What happens when you burn iron in space? The European Space Agency is torching iron powder in microgravity, to find out. They aren’t doing it for the fun of it, but to understand something called “discrete burning.” It turns out that this process might enable more efficient iron-burning furnaces right here on Earth. It could eventually join other renewable energy sources as a way to combat the release of greenhouse gases in our atmosphere.
So, why burn iron? In astrophysics, when a hugely massive star gets to the “iron-burning” phase, it spells catastrophe in the form of a supernova. That’s because it takes more energy to consume the iron in the star’s core than the star can put out. But, “burning” iron in microgravity is a different chemical process.
When you burn something, you’re adding oxygen to the material you want to burn. The process gives off heat, plus other byproducts. If you’re burning wood or something like that, the by-products are ash and carbon dioxide (a greenhouse gas).
When iron (or other metal) powder burns, it reacts with air to form oxides. In the process, they create a lot of energy (and light). In the case of iron, the leftover is basically iron oxide—good old rust. And, people can reprocess the rust to remove the oxygen. Essentially, you get iron back. No carbon dioxide gets produced and no other dangerous gases show up in the process.
Most of us have experienced burning metals when we set off fireworks or played with sparklers during holiday celebrations. Those are great toys, but they’re also mini-energy sources. What happens if you scale up such iron- and metal-burning processes? You get heat and energy on a much larger scale. That’s what the ESA scientists wanted to test, for reasons relating to future exploration of the Moon and beyond.
Here’s what it looks like when iron dust is burned in a controlled chamber. It gives off heat and light. This is the process of discrete burning. Courtesy ESA.
To test the iron-burning process, the agency sent up a series of parabolic flights on zero-g aircraft and rocket launches. Onboard “ovens” contained iron dust that floated free and ignited discretely. Such discrete burning is rare here on Earth, but the physics of it is worth researching for space-based use. The idea was to see if discrete burning could be a useful technology in such places as lunar bases. To get a mental image of the process, think of a forest fire where one tree burns, and then when things get hot enough, the fire jumps to a neighboring tree.
Video of iron burning on an ESA parabolic flight aboard the Falcon-20 aircraft of the Canadian National Research Centre. The view shows iron metal dust igniting as it reaches combustion temperature. The view is slowed down 30 times. Courtesy ESA.
High-speed cameras captured views of the experiments onboard the aircraft and rockets. The images and data were then fed into computer models that scientists are using to understand if iron-burning plants are possible in various environments.
Applications in Space and on Earth
Metal-burning processes might seem unusual to many people—almost science-fictiony. It’s not a completely new idea, though. A whole community of researchers is looking into the process here on Earth for sustainable energy production. And, it’s not new to the industry. In the Netherlands, the Swinkels Family Brewery embraced iron burning several years ago to convert its brewing process from fossil fuels to a more ecologically sustainable process.
In space, while there are no colonies or stations on the Moon yet, ESA scientists see a time when sustainable metal-burning energy plants will be needed there as well. One possible scenario is to use solar energy to produce aluminum and silicon powder from lunar minerals and get hydrogen and oxygen from lunar ice. The hydrogen would be used to convert lunar dust that is high in iron and titanium to produce water and iron powder. The metallic powders and oxygen from the water ice could be turned into propellants for rockets or ground transportation and the water by-product becomes drinking water.
The iron fuel demo plant in Eindhoven, The Netherlands. Courtesy ESA.
The sustainable fuels industry is seriously looking at metal burning as a future source of “clean energy.” There’s already a demonstration plant up and running experiments in the Netherlands, near Eindhoven. The goal is to find out how much of this energy can be generated as a replacement for fossil fuels. It uses iron powder and generates about 1MW of steam. Based on this experimental model, other companies are looking into metal burning for heavy industrial uses.
One of the most interesting (and confounding) discoveries made by the James Webb Space Telescope (JWST) is the existence of “impossibly large galaxies.” As noted in a previous article, these galaxies existed during the “Cosmic Dawn,” the period that coincided with the end of the “Cosmic Dark Age” (roughly 1 billion years after the Big Bang). This period is believed to hold the answers to many cosmological mysteries, not the least of which is what the earliest galaxies in the Universe looked like. But after Webb obtained images of these primordial galaxies, astronomers noticed something perplexing.
The galaxies were much larger than what the most widely accepted cosmological model predicts! Since then, astronomers and astrophysicists have been racking their brains to explain how these galaxies could have formed. Recently, a team of astrophysicists from The Hebrew University of Jerusalem Jerusalem published a theoretical model that addresses the mystery of these massive galaxies. According to their findings, the prevalence of special conditions in these galaxies (at the time) allowed highly-efficient rates of star formation without interference from other stars.
This image shows one of the most distant galaxies known, called GN-108036, dating back to 750 million years after the Big Bang that created our universe. Credit: NASA/ESA/JPL-Caltech/STScI/University of Tokyo
According to the Lambda-Cold Dark Matter (LCDM) model, which best explains what we have observed of the cosmos, the first stars and galaxies formed during the “Cosmic Dark Age.” The name refers to how the only sources of photons during this period were from the Cosmic Microwave Background (CMB) and those released by the clouds of neutral hydrogen that shrouded the Universe. Once galaxies began to form, the radiation from their hot and massive stars (1000 times more massive than our Sun) began reionizing the neutral hydrogen.
This period is known as the Epoch of Reionization (ca. 1 billion years after the Big Bang), where the Universe gradually became transparent and visible to modern instruments. Thanks to Webb’s extreme sensitivity to infrared light, astronomers have pushed the boundary of what is visible, spotting an abundance of massive galaxies that existed just half a billion years after the Big Bang. According to the LCDM model, there simply wasn’t enough time since the Big Bang for so many galaxies to have formed and become so massive. As Professor Dekel shared in a press release from The Hebrew University of Jerusalem:
“Already in the first half-billion years, researchers identified galaxies that each contain about ten billion stars like our sun. This discovery surprised researchers who tried to identify plausible explanations for the puzzle, ranging from the possibility that the observational estimate of the number of stars in galaxies is exaggerated, to suggesting the need for critical changes in the standard cosmological model of the Big Bang.”
According to the model put forth by Dekel and his colleagues, the prevalence of special conditions in these galaxies would have allowed for high rates of star formation. These include the high density and low abundance of heavy elements and feedback-free starbursts (FFBs). To break it down, prevailing theories of galaxy formation indicate that the hydrogen permeating the early Universe collapsed into giant spherical clouds of Dark Matter, where it collected together to give birth to the first population of stars (Population III).
Artist’s illustration of Population III stars, the earliest stars in the Universe. Credit: Wikimedia Commons
These theories further state that the stars were almost entirely composed of hydrogen, which was slowly fused in their interiors to create heavier elements (metals). These elements were distributed throughout early galaxies when Population III stars reached the end of their lifespans and blew off their outer layers in supernovae. As a result, more recent stellar populations (Population II and I) have had higher metal content (aka. “metallicity”). To date, astronomers have observed that galaxies’ star-formation efficiency (SFE) is low, with only about 10% of the gas falling into clouds becoming stars.
This low efficiency results from the remaining gas being heated or blown out of galaxies by stellar winds or shock waves generated by supernovae. In contrast, Dekel and his team theorized that low-metallicity massive stars were subject to a process they call “feedback-free starburst” (FFB). In essence, star-forming clouds in the early Universe had a density that allowed gas clouds to collapse rapidly into stars 1 million years before they would have developed winds and supernovae. This created a “window of opportunity” where the absence of feedback allowed the rest of the gas to form stars.
This high-efficiency star formation explains the abundance of massive galaxies observed by Webb so soon after the Big Bang. As Dekel concluded, the implications their theory has will be the subject of follow-up investigations:
“The publication of this research marks an important step forward in our understanding of the formation of primordial massive galaxies in the Universe and will no doubt spark further research and discovery. The predictions of this model will be tested using the accumulating new observations from the Webb Space Telescope, where it seems that some of these predictions are already confirmed.”
Artist’s impression of GNz7q, a primordial ancestor to modern supermassive black holes (SMBHs). Credit: NASA/ESA/STScI.
Of particular interest to astronomers are the primordial supermassive black holes (SMBHs) one thousand times as massive as our Sun that existed about 1 billion years after the Big Bang. Astronomers were surprised to observe SMBHs this massive at the center of early galaxies since (once again) it was assumed that they didn’t have enough time to form. Future observations will attempt to find the seeds of these black holes using Webb and observatories like the Laser Interferometer Space Antenna (LISA). Dekel and his colleagues hope they find these seeds among clusters of FFBs that went supernova.
NASA’s Kepler spacecraft ended its observations in October 2018 after nine and a half years, a solid six years beyond its planned duration. It discovered 2,711 confirmed exoplanets and another 2,056 exoplanet candidates as of August 2022.
Now, astronomers at MIT and the University of Wisconsin uncovered three more exoplanets in the data from Kepler’s final days of observations. They needed the help of dedicated amateurs to do it.
Kepler was still operating when NASA launched Kepler’s successor, the Transiting Exoplanet Survey Satellite (TESS,) in August 2018. When Kepler’s mission ended later that year, it passed the planet-hunting baton over to TESS. TESS is doing great, but Kepler still accounts for over half of the confirmed exoplanets we know of. That’s impressive, and the number ticks a little higher with the newest three.
Kepler worked hard right up until its end. As it ran out of fuel for its reaction control system in October 2018, it kept watching stars in its targeted part of the sky for the tell-tale dips in light that signal a passing planet. It spotted three dips around three separate stars in the same section of the sky. Two of those dips are now confirmed exoplanets, and the other is a candidate awaiting confirmation.
A new paper in Monthly Notices of the Royal Astronomical Society presents the findings. It’s titled “Kepler’s last planet discoveries: two new planets and one single-transit candidate from K2 campaign 19.” The lead author is Elyse Incha, from the University of Wisconsin at Madison. Other authors come from NASA, CfA Harvard and Smithsonian, and the University of North Carolina. Amateur astronomers Tom Jacobs and Daryll LaCourse are also part of the team.
“As some of the last discoveries ever made by the Kepler space telescope, these planet candidates hold significance both sociologically and scientifically.”
From ‘Kepler’s last planet discoveries: two new planets and one single-transit candidate from K2 campaign 19.’
When Kepler began to run out of fuel, it worked hard to fulfill its mission. It relied on its reaction control system, which included reaction wheels and hydrazine thrusters. As it ran out of hydrazine, it struggled to keep itself pointed at its targets. For nearly a month, results were dicey.
For about 8.5 days, it was pointed off-center. It eventually got itself oriented properly for about 7.5 days and performed its observations normally during that period. Then things took a turn for the worse. Kepler could only point itself erratically as the thrusters could only burn intermittently, struggling to keep the spacecraft functioning. This erratic period lasted about 11 days.
The data from the final 11 days was incomplete. Only parts of light curves from that period were usable. After 11 days of that, the Kepler team faced the end. There simply wasn’t enough thruster fuel to continue.
That marked the end of Kepler’s 19th observing campaign and the end of its mission. Kepler recorded 27 days of data during campaign 19, but much of it was compromised. Only 7.5 days of the data were suitable for reduction with existing pipelines. (Missions like Kepler gather a massive amount of raw data that has to be processed with data pipelines to become usable.)
The research team behind the new paper says they focused on the 7+ days of precise photometry from the middle of campaign 19 and processed them into light curves. “This process removed systematic errors from Kepler’s instability, leaving behind clean light curves,” they explain in their paper.
“We were curious to see whether we could get anything useful out of this short dataset,” co-author Andrew Vanderburg from MIT’s Kavli Institute said in a press release. “We tried to see what last information we could squeeze out of it.”
This created an enormous number of light curves to examine, all of them by human eyes. “The light curves of all 33,000 stars were searched by members of our team by eye,” they explain, by using a standard process outlined by other exoplanet researchers. After some detailed processing necessitated by Kepler’s erratic pointing, the researchers identified three light curves that indicated planets orbiting stars.
This figure from the paper shows the light curves from the three stars hosting the exoplanets. They all have the prefix EPIC, which stands for Ecliptic Plane Input Catalog, a publicly searchable database of stars and planets associated with Kepler’s K2 mission, the second part of its overall mission. Image Credit: Incha et al. 2023.
“We have found what are probably the last planets ever discovered by Kepler, in data taken while the spacecraft was literally running on fumes,” says Andrew Vanderburg, assistant professor of physics at MIT’s Kavli Institute for Astrophysics and Space Research. “The planets themselves are not particularly unusual, but their atypical discovery and historical importance makes <sic> them interesting.”
K2-416 b and K2-417 b are the two confirmed exoplanets. K2-416 b is about 2.6 times larger than Earth and orbits its star, an M-dwarf, every 13 days. K2-417 b is a little larger, about 3 times larger than Earth. It orbits its star, a G-type star, every 6.5 days.
The third planet, EPIC 246251988 b, is still a candidate and retains the EPIC prefix. It’s the largest of the three, about 4 times larger than Earth. It orbits its star, also an M-dwarf, every 10 days and is much further away from us than the other two.
The discovery involved a lot of human eye work. The Visual Survey Group (VSG) is a team of amateur and professional astronomers that hunt for exoplanets in telescope data. As of 2022, the VSG has visually surveyed over 10 million light curves and authored 69 peer-reviewed papers. The group has proven its value by identifying objects in light curve data that automated search programs either discarded or overlooked. VSG’s primary focus is exoplanets, but they’ve also found cataclysmic variables, eclipsing binaries, and ‘black swans,’ which are unpredictable events beyond normal expectations.
“They (VSG) can distinguish transits from other wacky things like a glitch in the instrument,” Vanderburg says. “That’s helpful, especially when your data quality begins to suffer like it did in K2’s last bit of data.”
Initially, the team examined the 7.5 days of strong data. In it, they found single transits for three separate stars. Then they examined the final 11 days of lower-quality observations. They needed to find additional transits to confirm them as planets. They found additional transits for two of the planets, K2-416 b and K2-417 b. The team found additional data from NASA’s TESS for one of the planets, K2-417 b, which also helped confirm it.
This figure from the research shows both transits detected for each newly confirmed exoplanet. Image Credit: Incha et al. 2023.
“Those two are pretty much, without a doubt, planets,” Incha said. “We also followed up with ground-based observations to rule out all kinds of false positive scenarios for them, including background star interference, and close-in stellar binaries.”
Eclipsing binaries (EBs) can appear as exoplanet transits and must be eliminated as a possibility before a candidate planet is confirmed. As they orbit one another, EBs can block each other’s light, creating dips from our perspective. The team examined historical observations of both stars from decades ago to eliminate the possibility that any of their light curves were caused by EBs.
This figure is a comparison of images of each star. The top row is images of the stars from a sky survey done in the 1950s, and the bottom row is images taken with Pan-STARRS. Orange stars mark the locations of all three stars. The first two comparisons eliminate the possibility of EBs, while for the third star, the proper motion is too small to eliminate the possibility. It remains a candidate. Image Credit: Incha et al. 2023.
Despite the team’s work, they were not able to conclude that the third transiting event is, in fact, an exoplanet. It could very well be a high-mass brown dwarf. “Our constraints for EPIC 246251988 are weakest because it lacks a precisely measured orbital period, and we struggle to confidently rule out even high-mass brown dwarfs in the long-period tail of the probability distribution,” the authors explain in their paper. “Nevertheless, the preponderance of the evidence points to a planetary mass for any companion orbiting EPIC 246251988.”
The three planets are not unusual. They’re fairly typical of the population of sub-Neptune size objects detected by the transit method. Of the over 5400 confirmed exoplanets, over 1800 of them are Neptune-like. That’s about 33%. These planets have radii that indicate the presence of a volatile envelope of some size.
This figure from the research shows how the three new planets compare to the population of known transiting exoplanets. The x-axis shows the orbital period, and the y-axis shows the radius. All three are fairly typical. Image Credit: Incha et al. 2023.
These are likely the final three planets that Kepler found. The team rigorously examined the light curves from 33,000 stars captured during the spacecraft’s final days to find them, and because human eyes were involved, it’s unlikely there are any more transits in all those curves. But they may not be the last exoplanets found in Kepler’s vast collection of data.
“These are the last chronologically observed planets by Kepler, but every bit of the telescope’s data is incredibly useful,” Incha says. “We want to make sure none of that data goes to waste, because there are still a lot of discoveries to be made.”
“As some of the last discoveries ever made by the Kepler space telescope, these planet candidates hold significance both sociologically and scientifically,” the researchers write in the conclusion to their paper. “We hope our work will help ensure that all Kepler data are utilized to its full potential so that no planets are left behind.”
The Pinwheel Galaxy, also known as M101, is a spiral galaxy just 21 million light years away. It’s a popular galaxy for photographs because it’s oriented to us face-on. This means you can see the bright whorled spirals and dark cloud regions, even in amateur photographs. Since it’s relatively close and bright, you can get a good view of it, even with a small telescope. It also happens to have a supernova at the moment.
The last time the Pinwheel Galaxy had a visible supernova was in 2011. That one was a Type Ia supernova, the kind used to measure cosmic distances. This new one appeared in May and is a Type II supernova. These are also known as core-collapse supernovae since they occur when a massive star runs out of elements to fuse and its core collapses under its own weight to become a neutron star.
The supernova is currently at about a magnitude 11, meaning that if you have dark skies and at least a 4-inch telescope, you can see it with your own eyes. If you don’t have such luxuries, there are lots of captured images of the supernova popping up on the web, since it’s now a popular target for amateur astronomers. The supernova, named SN 2023ixf, is expected to brighten a bit more over the next couple of months before gradually fading.
On the cosmic scale, this supernova is remarkably close. Astronomers observe supernovae all the time, but it is only every decade or so that we get to observe one so near us. SN 2023ixf observations will help astronomers better understand the evolution of core-collapse supernovae, as well as how they enrich the universe with heavy elements.
So if you have the chance, grab your telescope or reach out to your local astronomer, before this brief candle goes out.
Robots will be one of the keys to the expanding in-space economy. As launch costs decrease, hopefully significantly when Starship and other massive lift systems come online, the most significant barrier to entry for the space economy will finally come down. So what happens then? Two acronyms have been popping up in the literature with increasing frequency – in-space servicing, assembly, and manufacturing (ISAM) and On-orbit servicing (OOS). Over a series of articles, we’ll look at some papers detailing what those acronyms mean and where they might be going shortly. First, we’ll examine how robots fit into the equation.
Space robots have been around since 1981 when the Shuttle Remote Manipulator System (SRMS) was launched with the space shuttle, whose astronauts then operated them. They have expanded far beyond that original use case in the last forty years, playing an increasingly important role in everything from assembling the International Space Station (ISS) to more recently proof-of-concept missions to service a failing satellite in Earth’s orbit.
A new paper from the State Key Laboratory of Robotics and Systems at the Harbin Institute of Technology in China details some of the work that still needs to be done to realize the dream of fully functional robots in space. It breaks that work down into five different functional areas.
UT video discussing whether robots or humans should explore space.
First, and one familiar to anyone who spends time with autonomous robots, is vision. Vision systems are consistently being improved here on Earth, especially those tied to the operation of autonomous cars. However, while the visual surrounding might not be near as chaotic in space, it can be challenging to have a robot visually understand what it is looking at, especially if a satellite is tumbling uncontrollably.
Pattern recognition, such as circles placed around the docking ports of a satellite expecting to be serviced (known in the jargon as “cooperative”), is still difficult. Partly that is because the computational load of doing the recognition algorithm must be done on the robot itself. That requires increased computational power, directly related to increased power consumption and heat that must be dealt with. Recognizing an “un-cooperative” satellite that isn’t designed to accept help from a robot is even more difficult, especially in real-time.
Once a robot sees where it’s going and what it’s trying to interact with, the next step is to get there and effectively interact with the thing. There are several factors to consider here, and the paper calls them collectively “motion and control” technologies.
Timeline of different robots in space.
Credit – Ma et al.
They present solutions to several unique control problems, including how to deal with the forces of a robot when there is very little gravity affecting it. In particular, how do movement commands, and especially trying to move specific objects, cause things like vibrations in the body and manipulator of the robot? This is especially true if the robot itself isn’t anchored to a much larger weight, such as the ISS or a space shuttle. Dynamic control algorithms can help dampen some of the more dangerous vibrations, potentially shaking the robot apart if left uncontrolled.
But even if there was a control system to dampen vibrations, other coordination factors can still be complex, including coordinating multiple arms to interact with an object. While that has been done before, it still proves difficult to do the coordination simultaneously, as it does with robots on Earth.
When a robot (or its manipulator) reaches its intended target, another technology has to interact with it – its end-effector. In robotics, end-effectors are how the robot interacts with objects. They’re the equivalent of human hands but can be much more functional, as they can both be made out of things that human hands are not made out of (screwdrivers) and can be switched out to something else entirely, such as by switching from a screwdriver to a soft-gel gripper. The possibilities of end-effectors and a robot’s efficiency at switching between end-effectors are endless, and plenty of technical work still needs to be done to make robots as capable as they can be in space.
Video discussing the usefulness of robots in space.
Credit – Analytics Insight YouTube Channel
One method to help effectively operate a robot’s end-effector is to allow a human to teleoperate it. This has been relatively common practice for most of the existence of robots in space, with astronauts operating the SRMS from inside the shuttle or the Canadarm2 from inside the ISS. However, teleoperation takes time, and an astronaut’s time is extremely precious. So efforts are underway to teleoperate robots in space from the ground.
We’ve recently reported on some efforts for the reverse, where an astronaut controlled a robot back on Earth. Those experiments aimed to prove the concept of operating robots down on the surface of other worlds like the Moon or Mars. This form of teleoperation would still suffer from the same delay difficulty – and what’s more, the delay might change depending on where a robot is in its orbital path.
Various solutions have been posed to this problem, including a virtual reality control setup that predicts where the robot will be at the end of the time delay so the operator can plan ahead without waiting for feedback. Force feedback is also a popular option, though it still suffers from the same time delay issues. Numerous technical solutions exist to this hurdle, but nothing can eliminate the fact that signals don’t transmit instantaneously over long distances.
ESA is leading the charge on space robotics. Here is an interview with some of their experts.
Credit – ESA YouTube Channel
Even back on Earth, there are still challenges. As noted in the paper, high-fidelity ground verification is difficult. Verification in engineering means proving that something works as expected in the environment, it’s intended to work in. That is almost impossible for a robot meant to operate in microgravity since it would be prohibitively expensive to launch a verification prototype into microgravity and deal with all the issues that inevitably crop up during verification testing.
Several technical solutions to the problem have been in use for a while, including suspending the robot in pockets of forced air to simulate floating, using either freefall or a parabolic flight on an airplane to test how it would operate in those conditions, or even dunking it in a pool and seeing how it would operate underwater.
Hardware-in-the-loop is the most promising new technology used in other industries. This models the expected behavior of the robotic system and mimics specific environments via software that the robot might experience in space. However, creating the models for this system is complex and can lead to inaccuracies in the verification test itself. So far, there is no optimal solution for ensuring a robot will operate in space while it is still being developed on the ground.
The Canadarm2 robotic arm is seen grappling the Orbital ATK S.S. Gene Cernan Cygnus resupply ship on Nov. 14, 2017 for berthing to the the International Space Station.
Credit: NASA TV
Ironically, robot operation in space itself might solve this last problem by creating a large enough infrastructure in space to allow for the design and assembly of robots themselves in space. That is still a long way off, but numerous teams worldwide are working on making it a reality. Someday it will be, and overcoming these technical challenges will help it become so.
A recent study published in the Proceedings of the National Academy of Sciences, a pair of researchers from the University of Florida (UF) examine orbital eccentricities for exoplanets orbiting red dwarf (M dwarf) stars and determined that one-third of them—which encompass hundreds of millions throughout the Milky Way—could exist within their star’s habitable zone (HZ), which is that approximate distance from their star where liquid water can exist on the surface. The researchers determined the remaining two-thirds of exoplanets orbiting red dwarfs are too hot for liquid water to exist on their surfaces due to tidal extremes, resulting in a sterilization of the planetary surface.
Artist’s illustration of a young red dwarf star with three exoplanets orbiting around it. (Credit: NASA/JPL-Caltech)
“I think this result is really important for the next decade of exoplanet research, because eyes are shifting toward this population of stars,” said Sheila Sagear, who is a PhD student at UF and lead author of the study. “These stars are excellent targets to look for small planets in an orbit where it’s conceivable that water might be liquid and therefore the planet might be habitable.”
For the study, Sagear and her advisor, Dr. Sarah Ballard, analyzed the orbital eccentricities of 163 exoplanets orbiting red dwarf stars across 101 systems using data from NASA’s Kepler mission. For context, red dwarf stars are approximately the size of Jupiter, so they’re much smaller than our own Sun. This smaller size means red dwarfs give off far less energy and heat than our Sun, meaning the HZ exists much closer to the star, resulting in shorter orbital periods for planets that orbit within the HZ.
Illustration depicting habitable zones for various types of stars displaying too hot (red), too cold (blue), and just right (green) for liquid water to exist on a planetary surface. Since red dwarfs are cooler than our own Sun, their habitable zone is closer to the star. (Credit: NASA/Kepler Mission/Dana Berry)
A planetary body’s orbital eccentricity refers to the shape of its orbit. While Earth’s orbit is almost perfectly circular, astronomers have discovered planetary bodies both within and beyond our solar system to exhibit more eccentric, or oval-shaped orbits. Eccentric orbits can result in massive fluctuations within the interiors of planetary bodies, regardless of their size. One such example within our solar system is Jupiter’s moon, Io, whose eccentric orbit results in it being the most volcanically active body in our solar system.
Throughout its orbit, Io is constantly stretched and compressed from the gravitational interactions with Jupiter since its distance changes, becoming closer at times and farther away from Jupiter at other times. Over great amounts of geologic time, the interior of Io heats up from the friction being produced within its interior, which leads to heat, and the volcanic activity we observe to this very day. This process is known as tidal heating, which is what this most recent study explores with exoplanets.
In the end, Sagear and Dr. Ballard discovered that red dwarf stars possessing multiple exoplanets held the highest promise of exhibiting more circular orbits much like the Earth, meaning they could house liquid water on their surfaces. In contrast, the researchers discovered that red dwarfs boasting only one exoplanet were more likely to exhibit an orbit with a higher eccentricity, resulting in it experiencing tidal extremes, much like Jupiter’s Io, and less likely to house liquid water on its surface.
While the study found that only one-third of exoplanets in the 163-sample size could possibly house liquid water on their surfaces, this also means that there are potentially hundreds of millions of these worlds throughout just the Milky Way Galaxy.
Launched in 2009, NASA’s Kepler mission has been instrumental in expanding our understanding of exoplanets and the likelihood of their habitability. During its 9-year mission that ended in 2018 after its fuel was expended, Kepler confirmed the existence of almost 2,800 exoplanets with almost 2,000 still potentially awaiting confirmation, known as exoplanet candidates. While this most recent study encompassed a small slice of those confirmed exoplanets, the data from Kepler will undoubtedly keep scientists busy for the next several years.
Artist rendition of the Kepler telescope searching for exoplanets. (Credit: NASA/Kepler mission/Wendy Stenzel)
What new discoveries will scientists make about M dwarfs, their exoplanets, and their characteristics? Only time will tell, and this is why we science!
The habitable zone is the region around a star where planets can maintain liquid water on their surface. It’s axiomatic that planets with liquid water are the best places to look for life, and astronomers focus their search on that zone. As far as we can tell, no water equals no life.
But new research suggests another delineation in solar systems that could influence habitability: The Soot Line.
Even though Earth is 2/3 covered in oceans, it’s still considered a water-poor planet. Our planet is only about 0.1% water by mass. But, obviously, that water is critical for life. Cells can’t perform their functions without water.
But carbon is critical for life, too, and Earth life is called carbon-based life. Carbon is unique in its ability to form diverse compounds, and to form polymers at Earth temperatures. It’s the second-most abundant element in the human body, after oxygen.
This illustration helps show how critical carbon is to all life. Here on Earth, cell membranes are composed of phospholipid molecules dissolved in liquid water. A phospholipid has a backbone of carbon atoms (gray) and also contains hydrogen (sky blue), phosphorus (yellow), oxygen (red), and nitrogen (blue). Credit: Ties van Brussel
But Earth is actually carbon-poor, and only 0.024% of the planet’s crust is carbon. That’s because it formed inside the Solar System’s soot line, where carbon is less plentiful. But what if sooty exoplanets that form outside a solar system’s soot line contain significantly more carbon? How could that affect habitability?
This is an artist’s impression of the super-Earth 55 Cancri e in front of its parent star. The exoplanet has far more carbon than Earth does, though it’s much too hot for life. Credit: ESA/NASA
The search for habitable exoplanets focuses on water and also on planets that formed similarly to ours. Planets form in protoplanetary disks that rotate around young stars, and those stars have a huge effect on the nature of the materials in the disk, including carbon. The Sun’s heat defines different frost lines at different distances from the Sun, and each frost line is relevant to a different volatile. Outside a particular frost line, pressure and temperature force a particular volatile to remain solid, while inside that line, the same volatile can sublimate to vapour.
Since solids are more likely to stick around and form planets, the region inside a particular chemical’s frost line will have fewer solids of that chemical, making it less available for planetary formation. This is why, or partly why, there’s so little water on Earth, while frozen water is abundant further away from the Sun. Earth formed inside the water frost line, and much of its water was most likely delivered later.
This image shows the relative locations of a solar system’s frost line and soot line. Image Credit: NASA
The soot line is similar to a frost line, but it concerns life-critical carbon. It’s the distance from a star where there’s not enough heat to vaporize carbon, and instead, the carbon in molecules stays solid. Since it’s solid, it’s more readily available for planet formation, so planets that form outside of the soot line should be more carbon-rich than Earth.
If Earth formed inside the soot line, then heat from the young Sun would’ve turned carbon-rich compounds into gas, which disperses much more easily. That meant there was less carbon in the solids that formed Earth, so Earth ended up with less carbon. Makes sense from our perspective.
When it comes to planets, habitability, and frost lines, the lines for water and carbon monoxide (CO) are of prime importance for exoplanet scientists. That’s because scientists think that these two compounds are the prime carriers of oxygen and carbon, both critical for life. The CO line is further away from the Sun by tens of AU than the water line because CO freezes at a much lower temperature. This should mean that planets closer to their stars, like Earth, have less carbon.
Most carbon is contained within CO, methane (CH4,) and carbon dioxide (CO2.) For a long time, that’s the picture scientists were working with. But recent research shows that most carbon is carried by refractory organics, which are materials with a very high sublimation temperature. In the new paper, these refractory organics are called ‘soot.’
Illustration showing one of the darkest known exoplanets – an alien world as black as fresh asphalt – orbiting a star like our Sun. The day side of the planet, called WASP-12b, eats light rather than reflects it into space. Astronomers think that the planet’s high carbon content plays a role in its low albedo. Credit: NASA, ESA, and G. Bacon (STScI)
Soots can stay solid at temperatures up to 500 Kelvin (226 C; 440 F.) And they have another important property. When they reach their destruction temperature, they decompose into simpler, more volatile species. That means their vaporization is irreversible, and that’s what leads to the soot line in a protoplanetary disk. The soot line is close to the star, and inside the soot line, refractory carbon is absent, but outside it, that critical source of carbon is available. But carbon can be tricky. “A unique property of the soot line,” the authors explain in their paper, “is that any carbon contained in the vapour that mixes outward remains in the gas and does not freeze out again as expected around traditional snow lines.”
So, planets that form outside the soot line can be rich in carbon. But planets can lose carbon while they’re still forming. Early in a protoplanetary disk, the temperature can change, and that can push the soot line further from the star. Earth’s low carbon inventory may reflect the fact that Earth gathered much of its material during this phase.
The soot line brings new complexity into our understanding of and search for potentially habitable exoplanets. This recent research shows that the frost line idea may be a bit too simple. Instead, researchers should take the soot line into account, and try to understand the carbon-rich sooty planets that can form outside it.
“It’s exciting because it leads to all kinds of endless possibilities.”
Professor Ted Bergin, University of Michigan
“For the water-poor Earth, the water ice line, or ice sublimation front, within the planet-forming disk has long been a key focal point,” the authors write in their paper. “We posit that the soot line, the location where solid-state organics are irreversibly destroyed, is also a key location within the disk. The soot line is closer to the host star than the water snow line and overlaps with the location of the majority of detected exoplanets.”
The region outside the soot line could include planets with more carbon than Earth, and that raises questions about the habitability of planets that form outside the line.
“It adds a new dimension to our search for habitability. It may be a negative dimension, or it may be a positive dimension,” Bergin said. “It’s exciting because it leads to all kinds of endless possibilities.”
As we’ve all learned in the last few years of exoplanet discovery, our Solar System isn’t representative of other systems. In other solar systems, we see planets much closer to their star than Mercury is to the Sun, and many more giant planets close to their stars. They also contain what are called Super-Earths and/or mini-Neptunes, something our system lacks.
“These are either big rocks or small gas giants—that’s the most common type of planetary system. So maybe, within all those other solar systems out in the Milky Way galaxy, there exists a population of bodies that we haven’t recognized before that have much more carbon in their interiors. What are the consequences of that?” Bergin said. “What this means for habitability needs to be explored.”
Our system doesn’t have a carbon-rich planet that formed between the soot line and the frost line, but other systems might. Unfortunately, we have no way of directly identifying these planets with current technology. So the researchers turned to models of planetary formation.
Carbon, Haze, and Habitability
Strange things happened inside the soot line when the team of researchers worked with models of planetary formation. They modelled silicate-rich worlds (the Earth is silicate rich) with 0.1% and 1.0% carbon by mass that form inside the soot line. They also varied the water content. They found that outgassing on these planets creates a methane-rich (CH4-rich) atmosphere. In our Solar System, the inner planets are methane-poor, and the outer planets are methane-rich, with Earth being the exception. Compared to its inner system siblings, Earth is methane-rich.
A methane-rich atmosphere provides an opportunity for hazes to form via interactions with protons from the Sun. We can see this happening on Saturn’s moon Titan, a methane-rich world with liquid methane on its surface.
“Planets that are born within this region, which exists in every planet-forming disk system, will release more volatile carbon from their mantles,” Bergin said. “This could readily lead to the natural production of hazes. Such hazes have been observed in the atmospheres of exoplanets and have the potential to change the calculus for what we consider habitable worlds.”
This artist’s illustration shows VHS 1256b, an exoplanet about 40 light-years away. The JWST detected methane in its atmosphere in March 2023. Image Credit: Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI)
The haze is a signal that an exoplanet contains significant volatile carbon in its mantle. Since carbon is the backbone of life, abundant carbon should affect its potential habitability. Carbon-rich haze planets that form between the soot line and the frost line might be an entirely new class of planet.
“If this is true, then there could be a common class of haze planets with abundant volatile carbon, and what that means for habitability needs to be explored,” he said. “But then there’s the other aspect: What if you have an Earth-sized world, where you have more carbon than Earth has? What does that mean for habitability, for life? We don’t know, and that’s exciting.”
But how can this research affect our understanding of exoplanets and our search for habitability?
Astronomers have detected planets with these characteristic hazes. “These hazes could readily be a by-product of birth between the soot and ice lines,” the authors write. With the advent of the James Webb Space Telescope, exoplanet scientists are poised to solidify their understanding of these hazes and what they might mean for carbon content and habitability.
“Such hazes, and the methane that drives their formation, are detectable via JWST transit spectroscopy, as demonstrated here, especially around stars lower in mass (and therefore size) than the Sun,” the authors write. “Thus, the presence or lack of hazes in the atmospheres of super-Earths or sub-Neptunes may allow us to discern whether they formed in situ from local materials or closer to the snow line and then migrated inward.”
This true-colour image of Titan, taken by the Cassini spacecraft, shows the moon’s thick, hazy atmosphere. Though the atmosphere is mostly nitrogen, it also contains about 2.7% methane, compared to Earth’s 0.00017%. Credit: NASA
For Earth-size planets, astronomers still need better models for their evolution. Carbon-poor, water-poor Earth is crowded with life. Could terrestrial carbon planets with much more carbon than Earth spawn different life on different pathways?
Carbon-rich exoplanets are known to exist. WASP 12-b has a carbon-to-oxygen ratio much higher than Earth’s. 55 Cancri e may be one-third carbon, compared to Earth’s 0.024%. In fact, 55 Cancri e might be a known example of the theoretical Carbon Planet, a planet with more carbon than oxygen.
Astronomers will keep finding more carbon-rich planets, in fact, they’ll keep finding more of every type of planet. The JWST and other future observatories will become even more adept at deciphering exoplanet atmospheres. Some day, astronomers will have the data and the models they need to understand carbon, the soot line, planet formation, and what it means for habitability.
The James Webb Space Telescope has observed a huge water vapor plume emanating from Saturn’s moon Enceladus. Astronomers say the plume reaches nearly 10,000 kilometers (6,200 miles) into space, which is about the equivalent distance as going from Ireland to Japan. This is the largest plume ever detected at Enceladus.
Using the sensitive NIRSpec (Near-Infrared Spectrograph) instrument onboard JWST, the researchers were searching for organic compounds in order to characterize the composition and structure of the diffuse plumes. However, their observations revealed only emissions of water. But this giant plume was much larger than expected.
Enceladus itself is just 505 km (314 miles) across, meaning the plume is 40 times as big. We’ve known about the water plumes – which are fueled by a massive subsurface ocean — since shortly after Cassini began studying Enceladus in 2005.
“These first observations with JWST (only a few minutes of integration time) demonstrate the power of this observatory for sensitively characterizing this ocean world, opening a new window into the exploration of Enceladus’ ongoing plume activity while preparing for future missions,” the team wrote in their preprint paper. The research team was led by Geronimo Villanueva from Goddard Space Flight Center and Heidi Hammel from the Association of Universities for Research in Astronomy (AURA). “More generally, JWST can provide detailed quantitative insights into H2O vapor-dominated geological and cryovolcanic activity elsewhere in the solar system.”
Researchers using the NASA/ESA/CSA James Webb Space telescope recently discovered a plume jetting out from the south pole of Saturn’s moon Enceladus and extending more than 40 times the size of the moon itself. This animation illustrates how the moon’s water plumes feed the moon’s torus. By analysing the Webb data, astronomers have determined roughly 30 percent of the water stays within this torus, and the other 70 percent escapes to supply the rest of the Saturnian system of water. Credit:NASA, ESA, CSA, G. Villanueva (NASA’s Goddard Space Flight Center), A. Pagan (STScI), L. Hustak (STScI)
On Twitter, Villanueva said it was “shocking” to detect a water plume that large.
The observed outgassing rate was at 300 liters a second, which could fill an Olympic-sized swimming pool in just a couple of hours. The researchers added that intriguingly, this outgassing rate is similar to the amount derived from closeup observations with Cassini 15 years ago. This suggests that the amount of eruption from Enceladus has been relatively stable over decadal timescales.
For such a tiny moon, Enceladus is incredibly intriguing. Its distance from the Sun means the moon should be a giant ice ball, but instead it is one of the most hydrothermally active places in our Solar System. Under its icy crust lies a global ocean of salty water and volcano-like jets spew water vapor from just under the moon’s surface. Tidal heating from Saturn and other moons likely create an internal environment warm enough to host liquid water.
The team said that the uniqueness of JWST for exploring Enceladus was most evident when probing with unparalleled sensitivity the narrow infrared emissions emanating from the plume.
The Integral Field Unit (IFU) aboard the NIRSpec (Near-Infrared Spectrograph) instrument allowed researchers to detect many spectral features characteristic of water originating from the plume as well as from within a torus around Enceladus. In this spectrum, the white lines are the data from Webb, and the best-fit models for water emission are overlaid in different colors –purple for the plume, green for the area central to the moon itself, and red for the surrounding torus. Credit: NASA, ESA, CSA, STScI, L. Hustak (STScI), G. Villanueva (NASA’s Goddard Space Flight Center)
They searched for CO2, CO, CH4, C2H6 and CH3OH molecular emissions across the plume, but none were detected – just water vapor. However, the researchers were also able to observe directly how the moon’s water vapor plumes feeds the water supply for the entire system of Saturn and its rings. A donut-shaped torus of water is located within Saturn’s E-ring. The team said as Enceladus orbits rapidly around Saturn (with a period of only 1.37 Earth days), the ejected water vapor is spread along and around its orbit, forming the large water ring around Saturn.
By analyzing the data from JWST, the astronomers determined that roughly 30 percent of the water stays within this torus, and the other 70 percent escapes to supply the rest of the Saturnian system with water.
The JWST observations were part of the Solar System Guaranteed-Time-Observations (GTO) program, and were performed on November 9, 2022. The observations focused on Enceladus’ trailing hemisphere.
The Cassini mission’s observations revealed just how intriguing this moon is. In its first flyby, the spacecraft passed within 1,167 kilometers (725 miles) of the moon and a magnetometer detected a ‘bending’ of Saturn’s magnetic field in the space above Enceladus, almost like it had an atmosphere. In subsequent flybys, Cassini found what appeared to be a surprisingly dense cloud of water vapor and ice grains over the south pole, as well as fissures and fractures on the surface, which were dubbed ‘tiger stripes.’ These fissures were found to be warmer than the rest of the moon, so clearly something was going on there. Enceladus was no dead little world. It was active.
ESA and NASA say that in the coming years Webb will serve as the primary tool for observing Enceladus, and discoveries from Webb will help inform future Solar System satellite missions that will look to explore the depth of the subsurface ocean, how thick the ice crust is, and more.
If you’ve ever played Kerbal Space Program, you know how difficult it can be to get your spacecraft into the orbit you want. It’s even more difficult in real life. This is why it’s pretty impressive to see a proposal to study all of Saturn’s large inner moons in one go.
At a broad level, orbits are pretty simple. Planets and moons are basically ellipses. Once set into motion, spacecraft generally follow an elliptical or parabolic path, so it’s just a matter of lining up your spacecraft’s orbit with your destination and point of origin. You can do the calculations by hand if you know the math. Several early science fiction authors such as Robert Heinlein and Hal Clement did just that to ensure their space-travel stories were accurate.
But these types of simple calculations only determine fly-by paths, and they don’t take into account energy-saving tricks such as gravitational slingshots. The energy demands of getting a spacecraft to the outer solar system are so high that even the early missions to Jupiter and beyond relied on gravitational assists, which are difficult to calculate. And as we’ve seen from missions such as Juno and Cassini, it’s extremely useful to put a spacecraft in orbit around a planet so we have plenty of time to gather data. Ideally, for something such as a mission to Saturn, you’d want to reach the ringed planet in a reasonable time, then move into a series of orbits around the planet that makes several flybys of interesting moons, but that’s a big ask for a mission.
One of the challenges has to do with orbital energy. To reach Saturn quickly, you’d need to build up a great deal of speed. To get into orbit you have to take much of that speed away. This is particularly challenging if you want your spacecraft to orbit deep in the planet’s gravitational well. For the Cassini mission, the team reached a compromise using orbits that dipped close to the inner moons of Saturn from time to time. This was fine because a main focus of Cassini was the moon Titan, which is relatively far away from Saturn.
Orbital transfer between two of Saturn’s moons, Dione and Tethys. Credit: Fantino, E., et al
For a return mission to Saturn, astronomers would really like to get a good view of Enceladus. We know it has plenty of liquid water, and it’s an excellent candidate for life. But it’s deep within Saturn’s gravitational well, with an orbital radius only one-fifth that of Titan. At the moment, the strongest proposed mission is the Enceladus Orbilander, which would orbit the moon for about 18 months. But this would prevent the mission from deeply studying other Saturnian moons.
This is where this new proposal comes in. Rather than simply focusing on Enceladus, why not spend time around all the major moons of Saturn? To achieve this, the team proposes a complex set of orbits that relies on an electric propulsion engine. Also known as an ion thruster, such an engine could provide a tiny amount of thrust over extended times. The idea is to gradually shift orbits rather than shifting orbits in a single go. These dynamic orbits are really difficult to calculate, but they are extremely energy efficient and can be adjusted over time.
In their proposal, the team shows how electric propulsion could power a mission to visit not only Enceladus and Titan, but also Dione, Tethys, and Mimas. Depending on priorities, the mission could be put in orbit around each of these moons, making several close approaches to each world. Depending on the length of the mission, the electric propulsion could be either solar or nuclear powered.
This initial proposal is just a proof of concept, but it shows that the next mission to Saturn doesn’t have to choose between Either Enceladus or another moon. It’s possible to take a grand tour of the Saturnian system if only we can be steely-eyed about the orbital paths we choose.
Enigmatic North Korea may attempt to put a satellite in orbit, as early as this week.
Satellite spotters worldwide may have a new clandestine target to hunt for in orbit soon. The North Korean government announced possible plans this week to field another satellite into orbit by mid-July. This comes after a public visit by leader Kim Jong Un and his daughter Kim Ju-Ae to a DPRK National Aerospace Development Administration (NADA) aerospace facility earlier this month. Kim “approved the future action plan of the preparatory committee,” according the Korean Central News Agency, and said that the satellite was “an urgent requirement of the prevailing security environment of the country.”
Kim Jong Un tours the NADA satellite facility. Credit: KCNA
This would suggest the payload in question is a military reconnaissance or spy satellite. Recent Navigational Warnings published alerting Japan and surrounding nations to a launch from the Sohae Space Center site out southward across the Yellow Sea also seem to bear this out. The launch window in the warnings run from May 30th to June 10th.
The blurred out top of the North Korean satellite shown in the state visit, along with possible sensors. Credit: KCNA w/annotations by Marco Langbroek
A Secretive Space Program
North Korea’s past satellite launches and ambitions to join the community of space-faring nations started on September 4th, 1998, with the failed launch of Kwangmyongsong-1. Four attempts later, and North Korea was finally successful in reaching orbit with Kwangmyongsong-3 Unit 2 (a backup spare for Kwangmyongsong-3) on December 12th, 2012. Kwangmyongsong-4 also reached orbit in 2016. If successful, this launch would most likely be designated Kwangmyongsong-5.
‘Kwangmyongsong’ means ‘bright star’ in Korean, alluding to a reference in a poem written by the late North Korean leader Kim Il Sung. In the past, North Korea used a 3-stage Unha rocket to reach orbit.
Possible side sensors (?) seen in the recent state visit. KCNA w/annotations by Marco Langbroek.
This comes after South Korea’s successful launch from the Naro Space Center last week, with the 3-stage Nuri/KSLV-2 rocket and the commercial NEXTSat-2 mission, so there’s probably more than a little ‘space race redux’ going on between the two rival nations on the peninsula.
Spying on Spysats
The warnings suggest two possible launch trajectories. One would see the satellite head into a 78 degree orbital inclination, while a second would head into a more complex ‘polar’ sun-synchronous orbit. This requires more fuel to reach and an additional ‘dogleg’ maneuver to attain. Sun-synchronous orbit allows for multiple imaging passes of a site with the same shadow angle, ideal for Earth-observing (and military reconnaissance) satellites.
“There is a lot unclear still,” Satellite tracker Dr. Marco Langbroek told Universe Today. “I think both insertion into a 97.2 degree inclined ~500 km Sun-synchronous orbit, or a ~78 degree non-synchronous orbit are possible. There is some expectation of something ‘new,’ as N-Korea has alluded to that.”
Potential launch tracks (blue) based on current navigational warnings, versus the last satellite launch by North Korea (blue). Credit: Marco Langbroek
Langbroek also notes that the Sun-synchronous path would also send the launch right over Taiwan immediately after launch, a risky move considering the current political climate. A traditional west-east inclination path could, however, allow the Hermit Kingdom to put something more substantial into orbit.
Watching the (Clandestine) Skies
Sleuthing out spysats in orbit is always fun to do, and is an important service carried out by satellite watchers worldwide. Often, backyard observers are the first to confirm or refute claims when classified missions are in orbit. Though U.S. Space Command’s Combined Space Operations Center (CSpOC) Space-Track (the central clearing house for assigning tracking IDs and orbital elements post launch) generally doesn’t post information on classified payloads fielded by the U.S. and allied states, it’ll most likely post elements for any North Korean launch placed in orbit.
Heavens-Above still lists Kwangmyongsong-3 Unit 2 on their front page as COSPAR ID 2012-072A. If the satellite is tiny (like previous attempts, which were only about +7th magnitude at their brightest) it may well fall below naked eye visibility; your best chance then is to note when it passes near a bright star (Heavens-Above can chart local passes versus star-fields) sit back and watch the assigned field with binoculars, and wait for the satellite to pass by.
We’ll note on Mastodon and Twitter if the launch occurs, and post sighting opportunities worldwide as the hunt for the satellite in Low-Earth Orbit unfolds.
