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In the solar system, there are more than 6,300 known comets. There are millions of asteroids. And among all these objects, only "Oumuamua – a cigar-shaped red asteroid – is known to have come from elsewhere. Until now.
A new discovery, revealed last week, excited astronomers. A comet named C / 2019 Q4 (Borisov), discovered on August 30 by an amateur astronomer from Crimea Gennady Borisov, has a trajectory and velocity suggesting that the object comes from outside the solar system.
Anxious telescopic eyes have turned to the location of the comet to try to extract as much information as possible. At the end of last week, we received our first color photo showing the distinctive gas release associated with an icy comet body approaching the sun.
And now, the first pre-printed papers arrive. Two separate teams analyzed the comet up to now: one looking at the color of the object and the other its spectrum, to see if they could learn about the composition of the body strange. . Their work still needs to be peer reviewed, but we can begin to examine their results with the scientific community.
Comets and asteroids are two distinct types of space objects. Asteroids are big pieces of rock and metal. Comets are made of ice and rock; when they travel near the sun, the heat produces a cloud of vapor and dust around the comet, which also moves away from the heat source, creating the famous cometary tail.
("Oumuamua is a nutty who has the characteristics of both a comet and an asteroid, or, possibly, neither one nor the other. always absent.)
We know what comets are in the solar system: the type of gas they emit, their size. We even know a little exocomets orbiting extraterrestrial stars.
For example, comets have been detected in orbit around the star Beta Pictoris; when the comet passes between us and the star, the quality of the star's light changes according to the comet's chemistry. These exocometes are very similar to our comets.
But an interstellar comet would be a data point that we could study closely – seeing how similar or different it is from our local comets could tell us more about the solar system itself.
If the comet is similar, it means that other planetary systems may be made of the same material as ours; but a really different composition and behavior could give us clues about the models of other planetary systems.
According to the two documents published so far, the C / 2019 Q4 (Borisov) looks a lot like our solar system comets. The first article is directed by Piotr Guzik and Michal Drahus from Jagellonian University in Poland and was found on arXiv; the other is led by astronomer Julia de León of the Instituto de Astrofísica de Canarias and published on the website of the Institute.
Guzik and his colleagues based their conclusions on the optical data obtained by the William Herschel telescope and the Gemini North telescope. They analyzed the red and green magnitudes and discovered that the color of the comet – very green and not very red – was essentially identical to that of the long-lived comets of the solar system from the Oort cloud.
De León and his colleagues studied the comet with the help of Gran Telescopio Canarias, obtaining three visible spectra of the comet with the help of OSIRIS instrument in order to analyze its chemical composition. These also showed that the comet resembled long-period comets in the solar system.
"We calculated the spectral slope in the range 0.55-0.90 μm, S = 10 ± 1% / 1000 A, a value roughly in the middle of the range of visible spectral slopes observed for cores and asteroids of comets in the orbits of comets, "they wrote in their paper.
"This suggests that comets formed in other stars [sic] may have a composition similar to that formed in the solar system and thus likely to be produced by similar processes. "
There are a few things to check. We do not know, precisely, how big it is – comet images are fuzzy due to outgassing, which makes it difficult to measure the rock in the interior.
Observations suggest up to now that its diameter is between 2 and 16 kilometers (1.2 and 10 miles). It's much bigger than the 170 meters of Oumuamua.
The origin of the comet must also be verified. This will probably take months of observations, carefully tracing the path of the object in the sky to better understand its trajectory.
However, unlike Oumuamua, which was only discovered when it was already emerging from the solar system, C / 2019 Q4 (Borisov) is still heading inland. Astronomers estimate that it will reach perihelion – its closest approach to the Sun – around December 8, 2019.
We can not wait to see the pictures.
Preprinted papers are available on arXiv and on the IAC website.
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