope a million miles from Earth.
The telescope was directed at an object even farther away — much farther away. Smith is studying a planet 901 light years away. That means light from its star takes 901 years to reach Earth.
The planet is named after this star, TOI-2031A, in accordance with NASA’s unpoetic, numbered naming conventions. The TOI stands for Transiting Exoplanet Survey Satellite Object of Interest.
Even though it was a clear night, the star was too faint to see with the naked eye. Its starlight captured in the space telescope was generated in the Middle Ages.
Smith and his research partners beat out other scientists for precious telescope time. Roughly 90% of research applications don’t make the cut each year in the competitive peer-review process.
Now they were hoping their calculations were correct and the planet would cross in front of its star during their allotted observation time.
Using the telescope’s powerful near-infrared spectrographic sensors, researchers would be able to learn more about the planet and its atmosphere as it transited its star’s face. As leader of the data analysis for the project’s first planet, Smith got to retrieve the data, what astrophysicists call the first look.
“It was a lifelong dream of mine coming true. I was up all night to get the first look at the data,” he said.
Smith and his research colleagues presented their findings on TOI-2031Ab at the American Astronomical Society meeting in Denver in April.
Physicists call planets outside our solar system exoplanets. To date, astrophysicists have identified about 6,400 of them.
Smith and his international collaborators from 19 other institutions are studying gas giants like Jupiter to learn more about their atmospheres and why so many of them orbit so close to their stars. The exopolanet is a quarter bigger in circumference than Jupiter, the biggest planet in our solar system, although it has 20% less mass.
Smith regularly travels to Ohio State University to meet with some of his project co-authors, grad student Everett McArthur and Professor Ji Wang. And he talks regularly with Peter Gao from the Carnegie Science Institute.
“We’re trying to figure out how these big gas giants got there. We’re studying the formation and migration pathways of big planets,” Smith said. “Where do they form in their solar systems and how do they get so close to their stars?”
TOI-2031Ab was discovered just last year, the only known planet in its solar system. The exoplanet orbits its star closer than Mercury orbits the sun.
Its year lasts just six Earth days as it hurtles through space four times faster around its star.
Researchers can study its atmosphere using the portion of its star’s light that slices through its atmosphere on its way to the James Webb Space Telescope.
“The atmosphere is very similar to Jupiter’s — mostly hydrogen and helium, water and carbon dioxide,” Smith said.
Cincinnati Observatory astronomer Wes Ryle, who was not part of the study, said planets outside our solar system are helping us understand our own.
“Exoplanets are one of the hottest topics in astrophysics right now, with the ultimate goal of learning how our solar system compares to others and the likelihood of finding other habitable worlds,” Ryle said. “Studies like this help evaluate the role of gas giant planets and their migration in creating a planetary system.”
The historic 1845 telescope at the Cincinnati Observatory.
Credit
Andrew Higley
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