Exploring the Moon poses significant risks, with its extreme environment and hazardous terrain presenting numerous challenges. In the event of a major accident, assistance might take days or even weeks to arrive. To address this, Australian researchers have created a distress alert system based upon the COSPAS-SARSAT technology used for Earth-based search and rescue operations. It relies on low-power emergency beacons that astronauts could activate with minimal setup and use a planned lunar satellite network for communication and rescue coordination.
Fortunately I have never had to raise a distress call. I can imagine it though, somewhere remote, some sort of accident perhaps and need to summon assistance. Even on Earth, most mobile phone systems will be able to use a satellite signal to get a message out even if no cell signal. It’s not so easy on the Moon. Even communication is delayed by just over a second but if someone needs to come and help, then you are really in trouble. That’s what the team from Australia identified and have addressed in their paper published in October 2024.
Aldrin on the Moon. Astronaut Buzz Aldrin walks on the surface of the moon near the leg of the lunar module Eagle during the Apollo 11 mission. Mission commander Neil Armstrong took this photograph with a 70mm lunar surface camera. While astronauts Armstrong and Aldrin explored the Sea of Tranquility region of the moon, astronaut Michael Collins remained with the command and service modules in lunar orbit. Image Credit: NASA
As part of NASA’s Artemis program (which aims to create a sustained human presence on the Moon) astronauts will face significant dangers in isolated regions such as the lunar south pole. To address these challenges, researchers at the University of South Australia (UniSA) have been leading a project focused on developing an emergency response system. It’s designed to deliver critical safety warnings, enable incident reporting, and track the locations of astronauts that may be in trouble.
NASA’s Space Launch System rocket carrying the Orion spacecraft launches on the Artemis I flight test, Wednesday, Nov. 16, 2022, from Launch Complex 39B at NASA’s Kennedy Space Center in Florida. Credit: NASA/Joel Kowsky.
The Artemis program is the focus of returning humans to the Moon. If successful it will mark the first crewed lunar missions since the days of the Apollo missions. With a focus on exploration and scientific discovery, Artemis aims to land astronauts, including the first woman and the first person of colour, on the Moon’s surface in 2025.
Scientists from Adelaide and the United States are collaborating to develop a satellite constellation – like those launched by SpaceX but on a smaller scale – dedicated to improving communication and navigation on the Moon. The system will allow astronauts to transmit emergency alerts to a network of satellites which will then forward the data to Earth or nearby lunar stations.
Founder of Safety from Space and adjunct researcher Dr Mark Rice explains that the system can provide continuous communication with astronauts for up to 10 hours! Even if they are in mountainous or heavily cratered terrain, the system will perform well. The group Safety from Space was formed in 2018 and has been awarded $100,000 from the Government to help with lunar search and rescue (LSAR) initiatives. The trial aims to provide astronauts with a lighter, more reliable radio beacon with a much longer battery life.
If successful, the solution could enable significant Australian contributions to the Artemis program. It could even help to improve emergency communications here on Earth, especially in areas where mobile phone signals are not reliable.
Volcanoes are not restricted to the land, there are many undersea versions. One such undersea volcano known as Hunga Tonga-Hunga Ha’apai off the coast of Tonga. On 15th January 2022, it underwent an eruption which was one of the most powerful in recent memory. A recent paper shows that seismic waves were released 15 minutes before the eruption and before any visible disruption at the surface. The waves had been detected by a seismic station 750km away. This is the first time a precursor signal has been detected.
Undersea volcanoes are openings in the Earth’s crust beneath the ocean, where magma from the mantle escapes, triggering eruptions. They are surprisingly common, with most of Earth’s volcanic activity occurring underwater, particularly along mid-ocean ridges and subduction zones. They play a vital role in creating new seafloor through seafloor spreading, as magma cools and solidifies into basaltic crust. Some grow so tall that they rise above the ocean’s surface, forming volcanic islands such as Iceland and Hawaii. Their eruptions release significant amounts of gas, heat, and minerals into the surrounding water, shaping marine ecosystems.
An erupting undersea volcano forms a new island off the coast of Nishinoshima, a small unihabited island in the southern Ogasawara chain of islands. The image was taken on November 21, 2013 by the Japanese Coast Guard.
The Hunga Tonga-Hunga Ha’apai volcano is an undersea volcano located in the South Pacific. It became well known after its massive eruption in January 2022. The eruption was one of the most powerful volcanic events of the 21st century, triggering tsunamis that affected coastlines as far away as Japan and the Americas. The explosion released a plume of ash, gas, and water vapour, reaching over 50 kilometres into the atmosphere, making it the highest plume ever recorded. It impacted global weather patterns and temporarily increased water vapour in the stratosphere.
The eruption of January 2022 formed a caldera on Hunga Tonga-Hunga Ha’apai. There were disturbances that were recorded by many surface stations and satellites in orbit. The data which had been captured revealed that the eruptions began just after 04:00 UTC on 15 January. There were a number of reports of seismic waves from around 15 minutes before the onset of eruption. In a paper published recently by lead author Takuro Horiuchi and a team from the University of Tokyo, they explore the wave detection and mechanics of the eruption.
Volcanic eruptions at Mt. Etna from orbiting NASA Terra Satellite. Acquired on January 11, 2011. NASA Earth Observatory Image of the Day on January 15, 2011. Credit: NASA Terra Satellite
The team aim to confirm that the event actually occurred just before the 04:00 published timestamp. If they can confirm this, it will help understand the processes that led to the violent eruption. At the time of the eruption, no seismic stations had been working on Tonga but data had been recorded as far away as Fiji and Futuna, both of which around 750km away from the volcano.
The study concluded that the waves which had been detected were Rayleigh waves – a type of seismic waves which are a combination of compression (longitudinal) and shearing (vertical) movements. The waves started around 03:45 on the 15th January 15 minutes before the onset of the eruption. This is the first time significant seismic activity has been seen before the eruption event. It demonstrates that seismic stations hundreds of kilometres away can be positively used to detect signals as precursors to eruptions.
Some binary stars are unusual. They contain a main sequence star like our Sun, while the other is a “dead” white dwarf star that left fusion behind and emanates only residual heat. When the main sequence star ages into a red giant, the two stars share a common envelope.
This common envelope phase is a big mystery in astrophysics, and to understand what’s happening, astronomers are building a catalogue of main sequence-white dwarf binaries.
Common envelope (CE) binaries are important because they’re the progenitors for Type 1a supernovae. When the main sequence star swells into a red giant, the compact and gravitationally powerful white dwarf draws matter away from it. This matter gathers on the surface of the white dwarf until it reaches a critical point and then detonates as a supernova.
CE binaries are also important because they can merge and emit gravitational waves, another astrophysical phenomenon that needs better understanding.
“Despite its importance, CE evolution may be one of the largest uncertainties in binary evolution,” the authors write in their research.
“Binary stars play a huge role in our universe,” said lead author Grondin. “This observational sample marks a key first step in allowing us to trace the full life cycles of binaries and will hopefully allow us to constrain the most mysterious phase of stellar evolution.”
In a Type Ia supernova, a white dwarf (left) draws matter from a companion star until its mass hits a limit, which leads to a supernova explosion. Image Credit: NASA
The research used massive data sets from three sources: the ESA’s Gaia spacecraft, The Pan-STARRS1 survey, and the 2MASS survey. The team used machine learning techniques to comb the dataset for candidate main sequence-white dwarf (MSWD) binaries in 299 open star clusters in the Milky Way. Open clusters were chosen because they can provide an independent age constraint for the system, allowing the researchers to trace the evolution of the binaries from before the CE phase to after the CE phase. The researchers found 52 high-probability candidates in 38 open clusters.
This number is a huge increase in the number of known MSWD binaries. Only two were known previously. Machine learning is a powerful tool that allows astronomers to work with huge data sets to uncover difficult-to-distinguish results, and this study is no exception.
“The use of machine learning helped us to identify clear signatures for these unique systems that we weren’t able to easily identify with just a few datapoints alone,” says co-author Joshua Speagle, a professor in the David A. Dunlap Department for Astronomy & Astrophysics and Department of Statistical Sciences at U of T. “It also allowed us to automate our search across hundreds of clusters, a task that would have been impossible if we were trying to identify these systems manually.”
Study co-author Maria Drout is also a professor in the David A. Dunlap Department for Astronomy & Astrophysics at U of T. Drout says that the team’s results illustrate how many things in our Universe are “hiding in plain sight” if we only had the tools to see them. As our telescope and survey tools become more discerning and gather larger data sets, our machine-learning tools are making these data sets less opaque.
Drout points out that finding the MSWD binaries in open clusters is the key.
Close-up of the Messier 35 open star cluster. Finding MSWD candidates in open clusters allows astrophysicists to constrain the ages of the binaries. Credit: Wikisky
“While there are many examples of this type of binary system, very few have the age constraints necessary to fully map their evolutionary history. While there is plenty of work left to confirm and fully characterize these systems, these results will have implications across multiple areas of astrophysics,” Drout explains.
The evolution of CE systems is poorly understood. Astrophysicists don’t know how energy is dissipated during the CE phase, how stellar metallicity affects the development of the CE, or how initial binary parameters predict post-CE orbital configurations. Those are just a few of their unanswered questions.
This study can’t answer all of those questions, but by producing the largest catalogue of MSWD binaries, the team is setting the stage for researchers to make progress.
Grondin and her co-researchers did follow-up spectroscopy on a subset of three systems with the Gemini and Lick observatories. They confirmed two of them to be MSWD binaries.
This figure from the research shows spectra for three high-probability MSWD candidates. The coloured lines are the spectra, and the black lines are representative models of M-type main sequence stars. The authors chose these three as representative samples from their catalogue. They also say that the top panel, from Alessi12-c1, is a clear MSWD binary, while the bottom two are likely red dwarf white dwarf pairs. Image Credit: Grondin et al. 2024.
They also retrieved archival light curves from TESS, Kepler, and the Zwicky Transient Facility. All three candidates showed clear variability in their light curves. That could indicate rapid M-dwarf rotation or ellipsoidal modulations in a short-period binary. The researchers explain that the catalogue could be contaminated, though not very significantly, by single WDs or MS+MS binaries.
Natal kicks likely influence the results. Many of the MSWD candidates show offsets from their host clusters, suggesting that natal kicks were imparted when the WD formed or during common envelope ejection. Since 78% of the open clusters they observed lacked candidates, the authors think that some MSWD binaries were ejected from their clusters by natal kicks.
“Ultimately, this catalog is a first step to obtaining a set of observational benchmarks to better link post-CE systems to their pre-CE progenitors,” the authors write in their research.
More spectroscopic observations of the candidates will help confirm more of them as MSWD binaries. An expanded search could also help identify MSWD candidates that have been ejected from their clusters by natal kicks.
As is often the case in astronomy and astrophysics, a larger dataset is needed before researchers can reach any conclusions.
“Ultimately, this catalogue is a necessary first step in a larger effort to provide observational constraints on the CE phase,” the authors write, noting that a detailed characterization of some of the candidates in this sample is already underway. The larger sample will allow researchers to link the masses of post-CE binaries with pre-CE progenitors.
“With these observational benchmarks, this sample will aid in efforts to unlock important new insights into one of the most uncertain phases of binary evolution,” the authors conclude.
11 million years ago, Mars was a frigid, dry, dead world, just like it is now. Something slammed into the unfortunate planet, sending debris into space. A piece of that debris made it to Earth, found its way into a drawer at Purdue University, and then was subsequently forgotten about.
Until 1931, when scientists studied and realized it came directly from Mars. What has it told them about the red planet?
11 million years ago, the Himalayas were rising on a warmer, more humid Earth. Early ape species made their home in an Africa covered by tropical forests. Diverse mammal species roamed the continents.
At the same time, on Mars, the frigid wind blew across a desiccated, forlorn world. The planet’s thin atmosphere is a weak barrier to meteorites, and the planet’s cratered surface bears witness to its nakedness. Some impacts were powerful enough to launch debris into space beyond the planet’s gravitational pull. The meteorite in the drawer is one such piece of debris.
“Many meteoroids are produced by impacts on Mars and other planetary bodies, but only a handful will eventually fall to Earth.”
Marissa Tremblay, Purdue University
The meteorite was long forgotten in its storage place until 1931. Scientists identified it as a piece of Mars, and now new research is uncovering clues about Mars’ past hidden in the 800-gram piece of rock.
This image shows a page from an article published in Popular Astronomy in 1935. Image Credit: Popular Astronomy.
11 million years ago is not a long time in geological and planetary terms, and the number fits neatly into most people’s imaginations. But rock has deep temporal roots, and the meteorite that reached Earth is an igneous rock that dates back 1.4 billion years. That much time is more difficult to understand, but science is at its best when it opens human minds to a more fulsome understanding of nature.
The meteorite, named “Lafayette” after the city in Indiana that’s home to Purdue University, is the subject of new research published in Geochemical Perspectives Letters. It’s titled “Dating recent aqueous activity on Mars,” and the lead author is Marissa Tremblay. Tremblay is an assistant professor with the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at Purdue University.
There’s ample evidence that some minerals on Mars formed in the presence of water. Though Lafayette itself is an igneous rock 1.4 billion years old, some of the minerals it contains are younger.
“Dating these minerals can therefore tell us when there was liquid water at or near the surface of Mars in the planet’s geologic past,” Tremblay said. “We dated these minerals in the Martian meteorite Lafayette and found that they formed 742 million years ago. We do not think there was abundant liquid water on the surface of Mars at this time. Instead, we think the water came from the melting of nearby subsurface ice called permafrost, and that the permafrost melting was caused by magmatic activity that still occurs periodically on Mars to the present day.”
Lafayette is one of the Nakhlite meteorites, an igneous rock that formed from basaltic lava around 1.4 billion years ago. Scientists think these rocks formed in one of Mars’ large volcanic regions: Elysium, Syrtis Major Planum, or the largest one, Tharsis, which is home to the three shield volcanoes, Tharsis Montes.
A colourized image of the surface of Mars taken by the Mars Reconnaissance Orbiter. The line of three volcanoes is the Tharsis Montes, with Olympus Mons to the northwest. Valles Marineris is to the east. The researchers think that the Lafayette meteorite came from the Tharsis volcanic region, or one of Mars’ other, smaller volcanic regions. Image: NASA/JPL-Caltech/ Arizona State University
Ancient rocks and their embedded minerals contain information about Mars’ ancient past. The history of Mars’ hydrological cycle is a key objective in our ongoing study of Mars. This research is focused on a particular mineral in Lafayette called iddingsite. It forms when basalt is weathered in the presence of water.
The difficulty with meteorites and the clues they contain about ancient Mars is that they’ve been exposed to and potentially altered by the heat of the initial impact and the heat of entry into Earth’s atmosphere. The chemical signals inherent in rock can become muddied. But Lafayette is different. It’s clear that it was blasted off of Mars 11 million years ago.
“We know this because once it was ejected from Mars, the meteorite experienced bombardment by cosmic ray particles in outer space that caused certain isotopes to be produced in Lafayette,” Tremblay says. “Many meteoroids are produced by impacts on Mars and other planetary bodies, but only a handful will eventually fall to Earth.”
“The age could have been affected by the impact that ejected the Lafayette Meteorite from Mars, the heating Lafayette experienced during the 11 million years it was floating out in space, or the heating Lafayette experienced when it fell to Earth and burned up a little bit in Earth’s atmosphere,” Tremblay said. “But we were able to demonstrate that none of these things affected the age of aqueous alteration in Lafayette.”
Study co-author Ryan Ickert is a senior research scientist in Purdue’s EAPS. Ickert uses heavy radioactive and stable isotopes to study geological processes over time. He showed how isotope data used to date water-rock interactions on Mars were problematic and that the data had likely been polluted by other processes. According to Ickert, he and his colleagues got it right this time.
“This meteorite uniquely has evidence that it has reacted with water. The exact date of this was controversial, and our publication dates when water was present,” he says.
This figure from the research shows a cross-section of the Lafayette meteorite. Ol is an olivine grain surrounded by augite crystals (Px). Iddingsite (Id) is present in veins that travel through the rock. Though Lafayette formed over 1.3 billion years ago, the Iddingsite veins formed later, about 742 million years ago, when water seeped through the cracks. Image Credit: Tremblay et al. 2024.
The researchers used a novel technique involving the isotopes Argon 40 and Argon 39 to date Lafayette’s exposure to water and its formation of Iddingsite. That showed them that the exposure occurred 742 million years ago. Their explanation is that magmatic activity melted subsurface ice, and the water subsequently found its way into cracks in the igneous rock, altering some of the olivine into Iddingsite.
All this from a meteorite that was lost in a drawer.
The Solar System is a puzzle. It’s an artifact of Nature’s ordered complexity, but at the same time, it’s shaped by Nature’s steadfast chaos. Each molecule, each tiny piece of rock, including the Lafayette meteorite, is a part of it. Each piece holds a clue to the puzzle.
“We can identify meteorites by studying what minerals are present in them and the relationships between these minerals inside the meteorite,” said Tremblay. “Meteorites are often denser than Earth rocks, contain metal, and are magnetic. We can also look for things like a fusion crust that forms during entry into Earth’s atmosphere. Finally, we can use the chemistry of meteorites (specifically their oxygen isotope composition) to fingerprint which planetary body they came from or which type of meteorite it belongs to.”
Dating these rocks, these pieces of the puzzle, is difficult. However, this research has made progress by developing a novel way to date minerals in the Lafayette meteorite.
“We have demonstrated a robust way to date alteration minerals in meteorites that can be applied to other meteorites and planetary bodies to understand when liquid water might have been present,” Tremblay concluded.
CubeSats are becoming more and more capable, and it seems like every month, another CubeSat is launched doing something new and novel. So far, technology demonstration has been one of the primary goals of those missions, though the industry is moving into playing an active role in scientific discovery. However, there are still some hurdles to jump before CubeSats have as many scientific tools at their disposal as larger satellites. That is where the Space Industry Responsive Intelligent Thermal (SpIRIT) CubeSat, the first from the Univeristy of Melbourne’s Space Lab, hopes to make an impact. Late in 2023, it launched with a few novel systems to operate new scientific equipment, and its leaders published a paper a few months ago detailing the progress of its mission so far.
SpIRIT represents a first not only for the Melbourne Space Lab but also for Australia as a whole. Their space agency was first set up in 2018 and began funding the SpIRIT project in 2020, as the COVID pandemic started making joint development efforts difficult. To contribute to the nation’s overall learning of how to build and control CubeSat, as much equipment as possible was sourced directly from Australian companies, including an ion drive from Neumann Space and a solar panel platform from Inovor Technologies.
However, the most exciting part of the SpIRIT mission was the instruments explicitly designed for it. There were several interesting ones, including HERMES, an X-ray and gamma-ray detector; TheMIS, a thermal management system used to cool HERMES; LORIS, an edge computing system; and Mercury, for use in low-latency communications.
This video describes the importance of SpIRIT to the Australian space program.
Credit – Australian Space Agency YouTube Channel
Each system is designed to address a specific development problem plaguing CubeSats more generally. They aren’t typically able to capture light in specific wavelengths, such as gamma waves, because the sensors for those wavelengths, which include infrared, require active cooling systems that are too bulky to fit into a CubeSat’s space constraints.
Additionally, the sheer amount of data collected by modern sensors would be overwhelming for the communication links available to standard CubeSats. A single sensor could produce as much as 100Gb of data per day, while a standard downlink channel would allow only 1Gb of data to be sent back to Earth. Combining “edge computing,” where preliminary data processing is done on the CubeSat, with a low-latency communication line is SpIRIT’s solution to that problem. However, TheMIS would also have to deal with the additional heat generated by inefficiencies in the processing unit.
Preliminary results of the project look good, with HERMES beginning complete observations in March and TheMIS successfully managing thermal loads automatically. LORIS has successfully captured some camera images and started performing image recognition algorithms. Mercury has been more of a struggle, with intermittent communication happening throughout the satellite’s lifetime. Since the whole project has primarily been considered a technology demonstration mission, those growing pains are understandable and don’t seem to affect the overall mission operation.
Members of the Spirit Team discuss the development of the project.
Credit – ARES Unimelb YouTube Channel
In addition to technical derisking, many of the lessons the mission operators at the Melbourne Space Lab learned were about managing space projects more generally. Project management and personnel allocation might not be the most interesting topics, but they are necessary for completing a technical project like SpIRIT.
With over 2000 successful CubeSat launches, SpIRIT is another valuable industry contribution. As CubeSats become more widely used as scientific platforms, expect to see more and more efforts like SpIRIT reporting on their progress soon.
Buried in the treasure trove of the Gaia catalog were two strange black hole systems. These were black holes orbiting sun-like stars, a situation that astronomers long thought impossible. Recently a team has proposed a mechanism for creating these kinds of oddballs.
The two black holes, dubbed BH1 and BH2, are each almost ten times the mass of the Sun. That’s not too unusual as black holes go, but what makes these systems strange is that they each have a companion star with roughly the same properties as the Sun. And those stars are orbiting on very wide orbits.
The problem with this setup is that typically sun-like stars don’t survive the transition of a companion turning into a black hole. The end of a giant star’s life is generally violent. When they die, they tend to either eject their smaller companion from the system completely, or just outright swallow them. Either way, we don’t expect small stars to orbit black holes.
But now researchers have a potential solution. They tracked the evolution of extremely massive stars, no smaller than 80 times the mass of the Sun. They found at the end of their lives they eject powerful winds that siphon off enormous amounts of material. This prevents the star from swelling so much that it just swallows its smaller companion. Eventually the star goes supernova and leaves behind a black hole.
Then the researchers studied just how common this kind of scenario is. They found many cases where a sun-like star with a wide enough orbit could survive this transition phase. The key is that the strong winds coming from the larger star have to be powerful enough to limit its late stage violence while still weak enough to not affect the smaller star. The researchers found that this was a surprisingly common scenario and could easily explain the existence of BH2 and BH2.
Based on these results the researchers believe that there might be hundreds of such systems in the Gaia data set that have yet to be discovered. It turns out that the universe is always surprising us and always much more clever than we could ever realize.
SpaceX’s Starship launch system went through its sixth flight test today, and although the Super Heavy booster missed out on being caught back at its launch pad, the mission checked off a key test objective with President-elect Donald Trump in the audience.
Trump attended the launch at SpaceX’s Starbase complex in the company of SpaceX CEO Elon Musk, who has been serving as a close adviser to the once and future president over the past few months. In a pre-launch posting to his Truth Social media platform, Trump wished good luck to “Elon Musk and the Great Patriots involved in this incredible project.”
Starship is the world’s most powerful rocket, with 33 methane-fueled Raptor engines providing more than 16 million pounds of thrust at liftoff. That’s twice the power of the Saturn V rocket that sent Americans to the moon in the 1960s and early ’70s. The two-stage rocket stands 121 meters (397 feet) tall, with a 9-meter-wide (30-foot-wide) fairing.
Super Heavy had an on-time launch at 4 p.m. CT (22:00 UTC) and was set up to fly itself back to the launch tower to be caught by the giant “Mechazilla” arms that were successfully used during last month’s flight test. But four minutes after liftoff, mission controllers said the booster had to be diverted instead to make a soft splashdown in the Gulf of Mexico. SpaceX didn’t immediately report the reason for the diversion.
“It was not guaranteed that we would be able to make a tower catch today,” launch commentator Kate Tice said during today’s webcast. “So, while we were hoping for it … the safety of the teams and the public and the pad itself are paramount. We are accepting no compromises in any of those areas.”
While the booster settled majestically into the Gulf, the Starship second stage — known as Ship for short — continued on a track that sent it as high as 190 kilometers (120 miles). A plush banana was placed in Ship’s cargo bay as a zero-gravity indicator, and Tice wore a T-shirt bearing the words “It’s Bananas!” to play off the lighthearted theme.
Ship successfully relit one of its methane-fueled Merlin engines while in space, which was a key objective for today’s suborbital test. Relighting the engines under such conditions will be required in the future for Ship’s orbital maneuvers.
A little more than an hour after launch, Ship’s engines fired for a final time to make a controlled splashdown in the Indian Ocean. The daylight visuals, plus other data collected during the flight, will help SpaceX’s team fine-tune Starship’s design for future tests.
SpaceX plans to use Starship to accelerate deployment of its Starlink broadband satellites, as well as to fly missions beyond Earth orbit. The company has a $2.9 billion contract from NASA to provide a version of Starship that’s customized for lunar landings, starting as early 2026. And Musk has said Starship could take on uncrewed missions starting that same year — with the first crewed mission set for launch in 2028 if everything goes right.
NASA Administrator Bill Nelson referred to those future flights in a message on Musk’s X social-media platform:
Congrats to @SpaceX on Starship's sixth test flight. Exciting to see the Raptor engine restart in space—major progress towards orbital flight.
Starship’s success is #Artemis’ success. Together, we will return humanity to the Moon & set our sights on Mars. pic.twitter.com/tuwpGOvT9S
Thanks to the Hubble Space Telescope, we all have a vivid image of the Crab Nebula emblazoned in our mind’s eyes. It’s the remnant of a supernova explosion Chinese astronomers recorded in 1056. However, the Crab Nebula is more than just a nebula; it’s also a pulsar.
The Crab Pulsar pulsates in an unusual ‘zebra’ pattern, and an astrophysicist at the University of Kansas thinks he’s figured out why.
When massive stars explode as supernovae, they leave behind remnants: either a stellar-mass black hole or a neutron star. SN 1054 left behind the latter. The neutron star is highly magnetized and spins rapidly, emitting beams of electromagnetic radiation from its poles. As it spins, the radiation is intermittently directed towards Earth, making it visible to us. In this case, it’s called a pulsar.
Pulsars are complex objects. They’re extremely dense and can pack up to three solar masses of material into a sphere as small as 30 km in diameter. Their magnetic fields are millions of times stronger than Earth’s, they can rotate hundreds of times per second, and their immense gravity warps space-time. And their cores are basically huge atomic nuclei.
One result of their complexity is their radio emissions, and this is especially true of the Crab Pulsar.
Pulsars are known for their main pulse (MP), but they also emit other pulses that are more difficult to detect. In 2007, radio astronomers Hankins and Eilek discovered a strange pattern in the Crab Pulsar’s high-frequency radio emissions. This is the only pulsar known to produce these patterns between the pulsar’s main pulse (MP) and its intermittent pulse (IP).
“The mean profile of this star is dominated by a main pulse (MP) and an interpulse (IP),” Eilek and Hankins wrote in their paper. However, there are two additional pulses called HFC1 and HFC2 that create the zebra pattern.
This figure shows the mean profile of the Crab pulsar over a wide range of frequencies. The MP and IP are shown by dashed lines at pulse phases 70° and 215°. However, between 4.7 and 8.4 GHz, the IP is offset from the IP at lower and higher frequencies. This constitutes the Crab Pulsar’s ‘zebra’ pattern. Two new high-frequency components also appear (labelled HFC1 and HFC2). Image Credit: Moffett & Hankins 1996.
Nobody has succeeded in explaining this unusual pattern. However, new research published in Physical Review Letters may finally explain it. The author is Mikhail Medvedev, who specializes in Theoretical Astrophysics at the University of Kansas. His research is “Origin of Spectral Bands in the Crab Pulsar Radio Emission.”
Medvedev says that the Crab Pulsar’s plasma-filled magnetosphere acts as a diffraction screen to produce the zebra pattern. This can explain the band spacing, the high polarization, the constant position angle, and other characteristics of the emissions.
This figure shows the overall geometry of the crab pulsar system. The red star is the pulsar. Its emissions pass through the plasma-filled magnetosphere, which acts as a diffraction screen, producing the zebra pattern of pulses. Image Credit: Medvedev 2024.
A typical pulsar emits radio emissions from its poles, as shown in the figure below. They sometimes emit two signals per rotation period, one radio and one high frequency. They appear in a different phase of the rotation, with the higher frequency emission produced outside the light cylinder, the region where linear speed approaches the speed of light.
This figure shows how a standard pulsar emits radio emissions. Electrons and positrons are accelerated through one of the gaps in the magnetosphere. They stream along the open magnetic field lines and emit coherent radio emissions from the poles. Image Credit: National Radio Astronomy Observatory.
But the Crab Pulsar is different.
“The Crab pulsar is, in contrast, very special. Its radio main pulse and interpulse are coincident in phase with high-energy emission, indicating the same emission region,” Medvedev explains.
Medvedev explains that the High-Frequency Interpulse (HFIP) produced by the diffraction effect creates the zebra pattern. “The spectral pattern of the high-frequency interpulse (HFIP), observed between about
?~5 and ?~30 GHz is remarkably different and represents a sequence of emission bands resembling the
“zebra” pattern,” he writes.
This simple schematic helps explain the diffraction effect. The different colours represent different densities in the plasma field. Regions of the magnetosphere with different densities either co-rotate with the pulsar or not, helping create the zebra pattern in the emissions. Image Credit: Medvedev 2024.
Medvedev’s proposed model has an additional benefit. He says it can be used to perform tomography on pulsars to uncover more details about their powerful magnetospheres.
“The model allows one to perform “tomography” of the pulsar magnetosphere,” he writes.
“We predict that this HFIP properties can also be observed in other pulsars if their radio and high energy emission are in phase. This would happen if the radio emission is produced in the outer magnetosphere as opposed to the “normal” emission from the polar region,” Medvedev explains.
This composite image of the Crab Nebula features X-rays from Chandra (blue and white), optical data from Hubble (purple), and infrared data from Spitzer (pink). Chandra has repeatedly observed the Crab since the telescope was launched into space in 1999. Image Credit: X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA-JPL-Caltech
Medvedev says his model can also explain the HFC1 and HFC2 in the Crab Pulsar’s emissions spectrum. They’re also artifacts of his proposed diffraction model. “We propose that these high-frequency components are the reflections off the magnetosphere of the same source producing the diffracted HFIP,” he explains.
“To conclude, we propose a model, which explains the peculiar spectral band structure (the zebra pattern) of the high-frequency interpulse of the Crab pulsar radio emission,” Medvedev writes.
The existence of gigantic black holes in the very early universe challenges our assumptions of how black holes form and grow. New research suggests that these monsters may have found their origins in the earliest epochs of the Big Bang.
For years astronomers have been troubled by observations of fully grown supermassive black holes before the universe was even a billion years old. This is challenging because as far as we know the only way to make black holes is through the deaths of massive stars. And the only way for them to grow is either through mergers or the accumulation of material. Following these known mechanisms it’s extremely difficult to build the observed black holes, which have masses hundreds of millions of times that of the Sun, so quickly.
And so astronomers have been long attempting to find some other way to explain how these giant black holes arrive on the cosmic scene. In a new paper, a team of researchers point to an seemingly unlikely scenario: the first microseconds of the Big Bang.
In the 1970s Stephen Hawking hypothesized that the tumultuous epochs of the incredibly early universe would cause random fluctuations of matter to spontaneously collapse to form black holes. These primordial black holes might even persist to the present day, and astronomers have even gone so far as to propose that these black holes explain dark matter.
But observations have placed considerable constraints on the populations of primordial black holes. They simply can’t be a major constituent of the universe, otherwise we would have seen evidence for them by now.
But in the new paper the researchers point out that they don’t need to be common to form the seeds of supermassive black holes. They can be incredibly rare, making up less than 1% of all the mass in the universe. But if they are formed in the early universe, then slowly over time they can accrete new material and merge with each other, especially in the first few hundred million years as galaxies are first forming.
This scenario would mean that giant black holes would form not after the appearance of the first stars, but in parallel with them. Then by the time stars and galaxies appear the black holes are already fully grown.
The researchers were able to find a scenario that could explain the observed population of giant black holes in the young universe. However, this is only the first step in the research. The next is to fine-tune these models and incorporate them in more detailed simulations of the evolution of the early universe to see just how plausible this scenario is.
The 2024 China International Aviation and Aerospace Exhibition was held in Zhuhai last week – from November 12th to 17th, 2024. Since 1996, and with support from the Chinese aerospace industry, this biennial festival features actual products, trade talks, technological exchanges, and an air show. This year’s big highlight was China’s newly announced reusable space cargo shuttle, the Haolong (Chinese for “dragon”). According to chief designer Fang Yuanpeng, the spacecraft has entered the engineering phase and will be ready for space in the near future.
The Haolong shuttle is being developed by the Chengdu Aircraft Design and Research Institute, which has developed several Chinese fighter jets in the past. It has a large wingspan, measuring eight meters (26.25 ft) in width and about 10 meters (33 ft) long, with a high lift-to-drag ratio. From the image provided (above), the design is clearly inspired by the now-retired Space Shuttle and features the same type of payload bay with two bay doors. While the cargo shuttle has a comparable wingspan (8.7 m; 29 ft), it is significantly shorter than the Space Shuttle, which measured 56.1 m (184 ft) in length.
This makes the Haolong (in terms of size) more akin to the X-37B and China’s Shenlong spaceplane. Like these spaceplanes, the Haolong spacecraft will be autonomous and feature cutting-edge aviation technologies. The design was one of several concepts issued in response to a solicitation by the China Manned Space Agency (CMSA) for low-cost and commercial cargo spacecraft. These will provide logistical support for China’s Tiangong space station as it undergoes expansion in the coming years.
Artist’s impression of China’s reusable Shenlong spaceplane. Credit: China Aerospace Studies Institute
According to the state-owned news agency Xinhua, the winners of the solicitation were announced on October 29th. This included the CMSA’s Haolong shuttle and the Qingzhou spacecraft, an integrated cargo capsule submitted by the Innovation Academy for Microsatellites of the Chinese Academy of Sciences (IAMCAS). According to Lin Xiqiang, the deputy director of the CMSA, both companies won contracts for the flight verification phase of their proposals. According to Fang, the space shuttle Haolong will launch into orbit via a commercial carrier rocket, make atmospheric reentry, and land horizontally on a runway.
Once it reaches orbit, it will unfold its solar panels and open its docking shield. The shuttle’s rear will dock with Tiangong, where taikonauts can access the cargo bay and transfer the payload to the space station. According to Fang, “the Hoalong can receive maintenance similar to an aircraft after landing, so it can conduct another mission.” The spacecraft has already completed the design phase and is moving into engineering development. Fang indicated that this phase is well underway and will be followed by the cargo mission phase. “I believe that the public will see it soon,” he said.
Meanwhile, the Qingzhou cargo spacecraft has a cargo volume of up to 27 cubic meters, which is expected to provide logistics flexibility and significantly reduce transportation costs. According to Xinhua, Qingzhou also has an intelligent transportation system capable of supporting crewed and uncrewed in-orbit experiments. The cargo spacecraft is scheduled to be launched by the Lijian-2, a reusable rocket currently under development by CAS Space. This rocket is one of several reusable medium-lift launch vehicles China plans to debut in the coming years.
Lin also noted that “this strategic move will not only slash cargo transportation costs for the space station but also pave the way for new opportunities in the growth of the country’s commercial space industry.” According to market research, China’s commercial space industry is expected to reach a market value of 2.34 trillion yuan ($323.35 billion) by the end of 2024.
In recent years, astronomers have developed techniques to measure the metal content of stars with extreme accuracy. With that capability, astronomers have examined sibling stars to see how their metallicity differs. Some of these co-natal stars have pronounced differences in their metallicity.
New research shows that stars engulfing rocky planets are responsible.
Co-natal stars are born in the same giant molecular cloud (GMC), though they’re not necessarily in binary relationships with each other. These stars are expected to have very similar metallicities, even though no GMC is totally homogenous and small differences are common in the stars that form together. But when the differences are pronounced, there must be some other explanation.
New research titled “Metal pollution in Sun-like stars from destruction of ultra-short-period planets” suggests that rocky planets are the source of these discrepancies. The authors are Christopher E. O’Connor and Dong Lai from Northwestern University and Cornell University, respectively. The research is on the pre-print server arxiv.org and has been submitted to the AAS journals.
“Detailed studies of chemical composition among co-natal stellar pairs—stars with a common origin—reveal unexpectedly large differential abundances among refractory elements,” the authors write. The authors refer to this as pollution after a similar thing that happens in white dwarfs. The source of this pollution is rocky planets, which are rich in metals.
Ultra-short-period (USP) exoplanets orbit their stars very closely and typically complete an orbit in only a few hours. They have similar compositions to Earth and are seldom more than two Earth radii. Their origins are not clear. They could have formed further out and then migrated closer to their star, or they could be the remains of much larger planets that lost their atmosphere due to stellar irradiation.
This artist’s rendering shows a star stripping away a planet’s atmosphere. Image Credits: NASA/GSFC
USP planets are not very common. Only about 0.5% of Sun-like stars have them. They’re very hot, so their surfaces are melted, and they’re tidally locked to their stars.
Though uncommon, they may form in greater numbers and then be consumed by their stars.
“Short-period exoplanets are potentially vulnerable to tidal disruption and engulfment by their host stars,” the authors write. Research shows that between 3 to 30% of co-natal, main-sequence, Sun-like (FGK) stars have engulfed rocky planets between 1 to 10 Earth masses.
There are many ways this can happen. “Many forms of violent dynamical evolution are possible in planetary systems, each potentially able to inject a planet into the star,” O’Connor and Lai write. However, evidence shows that, at most, about 2% of single FGK stars are polluted by all violent mechanisms combined.
Astronomers have proposed three main scenarios where stars can engulf USP planets.
One is called high-eccentricity (high-e) migration. In this scenario, a proto-USP becomes very close to its star and has a high eccentricity. Because of its proximity to the star and its gravitational draw, the planet rapidly loses its eccentricity and adopts a circular orbit.
Another is low-eccentricity (low-e) migration. In this scenario, the USP migrates towards its star more slowly. Low-e migration occurs in compact systems with three or more planets, which helps moderate its eccentricity.
The well-known TRAPPIST-1 system is an example of a compact, multi-planet system. Image Credit: By NASA/JPL-Caltech – Catalo, Public Domain
The third scenario is obliquity-driven migration. In this scenario, a companion planet to the USP excites the USP’s obliquity and captures it in a secular spin-orbit resonance. The USP rapidly migrates towards its star, but the migration ends when the USP escapes the resonance.
The authors developed a model to predict the number of USPs that form and the time it takes for them to become engulfed. Their model can reproduce both the low observed occurrence of USPs around Sun-like stars and their polluted metallicity. Their results favour the low-e migration scenario where USPs are part of compact, multi-planet systems.
“We find that USP engulfment is a natural consequence of the low-e migration scenario. A connection between USPs and engulfed rocky planets in Sun-like stars, therefore, seems plausible,” they write.
Their results show that USPs become engulfed between 0.1 and 1 gigayear after they form. If this engulfment is the main source of pollution in Sun-like stars, the authors say there’s a correlation between pollution and compact, multi-planet systems. “Some 5–10% of polluted stars should have a transiting planet of mass ? 5M? and period ~ 4–12 days,” they explain. They also predict the reverse: there should be an anti-correlation between USP occurrence and pollution.
The authors point out some caveats regarding their results.
The signatures of metallicity pollution can fade over time. The metals can settle into the star, making the signal disappear. Depending on how effective that is, it could mean our understanding of how many stars are polluted is inaccurate. It could mean more than 30% of Sun-like stars are polluted.
When a star eats a planet, it changes the star’s metallicity, which astronomers call pollution. But the signal from the pollution can fade as the metals sink into the star. Image Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Garlick/M. Zamani
The second caveat is that more violent mechanisms could inject planets into their stars. Planet-planet scattering could drive planets into engulfment, especially rocky Super-Earths. However, the authors explain that “We find only ~ 1% of stars can be polluted through the violent destruction of super-Earths, despite their ubiquity as exoplanets.”
Their final caveat concerns Hot Jupiters (HJs). These gas-giant planets orbit very closely to their stars. Astronomers believe that HJs are destroyed by engulfment during their stars’ main sequence lifetime. HJs also have a similar occurrence rate as USPs around Sun-like stars. It’s a fair question to ask if they contribute to the observed metallicity pollution.
This illustration shows a Jupiter-mass exoplanet getting perilously close to its star. If they become engulfed, they may produce a different signature on the star than a rocky planet does. Image Credit: C. Carreau / ESA.
The authors say it’s possible that high-eccentricity migration can drive HJs into stellar engulfment. However, they also point out that there’s good reason to doubt that. “Again, an engulfed HJ may not produce a similar chemical signature to a rocky planet: the masses and bulk metallicities of HJs vary
widely,” they write. All of the hydrogen and helium in HJs could also dilute the extra metals. Additionally, tidal disruption of HJs may not lead directly to engulfment. It’s possible that mass transfer could reduce the HJ down to a super-Earth remnant made of the original core and a residual atmosphere.
According to O’Connor and Lai, more study is needed before we can understand how HJs might contribute to stellar pollution.
Their results also show that a main sequence star can only form one USP during its main sequence, so only one can be engulfed. In a compact system, only the innermost planet can suffer enough tidal decay to become a USP.
In their conclusion, the authors write that stars hosting USPs should have ages and kinematics similar to Milky Way field stars and should rarely show signs of previous planet engulfment. They also conclude that polluted FGK stars should host compact multi-planet systems.
Back in 2007, I talked with Rob Manning, engineer extraordinaire at the Jet Propulsion Laboratory, and he told me something shocking. Even though he had successfully led the entry, descent, and landing (EDL) teams for three Mars rover missions, he said the prospect of landing a human mission on the Red Planet might be impossible.
But now, after nearly 20 years of work and research — as well as more successful Mars rover landings — Manning says the outlook has vastly improved.
“We’ve made huge progress since 2007,” Manning told me when we chatted a few weeks ago in 2024. “It’s interesting how its evolved, but the fundamental challenges we had in 2007 haven’t gone away, they’ve just morphed.”
Image of the Martian atmosphere and surface obtained by the Viking 1 orbiter in June 1976. (Credit: NASA/Viking 1)
The problems arise from the combination of Mars’ ultra-thin atmosphere—which is over 100 times thinner than Earth’s — and the ultra-large size of spacecraft needed for human missions, likely between 20 – 100 metric tons.
“Many people immediately conclude that landing humans on Mars should be easy,” Manning said back in 2007, “since we’ve landed successfully on the Moon and we routinely land human-carrying vehicles from space to Earth. And since Mars falls between the Earth and the Moon in size and in the amount of atmosphere, then the middle ground of Mars should be easy.”
But Mars’ atmosphere provides challenges not found on Earth or the Moon. A large, heavy spacecraft streaking through Mars’ thin, volatile atmosphere only has just a few minutes to slow from incoming interplanetary speeds (for example, the Perseverance rover was traveling 12,100 mph [19,500 kph] when it reached Mars) to under Mach 1, and then quickly transition to a lander to slow to be able to touch down gently.
Universe Today publisher Fraser Cain’s video about the challenges of landing Mars, with more details in this article.
In 2007, the prevailing notion among EDL engineers was that there’s too little atmosphere to land like we do on Earth, but there is actually too much atmosphere on Mars to land heavy vehicles like we do on the Moon by using propulsive technology alone.
“We call it the Supersonic Transition Problem,” said Manning, again in 2007. “Unique to Mars, there is a velocity-altitude gap below Mach 5. The gap is between the delivery capability of large entry systems at Mars and the capability of super-and sub-sonic decelerator technologies to get below the speed of sound.”
The largest payload to land on Mars so far is the Perseverance rover, which has a mass of about 1 metric ton. Successfully landing Perseverance and its predecessor Curiosity required a complicated, Rube Goldberg-like series of maneuvers and devices such as the Sky Crane. Larger, human-rated vehicles will be coming in even faster and heavier, making them incredibly difficult to slow down.
Rob Manning, Chief Engineer for NASA’s Jet Propulsion Laboratory, and the Sky Crane for landing rovers on Mars. Credit: NASA/JPL-Caltech/Keck Institute
“So, how do you slow down to subsonic speeds,” Manning said now in 2024 as the chief engineer at JPL, “to get to speeds where traditionally we know how to fire our engines to enable touchdown? We thought bigger parachutes or supersonic decelerators like LOFTID (Low-Earth Orbit Flight Test of an Inflatable Decelerator) tested by NASA) would allow us to maybe slow down better, but there were still issues with both those devices.”
“But there was one trick we didn’t know anything about it,” Manning continued. “How about using your propulsion system and firing the engines backwards —retro propulsion — while you are flying at supersonic speeds to shed velocity? Back in 2007, we didn’t know the answer to that. We didn’t even think it was possible.”
Why not? What could go wrong?
“When you fire engines backwards as you are moving through an atmosphere, there’s a shock front that forms and it would be moving around,” Manning explained, “so it could come along and whack the vehicle and cause it to go unstable or cause damage. You’re also flying right into the plume of the rocket engine exhaust, so there could be extra friction and heating possibilities on the vehicle.”
All of this is very hard to model and there was virtually no experience doing it, as in 2007, no one had ever used propulsive technology alone to slow and then land a spacecraft back on Earth. This is mostly because our planet’s beautiful, luxuriously thick atmosphere slows a spacecraft down easily, especially with a parachute or creative flying as the space shuttle did.
“People did study it a bit, and we came to the conclusion it would be great to try it and find out whether we could fire engines backwards and see what happens,” Manning mused, adding that there wasn’t any extra funding laying around to launch a rocket just to watch it come down again to see what happened.
A SpaceX Falcon-9 rocket poised to launch Dragon from Cape Canaveral. Credit: NASA
But then, SpaceX started doing tests in attempt to land their Falcon 9’s first stage booster back on Earth to re-use them.
“SpaceX said they were going to try it,” Manning said, “And to do that they needed to slow the booster down in the supersonic phase while in Earth’s upper atmosphere. So, there’s a portion of the flight where they fire their engines backwards at supersonic speeds through a rarified atmosphere which is very much what’s like at Mars.”
As you can imagine, this was incredibly intriguing to EDL engineers thinking about future Mars missions.
After a few years of trial, error, and failures, on September 29, 2013, SpaceX performed the first supersonic retropropulsion (SRP) maneuver to decelerate the reentry of the first stage of their Falcon 9 rocket. While it ultimately hit the ocean and was destroyed, the SRP actually worked to slow down the booster.
NASA asked if their EDL engineers could watch and study SpaceX’s data, and SpaceX readily agreed. Beginning in 2014, NASA and SpaceX formed a three-year public-private partnership centered on SRP data analysis called the NASA Propulsive Descent Technology (PDT) project. The F9 boosters were outfitted with special instruments to collect data specifically on portions of the entry burn which fell within the range of Mach numbers and dynamic pressures expected at Mars. Additionally, there were visual and infrared imagery campaigns, flight reconstruction, and fluid dynamics analysis – all of which helped both NASA and SpaceX.
To everyone’s surprise and delight, it worked. On December 21, 2015, an F9 first stage returned and successfully landed on Landing Zone 1 at Cape Canaveral, the first-ever orbital class rocket landing. This was a game changing demonstration of SRP, which advanced the knowledge and tested the technology of using SRP on Mars.
View of SpaceX Falcon 9 first stage approaching Landing Zone 1 on Dec. 21, 2015. Credit: SpaceX
“Based on the analyses completed, the remaining SRP challenge is characterized as one of prudent flight systems engineering dependent on maturation of specific Mars flight systems, not technology advancement,” wrote an EDL team, detailing the results of the PDT project in a paper. In short, SpaceX’s success meant it wouldn’t require any fancy new technology or breaking the laws of physics to land large payloads on Mars.
“It turns out, we learned some new physics,” Manning said. They found that the shock front ‘bubble’ created around the vehicle by firing the engines somehow insulates the spacecraft from any buffeting, as well as from some of the heating.
EDL engineers now believe that SRP is the only Mars entry, descent and landing technology that is intrinsically scalable across a wide range and size of missions to shed enough velocity during atmospheric flight to enable safe landings. Alongside aerobraking, this is one of the leading means of landing heavy equipment, habitats and even humans on Mars.
But still, numerous issues remain unsolved when it comes to landing a human mission on Mars. Manning mentioned there are multiple unknowns, including how a big ship such as SpaceX’s Starship would be steered and flown through Mars’ atmosphere; can fins be used hypersonically or will the plasma thermal environment melt them? The amount of debris kicked up by large engines on human-sized ship could be fatal, especially for the engines you’d like to reuse for returning to orbit or to Earth, so how do you protect the engines and the ship? Mars can be quite windy, so what happens if you encounter wind shears or a dust storm during landing? What kind of landing legs will work for a large ship on Mars’ rocky surface? Then there are logistics problems such as how will all the infrastructure get established? How will ships be refueled to return home?
“This is all going to take a lot of time, more time than people realize,” Manning said. “One of the downsides of going to Mars is that it is hard to do trial and error unless you are very patient. The next time you can try again is 26 months later because of the timing of the launch windows between our two planets. Holy buckets, what a pain that is going to be! But I think we’re going to learn a lot whenever we can try it for the first time.”
And at least the supersonic retropropulsion question has been answered.
“We’re basically doing what Buck Rogers told us to do back in the 1930s: fire your engines backwards while you’re going really fast.”
