The discovery of the first interstellar comet was officially recognized

The discovery of the first interstellar comet was officially recognized
The discovery of the first interstellar comet was officially recognized
Anonim

Crimean amateur astronomer Gennady Borisov at the end of August 2019 discovered an alien comet originating from another planetary system. Now it was officially recognized, and soon Borisov's comet will approach the Earth.

1024px-comet_p1_mcnaught02 _-_ 23-01-07-edited

The Minor Planet Center, one of the organizations of the International Astronomical Union, has officially confirmed the discovery of comet C / 2019 Q4 (Borisov) by astronomer Gennady Borisov. Less than a year ago, other astronomers discovered the first interstellar asteroid. Both events indicate a high frequency of occurrence of objects from other systems in the vicinity of the Sun. The newly discovered comet by the end of 2019 should approach the Earth at a distance of up to 150 million kilometers, which will allow observing its behavior in detail.

The comet can reach the seventeenth stellar magnitude, that is, it will be relatively bright in the earth's sky. The object flies so fast that the gravity of the Sun is not able to hold it, therefore, starting in 2020, the comet will begin to move away and after thousands of years will leave the solar system. The discovery is reported in a circular letter from the Minor Planet Center.

Unprecedented orbit

Comet C / 2019 Q4 (Borisov) is named after its discoverer - an employee of the Crimean Astronomical Station of the Sternberg State Astronomical Institute, Moscow State University, Gennady Borisov. Borisov works as an engineer at the station, astronomy is a hobby for him. However, he achieved great success in it: even before 2019, he discovered seven "ordinary" comets and about three dozen asteroids. On August 30, 2019, an amateur astronomer, using a small 65-centimeter telescope, which he once assembled on his own, tracked a new object with very unusual parameters.

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Comet C / 2019 Q4 (Borisov) in the center of the image, its small tail is visible / © Gennady Borisov

First, its speed relative to the Sun was 30.5 kilometers per second. Secondly, as subsequent observations, including by other astronomers, have shown, it has an extremely unusual orbit - its eccentricity is more than three. Until now, all bodies discovered in the solar system had an eccentricity much less, less than 1, 2.

Eccentricity is a numerical characteristic showing the degree of deviation of the so-called conical section from a circle. In the case of celestial bodies with an eccentricity equal to zero, the orbit is completely circular - it has no deviations from the circle. When it is greater than zero, but less than one, the orbit is ellipsoidal, that is, it resembles an oval, and the higher the eccentricity, the more elongated this oval. When the eccentricity value is from one and higher, the orbit ceases to be closed and becomes first parabolic (eccentricity equal to one), and then hyperbolic. With an eccentricity equal to infinity, the orbit turns into a straight line.

From this it is obvious that any body with an orbital eccentricity above unity leaves the solar system. However, if its speed is below 16.4 kilometers per second, that is, the third cosmic speed, it will not be able to leave its body: the gravity of the Sun will slow down the body, and the eccentricity of its trajectory will begin to fall until it falls below unity.

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The trajectory of Borisov's comet is highlighted in green and blue-green, it is clearly seen that it passes through the solar system through and through

Before Borisov's discovery, only two bodies were known with an eccentricity of noticeably more than one. The first is comet C / 1980 E1 (Bowell), discovered in 1980, its eccentricity was 1.057. Nevertheless, it was a completely ordinary comet from the solar system.Astronomers watched as she received an eccentricity of more than unity in the eighties, due to the momentum she received from a gravity assist near Jupiter. Then the gravity of the huge planet gave the comet a speed of more than 23 kilometers per second and slightly changed its trajectory, which allowed the object to start leaving the solar system.

The second object with an orbital eccentricity of more than one - more precisely, 1, 20 - was asteroid 1I / Oumuamua, discovered in 2018. Analysis of its orbit showed that it was born outside the solar system and just flies through it at a speed of 26.33 kilometers per second. So this object received the status of the first known interstellar asteroid.

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Asteroid 1I / Oumuamua as seen by the artist

Comet C / 2019 Q4 (Borisov) differs from 1I / Oumuamua in that its speed is noticeably higher, and in addition, it has a coma - a tail, indicating that the comet is actively emitting gases. In addition, its eccentricity is higher than three, that is, much more than that of any previously known body. The comet sweeps through our system with a fairly moderate deviation from a straight trajectory - "right through".

Due to such unusual parameters, the Minor Planet Center, located in the United States, compared observations of the new body with various telescopes around the world for a long time to make sure that its extremely exotic trajectory parameters were not an observation error, but reality. And now, finally, on September 12, 2019, he officially recognized the discovery.

What will the discovery give astronomers?

The discovery of the first interstellar comet itself is an extremely important event, but many details of subsequent observations of the comet itself are also significant for science. By December 2019, it should approach the Earth by about 150-160 million kilometers, while the distance from the comet to the Sun will be close to 300 million kilometers.

At such a distance, the radiation from our star will heat up the "alien" enough to actively evaporate almost all volatile components from it. These are frozen carbon monoxide, carbon dioxide, water vapor, possibly methane, and much more. Based on the specific composition of the coma, it will be possible to make unique observations and understand how the composition of comets in other planetary systems differs from the composition of their counterparts from our system.

This is especially interesting because some objects in the solar system have long been suspected of "non-native" origin. For example, the asteroid 2015 BZ509, discovered in 2015, rotates in an orbit very similar to that of Jupiter, but in the opposite direction. In theory, all objects formed from a protoplanetary disk should rotate in the same direction as the disk that generated them. If some body rotates "against the grain", then there is a high probability that we are facing a migrant, a body once captured by the gravity of the Sun and its planets.

If the analysis of the spectra of Borisov's comet shows a similarity of its composition with the same 2015 BZ509, while differing from the composition of other comets in our system, then it will become much easier to identify captured interstellar asteroids and comets inside our system. Knowing about their origin, it will be possible to send robotic probes there, as was done with the Itokawa asteroid or the Churyumov-Gerasimenko comet. In-situ exploration is capable of yielding far more detail than any, even the most thorough examination of images of interstellar wanderers. Understanding how the composition of bodies outside our system differs from local ones and how much, it will be much easier to understand the evolution of planetary systems as a whole.

In addition, the very frequency of detecting interstellar objects passing through the inner regions of the solar system is a very important parameter that allows one to assess several points at once. For example, it will be possible to understand the total number of comets, typical for other stellar systems. It is possible to calculate the probability of the capture of interstellar bodies by the Sun, but while we do not know the number of such bodies in the surrounding galactic space, there is not much sense from these calculations.

How often do objects from other star systems bombard the Earth?

Finally, the issue with interstellar comets and asteroids has another, very mundane side: the safety of our planet. An asteroid or a comet from our system can rarely "sneak up" on the Earth unnoticed. Like the Earth, they revolve around the Sun, and therefore their orbits are closed: they fly in an ellipse or even a circle. Therefore, the "locals" are gradually approaching us, over and over again flying closer and closer, due to the influence of the gravity of our planet on their trajectory.

This means that they practically cannot strike suddenly: NASA tracks their trajectories and possible dates of intersection with the Earth in advance. Over the years, or even decades, one can prepare for a rapprochement with any dangerous body, organize the sending of a nuclear weapon to it (Russian researchers have already calculated such a scenario) that could divert even a large asteroid from a dangerous course.

This is not the case with "interstellar" asteroids and comets. Let's imagine for a second that the path C / 2019 Q4 accidentally intersects with the Earth. Having discovered the comet on August 30 and only by September 12, having found out its trajectory, earthlings would have had very little time before the December collision (it is in December that Borisov's comet will approach us at a minimum distance). In three to four months it is impossible to prepare an expedition capable of deflecting the trajectory of another celestial body.

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Asteroid 1I / Oumuamua in 2018 came close to Earth just months after its discovery - and if he collided with it, making a powerful explosion, there would be nothing to stop the "alien"

And this is not just a theory. After 2018 and the discovery of asteroid 1I / Oumuamua, astronomers tried to find in the trajectories of celestial bodies recently falling to Earth those that would have a large eccentricity of the orbit, indicating an origin from another system. It turned out that in 2014 one such meteoroid exploded in the atmosphere over Papua New Guinea. Its size was only 0.9 meters, so it gave only a bright flash in the stratosphere and zero destruction on the surface.

But in its place there could be a much larger object, and, as we remember, an asteroid ten kilometers in diameter, when it hits the Earth, gives an explosion of 100 million megatons. Sixty-six million years ago, an explosion of just such a power led to the death of all types of large terrestrial creatures on our planet. Therefore, it would be extremely interesting to find out with what frequency large bodies like Borisov's comet or 1I / Oumuamua fly into our system. If they do this often enough, humanity should think in advance about the means of defense against them.

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