- 3299 - COMETS - Vesta and Bern.-Bern. - An enormous comet, possibly the largest one ever detected, is barreling toward the inner solar system with an estimated arrival time of 10 years from now.
--------------------- 3299 - COMETS - Vesta and Bern.-Bern.
- This comet, known as the “Bernardinelli-Bernstein comet” ( C/2014 UN271 ), is at least 62 miles across. This a is about 1,000 times more massive than a typical comet. It's so large that astronomers previously mistook it for a dwarf planet.
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- But a closer analysis of the object revealed that it was moving rapidly through the Oort cloud which is a vast scrapyard of icy rocks, billions of miles from Earth. The object appeared to be headed our way, and it even had a glowing tail, or "coma", behind it. This tail is a clear indication of an icy comet approaching the relatively warm inner solar system.
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- This enormous rock poses no threat to Earth. Right now, Bernardinelli-Bernstein (BB) is cruising through the Oort cloud at about 29 times the distance between Earth and the sun, or 29 astronomical units (AU). The comet's closest approach to Earth will occur sometime in the year 2031, when scientists predict the comet will swoop within 10.97 AU of the sun, putting it just outside of Saturn's orbit.
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- While that's far enough from Earth that humans won't be able to see the comet without telescopes, it's considerably closer than the rock's last visit to our part of the solar system. After modeling the comet's trajectory, they calculated that comet BB made its last approach 3.5 million years ago, coming within 18 AU of the sun.
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- Since then, the comet traveled as far as 40,000 AU away, deep into the mysterious Oort cloud.
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- BB is a 'new' comet in the sense that there is no evidence for a previous approach closer than 18 AU. In other words, humans have never laid eyes on it before.
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- We owe our current view of the large, distant comet to the Dark Energy Survey (DES) (August 2013 to January 2019). During this survey, astronomers mapped 300,000,000 galaxies in the southern sky, discovering more than 800 previously unknown objects beyond the orbit of Neptune. The Bernardinelli-Bernstein comet was one of those objects.
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- Getting a closer look at the comet could help scientists understand a bit more about the chemical composition of the early solar system, as comets from deep in the Oort cloud are thought to be relatively unchanged since they were booted away from the sun billions of years ago.
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- With millions of years separating the comet's next close approach from its following one, it'll be a once-in-a-lifetime brush with the early solar system. If an asdteroid is big enough we can call it a “dwarf planet“.
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- The dwarf planet “Vesta” is helping scientists better understand the earliest era in the formation of our solar system. Data from meteorites derived from Vesta was used to resolve the "missing mantle problem" and push back our knowledge of the solar system to just a couple of million years after it began to form.
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- “Vesta” is the second-largest body in the asteroid belt at 500 kilometers across. It's big enough to have evolved in the same way as rocky, terrestrial bodies like the Earth, moon and Mars.
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- Early on, these asteroids were balls of molten rock heated by collisions. Iron and the “siderophiles“, or 'iron-loving' elements such as rhenium, osmium, iridium, platinum and palladium, sank to the center to form a metallic core, leaving the mantle poor in these elements. As the planet cooled, a thin solid crust formed over the mantle. Later, meteorites brought iron and other elements to the crust.
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- Most of the bulk of a planet like Earth is “mantle“. But mantle-type rocks are rare among asteroids and meteorites. Planetary scientists have called this the "missing mantle problem."
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- Three recently discovered meteorites do include mantle rock, called “ultramafics” that include mineral olivine as a major component. Precise analysis of isotopes create a fingerprint that allowed scientists to identify the meteorites as coming from Vesta or a very similar body.
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- "The “Dawn” space mission remotely observed rocks from the largest south pole impact crater on Vesta in 2011 but did not find mantle rock. Because it is so small, Vesta formed a solid crust long before larger bodies like the Earth, moon and Mars.
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- The siderophile elements that accumulated in its crust and mantle form a record of the very early solar system after core formation. Over time, collisions have broken pieces off Vesta that sometimes fall to Earth as meteorites.
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- Because Vesta formed very early, it's a good template to look at the entire history of the Solar System. This pushes us back to two million years after the beginning of solar system formation.
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- Vesta and the larger inner planets could have got much of their material from the asteroid belt. But a key finding from this study was that the inner planets (Mercury, Venus, Earth and moon, Mars and inner dwarf planets) got most of their mass from colliding and merging with other large, molten bodies early in the solar system.
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- The asteroid belt itself represents the leftover material of planet formation, but did not contribute much to the larger worlds.
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- Scientists have estimated that Comet Bernardinelli-Bernstein was the largest such icy body identified to date, perhaps more than 100 miles across. The "megacomet" has a new distinction: it sprouted a tail remarkably far from the sun, suggesting more revelations to come.
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- Trans-Neptunian objects (TNOs) are hunks of rock that circle the sun but remain out beyond Neptune's orbit. That's about 30 times the Earth's average distance from the sun, which is about 93 million miles, or, an AU. But most TNOs never stray farther from the sun than a few hundred astronomical units.
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- The Dark Energy Survey was a survey designed to help scientists understand dark energy, a mysterious substance that scientists have not yet seen directly but is believed to make up 68% of the universe and warps our view of other galaxies.
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- The project captured more than 80,000 images of the sky, revisiting specific patches about every two weeks. In each image are tens of thousands of cosmic objects of all shapes and sizes.
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- When you take an image of the sky, you're not taking just an image of the galaxies, you're taking an image of everything that is between you and them. So you get things like stars, you get airplanes, you get asteroids, and everything else in between.
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- Bernardinelli and Bernstein reserved time on a supercomputer and set about designing a way to spot TNOs within the Dark Energy Survey images. Using the time and location of each image to stack up solar system views, the researchers set the algorithm to identify when at least seven different images lined up to show a speck moving according to the laws that govern the movement of solar system objects.
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- Although seven different images was the minimum setting, the massive comet turned up in 20 or 30 separate images. When the survey was operating the comet was already only 25 AU from the sun by 2017.
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- Based on the object's brightness and distance, the scientists initially estimated that the comet's nucleus, the icy rock at its core, was 60 to 120 miles wide. Ironically, if the detection had turned out to be one of the TNOs the study was really targeting, it would have been unremarkable, since scientists know of plenty of TNOs of that size.
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- But as far as comets go, that size estimate is truly massive. Among the comets scientists have studied in detail, only two are in the same class: Comet Hale-Bopp, which made a close approach to Earth in 1997, and Comet C/2002 VQ94 (LINEAR), which came no deeper into the solar system than Jupiter's orbit.
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- Large comets are rare because the same vaporizing ice that makes them so spectacular to see robs them of their being, so every pass by the sun leaves the comet a little bit smaller than before.
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- The young solar system sported a ring of small, icy rubble surrounding the massive planets. But when the planets migrated through the solar system, their huge gravity kicked the frozen rubble around. Some flew out into interstellar space; some ended up in what scientists call the ‘Kuiper Belt“, where Pluto orbits; some ended up in the much more distant Oort Cloud where comets like Bernardinelli-Bernstein lurk.
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- From there, as tides flow through the Milky Way and neighboring stars pass our solar system, gravity occasionally kicks a snowball inward on a planetary adventure. There are plenty of Kuiper Belt objects that look like the new comet.
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- Comet Bernardinelli-Bernstein wasn't fully frozen and had already woken up a little by the time it first appeared in scientists' images. Comets grow their distinctive fuzzy comas when their ices warm up enough to vaporize away into a gaseous cloud surrounding the nucleus.
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- The phenomena obscures the nucleus and brightens the comet which means that if Comet Bernardinelli-Bernstein was active in even the earliest sightings, scientists had overestimated its size.
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- Observations of Comet Bernardinelli-Bernstein gathered by an outpost of the Las Cumbres Observatory in South Africa in June 2021 show activity on the comet despite its huge distance from the sun.
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- Scientists have only spotted a handful of comets active so far from the sun, where temperatures are still too cold for, say, water ice to turn to vapor, a typical type of cometary activity. What's really unique about this object is not its size but how active it is at these large distances and what a great opportunity it gives us to characterize distant activity.
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- Given a 2021 discovery and a 2031 close approach to the sun, plus old observations from as early as 2010, gives scientists a decades-long look at the object that's rare for this class of comet that makes such long journeys.
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- Much of Comet Bernardinelli-Bernstein's journey, scientists will have practically continuous views due to the ‘Vera C. Rubin Observatory’ in Chile scheduled to begin observing in 2023. That facility will survey the southern sky once every three days, offering astronomers a detailed view of how the comet changes as it approaches the sun.
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- October 8, 2021 COMETS - Vesta and Bern.-Bern. 3299
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