New studies find the interstellar comet 2I/Borisov is the most "pristine" ever discovered.
One of the only interstellar visitors ever discovered traversing our Solar System, the rogue comet 2l/Borisov, is also one of the most "pristine" such space objects ever. The comet, which was first spotted in 2019 by the amateur Ukrainian astronomer Gennady Borisov, likely never flew too close to any star including our sun, which left its composition very similar to how it was upon formation.
Comets, which are space bodies made of frozen gas, rock, and ice, are usually impacted by the heat and radiation they encounter on their way. What's attractive to scientists in studying comets that haven't changed much in their lifetimes is that they have a similar composition to the gas and dust that was present at the formation of the Solar System 4.5 billion years ago. Analyzing pristine comets can lead to a deeper understanding of the Solar System's beginnings and evolution.
The 2I/Borisov comet is only the second interstellar object ever found in our Solar System. The first one was 1I/'Oumuamua, detected in 2017.
The new study, based on observations from the European Southern Observatory's Very Large Telescope (ESO's VLT) in Chile, was led by Stefano Bagnulo of the Armagh Observatory and Planetarium in Northern Ireland.
"2I/Borisov could represent the first truly pristine comet ever observed," said Bagnulo.
The 2I/Borisov interstellar comet captured with the VLT.Credit:ESO/O. Hainaut
As reported in Nature Communications, his team used a technique called polarimetry, which measures the polarization of light, to study the space body. This helped the team compare 2I/Borisov to other local comets. The properties of the new comet were quite different from others they found in the Solar System, except for Hale-Bopp, a comet discovered in 1995 which is also considered very pristine.
The study's co-author Alberto Cellino from the Astrophysical Observatory of Torino, Italy, commented upon this connection, arrived at by analyzing polarization along with the comet's color:
"The fact that the two comets are remarkably similar suggests that the environment in which 2I/Borisov originated is not so different in composition from the environment in the early Solar System.".
In a fascinating nod to just how powerful Earth's top telescopes have become, another set of ESO researchers published a different study in Nature Astronomy on the comet's composition using data from the Atacama Large Millimeter/submillimeter Array (ALMA). This team, led by astronomer Bin Yang, was able to gather many clues about 2I/Borisov's makeup from its coma – the envelope of dust surrounding it. Inside the coma, they discovered compact pebbles, grains around one millimeter in size. They could also tell that the relative amounts of carbon monoxide and water in the comet changed significantly as it came closer to the Sun.
This indicated to them that the materials in the comet came from different places in the cosmos. Matter in the comet's home star system was likely mixed in a discernible pattern that related to how far the comet was from its star, found the scientists. This was possibly affected by the presence of giant planets, which stirred up materials in their system through strong gravity. Astronomers think this kind of process also took place in the early period of the Solar System's life.
"Imagine how lucky we were that a comet from a system light-years away simply took a trip to our doorstep by chance," remarked Yang.
In 2029, the European Space Agency plans to launch the Comet Interceptor project that would allow scientists to study comets that speed through our Solar System with even greater precision.
Was ‘Oumuamua a rock or an alien scout? Harvard astronomer talks controversial hypothesis in new book
Ari Loeb, who suggested in 2018 that the mysterious object was an alien craft, is back to discuss the evidence.
If we became especially interested in another solar system and wanted to send an exploratory craft, how would we do it? Even the nearest solar system—Proxima Centauri is its sun—is about 40,208,000,000,000 kilometers from here, so there's no way our scout could carry enough fuel to get there. Might we could use something like a light, or solar, sail? Light-sail craft already exist, and they do work.
Harvard University astronomer Avi Loeb made headlines in 2018 when he suggested that the extra-solar object 'Oumuamua—which, after all, does mean "scout" in Hawaiian—was just such a craft sent to have a look at our solar system. Since then, if anything he's become even more convinced, and Loeb has just published his reasoning and other thoughts in a new book, "Extraterrestrial: The First Sign of Intelligent Life beyond Earth."
But it's a rock
Credit: M. Kornmesser, European Southern Observatory (top)/ K. Meech et al., NASA (bottom)
The visual image that comes to mind in thinking about 'Oumuamua is the artist's rendition (above top) that was released by the European Southern Observatory when the object was discovered on its way out of our solar system in 2017. Listening to Loeb's claims, one may think, "What light sail? It's a rock."
However, it's all too easy to forget that this ubiquitous image is just an artists' rendition after all, based on the assumption that our visitor was a rock. It need not have looked like this at all. We have no idea what 'Oumuamua really looked like, since the image at the bottom shows the best look at the object we really got.
What is a light sail?
The camera on Planetary Society's Light Sail 2 capture an image of northern Brazil
Credit: Planetary Society
A light sail is a spacecraft constructed from panels of a lightweight, reflective material such as Mylar or polyimide treated with a metallic reflective coating. When photons from a star, such as our Sun, hit the sail, they give it a small push. When the photons bounce back off of the sail, they give it another one. It doesn't take much of a shove to move a light sail through a vacuum of space, and it's believed light sails can pick up quite a lot of speed as they go. Loeb himself is involved in the Breakthrough Starshot project that envisions light-sail craft shooting through space at 100 million miles an hour.
The first functioning light sail, LightSail Sail 2 was sent aloft by the Planetary Society in June 2019, and is currently orbiting the Earth. This year, NASA plans to deploy the NEA Scout mission that will send an 86-square-meter light sail off from Moon orbit to explore the near-Earth asteroid Itokawa.
To Loeb, the object's apparent appearance and behavior doesn't suggest a rock.
First off, what appears to be 'Oumuamua's shape—described as being about 100 meters long and resembling either a cigar or pancake—doesn't describe previously seen comets or asteroids. Second, 'Oumuamua was also exceptionally bright, 10 times moreso than space rocks typically seen whizzing around our solar system. This high level of reflectivity would consistent with a shiny, metallic surface.
Finally, 'Oumuamua accelerated as it whipped around the sun as if it was picking up energy from the star. While such behavior is common when comets speed up, pushed forward by evaporating gasses from the sun's warm, no such gases were observed with 'Oumuamua.
With all this in mind, Loeb, along with co-author Shmuel Bialy, published a controversial paper in Fall of 2018 in the Astrophysical Journal Letters hypothesizing the object might be an extraterrestrial craft. The paper suggested that maybe "'Oumuamua is a lightsail, floating in interstellar space," perhaps "debris from advanced technological equipment." It also posited an admittedly more "exotic" possibility, "that 'Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization."
Needless to say, the paper was met with a great deal of excitement. Did 'Oumuamua signify the presence of intelligent life beyond our solar system, or—as many scientists felt—was such conjecture unworthy of serious consideration?
Welcome to 2021
As the title of his new book implies, Loeb continues to assert the validity of his earlier analysis, demanding that the scientific community at least consider the possibility that 'Oumuamua was an exploratory craft.
One of the underlying themes of the book is Loeb's concern about the "health" of a scientific community that can't even entertain a hypothesis such as his and Bialy's. (This month, Scientific American published an extended and thought-provoking interview with Loeb.) In the book and interview, Loeb attributes his notoriety to an overreaction by the scientific community to his 2018 paper. While much of the book is autobiographical, Loeb claims he isn't interested in his own fame, and he recently stepped down from Harvard's Astronomy department.
"My message is that something is wrong with the scientific community today in terms of its health," Loeb told Scientific American, adding that too many in the science community are motivated by ego and self-image, when science should be about taking risks and trying to understand the world.
"People ask why I get this media attention. The only reason is because my colleagues are not using common sense," Loeb said. "Contrast string theory and multiverses with what I and many others say, which is that based on the data from NASA's Kepler mission, roughly half of the galaxy's sunlike stars have a planet about the size of the Earth, at about the same distance of the Earth from the sun, so that you can have liquid water on the surface and the chemistry of life as we know it. So if you roll the dice on life billions of times in the Milky Way, what is the chance that we are alone?"
For the first time, an object from outside our solar system is observed traveling through our neighborhood.
The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) telescope is located near the summit of the Haleakala volcano on Maui, and on October 19, 2017, post-doctoral researcher Rob Weryk noticed something odd moving west at an unusual 6.2° angle. Not sure what it was, he checked the observatory’s backlog and discovered an image of it from the night before. A team led by Karen Meech of University of Hawaii's Institute of Astronomy next examined October 22 imagery of the object captured by the Canada-France-Hawaii Telescope (CFHT) on the big island at Maunakea. The object’s unique angle of trajectory signified that it had to come from outside our solar system.
NASA’s Thomas Zurbuchen says, “For decades we've theorized that such interstellar objects are out there, and now — for the first time — we have direct evidence they exist. This history-making discovery is opening a new window to study formation of solar systems beyond our own.” The International Astronomical Union had to invent a new category for it, and designated it as A/2017 UI.
PAN-STARRS1 at sunset (ROB RATKOWSKI)
Though it was first thought to be a comet, the October 22 CFHT images had been time-resolved to the A/2017 UI’s rate of motion and revealed a lack of cometary traits, leading to the conclusion that it’s an asteroid.
That unique trajectory is just one of the odd things about the asteroid: Its physical appearance is also surprising. Astronomers observed that it varied in brightness by a factor of ten due to spinning on its axis every 7.3 hours. “This unusually big variation in brightness means that the object is highly elongated: about ten times as long as it is wide, with a complex, convoluted shape,” according to Meech. NASA estimates that it’s “up to one-quarter mile (400 meters) long and highly elongated — perhaps 10 times as long as it is wide.”
And it’s very old. The team saw that A/2017 UI “had a reddish color, similar to objects in the outer solar system, and confirmed that it is completely inert, without the faintest hint of dust around it.” It’s thus believed to be composed exclusively of rock and metals without any water or ice, its color being produced by exposure over hundred of millions of years to cosmic-ray radiation as it wandered across the galaxy and into our view. The U of H team named the asteroid 'Oumuamua, (pronounced “oh MOO-uh MOO-uh”) which roughly, and hauntingly means, "a messenger that reaches out from the distant past."
Coming from somewhere in the vicinity of the star Vega — though it was there before Vega was — Oumuamua continues its lonely journey unattached to any system. NASA estimates that as of November 20 it’s moving about 85,700 miles per hour or 38.3 kilometers per second. By mid-December 2017 it will pass from our view on its way out of our solar system, in the direction of the constellation Pegasus.