Through the Artemis Program, NASA will send the first astronauts to the Moon since the Apollo Era before 2030. They will be joined by multiple space agencies, like the ESA and China, who plan to send astronauts (and “taikonauts”) there for the first time. Beyond this, all plan to build permanent habitats in the South Pole-Aitken Basin and the necessary infrastructure that will lead to a permanent human presence. This presents many challenges, the most notable being those arising from the nature of the lunar environment.
Aside from the extremes in temperature, a 14-day diurnal cycle, and the airless environment, there’s the issue of lunar regolith (aka moondust). In addition to being coarse and jagged, lunar regolith sticks to everything because it is electrostatically charged. Because of how this dust plays havoc with astronaut health, equipment, and machinery, NASA is developing technologies to mitigate dust buildup. Seven of these experiments will be tested during a flight test using a Blue Origin New Shepard rocket to evaluate their ability to mitigate lunar dust.
Another major problem with lunar regolith is how it gets kicked up and distributed by spacecraft plumes. With essentially no atmosphere and lower gravity (16.5% of Earth’s), this dust can remain aloft for extended periods of time. Its jagged nature, resulting from billions of years of meteor and micrometeoroid impacts and a total lack of weathering, is abrasive to any surface it comes into contact with, ranging from spacesuits and equipment to human skin, eyes, and lungs. It will also build up on solar panels, preventing missions from drawing enough power to survive a lunar night.
In addition, it can also cause equipment to overheat as it coats thermal radiators and accumulates on windows, camera lenses, and visors, making it harder to see, navigate, and acquire accurate images. Kristen John, the Lunar Surface Innovation Initiative technical integration lead at NASA’s Johnson Space Center, said in a NASA press release: “The fine grain nature of dust contains particles that are smaller than the human eye can see, which can make a contaminated surface appear to look clean.”
These technologies were developed by NASA’s Game Changing Development program within the agency’s Space Technology Mission Directorate (STMD). The “Lunar Gravity Simulation via Suborbital Rocket” flight test will study regolith mechanics and lunar dust transport in a simulated lunar gravity environment. The payload includes projects for mitigating and cleaning dust using multiple strategies. They include:
ClothBot:
This compact robot is designed to simulate and measure how dust behaves in a pressurized environment, which astronauts could bring back after conducting Extravehicular Activities (EVAs). The robot relies on pre-programmed motions that simulate astronauts’ movements when removing their spacesuits (aka “doffing”), releasing a small dose of lunar regolith simulant. A laser-illuminated imaging system will then capture the dust flow in real-time while sensors record the size and number of particles.
Electrostatic Dust Lofting (EDL):
The EDL will examine how lunar dust is “lofted” (kicked up) when it becomes electrostatically charged to improve models on dust lofting. During the lunar gravity phase of the flight, a dust sample will be released that the EDL will illuminate using a UV light source, causing the particles to become charged. The dust will then pass through a sheet laser as it rises from the surface while the EDL observes and records the results. The EDL’s camera will continue to record the dust until the mission ends, even after the lunar gravity phase ends and the UV light is shut off.
Hermes Lunar-G:
The Hermes Lunar-G project, developed by NASA, Texas A&M, and Texas Space Technology Applications and Research (T-STAR), is based on a facility (Hermes) that previously operated on the International Space Station (ISS). Like its predecessor, the Lunar-G project will rely on repurposed Hermes hardware to study lunar regolith simulants. This will be done using four canisters containing compressed lunar dust simulants. When the flight enters its lunar gravity phase, these simulants will decompress and float around in the canisters while high-speed cameras and sensors capture data. The results will be compared to microgravity data from the ISS and similar flight experiments.
The data obtained by these projects will provide information on regolith generation rates, transport, and mechanics that will help scientists refine computational models. This will allow mission planners and designers to develop better strategies for dust mitigation for future missions to the Moon and Mars. Already, this challenge informs several aspects of NASA’s technological developments, ranging from In-Situ Resource Utilization (ISRU) and construction to transportation and surface power. Said John:
“Learning some of the fundamental properties of how lunar dust behaves and how lunar dust impacts systems has implications far beyond dust mitigation and environments. Advancing our understanding of the behavior of lunar dust and advancing our dust mitigation technologies benefits most capabilities planned for use on the lunar surface.”
The test flight and vehicle enhancements that will enable the simulation of lunar gravity are being funded through NASA’s Flight Opportunities program.
Further Reading: NASA
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New research suggests that our best hopes for finding existing life on Mars isn’t on the surface, but buried deep within the crust.
Several years ago NASA’s Curiosity rover measured traces of methane in the Martian atmosphere at levels several times the background. But a few months later, the methane disappeared, only for it to reappear again later in the year. This discovery opened up the intriguing possibility of life still clinging to existence on Mars, as that could explain the seasonal variability in the presence of methane.
But while Mars was once home to liquid water oceans and an abundant atmosphere, it’s now a desolate wasteland. What kind of life could possibly call the red planet home? Most life on Earth wouldn’t survive long in those conditions, but there is a subgroup of Earthly life that might possibly find Mars a good place to live.
These are the methanogens, a type of single-celled organism that consume hydrogen for energy and excrete methane as a waste product. Methanogens can be found in all sorts of otherwise-inhospitable places on Earth, and something like them might be responsible for the seasonal variations in methane levels on Mars.
In a recent paper submitted for publication in the journal AstroBiology, a team of scientists scoured the Earth for potential analogs to Martian environments, searching for methanogens thriving in conditions similar to what might be found on Mars.
The researchers found three potential Mars-like conditions on Earth where methanogens make a home. The first is deep in the crust, sometimes to a depth of several kilometers, where tiny cracks in rocks allow for liquid water to seep in. The second is lakes buried under the Antarctic polar ice cap, which maintain their liquid state thanks to the immense pressures of the ice above them. And the last is super-saline, oxygen-deprived basins in the deep ocean.
All three of these environments have analogs on Mars. Like the Earth, Mars likely retains some liquid water buried in its crust. And its polar caps might have liquid water lakes buried underneath them. Lastly, there has been tantalizing – and heavily disputed – evidence of briny water appearing on crater walls.
In the new paper, the researchers mapped out the temperature ranges, salinity levels, and pH values across sites scattered around the Earth. They then measured the abundance of molecular hydrogen in those sites, and determined where methanogens were thriving the most.
For the last step, the researchers combed through the available data about Mars itself, finding where conditions best matched the most favorable sites on Earth. They found that the most likely location for possible life was in Acidalia Planitia, a vast plain in the northern hemisphere.
Or rather, underneath it. Several kilometers below the plain, the temperatures are warm enough to support liquid water. That water might have just the right pH and salinity levels, along with enough dissolved molecular hydrogen, to support a population of methanogen-like creatures.
Now we just have to figure out how to get there.
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Entanglement is perhaps one of the most confusing aspects of quantum mechanics. On its surface, entanglement allows particles to communicate over vast distances instantly, apparently violating the speed of light. But while entangled particles are connected, they don’t necessarily share information between them.
In quantum mechanics, a particle isn’t really a particle. Instead of being a hard, solid, precise point, a particle is really a cloud of fuzzy probabilities, with those probabilities describing where we might find the particle when we go to actually look for it. But until we actually perform a measurement, we can’t exactly know everything we’d like to know about the particle.
These fuzzy probabilities are known as quantum states. In certain circumstances, we can connect two particles in a quantum way, so that a single mathematical equation describes both sets of probabilities simultaneously. When this happens, we say that the particles are entangled.
When particles share a quantum state, then measuring the properties of one can grant us automatic knowledge of the state of the other. For example, let’s look at the case of quantum spin, a property of subatomic particles. For particles like electrons, the spin can be in one of two states, either up or down. Once we entangle two electrons, their spins are correlated. We can prepare the entanglement in a certain way so that the spins are always opposite of each other.
If we measure the first particle, we might randomly find the spin pointing up. What does this tell us about the second particle? Since we carefully arranged our entangled quantum state, we now know with 100% absolute certainty that the second particle must be pointing down. Its quantum state was entangled with the first particle, and as soon as one revelation is made, both revelations are made.
But what if the second particle was on the other side of the room? Or across the galaxy? According to quantum theory, as soon as one “choice” is made, the partner particle instantly “knows” what spin to be. It appears that communication can be achieved faster than light.
The resolution to this apparent paradox comes from scrutinizing what is happening when – and more importantly, who knows what when.
Let’s say I’m the one making the measurement of particle A, while you are the one responsible for particle B. Once I make my measurement, I know for sure what spin your particle should have. But you don’t! You only get to know once you make your own measurement, or after I tell you. But in either case nothing is transmitted faster than light. Either you make your own local measurement, or you wait for my signal.
While the two particles are connected, nobody gets to know anything in advance. I know what your particle is doing, but I only get to inform you at speed slower than light – or you just figure it out for yourself.
So while the process of entanglement happens instantaneously, the revelation of it does not. We have to use good old-fashioned no-faster-than-light communication methods to piece together the correlations that quantum entanglement demand.
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Neutrinos are tricky little blighters that are hard to observe. The IceCube Neutrino Observatory in Antarctica was built to detect neutrinos from space. It is one of the most sensitive instruments built with the hope it might help uncover evidence for dark matter. Any dark matter trapped inside Earth, would release neutrinos that IceCube could detect. To date, and with 10 years of searching, it seems no excess neutrinos coming from Earth have been found!
Neutrinos are subatomic particles which are light and carry no electrical charge. Certain events, such as supernovae and solar events generate vast quantities of neutrinos. By now, the universe will be teeming with neutrinos with trillions of them passing through every person every second. The challenge though is that neutrinos rarely interact with matter so observing and detecting them is difficult. Like other sub-atomic particles, there are different types of neutrino; electron neutrinos, muon neutrinos and tau neutrinos, with each associated with a corresponding lepton (an elementary particle with half integer spin.) Studying neutrinos of all types is key to helping understand fundamental physical processes across the cosmos.
The IceCube Neutrino Observatory began capturing data in 2005 but it wasn’t until 2011 that it began full operations. It consists of over 5,000 football-sized detectors arranged within a cubic kilometre of ice deep underground. Arranged in this fashion, the detectors are designed to capture the faint flashes of Cherenkov radiation released when neutrinos interact with the ice. The location near the South Pole was chosen because the ice acts as a natural barrier against background radiation from Earth.
Using data from the IceCube Observatory, a team of researchers led by R. Abbasi from the Loyola University Chicago have been probing the nature of dark matter. This strange and invisible component of the universe is thought to make up 27% of the mass-energy content of the universe. Unfortunately, dark matter doesn’t emit, absorb or reflect light making it undetectable by conventional means. One train of thought is that dark matter is made up of Weakly Interacting Massive Particles (WIMPs.) They can be captured by objects like the Sun leading to their annihilation and transition into neutrinos. It’s these, that the team have been hunting for.
The paper published by the team articulates their search for muon neutrinos from the centre of the Earth within the 10 years of data captured by IceCube. The team searched chiefly for WIMPs within the mass range of 10GeV to 10TeV but due to the complexity and position of the source (the centre of the Earth,) the team relied upon running Monte Carlo simulations. The name is taken from casino’s in Monaco and involves running many random simulations. This technique is used where exact calculations are unable to compute the answer and so the simulations are based on the concept that randomness can be used to solve problems.
After running many simulations of this sort, the team found no excess neutrino flux over the background levels from Earth. They conclude however that whilst no evidence has been found yet, that an upgrade to the IceCube Observatory may yield more promising results as they can probe lower neutrino mass events and hopefully one day, solve the mystery of the nature of dark matter.
Source : Search for dark matter from the centre of the Earth with ten years of IceCube data
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A team of astronomers have detected a surprisingly fast and bright burst of energy from a galaxy 500 million light years away. The burst of radiation peaked in brightness just after 4 day and then faded quickly. The team identified the burst, which was using the Catalina Real-Time Transient Survey with supporting observations from the Gran Telescopio Canarias, as the result of a small black hole consuming a star. The discovery provides an exciting insight into stellar evolution and a rare cosmic phenomenon.
Black holes are stellar corpses where the gravity is so intense that nothing, not even light can escape. They form when massive stars collapse under their own gravity at the end of their life forming an infinitely small point known as a singularity. The region of space around the singularity is bounded by the event horizon, the point beyond which, nothing can escape. Despite the challenges of observing them, they can be detected by observing the effects of their gravity on nearby objects like gas clouds. There are still many mysteries surrounding black holes so they remain an intense area of study.
A team of astronomers led by Claudia Gutiérrez from the Institute of Space Sciences and the Institute of Space Studies of Catalina used data from the Catalina Real-Time Transient Survey (CRTS) to explore transient events. The CRTS was launched in 2004 and is a wide field survey that looks for variable objects like supernova and asteroids. It uses a network of telescopes based in Arizona to scan large areas of sky to detect short-lived events. It has been of great use providing insights into the life cycle of stars and the behaviour of distant galaxies.
The team detected the bright outburst in a galaxy located 500 million light years away and published their results in the Astrophysical Journal. The event took place in a tiny galaxy about 400 times less massive than the Milky Way. The burst was identified as CSS161010, it reached maximum brightness in only 4 days and 2.5 days later had it’s brightness reduced by half. Subsequent work revealed that previous detection had been picked up by the All-Sky Automated Survey for SuperNovae. Thankfully the detection was early enough to allow follow up observations by other ground based telescopes. Typically these types of events are difficult to study due to their rapid evolution.
Only a handful of events like CSS161010 have been detected in recent years but until now their nature was a mystery. The team led by Gutiérrez have analysed the spectral properties and found hydrogen lines revealing material travelling at speeds up to 10% of the speed of light. The changes observed in the hydrogen emission lines is similar to that seen in active galactic nuclei where supermassive black holes exist. The observation suggests it relates to a black hole, although not a massive one.
The brightness of the object reduced 900 times over the following two months. Further spectral analysis at this time still revealed blue shifted hydrogen lines indicating high speed gas outflows. This was not something usually seen from supernova events suggesting a different origin. The team believe that the event is the result of a small black hole swallowing a star.
Source : Astronomers detected a burst caused by a black hole swallowing a star
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Meet the brown dwarf: bigger than a planet, and smaller than a star. A category of its own, it’s one of the strangest objects in the universe.
Brown dwarfs typically are defined to have masses anywhere from 12 times the mass of Jupiter right up to the lower limit for a star. And despite their names, they are not actually brown. The largest and youngest ones are quite hot, giving off a steady glow of radiation. In fact, the largest brown dwarfs are almost indistinguishable from red dwarfs, the smallest of the stars. But the smallest, oldest, and coldest ones are so dim they can only be detected with our most sensitive infrared telescopes.
Unlike stars, brown dwarfs don’t generate their own energy through nuclear fusion, at least not for very long. Instead they emit radiation from the leftover heat of their own formation. As that heat escapes, the brown dwarf continues to dim, sliding from fiery red to mottled magenta to invisible infrared. The greater the mass at its birth, the more heat it can trap and the longer it can mimic a proper star, but the ultimate end fate is the same for every single brown dwarf, regardless of its pedigree.
At first it may seem like brown dwarfs are just extra-large planets, but they get to do something that planets don’t. While brown dwarfs can’t fuse hydrogen in their cores – that takes something like 80 Jupiter masses to accomplish – they can briefly partake in another kind of fusion reaction.
In the cooler heart of a brown dwarf, deuterium, which is a single proton and neutron, can convert into Helium-3, and in the process release energy. This process doesn’t last long; in only a few million years even the largest brown dwarfs use up all their available deuterium, and from there they will just cool off.
As for their size, they tend not to be much larger in diameter than a typical gas giant like Jupiter. That’s because unlike a star, there isn’t an additional source of energy, and thereby pressure, to prop themselves up. Instead, all that’s left is the exotic quantum force known as degeneracy pressure, which means that you can only squeeze so many particles into so small a volume. In this case, brown dwarfs are very close to the limit for degeneracy pressure to maintain their size given their mass.
This means that despite outweighing Jupiter, they won’t appear much larger. And unlike Jupiter, they are briefly capable of nuclear fusion. After that, however, they spend the rest of their lives wandering the galaxy, slowly chilling out.
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In 1971, the Soviet Mars 3 lander became the first spacecraft to land on Mars, though it only lasted a couple of minutes before failing. More than 50 years later, it’s still there at Terra Sirenum. The HiRISE camera NASA’s Mars Reconnaissance Orbiter may have imaged some of its hardware, inadvertently taking part in what could be an effort to document our Martian artifacts.
Is it time to start cataloguing and even preserving these artifacts so we can preserve our history?
Some anthropologists think so.
Justin Holcomb is an assistant research professor of anthropology at the University of Kansas. He and his colleagues argue that it’s time to take Martian archaeology seriously, and the sooner we do, the better and more thorough the results will be. Their research commentary, “The emerging archaeological record of Mars,” was recently published in Nature Astronomy.
Artifacts of the human effort to explore the planet are littered on its surface. According to Holcomb, these artifacts and our effort to reach Mars are connected to the original human dispersal from Africa.
“Our main argument is that Homo sapiens are currently undergoing a dispersal, which first started out of Africa, reached other continents and has now begun in off-world environments,” said lead author Holcomb. “We’ve started peopling the solar system. And just like we use artifacts and features to track our movement, evolution and history on Earth, we can do that in outer space by following probes, satellites, landers and various materials left behind. There’s a material footprint to this dispersal.”
It’s tempting to call debris from failed missions wreckage or even space junk like we do the debris that orbits Earth. But things like spent parachutes and heat shields are more than just wreckage. They’re artifacts the same way other cast-offs are artifacts. In fact, what archaeologists often do in the field is sift through trash. “Trash is a proxy for human behaviour,” said one anthropologist.
In any case, one person’s trash can be another person’s historical artifact.
“These are the first material records of our presence, and that’s important to us,” Holcomb said. “I’ve seen a lot of scientists referring to this material as space trash, galactic litter. Our argument is that it’s not trash; it’s actually really important. It’s critical to shift that narrative towards heritage because the solution to trash is removal, but the solution to heritage is preservation. There’s a big difference.”
14 missions to Mars have left their mark on the red planet in the form of artifacts. According to the authors, this is the beginning of the planet’s archaeological record. “Archaeological sites on the Red Planet include landing and crash sites, which are associated with artifacts including probes, landers, rovers and a variety of debris discarded during landing, such as netting, parachutes, pieces of the aluminum wheels (for example, from the Curiosity rover), and thermal protection blankets and shielding,” they write.
Other features include rover tracks and rover drilling and sampling sites.
We’re already partway to taking our abandoned artifacts seriously. The United Nations keeps a list of objects launched into space called the Register of Objects Launched into Outer Space. It’s a way of identifying which countries are liable and responsible for objects in space (but not which private billionaires.) The Register was first implemented in 1976, and it says that about 88% of crewed spacecraft, elements of the ISS, satellites, probes, and landers launched into space are registered.
UNESCO also keeps a register of heritage sites, including archaeological and natural sites. The same could be done for Mars.
There’s already one attempt to start documenting and mapping sites on Mars. The Perseverance Rover team is documenting all of the debris they encounter to make sure it can’t contaminate sampling sites. There are also concerns that debris could pose a hazard to future missions.
According to one researcher, there is over 1700 kg (16,000) pounds of debris on Mars, not including working spacecraft. While much of it is just scraps being blown around by the wind and broken into smaller pieces, there are also larger pieces of debris and nine intact yet inoperative spacecraft.
So far, there have been only piecemeal attempts to document these Martian artifacts.
“Despite efforts from the USA’s Perseverance team, there exists no systematic strategy for documenting, mapping and keeping track of all heritage on Mars,” the authors write. “We anticipate that cultural
resource management will become a key objective during planetary exploration, including systematic surveying, mapping, documentation, and, if necessary, excavation and curation, especially as we expand
our material footprint across the Solar System.”
Holcomb and his co-authors say we must understand that our spacecraft debris is the archaeological record of our attempt to explore not just Mars but the entire Solar System. Our effort to understand Mars is also part of our effort to understand our own planet and how humanity arose. “Any future accidental destruction of this record would be permanent,” they point out.
The authors say there’s a crucial need to preserve things like Neil Armstrong’s first footsteps on the Moon, the first impact on the lunar surface by the USSR’s Luna 2, and even the USSR’s Venera 7 mission, the first spacecraft to land on another planet. This is our shared heritage as human beings.
“These examples are extraordinary firsts for humankind,” Holcomb and his co-authors write. “As we move forward during the next era of human exploration, we hope that planetary scientists, archaeologists and geologists can work together to ensure sustainable and ethical human colonization that protects
cultural resources in tandem with future space exploration.”
There are many historical examples of humans getting this type of thing wrong, particularly during European colonization of other parts of the world. Since we’re still at (we hope) the beginning of our exploration of the Solar System, we have an opportunity to get it right from the start. It will take a lot of work and many discussions to determine what this preservation and future exploration can look like.
“Those discussions could begin by considering and acknowledging the emerging archaeological record on Mars,” the authors conclude.
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In 2019, astronomers observed an unusual gravitational chirp. Known as GW190521, it was the last scream of gravitational waves as a black hole of 66 solar masses merged with a black hole of 85 solar masses to become a 142 solar mass black hole. The data were consistent with all the other black hole mergers we’ve observed. There was just one problem: an 85 solar mass black hole shouldn’t exist.
All the black hole mergers we’ve observed involve stellar mass black holes. These form when a massive star explodes as a supernova and its core collapses to become a black hole. An old star needs to be at least ten times the mass of the Sun to become a supernova, which can create a black hole of about 3 solar masses. Larger stars can create larger black holes, up to a point.
The first generation of stars in the cosmos were likely hundreds of solar masses. For a star above 150 solar masses or so, the resulting supernova would be so powerful that its core would undergo what is known as pair-instability. Gamma rays produced in the core would be so intense they decay into an electron-positron pair. The high-energy leptons would then rip apart the core before gravity could collapse it. To overcome the pair-instability, a progenitor star would need a mass of 300 Suns or more. This means that the mass range of stellar black holes has a “pair-instability gap.” Black holes from 3 solar masses to about 65 solar masses would form from regular supernovae, and black holes above 130 solar masses could form from stellar collapse, but black holes between 65-130 solar masses shouldn’t exist.
For GW190521, the 66 solar mass black hole is close enough to the limit that it likely formed from a single star. The 85 solar mass black hole, on the other hand, is smack-dab in the middle of the forbidden range. Some astronomers have argued that the larger black hole might have formed from a hypothetical boson star known as a Proca star, but if that’s true, then GW190521 is the only evidence that Proca stars exist. More likely, the 85 solar mass black hole formed from the merger of two smaller black holes, making GW190521 a staged merger. The difficulty with that idea is that black hole mergers are often asymmetrical, in a way that the resulting black hole is kicked out of its region of origin. Multiple black hole mergers would only occur under certain circumstances, which is where a new study in The Astrophysical Journal comes in.
The authors looked at how the mass, spin, and motion of a merging black hole pair determine the mass, spin, and recoil velocity of the resulting black hole. By creating a statistical distribution of outcomes, the team could then work backwards. Given the mass, spin, and velocity of a “forbidden” black hole relative to its environment, what were the properties of its black hole ancestors? When the authors applied this to the progenitors of GW190521, they found that the only possible ancestors would have given a relatively large recoil velocity. This means that the merger must have occurred within the region of an active galactic nucleus, where the gravitational well would be strong enough to hold the system together.
This work has implications for what are known as intermediate mass black holes (IMBHs), which can have masses of hundreds or thousands of Suns. It has been thought that IMBHs form within globular clusters, but if the recoil velocities of black hole mergers are large, this would be unlikely. As this study shows, GW190521 could not have occurred in a globular cluster.
Reference: Araújo-Álvarez, Carlos, et al. “Kicking Time Back in Black Hole Mergers: Ancestral Masses, Spins, Birth Recoils, and Hierarchical-formation Viability of GW190521.” The Astrophysical Journal 977.2 (2024): 220.
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Telling time in space is difficult, but it is absolutely critical for applications ranging from testing relativity to navigating down the road. Atomic clocks, such as those used on the Global Navigation Satellite System network, are accurate, but only up to a point. Moving to even more precise navigation tools would require even more accurate clocks. There are several solutions at various stages of technical development, and one from Germany’s DLR, COMPASSO, plans to prove quantum optical clocks in space as a potential successor.
There are several problems with existing atomic clocks – one has to do with their accuracy, and one has to do with their size, weight, and power (SWaP) requirements. Current atomic clocks used in the GNSS are relatively compact, coming in at around .5 kg and 125 x 100 x 40 mm, but they lack accuracy. In the highly accurate clock world terminology, they have a “stability” of 10e-9 over 10,000 seconds. That sounds absurdly accurate, but it is not good enough for a more precise GNSS.
Alternatives, such as atomic lattice clocks, are more accurate, down to 10e-18 stability for 10,000. However, they can measure .5 x .5 x .5m and weigh hundreds of kilograms. Given satellite space and weight constraints, those are way too large to be adopted as a basis for satellite timekeeping.
To find a middle ground, ESA has developed a technology development roadmap focusing on improving clock stability while keeping it small enough to fit on a satellite. One such example of a technology on the roadmap is a cesium-based clock cooled by lasers and combined with a hydrogen-based maser, a microwave laser. NASA is not missing out on the fun either, with its work on a mercury ion clock that has already been orbitally tested for a year.
COMPASSO hopes to surpass them all. Three key technologies enable the mission: two iodine frequency references, a “frequency comb,” and a “laser communication and ranging terminal.” Ideally, the mission will be launched to the ISS, where it will sit in space for two years, constantly keeping time. The accuracy of those measurements will be compared to alternatives over that time frame.
Lasers are the key to the whole system. The iodine frequency references display the very distinct absorption lines of molecular iodine, which can be used as a frequency reference for the frequency comb, a specialized laser whose output spectrum looks like it has comb teeth at specific frequencies. Those frequencies can be tuned to the frequency of the iodine reference, allowing for the correction of any drift in the comb.
The comb then provides a method for phase locking for a microwave oscillator, a key part of a standard atomic clock. Overall, this means that the stability of the iodine frequency reference is transferred to the frequency comb, which is then again transferred to the microwave oscillator and, therefore, the atomic clock. In COMPASSO’s case, the laser communication terminal is used to transmit frequency and timing information back to a ground station while it is active.
COMPASSO was initially begun in 2021, and a paper describing its details and some breadboarding prototypes were released this year. It will hop on a ride to the ISS in 2025 to start its mission to make the world a more accurately timed place—and maybe improve our navigation abilities as well.
Learn More:
Kuschewski et al – COMPASSO mission and its iodine clock: outline of the clock design
UT – Atomic Clocks Separated by Just a few Centimetres Measure Different Rates of Time. Just as Einstein Predicted
UT – Deep Space Atomic Clocks Will Help Spacecraft Answer, with Incredible Precision, if They’re There Yet
UT – A New Atomic Clock has been Built that Would be off by Less than a Second Since the Big Bang
Lead Image:
Benchtop prototype of part of the COMPASSO system.
Credit – Kuschewski et al
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Binary stars are common throughout the galaxy. Roughly half the stars in the Milky Way are part of a binary or multiple system, so we would expect to find them almost everywhere. However, one place we wouldn’t expect to find a binary is at the center of the galaxy, close to the supermassive black hole Sagittarius A*. And yet, that is precisely where astronomers have recently found one.
There are several stars near Sagittarius A*. For decades, we have watched as they orbit the great gravitational well. The motion of those stars was the first strong evidence that Sag A* was indeed a black hole. At least one star orbits so closely that we can see it redshift as it reaches peribothron.
But we also know that stars should be ever wary of straying too close to the black hole. The closer a star gets to the event horizon of a black hole, the stronger the tidal forces on the star become. There is a point where the tidal forces are so strong a star is ripped apart. We have observed several of these tidal disruption events (TDEs), so we know the threat is very real.
Tidal forces also pose a threat to binary stars. It wouldn’t take much for the tidal pull of a black hole to disrupt binary orbits, causing the stars to separate forever. Tidal forces would also tend to disrupt the formation of binary stars in favor of larger single stars. Therefore astronomers assumed the formation of binary stars near Sagittarius A* wasn’t likely, and even if a binary formed, it wouldn’t last long on cosmic timescales. So astronomers were surprised when they found the binary system known as D9.
The D9 system is young, only about 3 million years old. It consists of one star of about 3 solar masses and the other with a mass about 75% that of the Sun. The orbit of the system puts it within 6,000 AU of Sag A* at its closest approach, which is surprisingly close. Simulations of the D9 system estimate that in about a million years, the black hole’s gravitational influence will cause the two stars to merge into a single star. But even this short lifetime is unexpected, and it shows that the region near a supermassive black hole is much less destructive than we thought.
It’s also pretty amazing that the system was discovered at all. The center of our galaxy is shrouded in gas and dust, meaning that we can’t observe the area in the visible spectrum. We can only see stars in the region with radio and infrared light. The binary stars are too close together for us to identify them individually, so the team used data from the Enhanced Resolution Imager and Spectrograph (ERIS) on the ESO’s Very Large Telescope, as well as archive data from the Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI). This gave the team data covering a 15-year timespan, which was enough to watch the light of D9 redshift and blueshift as the stars orbit each other every 372 days.
Now that we know the binary system D9 exists, astronomers can look for other binary stars. This could help us solve the mystery of how such systems can form so close to the gravitational beast at the heart of our galaxy.
Reference: Peißker, Florian, et al. “A binary system in the S cluster close to the supermassive black hole Sagittarius A.” Nature Communications 15.1 (2024): 10608.
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