(ORDO NEWS) — Right now, the huge comet Bernardinelli-Bernstein, aka C / 2014 UN 271, is flying towards the Sun. Astronomers have long suspected that this tailed guest, discovered back in 2014, is unusually large.
Now they have measured the diameter of its core using the ALMA radio telescope and got no less than 137 ± 17 kilometers. This is a huge figure: typical cometary nuclei are measured in units or the first tens of kilometers.
Humanity has never seen such large comets, except for the object Chiron from a group of centaurs grazing between Jupiter and Neptune. But whether to consider centaurs as comets or asteroids is a big question, rather, it is something in between. The previous record holder is Comet Hale-Bopp, with a nucleus about 74 kilometers across.
Readers in their thirties should remember what a majestic sight Comet Hale-Bopp presented in 1997. The huge tailed beast was brighter than any night luminary, except for Venus and the Moon. Those who are late to be born and grow up should not despair: they are more likely to live to see the next visit of Halley’s famous comet in 2061.
But the comet Bernardinelli-Bernstein, alas, will not give us a show of unearthly beauty in every sense: in 2031 it will miss the Sun in 11 astronomical units (AU), that is, it will not cross the orbits of Saturn either. Recall that one astronomical unit is equal to the distance from the Earth to the Sun (150 million kilometers).
On the other hand, this means that a visitor from outer space certainly does not threaten the Earth. What can not but rejoice: a 140-kilometer object would destroy all life, except, perhaps, bacteria that live deep in the earth’s crust.
Fortunately, collisions with bodies of this magnitude only occurred during the era of the formation of the Earth, when the solar system was clogged with construction debris. So what is surprising is not what passed this time, but the fact that such a huge comet showed up to visit at all.
What are they made of
What is a comet anyway? This is an icy body that periodically comes so close to the Sun that it begins to evaporate and, in connection with this, grows a tail.
Far from the Sun, a comet is an “icy asteroid”: a compact object a few kilometers in size (rarely tens of kilometers) without any atmosphere, much less a tail. It is often called a ball of dirty snow: the comet consists mainly of ice, and not only water. Frozen water is accompanied by no less frozen ammonia, methane and carbon dioxide.
But water still prevails. There is a version that even ammonia and other “non-water” ice is contained in comets in the form of hydrates – compounds with water. Such a theory explains the spectra of comets better than the simplest one, where exotic ices are present in their pure form.
There is no secret in the abundance of water, since H2O is generally the most common of the complex (i.e., consisting of two or more chemical elements) substances in the Universe. After all, this is a combination of hydrogen, of which space consists of 77%, with oxygen holding an honorable third place (in second place is proud helium, which hates to enter into chemical bonds).
By the way, planetary scientists are still arguing about the role of comets falling on the young Earth in the formation of the oceans. According to some estimates, we have to thank the caudate for at least a third of the life-giving moisture on our planet.
In addition to ice, comets contain silicate rocks in different serving options: from fine dust to large rocks. A very interesting component of the comet cocktail is organic matter. Basically, these are the simplest compounds like the already mentioned methane or hydrogen cyanide (HCN).
But there are also more interesting substances. For example, as much as 45 percent of the solid particles captured by the Rosetta probe in the atmosphere of comet Churyumov-Gerasimenko were organic, and mostly complex. Comets may have played a role in supplying the ancient Earth with the organic substrate from which life originated.
Finally, comets also contain metals, albeit in very small quantities. In the now popular film Don’t Look Up (the title of which was erroneously translated as Don’t Look Up), the tailed celestial body turns out to be a storehouse of rare metals important to the electronics industry.
Some techno-billionaire wants to get some kind of wealth, and this adventure does not end with anything good for the Earth. In reality, it is in vain for metal-hungry magnates to rely on comets, it is better to turn their attention to some asteroids. Better yet, learn how to recycle waste, but that’s another story.
How to grow a tail
What happens to a comet as it approaches the sun? Under the sun’s rays, the ice begins to evaporate. A powerful stream of gases carries along the dust. “Ice asteroid” turns into a comet nucleus , shrouded in atmosphere – coma . The nucleus and coma is the comet’s head , but it doesn’t have a tail yet.
The coma usually appears at a distance of about 10 AU. from the sun. Comet Bernardinelli-Bernstein distinguished itself here too: the first signs of outflow of gases were visible already from 24 AU. Why? First, this comet is already very large. Secondly, this appears to be her first visit to the Sun, and she has barely begun to use up her ice supply.
At a distance of 3-4 a.u. the comet’s tail begins to grow from the sun. This is the substance of the coma, which is pulled out by the pressure of sunlight into a plume directed away from the Sun.
The tail of a comet can stretch for tens and even hundreds of millions of kilometers. It is so rarefied that, from the point of view of an earth engineer, it is a deep vacuum, so that astronomers call comet tails “visible nothingness.” In such a rarefied environment, each atom is left to itself.
So, when it absorbs a photon of sunlight, it does not collide with other atoms, but emits exactly the same photon. This is how light emerges from the void. There are, however, more subtle and not fully understood mechanisms of luminescence.
To date, more than 3,600 comets are listed in the NASA Jet Propulsion Laboratory database. These numbers are updated regularly, because even an amateur telescope can detect a new comet, and even professional sky patrol systems open them in batches.
More than 2800 of these comets (nearly 80%) are long-period comets, that is, they complete one revolution in more than 200 years. Moreover, this “more” often means tens and hundreds of millennia. They come to us from the little-studied outskirts of the solar system.
The remaining approximately 800 caudates are short-period. The fastest of them is Comet Encke, which circles the Sun in a little more than three years. And, for example, the more power-law Halley’s comet spends 76 years on one revolution.
It is believed that all short-period comets started out as long-period comets, but were then led astray by the gravity of the giant planets and stuck in the close vicinity of the Sun. All such poor fellows are divided into families according to the names of the planets that captured them: the family of Jupiter, Saturn, Uranus and Neptune.
On the outskirts of the domain of the Sun, many tiny ice bodies are found. But almost all of them never cross even the orbits of Neptune. What makes the core of the future comet abruptly change course and go on a dizzying voyage to the star?
In the middle of the 20th century, it was believed that this was a collision of cometary nuclei with each other. However, such an accident can reduce the semi-major axis of the orbit (it is also the average distance to the Sun), but not increase it in any way. And the orbits of long-period comets are very, very elongated and extended. It turns out that the birthplace of comets lies incredibly far from our star.
Thus, in the constructions of theorists , the Oort cloud was born , which begins in the thousands and ends in hundreds of thousands of astronomical units from the star. The comet nuclei dormant there are so weakly connected with the Sun that their orbit can be disturbed not only by a collision with each other, but also, for example, by the gravity of a passing star.
The Oort Cloud has never been seen. No telescope can see small cold objects at such a distance. Its existence is a hypothesis designed to explain the origin of long-period comets. In recent years, this hypothesis has faltered.
The fact is that much closer to the Sun (in tens of astronomical units), the Kuiper belt was discovered, and behind it – a scattered disk. There are enough not only small objects that can become cometary nuclei, but also large ones that can accelerate future comets with their gravity.
With such a gravitational kick, the orbit can be greatly stretched, so that an object from the 50th astronomical unit will look like an alien from a hypothetical Oort cloud. In this regard, some astronomers believe that it is time to get out Occam’s razor and shave off this cloud with it. However, the community as a whole is not yet ready for such a radical step.
How Comets Die
Nothing lasts forever, not only under the moon, but also above it. So comets are not only born: they age and die.
The mechanism of comet aging is obvious. The coma and tail are made up of the evaporating matter of the comet’s nucleus. Everything that evaporates will eventually evaporate completely.
In 1986, the Soviet Vega-1 and Vega-2 spacecraft, as well as the European Giotto, approached Halley’s Comet. They found that the comet’s nucleus was as black as fresh asphalt: it reflected only 4 percent of the incident light. Nice ice cube! The fact is that only in the memory of mankind this comet went around the Sun already 32 times (records about it exist from 467 BC).
As the ice evaporated, dust mixed with it settled on the surface and eventually formed a dense crust. It could protect the ice from further evaporation, if it were solid, without holes and cracks (which, of course, is not the case). By the way, it happened at the moment of closest approach to the Sun, so that the surface of the core was heated to almost 90 degrees Celsius.
Every second, the celestial body lost 45 tons of gas and 5-8 tons of dust. At this rate, the most famous comet will last about 1300 more revolutions. If before that it does not fall apart, turning into a meteor shower, as is often the case with loose “clods of snow.” If the refractory remnant of the nucleus retains its integrity, it will pass into the category of extinct comets, which differ from asteroids only in their glorious history.
Threat from the sky
A more epic, but also much rarer scenario for the death of a comet is a fall onto a planet. Astronomers have seen such an event with their own eyes only once, when fragments of comet Shoemaker-Levy crashed into Jupiter in 1994. True, in 2009, observers noticed in the atmosphere of the giant planet something similar to a trace of a fresh impact, but this time the collision itself was left behind the scenes.
Have comets hit Earth? Undoubtedly. Has this happened in historical time? Quite possible. There is a hypothesis that the Tunguska body was a fragment of a cometary nucleus. Despite the 10-megaton explosion that knocked down the forest for tens of kilometers around, neither a crater nor meteorite fragments were found.
It is easy to combine this with the fall of a “clod of dirty snow”, but not a stone asteroid. In addition, the meteorite came from a direction coinciding with the radiant of the Taurid meteor shower, and it is associated with Encke’s comet.
In the movie Don’t Look Up, a comet with a nucleus 9 kilometers in diameter is approaching Earth. The process of discovering the comet and calculating the orbit is shown with numerous errors, but okay. The authors pathetically call the tailed “planet killer” and threaten that it will destroy “everything alive.”
Scientists are trying to convey to society that it is necessary to at least try to destroy it or force it to change its orbit, but society … society is such a society. From the bacchanalia of managerial idiocy, the project of a tech billionaire crystallizes.
He wants to send robots to the comet that will crush the comet’s nucleus into 30 pieces. After that, each robot (and it is only several times larger than a human) will take its fragment of a comet into a gentle embrace and gently lower it to Earth. Well, there it will already be possible to profit from who knows where the metals taken on the comet. By the way, robots
The idea fails safely: the comet cannot be crushed. Neither the mythical “quantum fuses” nor the “nuclear reactions studied at CERN” help (what-what reactions? There were atomic bombs on board private drones, or did CERN discover nuclear reactions in a block of ice?). When an untouched comet does fall, it causes earthquakes and volcanic eruptions all over the Earth.
The points. The fall of a nine-kilometer object will cause huge tsunamis and possibly massive fires. They may be followed by something like a nuclear winter. This is approximately the scenario of the death of dinosaurs, as described by supporters of the asteroid hypothesis.
Few will seem to anyone, but the total destruction of life on Earth is out of the question. The earthquake will be only one and local – at the moment of impact. Volcanoes will not notice what is happening at all.
And most importantly: the thirtieth part of a nine-kilometer comet nucleus (if it is spherical) will have a diameter of almost three kilometers.
Dividing by 30 is not diameter, but volume, although in Hollywood they may not have heard of school geometry. And such a colossus will move at a speed of tens of kilometers per second. Well, how could a robot several meters in size “hold and plant” this?
Perhaps, such creative developers should not be trusted with the creation of not only flying robots, but also kitchen stools. In general, the Universe, as usual, is much more complex and interesting than idle fiction. Take your eyes off the movie screen and look up. There are comets out there somewhere.
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