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NAU Astronomer Describes Discovery Of Distant Space Rock ‘Farfarout’

NOIRLab/ NSF/ AURA/ J. da Silva.

A team of astronomers has confirmed the discovery of the furthest-known object in the solar system, nicknamed “Farfarout.” The team found it in 2018 and has been tracking it ever since. It’s smaller than Pluto and takes a thousand years to make an orbit around the sun. KNAU’s Melissa Sevigny spoke with Chad Trujillo of Northern Arizona University about the finding, which is part of his ongoing survey of the distant reaches of the solar system. 

Tell me what you know about this object, which you’re calling Farfarout?

Farfarout, the most interesting thing about it is it’s at 132 Astronomical Units from the Sun. So one Astronomical Unit, we say AU, is the distance between the Earth and the Sun. Neptune, which is the furthest giant planet out there, is at 30 AU. So this is more than four times further away than Neptune. And so it’s the furthest object ever observed in the solar system.

So it’s less empty out there than people originally thought it was.

For sure. People used to think there was just Pluto and nothing else and now we know there’s the whole Kuiper Belt, but it does seem there’s this population of objects that go very far out.

What else do you know about it, do you have any details about the size or what it’s made out of?

We don’t know much about what it’s made out of, because it’s really faint…. But it’s probably icy because it’s so far away. We do know maybe a little more about the size…. it’s probably about 400 kilometers in diameter. That is kind of on the edge of dwarf planet size….  So we think it’s probably spherical and probably would qualify as a dwarf planet but we would have to really know more about it to say that for certain.

Can you tell me just briefly how you go about finding these very faint, very distant objects?

To find these distant objects we go to large telescopes with wide fields of views. One of our favorites is the Subaru telescope on Mauna Kea in Hawaii, where there’s a whole collection of telescopes, but the Subaru telescope is an 8-meter diameter mirror, which is really big…The other telescope we use is the Cerro Tololo Inter-American Observatory 4-meter telescope in Chile…. So we take two images 24 hours apart and then we see the objects moving. Just like if you’re in your car driving down the highway, things that are very close appear to pass by very quickly, and things in the distance like mountains or distant trees or something, they appear to move very slowly. This is the same idea, except in the astronomy context it’s the Earth that’s moving rather than your car on the highway. So very distant objects move very slowly. That’s how we can almost immediately tell something’s really distant.

You’ve been doing this for quite a while and discovered all sorts of new things out there, but I’m wondering, how do you feel when you spot a new object like Farfarout?

It’s definitely exciting to see something that’s really distant, I mean… you have to look at these data for hours and hours and hours, I don’t even know how many hours I spent looking at these data…  I think one of the most interesting things about Farfarout is that it really goes to show that there’s more things to be discovered out there.… I think the discovery of this one object really tells us it’s just the tip of the iceberg, so to speak, there’s a lot more out there remaining to be discovered.

Chad Trujillo, thank you so much for speaking with me.

Thanks a lot, Melissa.


Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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