Tens of thousands of pieces of space debris are hurtling around Earth right now. These defunct satellites, spent rocket stages, collision fragments and even a toolbox threaten active spacecraft and could trigger cascading disasters that make space unusable for generations. Since removing just a single piece of debris can cost tens of millions of dollars, the critical question becomes which ones should we prioritise?

It was during a spacewalk around the ISS that astronauts dropped a toolbox that now poses a threat to future space travellers. (Credit : NASA)

The numbers tell a sobering story. NASA data shows the monthly count of objects in Earth's orbit continues to climb relentlessly, while computer simulations predict an alarming future. Without intervention, low Earth orbit could become so cluttered with debris that catastrophic collisions become routine, potentially triggering a runaway chain reaction known as Kessler Syndrome.

A few years ago, eleven international teams of space experts tackled this challenge by each creating a ranked list of the 50 most concerning objects in low Earth orbit. Although they used different approaches, 20-40% of the objects ended up on several experts' lists, showing remarkable consensus given the complexity of the problem. However, their lists didn't perfectly match. Now, researchers from France and Spain have applied social choice theory, the mathematical study of voting and collective decision making to this conundrum, revealing how different ways of combining expert opinions lead to dramatically different conclusions about our most urgent space threats.

International space agencies agree that simply preventing new debris isn't enough. To stabilise the space environment, experts estimate we need to actively remove five to ten large pieces of debris, each bigger than 10 centimetres, every year before they fragment into thousands of smaller, untrackable pieces.

Orbital Debris strike on one of the window’s within the International Space Station.

(Credit : NASA)

Thankfully, the technology for space cleanup missions is rapidly advancing, with the first operational tests scheduled for later in 2025 and 2026. But with removal costs in the tens of millions of dollars per object, choosing the right targets is crucial.

The eleven expert teams used sophisticated methods to evaluate space debris, considering factors like mass, collision probability, orbital lifetime, and proximity to operational satellites. Despite using different approaches, they showed remarkable agreement with 20-40% of objects appeared on multiple lists. Only one object appeared on every expert's list, while their collective work identified 273 different pieces of concerning debris across all lists.

This level of consensus is quite impressive given the complexity of weighing multiple risk factors. However, the remaining disagreements still matter significantly when deciding where to spend tens of millions of dollars on removal missions.

Illustration of a satellite breaking up into multiple pieces at higher altitudes.

(Credit : ESA)

The original study combined the expert opinions using a hybrid scoring method, multiplying each object's Borda score (based on its ranking positions) by the number of lists it appeared on. This approach identified object 22,566 as the most concerning piece of debris.

However, the new research demonstrates that this conclusion depends entirely on the aggregation method chosen. Using the classic Borda count alone, object 22,220 emerges as the top priority. Apply the Condorcet winner principle, which seeks the object that would beat all others in head to head comparisons, and object 27,006 takes the lead. These aren't minor technical differences though. Each method reflects different philosophical approaches to collective decision making, with real implications for where humanity spends its limited space cleanup resources.

The researchers argue for fundamental changes in how we approach space debris prioritisation. Rather than forcing experts to rank exactly 50 objects, they suggest allowing each team to identify however many objects they consider truly concerning. This acknowledges that the threshold for "concerning" debris shouldn't be artificially constrained by committee decisions.

They also propose moving from ranked ballots to evaluative voting, where experts would categorise debris as "extremely hazardous," "hazardous," or "acceptable risk" based on absolute criteria rather than relative comparisons. This approach would be more robust to changes in the candidate pool and better reflect how experts actually think about risk assessment.

This research illuminates a broader challenge in scientific decision making, how to fairly aggregate expert opinions when stakes are high and resources are limited. The space debris problem resembles other collective choices, from pandemic response priorities to climate change mitigation strategies, where multiple valid perspectives must be reconciled into policies.

The study also reveals a critical gap in current debris removal planning, the failure to account for removal costs and dynamic effects. When one piece of debris is removed, the risk profiles of remaining objects change, suggesting we need more sophisticated approaches that consider removal sequences rather than individual targets.

As private space companies launch thousands of new satellites and space tourism takes off (if you will pardon the pun,) the orbital environment will only become more crowded. The methods we develop today for democratically choosing which space junk to remove, combining expert knowledge with fair aggregation techniques, may determine whether future generations inherit accessible space or a debris filled orbital wasteland that takes centuries to clear.

Source : 

• These are the Most Concerning Pieces of Space Debris

In the vast expanse between Uranus and Neptune, a team of researchers have uncovered something really quite extraordinary, a minor planet that has been locked in precise gravitational manouevres with Uranus for at least a million years. This discovery sheds new light on the complex dynamics that govern our Solar System's outer reaches.

The object in question, designated 2015 OU₁₉₄, belongs to a class of small bodies called Centaurs, rocky and icy objects that orbit between Jupiter and Neptune. What makes this particular Centaur special is its remarkably stable relationship with Uranus, locked in what is known as a 3:4 mean motion resonance. This means that for every three orbits 2015 OU₁₉₄ completes around the Sun, Uranus completes exactly four. This precise mathematical relationship creates a gravitational partnership that keeps the two objects in a stable dance, preventing them from colliding or drifting apart.

Uranus, the 7th planet in the Solar System seems to have an asteroid tagging along.

(Credit : NASA)

The discovery came about through detective work with archival observations. Researchers led by Daniel Bamberger from the Northolt Branch Observatories in Germany, located additional observations of 2015 OU₁₉₄ from 2017 and 2018, extending the object's data points from just one year to 3.5 years. This longer observation period was crucial for understanding the object's true orbital behavior.

Computer simulations revealed the remarkable stability of this relationship. The resonance has remained stable for at least 1,000 years in the past, probably even 1 million years and is predicted to continue for another 500,000 years into the future. This longevity suggests that the gravitational partnership formed early in our Solar System's history and has persisted through countless changes.

What makes this discovery particularly significant is that no objects has previously been found in resonance between the orbits of Uranus and Neptune. It’s a region of space, while containing many small bodies, that appears to lack the kind of stable orbital relationships commonly found elsewhere in the Solar System.

The asteroids of the inner Solar System, where they are far more numerous than the outer Solar Sytem, are plotted on this diagram.

(Credit : MDF)

The researchers didn't stop with just one object though. Their investigation uncovered additional candidates, including 2013 RG₉₈, which also appears to maintain this same 3:4 resonance with Uranus for several hundred thousand years. A third candidate, 2014 NX₆₅, shows strong gravitational influence from Neptune, suggesting the complex interplay of forces in this region.

The existence of these Uranus resonant objects suggests that similar relationships may be more common than previously thought. As our survey capabilities improve and we discover more objects in the outer Solar System, we may find that these gravitational partnerships are common and fundamental to understanding how small bodies are distributed throughout the region.

Source : 

• A minor planet in an outer resonance with Uranus

From one perspective, the Sun is a benevolent orb of plasma and its warmth makes Earth habitable and has kept if habitable for billions of years, allowing complex things like human beings to evolve. From another perspective, it's a malevolent orb that sends deadly UV radiation our way, and sometimes erupts and hurls massive blobs of plasma toward Earth. The truth is somewhere in the middle, and NASA launched the Parker Solar Probe to flesh out that truth.

NASA launched the Parker Solar Probe (PSP) in 2018 and its mission is to examine the Sun's coronal plasma and its magnetic field. To do this, it has to get close. NASA describes it as a mission to "touch the Sun," and that's pretty accurate. Throughout its mission it has gotten progressively closer, setting a new record each time for closest approach to the Sun. On Dec. 24, 2024, the spacecraft flew just 6.1 million km (3.8 million miles) from the solar surface.

That is incredibly close, but luckily, the spacecraft has several layers of protection. The PSP is also the fastest-moving spacecraft ever built. It was travelling at 692,000 km/h (430,000 mph) during its 2024 flyby, and didn't spend much time that close to the star.

The result of this daring piece of coronal navigation is the closest images yet of our star. The PSP carries four main instruments, and one of them is WISPR, the Wide-field Imager for Solar Probe. WISPR has two radiation-hardened cameras that can withstand the Sun's power. It's job is to image the corona, the solar wind, and other phenomena near the Sun. On the last flyby, WISPR showed us the solar corona and the solar wind in a way we've never seen before.

“Parker Solar Probe has once again transported us into the dynamic atmosphere of our closest star,” said Nicky Fox, associate administrator, Science Mission Directorate at NASA Headquarters in Washington. “We are witnessing where space weather threats to Earth begin, with our eyes, not just with models. This new data will help us vastly improve our space weather predictions to ensure the safety of our astronauts and the protection of our technology here on Earth and throughout the solar system.”

There are important implications for understanding or misunderstanding the solar wind and coronal mass ejections (CME). They're ever present forces in the Solar System. The wind is a stream of charged particles that constantly flows outward from the Sun. It's responsible for the gorgeous aurorae that we love to gaze it, but it's also responsible for damaging power grids and satellites. As we expand into cislunar space and crowd more satellites into Low-Earth Orbit, it's important that we understand not only the solar wind, but everything that flows from the Sun, including coronal mass ejections (CME).

While the solar wind is a continuous phenomenon, coronal mass ejections are episodic. They're ejections of plasma that can reach Earth. CMEs can contain billions of tons of plasma moving at high speeds. Only a small number of them reach Earth, but when they do, they can also cause geomagnetic storms that can damage power grids and other equipment.

The Parker Solar Probe is named after the American heliophysicist Eugene Parker, who coined the term 'solar wind in 1958. His theories, though they faced stiff resistance at the time, revolutionized our scientific understanding of the Sun. Multiple spacecraft have been launched to study the Sun and the solar wind, but the Parker Solar Probe has outdone them all.

Each mission has revealed more about the Sun and the solar wind, but none have come as close to the star as the PSP. It also has the advantage of the most modern technologies and instruments. One of the things its revealed is the nature of so-called switchbacks.

When measured near Earth, the solar wind is pretty much constant. But closer to the Sun, things are more chaotic. The Sun has extremely powerful magnetic fields, and when the PSP came within 14.7 million miles of the Sun, it showed us that some of those fields zig-zag. These zig-zagging fields are called switchbacks. The PSP also showed us that these switchbacks are more common than thought, and that they come in clumps.

As the PSP got progressively closer and travelled through the Sun's corona, it noticed that the corona's boundary was uneven and complex. Getting even closer in subsequent flybys, it was able to pinpoint the source of the switchbacks. The source is patches on the Sun where magnetic funnels form and images showed that the switchbacks are partly responsible for the fast solar wind, one of the wind's two components.

“The big unknown has been: how is the solar wind generated, and how does it manage to escape the Sun’s immense gravitational pull?” said Nour Rawafi, the project scientist for Parker Solar Probe at the Johns Hopkins Applied Physics Laboratory. “Understanding this continuous flow of particles, particularly the slow solar wind, is a major challenge, especially given the diversity in the properties of these streams — but with Parker Solar Probe, we’re closer than ever to uncovering their origins and how they evolve.”

The slow solar wind is twice as dense as the fast solar wind, and interplay between the two seems to create moderately strong conditions on Earth that can rival conditions generated by CMEs. The slow solar wind appears to originate from the Sun's equatorial regions, but scientists are still debating what structures they originate in and how the material is released.

“We don’t have a final consensus yet, but we have a whole lot of new intriguing data,” said Adam Szabo, Parker Solar Probe mission scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

We've learned a lot about the Sun in recent decades, and the PSP is poised to show us more and hopefully provide answers to our most probing questions. It's next perihelion will be in September, 2025, when it will again fly through the solar corona. That approach will gather even more data on the slow solar wind and other facets of the Sun.

It will also give us more stunning images.

Astrobiology can be split into two very distinct fields. There’s the field that astronomers are likely more familiar with, involving large telescopes, exoplanets, and spectroscopic signals that are pored over to debate whether they show signs of life. But there is another camp, collective known as the Origins researchers that focus on developing a scientific understanding of how life originally developed on Earth. A new paper from Cole Mathis at Arizona State and Harrison B. Smith at the Institute of Science in Tokyo suggests a new path forward to tackling those challenges - set them up as competitions and let a hefty prize motivate scientific teams and individuals to pursue them.

The paper, which was published on arXiv, is a response to NASA’s Decadal Astrobiology Research and Exploration Strategy (DARES) call for community input. It calls on the “challenge” funding model popularized by organizations like the X Prize, and the Defense Research Advanced Projects Agency (DARPA), whose early autonomous driving challenges inspired the self-driving cars that are finally starting to navigate public roadways.

A similar method could be used to stimulate research into specific, measurable, and important “origins” research according to Drs. Mathis and Smith. They point out that one hurdle holding back development in this field is a lack of consensus on even simple definitions, such as “what is life?”. However, they lay out five different “finish lines” that, though some of them would prove certain theories, lack of progress towards them could also be held up as proof of opposing theories.

One finish line will attempt to solve the debate of whether metabolism or genetics were developed first in the course of life. It focuses on creating a biological pathway known as the pentose phosphate pathway (PPP) using abiotic chemistry. If possible, it would make a strong case that the “metabolism first” camp is correct.

A second finish line utilizes the concept of “assembly theory”, a framework developed by Leroy Cronin and Sara Walker, that quantifies the complexity of organic molecules, and draws a distinct line at a certain complexity level, showing that anything more complex must be made within a biological system. The challenge the authors put forward is to create a sufficiently complex molecule using only abiotic chemistry.

The third challenge attempts to settle the debate between “determinism” and “contingency”. In the determinism world view, if we manage to rewind life back to its early beginnings, would the same process happen in the same way all over again if given the same starting conditions? Or, according to the “contingency” theory, would small differences in the chemistry makeup of early life lead to massive differences in the biochemistry of later lifeforms. The challenge itself is to design an organic chemistry experiment where exactly the same initial conditions can lead to different products. If someone manages to do this, it would prove the “contingency” theory of early life formation.

The fourth challenge tackles self-replication, by requiring a team to make polymers that can self-replicate but still overcome “Eigen’s error threshold”. According to the information theory developed by Manfred Eigen that goes along with replicators passing data to the new copies of themselves, early replicators would have to be much smaller than would be necessary to contain any error-correcting biological machinery common when our cells copy their own DNA during the replication process. Understanding how early life got through this bottle neck to develop reliable error checking systems without losing all their information once they cross the threshold in terms of size is at the problem at the heart of this challenge.

Scientists have long thought that, somewhere in the process of evolution, there was a transition from RNA to DNA. However, that has never actually been proven, and the fifth and final challenge pushes researchers to prove that the RNA to DNA jump can be made gradually. If such a jump is infeasible, that would call into question the significance of RNA in the overall scheme of the development of life on Earth.

These challenges are well defined, measurable, and have an obvious tie back to the fundamental challenge of understanding where life originally came from. Whether or not NASA, especially with its own current funding challenges, would be willing to back a challenge-based structure to pursue these efforts remains to be seen. But there are plenty of other challenge-based funding supporters out there, such as the team around the Evolution 2.0 challenge and the X Prize itself. Astrobiology research remains key to understanding our place in the universe - it might be time to consider a different path to how we approach it.

Learn More:

• C. Mathis & H. B. Smith - Challenge-Based Funding to Spark Origins Breakthroughs
• UT - Astrobiology: Why study it? How to study it? What are the challenges?
• UT - NASA's Future Telescope Could Solve the Mystery of Life's Origins
• UT - Is There a Fundamental Logic to Life?

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.