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Coast to Coast AM topics

July 29, 2005

Welcome to Bad Astronomy!

This page has images and links that George Noory and I discussed on the Coast to Coast AM radio show on Friday night, July 29, 2005.

If you are curious about the other times I have been on C2C, then you can read the pages I wrote for my appearances on December 22, 2004, July 5, 2004, February 26, 2004, and November 15, 2003.

We're all familiar with the solar system: one star -- the Sun -- in the center, 4 inner planets, an asteroid belt, four giant planets, and then Pluto.

This may now change. Two new objects were announced today, and both are big, maybe as big as Pluto. One is almost certainly bigger than Pluto! If this pans out, then we'll either have to say there are 10 planets in the solar system, or we'll have to redefine Pluto as something other than a planet. Why? Well, let's discuss.

animation of EL61
Animation of 2003 EL61, showing its motion over a period of several days (clicking it will take you to the discovery page)

Most people are unaware that beyond Pluto is a vast collection of large icy bodies, what you might think of as giant comets. They have lots of different names: Trans-Neptunian Objects, Kuiper Belt Objects, Plutinos, Oort Cloud Comets, etc. Basically, these objects come in two regions: an inner, flat disk that goes from beyond Pluto out to about 50 - 100 times the distance of the Earth to the Sun, and a more spherical "cloud" of objects that probably goes out about a trillion miles from the Sun.

No one has ever directly observed an object in that big cloud, but many objects have been seen in the inner disk. Some people (me included) think that Pluto is more like these objects than it is like a planet. Think of it as the King of the Kuiper Belt Objects (or KBOs).

Pluto, it turns out, is also brighter than most of these objects. It happens to be bigger, but it is also more reflective: it reflects about 55% of the light that hits it. That's reflective! Most other KBOs only reflect about 4% of the light that hits them. They're pretty black, or probably dark red. Scientists call this reflectivity albedo.

When these things are spotted, we can detect their motion across the sky. By using some pretty fierce math (invented by Isaac Newton!) the orbit of the object can be calculated, and from that the distance can be found. If we know the distance, and we know how bright it is, and we know (well, guess really) it's albedo, we can calculate the size.

It's really not quite that simple, but it's close. Think of it this way: a dark object will look dimmer than a reflective one, right? So if we know how bright it is, if it's dark it has to be bigger than if it's reflective. The albedo can be guessed at using color information, and other techniques.

images of 2003 UB313
Image of 2003 UB313, showing its motion over a period of several days (clicking it will take you to the NASA announcement)

The two new objects, called 2003 EL61 and 2003 UB313, were actually first seen in images taken back in 2003. But for EL61, the orbit wasn't known until literally yesterday as I write this (July 28, 2005). For UB313, the orbit was known, but the astronomers were waiting until they could analyze their observations with the Spitzer Space Telescope before they announced their discovery. When the news about EL61 hit, they decided they might as well talk about it now.

Using a guess at the albedo, astronomers think that EL61 is about 980 miles across (70% of Pluto's size). Even better: it has a moon! The Moon is about 1% the mass of EL61, and takes 49 days to orbit it. Many objects like this have moons, but this means we can calculate the mass (again, with Isaac Newton's help). Turns out, the mass of EL61 is about 32% that of Pluto's.

And things get even more interesting. Using a guess at the albedo (and the fact that Spitzer did not see it, meaning it must be less than 2000 miles across), the discovery team found UB313 to be (get this) 1600 miles across- bigger than Pluto! Even if UB313 is 100% reflective -- a perfect mirror -- it is still bigger than Pluto. This needs to be confirmed, but if it's true, Pluto is no longer the last planet. UB313 is the last one.

The last known one. There might be more out there, even bigger. I'd bet on it. I've been saying for years that we will almost certainly find something bigger than Pluto out there in the dark, cold reaches of our solar system (I've said so on Coast to Coast several times, actually). There might be something as big as Earth out there, but so far away and so dark we've been unable to detect it. And no, I do not mean anything at all like Planet X. James McCanney, Nancy Lieder, and the rest are still just as wrong about that, as again I have been saying all along.

This is real science folks, and it's an exciting adventure, full of surprises and hidden treasures. I love this.

Remember: the Universe is wonderful enough without having to make up nonsense about it.


©2008 Phil Plait. All Rights Reserved.


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