Since that date, Pluto has been officially classified as a dwarf planet along with four other confirmed dwarf planets in the outskirts of the solar system.
This decision sparked outrage around the world, and the controversy is still very much alive today. Astronomers in favor of Pluto's demotion argued that a planet by definition should have cleared its orbit around the sun. Pluto and the more distant dwarf planets fail to meet this criterion.
On Aug. 24, 2006, the International Astronomical Union (IAU) decided that Pluto wasn't a planet anymore. (Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute)
Why it mattered
When Pluto was reclassified as a dwarf planet, many astronomers and scientists weren't happy with the result.
"I'm embarrassed for astronomy," said Alan Stern, leader of NASA's New Horizon's mission to Pluto and a scientist at the Southwest Research Institute. "Less than 5 percent of the world's astronomers voted."
Stern argued that according to the IAU's new definition, many other planets in our solar system would fail to meet the same criterion. Earth, Mars, Jupiter and Neptune, for example, all share their orbits with asteroids.
But if Pluto were to keep its planetary status, many of the solar system's dwarf planets would also need to be classified as planets — and there could be hundreds in our solar system.
ESA's Sentinel-1 mission captured remarkable imagery showing significant ice loss and calving at the Petermann Glacier. (Image credit: ESA)
The massive glaciers of Greenland are disappearing right before our very eyes in new satellite imagery.
What is it?
Petermann Glacier in northwest Greenland connects the Greenland ice sheet to the Arctic ocean. Petermann's "ice tongue" has previously measured 43 miles (70 kilometers) long and 9 miles (15 km) wide. But new satellite imagery has revealed the glacier's floating "ice tongue" has broken apart in the glacier's most dramatic loss of floating ice since 2012.
On August 4, 2026, the European Space Agency's Copernicus Sentinel-1 missioncaptured imagery of the glacier that revealed that a 29 square mile (76 square km) section of the ice tongue has broken away. This is the most significant ice calving event (where ice breaks off of a glacier) seen in the Arctic since 2020.
"Satellite missions such as Sentinel-1 provide the systematic, long-term observations needed to track these changes, helping scientists better understand the processes driving calving and the wider impacts on the polar environment, and ultimately the Earth system as a whole," ESA Earth scientist Martin Wearing said in a statement.
A moving image showing the ice calving in the Petermann glacier in August 2026. (Image credit: ESA)
Why is it incredible?
It is no secret that worsening climate change is contributing to significant ice loss. Antarctica has lost 5,000 square miles (12,950 square km) of grounded ice over the last three decades. Warming oceans are consistently eroding the arctic ice we have left which, when melted, contributes to rising sea levels.
But knowledge is power, and by studying Earth from the vantage point of space, Earth scientists can gather critical information about our changing planet.
"By studying Arctic ice islands, we will gain knowledge that can be transferred across polar regions. This is critical for understanding how the calving and deterioration of ice islands impact glacier dynamics, sea-level rise and the ocean environment," Anna Crawford, a glaciologist at the University of Stirling, said in the same statement.
The Milky Way has something of a torrid and violent history, given that our galaxy has fueled its own growth by cannibalistically devouring smaller galaxies. Now, astronomers have discovered evidence of our galaxy's earliest bout of cannibalism in the form of "scarring" at the heart of the Milky Way left behind by a galactic morsel it devoured around 12 billion years ago.
Working as part of the ARMA (Cluster Ages to Reconstruct the Milky Way Assembly) project, the team behind this discovery used dense conglomerations of ancient stars called globular clusters to find traces of a merger that occurred around 1.8 billion years earlier than the previously earliest known event of this type.
Prior to this, the history of the Milky Way colliding and merging with both smaller and larger galaxies had only been reconstructed up to around 10 billion years ago, around 3.8 billion years after the Big Bang. The earliest bout of cosmic cannibalism involved the collision with and consumption of the dwarf galaxy Gaia-Enceladus about 10 billion years ago. That means the earliest history of the Milky Way was, until now, shrouded in mystery.
"This work tells us what happened to the Milky Way in its infancy," team member Chiara Zerbinati of the Department of Physics and Astronomy at the University of Bologna, Italy, said in a statement. "It sheds light on a particularly significant event that influenced the entire subsequent evolution of the galaxy. If one of humanity's great questions is 'where do we come from?', we offer at least a piece of the answer."
A helping hand from Hubble
The key development in the quest to delve further back into the history of the Milky Way was delivered by the Hubble Space Telescope.
"We started with the ambition of reconstructing the assembly history of the Milky Way, that is, all the galactic merger events that led to its current appearance," team leader Davide Massari of the Italian Institute for Astrophysics (INAF) said. "We used globular clusters as tracers: especially in the inner regions of the galaxy, where extinction is highest, they are the only objects for which we can obtain excellent measurements of both orbital motion and age."
Astronomers developed a technique using Hubble data that allowed them to discover the ages of globular clusters with a far greater precision than had ever been possible before. This revealed that the globular clusters at the heart of our galaxy can be categorized in three distinct ways based upon their age and their metallicity, a measure of elements heavier than hydrogen and helium, which astronomers refer to as metals.
One group of globular clusters could be linked directly to the Gaia-Enceladus merger; one belonged to the original Milky Way; but there also existed a third group distinct enough from the other two groups that it must have come from some hitherto undiscovered merger event.
NGC 6397 as seen by Euclid. This is the second closest globular cluster to Earth, located about 7,800 light-years away. (Image credit: ESA/Euclid/Euclid Consortium/NASA, image processing by J.-C. Cuillandre (CEA Paris-Saclay), G. Anselmi)
The team was able to deduce some things about this doomed galaxy from this third group of globular clusters. They found the unfortunate galaxy had around the same mass as Gaia-Enceladus, about 500 million times the mass of the sun. For comparison, the Milky Way today has a mass of around 1.5 trillion solar masses.
The researchers also found that most of the matter from this devoured dwarf galaxy was dumped into the Milky Way within 20,000 light-years of our galaxy's heart. They also gave a name to this violent, yet formative cosmic event.
"The final name, Low-energy-Kraken-Heracles (LKH), is an acronym that pays homage to the three papers that first hypothesized the existence of this ancient galactic encounter," Massari concluded.
The team's research was published on Monday, August 17, in the journal Nature Astronomy.
In August of 2006, astronomers at the International Astronomical Union (IAU) democratically voted to reclassify Pluto as a dwarf planet — but 20 years later, with our greater knowledge and understanding of planetary systems, is it time to revisit the controversial decision? Should Pluto be called a planet again?
For several years before the IAU vote, there had been agitators among the astronomical community lobbying for our solar system's nine worlds to become eight, and for Pluto's planetary status to be revoked. In 2000, Neil DeGrasse Tyson even went as far as to remove Pluto from the planets display at the Hayden Planetarium in New York. The questioning of Pluto's status began even earlier, in the 1990s, with the discovery of distant objects in the Kuiper belt beyond Neptune which had similar orbits to Pluto.
It all came to a head in July of 2005 with the discovery of Eris, which is a Pluto-size body even further from the sun than Pluto is. Was Eris the 10th planet? If it was not a planet, then how could we still call Pluto a planet? A year later, the issue was debated at a meeting of the IAU, where astronomers from all over the world convened to discuss various conundrums. Numerous proposals and counter-proposals were put forward, some of which even increased the number of recognized planets to as many as 14. But in the end, Pluto became a dwarf planet.
Though Pluto was officially "reclassified," to many in the public it seemed as though Pluto had experienced a demotion. This viewpoint was the one promoted by those scientists who were against the decision such as Alan Stern, who was the principal investigator on the New Horizons mission to Pluto. Stern's spacecraft would launch in 2005 on a journey to a planet, but arrive at a dwarf planet in 2015.
Some argued that Pluto was still a kind of planet, just a small one. This argument is undermined somewhat by the IAU giving Pluto a minor planet number — 134340 — which is typically reserved for asteroids. Nationalistic arguments from some in the United States said Pluto should remain a planet because it was discovered by an American astronomer, Clyde Tombaugh, at Arizona's Lowell Observatory in 1930. And when New Horizons reached Pluto, it revealed not a minor body, but rather a complex world in its own right.
What is Pluto?
Nevertheless, for 20 years, Pluto has remained a dwarf planet, but on the anniversary of that fateful IAU vote, is it time to revisit that decision? Paul Byrne, a planetary astronomer at the University of Washington in St Louis, certainly thinks so.
"Yes, Pluto is a planet," he told Space.com. And not just Pluto, but the other dwarf planets too: Ceres, Eris, Makemake and Haumea, not to mention the likes of Sedna and Quaoar that are dwarf planets in all but name.
"Ultimately I think they are all planets and I don't think there's any benefit to not including Pluto as a planet," Byrne said.
To a point this entire debate is semantics, and Byrne accepts this viewpoint, reminding us that: "Nature doesn't care what we call Pluto."
However, perception is another matter, which is where Byrne thinks that the IAU's 2006 decree ultimately failed us. Byrne describes how, when he gives public talks about the planets, members of the audience don't ask questions about Pluto's amazing active nitrogen glaciers or what formed its giant heart-shaped feature. Instead, they want to know why it was demoted. The entire issue has got in the way of presenting the science to the public.
"We've done a massive disservice to the public from a science communication perspective," Byrne said. "The messaging has got in the way of trying to understand what Pluto is."
Pluto's active nitrogen glaciers are typical of planetary processes. (Image credit: NASA/JHUAPL/SwRI)
One of the arguments in 2006 was that models of the solar system's formation predict that there could be hundreds of objects like Pluto and Eris that remain undiscovered in the Scattered Disk and the Oort Cloud, which is a vast unexplored region that could extend up to a light-year from the sun.
"One of the issues people brought up was, how would kids remember the names of 200 planets?" said Byrne. "But just look at how many Pokémon there are that kids know the names of. If ultimately there are 200 planets in the solar system, then so what?"
The IAU definition of a planet
Semantics or not, how we categorize celestial objects has to be grounded in some kind of scientific thinking. In 2006, the IAU came up with a three-point plan on what makes a planet.
First, a planet had to be in hydrostatic equilibrium, meaning that its gravity has pulled it into a spherical shape. Furthermore, its interior will have become differentiated, with the heavier elements sinking to the core. Everyone seems to agree with this part of the planetary definition.
Pluto's gravity has shaped it into a spherical object. (Image credit: NASA/JHUAPL/SwRI)
Second was that it must be in orbit around the sun, so a moon isn't a planet because a moon doesn't orbit the sun, it orbits a planet instead (though Byrne notes that if he had his way, he'd call the large moons planets too). Strictly speaking, this rules out exoplanets because they don't orbit our sun, but common sense dictates that they're fine because they orbit their own star instead. However, what about rogue planets that wander interstellar space alone? Astronomers are now beginning to discover very many of these free-floating worlds. It could be argued that most of these did indeed form in orbit around a star only to be ejected, so it's okay to still call them planets, but some rogue planets seem to have formed directly from the collapse of a gas cloud without having a parent star. Such planets fall through the gaps in the IAU's definition.
It's the third point that draws the critics' ire the most. It states that to be a planet, an object must have cleared its neighborhood. In other words, it must be dominant in the region around its orbit, its gravity having swept away any other bodies. Pluto fails at this because its orbit actually crosses Neptune's, and it's accompanied by other Kuiper belt objects in neighboring orbits. But then you could say Neptune mustn't be a planet because it has Pluto infringing on its orbital realm. And what about the existence of near-Earth asteroids? Does their existence mean that Earth isn't a planet because it hasn't cleared those away yet? There certainly does seem to be some sloppiness in this part of the definition of a planet, perhaps resulting from the somewhat rushed nature of the vote 20 years ago.
Planetary processes
But if the IAU decision were to be rejected, what should replace it? How should we classify planets? Byrne has some ideas.
"Being round and having some amount of differentiation makes a lot of sense to me," he said. "Geophysically, if they are big enough to pull themselves into balls, then they are big enough to have undergone some kind of internal chemical processing and are capable of having some kind of active geology, in terms of the outgassing of volatiles to form an atmosphere, volcanism, surface geomorphological processes, even a short-lived magnetic field. That's why I count the moon as a planet because it has had these planetary processes."
Byrne acknowledges that gas giants don't have these properties since they have no solid surface, but no one is doubting Jupiter's planetary credentials, and when it comes to Uranus and Neptune we don't actually know whether or not there is some sort of super-Earth itself lurking deep within them.
The moniker "dwarf" doesn't impress Byrne either. To him, it sounds like it implies there is a hierarchy of planets with the gas giants at the top and the dwarf planets at the bottom.
The New York Times article from when Pluto was discovered. (Image credit: The New York Times Archive)
"There is no natural hierarchy; they don't form according to one," he said. And although Pluto, Eris and the other dwarf planets are made from detritus left over from the construction of the solar system, they still coalesced in the same way as the other planets, in the sense that building blocks came together to form these larger objects.
A counterargument to Pluto being a planet, however, is that if it is just one of 200, then it is nothing special; it would become forgotten and ultimately treated almost incidentally. As a dwarf planet, it is the standard bearer of its kind, the guardian of an entire realm of similarly sized worlds. It's a choice between being a big fish in a little pond, or a little fish in a big pond.
The other 200 planets?
The real test will come when astronomers begin to discover some of these purported 200 or so planets far from the sun. As long as they are all roughly Pluto-size, there will be no debate — but what happens when astronomers discover one the size of Mars, or one even as large as Earth? We would surely think of an object so large as a planet. Perhaps this world would have formed closer to the sun but was kicked out through gravitational interactions with one of the giant planets, but on the other hand perhaps it formed out there in the outer solar system from the same detritus as Pluto did.
"By the IAU definition it would fail to be defined as a planet because it wouldn't have cleared its neighborhood," said Byrne. "If we did find such a planet it would be another nail in the coffin of trying to distinguish these things solely on the basis of where they are and not what they are."
Whatever the case, if Pluto is to be a planet again, it must deserve to be so scientifically. Nostalgia, or nationalistic pride, or giving kids names of planets to remember aren;t sufficient reasons to revoke the original IAU decision. Revisiting the name "dwarf planet" and finding a more appropriate category could be the way to go instead.
Or, perhaps we just don't have the words to describe the things that we are discovering. Concepts such as planets are rooted in history going back millennia when there was no understanding what these wandering "stars" really were, so perhaps it is not surprising that we are now running into difficulty when trying to apply the term "planet" to our modern understanding of the different types of worlds. If there is no way of categorizing these objects that is consistent and satisfactory to everyone, then perhaps we ought to stop worrying so much about it.
Whatever we decide to call it, Pluto will always be Pluto.
A misbehaving coronal mass ejection (CME) that blew out a hidden cloud of charged particles aimed at Earth has been tracked by a record 17 spacecraft spread throughout the solar system, revealing the CME to be surprisingly lopsided.
CMEs are "burps" from the sun – huge clouds of magnetized plasma belched out from the sun's hot outer atmosphere, the corona, by the energy resulting from a solar flare. The magnetized CME cloud then expands out into the solar system, and the charged particles that the cloud contains are a significant radiation hazard to astronauts, spacecraft and even passengers on jet liners, but they also have a beautiful side as they can trigger the beautiful lights of the aurora when they intercept Earth.
CMEs occur on a regular basis, but one that erupted from the sun at 00:48 UT (7:48 p.m. ET) on Dec. 15, 2024 proved to be rather special.
"We used observations from 17 spacecraft to track and characterize this CME," Adrienn Luspay-Kuti of Johns Hopkins University Applied Physics Laboratory, who led the research that drew all the observations together, told Space.com. "This was a record number of spacecraft for tracking and characterizing a single CME, and gave us an exceptionally detailed view of how the CME evolved."
The previous record had been 10 spacecraft, but they had mostly been in a rough line from the sun through to the Earth and beyond, meaning that their measurements were somewhat one-dimensional. This time, for the December 2024 CME, the spacecraft were spread far and wide, not just at different distances from the sun, but also substantially wide of the Earth–sun line.
They revealed that the CME had two asymmetric lobes, one moving faster than the other. One of those lobes, which headed for Earth and Mars, would have gone unseen, obscured by the larger but slower lobe that left the sun at a tangent, were it not for the wide spread of the spacecraft.
"Our observations showed a fast lobe propagating through the Earth–Mars sector and a much slower lobe farther west toward STEREO-A," said Luspay-Kuti. STEREO-A is one half of NASA's two-spacecraft space weather monitoring system known as the Solar Terrestrial Relations Observatory.
The onset of the CME was seen by the joint NASA–ESA Solar and Heliospheric Observer (SOHO), which has been constantly monitoring the sun for more than 30 years. Yet it only saw the slower lobe that erupted at an angle to Earth; the faster lobe heading for our planet was missed, obscured by the slower, larger lobe.
A schematic of the CME has its two lobes progressing through the solar system and encountered various spacecraft and satellites. (Image credit: Johns Hopkins Applied Physics Lab)
The CME was next detected at a distance from the sun of 0.35 astronomical units (AU; 1 AU is the distance of Earth from the sun) on Dec. 16 moving through space near Mercury and the European Space Agency's BepiColombo mission (which finally arrives into orbit around the innermost planet in November 2026).
The next detection, on Dec. 17, was of the "hidden" component arriving at Earth, where a multitude of spacecraft picked it up. The CME was not strong enough to produce significant aurorae. Intriguingly Europe's Solar Orbiter mission, on an elongated orbit around the sun and at the time 0.94 AU from the sun and just 10 degrees off the Earth–sun line, did not detect the CME. This non-detection was actually vital since it helped to constrain the shape of the CME.
Then on Dec. 18, the slower moving lobe reached NASA's STEREO-A spacecraft, which orbits the sun at the same distance as Earth — 1 AU —- but substantially ahead of Earth in its orbit. The lobe that intersected the Earth had an average velocity of 522 miles (840 kilometers) per second, but the other lobe dragged its feet, moving at an average of 332 miles (534 km) per second from the sun and past BepiColombo and STEREO-A. In fact, by the time it reached STEREO-A, it had slowed to about 248.5 miles (400 km) per second. Both lobes decelerated as a result of friction with the regular solar wind that the CME was overtaking, and the range of velocities measured in the CME told researchers that the solar eruption was not traveling as a single, unified front.
Beyond Earth NASA's Europa Clipper mission, on which Luspay-Kuti is the Principal Investigator for the spacecraft's Plasma Instrument for Magnetic Sounding (PIMS) experiment, detected the faster moving lobe at 1.19 AU as the spacecraft was cruising to Mars for a gravity assist to help it on its journey to Jupiter. At the red planet, the now-defunctMAVEN mission also detected the CME on Dec. 19 to Dec. 20.
To have not only so many spacecraft follow the progress of a CME but also enough spacecraft off the Earth–sun line to measure the shape of the CME, at least in two dimensions, is a significant step forward in understanding and forecasting the propagation of CMEs.
The CME seen by the Solar Dynamics Observatory (top left), SOHO (top right) and STEREO-A (bottom left and right). The fast moving Earth-directed lobe was obscured by the southward-directed slower lobe. (Image credit: Luspay-Kuti et al.)
"This matters for future human exploration because a missed CME can mean losing valuable warning time," said Luspay-Kuti. "Fast CMEs can drive shocks that accelerate high-energy particles, which can pose a radiation hazard to astronauts outside Earth's protective magnetic field. This is why observations from multiple viewpoints, including spacecraft away from the sun–Earth line and planetary missions operating during their cruise phase, will become increasingly important for space-weather forecasting as human exploration moves further from Earth."
The asymmetrical double-lobed structure of this particular CME was certainly a surprise. The cause of the asymmetry remains unclear at present, though Luspay-Kuti told Space.com that researchers are investigating. The main question is, how frequent are asymmetric CMEs?
"In the context of previous observations, this event is at the most extreme end of observed CME variability," said Luspay-Kuti. "Are highly asymmetric CMEs actually fairly common but we fail to recognize them because we don't have enough observational coverage, or are they genuinely rare?"
The 17 spacecraft that detected or imaged the CME across some or all of its various stages – the bow shock and turbulent sheath ahead of the magnetic cloud, the CME itself and the turbulent wake left in the solar wind after its passing – were the following: SOHO (initial imaging), BepiColombo, NASA's Solar Dynamics Observatory, STEREO-A, the four spacecraft of the Magnetospheric Multiscale (MMS) mission, the two spacecraft of the ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the sun) mission, NASA's Wind, ACE (Advanced Composition Explorer), GOES (Geostationary Operational Environmental Satellite) and DSCOVR (Deep Space Climate Observatory) missions, Europa Clipper, MAVEN and Solar Orbiter, the latter of which made measurements but did not detect the CME.
In the future, these missions will be joined by the European Space Agency's Vigil mission that will watch for space weather when it launches in 2031 for the sun–Earth L5 Lagrange point, 60 degrees behind Earth in its orbit and therefore providing additional off-axis monitoring.
The findings were published on Aug. 19 in the journal Science Advances.
Astronomers have discovered a hitherto unseen population of so-called "radio galaxies" with fading "radio lobes." The discovery reveals what happens when the supermassive black hole engines that power these vast, blooming outflows of plasma stall. This discovery increases our understanding of the life cycles of galaxies.
The team behind this research studied 14 candidates for faded or remnant radio galaxies found in a region of the sky over Earth, studied intensely by the XMM-Newton X-ray spacecraft, called the XMM–Newton Large-Scale Structure (XMM–LSS) field.
Radio galaxies are extremely bright in radio waves and feature vast lobes of gas that can stretch out for millions of light-years. Remnant radio galaxies represent the final stage in the evolution of radio galaxies, at which point the jets from the galaxies' central regions, or active galactic nuclei (AGNs) powered by feeding supermassive black holes, have switched off. Therefore, these jets can no longer replenish the vast radio lobes, causing them to gradually fade.
The researchers studied the XMM–LSS field using the MeerKAT radio telescope, an array of 64 antennas located in the desert-like region of the Northern Cape, South Africa, the Jansky Very Large Array, and the LOFAR (Low-Frequency Array) network.
This powerful combination of observations allowed them to study how radio emissions from the lobes of radio galaxies change as the particles within them "age" and lose energy.
This allowed the researchers to determine that 12 of the 14 candidates actually are remnant radio galaxies, while the other two remain active radio galaxies.
The team also discovered something striking about the 12 confirmed radio galaxy remnants.
Two examples of the newly discovered giant radio galaxies, each spanning millions of light-years. (Image credit: Pal, et al (2025))
One thing that really stood out in this study was the ages of these remnants, which appeared to have been fading for between 8 million and 42 million years, with the average "fade age" being 12 million years.
This age is younger than the ages measured for radio galaxy remnants, which could indicate that astronomers have been missing a population of short-lived remnants.
This wasn't the only extraordinary finding in this study. The scientists also found that the remnants they looked at exist in a wide range of evolutionary stages, with some having jets that have only just switched off, while others are more evolved, having "powered down" long ago.
The 'double boomerang' of an x-shaped radio galaxy. (Image credit: NRAO/AUI/NSF; SARAO; DES)
The new findings represent a major step forward in understanding the life cycles of radio galaxies, and also how supermassive black holes function as the engines powering jets that drive vast radio lobes.
The world just got its first good looks at some hardware that will make spaceflight history.
Last Thursday (Aug. 13), Japan unveiled the spacecraft that make up its Martian Moons eXploration (MMX) mission, which aims to snag samples of the Mars moon Phobos and haul them to Earth — something that has never been done.
The big reveal came at Tanegashima Space Center, the site from which MMX will launch toward the Red Planet atop an H3 rocket. And we just got some clarity about when that liftoff will take place.
Another look at MMX's Propulsion Module (back) and Exploration and Return Modules (front) at Tanegashima on Aug. 13, 2026. (Image credit: Yuichi YamazakiI/AFP via Getty Images)
If all goes according to plan, MMX will launch on Oct. 19 at 3:41 p.m. EDT (1941 GMT; 4:41 a.m. on Oct. 20 Japan time), the Japan Aerospace Exploration Agency (JAXA) announced on Thursday (Aug. 20). That's the first day of the mission's launch window, which extends through Nov. 7.
JAXA originally intended to launch MMX in 2024 but had to stand down due to issues with the H3. Mars and Earth align properly for interplanetary launches just once every 26 months, so this was a significant delay.
MMX will spend about a year traveling to Mars. Once in orbit around the Red Planet, the mission will map and study its two small moons, Phobos and Deimos, which are just 14 miles (22 kilometers) and 7.5 miles (12 km) wide, respectively.
Part of this work will help the mission team pick a landing site on Phobos, where they'll drop a 55-pound (25 kilograms) French-German rover called Idefix. That little robot — which is named after the dog in the French comic "Asterix" — will study Phobos' surface in detail using a variety of instruments.
The MMX spacecraft itself will then spiral down toward Phobos, eventually making contact and collecting about 0.35 ounces (10 grams) of material. MMX will leave Mars orbit with these samples in 2030 and deliver them to Earth for analysis a year later.
The mission aims to shed light on the nature and origin of Phobos and Deimos.
"Understanding how Mars and the two moons formed is a heavily debated topic in solar system science," JAXA officials wrote in a mission description.
"Remote-sensing observations by the MMX spacecraft and the detailed analyses of the returned sample will determine whether Phobos and Deimos are remnants of early Mars created from debris produced by a giant impact with the young planet, or whether the moons are asteroids captured by Mars's gravity that brought material from outer solar system," they added.
To date, no spacecraft has returned material from the Mars system. Russia tried to do so with its Phobos-Grunt mission, which aimed to sample the eponymous Red Planet moon, but that effort failed shortly after its November 2011 launch. (The Soviet Union also launched two probes to Phobos in 1988, but neither one of them met its mission objectives.)
NASA plans to collect and haul home pristine samples that have already been collected on the Martian surface by its Perseverance rover, but it's unclear when or if that will happen. The agency has deemed its original sample-return architecture too expensive and is currently investigating other options.
There are good reasons to believe that Japan will succeed where others have failed, however. The country has a history of small-body sample-return success; its Hayabusa mission brought home pieces of the asteroid Itokawa in June 2010, and Hayabusa2 did the same with material from the space rock Ryugu in December 2020.
A mysterious hum of gravitational waves that fills the cosmos may be the echo of "dark stars" that served as the seeds of the first supermassive black holes.
These low-frequency gravitational waves were detected back in 2023 using an array of cosmic lighthouses, or pulsars, in a so-called "pulsar timing array." Pulsars are neutron stars that spin rapidly and regularly while blasting out collimated beams of radiation from their poles that can be used to detect tiny fluctuations in space and time. Such fluctuations are caused by the gravitational waves, or ripples in spacetime.
For a long time, the source of this particular low-frequency gravitational wave background has been somewhat shrouded in mystery, but scientists have hoped that they may be encoded with the secrets of the universe as it was around 13 billion years ago. Indeed, the team behind this research believes this hum of spacetime ripples could help explain how supermassive black holes grew so rapidly before the universe was even a billion years old. They link this solution to hypothetical supermassive "dark stars" that may have collapsed and died in the early universe to birth massive black hole seeds, giving supermassive black hole growth a head start.
"Dark stars were originally proposed as objects that might be seen directly at cosmic dawn," Ilie said. "This work points to a completely different way of testing their possible role in cosmic history," team member Cosmin Ilie of Colgate University said in a statement. "Their descendants could leave a gravitational-wave imprint that persists all the way to the present-day universe."
Cosmic clocks and collapsing Dark Stars
Pulsar timing arrays detect gravitational waves when their passage squashes and stretches space as the waves ripple past them, causing tiny delays in the pulsars' beams of radiation reaching Earth.
Detecting a gravitational wave background,however, required monitoring pulsar timing arrays for many years.
"Pulsar timing arrays are usually thought of as probes of supermassive black-hole binaries in the relatively recent universe," Ilie said. "What our work shows is that the signal may also contain information about how the ancestors of those black holes formed at cosmic dawn.
"In that sense, gravitational waves observed today could provide a new window onto the birth of the first supermassive black holes."
An illustration shows a neutron star at the heart of a pulsar and its strong magnetic field beaming radiation from its poles as it spins. (Image credit: Robert Lea (created with Canva))
The currently favored explanation for this background is a cosmic history of binary black holes spiraling together before merging, particularly pairings with combined masses of over 1 billion times the mass of the sun.
However, that doesn't explain where these supermassive black holes came from and how the James Webb Space Telescope (JWST) is routinely detecting them before the universe was even 1 billion years old — despite the fact that the feeding and merger chains proposed to create supermassive black holes should take over 1 billion years.
Ilie and his Colgate University colleague Sohan Ghodla questioned if supermassive balck hole growth began with heavy seeds, and if these heavy seeds were created by the collapse of dark stars.
Dark stars are hypothetical primordial stars that, rather than producing energy through nuclear fusion, are instead powered by self-annihilating dark matterwithin their cores. As dark matter fuels these primordial stars, they would remain cool compared to other stellar bodies, allowing them to continue to accrete matter throughout their lives.
This process would continue until Dark Stars reached masses millions of times that of the sun and collapsed under their own gravity, creating massive black holes; seeds that collide and merge to form supermassive black holes.
An artist's concept of two black holes circling each other before merging (Image credit: NASA )
Ilie and Ghodla modeled the environment in which the resultant black hole seeds would exist and merge, calculating merger rates and the influence on the gravitational wave background.
They found supermassive dark star remnants could indeed provide a major, perhaps dominant, contribution to the gravitational wave background detected in 2023. That means the measurements provided by pulsar timing arrays could help determine how abundant heavy black hole seeds were in the early universe.
"Produce too many of these massive seeds, and you end up over-producing the pulsar timing array-detected signal," Ghodla said. "Produce too few, and you need other sources to efficiently assemble these supermassive black holes later in the life of the universe to match pulsar timing array observations."
An illustration of dark stars in a halo of dark matter. (Image credit: Robert Lea (created with Canva))
The key determining factor here would be the masses of the dark matter haloes in which the dark stars live and in which the heavy black hole seeds form.
Determining if the researchers' theory is correct may have to wait for improvements in pulsar timing array measurements of the gravitational wave background, along with a better understanding of populations of black holes and their characteristics in the early universe.
The team's research was published on Monday (August 17) in the journal Physical Review D.
The Chandelier Cluster, or globular cluster NGC 6723, as imaged by the Hubble Space Telescope. (Image credit: ESA/Hubble & NASA, A. Sarajedini, G. Piotto)
Stars scattered across the cosmos sparkle in the appropriately named Chandelier Cluster.
Every bright spot in this mesmerizing cosmic chandelier is an individual star in the cluster. Globular clusters typically contain older stars. In fact, they're known to hold some of the oldest stars in the galaxy, with some being 10 billion years old or older. Globular clusters are thought to contain some of the first stars, or the oldest stars in the universe.
As their name implies, globular star clusters are groups of stars. But this particular type of star cluster isn't just full of ancient stars; it's also giant. Globular star clusters can contain tens of thousands to millions of stars. And just in our Milky Way galaxy, there are about 150 known globular clusters.
Why is it incredible?
While this incredible image was captured by an ultra-powerful space telescope, backyard astronomers could spot the far-off globular cluster with binoculars or a telescope.
This type of star cluster is so visible because they are so massive and contain so many stars. With all those stars clumped together, even fainter globular clusters will typically be easier to spot than the smaller variety.
In fact, the Chandelier Cluster was discovered long before space telescopes were even a remote possibility. The cluster was discovered in 1826 by British astronomer James Dunlop.
For night sky enthusiasts, astrophotographers or casual skywatchers looking for this cluster, you can find it nestled in the constellation Sagittarius near the constellation Corona Australis. Have you ever spotted the Chandelier Cluster? Will you try to spot it now?
New research suggests that if dark matter is composed of "dark photons," it would not have heated the early cosmos like scientists previously thought. If correct, this discovery could represent a paradigm shift in the hunt for the universe's most mysterious stuff.
Dark matterremains so elusive because, despite outweighing the everyday matter that composes stars, planets, moons and our bodies by a ratio of five to one, it is effectively invisible. That is because it doesn't interact with light. And the fact that electrons, protons, and neutrons do interact with light (or, more accurately, electromagnetic radiation) has inspired the search for particles beyond the Standard Model of particle physics, leading to lots of hypothetical candidates for dark matter.
One of these candidates is the dark photon, the dark universe's version of a photon carrying a force other than electromagnetism, which is the responsibility of standard photons.
When dark photons have been considered in the past, scientists have concluded that they would have transformed into ordinary photons while still embedded in the thick and dense soup that filled the early cosmos. This would have further heated this already blisteringly hot plasma and left detectable traces of dark photons.
This severely limits the search parameters in which dark photons could exist — so much so that many cosmological observations rule out the existence of dark photons.
Now, new computer simulations show that the dismissal of dark photons may have been a little hasty. The conversion of dark photons to photons would have shut off before significant heating could occur.
That brings previously excluded search parameters back into play.
"These exclusions were saying the strength of dark matter had to be 10^8 times weaker than it actually can be," team member Anson Hook at the University of Maryland said in a statement. "This paper opens up a lot of new possibilities to look for dark matter."
An illustration of a dark photon, a candidate for dark matter. (Image credit: Robert Lea (created with Canva))
The team behind this research first saw hints that the transformation of dark photons to photons may not be as straightforward as scientists had assumed when they realized the amount of energy involved is suspiciously large. The problem, they began to suspect, was the fact that this process had been considered to be linear; in other words, the energy released gradually and steadily converts to plasma.
"The treatment for the last 15 years is a linear treatment. If you use that approximation, you can compute the amount of energy transfer, and it's very large," team member Junwu Huang of the Perimeter Institute said in the statement. "And I realized it's not possible."
Performing their first computer simulations, Huang and colleagues realized that the linear process fails to paint a complete picture.
"What we realized is that, as you are converting energy into the Standard Model plasma, the plasma actually goes crazy," Huang said. "There are a lot of nonlinearities in the system, and these nonlinearities basically shut off the energy conversion after a tiny amount of energy is converted."
Dark matter seen at the center of a galaxy. (Image credit: Mattia Di Mauro (ESO/Fermi-Lat))
The research represents a major widening of the parameters in which dark photons could exist, expanding this metaphorical hunting ground considerably. In fact, it could also impact the hunt for hypothetical particles beyond the Standard Model of particle physics.
"By calculating the early universe plasma correctly, experiments will probe new parameter spaces and potentially actually see something," team member Mohamad Shalaby of the Perimeter Institute said in the statement.
