The Tenth Planet Shrinks Under Hubble's Gaze

starexplorer2001 writes "An object called the 10th planet by some astronomers is not as large as previously thought. New images of 2003 UB313 (aka Xena) were delivered by the Hubble Telescope and showed up as only 1.5 pixels! Now, some are calling to demote Pluto and kill Xena."

Re:atomic?

[staticdaze]

This is off the top of my head, but I would think they could determine that "half pixel" based on the shade of the entire pixel relative to the "main" pixel that actually contains most of the body. If it's 75% darker, assume the object extends 25% into that pixel? Am I close?

misunderstanding?

[interactive_civilian]

I think the GPP meant atomic as in "smallest reduceable unit", which came from the Greek atomos which means "indivisible".

So, how do you get half a pixel on a screen? I too was under the impression that an individual pixel was either all on or all off...

Re:misunderstanding?

[helioquake]

So, how do you get half a pixel on a screen? I too was under the impression that an individual pixel was either all on or all off...

Do you guys know the concept of "resizing a ditital image"?

Subsampling of a pixel can be done by knowing the intensity values in the neighboring 8 pixels (or greater). In other words, you can derive the intensity value at the pixel boundary by taking the mean value of the intensity values detected in these two pixels.

In this case, the measured size is derived based on mathematical characterization of the apparent point source.

I ought to be able to say this in a simpler term, damn it...

Re:atomic?

[binarybum]

maybe, but this still seems bizarre - why not map the pixels into real space and give a value based on a non-discreet scale (like meters or football fields)?

Re:atomic?

[gameforge]

You guys are making this too complicated. NASA's site [nasa.gov] says: "Located 10 billion miles away, but with a diameter that is a little more than half the width of the United States, Xena is only 1.5 picture elements across in Hubble's Advanced Camera for Surveys' view."

Think projection in a 3D game. A pixel represents, at a projected distance of 10 billion miles, a width x. Xena is 1.5x.

The final image (as you all have pointed out) would require a minimum of two pixels of information to accurately reproduce the projected image from a distance of 10 billion miles. The second pixel would not have the intensity of the first. But from the image on the site, it looks like a lot more than two pixels of information were recorded; I don't see how they could magnify two pixels and get that.

Re:Stupid name

[mgblst]

How about this line from the article
 
  Nicknamed "Xena," 2003 UB313 was discovered last year.
 
So 2003 UB313 was discovered last year, in 2005 - doesn't that strike someone as a little odd.

What did Mike Brown Really say?

[bloodstar]

From TFA:

The reasons are simple. Even Mike Brown says there is no scientific basis for calling 2003 UB313 a planet. Here is what he said last year:

I will not argue that it is a scientific planet, because there is no good scientific definition which fits our solar system and our culture, and I have decided to let culture win this one.

He's using Mike Brown's acceptance of the generally accepted cultural view that planets are 'anything pluto sized or larger' as a way of discrediting 2003 UB313. In fact, Mike Brown had felt previously that the definition of Planet was unsatisfactory and threw out some ideas on how the definition could be altered. http://www.gps.caltech.edu/~mbrown/sedna/index.htm l#planets [caltech.edu] links to the text in question. Mike Brown has since come to the conclusion that culture is going to decide what defines a planet, not a bunch of scientists. So basicly, unless the scientists who want to change the definition of a planet can convince society to listen, it's going to be like a tree falling in a forest with no one around to hear it. Sure, it happened, but who cares?

a name is a soundbite

[Anonymous Coward]

I'm an astronomer (in a different sub-field), and I'm pretty happy with the situation as it stands. The whole is-it-a-planet-or-not debate gets people interested in astronomy, but it's of essentially no significance to us. It's only a name, we care about the reality of things and not the invented names given to them.
This is a cynical way to put it, and maybe some other astronomers care more than I do. I'd certainly like it if people were more interested in cutting edge research (or detailed politics, computer technology...) than naming stuff: a name is the ultimate in empty media-friendly soundbites. Still, everyone is comfortable expressing an opinion in this debate, it's nice like that.

Re:atomic?

[Oink]

This is true, but I think the question was aimed towards how they supposedly can divide a pixel since it's supposedly the smallest thing they can resolve. I actually worked on a cosmology project for a couple years, so I have at least a rudementary understanding of image capturing techniques. You can overcome the limitations of your CCD through a technique called dithering. The standard dither is 2x2, in which you take an image, move your image to the right by half a pixel, down by half a pixel, left by half a pixel, taking an image at each of these points. Now you can sort of average out these images and can actually resolve things that are smaller than a pixel.

There's a paper somewhere that claims that a 2x2 dither can also eliminate the effects from any 'reasonable' intrapixel variation. That is, if for example the edges of your pixels are slightly less sensitive than the centers, which is actually quite common. This makes dithering an extremely valuable technique in wide surveys where the characteristic size of an object in the sky is less than the size of a pixel. This is called undersampling. I could say more, but I think that answers the question. ;)

define "spherical"

[Anonymous Coward]

Then there's the problem of defining "spherical", and the planet wars erupt all over again. Earth is sort of spherical, but squashed a bit, so we get into how squishy/bumpy/whatever still qualifies as spherical enough.

I wish this 10th planet crap would die

[Tycho_Atreides]

Its not a damn 10th planet, its just a large kuiper balt object. So's pluto for that matter. Theyre not really planets, its just that UB313 isnt cool sounding enough to be on a headline. I highly doubt the story "Kuiper Belt object UB313 found to be of different size than previously ascertained".

Objects should be classified by common features

[Xerxes314]

The problem with this definition is that sphericity is not an interesting property.

The classes of object in the Solar System (according to shared features) are:

1. Gas Giants
2. Rocky Planets
3. Asteroids
4. Comets
5. Kuiper Belt Objects
6. Oort Cloud Objects (only Sedna yet observed?)

And then there are some asteroid-like bodies that have wandered off (Apollos, Jupiter Trojans, etc) and some kuiper-like bodies (Centaurs) that have wandered off. Moons are a bit trickier to classify, but we'll ignore them since they're not Sun-orbiting.

Planet is most sensibly defined to be the combination of the first two classes. They share such features as: circular in-plane orbits, large mass, common formation. The most important feature of these two classes is that they are small; four bodies each. A definition of planet that included thousands of objects would not be useful.

Since Pluto and 2003-UB_313 fall into the KBO class (sharing such features as: eccentric orbits, resonance with Neptune, icy composition, medium mass), they are not planets. Pluto was originally mistaken for a Gas Giant-type body; it's not, so it should have been declassified as a planet. However, the KBO class was unknown at the time, and Americans liked the idea of an American-discovered planet, so it got inappropriately included. As for 2003-UB_313, it's hardly surprising that the discoverer thinks that it's a planet, but his opinion should clearly not be taken seriously.

Xerxes