SPACE
The European Space Agency has released images showing some of the final orbits experienced by a European satellite before its fiery reintroduction to Earth's atmosphere.
The school-bus-sized European Remote Sensing (ERS-2) satellite reentered our planet's atmosphere over the Pacific Ocean on Feb. 21, almost 29 years after its launch in April 1995.
The Tracking and Imaging Radar (TIRA) at the Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR in Germany observed the spacecraft in the days and hours ahead of its demise.
Space debris is becoming a bigger and more visible issue as time goes on. The combined radar images from TIRA — in which the color represents radar echo intensity, not temperature — notably show the buckling and bending of one of ERS-2's solar arrays occuring earlier than expected. This could have implications in terms of understanding how spacecraft behave as they reenter the atmosphere.
"When predicting a satellite's reentry trajectory, experts treat it as one rigid object until almost the very end. If ERS-2's solar array was loose and moving independently a day early, it may have caused the satellite to interact with the atmosphere in ways we did not expect," said an ESA statement.
Precise data regarding the reentry is now being assessed. Of particular interest is whether the buckling of the array was related to the slightly-later-than-predicted reentry sequence. The outcome could help improve forecasts of future natural reentries, according to ESA.
ERS-2 made a "natural," or uncontrolled, atmospheric reentry. Its fuel and batteries were depleted to lower the risk of debris-creating explosions in orbit; it was, rather, left to be pulled back to Earth by gravity and atmospheric influence. Space agencies and companies are now moving to controlled reentries, whereby operators deliberately deorbit a spacecraft over sparsely populated areas of Earth such as the South Pacific Ocean.
Originally posted on Space.com.
Russian satellite narrowly avoids collision with US spacecraft, and NASA could do nothing to stop it
By Ben Turner
NASA's TIMED satellite narrowly avoided hitting a defunct Russian satellite in the early hours of the morning
An active NASA spacecraft has survived a near-miss with a defunct Russian satellite in low Earth orbit.
NASA's Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission spacecraft and Russia's Cosmos 2221 satellite were due to closely pass each other at around 1:30 am EST on Feb. 28, at an altitude of about 373 miles (600 kilometers), according to a statement released by NASA just an hour before the near-miss.
Had the two non-maneuverable satellites collided, it wouldn't have just doomed NASA's satellite — which monitors the effects of the sun on the Earth's atmosphere — but could have also potentially started a catastrophic collision cascade with other objects in orbit.
"A collision could result in significant debris generation," NASA and the Department of Defense representatives wrote in the statement.
The potential scenario of a cascade of satellite debris in low Earth orbit (the area of space within 1,200 miles or 2,000 km of Earth) is called Kessler syndrome, and was popularly depicted in the 2013 film "Gravity."
Related: 5,000-pound European satellite burns up over Pacific Ocean after 30 years in orbit
Although a cascade of this kind has yet to happen, scientists are increasingly concerned that the growing number of satellites and space junk is making it more likely. Currently, the Department of Defense tracks the 30,000 largest debris pieces, but there are many more that are too small to be followed, according to NASA.
These smaller chunks are a threat both to satellites and the International Space Station, which in 2022 had to perform evasive maneuvers to dodge the junk generated by a Russian anti-satellite test.
Scientists are currently working on ways to fix Earth's space junk problem. For example, a team of Australian scientists proposed removing smaller junk from space by blasting it with a laser, while the European Space Agency (ESA) plans to launch a four-armed robot to grab individual items of space junk.
The ESA is hoping to use the mission, scheduled for 2025, as a test for a much wider-reaching operation performed by a fleet of robot cleaners.
ESA's director general Jan Wörner has also called for new rules to make companies and agencies that launch satellites responsible for tidying up their litter.
US, Russian satellites may collide 600 km above Earth today, NASA on guard. Details here
NASA said a ‘potential collision’ is expected between the Thermosphere Ionosphere Mesosphere Energetics and Dynamics mission spacecraft and the Russian Cosmos 2221 satellite about 600 km above the earth on February 28 which could result in significant debris generation.A representational image. A collision of two spacecraft at an altitude of 600 km could lead to the generation of significant debris, says Nasa.
The National Aeronautics and Space Administration (NASA) on Wednesday said a ‘potential collision’ is expected between two satellites one, from the US and the other from Russia, about 600 km above the earth on February 28 which could result in significant debris generation.
The two satellites on collision course are Nasa’s Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission spacecraft and the Russian Cosmos 2221 satellite.
“The two non-maneuverable orbiting spacecraft are expected to make their closest pass at about 1:30 am EST on Wednesday, Feb. 28, at an altitude of about 373 miles (600 km)," NASA said in a statement.
The US Department of Defense is monitoring the situation, the space agency added.
“Although the spacecraft are expected to miss each other, a collision could result in significant debris generation. NASA and the Department of Defense will continue to monitor the situation," NASA said.
A collision of two spacecraft at an altitude of 600 km could lead to the generation of significant debris, posing additional risks to other satellites and spacecraft in similar orbits, experts said.
TIMED mission spacecraft
NASA’s Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission spacecraft (launched on December 7, 2001) plays a crucial role in the understanding of Earth's upper atmosphere. The TIMED mission studies the influence of the Sun and human activity on Earth’s mesosphere and lower thermosphere/ionosphere.
National Science Day 2024: Why is it celebrated on February 28?
The region is a gateway between Earth and space, where the Sun’s energy is first deposited into Earth’s environment making the TIMED mission vital for understanding atmospheric dynamics.
Developed in part by Johns Hopkins APL, the mission’s unrivalled 20-year dataset has provided crucial insights about space weather, Earth’s climate and the evolution of planetary atmospheres.
Cosmos 2221
Russian satellite Cosmos 2221 was launched in 1992 for surveillance and other military purposes. Cosmos 2221 was a Russian ELINT (Electronic and Signals Intelligence) satellite launched from the Plesetsk cosmodrome.
Preparing to Meet a Metal-Rich Asteroid
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: AGU Advances
The Psyche spacecraft launched on 13 October 2023 and is on its way to visit its prime target, asteroid 16 Psyche. The target was originally selected because asteroid Psyche was thought to represent a fragment of a metallic core, left behind when a differentiated planetesimal was broken apart. Being able to investigate such a body, and to compare it with the small metallic fragments – iron meteorites – that we can analyze in the laboratory, made for a compelling discovery mission proposal.
In a new commentary, Dibb et al. [2024] summarize the capabilities of the Psyche spacecraft and the science questions that they hope it will answer. They also provide the most up-to-date thinking on Psyche’s composition, which is ambiguous. It now seems unlikely to be a purely metallic body, but a comprehensive answer will have to await spacecraft Psyche’s arrival, in August 2029.
Citation: Dibb, S. D., Asphaug, E., Bell, J. F., Binzel, R. P., Bottke, W. F., Cambioni, S., et al. (2024). A post-launch summary of the science of NASA’s Psyche mission. AGU Advances, 5, e2023AV001077. https://doi.org/10.1029/2023AV001077
—Francis Nimmo, Editor, AGU Advance
Toppled Moon Lander Sends Back More Images, With Only Hours Left Until It Dies
CAPE CANAVERAL, Fla.—A moon lander that ended up on its side managed to beam back more pictures, with only hours remaining before it dies.
Intuitive Machines posted new photos of the moon’s unexplored south polar region Tuesday.
The company’s lander, Odysseus, captured the shots last Thursday shortly before making the first U.S. touchdown on the moon in more than 50 years. Odysseus landed on its side, hampering communication and power generation.
Once sunlight can no longer reach the lander’s solar panels, operations will end. Intuitive Machines expects that to happen sometime between Tuesday afternoon and early Wednesday. The mission, part of NASA’s effort to boost the lunar economy, was supposed to last until at least Thursday, when lunar nighttime sets in. NASA has six experiments on board.
Intuitive Machines is the first private business to land a spacecraft on the moon without crashing. Another U.S. company launched its own lunar lander last month, but a fuel leak doomed the mission and the craft came crashing back to Earth.
By Marcia Dun
'Mathematically perfect' star system being investigated for potential alien technology
By Sharmila Kuthunur published 1 day ago
A distant star system housing 6 planets that move in 'mathematically perfect' orbits has ignited a search for possible alien techno signatures.
Late last year, astronomers discovered a fascinating star system only 100 light-years away from us. Its six sub-Neptune planets circle very close to their host star in mathematically perfect orbits, piquing the interest of scientists searching for alien technology, or technosignatures, which they argue would offer compelling evidence of advanced life beyond Earth.
To be clear, no such evidence was found in the system, dubbed HD 110067. However, the researchers say they're not done looking yet. HD 11067 remains an interesting target for similar observations in the future.
In our own tiny pocket of the cosmos, radio waves from satellites and telescopes beaming out in the plane of our solar system, meaning that if somebody outside our solar system watched Earth cross the face of our sun, they'd maybe be able to pick up a signal that coincides with the planet's transit.
HD 110067 is viewed edge on from Earth, so we are seeing the six planets in the plane of their system — a view that gives us an excellent chance of picking up such a signal if there exists one, study co-author Steve Croft, a radio astronomer working with the life-searching Breakthrough Listen program at the University of California, Berkeley, told Live Science's sister site Space.com.
"Our technology in our own solar system has spread outside the habitable zone," Croft said. So technology-friendly civilization in HD 110067, if any, may have communication relays set up on multiple planets in the system, he said. "Even if it is a negative result, that still tells us something."
Related: What's the best evidence we've found for alien life?
When HD 110067's discovery was announced, Croft and his team used the world's largest fully steerable telescope, the Green Bank Telescope (GBT) in West Virginia, and searched the system for signs of alien technology. The researchers looked for signals that were continuously present when the telescope was pointed at the system and absent when directed away, the smoking gun of technosignatures local to HD 110067.
But such signals are difficult to distinguish from natural sources of radio waves and humankind's own technological signals, such as radio waves beaming from cell phones connected to Wi-Fi, SpaceX's Starlink satellite network in low Earth orbit. This creates a haystack of signals in which researchers look for a needle of a potential extraterrestrial signal, said Croft.
"I should add we don't know if there are needles in the haystack," he said. "We don't really know what the needles look like."
Despite this lack of sufficient knowledge of what alien technology looks like, the team employed a few techniques to ensure a detected signal is not local interference. For instance, if one were to build a transmitter in the hopes that somebody else would pick it up, that transmitter would pump a lot of energy into a narrow range of frequencies. Natural astrophysical phenomena, by contrast, beam radio waves across a much broader range.
Signals from such a transmitter placed on a planet spinning around a foreign star would drift in time when observed from Earth, "the same as when an ambulance goes past you, the sound of it shifts from very high to very low," study lead author Carmen Choza, an assistant researcher at the Search for Extraterrestrial Intelligence (SETI) Institute in California, told Space.com.
The search ultimately did not detect a technological signal — however, the results do not eliminate the existence of technosignatures in HD 110067, Croft said, but rather tell us that no signal was beamed in our direction at the time of the observations.
Meanwhile, the discovery team is refining the radii of the six detected planets using the European Space Agency's CHEOPS space telescope, and the planets' masses using HARPS-N and CARMENES instruments in Spain, Rafael Luque of the University of Chicago told Space.com.
Accurate data on sizes and masses of the planets would shed more light onto the system's chemical makeup. Using that information, it may be possible to somewhat "reverse engineer" the evolution of the system and its planets to learn their formation mechanisms, the team had shared late last year.
Scientists have long been searching for life outside our solar system in hopes of learning our place in the universe, by trying to answer one question that's being pondered over for thousands of years, "Are we alone?"
"Sometimes people ask me, 'what are your chances of success in the next 10 years?'" Croft said. "My answer to that is, "well, I don't know, but they are better than they were in the last 10 years because our searches are getting powerful all the time."
Croft echoed the words of SETI pioneer Jill Tarter: "We reserve the right to get smarter."
This research is described in a paper published last month in the journal Research Notes of the AAS.
Originally posted on Space.com.
A black hole discovery could force us to rethink how galaxies came to be
Peering deep into the infancy of the universe, the European Southern Observatory's Very Large Telescope (VLT) recently confirmed the discovery of the brightest and fastest growing quasar. Quasars are luminous objects in the night sky powered by gas falling into a large black hole at the center of a galaxy.
The discovery of this record-breaking object was fascinating enough. But another crucial aspect to the announcement is that it raises big questions about galaxy formation in the early universe. In particular, it remains puzzling how this quasar, which existed less than two billion years after the Big Bang, could have grown so large so quickly. Probing this conundrum could even lead to a rethink of how galaxies came to be.
Black holes, the densest objects in the universe, are given this name because their gravitational pull is so incredibly strong that not even light can escape their grasp. How then, can a black hole be the origin of such an intense light source?
Well, in some galaxies, where the black hole is sufficiently large, matter is being drawn in at a ferociously high rate. As it spirals in, violent collisions between gases, dust, and stars result in the emission of huge amounts of light energy. The bigger the black hole, the more violent the collisions and the more light is emitted.
The quasar that was the subject of the latest study, known as J0529-4351, has a mass equivalent to 17 billion suns and is incredibly large. There is a spiraling disk of matter spanning a width of seven light years at the center of the galaxy and the black hole is growing by accreting (accumulating) this matter. The disk's width is comparable to the distance between Earth and the next nearest star system, Alpha Centauri.
Hiding in plain sight
The black hole is growing rapidly by consuming a record-breaking amount of mass, equivalent to one sun each day. This intense accretion of matter releases an amount of radiative energy that's equivalent to a quadrillion (thousand trillion) suns.
This raises the question of why an object so bright has only just been identified in the night sky, despite decades of astronomical observations. It turns out that this sneaky quasar had been hiding in plain sight.
Despite its astonishing luminosity, J0529-4351 is very distant, meaning that it seamlessly blends in among a sea of dimmer stars that lie much closer to Earth. In fact, this quasar is so far away that the light it emits takes a whopping 12 billion years to reach us here on Earth.
The age of the universe is around 13.7 billion years. So this quasar existed just 1.7 billion years after the Big Bang, at the beginning of the universe.
The universe's expansion following the Big Bang is what permits us to measure the distance to, and therefore the age of, this quasar. A long-known simple formula called Hubble's law, states that knowing the velocity that an object is moving away from us allows us to calculate how far away it is.
The collisions that occur as matter spirals into this quasar's black hole raise it to scorching temperatures of 10,000°C. Under these conditions, the atoms in the system emit a characteristic spectrum of light.
These discrete frequencies of light form a sort of barcode that astronomers can use to identify the elemental compositions of objects in the night sky. As an object that's emitting light moves away from us, the frequency of that observed light undergoes a shift, much like how the sound frequency of an ambulance siren shifts depending on whether it is driving towards or away from you.
This shift seen in astronomical objects is known as redshift. This, along with Hubble's Law, has permitted both the age and the distance (both these properties are linked in cosmology) of J0529-4351 to be confirmed.
This bright beacon from the early universe has raised an important question that is baffling astronomers: how could this black hole, in such a relatively short period of time, grow so fast into such a massive object? Under well accepted models of the early universe, it should have taken longer for it to grow to this size.
What's more, by tuning the artificial intelligence (AI) models used to scan telescope data for these unusual objects, more could still be found in the coming years. If they resemble J0529-4351, physicists would need to seriously rethink their models of the early universe and galaxy formation
The fastest-growing black hole ever observed will be the perfect target for a system called Gravity+, an upcoming upgrade to an instrument on the Very Large Telescope called an interferometer. This interferometer is an ingenious way of combining data from the four separate telescopes that actually make up the VLT.
Gravity+ is designed to accurately measure the rotational speed and mass of black holes directly, especially those that lie far away from the Earth.
Furthermore, the European Southern Observatory's's Extremely Large Telescope, a 39-meter diameter reflecting telescope, is currently under construction in the Chilean Atacama Desert. This is designed for detecting the optical and near-infrared wavelengths characteristic of distant quasars and will make identifying and characterizing such elusive objects even more likely in the future.
Provided by The Conversation
This article is republished from The Conversation under a Creative Commons license. Read the original article.
How dwarf galaxies lit up the
Universe after the Big Bang
An illustration of the reionization of the Universe, which transitioned from a cauldron (red, right) of subatomic particles to a sea of neutral hydrogen gas dotted with early stars (middle) to its current transparent state (left). Credit: Mark Garlick/SPL
Astronomers have used the James Webb Space Telescope (JWST) to show that faint miniature galaxies cleared the early Universe of its obfuscating fog of atomic hydrogen — allowing starlight to shine through the cosmos for the first time.
The research, published today in Nature 1 , provides evidence that dwarf galaxies roughly 100 times smaller than the Milky Way triggered the process known as reionization, which changed the course of cosmic history. “The Universe became transparent,” says Hakim Atek, an astrophysicist at the Paris Institute of Astrophysics and lead author of the study. “It’s because of reionization that we are able to see distant galaxies.”
Emerging from a cosmic dark age
For around 380,000 years after the Big Bang, the Universe was a hot, dense furnace of subatomic particles. As the cosmos cooled, the free electrons and protons combined to form a gas of neutral hydrogen atoms.
What followed was a dreary period of darkness. This lasted until the gas collapsed in places to fuse and form the first stars, which produced ultraviolet (UV) light. However, the remaining gas permeating the Universe either absorbed or scattered this light. As a result, the Universe resembled a foggy forest speckled with dim, flickering fireflies, and light sources were visible only for short distances.
Astronomers detect light from the Universe’s first stars
To render space transparent, something needed to bombard this gas with powerful ‘ionizing’ radiation, which could transform the neutral hydrogen atoms into charged particles, or ions, of hydrogen. The three candidates were energetic light jets called quasars, which are powered by supermassive black holes; massive galaxies roughly the same size as the Milky Way; and, finally, the minnows — dwarf galaxies.
Massive galaxies would have absorbed much of their own UV light, says Claudia Scarlata, an astrophysicist at the University of Minnesota in Minneapolis. And there might have been too few quasars to orchestrate the whole process. Dwarf galaxies, however, were small enough to allow easy escape of the UV light that they generated.
Observations of younger dwarf galaxies, closer to Earth, suggest that they can emit ionizing radiation. All the same, “there’s nothing like actually having the data from the early galaxies to confirm that”, says James Rhoads, an astrophysicist at NASA Goddard Space Flight Center in Greenbelt, Maryland. But dwarf galaxies from the epoch of reionization are too tiny and too dim to detect — even for the JWST.
Tale of two telescopes
To overcome this, the authors took advantage of a ‘natural telescope’: a cluster of galaxies located about 1.2 million parsecs from Earth. This cluster is so enormous that it warps light passing through it, thereby magnifying any light source located behind the lens, as observed from Earth.
The authors harnessed this lens to observe eight dwarf galaxies from the era of reionization, when the Universe was less than one billion years old. The galaxies are the faintest objects ever observed from that time.
First glimpse of lone black hole delights astronomers
Using data gathered by the JWST, the astronomers analysed the wavelengths of UV light from these galaxies. This allowed the team to estimate that even these faint, small galaxies could have expunged hydrogen gas around them easily. The researchers also estimate that dwarf galaxies were abundant enough up to one billion years after the Big Bang to have ionized the entire Universe, even if 5% of their ionizing radiation escaped into intergalactic space.
Small galaxies were the first to form in the Universe, which “probably makes it easier to start the [reionization] process early” in the history of the cosmos, Rhoads says. As each galaxy emitted radiation, it effectively blew a bubble of transparency that expanded into neutral gas. Eventually, all the bubbles from all the galaxies overlapped to complete the transformation.
Dwarf galaxies would have blown bubbles smaller than those produced by quasars and massive galaxies, and such small bubbles might have ensured that reionization proceeded homogeneously across the Universe. This, in turn, had implications for the architecture of the present-day Universe, Atek says.
doi: https://doi.org/10.1038/d41586-024-00594-8
References
Atek, H. et al. Nature https://doi.org/10.1038/s41586-024-07043-6 (2023).
Scientists have narrowed down the likely hiding place of the elusive "Planet Nine," after ruling out more than three-quarters of the hypothetical world's suspected orbital pathway. In a new study, the researchers — who have been looking for the planet for almost a decade — said they believe they could find the elusive world in the next few years.
Planet Nine, also known as Planet X, is a theoretical planet that is rumored to exist in the outer solar system. The Planet Nine hypothesis was first proposed in 2016 by Caltech astronomers Michael Brown and Konstantin Batygin. The pair put forward their hypothesis after other astronomers detected a series of objects in the Kuiper Belt — a large disk of asteroids and comets beyond the orbit of Neptune — that had unusually warped orbits around the sun. After analyzing these objects, Brown and Batygin decided that only a massive planet's gravitational pull could explain the orbital anomalies.
In the years since, Brown and Batygin (along with others) have filled in more pieces of the Planet Nine puzzle: The enigmatic entity is likely around seven times more massive than Earth, which would make it the fifth-largest planet in the solar system, and it's probably located somewhere between 500 and 600 astronomical units from the sun (between 500 and 600 times farther away than Earth is from our home star).
However, there is still some uncertainty about Planet Nine's eliptical orbit, which could take anywhere between 5,000 and 10,000 years to complete and is likely slightly tilted compared with the orbits of the known planets, or where it is in its orbital cycle. As a result, all previous attempts to find the planet have fallen short.
In the new study, which was uploaded to the preprint database arXiv on Jan. 31, Brown, Batygin and Matthew Holman, an astrophysicist at Harvard University, used data collected by the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) observatory in Hawaii to search for Planet Nine along and around its suspected orbital pathway.
The trio analyzed 78% of the region where Planet Nine is likely to be; the rest of this space currently lies too far away for Pan-STARRS to see it clearly. Yet Planet Nine was nowhere to be seen. (These findings have not yet been peer-reviewed.)
"We have ruled out most of the places where the planet could be," Brown told Live Science. "Now we have to do the much harder job of searching the area that is further away."
Related: 10 out-of-this-world solar system discoveries made in 2023
Using the Pan-STARRS data, the team scoured Planet Nine's orbital pathway at monthly intervals. The goal was to detect bright objects that moved positions every month.
This may sound straightforward, "but there are many things in the sky that change month after month," such as asteroids and comets, Brown said. "As a result, it's like playing a game of connecting the dots in a very computationally intensive way."
To ensure they didn't miss Planet Nine, the team added more than 50,000 fake Planet Nines to the data. They "spotted" 99.9% of these decoy planets, meaning the chances of the team having missed Planet Nine in the search region are "really small," Brown said. As a result, the team thinks Planet Nine is somewhere in the most distant 22% of its proposed orbital pathway.
RELATED STORIES—Elusive Planet Nine could be surrounded by hot moons, and that's how we'd find it
—What if Planet Nine is a baby black hole?
—Elusive Planet Nine could be an alternative form of gravity masquerading as a planet
Brown and Batygin are currently working on the "next level" of the survey by using data from the Subaru Telescope, also in Hawaii. This data should also be able to help them sort through most of the space that they have been unable to reach, as well as increase their certainty that Planet Nine isn't in the space already surveyed.
If that fails, the upcoming Vera C. Rubin Observatory, which is due to switch on in 2025, could help find the planet.
"Within a year of that telescope operating, I think we'll find it," Brown said.
Some intelligent civilizations could be trapped on their worlds
Evolution has produced a wondrously diverse variety of lifeforms here on Earth. It just so happens that talking primates with opposable thumbs rose to the top and are building a spacefaring civilization. And we're land-dwellers. But what about other planets? If the dominant species on an ocean world builds a technological civilization of some sort, would they be able to escape their ocean home and explore space?
A new article in the Journal of the British Interplanetary Society examines the idea of civilizations on other worlds and the factors that govern their ability to explore their solar systems. Its title is "Introducing the Exoplanet Escape Factor and the Fishbowl Worlds (Two conceptual tools for the search of extra-terrestrial civilizations)." The sole author is Elio Quiroga, a professor at the Universidad del Atlántico Medio in Spain.
We have no way of knowing if other extraterrestrial intelligences exist or not. There's at least some possibility that other civilizations exist, and we're certainly in no position to say for sure that they don't. The Drake equation is one of the tools we use to talk about the existence of ETIs. It's a kind of structured thought experiment in the form of an equation that allows us to estimate the existence of other active, communicative ETIs. Some of the variables in the Drake equation are the star formation rate, the number of planets around those stars, and the fraction of planets that could form life and on which life could evolve to become an ETI.
In his new research article, Quiroga comes up with two new concepts that feed into the DE: the exoplanet escape factor and fishbowl worlds.
Planets of different masses have different escape velocities. Earth's escape velocity is 11.2 km/s (kilometers per second), which is more than 40,000 km/h. The escape velocity is for ballistic objects without propulsion, so our rockets don't actually travel 40,000 km/h. But the escape velocity is useful for comparing different planets because it's independent of the vehicle used and its propulsion.
Super-Earths have much greater masses and much higher escape velocities. While there's no exact definition of a super-Earth's mass, many sources use the upper bound of 10 Earth masses to define them. So, an ETI on a super-Earth would be facing a different set of conditions than we do here on Earth when it comes to space travel.
In this work, Quiroga implements the exoplanet escape factor (Fex) and the exoplanet escape velocity (Vex.) By working with them, he arrives at a sample of escape velocities for some known exoplanets. Note that the composition of the planets isn't critical, only their masses.
Quiroga points out that a planet with a Fex value of <0.4 would struggle to hold onto any atmosphere anyway, making life unlikely. Conversely, a Fex value of >2.2 would make space travel unlikely. "Values of Fex > 2.2 would make space travel unlikely for the exoplanet's inhabitants: they would not be able to leave the planet using any conceivable amount of fuel, nor would a viable rocket structure withstand the pressures involved in the process, at least with the materials we know (as far as we know, the same periodic table of elements and the same combinations of them govern the entire universe)."
"It could, therefore, be the case that an intelligent species on these planets would never be able to travel into space due to sheer physical impossibility," Quiroga writes. In fact, they may never conceive of the idea of any type of space travel at all. Who knows?
Of course, space exploration isn't a one-way street. Astronauts have to return from space, and a planet's mass affects that. Re-entry imposes its own difficulties on a super-Earth ten times more massive than our planet. The atmospheric density also plays a role. A spacecraft needs to control its velocity and frictional heating when re-entering, and that's more difficult on a more massive planet, just as escaping is.
Quiroga also talks about the idea of the "fishbowl worlds." These are the planets above Fex 2.2 from which escape is physically impossible. What could life for an intelligent species be like on a Fishbowl world?
In his research article, Quiroga invites us to be speculative with a nod to science fiction. Imagine an ocean world that's home to an intelligent species. In a fluid environment, unaided communication travels much further than in an atmosphere like Earth's. Unaided signals could travel for hundreds of kilometers.
In an environment like that, "… communication between individuals could be feasible without the need for communication devices," Quiroga explains. So, the impetus to develop communication technologies might not be there. In that case, Quiroga says, the technology may not have developed and the civilization might not be considered "communicative" at all, one of the keys to the definition of an ETI.
"Telecommunications technology might never emerge on such a world, even though it could be home to a fully developed civilization," Quiroga writes. "Such a civilization would not be "communicative" and would not be contemplated in the Drake equation."
Other circumstances could effectively trap civilizations on their home worlds. On a planet with continuous, unbroken cloud cover, the starry sky would never be visible. How would that affect a civilization? Can you wonder about the stars if you can't see them and don't know they're there? Of course not. A similar thing is true in a binary star system with no nighttime. Stars would never be visible and would never be objects and sources of wonder.
Ocean worlds present a similar conundrum. On ocean worlds or moons with warm oceans and frozen ice shells kilometers thick, any inhabitants would have extremely limited views of the universe they inhabit. It's difficult to imagine a technological civilization arising in an ocean under several kilometers of ice. But we're in no position to judge whether that's possible or not.
Quiroga's exoplanet escape factor (Fex) can help us imagine what kinds of worlds could host ETIs. It can help us anticipate the factors that prevent or at least inhibit space travel, and it brings more complexity into the Drake equation. It leads us to the idea of Fishbowl worlds, inescapable planets that could keep a civilization planet-bound forever.
Without the ability to ever escape their planet and explore their solar systems, and without the ability to communicate beyond their worlds, could entire civilizations rise and fall without ever knowing the universe they were a part of? Could it happen right under our noses, so to speak, and we'd never know?
More information: Elio RodrÃguez, Introducing the Exoplanet Escape Factor and the Fishbowl Worlds (two conceptual tools for the search for extra terrestrial civilizations), Journal of the British Interplanetary Society (2024). DOI: 10.59332/jbis-076-10-0365
Provided by Universe Today If Hycean worlds really exist, what are their oceans like?
Galaxies look fixed in astronomical photos, but of course they’re dynamic systems ever in motion. The closest stars to Earth at Alpha Centauri will eventually close to within about 3 light years if we wait thirty thousand years or so. After that, as the system moves away again, Ross 248 will emerge as the closest interstellar target, closing to about the same distance before moving off into the night. But that will require waiting a bit longer, on the order of another 6000 years. We might also keep an eye on Gliese 445, which in 46,000 years or so will close to less than 4 light years of the Sun.
So everything is moving all the time, and we can say something more about future encounters. The REsearch Consortium On Nearby Stars (RECONS) has found that within the local 10-parsec volume, 81 percent of the 357 main sequence stars in its stellar census are less than half as massive as the Sun. That’s about the current estimate for the percentage of stars in the galaxy that are M-dwarfs, and we might expect that most close passages to our system have been and will be with this type of star.
The average distance between these stars is 3.85 light years, which again is close to what we see locally, since the Alpha Centauri stars are not far beyond that range from us. In this collection of stars, 232 single-star systems appear, and 85 multiples. This has led to interesting speculations, such as Bradley Hansen and Ben Zuckerman’s work at UCLA arguing that if stars get close enough, interstellar flight between them is more feasible. Suppose a star at 14,000 AU and the prospect seems more workable.
Stars do indeed get that close, as the example of Gliese 710 shows. If we’re patient, we can wait out the 1.3 million years it is projected for this to happen, for this star, on the borderline between M-dwarf and K-class, is headed our way from its current vantage in the constellation Serpens Cauda. As it will eventually be well inside the Oort Cloud, we can imagine quite an impact on cometary orbits and planetary ones as well over the long haul, as the paper I’m about to discuss shows. But before leaving Hansen and Zuckerman, let me mention that they calculate that if we widen the timeframe to a billion years, the likelihood of a star getting as close as 5000 AU is 81 percent.
Now let’s flip the question backward in time. Scholz’s Star (WISE J072003.20-084651.2) moved near our system about 70,000 years ago, reaching by current estimates somewhere between 52,000 AU and 68,000 AU from the Sun. Here we’ve got a binary consisting of an M-dwarf and a probable brown dwarf companion at 0.8 AU.
Image: Now about 20 light years away, Scholz’s Star (red star in the center) and its brown dwarf companion passed close to the Solar System and remained within 100,000 AU for a period of roughly 10,000 years. Image Credit: ESO VPHAS / Wikimedia Commons CC BY-SA 4.0.
Nathan Kaib (Planetary Science Institute) and Sean Raymond (Laboratoire d’Astrophysique de Bordeaux, CNRS) have gone to work on the question of passing stars as it relates to the Solar System’s evolution. Study the changes that have occurred in Earth’s climate over the millennia and it appears that fluctuations in the eccentricity of Earth’s orbit are involved. Kaib points to a specific episode that is illuminated by the analysis in this paper:
“One example of such an episode is the Paleocene-Eocene Thermal Maximum 56 million years ago, where the Earth’s temperature rose 5-8 degrees centigrade. It has already been proposed that Earth’s orbital eccentricity was notably high during this event, but our results show that passing stars make detailed predictions of Earth’s past orbital evolution at this time highly uncertain, and a broader spectrum of orbital behavior is possible than previously thought.”
So we’re digging into the history of our planet’s orbit, along with that of the other planets. The authors’ research shows that stellar encounters are not uncommon. A star passes within 50,000 AU on average every million years, and within 10,000 AU every 20 million years. To study the matter, Kaib and Raymond use a hybrid integrator – a set of specialized numerical methods – called MERCURY to simulate these encounters, under conditions described in the paper. The computer runs show that orbital changes to Earth do indeed result, or are at least accelerated, by perturbations from other stars.
Complicating these calculations is the fact that orbital evolution is chaotic, so that beyond timescales on the order of 100 million years, it is impossible to do more than characterize it statistically. The authors point out that even the long-term stability of the Solar System is not guaranteed, as over the Sun’s lifetime there is a 1 percent chance that Mercury will be lost by collision with either the Sun or Venus.
Earth’s past or future orbital evolution can only be confidently predicted inside a time horizon much shorter than Earth’s age, as small uncertainties in current planetary orbits eventually lead to dramatically divergent behavior. The time horizon set by the internal chaos among the Sun’s eight planets is ∼70 Myr, but additional strong chaos resulting from encounters between large asteroids shortens the horizon by another ∼10 Myr (Laskar et al. 2011b). However, inside this time horizon, backward integration of the Sun’s planets has been used to predict the detailed past orbital evolution of the Earth (Laskar et al. 2004).
Such perturbations make it difficult to pin down Earth’s orbital evolution the farther back in time we go, and it appears as well that perturbations from asteroid interactions are less significant than stellar encounters in degrading our ability to predict orbital changes. That’s useful information, because most simulations of the long-term evolution of the planetary orbits have modeled the Solar System in isolation. Changes in Earth’s orbit can also be the result of interactions with the giant planets, but a passing star can affect their orbits, which in turn impacts Earth’s orbital trajectory. Indeed, adding the giant planets to the simulations shows what a major factor these worlds are on Earth’s orbit once they themselves are perturbed by the passing star. Kaib and Raymond call them “a dynamical link that ultimately allows the Milky Way’s stars to influence the long-term evolution of Earth’s orbit.”
The paper turns to a specific encounter, that with the star HD 7977, which is a G-class star in Cassiopeia now some 250 light years away. 2.8 million years ago, this star moved past the Solar System at about 27 kilometers per second, its trajectory taking it somewhere in the neighborhood of 13,200 AU from the Sun, although the authors point out the wide cone of uncertainty about the distance, which may have been as little as 3900 AU. The ‘impulse gradient’ that shows the level of perturbation to the planets was over an order of magnitude higher than the norm during this time.
Working this into their models, the authors find that the median value of 13,200 AU would have had little effect on the Solar System’s long term chaotic evolution, but a passage at 3900 AU would have affected the eccentricity of Earth’s orbit. This is in addition, of course, to whatever effect such a close passage would have on Oort Cloud objects. A passage at 3900 AU would be one of the ten most powerful encounters experienced in the history of our system given the star’s above average mass and an encounter velocity that is below the average.
Image: Illustration of the uncertainty of Earth’s orbit 56 million years ago due to a potential past passage of the Sun-like star HD7977 2.8 million years ago. Each point’s distance from the center corresponds to the degree of ellipticity of Earth’s orbit, and the angle corresponds to the direction pointing to Earth’s perihelion, or closest approach distance to the Sun. 100 different simulations (each with a unique color) are sampled every 1,000 years for 600,000 years to construct this figure. Every simulation is consistent with the modern Solar System’s conditions, and the differences in orbital predictions are primarily due to orbital chaos and the past encounter with HD 7977. Credit: N. Kaib/PSI.
What’s notable here is that the authors have demonstrated that stellar encounters can be significant drivers for system evolution, an area not as widely studied as the internal dynamics of the Solar System. Here’s their conclusion:
…stellar encounters significantly accelerate the chaotic diffusion of Earth’s orbit and the time back to which numerical simulations can confidently predict Earth’s orbital evolution is ∼10% shorter than previously thought. Second, this chaotic divergence that stellar passages impart on Earth’s orbit results from their perturbations to the giant planets’ orbits, and these perturbations roughly scale with the velocity impulse gradients of stellar encounters. Third, the known encounter with HD 7977 2.8 Myr ago has the potential to unlock new sequences of Earth’s past orbital evolution beyond 50 Myr ago that have not been considered or generated in previous modeling efforts. Although it takes tens of Myr for the effects of stellar passages to significantly manifest themselves, the long-term orbital evolution of the Earth and the rest of the planets is linked to these stars.
We seem to have overestimated our ability to describe Earth’s orbital state in earlier eras given what we’re learning about the disruptive effects of stellar encounters. These close brushes with other stars can potentially cause changes in eccentricity that have been overlooked. Factoring stellar encounters into future models is going to be complicated, and necessary.
The paper is Kaib & Raymond, “Passing Stars as an Important Driver of Paleoclimate and the Solar System’s Orbital Evolution,” Astrophysical Journal Letters 962 (14 February 2024) L28 (full text). The Hansen and Zuckerman paper I mentioned above is “Minimal conditions for survival of technological civilizations in the face of stellar evolution,” Astronomical Journal Col. 161, No. 3 (25 February 2021) 145 (full text). See also Bobylev & Bajkova, “Search for Close Stellar Encounters with the Solar System Based on Data from the Gaia DR3 Catalogue,” Astronomical Letters Vol. 48 (13 February 2023), 542-549 (abstract).
No comments:
Post a Comment