Astronomers possibly solve the mystery of how the enormous Oort cloud, with over 100 billion comet-like objects, was formed.
- The Oort cloud is a gigantic "cloud" at the edge of the solar system, about 3,000 times the distance between the Earth and the Sun.
- Astronomers used computer simulations to reconstruct the first 100 million years of the Oort cloud's existence.
- The Oort cloud may consist of the "leftovers" from the solar system's formation
Astronomers have calculated the first 100 million years of the history of the gigantic Oort cloud – a theoretical entity that contains 100 billion or so comet-like objects and forms a giant spherical shell around the sun and the rest of the solar system. NASA describes it as "a big, thick-walled bubble made of icy pieces of space debris the sizes of mountains and sometimes larger."
The Oort cloud was named after Dutch astronomer Jan Hendrik Oort, who discovered it in the 1950s. He was looking to understand why some comets in the solar system have elongated orbits. Scientists now believe the Oort Cloud is the source of most such comets.
The cloud is believed to be extremely far from the sun, many times more distant than the outer reaches of the Kuiper belt, the area of the solar system past the orbit of Neptune that contains comets, asteroids, and small icy space bodies as well as the dwarf planet Pluto.
According to NASA, the inner edge of the Oort cloud is likely between 2,000 and 5,000 AU (astronomical units or Earth-Sun distances) from the sun. The outer edge is probably 10,000 to 100,000 AU from the sun. By comparison, the Kuiper belt is about 30 to 50 AU away from the sun.
Oort cloud: the leftovers of the solar system
In a preprint article (accepted for publication in Astronomy & Astrophysics), a team of astronomers from Leiden University in the Netherlands describe how they used sophisticated computer simulations to determine how the Oort cloud formed.
They took a new approach by starting from separate events that might have happened in the early days of the universe and connecting them together. This allowed them to map out the full history of the origins of the gargantuan cloud.
As explained in their press release, the scientists used the ending calculations from one event as the starting calculation for the next event.
Protoplanetary disk.Credit: Pat Rawlings / NASA
Their simulations confirmed that the Oort cloud is what remained of the protoplanetary disk of gas and debris from which it is believed our solar system formed about 4.6 billion years ago.
The cloud has comet-like objects made of debris from two places in the universe. Some of them are from nearby parts of the solar system, such as asteroids expelled by giant planets like Jupiter. Another group of objects in the Oort cloud comes from a thousand or so stars that were around when our sun was born, eventually drifting apart from each other.
"With our new calculations, we show that the Oort cloud arose from a kind of cosmic conspiracy," said astronomer and simulation expert Simon Portegies Zwart from Leiden University, adding, "in which nearby stars, planets, and the Milky Way all play their part. Each of the individual processes alone would not be able to explain the Oort cloud. You really need the interplay and the right choreography of all the processes together."
He added that the Oort cloud was ultimately produced by "the interplay and the right choreography of all the processes together."
As it is so far away, humanity hasn't yet built a telescope powerful enough to see the small, faint objects of the Oort cloud directly. By some estimates, it would take telescopes that are 100 billion times better than what we currently have to see into the cloud. Even the new James Webb Telescope that's launching later in 2021 is unlikely to be able to see that far, confirmed Nobel laureate (and James Webb Telescope scientist) Dr. John Mather.
It would also take humanity a long time to reach the Oort cloud. As NASA estimated, even if you consider that the Voyager 1 probe can cover about a million miles every day, it would take it about 300 years to reach the inner edge of the Oort Cloud. And to get all the way through, it would likely require another 30,000 years.
The helicopter's sixth mission almost went down in disaster.
- The Ingenuity Mars Helicopter was out on a photo-taking mission when it started to act strangely.
- It kept changing its speed and tipping back and forth.
- A single error threw its entire navigation system into confusion.
Something went wrong on the Ingenuity Mars Helicopter's sixth flight. Not to worry, though: the copter is fine. The story of what went wrong and why it's okay now reminds us once again just how impressively smart space engineers have to be and usually are.
An image taken by the helicopter during its sixth missionCredit: NASA / JPL-Caltech
The helicopter was sent aloft to take stereo images of a region of interest. The plan was for it to ascend to a height of ten meters and then travel at a speed of four meters per second for 150 meters to the southwest, capturing images as it flew. Next, it was to travel 15 meters to the south with its camera facing westward, and then finally 50 meters to the northeast where it was to land.
At the end of the mission's first leg, however, telemetry revealed that the helicopter had begun adjusting its velocity and repeatedly tilting backward and forward. It kept on with this strange behavior before successfully landing at the end of the mission's third leg.
How the helicopter knows where it is
Credit: NASA / JPL-Caltech
Here's how things normally work.
The helicopter's navigation system has two parts. The first is an onboard inertial measurement unit (IMU). This device keeps track of the helicopter's acceleration and rotation. It monitors these aspects of its motion 500 times per second, allowing the craft to estimate where it is, how fast it's traveling, and its attitude. (IMUs also feature prominently in the navigation systems of autonomous cars back here on Earth.)
However, this is just an estimate, and since small errors build up over time, the IMU alone is not enough to keep the helicopter on course. A second system confirms the IMU estimate or alerts the craft that something has gone wrong.
This system involves a downward-pointing camera that takes time-stamped images of the ground beneath the helicopter during most of a flight. It fires each image directly to the craft's navigation system, where:
- The copter makes note of the timestamp to know when the image was captured.
- An algorithm predicts what the image should be based on the last image it received and the time that's elapsed since that first image was taken. (The system recognizes colors and topographical features such as sand ripples and rocks.)
- The algorithm examines the newest image for the predicted features.
- If it doesn't see what it expects — in other words, there's some kind of discontinuity — it corrects its IMU estimates of the craft's position, velocity, and altitude and makes adjustments accordingly.
This all happens incredibly quickly — the down-facing camera takes 30 images per second.
What went wrong
Apparently, for unknown reasons, about 54 seconds into the flight, a glitch occurred in the system responsible for transferring the down-facing images to the navigation system, and one single image got lost along the way. This had the effect of throwing the timestamp of all of the subsequent images off.
For the rest of the flight, the Ingenuity Mars Helicopter was unsure where it was. Its weird behavior was a frantic — not really, it's a machine — attempt to respond as the discrepancy compounded over time.
Anticipating such surprises, the designers built into the algorithm a stability margin that allows the craft to remain relatively stable even if it encounters a significant number of errors, as happened here. As chief pilot of the craft Håvard Grip puts it: "This built-in margin was not fully needed in Ingenuity's previous flights, because the vehicle's behavior was in-family with our expectations, but this margin came to the rescue in Flight Six."
The system also had one final trick up its sleeve that allowed the confused craft to land safely. When a craft is close to the Martian surface, either landing or taking off, a lot of dust gets kicked up. Concerned that flying dust would create problems for the algorithm, the craft is programmed to ignore the images once the craft's altitude is one meter or less.
In this case, that meant that the helicopter set aside the confused image system during landing, relying solely on its IMU. We'll give Grip the final word:
"In a very real sense, Ingenuity muscled through the situation, and while the flight uncovered a timing vulnerability that will now have to be addressed, it also confirmed the robustness of the system in multiple ways."
Determining if the universe is infinite pushes the limits of our knowledge.
- The size and shape of the universe has yet to be resolved.
- The size of the universe is linked to understanding its shape and the limits of our observations.
- New studies and going deeper into space will help us answer the question: "Is the universe infinite?"
Does the universe keep extending endlessly into the abyss of space, or does it have a defined end?
Of all the scientific questions you may ponder, "Is the universe infinite?" is one of the hardest. It is impossible to answer with certainty at this point. Scientists have proposed both possibilities, and each has its own supporters and detractors. Determining whether the universe has some kind of boundary ultimately depends on figuring out its shape, size, and how much of it we can actually observe.
Is the universe infinite? And what shape is it?
The shape of the universe would have a lot to do with its size. Cosmologists have theorized that a universe would likely come in one of three possible shapes, which are dependent on the curvature of space. As described in Discover Magazine, the universe could be flat, having no curvature, but spatially infinite. Or it could be open, shaped like a saddle (with negative curvature) and also infinite. Or it could be closed, look like a sphere, and be spatially finite.
So which shape really is it? Nobel Prize-winning cosmologist John Mather of NASA's Goddard Space Flight Center, also the chief scientist for the James Webb Space Telescope, maintains that recent observations of cosmic microwave background radiation (CMB) remaining from the time of the Big Bang support the idea of the universe being flat, without any curvature (at least to the limit of what is observable).
"The universe is flat like an [endless] sheet of paper," shared Mather. "According to this, you could continue infinitely far in any direction and the universe would be just the same, more or less."
The geometry of the universe is determined by the density parameter Ω within cosmological Friedmann Equations.Credit: NASA / WMAP Science Team
Measuring the size of the universe
Current calculations say that the observable universe extends 46.5 billion light-years in every direction, making its diameter 93 billion light-years across.
Consider this: The age of the universe is 13.8 billion years, which means it took 13.8 billion light-years for the light from the farthest edge of the observable universe to reach us. But in that time, the universe has continued to expand at a rate that appears to be speeding up. Now, the edge of the observable universe has moved and is 46.5 billion light-years away.
These gargantuan numbers are almost impossible to grasp. How did scientists come up with them?
As shared in an interview with BBC by Caitlin Casey, an astronomer at the University of Texas at Austin, scientists use a variety of tools and methods called "the cosmic distance ladder" to estimate distances between objects in the vastness of space. They start out with distances they can actually measure directly, like through bouncing radio waves off nearby bodies in the solar system, noting the time required for the waves to come back to Earth.
For distances that are harder to gauge, like those for galaxies at the boundary of the universe, astronomers utilize inferences based on calculations and observational evidence.
For instance, they employ "parallax measurement" that relies on measuring a star's shift in relation to objects in its background, as well as "main sequence fitting," which takes advantage of our knowledge of stellar evolution. (Stars evolve over time, changing size and brightness.) Knowledge of how brightness is connected to distance is paramount in determining the location of distant objects. So is analysis of redshift, which involves measuring changes in the wavelengths of light coming from faraway galaxies.
What about the unobservable universe?
If you notice, the numbers above pertain to the observable universe, the ball-like part of the universe that can be somehow seen from Earth or detected using our space telescopes and probes. But what about parts of the universe we cannot see? Some portions of the universe may be just too far away for the light emitted after the Big Bang to have had sufficient time to reach us here on Earth.
One study from a group of UK scientists estimated that if you take that into account, the actual size of the universe could be at least 250 times larger. They found that if you refer to space in terms of a so-called Hubble volume, which is similar to the volume of space in the visible universe, a closed and finite universe would contain roughly 250 to 400 Hubble volumes.
Another possibility entertained by scientists like Nobel Prize-winning Roger Penrose is that the Big Bang was just one of the periods of cosmic regeneration that our universe has experienced. There could have been multiple Big Bangs, followed by Big Crunches, periods in which a universe would stop expanding and collapse upon itself.
If all we know about the universe is derived from how it expands after the latest Big Bang, the questions if the universe is infinite or what size it may be are almost moot. As is often the case, more study and confirmation of our theories is needed.
Is there an edge to the universe?
Whether we have a finite universe or an infinite universe like an ever-expanding bubble, does it still have an "edge"? Is there some place you can go and say, "Yep, this is the end of the universe"? The simple answer is likely no.
As explained to LiveScience by Robert McNees, an associate professor of physics at Loyola University Chicago, the universe is isotropic. That means it follows the so-called "cosmological principle" and has the same properties and follows the same laws of physics in all directions.
If that is so, then the universe is much like the surface of a balloon. Imagine being an ant walking along a balloon. You wouldn't know there's an edge to it if you kept walking forward. You'd likely come back to where you started eventually, but the journey around and around could keep going without end.
If someone were to blow more air into the balloon as you keep walking along it, you'd experience some parts of the balloon moving farther away from you. Still, you'd be no closer to finding the balloon's edge.
Much like the ants, we're unlikely to get to the end of the universe. But we may still be able to answer one day "is the universe infinite" or does it have an actual boundary?
A new AI-generated map of dark matter shows previously undiscovered filamentary structures connecting galaxies.
- Scientists use artificial intelligence to produce a new map of dark matter in the local universe.
- The map's precision may lead to new insights into dark matter and the future of our universe.
- The map contains previously unknown "hidden bridges" that link galaxies.
A new map derived with the help of artificial intelligence reveals previously unknown "bridges" linking galaxies in the local universe. The bridges are in the form of filamentary structures. The scientists hope their map, published along with their paper in the Astrophysical Journal, can provide fresh insights into dark matter and the history of our universe.
While dark matter is an accepted notion, thought to make up 80 percent of all the matter in the universe, it has been hard to find. Scientists have, however, inferred much about the existence and behavior of dark matter by observing its gravitational influence on other space objects.
The universe has a dark matter skeleton
Cosmologists believe that dark matter serves as the filamentary skeleton of the cosmic web, which in turn, makes up the large-scale structure of the universe that partially controls the motion of galaxies and other cosmic systems.
While it's not proven possible yet to directly measure how dark matter is distributed in our local universe, the international team behind the research used AI to create a new map. The "local universe," which includes us, is an area about 1 billion light-years in radius where galaxies and related space objects are "essentially frozen in their present day configurations" and cosmic evolution effects are negligible, the astronomers explain.
"Ironically, it's easier to study the distribution of dark matter much further away because it reflects the very distant past, which is much less complex," said one of the study's authors, Donghui Jeong, associate professor of astronomy and astrophysics at Penn State. "Over time, as the large-scale structure of the universe has grown, the complexity of the universe has increased, so it is inherently harder to make measurements about dark matter locally."
A map of dark matter within the local universe. Smaller filamentary features (yellow) act as hidden bridges between galaxies. Dark matter's gravitational influence on galaxies is indicated by black dots. Prominent features of the universe are shown by red dots and X marks the Milky Way. CREDIT: Hong et. al., Astrophysical Journal.
Creating a better dark matter map
Cosmic web maps created previously relied on simulating the 13.8-billion-year evolution of the universe from early stages to present day. Such efforts required a tremendous amount of computation and did not yet produce accurate representations of the local universe, leading researchers to devise a novel approach. For the new map, they focused on utilizing machine learning to create a model based on the distribution and motion of galaxies. This allowed them to estimate how dark matter is distributed.
The AI was trained on simulated galaxies similar to the Milky Way using Illustris-TNG — an ongoing series of simulations that features galaxies, dark matter, gasses, and other matter.
Jeong explained that if you feed specific information into the model, it can fill out the gaps, relying on what it has already processed. The scientists further confirmed the mapping by applying it to real local galaxy data from the Cosmicflows-3 catalog of distance information about nearly 18 thousand galaxies.
The resulting map features major structures in our local universe like the "local sheet," which contains the Milky Way. Nearby galaxies and the "local void" — a nearby region of empty space — are also represented. What's more, the map allowed researchers to spot new structures. In particular, they hope to study in greater depth the small filamentary structures they discovered that appear to link galaxies. Jeong called them "hidden bridges."
Jeong believes these filaments can provide insight into the future of our galaxy. One particular question of note is whether the Milky Way would eventually collide with the Andromeda galaxy.
"Because dark matter dominates the dynamics of the universe, it basically determines our fate," shared Jeong. "So we can ask a computer to evolve the map for billions of years to see what will happen in the local universe. And we can evolve the model back in time to understand the history of our cosmic neighborhood."
Further studies that include galaxy data from new astronomical surveys will be needed to perfect the map's accuracy.
Since 1957, the world's space agencies have been polluting the space above us with countless pieces of junk, threatening our technological infrastructure and ability to venture deeper into space.
- Space debris is any human-made object that's currently orbiting Earth.
- When space debris collides with other space debris, it can create thousands more pieces of junk, a dangerous phenomenon known as the Kessler syndrome.
- Radical solutions are being proposed to fix the problem, some of which just might work. (See the video embedded toward the end of the article.)
In 1957, the Soviet Union launched a human-made object into orbit for the first time. It marked the dawn of the Space Age. But when Sputnik 1's batteries died and the aluminum satellite began lifelessly orbiting the planet, it marked the end of another era: the billions of years during which space was pristine.
Today, the space above Earth is the world's "largest garbage dump," according to NASA. It's littered with 8,000 tons of human-made junk, called space debris, left by space agencies over the past six decades.
The U.S. now tracks more than 25,000 pieces of space junk. And that's only the debris that ground-based radar technologies can track. The U.S. Space Surveillance Network estimates there could be more than 170 million pieces of space debris currently orbiting Earth, with the majority being tiny fragments smaller than 1 mm.
Space debris: Trashing a planet
Space debris includes all human-made objects, big and small, that are orbiting Earth but no longer serve a useful function. A brief inventory of known space junk includes: a spatula, a glove, a mirror, a bag filled with astronaut tools, spent rocket stages, stray bolts, paint chips, defunct spacecraft, and about 3,000 dead satellites — all of which are orbiting Earth at speeds of roughly 18,000 m.p.h.
By allowing space debris to accumulate unchecked, we could be building a prison that keeps us stranded on Earth for centuries.
Most space junk is floating in low Earth orbit (LEO), the region of space within an altitude of about 100 to 1,200 miles. LEO is also where most of the world's 3,000 satellites operate, powering our telecommunications, GPS technologies, and military operations.
"Millions of pieces of orbital debris exist in low Earth orbit (LEO) — at least 26,000 the size of a softball or larger that could destroy a satellite on impact; over 500,000 the size of a marble big enough to cause damage to spacecraft or satellites; and over 100 million the size of a grain of salt that could puncture a spacesuit," wrote NASA's Office of Inspector General Office of Audits.
If LEO becomes polluted with too much space junk, it could become treacherous for spacecraft, threatening not only our modern technological infrastructure, but also humanity's ability to venture into space at all.
By allowing space debris to accumulate unchecked, we could be building a prison that keeps us stranded on Earth for centuries.
An outsized problem
Space debris of any size poses grave threats to spacecraft. But tiny, untrackable micro-debris presents an especially dreadful problem: A paint fragment chipped off a spacecraft might not seem dangerous, but it careens through space at nearly 10 times the speed of a bullet, packing enough energy to puncture an astronaut's suit, crack a window of the International Space Station, and potentially destroy satellites.
Impacts with space debris are common. During the Space Shuttle era, NASA replaced an average of one to two shuttle windows per mission "due to hypervelocity impacts (HVIs) from space debris." To be sure, some space debris are natural micrometeoroids. But much of it is human-made, like the fragment that struck the starboard payload bay radiator of the STS-115 flight in 2006.
"The debris penetrated both walls of the honeycomb structure, and the shock wave from the penetration created a crack in the rear surface of the radiator 6.8 mm long," NASA wrote. "Scanning electron microscopy and energy dispersive X-ray detection analysis of residual material around the hole and in the interior of the radiator shows that the impactor was a small fragment of circuit board material."
The European Space Agency notes that any fragment of space debris larger than a centimeter could shatter a spacecraft into pieces.
Impact chip on the ISSCredit ESA
To dodge space junk, the International Space Station (ISS) has to conduct "avoidance maneuvers" a couple times every year. In 2014, for example, flight controllers decided to raise the ISS's altitude by half a mile to avoid collision with part of an old European rocket in its orbital path.
NASA has strict guidelines for how it decides to perform these maneuvers.
"Debris avoidance maneuvers are planned when the probability of collision from a conjunction reaches limits set in the space shuttle and space station flight rules," NASA wrote. "If the probability of collision is greater than 1 in 100,000, a maneuver will be conducted if it will not result in significant impact to mission objectives. If it is greater than 1 in 10,000, a maneuver will be conducted unless it will result in additional risk to the crew."
These precautionary measures are becoming increasingly necessary. In 2020, the ISS had to move three times to avoid potential collisions. One of the latest close-calls came with such little warning that astronauts were instructed to take shelter in the Russian segment of the space station, in order to be closer to their Soyuz MS-16 spacecraft, which serves as an escape pod in case of an emergency.
The Kessler syndrome
The hazards of space debris grow exponentially over time. That's because of a problem that NASA scientist Donald J. Kessler outlined in 1978. The so-called Kessler syndrome states that as space becomes increasingly packed with spacecraft and debris, collisions become more likely. And because each collision would create more debris, it could trigger a chain reaction of collisions — potentially to the point where near-Earth space becomes a shrapnel field through which safe travel is impossible.
A paint fragment chipped off a spacecraft might not seem dangerous, but it careens through space at nearly 10 times the speed of a bullet, packing enough energy to puncture an astronaut's suit, crack a window of the International Space Station, and potentially destroy satellites.
The Kessler syndrome may already be playing out. Perhaps it began with the first known case of a spacecraft being severely damaged by artificial space debris, which occurred in 1996 when the French spy satellite Cerise was struck by a piece of an old European Ariane rocket. The collision tore off a 13-foot segment of the satellite.
The next major space debris incident occurred in 2007 when China conducted an anti-satellite missile test in which the nation destroyed one of its own weather satellites, triggering international criticism and creating more than 3,000 pieces of trackable space debris, most of which was still in orbit ten years after the explosion.
Then, in 2009, an unexpected collision between communications satellites — the active Iridium 33 and the defunct Russian Cosmos-2251 — produced at least 2,000 large fragments of space debris and as many as 200,000 smaller pieces, according to NASA. About half of all space debris currently orbiting Earth came from the Iridium-Cosmos collision and China's missile test.
There's more. Russia's BLITS satellite was spun out of its orbital path in 2013 after being struck by a piece of space debris suspected to have come from China's 2007 missile test; the European Space Agency's Copernicus Sentinel-1A satellite was struck by a tiny particle in 2016; and a window of the ISS was hit by a small fragment that same year.
As nations and private companies plan to send more satellites into orbit, collisions and impacts could soon become more common.
The promise and peril of satellite mega-constellations
Space organizations have recently begun launching satellites into low Earth orbit at an unprecedented pace. The goal is to create "mega-constellations" of satellites that provide high-quality internet access to virtually all parts of the planet.
Internet-providing satellites have existed for years, but they're typically expensive and provide slower service than land-based internet infrastructure. That's mainly because it can take a relatively long time for a signal to travel from the satellite to the user due to the high altitudes at which many of these satellites float above us in geostationary orbit.
China and companies like SpaceX, OneWeb, and Amazon aim to solve this problem by launching thousands of satellites into lower orbits in order to reduce signal latency, or the time it takes for the signal to travel to and from the satellite. But some space experts worry satellite mega-constellations could create more space debris.
"We face entirely new challenges as hundreds of satellites are launched every month now — more than we used to launch in a year," Thomas Schildknecht of the International Astronomical Union said at a European Space Agency conference in April. "The mega-constellations are producing huge risks of collisions. We need more stringent rules for traffic management in space and international mechanisms to ensure enforcement of the rules."
A 2017 study funded by the European Space Agency found that the deployment of satellite mega-constellations into low Earth orbit could increase the number of catastrophic collisions by 50 percent. Still, it remains unclear whether sending more satellites into space will necessarily cause more collisions.
SpaceX, for example, claims that Starlink satellites aren't at significant risk of collision because they're equipped with automated collision-avoidance propulsion systems. However, this system seemed to fail in 2019 when a Starlink satellite had a close call with a European science satellite named Aeolus. The company later said it had fixed the bug.
A batch of 60 Starlink test satellites stacked atop a Falcon 9 rocket.Credit SpaceX
Currently, there are no strict international rules governing the deployment and management of satellite mega-constellations. But there are some international efforts to curb space debris risks.
The most concerted effort is the Inter-Agency Space Debris Coordination Committee (IADC), a forum that comprises 13 of the world's space agencies, including those of the U.S., Russia, China, and Japan. The committee aims "to exchange information on space debris research activities between member space agencies, to facilitate opportunities for cooperation in space debris research, to review the progress of ongoing cooperative activities, and to identify debris mitigation options."
The IADC's Space Debris Mitigation Guidelines list three broad goals:
1. Preventing on-orbit break-ups
2. Removing spacecraft from the densely populated orbit regions when they reach the end of their mission
3. Limiting the objects released during normal operations
But even though the world's space agencies recognize the gravity of the space debris problem, they're reluctant to act because of an incentives-based dilemma.
Space debris: A classic tragedy of the commons
Space debris is everyone's problem, but no one entity is obligated to solve it. It's a tragedy of the commons — an economic scenario in which individuals with access to a shared and scarce resource (space) act in their own best interest (spend the least amount of money). Left unchecked, the shared resource is vulnerable to depletion or corruption.
For example, the U.S. by itself could develop a novel method for removing space debris, which, if successful, would benefit all organizations with assets in space. But the odds of this happening are slim because of a game-theoretical dilemma.
"[In space debris removal] each stakeholder has an incentive to delay its actions and wait for others to respond. This makes the space debris removal setting an interesting strategic dilemma. As all actors share the same environment, actions by one have a potential immediate and future impact on all others. This gives rise to a social dilemma in which the benefits of individual investment are shared by all while the costs are not. This encourages free-riders, who reap the benefits without paying the costs. However, if all involved parties reason this way, the resulting inaction may prove to be far worse for all involved. This is known in the game theory literature as the tragedy of the commons."
Similar to trying to curb climate change, there's no clear answer on how to best incentivize nations to mitigate space debris. (For what it's worth, the game theoretical model in the 2018 study found that a centralized solution — e.g., one where a single actor makes decisions on mitigating space debris, perhaps on behalf of a multinational coalition — is less costly than a decentralized solution.)
Although space organizations have been slow to act, many have been exploring ways to remove space junk from orbit and prevent new debris from forming.
Cleaning up space debris
Space organizations have proposed and experimented with many ways to remove debris from space. Although the techniques vary, most agree on strategy: get rid of the big stuff first.
That's because collisions involving large objects would create lots of new debris. So, removing big debris first would simultaneously clean up low Earth orbit and slow down the phenomenon of cascading collisions described by the Kessler syndrome.
To clean up low Earth orbit, space organizations have proposed using:
- Electrodynamic tethers: In 2017, the Japanese Aerospace Exploration Agency attempted to remove space debris by outfitting a cargo ship with an electrodynamic tether — essentially a fishing net made of stainless steel and aluminium. The craft then tried to "catch" space debris with the aim of dragging it into lower orbit, where it would eventually crash to Earth. The experiment failed.
- Ultra-thin nets: NASA's Innovative Advanced Concepts program has funded research for a project that would deploy extremely thin nets designed to wrap around space debris and drag them down to Earth's atmosphere.
- "Laser brooms": Since the 1990s, space researchers have proposed using ground-based lasers to strategically heat one side of a piece of space debris, which would change its orbit so that it re-enters Earth's atmosphere sooner. Because the laser systems would be based on Earth, this strategy could prove to be relatively affordable.
- Drag sails: As a relatively passive way to accelerate the de-orbit of space junk, NASA and other space organizations have been exploring the viability of attaching sails to space junk that would help guide debris back to Earth. These sails could either be packed within new satellites, to be deployed once the satellites are no longer useful, or attached to existing space junk.
Illustration of Brane Craft Phase II, which would use thin nets to capture space debris.Credit Siegfried Janson via NASA
But perhaps one of the most promising solutions for space debris is the ESA-funded ClearSpace-1 mission. Set to launch in 2025, ClearSpace-1 intends to be the first mission that successfully removes space debris from orbit. The goal is to launch a satellite into orbit and rendezvous with the upper stage of Europe's Vega launcher, which was left in space after a 2013 flight.
Once the satellite meets up with the debris, it will try to capture the junk with a robotic arm and then perform a controlled atmospheric reentry. The task will be challenging, in part because space junk tumbles as it flies above Earth, meaning the satellite will have to match its movements in order to safely capture it.
Freethink recently spoke to the ClearSpace-1 team to get a better understanding of the mission and its challenges.
But not all space debris removal strategies center on technology. A 2020 paper published in PNAS argued that imposing taxes on each satellite in orbit would be the most effective way to clean up space. Called "orbital use fees," the plan would charge space organizations an annual fee of roughly $235,000 per each satellite that's in orbit. The fee would, in theory, incentivize nations and companies to declutter space over time.
The main hurdle of orbital-use fees is getting all of the world's space organizations to agree to such a plan. If they do, it could help eliminate the tragedy of the commons aspect of space debris and potentially quadruple the value of the space industry by 2040.
"The costly buildup of debris and satellites in low-Earth orbit is fundamentally a problem of incentives — satellite operators currently lack the incentives to factor into their launch decisions the collision risks their satellites impose on other operators," the researchers wrote. "Our analysis suggests that correcting these incentives, via an OUF, could have substantial economic benefits to the satellite industry, and failing to do so could have substantial and escalating economic costs."
No matter the solution, cleaning up space debris will be a complex and expensive challenge that requires a coordinated, international effort. If the global community wants to maintain modern technological infrastructure and venture deeper into space, conducting business as usual isn't an option.
"Imagine how dangerous sailing the high seas would be if all the ships ever lost in history were still drifting on top of the water," Jan Wörner, European Space Agency (ESA) director general, said in a statement. "That is the current situation in orbit, and it cannot be allowed to continue."