ISON: The Comet of the Century... or Is It?

When astronomers spotted Comet ISON in 2012, some christened it the "Comet of the Century." It initially failed to live up to the hype. But this month, ISON blazed brighter and sprouted several tails. Astronomers like Andrew Fraknoi are following the comet as it scrapes past the sun, where it could be destroyed—or emerge, even more spectacular than before.

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IRA FLATOW, HOST:

This is SCIENCE FRIDAY. I'm Ira Flatow. While everyone is shopping at the mall during the holiday season, I've got something better for you to do. Check out comet ISON. Comet ISON is flying toward the sun at over 150,000 miles per hour. It's making its closest approach on Thanksgiving Day and you can check it out after it comes back around the sun, but will it fly too close?

Will it be vaporized by the sun's heat, torn to pieces by the sun's gravity? Astronomers are very excited and they'll be following that dramatic flyby next Thursday as you tuck into your turkey. Andrew Fraknoi is chair of the astronomy department at Foothill College in Los Altos Hills, California. He joins us from KQED. Welcome back.

ANDREW FRAKNOI: Oh it's nice to be back with you, Ira.

FLATOW: Why don't we really know what's going to happen with this comet?

FRAKNOI: Well, this comet is a virgin comet, if I can put it delicately. It's the first time that it's coming by the sun and it's also a sun-grazer, which means it's going to come incredibly close to the heat and the gravity of our own star. And so when stars - I'm sorry, when comets fly so close to the sun, we really don't know what their fate is going to be. This is kind of a cliffhanger if you will.

There are three different ways that the comet may react to being so close to the sun. It may, like you and I, fall apart under the threat of everything. It may actually be completely gone or it may reemerge with just a shadow of its former self, as a trail of just gas and dust. We have to just wait and see what happens to it.

FLATOW: Because this was really heavily promoted as a comet of the century, so to speak, when we first...

FRAKNOI: Well, that's exactly what the problem was, that it's a new comet and new comets, when they first come into the solar system, tend to act a little bit irresponsibly. They don't have the consistency of a good old comet that's been around the block a few times. And at first it seemed very bright and then it faded out and we were very dispirited.

But now it's kind of acting up again and it's having more promise, in the last few days, of becoming a good comet.

FLATOW: When will it be visible to we non-professionals, like ourselves?

FRAKNOI: Well, right now it's getting too close to the sun, so you really have to be a professional astronomer to have a spacecraft around the sun to see it, and that, by the way, is what we're going to be doing. We will have a number of spacecraft, ones that are orbiting Mercury and ones that are looking at the sun, which will be making measurements and taking pictures of the comet, even when we earthbound observers can no longer see it.

But then as we go past this perihelion that's whizzing by the sun at Thanksgiving Day, in the early days of December it will again become visible in our skies if the comet survives.

FLATOW: If it survives. And how big is this comet?

FRAKNOI: Well, that's interesting too. The first measurements indicated it was about three miles wide, but now newer measurements from telescopes we have in space tell us that it's less than a mile wide. Now, that's still pretty big for a comet, but the smaller the comet is, the smaller the icy piece of material which is the central part of the comet is, the harder it is for it to survive.

So the smaller the comet is, the more danger there is that the sun is going to get it on Thanksgiving Day. And so we're hoping that this is big enough. The estimates now are, you know, maybe three-quarters of a mile or so. We hope that's big enough so that either the whole comet or the comet broken into pieces will come out from the other side of its encounter with the sun and will be visible.

FLATOW: 1-800-989-8255 is our number. Let's assume the comet is intact and it comes around the sun and it survives. It's going to have a tail, but the tail's going to really be in front of it, isn't it?

FRAKNOI: That's right. That's a funny name, the tail of a comet. When the comet is coming in, the tail is indeed behind it. But as the comet rounds the sun and goes out of the solar system, what produces the tail is the gas pressure, the wind of the sun and the light of the sun, so the tail of a comet always points away from the sun and on its way out the tail leads the comet.

FLATOW: Is it possible that the comet could break up into a bunch of smaller comets when it comes around?

FRAKNOI: Absolutely. This has happened to a number of sun-grazing comets, that the comet itself breaks apart and that's actually good news for observers. If you break the comet into several smaller pieces, then you have more surface area of the ice to evaporate and that will produce a greater amount of material coming off the comet.

The unfrozen ice and the dust that's released will make a bigger cloud around the comet, which will make the comet easier to see. So as Neil Sedaka used to say, breaking up is hard to do, but we hope that the comet is going to do that so it will be an even more spectacular object.

FLATOW: Come-a-come-a-down, dobbie-do-bop.

FRAKNOI: There you go.

FLATOW: We won't see it though as a bunch of, like a fleet of comets, right? I mean, to our eye it will look just like a single comet if it breaks up?

FRAKNOI: It may or it may not. We've certainly seen comets where the chunks have moved apart enough so that they become visible as individual comets, and certainly our better telescopes, which can focus in in more detail on the comet will reveal the broken nature of it, the fragmentary nature of it. So there's a whole series of telescopes, both on earth and in space, that are watching this comet.

We have many more eyes on it than we have had in comets of the past that have done this, so whatever the comet winds up doing, we'll have a wonderful view on the Web, even if you yourself personally can't see it in the early dawn sky when it's visible. Check out the many websites that are keeping track of the pictures and the data coming back from this remarkable object.

FLATOW: Let's go to the phones to our nation's capitol, Ben(ph) in Washington. Hi. Ben, are you there?

BEN: Yes, hi. Thank you - yes, hi. Can you hear me?

FLATOW: Yes, go ahead.

BEN: Thank you very much for taking my call. This is quite exciting. I remember seeing an article, I think it may have been on Huffington Post, about how some scientists were a little confused because they have some trajectory estimates and measurements that had changed and I was wondering if the guest had any comments about that.

And also, you know, given the general characteristics of a comet, you know, having ice, what are the assumptions in terms of it being close to the sun and any of that ice really being able to survive?

FLATOW: Thanks. Breaking up there. Yeah, Andrew?

FRAKNOI: This is exactly the issue with comets. Comets are chunks of ice that come toward us from the deep freeze of space, and as they get closer to the sun, the sun evaporates the ice and loosens the dust that was frozen in there for billions of years, and that's what makes comets so spectacular. So we fully expect that the ice will in fact be giving way under the heat of the sun. The question is, how much will this close encounter with the sun, only about as big a distance as the sun's size itself, away from the sun, how much of the ice will it destroy, how much of the comet will survive?

As far as trajectories are concerned, we've been pretty steady in our estimates of the trajectory. Where scientists have been changing their minds is the brightness estimates of the comets. How bright will it be, and that was a tough one because it is a fresh comet, so we had no history to judge by. We're looking forward, though, to a hope that the comet will survive and that it will be one of the better comets when it comes out the other side of the sun.

FLATOW: Let me talk about something else for a second, because I know you're the right buy to talk about. You know all this stuff. There was a six-tailed comet that was photographed a few weeks ago. We heard about that a few weeks ago. But it was sort of half comet, half asteroid.

FRAKNOI: That's right. This is one of the other things. Nature doesn't like it when we astronomers oversimplify the universe. So we've been dividing the cosmic garbage that's out there, left over from the formation of the solar system, into two categories. The icy garbage is called comets, and the rocky garbage is called asteroids.

And nature thumbs her nose at us and said: Well, it's not that simple. And we've been finding a number of objects that are a cross between a rocky asteroid and an icy comet. And what you're talking about is a recent discovery of an asteroid in the asteroid belt that had jets on it, just the kind of jets that happen when a comet starts to evaporate and material comes flying out of it.

So here is an asteroid acting like a comet with six different jets, and it, again, defies this over simplistic classification. There are comets that have asteroid properties, asteroids that have comet properties. Nature is always more complex than we try to make it.

FLATOW: Have astronomers assigned a name to this kind of thing?

FRAKNOI: Well, there is - those that are a cross between a comet and asteroid are called centaurs, after the myth beings that were half-man, half-horse. These centaurs are half-comet, half-asteroid.

FLATOW: And it changed, the number - the jets on it were changing over time, the direction they were heading in?

FRAKNOI: That's right. So it was spinning up, this asteroid-comet combo, in an odd way, in ways that were, at the beginning, quite hard to explain. And there's still some theorists wrapping their minds around this bizarre, binary behavior, double-character behavior of this particular object.

FLATOW: I've only got a couple of minutes. I don't want to let you before you can give us a little preview of what to look for this winter in the sky. Any interesting stuff to look at?

FRAKNOI: Well, so, as far as comet ISON is concerned, what you want to do in December is to follow along, get a website that's got maps on it. It's going to be best in early December, in the early morning sky. So you'll have to get up before the sun does if comet ISON is good. Later in December, the comet will be fainter, but it will be visible, then, in the evening sky, as well.

And as we go toward January, the comet is going to start to approach the North Star. It's going to become, actually, visible all night long as a kind of northern constellation, as a northern object. So, in the first part of December, it's a dawn object. Then later on it, will be both visible in the morning and in the evening sky.

FLATOW: Party time for comet-watchers.

FRAKNOI: It is now. By then, it might be quite faint. And, remember, we're not promising anything. The Comet Hunter, David Levy, likes to say that comets are like cats. They have a tail and they do precisely what they want. So we can't promise you that this comet will be good in December, but as they say on the radio, stay tuned. We'll have more news after Thanksgiving.

FLATOW: Do we have a meteor shower coming up at all this...

FRAKNOI: Well, there are meteor showers regularly during the year. There is going to be one in the middle of December. But that's also something, I think, that generally, people don't understand, that a meteor shower is something that comes from the leftover dust and dirt left by previous comets. So as comets come by again and again, like your little brother, they leave a lot of dirt in their path, and it's that dirt that then causes shooting stars, which are the dirt pieces burning up in the Earth's atmosphere.

FLATOW: Thank you, Andrew. Informative, as always. Have a good holiday season.

FRAKNOI: You, too. Enjoy the turkey, and keep your fingers crossed for comet ISON.

FLATOW: We'll be doing that. Thank you. Andrew Fraknoi's chair of the astronomy department at Foothill College in Los Altos Hills, California. We're going to take a break. When we come back we're going to talk about why it's good to be a little nuts, or a lot of nuts. So, stay with us, we'll be right back after this break.

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