2I/Borisov: Another Interstellar Visitor Flashes By

Space isn’t really so empty as we might think. There are planets, moons, asteroids, comets, and rings. And dust. Beyond our local neighborhood, there’s also gas, lots of it. And, of course, we get the errant comet or asteroid from another solar system, like the newly found 2I/Borisov.

Earlier this year, an amateur astronomer named Gennadiy Borisov was out observing. On August 30, he found something that looked like a comet. He reported his find in a notification to the IAU. Other observers went to work looking at it, too. Using their observations, the IAU Minor Planet Center came up with a preliminary orbit. It turns out this thing isn’t just any comet. It’s coming from outside the solar system. Its official designation means it’s the second interstellar object and it was discovered by Borisov.

2I/Borisov is Hyperbolic!

This alien comet is in a hyperbolic orbit. That means its origin is from outside the solar system and it will (unless captured gravitationally by the Sun (unlikely), end up sailing right through our planetary system and back out to interstellar space. A hyperbolic orbit is not a “closed” orbit. That is, it isn’t an ellipse (like a squashed egg) It’s open-ended. (Geometry students will remember hyperbolas from their studies of ellipses, arcs, and so on).

Objects that follow such orbits into the solar system seem rare. They may not be as numerous as stuff from within our region of space. It’s also possible that we’ve spotted them before, but didn’t realize their origins. But, it makes sense that they’re out there. Planetary systems lose objects in the normal course of their evolution. So, there’s no reason some of them aren’t coming this way for a quick fly-by.

Recall that in 2017, astronomers spotted ‘Oumuamua. This is an asteroid-type object also on a hyperbolic orbit. It passed within 38,624,256 kilometers (24 million miles) of the Sun before heading back out to interstellar space. Planetary scientists are still studying data taken during its flyby.

Hubble Space Telescope Looks at 2I/Borisov

The Hubble Space Telescope studied 2I/Borisov as it swept past Earth at a distance of 418,429,440 kilometers (260 million miles). It will continue to observe for a few months as the comet makes its way out past Jupiter and to interstellar space.

Unlike ‘Oumuamua, which really didn’t exhibit much in the way of cometary characteristics, 2I/Borisov looked more like a comet. It had a central nucleus, surrounded by a dust cloud (coma). A spectroscopic study (made by dissecting the light from the comet) should give astronomers info about its chemical composition. They should also be able to get a good idea of the type of star system where it was born.

With a better idea of its path through space, eventually, they might be able to figure out WHERE it came from. However, that’s not what HST was programmed to do. Its instruments are focused on imaging and data about the object itself. The best way to figure out the origin of an interstellar visitor is to trace its trajectory as far as possible. With that data, astronomers can extrapolate a very probable path through space. If there’s a star system along the way, that might be its home. However, we may never know for sure. Things are in constant motion in our galaxy. An object from a distant area could well have its trajectory changed over long periods of time.

Need More Data about 2I/Borisov!

Hubble observations, as well as studies using other telescopes, will be used to help astronomers in an other way. Information about this comet could help them understand the origins of comets and other small bodies. We know where they are in our current solar system (the Oort Cloud and Kuiper Belt). Are they in the same places in other star systems? How do they evolve over time? What can our Kuiper Belt tell us about other system’s “cometary belts“?

Astronomers and planetary scientists are constructing very accurate models of how these small bodies formed in the early solar system. They also look at how comets and asteroids scattered around. Do they do the same thing at other stars? This comet’s data will help answer that and other questions.

A Peek at a Neighbor’s Business

Astronomers know the general properties of stars. They can deduce some information about their planetary systems just by studying orbital characteristics of the star and its planets. However, the key to understanding their chemistries is in spectroscopic data. Spectroscopy of light from objects is like getting a peek into the characteristics of the systems where they exist. In this case, spectroscopy of 2I/Borisov will lift the veil on conditions in its home system.

So, think of this comet as a treasury of clues about where it originated. While the comet is still in OUR solar system, astronomers will continue to study it with all the modern tools. Eventually, however, the comet will leave the solar system, leaving behind a great deal of dust, information, and clues to its origins and makeup. Eventually, what we learn from it will help us understand the conditions at our stellar neighbors.

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