As NASA prepares for a return to the Moon through the Artemis program, one of the biggest health concerns for astronauts has been lunar dust. The fine, abrasive particles known as the regolith that coat the Moon's surface have long worried scientists, especially after Apollo astronauts experienced respiratory problems after their missions. However, groundbreaking research from the University of Technology Sydney has delivered surprisingly reassuring news: lunar dust is less harmful to human lung cells than previously feared, and significantly less toxic than common Earth based air pollution.

NASA’s Space Launch System rocket carrying the Orion spacecraft launches on the Artemis I flight test.

(Credit : Joel Kowsky)

The study, led by PhD candidate Michaela B. Smith, represents the most comprehensive analysis yet of how lunar dust affects human health. Smith investigated the impact of lunar dust simulants on human lung cells in the lab. She then compared the effects to those of airborne particulate matter collected from a busy street in Sydney.

The results were striking. While lunar dust can act as a physical irritant, it did not cause the severe cellular damage or inflammation seen from the urban Earth dust. Smith emphasises this crucial distinction “..between a physical irritant and a highly toxic substance".

Buzz Aldrin's bootprint in the lunar soil

(Credit : NASA)

The research focused on the tiniest particles, those measuring 2.5 micrometers or smaller which are small enough to bypass the body's natural defences and penetrate deep into the lungs. Using two different types of lung cells representing both upper and lower respiratory regions, the team discovered that Earth dust induced a greater inflammatory response and was more toxic to the cells than the lunar dust simulants.

This finding addresses concerns that arose from the Apollo missions, where astronauts experienced respiratory issues after fine dust that had clung to their spacesuits became airborne in the confined cabin and was subsequently inhaled, leading to respiratory issues, sneezing, and eye irritation.

The key difference lies in how the dust affects cells. The study suggests the primary mechanism of toxicity from lunar dust is mechanical damage caused by the particles' irregular shape and rough edges. Crucially, the lunar simulants did not cause significant damage through a process known as oxidative stress (damage caused by unstable molecules), a process often associated with fine particle toxicity.

"Any dust, if you inhale it, you'll sneeze, cough, and have some physical irritation. But it's not highly toxic like silica, where you end up with silicosis from being on a construction site for 10 years”

- Michaela B. Smith, lead author.

Despite these encouraging findings, NASA continues taking dust exposure seriously. The space agency has developed innovative engineering solutions, including ingenious suits that are attached to the outside of the rover, where the astronaut will climb in and out from inside, and the suit never goes inside, which prevents the dusty suit from ever contaminating the internal cabin environment.

This research provides crucial data for planning long term lunar missions and establishing permanent bases on the Moon, helping to ensure astronaut safety while reducing one significant health concern for humanity's next giant leap.

Source : 

• Lunar Dust Less Toxic Than City Pollution, Study Finds.

{ https://www.universetoday.com/ }

Hycean worlds are also called ocean worlds. They're planets covered in oceans that also have thick hydrogen atmospheres. There are no confirmed Hycean worlds—also called ocean worlds—but many candidates. Even though they're only candidates so far, researchers are curious about their habitability. New research examines the role tidal heating plays in their potential habitability.

If hycean planets do exist, they're likely common around red dwarfs (M dwarfs.) Red dwarfs are the most plentiful type of star in the galaxy, and Hycean worlds' thick hydrogen atmospheres might protect them from the devastating flaring behaviour of these small, long-lived stars. Hycean worlds may have larger habitable zones because of all their water, but their hydrogen atmospheres may contribute to the runaway greenhouse effect. When it comes to habitability, these hypothetical worlds are intriguing and mysterious.

In new research to appear in The Astrophysical Journal, the authors argue that for Hycean worlds close to their low-mass stars, tidal heating may be an important factor in determining their habitable zones. It's titled "Tides Tighten the Hycean Habitable Zone," and the lead author is Joseph Livesey. Livesey is from the Department of Astronomy and the Wisconsin Center for Origins Research, both at the University of Wisconsin-Madison.

When a new exoplanet is discovered, one of the first things scientists and the public want to know is if it's in the star's habitable zone. Researchers have made significant progress understanding the habitable zones for rocky planets. "Many studies have parameterized the habitable zone (HZ) for terrestrial exoplanets," the authors write. "The exact HZ boundaries can vary based on key characteristics such as stellar host type, planetary mass, atmospheric composition, and more."

But hycean worlds are much different than terrestrial worlds. They're sub-Neptunes with significant water layers and atmospheres dominated by hydrogen. They're oddballs, and determining if they are in habitable zones requires a different approach than with rocky planets.

In our Solar System, some of the gas giant moons have frozen shells with liquid oceans underneath. They're far too distant for the Sun to warm them. It's tidal flexing that maintains their liquid oceans. As moons like Europa and Enceladus orbit Jupiter and Saturn, the much-larger gas giants pull on the moons and they flex in response. That action creates heat. So, in effect, tidal flexing creates a habitable zone that's isolated from the Sun.

Since many hycean worlds are expected to orbit their stars closely, can tidal heating alter their habitable zones?

The researches say that the Hycean Habitable Zone (HHZ), when compared to the terrestrial habitable zone, may include smaller semi-major axes and could even extend to unbound planetary orbits. A near total absence of GHGs other than hydrogen along with a high albedo allows closer orbital proximity to the star, while internal heating from radiogenic sources, high pressures, a liquid water layer, and larger planet masses extend the HHZ outward.

Tidal heating creates another heat source aside from stellar radiation. Hycean worlds following moderately eccentric orbits experience tidal flexing and heating that shifts the HHZ outward. This creates a smaller HZ than previous estimates based on stellar heating.

Moderately eccentric orbits are common. Our Solar System has massive outer planets that have shifted the orbit of smaller planets into eccentricity. Many other solar systems are likely to have them too, meaning they're shifting smaller planets into eccentricity.

"These outer companions do occur in planetary systems around M dwarfs; the occurrence rate of giants in such systems has been found to be ∼ 10%, and the occurrence rate of planets in the range 10–100M⊕ is ∼ 20%," the authors write.

This figure shows The HHZ (blue shaded regions) and dark HHZ (red shaded regions) around a 0.12M⊙ star for a 7M⊕, 1.7R⊕ Hycean planet with tidal heating. The dark HHZ indicates a tidally-locked Hycean planet that can be habitable on its nightside. The low-opacity contours show the habitable zone locations without tidal heating, and the high-opacity contours show the habitable zone location where tidal heating is included. The dotted and dashed lines indicate the conservative and optimistic habitable zones for terrestrial planets.

Image Credit: Livesey et al. 2025. The Astrophysical Journal.

The above image shows how tidal heating shifts the HHZ around low-mass stars. However, most hycean candidates are orbiting more massive stars. The researchers found that the effect of tidal heating on the HHZ depends on the star's mass. They found that around more massive stars, the tidal heating effect isn't as pronounced.

This figure shows the HHZ and dark HHZ around stars of various mass for a 7M⊕, 1.7R⊕ Hycean planet. The orbital eccentricity for this planet is based on the Hycean candidate world K2-18 b, a planet known for evidence of potential biosignatures. The dotted line represents the stellar mass in the previous figure of 0.12 solar masses. "Clearly, the effect of tides on the extent of the habitable zone becomes negligible at high stellar masses," the researchers explain. Image Credit: Livesey et al. 2025.

The Astrophysical Journal.

This research shows that tidal flexing on ocean worlds shifts their habitable zones outward. The effect relies on a more massive companion planet that can introduce eccentricity into the hycean world's orbit.

"Hycean planets are likely to exhibit stronger tidal responses than a fiducial terrestrial world," the researchers explain. "We expect tides to have little effect on a lone planet at such small orbital radii. However, the presence of a large outer companion with moderate eccentricity will force an eccentricity cycle that periodically and indefinitely heats the interior of the planet in question, and push out the inner boundaries of the HHZ."

Though hycean worlds are only hypothetical at this point, their confirmation may not be too distant. Exoplanet scientists are intrigued by them because of their potential for habitability. Their extended atmospheres also make them desirable targets for atmospheric spectroscopy with telescopes like the JWST. K2-18b is a prime example of their potential. It's a candidate hycean world that repeatedly generated headlines when astronomers found evidence of water vapor, then carbon dioxide and methane, then the potential biosignature dimethyl sulfide in its atmosphere.

"A recent possible detection of dimethyl sulfide (DMS) in the atmosphere of the potential hycean exoplanet K2-18 b may indicate the presence of ocean-faring life; the only major source of DMS on Earth is phytoplankton," the authors write. They point out that on hycean worlds with deep oceans, the ocean tides generate a significant amount of heat that can be used by organisms. This sets them apart from Earth, where the tidal energy is dissipated. "We suggest, therefore, that strong tides on hycean planets could yield a significant power source for life and ultimately accelerate biological evolution," they explain.

If our Solar System seems stable, it's because our short lifespans make it seem that way. Earth revolves, night follows day, the Moon moves through light and shadow, and the Sun hangs in the sky. But in reality, everything is moving and influencing everything else, and the fine balance we observe can easily be disrupted. Could passing stars have disrupted Earth's orbit and ushered in dramatic climatic changes in our planet's past?

A stellar flyby is when another star passes close enough to our Solar System to cause some disruption. Our neighbourhood in the Milky Way is relatively sparsely populated, so stellar flybys are rarer than in other parts of the galaxy. But they still occur.

The most well-known one was probably Scholz's star. About 70,000 years ago, it passed through the Oort Cloud, our Solar System's outlying repository of long-period comets and icy planetesimals. It may have perturbed some comets from the Oort Cloud, but if it did, we won't know for a couple of million years. That's how long it would take for a comet to reach the inner Solar System.

Scholz's star illustrates the risk of stellar flybys. Scientists have wondered if these flybys have affected Earth's climate in the past by altering the planet's orbit. New research that will appear in The Astrophysical Journal examines stellar flybys to see if this is true. It's titled "No influence of passing stars on paleoclimate reconstructions over the past 56 million years." The authors are Richard Zeebe and David Hernandez. Zeebe is from the School of Ocean & Earth Science & Technology at the University of Hawaii, and Hernandez is from the Department of Astronomy at Yale University.

"Passing stars (also called stellar flybys) have notable effects on the solar system’s long-term dynamical evolution, injection of Oort cloud comets into the solar system, properties of trans-Neptunian objects, and more," the authors write. "Based on a simplified solar system model, ... it has recently been suggested that passing stars are also an important driver of paleoclimate before ∼50 Myr ago, including a climate event called the Paleocene-Eocene Thermal Maximum (PETM) (∼56 Myr ago)."

The PETM saw a 5–8 °C (9–14 °F) rise in global temperature and a massive influx of carbon into the atmosphere and oceans. It took 10,000 or 20,000 years for the temperature to rise and it lasted for about 100,000 or 200,000 years. Its effect on the biosphere was massive. Many marine organisms went extinct, tropical and sub-tropical regions extended toward the poles, and primates and other mammals appeared.

The Paleocene–Eocene Thermal Maximum was a prominent hyperthermal episode in Earth's climatic history. Its cause is unclear.

Image Credit: Svensen 2012. https://doi.org/10.1038/483413a

The cause is still debated, and there are several hypotheses. They include volcanic eruptions, comet impact, the release of methane clathrates, and orbital forcing. Researchers think that the giant planets play an important role during stellar flybys. When a roaming star passes by, the giant planets' gravitational fields can amplify the effect of the flyby and then alter the orbits of the smaller planets.

To find out if stellar flybys could be responsible for the PETM and other climatic changes, the researchers used a state of the art model of the Solar System and random stellar parameters in 400 simulations. The total number of stellar flybys was 1,800.

Other researchers who examined the same issue found that stellar flybys could've altered Earth's paleoclimate. [Kaib & Raymond (2024)] (https://iopscience.iop.org/article/10.3847/2041-8213/ad24fb) said, "Here we present simulations that include the Sun's nearby stellar population, and we find that close-passing field stars alter our entire planetary system's orbital evolution via their gravitational perturbations on the giant planets." They also wrote "Although it takes tens of Myr for the effects of stellar passages to significantly manifest themselves, the long-term orbital evolution of the Earth and the rest of the planets is linked to these stars."

However, Zeebe and Hernandez reached a different conclusion. "In contrast to Kaib and Raymond, we find no influence of passing stars on paleoclimate reconstructions over the past 56 Myr," they write.

This global map shows what Earth looked like 45 million years ago.

Image Credit: By Scotese, Christopher R.; Vérard, Christian; Burgener, Landon; Elling, Reece P.; Kocsis, Ádám T. - "Phanerozoic-scope supplementary material to "The Cretaceous World: Plate Tectonics, Paleogeography, and Paleoclimate (doi:10.1144/sp544-2024-28)" from the PALEOMAP project". doi:10.5281/zenodo.10659112 https://zenodo.org/records/10659112, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=155112444

One of the reasons for the different results is the completeness of the models used to understand the flybys. Some Solar System models, for example, excluded the Moon.

"Running accurate state-of-the-art solar system models that include all known secondary effects is computationally expensive," the authors write. "As a result, long-term studies on, e.g., Gyr-timescale tend to be based on simplified solar system models, or the outer planets alone."

By using a more complete Solar System model, Zeebe and Hernandez showed that stellar flybys are not likely behind Earth's dramatic paleoclimate shifts, like the PETM. They point out that the Moon has a stabilizing effect, and models that exclude it reach suspect conclusions.

"In contrast, using a state-of-the-art solar system model, including a lunar contribution and J2 (the Moon and Sun's quadrupole moment), and random stellar parameters, we find no influence of passing stars on paleoclimate reconstructions over the past 56 Myr," the authors explain. Even extremely close flybys seem to have no effect.

There have been many stellar flybys in the past and there'll be many more in the future. The orange dwarf Gliese 710 is expected to come within 0.1663 light-years or 10,520 astronomical units in about 1.29 million years. It has an 86% chance of passing through the Oort Cloud, and some researchers say it could trigger a swarm of comets into the inner Solar System. Could this flyby trigger a dramatic shift in Earth's climate?

There's a lot of uncertainty, and understanding the past and future of stellar flybys and how they might affect Earth's climate comes down to how detailed our scientific models are.

"Our results indicate that a complete physics model is essential to accurately study the effects of stellar flybys on Earth’s orbital evolution," the authors conclude.