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Planetary scientists have discovered more than 15,000 km of ancient riverbeds in Noachis Terra, a region in Mars’ southern highlands. This discovery suggests that Mars may once have been much wetter than previously thought.

The nature of the Martian climate during the Noachian-Hesperian transition, a period of geologic and climatic changes around 3.7 billion years ago, and how surface features such as valley networks and lakes associated with liquid water formed, is debated.

There are two theories: the first is that warm and wet conditions persisted on early Mars long enough that liquid water was stable on the surface for extended periods; the second is that Mars was generally cold and dry, and that geological features indicative of flowing water were formed only very sporadically by meltwater from ice sheets during short climate excursions.

Noachis Terra is a region where ‘warm, wet’ climate models predict high rates of precipitation.

In new research, Open University Ph.D. student Adam Losekoot and his colleagues looked at fluvial sinuous ridges, also known as inverted channels, across this region.

“These are believed to have formed when sediment deposited by rivers hardened and was later exposed as the surrounding material eroded,” the authors said.

“Similar ridges have been found across a range of terrains on Mars.”

“Their presence suggests that flowing water was once widespread in this region, with precipitation being the most likely source of this water.”

They found fluvial sinuous ridges to be common across Noachis Terra, with a cumulative length of more than 15,000 km.

These are often isolated segments, but some systems are hundreds of km in length.

“Studying Mars, particularly an underexplored region like Noachis Terra, is really exciting because it’s an environment which has been largely unchanged for billions of years,” Losekoot said.

“It’s a time capsule that records fundamental geological processes in a way that just isn’t possible here on Earth.”

For the study, the researchers used data from three orbital instruments: the Context Camera (CTX), the Mars Orbiter Laser Altimeter (MOLA) and the High Resolution Imaging Science Experiment (HiRISE).

These datasets allowed them to map the locations, lengths and morphologies of ridge systems across a wide area.

“Our work is a new piece of evidence that suggests that Mars was once a much more complex and active planet than it is now, which is such an exciting thing to be involved in,” Losekoot said.

“The fact that the ridges form extensive interconnected systems suggests that the watery conditions must have been relatively long-lived, meaning Noachis Terra experienced warm and wet conditions for a geologically relevant period.”

“These findings challenge existing theories that Mars was generally cold and dry, with a few valleys formed by ice-sheet meltwater in sporadic, short periods of warming.”

The scientists presented their results on July 10 at the Royal Astronomical Society’s National Astronomy Meeting 2025 in Durham, the United Kingdom.

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Adam Losekoot et al. The Fluvial History of Noachis Terra, Mars. NAM 2025

When the first astronauts walked on the Moon as part of the Apollo Program, the concept of lunar habitats ceased being the stuff of science fiction and became a matter of scientific study. With several space agencies planning on sending crewed missions to the Moon in the coming decade, these plans have become the subject of scientific interest again. Structures that will enable a “sustained program of lunar science and development” is the long-term aim of NASA’s Artemis Program. China and the ESA have similar plans with the International Lunar Research Station (ILRS) and the Moon Village.

To limit the amount of materials that need to be launched for the Moon and reduce reliance on Earth, these plans will incorporate local resources for building materials and resources – in-situ resource utilization (ISRU). In a recent study, researchers from Poland and the UK proposed a developmental pathway for a lunar habitat that begins with a dome built using a regolith-based geopolymer. This dome would enclose a 17-meter (~56 ft) diameter crater in the Mare Tranquillitatis region that would house all the necessary buildings for a lunar base.

The research was led by Magdalena Mrozek, a Research Assistant with the Faculty of Civil Engineering at the Silesian University of Technology in Gliwice, Poland. She was joined by Dawid Mrozek and Mateusz Smolana, also researchers from the Silesian University of Technology, and Lorna Anguilano, a Senior Research Fellow with the Brunel University London, and the Assistant Director of the Wolfson Centre for Sustainable materials development and Processing. The paper that describes their findings recently appeared in Scientific Reports.

Apollo-12 astronaut Alan L. Bean operating on the lunar lander. Credit: NASA

The concept outlined in their paper represents a simplified concept for a lunar base that would leverage ISRU and the production of geopolymers on-site. The site location also offers several advantages, not the least of which is protection from meteoroid impacts and the ejecta these produce. They also selected a mare region, which are lower in elevation than highland terrains and have a higher crater density. In addition, the Mare Tranquillitatis region near the Apollo 11 landing site (0.67 North by 23.47 East) was selected because of the sample data provided by moonrocks brought back by the Apollo-12 astronauts. As Mrozek told Universe Today via email:

The concept of utilizing a crater for construction holds considerable economic significance, as it diminishes the volume of structural materials needed by concentrating solely on the implementation of a cover. In the phase of our research presented in this paper, the specific location of the crater was not a primary focus. We selected a crater with dimensions appropriate for our design, situated in a region where the temperature range would facilitate the production of geopolymers without the need for supplementary energy.

The authors analysed the concept of a covering lid for their hypothetical lunar crater, which measures 17 meters (~56 ft) in diameter and 6 meters (~20 ft) in depth. This is consistent with craters in the Mare Tranquillitatis region, which average about 20 meters by 8 meters (65.5 by 26.25 ft). The next step was to conduct a numerical analysis to identify the appropriate dimensions and shapes for a lunar structure that could handle the load transfers and maintain an Earth-like atmospheric pressure (1,013.25 millibars or 1 bar) within. The next step was to select building materials that could handle the internal stress distributions and be produced on-site using local resources.

Ultimately, they selected lunar regolith-based geopolymers (GP), which consist of synthetic, inorganic monomers primarily composed of aluminium and silicon and have distinctive mechanical properties analogous to cement concrete. This is advantageous given that lunar regolith contains an average of 45% silicon oxide (SiO) by weight. The geopolymer they created consisted of a sodium hydroxide (NaOH) solution, sodium silicate water glass (NaO x nSiO x nHO), and the lunar highlands regolith simulant LHS-1 produced by Exolith Lab.

Location of the site for the analysed structure—a hypothetical crater near a 0.67 latitude North and a 23.47 longitude East within the selenographic coordinate system. Credit: NASA

“The creation of building materials from original lunar regolith is not a viable option; therefore, one of the available lunar regolith simulants on the market must be used,” said Mrozek. “We selected LHS, produced by Space Resource Technologies. Utilizing this material, we developed a geopolymer, which was subsequently tested to obtain the strength parameters that were input into the numerical model. The forces acting on a lunar structure differ significantly from those experienced on Earth; consequently, we needed to abandon certain methodologies applicable on Earth and re-examine the problem from a novel perspective.

The curing conditions for the samples were subjected to were selected to simulate lunar conditions in the Mare Tranquillitatis region. While temperatures range from 120 °C during lunar day and -180 °C during lunar night (248 to -292 °F), they do not drop below 60 °C (140 °F) for seven terrestrial days, which is conducive to the geopolymerisation process. With these considerations in mind, the team cured their samples in a thermal vacuum chamber at 60 °C and a pressure of 50 hPa (50 millibars), consistent with the near-vacuum conditions on the Moon.

After a total curing period of 28 days, the materials were subjected to bending and compression tests and analyzed using electron microscopy (SEM) and X-ray diffraction (XRD). These tests revealed that their regolith-based geopolymer had strength and elasticity comparable to masonry cement-sand calcium-silicate. The geopolymer and the design they selected could very well enable the construction of lunar bases in cratered mare regions, thus realizing a key goal of NASA’s Artemis Program. Said Mrozek:

We are civil engineers, which is why our paper concentrates on this specific area of inquiry. However, we are currently collaborating with a diverse range of specialists from various countries in disciplines such as architecture, physics, geology, and chemistry. We are currently engaged in preparations for the initiation of a project of a lunar base, which will be significantly more complex and detailed.

Further Reading: Nature

Researchers suspect that two meteorites found in the Sahara Desert in 2023 may originally have come from Mercury, which would make them the first identified fragments of the solar system’s innermost planet.

The least studied and most mysterious of the solar system’s rocky planets, Mercury is so close to the sun that exploring it is difficult even for probes. Only two uncrewed spacecraft have visited it to date — Mariner 10, launched in 1973, and MESSENGER, launched in 2004. A third, BepiColombo, is en route and due to enter orbit around the planet in late 2026.

Scientists know little about Mercury’s geology and composition, and they have never been able to study a fragment of the planet that landed on Earth as a meteorite. In contrast, there are more than 1,100 known samples from the moon and Mars in the database of the Meteoritical Society, an organization that catalogs all known meteorites.

These 1,100 meteorites originated as fragments flung from the surfaces of the moon and Mars during asteroid impacts before making their way to Earth after a journey through space.

Not every planet is likely to eject fragments of itself Earth-ward during collisions. Though Venus is closer to us than Mars is, its greater gravitational pull and thick atmosphere may prevent the launch of impact debris. But some astronomers believe that Mercury should be capable of generating meteors.

“Based on the amount of lunar and Martian meteorites, we should have around 10 Mercury meteorites, according to dynamical modeling,” said Ben Rider-Stokes, a postdoctoral researcher in achondrite meteorites at the UK’s Open University and lead author of a study on the Sahara meteorites, published in June in the journal Icarus.

“However, Mercury is a lot closer to the sun, so anything that’s ejected off Mercury also has to escape the sun’s gravity to get to us. It is dynamically possible, just a lot harder. No one has confidently identified a meteorite from Mercury as of yet,” he said, adding that no mission thus far has been capable of bringing back physical samples from the planet either.

If the two meteorites found in 2023 — named Northwest Africa 15915 (NWA 15915) and Ksar Ghilane 022 (KG 022) — were confirmed to be from Mercury, they would greatly advance scientists’ understanding of the planet, according to Rider-Stokes. But he and his coauthors are the first to warn of some inconsistencies in matching those space rocks to what scientists know about Mercury.

The biggest is that the fragments appear to have formed about 500 million years earlier than the surface of Mercury itself. However, according to Rider-Stokes, this finding could be based on inaccurate estimates, making a conclusive assessment unlikely. “Until we return material from Mercury or visit the surface,” he said, “it will be very difficult to confidently prove, and disprove, a Mercurian origin for these samples.”

But there are some compositional clues that suggest the meteorites might have a link to the planet closest to the sun.

Hints of Mercurian origins

It’s not the first time that known meteorites have been associated with Mercury. The previous best candidate, based on the level of interest it piqued in astronomers, was a fragment called Northwest Africa (NWA) 7325, which was reportedly found in southern Morocco in early 2012.

Rider-Stokes said that was the first meteorite to be potentially associated with Mercury: “It got a lot of attention. A lot of people got very excited about it.” Further analysis, however, showed a richness in chrome at odds with Mercury’s predicted surface composition.

More recently, astronomers have suggested that a class of meteorites called aubrites — from a small meteorite that landed in 1836 in Aubres, France — might come from Mercury’s mantle, the layer below the surface. However, these meteorites lack a chemical compatibility with what astronomers know about the planet’s surface, Rider-Stokes said. “That’s what’s so exciting about the samples that we studied — they have sort of the perfect chemistry to be representative of Mercury,” he said.

Most of what is known about Mercury’s surface and composition comes from NASA’s MESSENGER probe, which assessed the makeup of the planet’s crust from orbit. Both meteorites from the study, which Rider-Stokes analyzed with several instruments including an electron microscope, contain olivine and pyroxene, two iron-poor minerals confirmed by MESSENGER to be present on Mercury.

The new analysis also revealed a complete lack of iron in the space rock samples, which is consistent with scientists’ assumptions about the planet’s surface. However, the meteorites contained only trace amounts of plagioclase, a mineral believed to dominate Mercury’s surface.

The biggest point of uncertainty, though, is still the meteorites’ age. “They are about 4.5 billion years old,” Rider-Stokes said, “and most of Mercury’s surface is only about 4 billion years old, so there’s a 500 million-year difference.”

However, he said he thinks this discrepancy is not sufficient to rule out a Mercurian origin, due to the limited reliability of MESSENGER’s data, which has been also used to estimate the age of Mercury’s surface layer.

“These estimates are based on impact cratering models and not absolute age dating, and therefore may not be entirely accurate,” Rider-Stokes said. “It doesn’t mean that these samples aren’t good analogs for regional areas on the surface of Mercury, or the early Mercurian crust that is not visible on the modern surface of Mercury.”

With more modern instruments now available, BepiColombo, the European Space Agency probe that will start studying Mercury in early 2027, may be able to answer long-standing questions about the planet, such as where it formed and whether it has any water.

Having material confirmed to have come from other planetary bodies helps astronomers understand the nature of early solar system’s building blocks, Rider-Stokes said, and identifying fragments of Mercury would be especially crucial since a mission to gather samples from the planet closest to the sun and bring them back would be extremely challenging and expensive.

Clues to planet formation

Sean Solomon, principal investigator for NASA’s MESSENGER mission to Mercury, said in an email that he believes the two meteorites described in the recent paper likely did not originate from Mercury. Solomon, an adjunct senior research scientist at Columbia University in New York City, was not involved with the study.

The primary reason Solomon cited for his doubts is that the meteorites formed much earlier than the best estimates for the ages of rocks now on Mercury’s surface. But he said he thinks the samples still hold research value.

“Nonetheless, the two meteorites share many geochemical characteristics with Mercury surface materials, including little to no iron … and the presence of sulfur-rich minerals,” he added. “These chemical traits have been interpreted to indicate that Mercury formed from precursor materials much more chemically reduced than those that formed Earth and the other inner planets. It may be that remnants of Mercury precursor materials still remain among meteorite parent bodies somewhere in the inner solar system, so the possibility that these two meteorites sample such materials warrants additional study.”

Solomon also noted that it was difficult to persuade the planetary science community that there were samples from Mars in meteorite collections, and that it took precise matching of their chemistry with data about the surface of Mars taken by the Viking probes to convince researchers to take a closer look. Lunar meteorites were also not broadly acknowledged to be in meteorite collections until after the existence of Martian meteorites had been demonstrated in the 1980s, he added, even though the Apollo and Luna missions had returned abundant samples of lunar materials more than a decade earlier.

Once samples are confirmed to be from a planetary body, Solomon said, they can provide crucial information not available from remote sensing by an orbiting spacecraft on the timing of key geological processes, the history of internal melting of the body, and clues to planet formation and early solar system processes.

Rider-Stokes plans to continue the discussion around these meteorites at the annual meeting of the Meteoritical Society, which takes place in Perth this week. “I’m going to discuss my findings with other academics across the world,” he said. “At the moment, we can’t definitively prove that these aren’t from Mercury, so until that can be done, I think these samples will remain a major topic of debate across the planetary science community.”

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