A new study examines how variations in the strength of gravity affect muscle health in mice aboard the International Space Station. The work pinpoints 0.67g as a turning point – lower than this, and muscle begins to deteriorate. The research also identifies 11 metabolites that change as gravity weakens. These metabolites could be used as biomarkers to monitor muscle health in astronauts one day, Ryosuke Tsuji and colleagues suggest. It’s well known that spaceflight changes the musculoskeletal system. For example, in microgravity, the molecular processes that govern muscle health begin to go haywire. Now, Tsuji et al. ask: is there a specific level of gravity at which muscle deterioration begins? They examined 24 male mice aboard the International Space Station across a range of artificial gravity settings, exposing the animals to microgravity, 0.33g, 0.67g, and 1g conditions for up to 28 days. Then, they looked at changes to the animals’ grip strength and atrophy of the soleus, a hindlimb muscle that is particularly sensitive to changes in gravity. Results revealed that 0.33g was enough gravity to prevent full muscle atrophy. However, muscle myofibers did change in composition. At the higher value of 0.67g, muscles showed no deterioration in function nor change in myofiber concentrations. “Considering that a journey to Mars would require approximately 8 to 9 months, it is essential to assess whether the protective effects observed here will persist during extended spaceflight,” Tsuji et al. write. They subsequently performed metabolomics on plasma from mice, discovering 11 metabolites that varied based on gravity conditions. With further research, these might provide useful indicators of muscle deterioration in astronauts.

For journalists monitoring how spaceflight alters the body, a 2026 Science Advances study involving ISS experiments pinpointed specific intracellular RNA alterations associated with known space travel-related health issues: www.science.org/doi/10.1126/sciadv.adw7832

Hydrogen atmosphere could keep exomoons habitable for billions of years

Could there be simple life floating within the freezing lakes of methane on Titan? A new study presents one of the first experimental tests of the azotosome hypothesis, which proposes that molecules on Titan could form stable closed membranes similar to cells. The findings contradict the hypothesis, showing that the ingredients of Titan’s lakes are more likely to form crystal-like structures instead of membrane-like compartments. Titan is Saturn’s largest moon and has long piqued the interest of astronomers due to its many similarities with Earth. The moon boasts a dense atmosphere and is one of the few places in the Solar System that possesses large bodies of surface liquid. Unlike on Earth, Titan’s seas and lakes are made of liquid methane and ethane, which are extremely cold. Nevertheless, Titan is a prime candidate in the search for extraterrestrial life, with some scientists theorizing that exotic life could form within the moon’s standing methane lakes. One hypothesis posits that compounds named acrylonitriles could assemble into self-enclosed structures called azotosomes capable of housing biochemical reactions. However, models have yielded conflicting results about whether and how azotosomes could form. Here, Tuan Vu and Robert Hodyss performed some of the first experimental tests of the azotosome hypothesis. Using microscopy and calorimetry, they interrogated the chemical behavior and thermodynamic properties of acrylonitrile-methane and acrylonitrile-ethane in liquid methane and ethane, under conditions that simulated Titan’s lakes. These studies revealed that acrylonitriles tended to crystallize within liquid methane and ethane, and didn’t form any structures resembling an azotosome. “This finding further reduces the prospect for vesicles on Titan from a thermodynamic standpoint, but it does not rule out the possibility that they might exist temporarily or be transiently stable,” Vu and Hodyss write. “Titan’s surface habitability thus remains an intriguing notion, whether by way of vesicles or other means.”