Previous: How Two Dead Stars Sparked a New Field of Astronomy
Next: The Brightest, Biggest Space News of 2019!



View count:2,673
Last sync:2019-12-20 20:30
This year, scientists have had a chance to study something pretty mind-boggling: a comet that came from outside of our solar system.

Host: Hank Green

SciShow has a spinoff podcast! It's called SciShow Tangents. Check it out at
Support SciShow by becoming a patron on Patreon:
Huge thanks go to the following Patreon supporters for helping us keep SciShow free for everyone forever:

Kevin Carpentier, Eric Jensen, Matt Curls, Sam Buck, Christopher R Boucher, Avi Yashchin, Adam Brainard, Greg , Alex Hackman, Sam Lutfi, D.A. Noe, Piya Shedden, Scott Satovsky Jr.Charles Southerland, Patrick D. Ashmore, charles george, Kevin Bealer, Chris Peters
Like SciShow? Want to help support us, and also get things to put on your walls, cover your torso and hold your liquids? Check out our awesome products over at DFTBA Records:
Looking for SciShow elsewhere on the internet?

This year, scientists have had a chance to study something pretty mind-boggling, a comet that came from outside of our solar system.  The comet appeared this summer and on December 8, it made its closest approach to the Sun.  It's called 2I/Borisov and it's only the second interstellar object we've ever detected, the second interstellar interloper, if you will.

It's traveled billions of kilometers to get here, and so long as it's in our neighborhood, there's a lot we can learn from it about regions of space far beyond our own.  In fact, there's a lot we're already learning.  Last week, NASA released a shiny new image of the comet and over the last few weeks, scientists have published a handful of new papers about it, and so far, all this research is demonstrating to 2I/Borisov is full of surprises.

The comet was discovered this August by a Crimean telescope engineer named (?~0:59) Borisov, who, for the record, discovered this comet using a telescope he built himself.  I have a hard time building Ikea furniture.  After Borisov saw the object, he submitted his findings to the astronomy community so more researchers could take a look and ultimately, everyone's early data indicated that something was super weird.  For one, this comet had a very weird orbit.  

Most objects around here travel in a closed loop around the Sun, but 2I/Borisov seemed to have highly hyperbolic orbit.  In other words, it wasn't actually orbiting the Sun.  Instead, it was on a path that would swing around our star and then zoom off into the distance, never to return.  Now, technically, it is possible that something within our solar system could get bumped into an orbit like that.  There's even some evidence of this happening on a smaller scale way out in the Oort cloud beyond Pluto, but 2I/Borisov was traveling on a path that was dramatically tilted compared to the rest of our neighborhood.

It also seemed to be moving especially fast at more than 30 km/sec.  So with that kind of speed and orbit, well, scientists eventually concluded that this thing wasn't from 'round here.  We mentioned this discovery on SciShow Space in late September, but since then, scientists have been observing 2I/Borisov as much as possible and some of their results have been published over the last few days or weeks. 

Using images from various ground and space telescopes, these researchers have characterized every aspect of the comet they could.  They've calculated its size and shape, the rate it's losing mass and how it reflects light in different wavelengths, something that can tell us about its composition, so now we know a few things.  Like the data showed that the comet's body, called the nucleus, is less than 500 meters across and they also show that it's dust tail, or coma, has a similar composition to some comets from the Oort cloud. 

In fact, based on these results, if this comet had come from inside our solar system, it would be pretty unremarkable, which, that's actually kind of remarkable, especially if you compare this comet to the only other interstellar visitor we know of, Oumuamua, which zoomed past us in 2017.  With its probably cigar-like shape and shiny surface, Oumuamua  was among the weirdest objects anyone had ever seen, so how come 2I/Borisov looks so normal, even though they're both from interstellar space?

Well, we don't know and it's way too early to make generalizations.  The most we can say from these two data points is that the two objects seem to come from two different spots.  By working back from their current trajectories, scientists think 2I/Borisov came from the general direction of the constellation Cassiopeia.  Meanwhile, Oumuamua likely came from somewhere in the direction of the star Vega.  So maybe that explains some of the differences, but also let's be honest.  Two data points representing all interstellar objects is just not a lot to go on.  

As telescopes get better and better at resolving faint objects, we may have better luck at making more discoveries like this, but until then, we'll be left with more questions than answers.  The good news is, one way or another, we are not done with 2I/Borisov yet.  While we only saw Oumuamua on its way out of the solar system, we caught 2I/Borisov while it was still coming in, so we have more time to observe it.  It'll be making its closest approach to Earth around December 28th, so we'll be able to study it with the best precision yet, and that means there will be plenty more to learn about our second visitor from interstellar space.

Thanks for watching this episode of SciShow Space News.  As December winds down, we wanted to remind you about our Pin of the Month club.  Every month here on SciShow, we release a new space-themed pin that you can use to celebrate your love of exploration and this month, we've got one of an astronaut riding around on the Apollo 17 lunar rover.  It was designed by one of the amazing animators on the SciShow team and it's really just so good also.  It's a great chance to tell people about that one time we drove buggies on the moon.  If you want to get a pin for you or a friend, they're only available until the end of the month.  You can find them at or in the  merch shelf down below this video.