Category: Science

There are some strange types of exoplanets that have no counterpart in our solar system. One of these types are super puff planets. These special balls have larger radii than Neptune, but only a few Earth masses. This means that they have a large volume and a low density. How this particular type of exoplanet forms is unclear, and current models of gas giant formation cannot explain them.

Kepler-51 is a 500-million-year-old Sun-like star about 2,620 light-years away that hosts three super-puff planets. One of them, Kepler-51d, is the coolest and least dense of the three. It’s the subject of new research in the Astronomical Journal. In it, the researchers test the three hypotheses that attempt to explain Kepler-51d and super-puffs in general.

The research is “The James Webb Space Telescope NIRSpec-PRISM Transmission Spectrum of the Super-Puff, Kepler-51d,” and the lead author is Jessica Libby-Roberts. Libby-Roberts is from the Department of Astronomy and Astrophysics and the Center for Exoplanets and Habitable Worlds, both at Pennsylvania State University.

“We think the three inner planets orbiting Kepler-51 have tiny cores and huge atmospheres that give them a density similar to cotton candy,” lead author Libby-Roberts said in a press release. “These extremely low-density super-puff planets are rare and defy conventional understanding of how gas giants form. And if it wasn’t difficult enough to explain how one gas giant formed, there are three in this system!”

Maintaining a large, puffy atmosphere requires a massive core with enough gravity to prevent the atmosphere from being ripped away. Typically, these types of planets are also further away from their stars, which also makes it harder for the star to remove their atmosphere. But Kepler-51d is only as far from its star as Venus is from the Sun. And because Kepler-51 is young, only about 500 million years old, it is more active than older stars like the Sun.

“Kepler-51 is a relatively active star, and its stellar winds should easily blow gases away from this planet, although the extent of this mass loss over Kepler-51d’s lifetime remains unknown,” Libby-Roberts said. “It’s possible that the planet formed further away and moved inward, but we still have a lot of questions about how this planet – and the other planets in this system – formed. What is it about this system that created these three really strange planets, a combination of extremes we haven’t seen anywhere else?”

Kepler-51d is one of the least dense exoplanets of this type and is also the coolest in the system. Its planetary mass is about 5.6 Earth masses and its radius is about 9.3 Earth radii. That means it has almost ten times the radius of Earth, but just over five times the mass of Earth. A planet of this size, light and cold defies our understanding of planet formation. The authors write that “…the observed properties of this planet cannot be easily explained by most planet formation theories.”

The exoplanet’s properties make it a valuable scientific target to test the various hypotheses that attempt to explain super-puffs.

As the title of the study makes clear, this research is based on JWST’s NIRSpec instrument. When NIRSpec captured the transmission spectrum of Kepler-51d’s atmosphere, it was featureless. There were no strong signs of molecular absorption. The spectrum looks like an inconspicuous slope.

This is the transmission spectrum of Kepler-51d observed with JWST/NIRSpec-PRISM, covering a range of 0.6–5.3 μm. This wavelength range is typically rich in chemical fingerprints. If they were present and detectable, molecules such as H2O, CO2 and NH3 would be visible in the spectrum. The problem is that the haze can obscure all of these features, creating the slope in the spectrum. Photo credit: Libby-Roberts et al. 2026. AnJ.

“At 350 K, we expect to observe a rich range of molecular features (methane, water, carbon dioxide and ammonia) assuming an aerosol-free chemical equilibrium atmosphere for Kepler-51d – especially given its extreme scale altitude of about 1700 km. Instead, the lack of clearly identifiable features in an extended H/He-rich atmosphere between 0.6 and 5.3 μm is a first for JWST,” the researchers write. However, some molecules containing carbon, oxygen, nitrogen and other chemicals must be present to trigger the formation of the haze.

There are three working hypotheses that attempt to explain super-puffs like Kepler-51d.

The first is that the planet has a massive hydrogen/helium shell. Planets typically don’t maintain this atmosphere because they are too bright. The loss of these atmospheres explains the observed Fulton gap or radius gap in the exoplanet population. While the exoplanet’s atmospheric spectrum is featureless, forward modeling shows that it likely has low metallicity for several reasons, supporting the H/He envelope hypothesis. However, to maintain this atmosphere, scientists must assume that a planet must be massive and not too close to its star, which contradicts this hypothesis.

The second hypothesis is that Kepler-51d exhibits high-altitude photochemical opacities. This is consistent with submicron-sized haze particles in the exoplanet’s upper atmosphere. Spectra of other super puffs show the same thing. Because opacities block all molecular features in the spectrum, the JWST results support this.

The third is that the planet actually has a ring system that is tilted toward us. That would make the planet appear larger than it is. This would in turn make the density appear much lower. The researchers found that a ring system can fit the data, but it must be a very short-lived system. This is because the planet is so close to its star that any ring system would be unstable. Since the planet is only about 500 million years old and the ring system could only survive for about 100,000 years, that means we would be very lucky to be able to observe it at just the right time for a ring system to exist. This is a very low probability and that is why researchers do not support this explanation.

Rings are made of dust and also block light in a uniform pattern. “Instead, we see a linear trend where more light is blocked at longer wavelengths,” Libby-Roberts said.

*This artist’s illustration features a super puff planet. With low masses and large radii, they defy our models of planet formation. Image source: By Pablo Carlos Budassi – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=136006077*

The researchers conclude that the high-altitude photochemical haze hypothesis best fits the evidence.

“We think the planet has such a thick layer of haze that absorbs the wavelengths of the light we look at, so we can’t really see the features underneath,” said study co-author Suvrath Mahadevan. Mahadevan is a professor of astronomy and astrophysics at Penn State Eberly College of Science. “It appears to be very similar to the haze we see on Saturn’s largest moon Titan, which contains hydrocarbons such as methane, but on a much larger scale. Kepler-51d appears to have a huge amount of haze – almost as large as the radius of Earth – and would be one of the largest we have seen on a planet to date.”

Lead author Libby-Roberts echoed Mahadevan’s comments. “Rings would have to be short-lived, made of very specific materials and arranged at just the right angle, which seems unlikely, but we can’t rule it out completely. If we could observe the planet at even longer wavelengths, such as with JWST’s mid-infrared instrument, we might be able to detect the materials that would be in a ring or see the full extent of the haze layer.”

Missions like Kepler TESS have shown us how diverse the exoplanet population is. Our models of planet formation are largely based on what we see in the solar system. But they are being put to the test by the discovery of super-puff planets like Kepler-51d.

“Before astronomers found planets outside our solar system, we thought we had a pretty good understanding of how planets formed,” Libby-Roberts said. “But we started finding exoplanets that didn’t fit our solar system at all, and we have these alien worlds that really challenge our understanding of planet formation. We haven’t found a solar system like ours yet, and if we can explain how all these different planets formed, we can better understand how we fit into the bigger picture and what place we occupy in the universe.”

Without detailed knowledge of Kepler-51d’s composition and structure, researchers cannot explain how the super puff formed. However, JWST’s NIRSpec spectrum can help rule out certain scenarios and limit others. The next step is to examine the other super-puff planets in the system using both NIRSpec and MIRI.

“Future observations of other super-puff planets in the Kepler-51 system using JWST could provide additional insights into how these planets (including Kepler-51d) formed and whether they all have a significant haze layer,” the researchers write. “At the moment, Kepler-51d is the only known planet with a featureless, tilted JWST transmission spectrum of 0.6-5.3 μm,” they conclude.

Most objects that astronomers and astrophysicists study have existed for billions of years. Things like supermassive black holes, the Milky Way, and even the Sun and Earth predate humanity by billions of years.

But not the Crab Nebula. It is the supernova remnant (SNR) of a supernova that exploded about 6,500 years ago. Its light reached Earth in 1054 and the exploding star is named SN 1054. Ancient astronomers recorded its appearance in the night sky, particularly Chinese astronomers, who called it a “guest star.”

The Crab Nebula is one of the most studied objects in astronomy. Its distinctive appearance makes it recognizable to more than just astronomers, and it has been imaged in detail many times by various telescopes, including the Hubble. His Crab Nebula image is like the space telescope’s calling card.

There’s a lot going on in a complex object like the Crab Nebula, also known as M1 and NGC 1952. In addition to being classified as an SNR, it is also a pulsar wind nebula. A central pulsar generates the winds that push an expanding bubble of high-energy particles outward. It also drives the outward propagation of magnetic fields.

*This image is a combination of optical light from Hubble (red) and X-ray light from Chandra Observatory (blue). The red star in the center is the Crab Pulsar, and the middle part of the image shows the Pulsar Wind Nebula. Image credit: Optical: NASA/HST/ASU/J. Hester et al. X-ray: NASA/CXC/ASU/J. Hester et al. – https://hubblesite.org/contents/media/images/2002/24/1248-Image.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=238064*

A typical pulsar emits one radio pulse per revolution. Some have two. In most pulsars the two appear at different parts of the rotation.

But the Crab Nebula stands out from other pulsars. Its two radio pulses and its high energy pulses appear in the same phase. These pulses look like a zebra pattern in their spectrum, with noticeable gaps between them, and astrophysicists are struggling to explain why.

New research in the Journal of Plasma Physics explains why the crab has its unusual zebra-striped pattern. It is entitled “Theory of striped dynamic spectra of the high-frequency interpulse of the Crab pulsar” and the sole author is Mikhail Medvedev. Medvedev is from the Department of Physics and Astronomy at the University of Kansas. This is not Medvedev’s first published research on the Crab Nebula and he has been working to understand these unusual pulses for years.

“This peculiar spectral pattern was first reported in 2007 and subsequently studied in detail,” writes Medvedev. “Despite considerable theoretical effort over the subsequent fifteen years, no satisfactory mechanism has been proposed to resolve the…puzzle.”

It all boils down to the crab’s magnetosphere.

Pulsars are strongly magnetized neutron stars. Their magnetic fields are compressed just like the neutron star itself. This makes them extremely amplified. They can be a billion times stronger. These extreme magnetic fields dominate almost everything about pulsars. In fact, pulsars are considered natural laboratories for extreme physics due to their magnetic fields, extreme gravity, and extreme rotations.

Medvedev’s research shows that gravity is responsible for the unusual zebra pattern.

“Gravity changes the shape of space-time,” Medvedev said in a press release.

“Light does not travel in a straight line in a gravitational field because space itself is curved,” he said. “What would be straight in flat spacetime becomes curved when gravity is strong. In this sense, gravity acts as a lens in curved spacetime.”

We know this to be the case because of gravitational lensing. This lensing effect has been discussed and researched extensively, but not when it comes to neutron stars, said Medvedev.

“In images of black holes, gravity alone shapes the structure,” he said. “Gravity and plasma work together in the crab pulsar. This represents the first real application of this combined effect.”

This animation consists of different frequency observations of the Crab Pulsar from five different observatories: the VLA (Radio) in red; Spitzer Space Telescope (infrared) in yellow; Hubble Space Telescope (visible) in green; XMM-Newton (ultraviolet) in blue; and Chandra X-ray Observatory (X-ray) in purple.

But there’s more to the Crab Nebula’s emission pattern than just zebra-like gaps. There are also high-frequency intergap emissions, but they do not have a broad spectrum like other pulsars.

“There is a remarkable pattern in the pulsar spectrum,” Medvedev said. “Unlike ordinary broad spectra – such as sunlight, which contains a continuous range of colors – the crab’s high-frequency intermediate pulse shows discrete spectral bands. If it were a rainbow, it would be as if only certain ‘colors’ appeared, with nothing in between.”

“The stripes are absolutely clear, with complete darkness in between,” Medvedev said. “There is a bright band, then nothing, bright band, nothing. No other pulsar shows this type of band. This uniqueness made the crab pulsar particularly interesting – and challenging – to understand.”

In his previous work, the physicist was able to explain the clear streaks in the pulsar’s radio emissions. The neutron star’s plasma caused diffractions in its electromagnetic pulses. They were largely responsible for the patrols.

However, the high contrast was still unclear. That changed when he took gravity into account.

“The previous theoretical model was able to reproduce fringes, but not with the observed contrast. Incorporating gravity provides the missing piece,” Medvedev said. “The plasma in the pulsar’s magnetosphere can be thought of as a lens – but a defocusing lens. In contrast, gravity acts as a focusing lens. Plasma tends to spread light rays; gravity pulls them inward. When these two effects are superimposed, there are certain ways in which they compensate for each other.”

The defocusing lens of plasma and the focusing lens of gravity are in a kind of tug-of-war that neither can ever win. The different forces create both in-phase and out-of-phase interference bands in the radio waves, creating the zebra pattern.

“For reasons of symmetry, there are at least two such paths for light,” he said. “When two nearly identical paths bring light to the observer, they form an interferometer. The signals are combined. At some frequencies they reinforce each other (in phase) and produce bright bands. At others they cancel each other (out of phase) and produce darkness. This is the essence of the interference pattern.”

There is still a lot of work to be done, even if the model explains the impulses of the Crab pulsar.

“It appears that little additional physics is required to qualitatively explain the streaks,” Medvedev said. “Quantitatively there may be refinements.”

“The pulsar rotates, and the inclusion of rotation effects could lead to quantitative, although not qualitative, changes,” Medvedev said.

Medvedev’s work could also lead to a better understanding of other rotating and gravitational objects. Pulsars themselves are difficult to study, and Medvedev’s work could advance the study of pulsars in general. For example, the exact source of a neutron star’s impulses is unknown, although the polar regions are strongly considered. In this case, scientists are not yet sure how far above the poles the impulses arise.

“Our model also imposes constraints on the source of the pulsar radio emission,” Medvedev writes.

A strange lack of stellar orbits around the core of the Small Magellanic Cloud (SMC) puzzled astronomers for decades. In addition, the SMC has a strange, irregular shape and exhibits a tidal current. Now a team of observers led by graduate student Himansch Rathore from the University of Arizona has discovered the reason why the stars don’t orbit. This is because the SMC crashed in the distant past directly through its neighbor, the Large Magellanic Cloud (LMC). This massive collision disrupted the star’s movements and sent them on completely different trajectories. It also disrupted the gas clouds within the SMC, creating a gas tail that stretched across space.

The team’s work provides unique insights into the way galaxies change over time. “We see a galaxy changing in live action,” Rathore said. “The SMC gives us a unique front-row view of a very transformative process that is critical to the evolution of galaxies.”

A closer look at the SMC

The Small Magellanic Cloud is a member of a trio of interacting galaxies that includes the Large Magellanic Cloud and our own Milky Way. The SMC is about 200,000 light-years away, while the LMC is about 158,000 light-years away. Both have sites of active star formation. The SMC is categorized as a dwarf irregular galaxy and has a mass equivalent to about 7 billion solar masses. However, not all of the mass is contained in stars. Most of the SMC’s mass is contained in huge clouds of gas that eventually become star formation sites. This happens when the clouds cool and gather. When conditions are right, this process creates hot, young stars that astronomers can study to understand the star formation process.

This visible light mosaic shows the LMC and SMC in relation to the plane of our own galaxy, the Milky Way. Dusty filaments create dark trails on the Milky Way’s bright midplane, visible at the top of the image. Below, about 21 degrees apart, lie the LMC and SMC, the closest large galaxies to our galaxy. The LMC and SMC orbit each other as well as our own Milky Way Galaxy. Photo credit: Axel Mellinger, Central Michigan University (via NASA Goddard Scientific Visualization Studio).

Astronomers have measured the movement of stars existing in the SMC using data from the Hubble Space Telescope and the Gaia mission. They discovered that the stars of the SMC do not orbit around the center of this galaxy like the stars in most other galaxies. This lack of orbital activity was puzzling until Rathore’s team thought about the impact of a collision on the SMC and LMC. A few hundred million years ago, the SMC crashed directly through the disk of the LMC. The LMC’s gravity destroyed the SMC’s internal structure and sent its stars into random, disordered motion. In addition, the gas in the LMC exerted enormous pressure on the gas of the SMC, destroying its gas rotation.

Because the LMC, SMC, and the Milky Way interact with each other, astronomers want to understand how this interaction affects all three galaxies. Astronomers found a gas bridge between the LMC and SMC, which was likely pulled from one of the galaxies during tidal interactions between the two galaxies. This bridge is busy forming stars in the shocked gas.

Large and small Magellanic clouds from GAIA data. Image credit: ESA/Gaia/DPAC – CC BY-SA 3.0 IGO.

Solve the mystery of disturbed stellar orbits

According to Gurtina Besla, a senior author of an article on the finding, the crash between LMC and SMC caused great damage to both. “The SMC experienced a catastrophic crash that injected a lot of energy into the system. It is by no means a ‘normal’ galaxy,” Besla said. To understand this crash, the team turned to computer simulations. First, they compared the known properties of the SMC and the LMC – their gas content, the star’s total mass and their positions relative to the Milky Way. They combined the simulations with theoretical calculations of how the collision affected the SMC’s gas as it plowed through the LMC’s dense gas environment. They also developed new methods for reading the scrambled stellar motions in a post-collision galaxy, tools that can now be used to properly interpret what telescopes are actually measuring in the SMC.

This is important because the SMC is small, gas-rich and poor in heavy elements – properties that made it a standard benchmark for the types of galaxies that existed early in the universe. A galaxy still affected by a collision may not be a clean reference point, Besla said. However, it can shed light on what impact collisions and interactions have had on galaxies over time.

This diagram shows the simulated gas distribution of the Magellanic System resulting from the tidal encounter between the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) as they orbit our home galaxy, the Milky Way. The solid line shows the calculated path of the LMC and the dotted line is the path of the SMC. Plot by G. Besla, background image of the Milky Way by Axel Mellinger (used with permission)

Other effects of a collision

Another study published by the team in 2025 showed that the collision also left a physical trace on the LMC that could help scientists study dark matter. At the center of the LMC is a rod-shaped structure that has tilted out of the plane of the galaxy due to the collision. Rathore, the lead author of the 2025 study, said the degree of tilt depends on how much dark matter the SMC contains, giving researchers a new way to measure a substance that has never been directly detected but could only be inferred from its gravitational effects.

“We are used to thinking of astronomy as a snapshot of time,” Rathore said. “But these two galaxies came very close together, passed right through each other and turned into something else.”

In addition, the interaction between the LMC, SMC and the Milky Way influences the shape of our galaxy. It appears that the LMC causes a deformation in the shape of the Milky Way’s star disk. It also pulls on our galaxy’s core, disrupting the halo and accelerating its speed through space. The SMC also contributes to this warping and pulling, contributing to the formation of the Magellanic Current. This is a trail of gas and stars that contributes to the colonization of the Milky Way.

More information

A Galactic Transformation – Understanding the Structural and Kinematic Imbalance of the SMC

A galaxy next door is changing, and astronomers can see it happening

This is part 4 of a series on topological defects. Read parts 1, 2 and 3.

That what? Yes, the Vortons. It’s not an anime monster hunting show. It is not an AI startup company. It’s a… it’s a thing. I find.

Listen, what I’m about to tell you is so hypothetical that even a string theorist might blush. Here we are deep in the annals of physics. I don’t want you to trust ANYTHING I’m about to say.

But that has never stopped us. So why stop now?

You see, cosmic string loops are supposed to be suicidal. They are these high voltage whips of spacetime that vibrate and oscillate so quickly that they SCREAM gravitational waves until they disappear into nothingness. Usually that’s the end of the story. The loop shrinks, it disappears and the universe is defective.

But that doesn’t HAVE to be the end of the story. I mean, cosmic strings are super hypothetical themselves, so we have a few possibilities.

Imagine a cosmic loop of strings that doesn’t just vibrate. It also rotates. Really, really fast. Why should they rotate? Why NOT, buddy? Who are you to say they could never turn? And when they spin, they have angular momentum (that’s kind of the definition). But as the loop releases energy, it becomes smaller. But you can’t just get rid of the angular momentum. This means that the smaller it gets, the faster it spins. And at a certain point, that internal spin is so strong that it begins to push OUTWARD.

That creates tension. The loop wants to shrink in on itself from its own tension. But the spinning mill wants to expand it again.

When these two forces find a perfect balance, shrinkage stops. The loop does not evaporate. It doesn’t disappear. It forms a permanent, indestructible, subatomic ring of pure field energy.

We call this a pretone. It is a small lump of cosmic thread, a defect that stubbornly refuses to disappear in this long night.

Oh, and it could be dark matter.

We don’t know what dark matter is, but we know what it does. It must be a particle or something like a particle. It must be hard. It has to be almost invisible. And it must have been there since the earliest moments of the Big Bang for it to take part in all the building of the cosmic web that it is so good at.

A pretone is…not a particle. But it’s small, about the size of a proton. It does not glow or emit light – it is a defect in space-time, not a “thing” in the usual sense of the word “thing”. There could be a billion of them passing through you and you would never notice… except that you would suddenly weigh more than a mountain. So I guess that counts as “noticing.” Because that’s the highlight. These things are sealed. They consist of the enclosed, high-energy vacuum of the early universe. And if the early universe was as chaotic as we think, then the Big Bang would have had to have been a presound-producing factory. A Vorton forge? I don’t know the right word – it just created a lot of buzz.

This is the story: phase transitions created many cosmic strings. Inflation has dragged it out. Then they vibrated against each other, creating an enormous number of loops that shrank until they became stuck as vortices. That would explain why we don’t see any cosmic strings anywhere. These missing defects are not really missing. They have just evolved into a nebula of dark matter that fills every galaxy.

This means that dark matter may not be an additional ingredient added to the cosmic recipe. It could simply be the remnants of the Big Bang. They are the scratch marks on the ground from when the universe was formed. It’s the construction debris we forgot to sweep up. The universe is anything but perfect. This is one of our reasons for existing. But do the imperfections stop with us – the dust and the stars – or do they extend to a much deeper, more fundamental level – a level so deep that it is frozen in the fabric of space-time? We don’t know if vortices exist, if they are responsible for dark matter, or if they even CAN exist. But that doesn’t matter. The truth is that we owe our existence to the fact that the universe is a bit messed up. If the Big Bang had been perfect, there would be no errors that could promote the growth of galaxies. There would be no branches in the field to provide the dark mass.

I don’t know about you, but I say it’s our mistakes that make us most beautiful.

The International Space Station (ISS), which has been continuously occupied for 26 years, is approaching retirement. By 2030, all participating space agencies will bring their astronauts home for the last time, and the station will be maneuvered so it burns up in Earth’s atmosphere. The legacy of this station is unmatched, and its successors (of which several are planned) will have extremely big shoes to fill. Nevertheless, there’s no shortage of space programs and commercial interests looking to place new space stations in orbit.

Some space agencies, such as NASA and the Indian Space Research Organization (ISRO), hope to deploy new stations. At the same time, China aims to expand its existing Tiangong station to double its current size while Roscosmos recently announced that it will recycle its existing ISS modules to create a space station crewed by Russian cosmonauts and international partners. As for the commercial sector, the companies hoping to participate, and the concepts they’re proposing are legion!

With multiple space agencies planning on taking the “next great leap” – going back to the Moon, to Mars, and beyond – space stations are part of an incremental approach to secure those next great leaps. And the orbital lanes in LEO could be getting a little crowded as a result.

The First Stations

Space stations are a means of establishing an enduring human presence in space. First deployed at the end of the Apollo Era, they represented humanity’s next step in space exploration. Before this, NASA and the Soviet space program were locked in a state of competition – the Space Race – where they were dedicated to “getting there first.” This included being the first to send a satellite (Sputnik) to space, the first man to space (Yuri Gagarin), and the first astronauts to land on the Moon (Neil Armstrong and Edwin “Buzz” Aldrin).

But with the success of the Apollo missions, which landed a total of six lunar modules and twelve astronauts on the lunar surface, the Space Race was officially over. It was at this point, during the early to mid-1970s, that NASA and the Soviets began contemplating their next moves. Having reached space many times over, they decided to focus on technologies that would enable long-duration stays in space. In essence, they shifted from getting to space to staying there.

*The Soviet Salyut-7 (left) and NASA’s Skylab (right). Credit: RKK Energia/NASA*

Having ceded the “Race to the Moon,” the Soviets achieved an early lead with the Salyut program. The program ran from 1971 to 1986 and launched four crewed scientific research stations and two crewed military stations that operated under the guise of the program (Almaz stations). The Salyut stations conducted research on the challenges of long-term spaceflight, as well as a variety of scientific experiments.

The stations also set several spaceflight records, including mission duration, extravehicular activities (EVAs), and the first crew handover in space. Salyut established a legacy for modular space stations and represented a critical step from single-module and docking-port stations to more complex ones. This would be realized with the Soviet-Russian Mir space station (Russian for “peace”), which remained in operation from 1986 until it was deorbited in 2001.

This station was made up of seven modules, including the Salyut-derived Mir core module*, the Kvant-1 and -2 modules (where scientific research was conducted), Kristall (microgravity manufacturing), Spektr (Earth-related studies), Priroda (Earth-sensing), and the docking module. Mir also established a precedent for international cooperation in space through the Interkosmos, Euromir, and Shuttle–Mir* programs.

Meanwhile, the U.S. responded with its own single-module station, Skylab, which was occupied between 1973 and 1974 but remained in orbit until 1979. The station was created from the third stage of a repurposed Saturn V rocket and deployed as a payload by the same rocket. Skylab was America’s first long-duration space station, containing an orbital workshop, a solar laboratory, and an Earth observatory, and was the site of hundreds of experiments.

While NASA hoped to create its own Space Station Freedom to succeed Skylab, and Roscosmos hoped to succeed Mir with Mir-2, these were cancelled in 1993 in favor of participation in the ISS. By 1998, NASA and Roscosmos had placed the foundational elements of the ISS in orbit, and expeditions commenced by 2000. Since then, NASA, Roscosmos, the Canadian Space Agency (CSA), the European Space Agency (ESA), and the Japan Aerospace Exploration Agency (JAXA) have added modules and elements that have enhanced the Station’s capabilities.

*Image of Space Shuttle Atlantis connected to Russia’s Mir Space Station by the crew of Mir-19 on July 4th, 1995. Credit: NASA*

ISS Retiring

Originally, the ISS was intended for a 15-year mission, and NASA planned to deorbit the station by 2016. But the mission has been repeatedly extended due to the vital research it enables and the international support its received. This culminated in the Space Frontier Act of 2018 in July 2018 and the Leading Human Spaceflight Act a few months later, both of which extended ISS operations until 2030.

In August 2022, Congress passed similar provisions in the Creating Helpful Incentives to Produce Semiconductors (CHIPS) and Science Act, which President Biden signed into law. While Russian officials have announced that they will withdraw from the ISS after 2024 (later pushed to 2025), Russian cosmonauts have continued to participate in joint missions with NASA and other space agencies. As of the publication of this article, no final departure date has been formalized.

Unfortunately, the continued occupation means that the oldest modules in the ISS are more than 20 years old. This has led to all kinds of maintenance issues over the years, not to mention health-related concerns. In terms of the former, the modules have experienced structural fatigue, persistent air leaks, and degrading hardware, with maintenance costs hovering around $1 billion annually. In September 2019, the Zvezda Service Module began experiencing higher-than-normal air leaks, which have persisted despite multiple repairs.

In terms of the latter, more than 25 years of continuous occupation by astronauts and cosmonauts have left the station filled with microorganisms that could pose health risks. In 2019, NASA shared the results of a comprehensive study of the microorganisms and fungi present on the ISS, which found diverse populations of both that “may include opportunistic pathogens.” In a 2022 interview with Russia’s state-owned RIA Novosti news agency, the Director of the Institute of Biomedical Problems at the Russian Academy of Sciences (RAS), Oleg Orlov, addressed these risks:

An analysis of the results of microbiological monitoring of the habitat of the ISS RS modules, carried out within the framework of the full-time medical control operations, indicates that the state of the ISS habitat is deteriorating. It is an objective process. Generalized results show that in 65% of the analyzed samples of the latest expeditions, microorganisms were found in quantities exceeding regulatory requirements.

Among the representatives of bacterial flora isolated from the habitat of the ISS, species that are of medical importance and are capable of causing allergic reactions and some types of soft tissue and upper respiratory tract diseases have been identified.

With the ISS slouching toward retirement and space agencies expressing doubts about further extensions, attention is shifting to what will replace this venerable workhorse and research platform in space.

The Lunar Gateway

In the near future, NASA hopes to deploy the Lunar Gateway in orbit around the Moon. This station is a collaborative project between NASA, the European Space Agency (ESA), the Japan Aerospace Exploration Agency (JAXA), and the Canadian Space Agency (CSA). This space station was conceived through concept studies conducted between 2012 and 2018, and was originally designated the Deep Space Habitat (DSH). By 2015, it was approved as part of NASA’s NextSTEP (Space Technologies for Exploration Partnerships) studies and began receiving funding for development.

In 2018, the International Space Exploration Coordination Group (ISECG) identified the Gateway as essential to lunar exploration, missions to Mars, and beyond. The modular design consists of a core composed of the Power and Propulsion Element (PPE) and the Habitation and Logistics Outpost (HALO). These modules will launch no sooner than 2027, followed by the European System Providing Refueling, Infrastructure and Telecommunications (ESPRIT), the Lunar International Habitation Module (Lunar I-HAB Module), the Canadarm3 robotic manipulator arms, and the Crew and Science Airlock Module.

The station will also be paired with reusable surface elements, collectively known as the “Artemis Base Camp,” which were announced in 2020 as part of NASA’s Lunar Surface Sustainability Concept. The base will include a Lunar Terrain Vehicle (LTV) to transport crew members around the landing zone, a pressurized Habitable Mobility Platform (HMP) for longer trips across the surface, and a lunar Foundation Surface Habitat (FSH) that will house up to 4 crew members during shorter surface stays.

On May 2nd, 2025, the second Trump administration released its FT 2026 budget request, which proposed canceling the Lunar Gateway program. However, the budget, signed into law on July 4th, allocated $2.6 billion to the Gateway, requiring $750 million to be spent between 2026 and 2028. Similarly, discussions have arisen about repurposing the Lunar Gateway for other missions.

This includes now-Administrator Jared Isaacman’s policy blueprint, “Project Athena,” in which he explored repurposing modules or propulsion-related hardware for a nuclear-powered tug vehicle. However, neither Isaacman nor NASA has announced any such plans.

Tiangong

The construction of China’s Tiangong (‘Heavenly Palace”) modular space station began with the deployment of the Tianhe (“Harmony of the Heavens”) core module in April 2021, and finished the following year with the deployment of the Wentian (“Quest for the Heavens”) and Mengtian (“Dreaming of the Heavens”) laboratory modules. The station is based on experience gained from its predecessors, Tiangong-1 (2011-2016) and Tiangong-2 (2016-2019), and has been continuously occupied by taikonauts since June 5th, 2022.

As of 2026, a total of 30 taikonauts have launched to Tiangong (Shenzhou-10 to -22), serving in crews of three for periods of about six months – though the station can accommodate up to six taikonauts during mission handovers. According to the China Manned Space Agency (CMSA), the station has conducted research into spacecraft rendezvous, permanent human operations in orbit, long-term autonomous spaceflight, bioregenerative life support systems (BRLSS), and autonomous cargo and fuel supply.

On October 4th, 2023, the Chinese Academy of Space Technology (CAST) announced that three new modules will be added, effectively doubling its size and crew capacity. Chinese state media have also stated that the station will foster international cooperation by accommodating crews from “several countries,” which may include ESA members. This is in keeping with plans to make Tiangong a successor to the ISS.

The planned expansion will also extend the mission’s duration to 2037, 10 years longer than previously announced. The research activities that are planned will include further studies into long-duration stays in space, space medicine, agriculture, technological innovations, and tests involving the Mengzhou spacecraft – Shenzhou’s replacement, which is designed to transport six or seven taikonauts to orbit or the Moon.

In this respect, Tiangong will also play a role in China’s plans to construct the International Lunar Research Station (ILRS) in collaboration with Roscosmos. Speaking of which…

Russian Orbital Station

In recent years, Russia has announced similar plans to build a successor station to the ISS. However, in December 2025, the Director of the Institute of Biomedical Problems of the Russian Academy of Sciences (RAS), Greg Orlov, announced that Russia would continue using the modules that make up the Russian Orbital Segment of the ISS after 2030, which would henceforth be known as the Russian Orbital Station (ROS), or *Rossiyskaya orbital’naya stantsiya*.

This represents a major change from what Russian officials have stated in recent years, which was their intent to create a new station to succeed the ISS. Plans for a Russian space station began in earnest in 2009 with the proposed Orbital Piloted Assembly and Experiment Complex (OPSEK). This plan called for a station that would include the six modules that make up the Russian Orbital Segment, but it was abandoned in 2017 in favor of maintaining participation in the ISS program.

*Artist’s concept for the Russian Orbital Station (ROS). Credit: Roscosmos*

The plans were revived after 2021, when Roscosmos announced it would terminate its involvement in the ISS by 2024, citing concerns about the condition of its aging modules. At this point, the OPSEK concept was renamed the Russian Orbital Service Station (ROSS), which would no longer include Russia’s ISS modules. The updated plan included launching the four core modules between 2027 and 2030, including the scientific and energy module, the Universal Node (UNM), the Gateway (SM), and the Base Module (BM). By 2035, up to three more modules were to be added, with the possibility of a private habitat for space tourism.

However, due to budget constraints arising from sanctions and the termination of international agreements (due to Russia’s invasion of Ukraine in 2022), Russian planners returned to the idea of reusing its ISS modules. Per this new plan, Russia will separate its modules from the ISS once the program is completed in 2030, forming the core of the ROS, with other modules to follow. However, given the age of the modules and associated health concerns (which Orlov addressed as recently as 2022), there is significant doubt that this plan will remain in place for long.

Bharatiya Antariksh

In 2019, the Indian Space Research Organization (ISRO) announced that it would build the Bharatiya Antriksh Station (BAS) in orbit by 2035. According to repeated ISRO statements, the station will build on the agency’s plans to begin sending crewed missions to orbit (Gaganyaan). As then-ISRO chief Sreedhara Somanath stated in October 2023:

Our Gaganyaan program is towards a human space flight capability to space, and once that happens, we will be able to look at space station building in subsequent modules. The timeline for this space station project spans the next 20 to 25 years. We will be definitely looking at manned exploration, a human spaceflight for a longer duration, space exercise there in our agenda.

Similar to China, India views this station as integral to its plans of becoming a major power in space exploration, science, and research in the coming decade. This will include completing the Ganganyaan program and conducting a crewed Moon landing by the year 2040. The development of the BAS is scheduled to begin with the launch of the first module (BAS-1), along with solar panels and a docking port compatible with ISS, in 2028.

*Artist’s impression of India’s proposed Bharatiya Antariksh Station (BAS). Credit: IBEF*

The BAS will feature a five-module configuration consisting of the Base Module (BAS-1), the Core-Docking Module (BAS-2), the Science research Module (BAS-3), the Laboratory Module (BAS-4), and the Common Working Module (BAS-5). The station will measure 27 by 20 meters (88.5 by 65.5 feet), orbit at an altitude of 400-450 km (250-280 mi), and house a crew of three to four. The ISRO has also stated that the station will be accessible by all major space agencies, including NASA, Roscosmos, the ESA, and JAXA.

And these are just the plans proposed by the world’s major or rising space agencies. Stay tuned for part II, where we will address the many concepts being explored by commercial space companies.

Europe is not supposed to look the way it does. Jupiter’s icy moon is marked by a chaotic patchwork of rugged terrain, crisscrossing ridges and disturbed surface regions, suggesting that something dynamic is happening beneath its frozen shell. Scientists have long suspected that beneath this ice lies a vast liquid ocean, kept warm by the gravitational effects of Jupiter’s enormous gravity. Now a new study using the James Webb Space Telescope adds a crucial piece to the puzzle, and the implications reach to the heart of astrobiology.

The surface of Europa, imaged by the Galileo spacecraft in the late 1990s (Source: NASA)

The research, led by Gideon Yoffe and colleagues, applied a sophisticated technique called spectral decomposition to JWST observations of Europe’s leading hemisphere. Think of it like a chemical fingerprint from a distance. Each molecule absorbs and reflects light at characteristic wavelengths, leaving a distinctive signature that a sufficiently sensitive telescope can detect and map. By analyzing nine separate spectral bands covering water ice, carbon dioxide and other compounds, the team was able to decipher the different chemical layers on Europa’s surface and reconstruct where each one is located.

They found that carbon dioxide, previously detected on Europa, was concentrated in a geologically chaotic region called the Tara Regio, an area where the surface appeared to have fractured and refrozen, attracting material from deeper depths. The working assumption was that it was a localized feature, but the new analysis suggests otherwise. Carbon dioxide accumulation extends well beyond the Tara region, spreading in a broad, lenticular distribution across multiple regions of the chaos terrain. Crucially, wherever carbon dioxide is richest, the ice itself has unusual textural properties, as if the surface had been reworked from below.

A series of images of Europa in different wavelengths from the James Webb Space Telescope. The different wavelengths indicate the presence of different forms of carbon dioxide on Europa (Source: NASA)

This combination, the pattern of carbon dioxide, and the anomalous ice texture suggest something more interesting than simple radiation-driven surface chemistry. The team’s results suggest that the distribution of volatiles across Europa reflects not only where the material is deposited, but also where the surface can best hold on to it. The microstructure of the ice itself may determine what is retained and where. This is a more subtle and physically rich picture than the simple story of carbon dioxide arriving and staying there.

Carbon dioxide is one of the six elements considered vital to life as we know it. If the surface deposits come from the subsurface ocean, as the concentration in geologically young Chaos terrain suggests, then that ocean contains carbon. It is also in chemical communication with the surface, exchanging material across the ice in ways that we are only beginning to understand and explore.

Europa Clipper, NASA’s dedicated mission to Jupiter’s moon, will begin its close flybys in 2031. If this is the case, the chemical map created by JWST will tell exactly where to look.

Source: Spectral decomposition reveals surface processes on Europa

NASA’s Double Asteroid Redirection Test (DART) spacecraft impacted the asteroid moon Dimorphos, which orbits the larger asteroid Didymos, in September 2022. The purpose of this mission was to test the kinetic impactor method, a possible strategy for changing the orbit of asteroids so that they do not pose a threat to Earth. The test was a success, as images from the Italian Space Agency’s LICIACube (traveling alongside the DART mission) showed after the impact. Combined with Earth-based observations, these confirmed that the moon’s orbit changed noticeably.

According to a recent update from NASA, DART’s impact also changed the orbits of both asteroids around the sun. Because Didymos and Dimorphos are part of a binary system and orbit each other around a common center of mass, changes to one asteroid affect the other. As an international team of researchers described in a study published in the journal Science Advances, observations showed that the 770-day orbital period of asteroids around the sun changed by a fraction of a second after the impact. This is a sign It is the first time that a man-made object has changed the orbit of a celestial body around the sun.

When DART hit Dimorphos, follow-up observations showed that the moon’s orbit shortened by 33 minutes. The impact also created a cloud of rocky debris that carried its own momentum away from the asteroid. This gave the asteroid momentum in addition to the impact, called the momentum amplification factor. According to the new study, the momentum amplification factor from DART’s impact was about two, meaning the debris doubled the force exerted by the spacecraft alone. This caused Didymos’ orbit to change by 0.15 seconds.

*This LICIACube image, taken moments after the impact on September 26, 2022, shows rocky debris spreading from Dimorphos. Image credit: ASI/NASA*

Thomas Statler, the chief solar system small body scientist at NASA Headquarters, said in a NASA press release:

This is a minor change in orbit, but given enough time, even a minor change can cause a significant deflection. The team’s astonishingly precise measurement reaffirms kinetic impact as a technique to protect Earth from asteroid threats, and shows how a binary asteroid could be deflected by impacting just one member of the pair.

To show that DART had a detectable impact on both asteroids, researchers had to measure Didymos’ orbit with extreme precision. To do this, the team combined radar and other ground-based observations and tracked the asteroid as it passed in front of background stars (also called occultations). This was challenging because tracking stellar occultations requires precise timing and being in the right location. The team relied on volunteer astronomers around the globe who recorded 22 stellar occultations between October 2022 and March 2025. Steve Chesley, co-leader of the study and senior research scientist at JPL, said:

Combined with years of ground-based observations, these stellar occultation observations were crucial in calculating how DART had changed Didymos’ orbit. This work is highly dependent on the weather and often requires travel to remote regions with no guarantee of success. This result would not have been possible without the efforts of dozens of volunteer occultation observers around the world. This technique allowed the team to obtain extremely precise measurements of the asteroid’s speed, shape and position.

*The infographic above shows Dimorphos’ current orbit around Didymos and its expected orbit after the DART impact. Image credit: NASA/Johns Hopkins APL*

“The change in the orbital speed of the binary star system was about 11.7 micrometers per second, or 1.7 inches per hour. Over time, such a small change in an asteroid’s motion can mean the difference between a dangerous object hitting or missing our planet,” added Rahil Makadia of the University of Illinois Urbana-Champaign and lead author of the study. However, both NASA and ESA have determined that the change in Didymos’ orbit poses no threat to Earth. Studying changes in Didymos’ motion also helped researchers calculate the densities of both asteroids, which revealed that Dimorphos is slightly less dense.

This supports the theory that it formed from rocky debris dropped by a rapidly spinning Didymos that eventually coalesced into a “debris pile” asteroid. Although Didymos is not a potentially hazardous object (PHO) and therefore does not pose a collision threat to Earth, the success of the DART mission demonstrates the effectiveness of the kinetic impactor method. The first step, however, is to detect PHOs far enough in advance that a kinetic impactor can be sent to rendezvous with them. This is the purpose of NASA’s Near-Earth Object (NEO) Surveyor mission: a next-generation space survey telescope and the first built for planetary defense.

Further reading: NASA

To understand how stars form, astronomers need to observe the process that occurs in galaxies. This simple fact is behind PHANGS, the “Physics at High Angular Resolution in Nearby GalaxieS” survey. It is a large-scale, multi-wavelength, multi-telescope survey of dozens of nearby spiral galaxies. Its targets are galaxies close enough that star formation features such as giant molecular clouds (GMCs), HII regions and star clusters can be resolved.

PHANGS began years ago with observations from telescopes such as ALMA and the Hubble. When the JWST was launched, it also took part. The core question PHANGS addresses is simple: How exactly do gases become stars and how does stellar feedback modulate the process?

PHANGS has created catalogs of data cited in more than 150 scientific papers. It was a major success for astronomers studying star formation and feedback. But a collection of beautiful images was also created, many of which were presented as “Image of the Week” (POTW), “Astronomy Image of the Day” (APOD) as well as other special images and even as an ESA/Hubble calendar. There is also a stamp with the JWST image of NGC 628.

The JWST image of the spiral galaxy NGC 628 is featured on a U.S. Postal Service stamp. Image source: NASA, ESA, Canadian Space Agency and Space Telescope Science Institute. US Postal Service.

The JWST has made an important contribution to PHANGS. It’s something of a missing link in the survey because it can see the dust better than other telescopes. This means it can detect earlier stages of star formation than its comrades.

But as Universe Today readers know, the telescope’s portraits of spiral galaxies are delicious as stand-alone images, even without the scientific context. We were all thrilled by the galactic portraits that JWST gave us in 2023. They placed the creative splendor of nature on a pedestal where it belongs.

This mosaic shows 19 galaxies imaged in near- and mid-infrared light by JWST as part of PHANGS. There is so much beauty and detail that it’s hard to digest it all. Image source: NASA, ESA, CSA, STScI, J. Lee (STScI), T. Williams (Oxford), PHANGS Team, E. Wheatley (STScI)

The latest ESA image of the month shows NGC 5134, a spiral galaxy about 65 million years away. The JWST was captured in both near-infrared and mid-infrared light. MIRI, the telescope’s mid-infrared instrument, captures the light emitted by warm dust in the galaxy. It shows the clumps and strands of gas interwoven throughout the galaxy. NIR, the near-infrared instrument, captures the light from the star clusters that populate the spiral arms.

Galaxies like NGC 5134 have a constant ebb and flow of gas. It’s almost like a giant circulatory system in which gas moves and is recycled through heating and cooling phases through galactic feedback. Individual stars with their stellar winds and supernove explosions play an important role.

The billowing gas clouds in the spiral arms are where most star formation occurs. The star populations differ in different parts of the arms. To understand this, we need to understand something crucial about spiral galaxies: the arms don’t rotate.

Although they look like giant rotating wind turbines, spiral galaxies are not. The arms don’t rotate, just density waves. The waves sweep through the galaxy, condensing the gas, and the arms respond by forming stars.

The inner edge of the arms is prestellar. There are still few stars here and the region is tracked by its CO emissions, recorded by ALMA and the JWST. Some of the interstellar medium is compressed and is visible as dark streaks.

Within each arm is the active star-forming region. The compressed gas collapses to form hot young stars, and the region also contains ionized nebulae, star clusters, protostars, and star clusters still embedded in thick dust, which were revealed by the JWST.

Star formation has dropped off at the trailing edge. Here we find older OB stars, stars drifting away from their birth clusters, and supernovae remnants and bubbles.

Outside the main arms we find intermediate stars such as F, G and K stars. It is also home to older red giants and AGB stars, as well as old open star clusters and diffuse gas. There are very few giant molecular star-forming clouds here.

*ESA’s Image of the Month comes from JWST and its efforts to understand the full complexity of star formation. In the nearby spiral galaxy NGC 5134, gas goes through hot and cold phases as it moves through the galaxy. The gas is compressed in the spiral arms, where hot young stars form. The spiral arms don’t actually move; rather, density waves spiral through the material of the galaxy. Image source: ESA/Webb, NASA & CSA, A. Leroy*

This JWST Image of the Month comes from the GO 3707 observation program. It focuses on the movement of gas in galaxies, which is clearly an important part of star formation. The JWST collected important information relevant to star formation, including detailed information about star clusters, the shape and form of the clouds in which stars form, the connections between gas and dust in the interstellar medium, and how energetic newly formed stars shape their surroundings.

Most galaxies lie beyond the reach of the JWST themselves. The telescope can take images of them, but extensive scientific details are only available for closer spirals such as NGC 5134 and the other spirals in PHANGS. What researchers learn from nearby galaxies can be applied to galaxies far out of reach, including the ones that fill the background of this Image of the Month.

What we learn from these galaxies also helps us understand our own Milky Way Galaxy. In some ways it’s harder to understand because we’re in it.

As far as we can tell, the Milky Way is also a spiral, although some details are unclear. The star formation process here is the same as elsewhere and is shaped by the spiral density waves. If we had a telescope far enough away, the Milky Way would probably appear as magnificent as NGC 5134.

Perhaps somewhere out there in the cosmic vastness, another intelligent species like us, lacking in wisdom but technologically advanced, is gazing upon our galaxy. Maybe they celebrate the Milky Way as an example of the creative power of nature.

Or maybe not.

In May 2024, people around the world witnessed beautiful auroras that occurred far beyond the Earth’s polar regions. Even the Aurora Borealis, usually confined to the Arctic Circle, was visible as far away as Mexico. This rare event was the result of a massive solar storm, the strongest in over 20 years. As always, this storm bombarded Earth with charged solar particles that interacted with the planet’s magnetosphere. The storm also reached Mars, which was observed by two European Space Agency (ESA) orbiters – the Mars Express and the ExoMars Trace Gas Orbiter (TGO).

Together, the two spacecraft captured images of the event and obtained detailed information about the amount of radiation that reached Mars: the equivalent of 200 days of what is normally exposed in just 64 hours. The data was presented in a study published in Nature Communications, in which an international team of researchers used a method developed by ESA to reveal how this storm affected Mars. The results could lead to a better understanding of space weather and how solar storms interact with planets.

The technique is known as radio occultation, in which the Mars Express probe sent a radio signal to the TGO as it disappeared over the Martian horizon. While ESA routinely uses orbiter-to-orbiter radio occultation on Earth, this was one of the few cases in which it was used around Mars. Essentially, the radio signal was refracted by layers in Mars’ atmosphere before being picked up by TGO, allowing scientists to learn more about each layer. Data from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission were also used to confirm the electron densities.

*To study the Martian atmosphere, ESA’s two Mars orbiters use a technique called “radio occultation”. Photo credit:ESA*

Colin Wilson, an ESA Mars Express and TGO project scientist and co-author of the study, said in an ESA press release:

This technique has actually been used to explore the solar system for decades, but using signals sent to Earth from a spacecraft. It was only about five years ago that we started using it on Mars between two spacecraft such as Mars Express and TGO, which typically use these radios to transmit data between orbiters and rovers. It’s great to see it in action.

The superstorm coincided with the return of the hyperactive sunspot region AR3664 to the Earth-facing side of the Sun. The explosion sent out an X2.9 class flare and a large cloud of material. a coronal mass ejection (CME) – towards Earth and Mars. On Mars, the storm caused a dramatic increase in electrons in two layers of its atmosphere – 110 and 130 km (68 and 80 miles) above the surface – by 45% and 278%, respectively, the most electrons ever observed in this region of Mars’ atmosphere. ESA research fellow Jacob Parrott, the study’s lead author, said:

The impact was remarkable: Mars’ upper atmosphere was flooded with electrons. It was the largest solar storm response we’ve ever seen on Mars. The storm also caused computer errors in both orbiters – a typical danger of space weather because the particles involved are so energetic and difficult to predict. Fortunately, the spacecraft were designed with this in mind and were built with radiation-resistant components and special systems to detect and correct these faults. They recovered quickly.

*ESA’s Swarm satellites are mapping Earth’s magnetic field as it is distorted by the May 2024 solar storm. Photo credit: ESA*

Thanks to Earth’s magnetosphere, the upper atmosphere’s response was less intense, as much of the storm’s particles were deflected away from the planet or toward the poles (causing the auroras). This highlights the differences between our planets and also shows the importance of studying how space weather affects different bodies in the solar system. Because solar storms can endanger astronauts and equipment in orbit, as well as disrupt satellites and power grids on the surface, predicting space weather is critical.

However, this is difficult because the Sun emits solar flares and CMEs unpredictably, so studying them is a matter of luck and timing. Fortunately, the team was able to use the new technology just ten minutes after the solar storm reached Mars. In total, the team captured the aftermath of three solar events that were part of the same storm but differed in the type of material ejected and the way it was carried out. These included a radiation burst, a high-energy particle burst, and a CME. Colin said:

The results improve our understanding of Mars by showing how solar storms release energy and particles into the Martian atmosphere – important because we know that the planet has lost both large amounts of water and most of its atmosphere to space, most likely due to the continuous wind of particles emanating from the Sun. But there’s another side: the structure and content of a planet’s atmosphere influences the propagation of radio signals through space. If Mars’ upper atmosphere is full of electrons, it could block the signals we use to explore the planet’s surface by radar. This would make this an important consideration in our mission planning – and impact our ability to study other worlds.

Further reading: ESA

In addition to being a staple of science fiction, the concept of megastructures has long been the subject of serious scientific study. As famed physicist Freeman Dyson originally proposed in 1960, “Malthusian pressures will ultimately drive an intelligent species” to “occupy an artificial biosphere completely surrounding its host star.” In short, he theorized that advanced civilizations would dismantle their planet (or planets) to create a structure (now called a “Dyson sphere”) that would harness all of their star’s energy and provide vast habitats.

Over time, scientists have proposed many variations of this structure, collectively known as “Dyson structures.” However, extensive research has contradicted these suggestions, arguing that such megastructures would be unstable. In a new study, famed engineer Colin R. McInnes shows how two specific megastructures – Dyson Bubbles and Stellar Engines – could be built to be passively stable over time. These findings could aid the search for extraterrestrial intelligence (SETI) by limiting the technosignatures these structures could produce.

Colin R. McInnes is Professor of Engineering at the University of Glasgow and Chair of the James Watt School of Engineering. His results are presented in an article that appeared in the Monthly Notices of the Royal Astronomical Society. Although the concept is several decades old, megastructures have received renewed attention thanks to the discovery of Boyajian’s star and other cases where stars exhibited periodic dimming, were low in luminosity, or were “missing.”

In addition to being a leading figure in the field of solar sails, reflectors and satellites, McInnes has also written an article on the stability of megastructures. As he summarized in this latest study, megastructures have been proposed for a range of endeavors, including asteroid orbit modification, climate engineering (e.g. solar shields), terraforming (following Ken Roy’s Shell World concept), and planetary orbit modification (moving them into the star’s habitable zone).

On larger scales, scientists have considered how giant swarms of reflectors could envelop a star, known as a Dyson swarm, bubble or Matrioshka brain, or how they could be used to alter a star’s orbit, known as a Stellar Engine or Shkadov Thruster. In the former case, the reflective surface ensures that radiation pressure keeps the swarm (which could support habitats) hovering above the star. In the latter, a flat reflecting disk remains bound to a star through gravitational coupling, causing the star to move.

Similar to what Dyson suggested in his original paper, these studies assume that advanced civilizations will experience exponential growth and increasing energy demands as they age. “Freeman Dyson envisioned a swarm of energy-harvesting elements enveloping a central star as the endpoint for a civilization with ever-increasing energy needs,” McInnes told Universe Today via email. “It is obviously difficult to infer motivations. However, because of the universality of the laws of physics, we can at least speculate about how such structures might be constructed.”

While the idea is popular among scientists, extensive research by physicists and civil engineers has cast doubt on the existence of megastructures. In short, they argued that such structures would be inherently gravitationally unstable. But as McInnes explained, it is possible that megastructures could be built in a way that would ensure long-term passive stability:

Many concepts, such as a rigid Dyson sphere or a ring world, are not in orbit, and therefore a small displacement can cause the structure to drift and collide with the host star. They therefore need active control measures to stabilize them. However, my interest lies in understanding ways in which ultra-large structures could be engineered to be passively stable. We can imagine that engineers, terrestrial or otherwise, would prefer passive stability to more complex active control measures.

The simplest design (he notes) for a Stellar Engine would probably be a flat reflective disk. Starting with an ultra-large disk, he calculated the stability of the structure according to first principles using a simplified model of a perfectly reflective rigid disk. He then used the functional forms of gravitational and radiation pressure forces to study the stability of a radial engine and orbiting reflectors (forming a Dyson bubble) in various configurations. McInnes said:

Stability analysis involves adding a small displacement to the equations of motion that describe such structures and then determining whether the displacement increases with time. By then considering ways to design the structure’s properties, such as its geometry or mass distribution, we can determine whether it can be stabilized so that small displacements do not increase and are limited. There is no set process as such; It’s about looking at the equations of motion and considering how the acting forces could be changed, for example through changes in the geometry or mass distribution of the structure.

Ultimately, his analysis showed that although an ideal radial engine consisting of a uniform, reflective, rigid disk is unstable, a reflective disk with mass concentrated at its edge can (in principle) be passively stable. By balancing the gravitational and radiation pressure forces, such a design would also maximize the star engine’s propulsion. Meanwhile, a self-stabilizing Dyson bubble or swarm would avoid (or minimize) collisions between the cloud’s elements and maintain equilibrium, provided the proper configuration and design considerations were taken into account.

These structures would also create telltale technosignatures that SETI researchers could look for in the future. While a Stellar Engine would scatter the light reflected from its star, a Dyson bubble would appear like a dense cloud surrounding a star, changing its spectral properties. In a static cloud, no flickering would be noticeable to observers, in contrast to a swarm of orbiting reflectors passing in front of the star’s disk. And as Dyson first predicted, any solid Dyson sphere would be detectable by the infrared excess produced by the radiant heat.

However, as McInnes added, this study is not the final word on megastructures and their potential stability. “The analysis in the paper is simplified and makes a number of assumptions,” he said. “However, it is a starting point for understanding how ultra-large structures can be engineered to be passively stable. For example, a dense Dyon bubble can apparently stabilize itself because light pressure falls faster than gravity as we move through the cloud of elements. Perhaps by understanding how such structures can be engineered to be passively stable, we can better predict the technosignatures associated with them.”

Further reading: MNRAS