A Backstory For Kuiper Belt Object ‘Arrokoth’

8:05 minutes

a red asteroid that looks like a snowman made out of two balls
New research of Arrokoth shows that it formed from a cloud in a solar nebula. Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Roman Tkachenko

This week, researchers published three reports in the journal Science giving some expanded results from the New Horizons spacecraft’s flyby of Arrokoth (formerly known as MU69).  The snowman-shaped Kuiper Belt object, they say, appears to have formed around 4.5 billion years ago in a localized collapsing cloud of dust, rather than via the repeated collisions of larger objects. The surface, the researchers say, is uniformly red, cold, and covered with methanol ice and other unidentified complex organic molecules. 

Purbita Saha, senior editor at Popular Science, joins Ira to talk about the findings and other stories from the week in science, including the latest on the coronavirus outbreak, a new analysis of food waste, and the murders of Homero Gonzalez and Raul Romero, two butterfly conservationists in central Mexico.

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Segment Guests

Purbita Saha

Purbita Saha is Senior Deputy Editor at Popular Science in New York, New York.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. Later in the hour paying respect to the world’s largest bodies of fresh water, as the sci-fi book club wraps up its dive into Dan Egan’s Death and Life of the Great Lakes. But first, remember that strange snowman shaped object in space formerly known as MU69 and then they briefly named it Ultima Thule and now it’s called Arrokoth? A lot of names going in there.

You’ll recall it was visited by the New Horizons space probe back about a year ago in January 2019. And what they found is– well spoiler alert –they found that it’s old and cold. Purbita Saha is senior editor at Popular Science and she’s here to review the findings published in the Journal of Science. Welcome back to Science Friday.

PURBITA SAHA: Hi, Ira. Happy Valentine’s Day.

IRA FLATOW: Oh, thank you. Thank you. You’re the first one to say that. So let’s talk about what’s in the news this week about the Kuiper Belt object that looks sort of like a snowman.

PURBITA SAHA: Right. So as you said, we got our first good look at Arrokoth, which is the name of this object last year after the New Horizons space probe flyby. And some people say it looks like a snowman. It’s this weird flattened two-part shaped object. And I think it personally–

IRA FLATOW: I think it’s a snowman.

PURBITA SAHA: You think it’s a snowman?

IRA FLATOW: I mean, it’s like two round things bumping together. Doesn’t it look something like that?

PURBITA SAHA: Yeah. Exactly. So bumping. We will come back to that in a little bit. I think it looks like a badly baked donut, but that’s just a personal reflection.

IRA FLATOW: Ooh, I’m hungry.

PURBITA SAHA: So New Horizons, the data it collected from this flyby took a while to be beamed back to NASA. And just this week the research team that’s combing through this data published three separate papers that look into what the origins of Arrokoth possibly are.

So like you said, it’s one of the most ancient objects that we’ve studied in space, probably dating back to 4.5 billion years when our solar system first formed. And so looking at the origins, there were two competing theories.

First the scientists tested could Arrokoth be a result of what we call hierarchical accretion which is essentially you have disparate parts from different regions of the solar system colliding at very high speeds. And when the dust clears, you end up with a planet.

IRA FLATOW: Snowman idea.

PURBITA SAHA: Or a snowman. Now Arrokoth isn’t a planet. It’s called what we say a planet planetesimal, so it’s a very undergrown planet. But these two different lobes of Arrokoth they’re so perfectly intact and undamaged. So scientists are like, how could that happen if we had all these materials?

IRA FLATOW: Yeah. It would be smashed apart and all kinds of stuff would happen.

PURBITA SAHA: Exactly. So they tried out this newer theory which is called cloud collapse. And essentially when gravity pulls together the gases and dust from a nebula, they squeeze into this clump that spins together slowly. And from this we have various pebbles that clumped together and potentially created the two different parts of Arrokoth.

And rather than colliding at a high speed, they had this slow dance where they bumped into each other and then became this one unified orbiting object.

IRA FLATOW: Cool. I like that.

PURBITA SAHA: Yeah. It’s pretty fun. And the scientists actually simulated this with models. And they saw that once they had the objects brushing together at speeds as slow as 9 miles per hour, that’s how they ended up with this perfect, although somewhat misshapen, formed body.

IRA FLATOW: So it’s more like a fender bender than a giant head on collision.

PURBITA SAHA: Yes, exactly.

IRA FLATOW: But do we know what it’s made out of? Did we find out?

PURBITA SAHA: Yes. So the surface is largely frozen methanol. And then underneath that, we have some really complex organic compounds, which give it the reddish glow. There might be water down there. New Horizons wasn’t quite able to figure that out. But you know, that’s always the existential question with the solar system.

IRA FLATOW: We love those kinds of questions. Let’s move on to another topic. The world has been keeping a close eye on the coronavirus outbreak, and it now has a new name, right?

PURBITA SAHA: Yes. So for a while there, we had been calling the coronavirus or this specific type of coronavirus the Wuhan coronavirus, because that’s the city that’s sort of been under siege in China from this disease. But the World Health Organization this week announced that they’ll be transitioning over to this new name, COVID-2019, which stands for coronavirus identified in 2019.

And the whole movement behind this is to prevent stigmas around the city of Wuhan, because we’ve seen in previous outbreaks such as MERS and SARS and swine flu, there are some real economic impacts that can precipitate from the world being gripped by anxiety from these diseases.

So the COVID-2019 specifically refers to the disease and not the virus. The virus has its own name, which is something long like SARS-CoV number 2– really rolls off the tongue. But there is this differentiation between the two.

IRA FLATOW: Now, I know that you just got back from a visit to Mexico. And where the monarch butterfly season is in full effect. What was that like?

PURBITA SAHA: You see the photos, you see the videos, people tell you their accounts and you still can’t– you still don’t know what to expect until you hike up this like mile-long path with people selling blackberries and strawberries along the sides. Tons of families from the local area and tourists walking up there with you.

And you finally get maybe like 4,000 feet into the Santa Marta mountains, and it’s just like you see the fluttering wings through the air. And every tree trunk and branch is just covered in orange. There’s no space for the butterflies to even land.

IRA FLATOW: That’s why it sounds like to me such a sad story that two environmentalists working to protect the butterfly habitat have been murdered in Mexico, right?

PURBITA SAHA: Right. So last month authorities in the state Michoacan found Homero Gomez Gonzalez dead. He had been a longtime advocate for this butterfly reserve which is constantly threatened by logging and also illegal clearing, because of the booming avocado industry. So Homero and this other activist who was found this month murdered, Raul Hernandez Romero, they had both been kind of leading this community effort to patrol the reserve and also raise awareness about these illegal activities to protect the butterfly habitat.

IRA FLATOW: I’ll have to keep following that story. Thank you very much for taking time to be with us today.


IRA FLATOW: Purbita Saha is a senior editor at Popular Science.

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