There's very little scientific debate about the existence of surface water on Mars in its past. The evidence at this point is overwhelming. Orbiter images clearly show river channels and deltas, and rovers have found ample minerals that only form in the presence of water. Now the scientific debate has moved on. Scientists are trying to learn the extent of Martian surface water, both on the planet's surface and through time.

NASA's Mars Reconnaissance Orbiter (MRO) is a prolific purveyor of images of Mars' surface. One of its most well-known image shows Jezero Crater, the landing site of the Mars Perseverance rover. Jezero Crater is an ancient paleolake filled by an ancient river that created a delta of sediments. The orbiter also identified clays and carbonate salts, minerals that were altered by water in the planet's past.

This image of Jezero Crater is one of the MRO's most well-known images. It shows clear evidence of flowing water. The colours map the location of different minerals, including water-altered clays and carbonate salts.

Image Credit: NASA/ JPL-Caltech/ MSSS/ JHU-APL.

There are two schools of thought around Mars' watery past. One says that water was stable on the Martian surface for long periods of time, while the other states that the water channels were carved during geologically brief periods of time when climate shifts caused ice sheets to melt. Call the first one the 'warm and wet' theory and the second one the 'cold and dry' theory. Both theories are well developed, and make predictions about what scientists will find when they dig deeper.

Some research into Noachis Terra supports the idea that water features there were carved by ice-related processes during short-lived periods of wetness, the cold and dry theory. This 2016 paper illustrates that point of view. "Our studied valleys' association with ice-rich material and abundant evidence for erosion caused by downslope flow of ice-rich material are consistent with a cold, wet Mars hypothesis where accumulation, flow, and melting of ice have been dominant factors in eroding crater valleys," those researchers concluded.

Not all regions of Mars have been studied equally, and the Noachis Terra is not as well-studied as some other regions. The 'warm and wet' climate theory predicts that Noachis Terra would've had high levels of precipitation. However, there's an overall lack of Valley Networks (VNs) in the region. Valley Networks are similar to Earth's river drainage basins and are compelling evidence of Mars' watery past.

This map of Mars shows important surface features, as well as all of the planet's surface regions. Noachis Terra is a southern highland region of heavily cratered ancient terrain.

Image Credit: By Jim Secosky modified NASA image. - http://planetarynames.wr.usgs.gov/images/mola_regional_boundaries.pdf, Public Domain,

New research presented at the Royal Astronomical Society's National Astronomy Meeting presented a different sort of evidence to support the high levels of precipitation predicted in Noachis Terra by the warm and wet theory. It's titled "The Fluvial History of Noachis Terra, Mars," and the lead researcher is Adam Losekoot. Losekoot is a PhD student at the Open University, a public research university in the UK.

"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. It's a time capsule that records fundamental geological processes in a way that just isn't possible here on Earth," Losekoot said in a press release.

The evidence Losekoot and his fellow researchers uncovered is in the form of Fluvial Sinuous Ridges.

"Noachis Terra, in Mars’ southern highlands, is a region where ‘warm, wet’ climate models predict high rates of precipitation, but is poorly incised by VNs," Losekoot explained. "We searched instead for Fluvial Sinuous Ridges (FSRs, aka inverted channels) here as they provide alternate evidence to VNs for stable surface water."

FSRs are winding, elevated features left behind from Mars' watery past. They form when water flows across the surface carrying sediment with it. The sediment deposits become harder than the rock in the surrounding terrain due to compaction and mineral precipitation. When Mars' water disappeared, aeolian erosion ate away at the softer, surrounding rock, leaving the elevated FSRs behind.

To find the FSRs in Noachis Terra, Losekoot and his co-researchers turned to NASA's MRO. No other mission has done more to reveal Mars' past than the MRO. They used data from its HiRISE and other instruments, as well as data from the Mars Orbital Laser Altimeter on the Mars Global Surveyor, to identify FSRs.

Losekoot and his co-researchers found 15,000 km of FSRs in Noachis Terra. "We find FSRs 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," Losekoot writes.

This HiRISE image shows two branches of an FSR. The river split into two then rejoined outside of the image. The lower branch is heavily eroded and quite spread out, the upper branch is narrower but more clearly preserved. They could've had different exposure times or undergone different geological processes. Or they could be from different periods of water activity. There are remnants of an infilling material within the ridge and a meander where the branch turns back towards the lower trunk. The mesa in between the branches could be a crater that was filled with the same sediment as the FSR.

Image Credit: HiRISE Image: ESP_085519_1585 NASA/JPL/University of Arizona. Licence type: Attribution (CC BY 4.0)

The FSRs are broadly distributed across Noachis Terra, and some are tens of meters tall. That means the water flowed for a long time.

"The broad distribution of FSRs suggests a broadly distributed source of water," Losekoot writes. "The most likely candidate is precipitation, suggesting a benign surface environment. For FSRs to have formed mature, interconnected systems, up to tens of meters high, these conditions must also have been relatively long-lived."

"This suggests that ~3.7 Ga, Noachis Terra experienced warm and wet conditions for a geologically relevant period," Losekoot explained.

This HiRISE image shows narrow FSR with a pointed pinnacle ridge. The pointed could indicate that this FSR has suffered heavy erosion for a long time until only a narrow peak remained, or it may be that only a narrow part of the original river infill has been preserved.

Image Credit: HiRISE Image: ESP_067439_1505 NASA/JPL/University of Arizona. Licence type: Attribution (CC BY 4.0)

The way the FSRs are distributed across Noachis Terra and their extent suggests that precipitation is responsible. They also form large, interconnected systems, which suggests the watery period was long-lived. This work supports the idea that Mars was warm and wet for a long time, rather than just for bursts of time when ice sheets melted.

This MRO CTX image gives an oblique view of part of a system of FSRs in Noachis Terra. It shows river tributaries that were probably active at the same time. The rivers meandered, and there are areas where the river banks burst and deposited fine layers of sediment. At the top of the image is a really clear example of an area where two FSRs intersect with an infilled crater. This is likely where the river flowed into the crater, filling it up and then breaching the other side to continue through the crater and down to the bottom of the image.

CTX image: MurrayLab_V01_E020_N-20_Mosaic. Image Credit: NASA/JPL/MSSS/The Murray Lab. Licence type: Attribution (CC BY 4.0)

"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," said Losekoot.

Was there once life on Mars? That question has been the subject of ongoing exploration and research for more than half a century, and is closely tied to questions about how and when life emerged on Earth. At present, there are six active missions exploring the Red Planet for possible evidence of past life (and possibly present), including NASA's Perseverance rover, the Curiosity rover, and the Mars Reconnaissance Orbiter (MRO), the UAE's Hope orbiter, the ESA's ExoMars Trace Gas Orbiter (TGO), and China's Tianwen-1 orbiter and rover. In the near future, they will be joined by Tianwen-3, a sample-return mission consisting of two spacecraft.

Similar to the NASA/ESA Mars Sample Return (MSR) mission architecture, the mission will include a lander/ascent vehicle to obtain the samples and an Orbiter/Earth-return element to bring them back to Earth. In recent news, the University of Hong Kong (HKU) announced that the scientific team will include Professor Yiliang Li, an astrobiologist from the Department of Earth Sciences. Li will be leading an HKU group responsible for selecting the mission's landing site: a region where liquid water once flowed and there's an abundance of materials that are likely to preserve evidence of past (or present) life.

Li was also the lead author on a paper that describes the mission's objective, which recently appeared in Nature Astronomy. He was joined by researchers from the Institute of Deep Space Sciences, the Deep Space Exploration Laboratory, the Chinese Academy of Geological Sciences, the CNSA Lunar Exploration and Space Engineering Center (LESEC), University of Science and Technology of China, the School of Remote Sensing and Information Engineering, the Key Laboratory of Earth and Planetary Physics, the Research Center for Planetary Science, the Beijing Institute of Spacecraft System Engineering (ISSE), and the Chinese Academy of Sciences (CAS), and the Chinese Academy of Geological Sciences.

The roadmap of the Chinese Mars Sample Return mission, which will be launched in 2028.

Credit: Hou, et al. (2025)

The search for evidence of life on Mars began with NASA's Viking 1 and 2 missions, consisting of an orbiter and lander element. The two landers set down in Chryse Planitia and Utopia Planitia, respectively, both of which are located in the Northern Lowlands. This region is believed to have once been a global ocean that spanned Mars' northern hemisphere, making it a promising location for NASA scientists to search for biosignatures. While the results were inconclusive, the search continues and has been bolstered by the arrival of missions like Pathfinder, Spirit and Opportunity, Curiosity, and Perseverance.

Astrobiological research has also benefited from recent discoveries made here on Earth. Based on the most recent fossilized evidence, scientists theorize that life emerged in Earth's oceans during the Archean Eon (ca. 4 billion years ago). Several lines of evidence also indicate that the evolution of microbial life during the first billion years was pivotal to Earth becoming a habitable planet. During Mars' Noachian Period (ca. 4.1 - 3.7 billion years ago), conditions were similar to Earth's, including a denser atmosphere, flowing water on the surface, and active volcanism. In other words, Mars had an environment favorable to the emergence of life while life was gaining a foothold on Earth.

To investigate this further, scientists hope to obtain samples from areas rich in hydrated minerals (which are essential to life) and where microbial activity could potentially be preserved for billions of years. As such, site selection is a crucial first step to any sample return mission, the protocol and strategy of which is detailed in the team's paper. Also described are the scientific payloads and the methods used to detect potential biosignatures in the returned samples. These samples will be extracted from a drill depth of 2 meters (~6.5 feet), which is critical since organic materials are safe from radiation and toxic perchlorites at this depth.

In accordance with the Committee on Space Research (COSPAR) Planetary Protection Policy, the team also recommends establishing a Mars Sample Laboratory on the outskirts of Hefei, a major hub for scientific research where many of China's leading research institutes are located. The laboratory will be equipped with the necessary scientific instruments to conduct a comprehensive analysis of the returned Mars samples while ensuring that they are safely contained to prevent exobiological contamination. If and when the samples are determined to contain no active biological agents, they will be released to designated laboratories for further detailed analyses.

The rover Zhurong, depicted in the image, became China's first rover to successfully land on the Martian surface in 2021.

Credit: CNSA

Due to the cancellation of the MSR mission, China is now poised to be the first country to return samples from Mars that could contain organic matter (and maybe even lifeforms!) The Tianwen-3 mission will build on the success of Tianwen-1, which successfully established orbit, landed on the surface, and deployed the Zhurong rover on Mars in 2021. In the process, China became the first nation to accomplish all three goals in a single mission, something the country hopes to do again in 2028. The CNSA released an Announcement of Opportunities (AO) on March 11th, which opened the mission to international collaboration.

The final selection of collaborators is scheduled for October 2025, and flight models of selected payloads are to be delivered in 2027. If everything goes according to plan, the samples will be returned to Earth by 2031.

Further Reading: Hong Kong University, Nature

We live in an exciting time of technological innovation and breakthroughs in astronomy, cosmology, and astrophysics. This is similarly true for the Search for Extraterrestrial Intelligence (SETI), which seeks to leverage advances in instrumentation and computing to find evidence of "technosignatures" in the Universe. While the scope has expanded considerably since Cornell Professor Frank Drake and colleagues conducted the first SETI experiment over sixty years ago (Project Ozma), the vast majority have consisted of listening to space for signs of possible radio transmissions.

A prime example is Breakthrough Listen (BL), a project launched by Breakthrough Initiatives in 2016 and the largest SETI experiment ever mounted. BI combines radio observations from the Green Bank Observatory and the Parkes Observatory with visible light observations from the Automated Planet Finder. In a recent study, an international team of astronomers examined 27 exoplanets selected from the Transiting Exoplanet Survey Satellite (TESS) archive and examined them for signs of artificial radio signals that went silent as they passed behind their stars.

The study was led by Rebecca Barrett, a SETI researcher and recent Masters of Science (Astrophysics) graduate from the University of Southern Queensland (UniSQ). She was joined by researchers from the UniSQ Center for Astrophysics, the SETI Institute, the Berkeley SETI Research Center, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Astronomy and Space Science, the Centre for Astrophysics and Supercomputing(CAS) at the Swinburne University of Technology, the International Centre for Radio Astronomy Research (ICRAR), and the Square Kilometer Array Observatory (SKAO).

The field of SETI has grown considerably in the past six decades, reflecting our expanding knowledge of the cosmos and astrophysical phenomena. Per the NASA Technosignature Report (released in 2018), the list of potential technosignatures includes gravitational waves (GWs), neutrinos, directed energy (optical communications or propulsion), and more. Nevertheless, surveys in the radio spectrum are still at the forefront of SETI investigations because the technology has a proven track record as a cost-effective means of communication. Moreover, radio waves are easily detected since they experience minimal scattering as they pass through planetary atmospheres and the interstellar medium (ISM).

The field has also been bolstered by the spate of exoplanet discoveries that have taken place in the past twenty years. To date, more than 5,900 exoplanets have been confirmed in over 4,400 planetary systems, with thousands more awaiting confirmation. For their study, the team carefully selected a frequency band of radio data from a large set of observations made by BI from 2018 to 2022. The team ensured that these observations' field of view (FoV) corresponded to a selection of 27 confirmed and candidate exoplanets detected by NASA's Transiting Exoplanet Survey Satellite (TESS).

Specifically, the team looked for indications of potential radio signals that were interrupted as these planets passed behind their respective stars (occulted). As Barrett told Universe Today via email:

Occultations could provide a unique opportunity to search for and localise technosignatures. Hypothetically, if a transmitting exoplanet were to pass behind its host star, the signal should be interrupted, resuming when it re-emerges. A signal could thus potentially be isolated from the surrounding noise and RFI by subtracting emission received from the system during eclipse from emission during transit. This concept will be explored in future works.

Using occultations to detect and confirm targets for SETI technosignature searchers has gained popularity in the last decade. However, the focus has been on planet-planet occultation and signal spillover, whereas Barrett and her colleagues explored planet-star occultation. Their work was based on Barrett's 2023 Master's thesis, which established the first limits using targets of interest (TOIs) designated by TESS. Unfortunately, all 27 TOIs were attributed to radio frequency interference (RFI), ruling out the possibility of technological activity.

Murriyang, CSIRO's Parkes radio telescope at the Parkes Observatory.

Nevertheless, this study is the first case where planet-star occultations were used for technosignature searches and will serve as a benchmark for similar SETI surveys in the near future. Said Barrett:

I personally plan to commence a PhD in 2026, where I hope to continue developing tools that will aid in the search for intelligent life. I was very fortunate to work alongside some of the leading experts in the field during this project, and will undoubtedly do so again in the future! I would hope that this work could inspire further SETI investigations toward exoplanets during occultation and help spur the development of an efficient method for isolating unique emissions that could be applied as a background check in mainstream transiting exoplanet surveys.

The preprint of their paper was published online by the University of Cambridge Press and is being reviewed by the Publications of the Astronomical Society of Australia.

Further Reading: 

• arXiv

If humanity intends to live and work beyond Earth, we need solutions for living sustainably in inhospitable environments. Even Mars, the most hospitable planet in the Solar System beyond Earth, is hostile to life as we know it. These include extreme temperature variations, a thin, unbreathable atmosphere, toxic soil, and higher-than-normal levels of solar and cosmic radiation. Given the distance between Earth and Mars and the time it takes to send missions there (6 to 9 months using conventional propulsion), these habitats must be closed-loop, self-sustaining environments that provide crews with food, water, and breathable air.

Last, but certainly not least, there's the problem of launching the necessary equipment, machinery, and building materials to the Moon, Mars, and other locations beyond Earth. Given the sheer mass of these payloads, launching them from Earth is neither practical nor cost-effective. This means resources must be harvested in situ to provide the necessary resources and building materials - aka. in-situ resource utilization (ISRU). In a recent paper, an international team led by Harvard Professor Robin Wordsworth showed how these challenges can be addressed with green algae grown inside habitats made of bioplastics.

The study was led by Robin Wordsworth, Gordon McKay Professor of Environmental Science and Engineering and a Professor of Earth and Planetary Sciences at Harvard University. He was joined by researchers from the Harvard School of Engineering and Applied Sciences (SEAS), Harvard Medical School, the Harvard & Smithsonian Center for Astrophysics (CfA), the School of Physics and Astronomy at the University of Edinburgh, and the Boston-based biomanufacturing company Circe.

For decades, NASA and other space agencies have investigated ways to leverage Martian and lunar resources to create building materials and finished structures. Many of these proposals have been mechanical in nature, combining 3D printing techniques with bonding elements and polymers or sintering to turn regolith into concrete or molten ceramics. Other concepts seek to utilize biological processes to grow habitats in extraterrestrial environments, often relying on mycelia or other strains of fungi and lichens. The concept proposed by Wordsworth and his colleagues leverages another biomanufacturing process that relies on algae to turn CO2 into bioplastics.

The 3D printer and the printed bioplastic in the Harvard team's experiment.

Credit: Wordsworth, et al. (2025)

For their experiment, the team 3D-printed a growth chamber made from bioplastic (polylactic acid). This chamber was filled with algae and placed in a carbon dioxide-rich environment similar to Mars. While the simulated environment had an atmospheric pressure of just 600 pascals (about 1% of Earth's atmosphere), pressure levels within the chamber were high enough for water to exist in a stable form. The bioplastic blocked harmful UV radiation while admitting enough light so photosynthesis could occur with the algae. This allowed the algae to grow and produce more polylactic acid, thereby growing the structure.

The concept replaces industrial processes and materials that are costly to manufacture and recycle with biomimicry, imitating how autotrophs grow naturally on Earth, using just carbon dioxide and water. As Wordsworth explained in a Harvard SEAS press release, their experiments are a first step toward the creation of habitats that do not require materials sent from Earth:

If you have a habitat composed of bioplastic, and it grows algae within it, that algae could produce more bioplastic. So you start to have a closed-loop system that can sustain itself and even grow through time. The concept of biomaterial habitats is fundamentally interesting and can support humans living in space. As this type of technology develops, it's going to have spinoff benefits for sustainability technology here on Earth as well.

In previous experiments, Wordsworth and his team demonstrated how sheets of silica aerogels could be used to conduct terraforming on a local scale. Also known as "paraterafforming," this method addresses both temperature and pressure issues by triggering a greenhouse effect that allows algae to grow more prolifically. Much like their experiment with bioplastics and algae growth, this method could be a pathway towards establishing a human presence beyond Earth.

The next step, said Wordsworth, is to demonstrate that their habitats also work in the vacuum conditions present on the Moon. The team also hopes to design a closed-loop production system to produce additional habitats. The Leverhulme Center for Life supported the research through the University grant, the Harvard Origins of Life Grant, and the National Science Foundation.

Further Reading: 

• Harvard SEAS, 
• Science Advances

Astronomers have studied the globular cluster 47 Tucanae extensively, but still have many questions. It may have an intermediate mass black hole in its center like Omega Centauri is expected to have. There are reasons to believe it may be the remnant of a dwarf galaxy that was gobbled up by the Milky Way, like other GCs. Also like other GCs, its center is extraordinarily dense with stars, and astronomers aren't certain how far the cluster spreads. Individual stars in 47 Tuc are difficult to observe because they're so tightly packed in the center and because they're difficult to differentiate from field stars on its outer edges. Can the Vera Rubin Observatory help?

Early data from the Vera Rubin and its Legacy Survey of Space and Time (LSST) were designed to test and refine the telescope's system. But it's still good quality data, and researchers are using it to not only understand how the Vera Rubin Observatory (VRO) performs, but also for concrete science results.

New research used the VRO's observations of 47 Tuc to uncover more stellar detail, including identifying stars in its core and in its outer regions. It's titled "47 Tuc in Rubin Data Preview 1: Exploring Early LSST Data and Science Potential." The lead author is Yumi Choi from the National Science Foundations National Optical-Infrared Astronomy Research Laboratory in Tucson, Arizona.

"We present analyses of the early data from Rubin Observatory's Data Preview 1 (DP1) for the globular cluster 47 Tuc field," the researchers write in their paper. The data is from four nights of observations with the VRO's Commissioning Camera (ComCam). The ComCam is a smaller 144-megapixel version of the VRO's full 3200-megapixel LSST Camera. The observations were made in the standard multiple bands (ugriz). u: Ultraviolet, g: Green (visible light), r: Red (visible light). i: Near-infrared, z: Further near-infrared.

The left and middle images are both from the VRO's ComCam. The image on the right is from Gaia. In all images, the center of 47 Tuc is tightly packed with stars and saturated with light.

Image Credit: Choi et al. 2025.

The authors explain that they wanted to address challenges in separating stars in 47 Tuc's crowded center from background stars in both the Milky Way and the Small Magellanic Clouds. "We compile a catalog of 3,576 probable 47 Tuc member stars selected via a combination of isochrone, Gaia proper-motion, and color-color space matched filtering," they write.

"The LSST ComCam imaging provided valuable early photometric measurements, while also revealing challenges from crowding, particularly near the core of 47 Tuc and toward the SMC," the authors explain.

The researchers did more than just detect 3,576 probable stars. They also detected RR Lyrae variable stars, which are common in globular clusters, and eclipsing binaries. "Further, we successfully crossmatched known variable stars within the 47 Tuc field against the DP1 data, recovering three RR Lyrae stars and two eclipsing binaries," they write. Eclipsing binaries can be difficult to detect with ground-based telescopes, and so can some variable stars. Despite "sparse temporal sampling" the ComCam was able to find them.

Crowded stellar fields like the tightly-packed core of 47 Tuc are challenging to observe. Astronomers combine multi-wavelength observations from multiple telescopes to achieve results. These first results from the VRO shows it has a big contribution to make. "Overall, while challenges remain, the DP1 data around 47 Tuc convincingly showcase Rubin Observatory’s strong potential for detailed stellar population and variability analyses in crowded stellar fields," the researchers write in their conclusion.

The Omega Centauri globular cluster. Globulars are characterized by their densely-packed centers, where differentiating between individual stars is challenging.

Image Credit: ESA/Hubble, NASA, Maximilian Häberle (MPIA)

"Continued improvements to the Rubin Science Pipelines and in-kind programs dedicated to crowded-field stellar photometry are expected to deliver even higher-quality results in future DP2 and DR1."

The VRO's main effort will be its 10-year Legacy Survey of Space and Time. The LSST is a wide-field, multi-band survey of the visible sky that is both rapid and deep. Its results will tell us more about multiple issues in astronomy: dark matter, dark energy, supernovae, the Milky Way's structure, and many more. It will also tackle globular clusters.

Astronomers still don't know exactly how GCs form and how they might be connected to a galaxy's dark matter. There are a host of outstanding questions.

Astronomers have hoped that the VRO will not only discover new globulars, but that it will also provide more precise measurements of individual GC stars. By providing precise, multi-band photometry for individual stars over a 10-year period, it will create accurate Color-Magnitude Diagrams (CMD) for vast numbers of stars in GCs. It will also observe tiny shifts in their positions over its decade-long survey. Not only that, but the VRO will observe GCs in other galaxies, allowing comparative study in away that hasn't been possible.

The entire space community has been anticipating the VRO's first light with great enthusiasm. With its first preliminary results in, it looks like the wait has been worth it and the observatory will deliver on its promise.

Earth is the only habitable world we know of and it remains habitable because of natural cycles that maintain a balanced climate. Earth's carbon cycle plays a critical role in maintaining its temperate climate, and carbonate rocks are a big part of it. Carbonate rocks like limestone and dolomite are huge carbon sinks, and if their carbon was released into the atmosphere, Earth's temperature would spike catastrophically, rendering our planet uninhabitable. Conversely, if all of Earth's carbon were locked away in rock, Earth would likely become glaciated, photosynthesis would cease, and a mass extinction would leave extremophiles as the sole survivors of life's rich, living heritage.

As long as Earth's carbon keeps cycling between rock and atmosphere in a reasonable balance, the planet maintains its habitability.

With Earth's carbon cycle as an example, what can we learn about Mars? There's rock-solid evidence that Mars had habitable conditions in its past, though those conditions haven't persisted. The planet was once warm and wet and is now frigid and dry. What part did a carbon cycle play in Mars's habitability and uninhabitability?

New research in Nature says that Mars went through periods of habitability and uninhabitability due to carbon cycling. It's titled "Carbonate formation and fluctuating habitability on Mars," and the lead author is Edwin Kite. Kite is an associate professor of Planetary Science in the Department of Geophysical Sciences at the University of Chicago.

"The cause of Mars’s loss of surface habitability is unclear, with isotopic data suggesting a ‘missing sink’ of carbonate," the paper states. "Past climates with surface and shallow-subsurface liquid water are recorded by Mars’s sedimentary rocks, including strata in the approximately 4-km-thick record at Gale Crater." Gale Crater was chosen as MSL Curiosity's exploration site largely because Mt. Sharp rises more than 5 km and its layered slopes preserve a stratigraphic geological record of Mars's history. The layers of clays and sulphate-rich deposits show how the planet experienced periods of wetness. The researchers explain that the water was patchy and intermittent, and persisted late into the planet's history.

This figure from 2021 research shows some of the detail in Mt. Sharp's stratigraphic layers. It shows the ancient conditions in which each layer of the mountain formed. Research shows that Mars had alternating periods of wet and dry until it dried out completely about 3 billion years ago.

Image Credit: NASA/JPL-Caltech/MSSS/CNES/CNRS/LANL/IRAP/IAS/LPGN

The researchers draw a parallel between Earth's and Mars's carbon cycles. They write that Mars's patchy and intermittent surface water is best explained by a carbon cycle that locks carbon away into sedimentary carbonate rocks. The research is based on NASA's MSL Curiosity rover and its exploration of Gale Crater. It landed there almost 13 years ago to study the crater's geology. Among other findings, it measured carbonate materials in the crater and found that they make up 11% of the rocks in the region.

Mars once had a carbon-rich atmosphere, and the authors reference a paper by other researchers showing that stratigraphic layers and carbonate rocks in Gale Crater are clear evidence of that cycle. What drove the cycle?

"Here we show that a negative feedback among solar luminosity, liquid water and carbonate formation can explain the existence of intermittent Martian oases," Kite and his co-researchers write. They developed a model to illustrate and explain what happened to Mars.

The researchers say that as the Sun has brightened over billions of years, that increasing luminosity supported liquid surface water on Mars. Just like on Earth, available water combined with atmospheric carbon to form weak carbonic acid. That acid created carbonate weathering that acts as a natural thermostat by sequestering carbon into rock.

But things didn't end there. The atmosphere's loss of carbon reduced carbon dioxide's contribution to Mars's atmospheric pressure. The lower atmospheric pressure allowed water to more easily vaporize away into the atmosphere. The researchers say that Mars underwent cycles of wet periods and dry periods due to chaotic orbital forcing.

This figure shows histograms of the durations of wet events at Gale and globally in blue. Red shows durations of dry intervals within the time span of wet events. The three different lines of each type correspond to three different random orbital histories. Globally dry periods are sometimes very long and could have driven any surface life to extinction.

Image Credit: Kite et al. 2025. Nature.

Mars suffers from unpredictable and chaotic changes to its axial tilt that affects its climate, and this forcing drives Mars's carbon cycle and its ancient periods of wet habitability and dry uninhabitability. "The negative feedback restricted liquid water to oases and Mars self-regulated as a desert planet," the researchers explain. The researchers also explain that Gale Crater's stratigraphic record "...faithfully records the expected primary episodes of liquid water stability in the surface and near-surface environment."

During these cycles, the atmosphere eventually thickens and approaches water's triple point. The triple point is a specific combination of pressure and temperature wherein water can exist in equilibrium in all three phases: vapour, liquid, and solid. Water's triple point is 0.01 °C (273.16 K) and 611.73 pascals (0.006 atm). The researchers explain that this restricted the sustained stability of liquid water and the planet's surface habitability.

This figure from the research illustrates the researchers' model. a shows the distribution of carbonate detections in sedimentary rocks and soil on Mars, with yellow showing abundant detections, red showing no detections, and brown representing unexplored areas. b shows the fluxes and feedbacks for geologic carbon and climate regulation on Mars and Earth. On Earth, volcanic CO2 output is regulated by rapid carbonate formation. On Mars, solar brightening increased the temperature slowly and is balanced by slow carbonate formation. However, Mars' chaotic orbital forcing means that water is only available for carbonate formation intermittently during orbital optima, leading to intermittent periods of warmth and surface water.

Image Credit: Kite et al. 2025. Nature.

The researchers' model has limitations just as all models do. For example, it assumes that the carbonate content at Gale Crater is representative of the whole of Mars. For this reason, they present their research as a testable idea rather than a definitive conclusion.

"Carbonate formation and surface liquid-water availability are linked by a negative feedback that can explain fluctuating habitability on Mars," the authors write in their conclusion. They write that this cycle can potentially explain the intermittent and patchy nature of oases on Mars, and the sedimentary rocks that entomb those oases. They also say their model can explain how Mars's surface habitability came to an end, a question that has motivated scientists for a long time, and speaks to our wider questions about life elsewhere in the Universe.

How did Earth, alone among the Solar System's rocky planets, become the home for life? How, among all this frigid lifelessness, did our planet become warm, hospitable, and life-sustaining? The answer to these questions is complex and multi-faceted, and part of the answer comes from cosmochemistry, an interdisciplinary field that examines how chemical elements are distributed.

The Solar System is a busy place where everything is in motion. It was even more chaotic 4.5 billion years ago, with planets still forming and planetesimals and planetary embryos whizzing around and crashing into one another. Somehow, in all that chaos, Earth received more than its share of carbonaceous chondrites and the amino acids and other life-enabling chemicals that came with them.

Cosmochemistry studies have shown that between 5% and 10% of Earth's mass came from carbonaceous chondrites that crashed into the young planet. Studies also show that a large chunk of that came from the Theia impactor that created the Moon. To test these ideas more rigorously, a trio of researchers used dynamical simulations of the Solar System's formation to see if they could replicate it.

The research is titled "Dynamical origin of Theia, the last giant impactor on Earth." The lead author is Duarte Branco from the Institute of Astrophysics and Space Sciences at the Lisbon Astronomical Observatory in Portugal. The research will be published in the journal Icarus.

One of the critical distinctions in cosmochemistry is the difference between carbonaceous chondrites (CCs) and non-carbonaceous meteorites (NCs). It divides the Solar System's meteor population into two groups and suggests that the Solar System contains two distinct reservoirs of material. CCs formed further from the Sun, likely beyond Jupiter, and carry more volatiles like water and organic compounds with them. NCs include things like iron meteorites, and contain fewer volatiles.

In order to test the idea that Theia delivered CCs and volatiles to Earth, the researchers ran detailed simulations of the Solar System. These were N-body simulations of the later stages of the growth of terrestrial planets.

The simulations began in the late stages of planetary growth after the Solar System's gaseous disk was dispersed. The available solid mass was divided into planetesimals and planetary embryos. The simulation included CCs that were scattered inward as Jupiter and Saturn were still growing and accreting matter. Because of the size distinction between planetesimal and planetary embryos, embryos have a higher possibility of interacting with the terrestrial planets and delivering CC material.

The researchers ran three types of simulations. The first they call small only and includes only small CC objects, or planetesimals. The second they call large only and includes only large CC objects, planetary embryos. The third includes both CC planetesimals and embryos and is called the mixed scenario.

For a subset of 10 simulations from each of those scenarios, they included the effect of the giant planet dynamical instability. This is known as the "Nice model" in astronomy and describes how the giant planets shifted their orbits from where they initially formed.

The goal was to determine how CCs and NCs were distributed in the Solar System and to understand how Earth ended up with more CCs than the other rocky planets, especially Mars. The researchers also wanted to understand if the Theia impact could be responsible for delivering a large amount of Earth's CC material.

One clear result is that the role of giant planet instability, especially Jupiter's shift to a different orbit, had a pronounced effect on Earth's accretion of CC material.

This figure shows snapshots from the mixed simulation scenario without giant planet dynamical instability. In early times, CC objects and NC bodies mix together where the terrestrial planets are forming. Some CCs remained orbiting between planets or were still too far to collide. By the simulation's end, four terrestrial planets existed, including good analogues for Earth and Mars.

Image Credit: Branco et al. 2025. Icarus

When the researchers added giant planet dynamical instability, things looked even more interesting. "The giant planet instability dramatically changed the evolution of the system causing a strong pulse of eccentricity excitement, which lead to a wave of collisions and ejections," the authors write. However, the final state of the system didn't change much.

This figure shows eccentricity and position snapshots over the time of the simulation, including giant planet dynamical instability. The final snapshot is the real Solar System.

Image Credit: Branco et al. 2025. Icarus

A critical part of the simulations concerns the Theia impactor. Previous research suggests that Theia may have been a carbonaceous object. If that's true, much of Earth's life-giving habitability may have resulted from that collision.

"In the mixed scenario with no giant planet instability, Earth’s final impactor included a CC component in more than half of all simulations. In 38.5% of simulations, the final impactor was a pure CC embryo, and in another 13.5%, the impactor was an NC embryo that had previously accreted a CC embryo," the researchers write.

Overall, the simulations paint a picture of the early Solar System where two distinct rings of planetesimals. An inner ring consisting of rocky planetesimals and an outer ring of carbonaceous chondrites. Later, as the ice giants migrated inward, they propelled CC material into the inner Solar System. Some of these were trapped in the asteroid belt, while more massive ones were preferentially scattered into the orbits of the rocky planets. "The late-stage accretion of the terrestrial planets involved a series of giant impacts between NC embryos and planetesimals, with occasional impacts of CC objects," the authors explain.

This scenario explains several things about the Solar System. It explains the masses and orbits of the terrestrial planets, and the orbital distribution of asteroids. It also matches the CC mass fraction of Earth and Mars, where Mars lacks the same concentrations of CC material as Earth. If the small only simulation were correct, where CC material was only in the form of planetesimals, the CC mass fraction of Mars and Earth would be roughly the same.

This figure compares the timing of the last giant impacts in 10 mixed simulations that were run both with and without the giant planet instability. The black line represents the point where both values are equal. Each point has two halves with the left half representing the impactor type in the simulation without the giant planet instability and the right half representing the simulation with the giant planet instability. Dry NC impactors are black, CC embryos are blue and CC+NC mixed embryos are green.

Image Credit: Branco et al. 2025. Icarus

The researchers set out to show that, in line with other research, Theia could've been Earth's final large impactor and that it contained ample CC material. They appear to have succeeded.

In the simulations, Earth's final giant impact was with Theia, and that object had higher concentrations of CC material which helped make Earth habitable. That result is in line with scientific thinking. The work shows that the last impact was after between 5 to 150 million years after gas dispersal. A large fraction of those were within 20 to 70 million years. There are uncertainties in the timing of the Theia impact and these results work within those.

The simulations also support other conclusions showing that CC embryos and planetesimals could've been accreted throughout Earth's growth, but were concentrated in later phases of growth.

"Within the context of this scenario, the last giant impactor on Earth contained a CC component in roughly half of all of the mixed simulations," the authors write. "In the majority of these (38% of simulations), Theia was a pristine CC embryo, and in the remainder of cases Theia was an NC embryo that had previously accreted a CC embryo."

The research also shows that Jupiter played an important role in the Solar System's architecture. It not only truncates the asteroid belt, but played an important role in determining the final composition of the terrestrial planets by scattering CC material from the outer Solar System into the path of the rocky planets, especially Earth.

A million things had to be just right for Earth to become the life-sustaining world it is today. How likely it is that there are other worlds out there like it is unknown. It may take more than being in a habitable zone for an exoplanet to support life. There may be a bewildering number of variables that have to go right, including outer giant planets that migrate and deliver carbon to rocky worlds in habitable zones.

RELATED VIDEOS

One of the most iconic cosmic scenes in the Universe lies nearly 3.8 billion light-years away from us in the direction of the constellation Carina. This is where two massive clusters of galaxies have collided. The resulting combined galaxies and other material are now called the Bullet Cluster, after one of the two members that interacted over several billion years. It's one of the hottest-known galaxy clusters, thanks to clouds of gas that were heated by shockwaves during the event. Astronomers have observed this scene with several different telescopes in multiple wavelengths of light, including X-ray and infrared. Those observations and others show that the dark matter makes up the majority of the cluster's mass. Its gravitational effect distorts light from more distant objects and makes it an ideal gravitational lens.

Astronomers pointed the infrared-sensitive James Webb Space Telescope (Webb) to view the Cluster in part to help refine its mass. The Bullet is actually two clusters, a smaller sub-cluster called the Bullet, and the larger one it collided with in the past. The observations provided extremely detailed images of the cluster's galaxy members, as well as a view of hundreds of other faint ones that lie beyond. They also mapped the distribution of hot gas, which appears to be in separate "blobs". Those gaseous regions helped them learn more about the distribution of dark matter in the cluster. “With Webb’s observations, we carefully measured the mass of the Bullet Cluster with the largest lensing dataset to date, from the galaxy clusters’ cores all the way out to their outskirts,” said Sangjun Cha, the lead author of a paper published in The Astrophysical Journal Letters. Not only that, but the Webb view also allows scientists to study the distant galaxies "behind" the cluster in great detail. Their distorted images also give clues to the distribution of dark matter in the lens.

This image shows the different wavelengths at which scientists studied the Bullet Cluster using JWST's NIRCam instrument. The circles show the two clusters (in blue with their hot gas clouds in red). The one on the left shows an elongated shape, which suggests it's been through more than one collision.

Credit: NASA, ESA, CSA, STScI, CXC

“Webb’s images dramatically improve what we can measure in this scene — including pinpointing the position of invisible particles known as dark matter,” said Kyle Finner, a co-author and an assistant scientist at IPAC at Caltech in Pasadena, California. Dark matter plays a role, not just in the Bullet Cluster's hot gas clouds, but also in the light from distant galaxies passing through and around the cluster.

What Happened with the Bullet?

When you look at the combined infrared and X-ray views of the Bullet Cluster, among other things, you see those blobs of hot gas. One is in the form of a bow shock whipped up when the smaller sub-cluster member passed through the larger galaxy cluster. That sent the temperature of the gaseous regions up to millions of degrees, which released X-ray emissions detectable by Chandra.

A Chandra X-ray view of hot gas clouds in the Bullet Cluster. This one gives the cluster its distinctive name. It lies entirely separated from the dark matter in the cluster. This indicates something about how dark matter behaved in the collision.

Credit: X-ray: NASA/CXC/SAO

To understand why astronomers find the Bullet Cluster so fascinating, it helps to understand how it got the way it appears in Chandra and Webb observations. Well more than four billion years ago, these two galaxy clusters began a close approach. Both clusters were rich in stars, gas, and dust. Like the rest of the Universe, they were permeated with dark matter. Eventually, the two clusters collided. The stars were largely "unhurt" by this, other than perhaps having their velocities through space slightly altered. The collision basically caused a separation of the hot gas and dark matter. The gas, being affected by ram pressure (caused by something moving through the interstellar/intergalactic medium), slowed down due to the collision. The dark matter, which interacts primarily through gravity, passed through without any problem. This separation provided key evidence for the existence of dark matter. "As the galaxy clusters collided, their gas was dragged out and left behind, which the X-rays confirm,” Finner said. Webb’s observations show that dark matter still lines up with the galaxies — and was not dragged away.

What the Cluster's Gravitational Lens Reveals

While we can't see the dark matter at all, its presence around and within the Bullet Cluster's galaxies turns it into a giant gravitational lens. Think of it as a cosmic magnifying glass that shows otherwise unseen things. It also does something remarkable: “Gravitational lensing allows us to infer the distribution of dark matter,” said James Jee, a co-author, professor at Yonsei University, and research associate at UC Davis in California. Jee suggests that we think of this gravitational lensing as working the same way that water in a pond magnifies the view of things in the pond. “You cannot see the water unless there is wind, which causes ripples,” Jee explained. “Those ripples distort the shapes of the pebbles below, causing the water to act like a lens.”

That lens reveals thousands of distant galaxies whose light is "smeared" and distorted by the gravitational effect of the dark matter lens. The distribution of those galaxies across the lens also helps astronomers map the distribution of the dark matter that makes it up.

The Webb NIRCam view of the Bullet Cluster, showing an infrared look at distant galaxies, with their images deformed by the gravitational effect of the dark matter.

Credit: Near-infrared: NASA/ESA/CSA/STScI;

Image processing: NASA/STScI/J. DePasquale

Now that astronomers know where that dark matter is distributed in the cluster, the images and data also show that the particles (no matter what they're made of) don't affect each other beyond whatever gravitational attraction they have toward each other. It implies that they act independently of each other. Now the trick is to figure out what kind of particles act as dark matter has been observed to do. Webb’s observations also show that dark matter still lines up with the galaxies — and was not dragged away during the chaos of the cluster collisions. These new observations place stronger limits on the behavior of dark matter particles.

For More Information

• NASA Webb 'Pierces' Bullet Cluster, Refines Its Mass
• A High-Caliber View of the Bullet Cluster through JWST Strong and Weak Lensing Analyses