Charon’s Red Cap, Mapping the Milky Way, and Crafty Crows

7:09 minutes

An enhanced color view of Pluto’s largest moon, Charon. Scientists have learned that reddish material in the north (top) polar region is chemically processed methane that escaped from Pluto’s atmosphere onto Charon. Credits: NASA/JHUAPL/SwRI
An enhanced color view of Pluto’s largest moon, Charon. Scientists have learned that reddish material in the north (top) polar region is chemically processed methane that escaped from Pluto’s atmosphere onto Charon. Credits: NASA/JHUAPL/SwRI

For more than a year, the New Horizons spacecraft has been beaming back photos of Pluto and its moon Charon. The images revealed that the icy moon has a red cap at its north pole. In a study out this week in Nature, scientists report that Pluto may be responsible for that wispy hue. Rachel Feltman, editor of The Washington Post’s Speaking of Science blog, discusses the details, plus other science stories from the week.

Segment Guests

Rachel Feltman

Rachel Feltman is author of Been There, Done That: A Rousing History of Sex, and is the host of “The Weirdest Thing I Learned This Week.”

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow. For over a year now, the New Horizon Space Probe has been beaming back photos of Pluto and its moon Charon. Remember seeing the whale’s tail for the first time? All these images are revealing details about the geology of the dwarf planet and its moon. And it’s also bringing up more questions. One mystery has been why Charon has a wispy red cap at its north pole. Scientists this week may have cracked that question. Here to talk about that and other selected short subjects in science is Rachel Feltman, editor of the Washington Post “Speaking of Science” Blog. Welcome back, Rachel.

RACHEL FELTMAN: Thanks for having me, Ira.

IRA FLATOW: Interesting stuff. What do we know about Charon now that we didn’t know before?

RACHEL FELTMAN: So one of the things that scientists spotted during the fly by was, first of all, Charon had a much more interesting surface than they expected. It wasn’t this old crater-marked rock. It had a bunch of interesting geology. It had these huge, you know, chasms bigger than the Grand Canyon. And one of the things they noticed is that it had this bright red spot on its north pole. And the intriguing thing was that this red spot looked an awful lot like the color of Pluto. And they thought maybe because Pluto had this wispy atmosphere they had just discovered and didn’t really have the gravitational strength to hold on to that atmosphere, maybe Charon grabbed some of it and was getting the molecules to paint itself red.

But they weren’t sure whether that could actually occur. They didn’t know whether there were places on Charon that were cold enough to actually trap the atmosphere. But this new study found that during Pluto and Charon’s orbit, there are these periods of 100 year winters where either pole will be plunged in total darkness for a century. And during that time, the temperature is around minus 430 degrees Fahrenheit.

IRA FLATOW: Like Game of Thrones on Pluto.

RACHEL FELTMAN: Yeah, exactly. Which is cold enough for Charon’s poles to hold on to frozen methane. So basically what’s happening is that these macromolecules called tholins make Pluto red. But some of the same methane that that is the source of those tholins gets sent over to Charon. As it escapes out into space, Charon captures some of it. And in the winter, the poles are cold enough to hold onto it. In the spring when it’s sunlight, they sublimate back into gas. But some of the heavier macromolecules stay on Charon, turn into tholins. Over the course of millions of years, it has turned the moon red.

IRA FLATOW: And there you have it.



IRA FLATOW: So simple an explanation.


How much longer is the Horizon going to be flying by Pluto and Charon?

RACHEL FELTMAN: Well, you know the fly by itself, you know, was really quick. It was over in just a few hours. They do have a few more months, I think, of sending back data from the flyby. And the mission has officially been extended so that in 2019 it’s actually going to be beaming back data about another more mysterious Kuiper belt object.

IRA FLATOW: Yeah. Well, we’re waiting. Speaking of mysterious things, there’s a new interactive map released this week. A map of the entire galaxy.



RACHEL FELTMAN: Yeah. So it’s the most complete sky map ever. And it’s from the Gaia Space Telescope. It’s one year into its observation phase. It’s orbiting the sun about a million miles farther out than Earth is. And it has these two telescopes that together power a billion pixel camera. And what it does is it just scans these billion stars over and over again, more than 70 times a star. And right now it has precisely mapped the positions and trajectories of two million of those stars. So the sky map we got this week was just those two million. And the rest of the billion are probably coming sometime in 2017.

What’s really cool is that they released all of the data because there is just so much that the team involved can’t possibly sift through all of it. So people can go online. The BBC had this great anecdote about schoolchildren teaching the reporters how to use the database.


And while they were showing them, they found a supernova.

IRA FLATOW: No kidding.


IRA FLATOW: No kidding. Those kids find the darnedest things.

RACHEL FELTMAN: [LAUGHING] So there’s so much stuff in there. So people should definitely take a crack at that. And the hope is that by getting these more accurate star distances, we can figure out some things we don’t know about the expansion of the universe about the behavior of dark matter. And also possibly discover some new planets because we’ll probably see some of those stars wobbling because of the planets orbiting them.

IRA FLATOW: Yeah. Because we know there’s a lot of dark matter there. But we don’t know what it is.


IRA FLATOW: Wow. That’s cool. Well, your last story is about crows. Right?


IRA FLATOW: We’ve always heard that they can use tools. We’ve seen them pick up sticks and use them for stuff like that. But not all crows are crafty.


IRA FLATOW: Turns out.

RACHEL FELTMAN: Well, so a lot of crows can learn to use tools. But so far until this week, there had only been one species of crow that was an innate tool user, which means even if you don’t teach hatchlings how to use sticks as tools, they’ll figure it out. It’s something innate that they’ve evolved to do. And researchers have now found a second species of crow that does this. The Hawaiian crow. And it was really cool.

They did it by basically just looking for crows that had the physical characteristics that would lend themselves most to picking up sticks. They have these really straight beaks and very large binocular fields of vision. And sure enough, when they went after that optimal stick-using crow, they found that they do have innate tool use. If you take the hatchlings away from their parents, they will still learn to use sticks to get food out of the ground.

And the other really interesting and sad thing is that these animals are extinct in the wild. There are only 109 of them left in one facility in Hawaii. And so basically, we came close to never knowing that they had evolved this really rare ability.

IRA FLATOW: Are there any thoughts about increasing the population or putting them out in the wild?

RACHEL FELTMAN: Well, you know, they are. The facility that they live in is trying to build the population back up. But you know 109 is barely large enough for the researchers to even do a real study on them. So it’s definitely going to be a long time before that species is not endangered.

IRA FLATOW: I guess they once did. They must have existed in the wild.


IRA FLATOW: Yeah? It’s kind of scary to have them all in one spot.


IRA FLATOW: You know? Don’t you think that may be some disease could come by and they’re all together in one kind of–

RACHEL FELTMAN: That’s true.

IRA FLATOW: You know?

RACHEL FELTMAN: I don’t want to think about that.


IRA FLATOW: No. Let’s think good thoughts as we say goodbye.


Always good to have you.


IRA FLATOW: Rachel Feltman, editor of the Washington Post “Speaking of Science” blog with us today.

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