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The Sun was half of a binary system, a new paper suggests
The theory could resolve some unanswered questions.
- Most stars begin in binary systems, why not ours?
- Puzzles posed by the Oort cloud and the possibility of Planet 9 may be solved by a new theory of our sun's lost companion.
- The sun and its partner would have become separated long, long ago.
If most stars form in binary pairs, what about our Sun? A new paper presents a model supporting the theory that the Sun may have started out as one member of a temporary binary system. There's a certain elegance to the idea — if it's true, this origin story could resolve some vexing solar-system puzzles, among them the genesis of the Oort Cloud, and the presence of massive captured objects like a Planet Nine.
The paper is published in Astrophysical Journal Letters.
The Oort cloud
Image source: NASA
Scientist believe that surrounding the generally flat solar system is a spherical shell comprised of more than a trillion icy objects more than a mile wide. This is the Oort cloud, and it's likely the source of our solar system's long-term comets — objects that take 200 years or more to orbit the Sun. Inside that shell and surrounding the planets is the Kuiper Belt, a flat disk of scattered objects considered the source of shorter-term comets.
Long-term comets come at us from all directions and astronomers at first suspected their origins to be random. However, it turns out their likely trajectories lead back to a shared aphelion between 2,000 astronomical units (AU) from the Sun to about 100,000 AU, with their different points of origin revealing the shell shape of the Oort cloud along that common aphelion. (An astronomical unit is the distance from the Sun to the Earth.)
No object in the Oort cloud has been directly observed, though Voyager 1 and 2, New Horizons, and Pioneer 10 and 11 are all en route. (The cloud is so far away that all five of the craft will be dead by the time they get there.) To derive a clearer view of the Oort cloud absent actually imagery, scientists utilize computer models based on planetary orbits, solar-system formation simulations, and comet trajectories.
It's generally assumed that the Oort cloud is comprised of debris from the formation of the solar system and neighboring systems, stuff from other systems that we somehow captured. However, says paper co-author Amir Siraj of Harvard, "previous models have had difficulty producing the expected ratio between scattered disk objects and outer Oort cloud objects." As an answer to that, he says, "the binary capture model offers significant improvement and refinement, which is seemingly obvious in retrospect: most sun-like stars are born with binary companions."
"Binary systems are far more efficient at capturing objects than are single stars," co-author Ari Loeb, also of Harvard, explains. "If the Oort cloud formed as [indirectly] observed, it would imply that the sun did in fact have a companion of similar mass that was lost before the sun left its birth cluster."
Working out the source of the objects in the Oort cloud is more than just an interesting astronomical riddle, says Siraj. "Objects in the outer Oort Cloud may have played important roles in Earth's history, such as possibly delivering water to Earth and causing the extinction of the dinosaurs. Understanding their origins is important."
Image source: Caltech/R. Hurt (IPAC)/NASA
The gravitational pull resulting from a binary companion to the Sun may also help explain another intriguing phenomenon: the warping of orbital paths either by something big beyond Pluto — a Planet 9, perhaps — or smaller trans-Neptunian objects closer in, at the outer edges of the Kuiper Belt.
"The puzzle is not only regarding the Oort clouds, but also extreme trans-Neptunian objects, like the potential Planet Nine," Loeb says. "It is unclear where they came from, and our new model predicts that there should be more objects with a similar orbital orientation to [a] Planet Nine."
The authors are looking forward to the upcoming Vera C. Rubin Observatory (VRO) , a Large Synoptic Survey Telescope expected to capture its first light from the cosmos in 2021. It's expected that the VRO will definitively confirm or dismiss the existence of Planet 9. Siraj says, "If the VRO verifies the existence of Planet Nine, and a captured origin, and also finds a population of similarly captured dwarf planets, then the binary model will be favored over the lone stellar history that has been long-assumed."
Missing in action
Lord and Siraj consider it unsurprising that we see no clear sign of the Sun's former companion at this point. Says Loeb, "Passing stars in the birth cluster would have removed the companion from the sun through their gravitational influence. He adds that, "Before the loss of the binary, however, the solar system already would have captured its outer envelope of objects, namely the Oort cloud and the Planet Nine population."
So, where'd it go? Siraj answers, "The sun's long-lost companion could now be anywhere in the Milky Way."
When it comes time for humanity to pick a new home, where will we go?
- Regardless of whether you think the Earth will suffer some catastrophe or not, most individuals believe that humanity will eventually have to live on another planet.
- There is no nearby planet that can support human life, however; we'll have to pick a good candidate and terraform it.
- Each celestial body presents its own unique challenges and requirements. Some need more carbon dioxide, others need less; some would become water worlds, others more Earth-like; and so on.
Whether you're feeling optimistic or pessimistic about humanity's long-term chances on Earth, most of us agree that we should colonize other planets. Whether that's out of humanity's sheer pioneering spirit or the pragmatic survival instinct to spread out so that a catastrophe on Earth doesn't wipe out the species, establishing a colony on a nearby planet seems like a must.
Trouble is, our neighboring celestial bodies are constantly bombarded by deadly radiation, lack water or oxygen, rain sulfuric acid, swing from extreme heat to cold, and possess many other inhospitable characteristics. No matter where we go in our solar system, we'll have to engage in one of the largest projects imaginable: terraforming. Depending on the environment we want to transform into a more Earth-like one, the nature of this project will vary tremendously. Here's some examples from some of the most likely candidates for terraforming in our solar system.
An artist's depiction of Mars' gradual transformation via terraforming.
Mars has always been an appealing target for terraforming, as it is arguably the most Earth-like planet in the solar system. It goes through similar seasons to Earth, has a relatively similar atmospheric composition, its day-night cycle is extremely close to our own, it possesses abundant water in the form of ice, and it lies in the Sun's habitable zone.
But the biggest problem with Mars is that it has no magnetosphere. Without an envelope of shielding magnetism, solar wind will blow away any atmosphere before it can accumulate. Proposals to create the right kind of atmosphere on Mars — like Elon Musk's flashy idea of nuking the polar ice caps to release stored CO2 and water vapor, thereby heating the planet up — won't work long term without a magnetosphere to protect the planet against solar wind. With Mars' current, flimsy atmosphere, between 1 and 2 kilograms of gas are lost to space every second. Not to mention that the lack of this protective magnetosphere also exposes the planet and all life on it to deadly radiation from the sun.
One proposal is to place a gigantic magnetic shield in orbit between Mars and the Sun to recreate the effects produced by, for instance, Earth's rotating iron outer core. This would be an incredible engineering task, likely requiring regular maintenance and fuel to keep the magnet powered. But it would be the first step to ensuring that Mars could be made habitable. Even prior to that point, Mars gradual growth of an atmosphere would make future exploration on the red planet easier and easier.
An artist's depiction of Venus if it were terraformed.
Compared to Mars, Venus has very little going for it. The surface temperature is 462°C, or 864°F; it has the opposite problem as Mars, with an atmosphere more than 90 times as dense as that of the Earth; and it's got no breathable oxygen. Not to mention that it's covered in volcanos and rains sulfuric acid. On the other hand, it's our closest planetary neighbor, and its gravity is about 90 percent that of Earth's compared to Mars' 38 percent, meaning our muscles and bones wouldn't atrophy while living there.
While Venus also suffers from a lack of a sufficiently strong magnetosphere, it's abundance of atmosphere means that concern can be put aside for a while in our hypothetical terraforming project. Venus's major problem is its excess of CO2, which makes the surface of the planet too hot for life and too heavy for humans.
One approach would be to use autonomous robots to expose Venus's underground deposits of calcium and magnesium, resulting in a chemical reaction that would store CO2 in a magnesium carbonate. This would need to be supplement by a bombardment of those elements mined from asteroids as well in order to remove enough carbon from the atmosphere for human life.
There are a variety of other methods, but they all rely on removing CO2 from the atmosphere rapidly. Seeing as how our inability to do that on Earth may be one of the biggest reasons to find another planet, Venus may not be the ideal target for terraforming in the future. An alternative to terraforming, however, would be to build a floating city in the Venusian clouds, a feat that isn't too far-fetched technologically.
A full-color image of Callisto as captured by NASA's Galileo spacecraft/
NASA/JPL/ DLR(German Aerospace Center)
Many of the Jupiter's Galilean moons are attractive targets for terraforming due to their high abundance of water, but only Callisto lies far enough away from the radiation belts generated by Jupiter's magnetosphere. On Earth, we're exposed to about 0.066 rems of radiation per day. In contrast, Ganymede receives 8 rems of radiation per day, Europa receives 540 rems per day, and Io receives a whopping 3,600 rems. Callisto, in contrast, is exposed to about 0.01 rems per day, which humans can tolerate.
The process of terraforming these moons would all follow essentially the same recipe. First, heat up their icy surfaces either through giant mirrors, nuclear devices, or some other method. Then, let the radiation from Jupiter split the resulting water vapor into hydrogen and oxygen — the hydrogen will be blown into space by solar wind, while the oxygen will settle close to the surface. Use bacteria to convert the moons' ammonia into nitrogen, and there's a breathable atmosphere.
Of course, these planets would be completely covered in oceans hundreds of kilometers deep, and Callisto wouldn't have its own magnetosphere to keep that atmosphere in place long term, but their abundance of water makes it an attractive target nonetheless. More concerning is the possibility that life already exists beneath the Galilean moons' icy surfaces, in the warm waters by thermal vents. If we were to discover such life, would it be ethical to disrupt the only alien life we have ever known?
A composite image of Titan in infrared as seen by NASA's Cassini spacecraft. Because Titan's atmosphere is so hazy, viewing it in the wavelengths of visible light is not possible. Using the infrared spectrum enables us to see through the clouds to the moon's surface.
The appeal of terraforming Titan lies in its vast reservoir of resources. Its hydrocarbon reserves (such as petroleum) are several hundred times greater than all known reserves on Earth. It's covered in a wide variety of organic compounds, particularly methane and ammonia, as well as a great deal of water. And its atmosphere is primarily nitrogen as well — a composition that scientists believe resembles that of early Earth's.
Together, these ingredients would be of significant benefit to any terraforming project. If Titan's atmosphere does resemble early Earth's, then transitioning to an atmosphere that resembles modern Earth would be (relatively) straightforward. One proposal would be to position mirrors in orbit to direct focused sunlight onto the moon's surface. Since the surface ice contains many greenhouse gases, this could warm Titan up considerably, releasing water vapor and consequently oxygenating the atmosphere. It also spends most of its time within Saturn's magnetosphere, protecting its atmosphere from the solar wind.
But perhaps more so than any other body in our solar system, Titan could already have extraterrestrial life owing to its abundance of organic chemicals. And, if all of Titan's ice were melted, it would become an ocean planet 1700 km deep, or over 1,000 miles deep, making the establishment of fixed, permanent structures a challenge.
There are challenges common to all of these potential candidates for terraforming. The big one, of course, is getting there. Many of these targets are incredibly distant. For a comparison, it took Voyager 1 a little over three years to get to Saturn, where Titan, the most distant candidate, is located, and a ship with all of the necessary equipment, people, and resources would be significantly slower than a lightweight probe. Then, there's the issue of establishing a semipermanent colony while the long work of terraforming goes on. It's difficult to speculate about the capabilities we'll have at our disposal when terraforming a planet becomes a feasible project, but it could be hundreds, possibly thousands of years before any of these planets are completely terraformed. And these are just some of the known issues: a project of this scale is bound to have unexpected problems and consequences. Despite these major challenges, the vast majority of humanity believes that establishing a second home in our solar system is a necessity — the question is, which will it be?
The author of 'How We Read' Now explains.
During the pandemic, many college professors abandoned assignments from printed textbooks and turned instead to digital texts or multimedia coursework.
As a professor of linguistics, I have been studying how electronic communication compares to traditional print when it comes to learning. Is comprehension the same whether a person reads a text onscreen or on paper? And are listening and viewing content as effective as reading the written word when covering the same material?
The answers to both questions are often “no," as I discuss in my book “How We Read Now," released in March 2021. The reasons relate to a variety of factors, including diminished concentration, an entertainment mindset and a tendency to multitask while consuming digital content.
Print versus digital reading
The benefits of print particularly shine through when experimenters move from posing simple tasks – like identifying the main idea in a reading passage – to ones that require mental abstraction – such as drawing inferences from a text. Print reading also improves the likelihood of recalling details – like “What was the color of the actor's hair?" – and remembering where in a story events occurred – “Did the accident happen before or after the political coup?"
Studies show that both grade school students and college students assume they'll get higher scores on a comprehension test if they have done the reading digitally. And yet, they actually score higher when they have read the material in print before being tested.
Educators need to be aware that the method used for standardized testing can affect results. Studies of Norwegian tenth graders and U.S. third through eighth graders report higher scores when standardized tests were administered using paper. In the U.S. study, the negative effects of digital testing were strongest among students with low reading achievement scores, English language learners and special education students.
My own research and that of colleagues approached the question differently. Rather than having students read and take a test, we asked how they perceived their overall learning when they used print or digital reading materials. Both high school and college students overwhelmingly judged reading on paper as better for concentration, learning and remembering than reading digitally.
The discrepancies between print and digital results are partly related to paper's physical properties. With paper, there is a literal laying on of hands, along with the visual geography of distinct pages. People often link their memory of what they've read to how far into the book it was or where it was on the page.
But equally important is mental perspective, and what reading researchers call a “shallowing hypothesis." According to this theory, people approach digital texts with a mindset suited to casual social media, and devote less mental effort than when they are reading print.
Podcasts and online video
Given increased use of flipped classrooms – where students listen to or view lecture content before coming to class – along with more publicly available podcasts and online video content, many school assignments that previously entailed reading have been replaced with listening or viewing. These substitutions have accelerated during the pandemic and move to virtual learning.
Surveying U.S. and Norwegian university faculty in 2019, University of Stavanger Professor Anne Mangen and I found that 32% of U.S. faculty were now replacing texts with video materials, and 15% reported doing so with audio. The numbers were somewhat lower in Norway. But in both countries, 40% of respondents who had changed their course requirements over the past five to 10 years reported assigning less reading today.
A primary reason for the shift to audio and video is students refusing to do assigned reading. While the problem is hardly new, a 2015 study of more than 18,000 college seniors found only 21% usually completed all their assigned course reading.
Maximizing mental focus
Researchers found similar results with university students reading an article versus listening to a podcast of the text. A related study confirms that students do more mind-wandering when listening to audio than when reading.
Results with younger students are similar, but with a twist. A study in Cyprus concluded that the relationship between listening and reading skills flips as children become more fluent readers. While second graders had better comprehension with listening, eighth graders showed better comprehension when reading.
Research on learning from video versus text echoes what we see with audio. For example, researchers in Spain found that fourth through sixth graders who read texts showed far more mental integration of the material than those watching videos. The authors suspect that students “read" the videos more superficially because they associate video with entertainment, not learning.
The collective research shows that digital media have common features and user practices that can constrain learning. These include diminished concentration, an entertainment mindset, a propensity to multitask, lack of a fixed physical reference point, reduced use of annotation and less frequent reviewing of what has been read, heard or viewed.
Digital texts, audio and video all have educational roles, especially when providing resources not available in print. However, for maximizing learning where mental focus and reflection are called for, educators – and parents – shouldn't assume all media are the same, even when they contain identical words.
Humans may have evolved to be tribalistic. Is that a bad thing?
- From politics to every day life, humans have a tendency to form social groups that are defined in part by how they differ from other groups.
- Neuroendocrinologist Robert Sapolsky, author Dan Shapiro, and others explore the ways that tribalism functions in society, and discuss how—as social creatures—humans have evolved for bias.
- But bias is not inherently bad. The key to seeing things differently, according to Beau Lotto, is to "embody the fact" that everything is grounded in assumptions, to identify those assumptions, and then to question them.
Ancient corridors below the French capital have served as its ossuary, playground, brewery, and perhaps soon, air conditioning.