Astronomers struggle to define 'planet'

Status
Not open for further replies.
G

GrnMarvl14

Lying
Joined
Jan 4, 2003
Messages
13,846
Reaction score
4
Original article.

(AP) -- Our solar system is suffering an identity crisis. For decades, it has consisted of nine planets, even as scientists debated whether Pluto really belonged. Then the recent discovery of an object larger and farther away than Pluto threatened to throw this slice of the cosmos into chaos.

Should this newly found icy rock known as "2003 UB313" become the 10th planet? Should Pluto be demoted? And what exactly is a planet, anyway?

Ancient cultures regularly revised their answer to the last question and present-day scientists aren't much better off: There still is no universal definition of "planet."

That all could soon change, and with it science textbooks around this planet.

At a 12-day conference beginning Monday, scientists will conduct a galactic census of sorts. Among the possibilities at the meeting of the International Astronomical Union in the Czech Republic capital of Prague: Subtract Pluto or christen one more planet, and possibly dozens more.

"It's time we have a definition," said Alan Stern, who heads the Colorado-based space science division of the Southwest Research Institute of San Antonio. "It's embarrassing to the public that we as astronomers don't have one."

The debate intensified last summer when astronomer Michael Brown of the California Institute of Technology announced the discovery of a celestial object larger than Pluto. Like Pluto, it is a member of the Kuiper Belt, a mysterious disc-shaped zone beyond Neptune containing thousands of comets and planetary objects. (Brown nicknamed his find "Xena" after a warrior heroine in a cheesy TV series; pending a formal name, it remains 2003 UB313.)

The Hubble Space Telescope measured the bright, rocky object at about 1,490 miles in diameter, roughly 70 miles longer than Pluto. At 9 billion miles from the sun, it is the farthest known object in the solar system.

The discovery stoked the planet debate that had been simmering since Pluto was spotted in 1930.

Some argue that if Pluto kept its crown, Xena should be the 10th planet by default - it is, after all, bigger. Purists maintain that there are only eight traditional planets, and insist Pluto and Xena are poseurs.

"Life would be simpler if we went back to eight planets," said Brian Marsden, director of the astronomical union's Minor Planet Center in Cambridge, Mass.

Still others suggest a compromise that would divide planets into categories based on composition, similar to the way stars and galaxies are classified. Jupiter could be labeled a "gas giant planet," while Pluto and Xena could be "ice dwarf planets."

"Pluto is not worthy of being called just a plain planet," said Alan Boss, an astrophysicist at the Carnegie Institution in Washington, D.C. "But it's perfectly fine as an ice dwarf planet or a historical planet."

The number of recognized planets in the solar system has seesawed based on new findings. Ceres was initially classified as a planet in the 1800s, but was demoted to an asteroid when similar objects were found nearby.

Despite the lack of scientific consensus on what makes a planet, the current nine - and Xena - share common traits: They orbit the sun. Gravity is responsible for their round shape. And they were not formed by the same process that created stars.

Brown, Xena's discoverer, admits to being "agnostic" about what the international conference decides. He said he could live with eight planets, but is against sticking with the status quo and would feel a little guilty if Xena gained planethood because of the controversy surrounding Pluto.

"If UB313 is declared to be the 10th planet, I will always feel like it was a little bit of a fraud," Brown said.

For years, Pluto's inclusion in the solar system has been controversial. Astronomers thought it was the same size as Earth, but later found it was smaller than Earth's moon. Pluto is also odd in other ways: With its elongated orbit and funky orbital plane, it acts more like other Kuiper Belt objects than traditional planets.

Even so, Pluto remained No. 9 because it was the only known object in the Kuiper Belt at the time.

When new observations in the 1990s confirmed that the Kuiper Belt was sprinkled with numerous bodies similar to Pluto, some scientists piped up. In 1999, the international union took the unusual step of releasing a public statement denying rumors that the ninth rock from the sun might be kicked out.

That hasn't stopped groups from attacking Pluto's planethood. In 2001, the Hayden Planetarium at New York's American Museum of Natural History unleashed an uproar when it excluded Pluto as a planet in its solar system gallery.

Earlier this year, NASA's New Horizons spacecraft began a 9 1/2-year journey to Pluto on a mission that scientists hope will reveal more about the oddball object.

The trick for astronomers meeting in Prague is to set a criterion that makes sense scientifically. Should planets be grouped by location, size or another marker? If planets are defined by their size, should they be bigger than Pluto or another arbitrary size? The latter could expand the solar system to 23, 39 or even 53 planets.

It's not an academic exercise - the public may not be open to a flood of new planets. Despite their differences, scientists agree any definition should be flexible enough to accommodate new discoveries.

"Science progresses," said Boss of the Carnegie Institution. "Science is not something that's engraved on a steel tablet never to be changed."
Click to expand...

I love scientific controversy. And I can't wait until this is resolved.
 
I've read about this article and saw that if the let pluto be a planet, any other rock measuring like pluto must be considered as a planet even if it is very small
 
I say wait for the Horizons mission to finish. The very reason it was sent out
was to explore the mystery of Pluto and Kuiper belt objects and possibly the
Oort cloud... if we could contact it that far out there. As it stands, Pluto has
been and always will be an oddball.

One of the few arguments of why it obtained planethood is partly due to the
fact of a rush of sorts in order to find the next planet out there. In the
early 1900's discoveries were being made left and right with more powerful
technology improving telescopes. Tombaugh, the scientist who discovered
Pluto, saw it had a slight arc much like the other planets, but was moving far
slower. He jumped to the conclusion this had to be a planet and was adopeted as such.

If Pluto had been discovered in today's practices, not only would we
probably express very little intrest in this chunck of ice, but just classify it
as 'another body' and give it a number much like what has been happening
to most asteriods and Kuiper objects.

I love Pluto's status as a planet, shoot, thats because I grew up
acknowledging it as such. It was a rebel, outclassed and undefined.
It's orbit, mal-aligned and confused by Neptune. It's size, dwarfed by
even Mercury. And even it's face, no true quality photos existed of it
surface (and still do not).

I would hate for it to loose a status after it's had one for so long, and I'm
sure the consortium is figuring out how to preserve it's brand appeal. Most of
all, scientists want to cover their behinds... We are after all dealing with
rocket scientists, some who have not only pushed Pluto's planethood, but
ingrained it in everyone's minds and now it comes down to a simple definition
which can utterly tarish the fabric of the scientist's domain: Admitting a mistake.
Science Guy: "Well, yeah after 70 years of calling Pluto a planet, um, we were wrong.
That's right, it's no planet, it was just a stupid piece of rock."
Mob: "What? Science wrong? I knew it! They must be WITCHES! BURN THEM!"

Still they may take the approach of calling Pluto and other's like it dwarf-planets
or planet-lite.

I always envisioned a grouping system of classification, for example:
Rocky Planets: Mercury, Venus, Earth, Mars.
Gas Giants: Jupiter, Saturn, Uranus, Neptune.
*Dwarfs: Pluto, Xena, Sedna ...etc.

*Now the dwarven category may consist of bodies that exist in the Kuiper
belt but are large enough to sustain spherical shape and behave enough
to follow a distinct orbit around the sun.

I see officals leaning more towards this and declaring the dwarven category
as optional planets, or intemediary planets: halfway between another piece of
rock and something that maintains known planetary composure.

Well thats my view in a nutshell... I think I may have messed something up. Just correct me if I'm wrong.
 
Here's the Definition:
"A planet is a celestial body that (a) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (b) is in orbit around a star, and is neither a star nor a satellite of a planet."
Click to expand...

What I've been finding out is that this will soon have an effect on our moon.
Because we all know the moon is slowly drifting away, when it does break free,
under the definition, it will become a planet too.

Of course, no one will have to worry about that for some millions of years down
the road.

The pending solar system:
ig295_planets_solarsystem_02.jpg
 
Last edited:
Sedna doesn't fall under the new definition?

And I love that under the new definition, all you need to become a planet is to be round and orbit the sun. Now we can make an artificial planet much more easily.
 
Is that in reference to my older post? Hmm, it was mere specualtion at the time.
Sedna was found by the same team who found Xena, so I thought that it may
get passed as well. Who knows, it too, may get planetary status, but as a 'pluton' planet though.
 
It was in reference to the solar map you showed. Shows all the other likely new planets, but no Sedna. From what I (vaguely) recall, Sedna meets the requirements. But, reading an article, I see no mention of Sedna. Or is it not included because it's in the Oort cloud? Now I'm confusing myself.
 
Perhaps it's too general of an object to be considered yet. I'm sure NASA only
wants to establish their new set of rules to something the public would find
acceptable. If they go about adding planets, they want to go for the objects
that appear the most planet-like and inherent of such definition.

I agree with you that Sedna will most likely follow suit as a planet. However, it's
current state does not allow for it to be easily recognized as such. For one,
it's smaller than the bodies being discused (sans-Ceres) and it's orbit is a lot
more askew with respect to the standard solar system. The general public
may be frustrated with finding these outward objects as planets right away
and only delay the defenition process.

Keep in mind, most of the articles refer to 'dozens more planets' being added
in regard to passing the new definition. This leaves room open for things like
Sedna and Quaoar or the two unnamed objects, 2005 FY9 and 2003 EL61.
 
Ceres, Charon, and 2003 UB313 "Xena" get automatic planet status if this definition is passed. However, I'm going to quote Stephen Colbert on this whole planet debate:

"Ceres, you're not a planet! You're just a fat ass-teroid!"
 
Now Pluto ISN'T a planet.

Much-maligned Pluto doesn't make the grade under the new rules for a planet: "a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit."

...

Instead, it will be reclassified in a new category of "dwarf planets," similar to what long have been termed "minor planets." The definition also lays out a third class of lesser objects that orbit the sun -- "small solar system bodies," a term that will apply to numerous asteroids, comets and other natural satellites.
Click to expand...

Ceres and Xena join Pluto in the dwarf planet definition. So we have 8 planets, and at least 3 dwarf planets. Astronomy class just got a lot more fun.
 
Because it's basically just a big, very cold, spherical rock with an oblong orbit. And I'm sure there's more. That's just all I can recall off the top of my head.
 
GrnMarvl13 said:
Because it's basically just a big, very cold, spherical rock with an oblong orbit. And I'm sure there's more. That's just all I can recall off the top of my head.
Click to expand...

But, Pluto was a planet for some reason. Well, I don't like the fact that Pluto is a Planetoid or an Astroid, or even a rock. For you people wo do not know what Planetoid means, it is a Planet and Astroid comine. It's a fact!
 
Last edited:
Pluto was proclaimed a planet because it was the largest object seen at that distance up to that point. And it's been debated since day one.

Pluto was discovered in 1930 by a fortunate accident. Calculations which later turned out to be in error had predicted a planet beyond Neptune, based on the motions of Uranus and Neptune. Not knowing of the error, Clyde W. Tombaugh at Lowell Observatory in Arizona did a very careful sky survey which turned up Pluto anyway.
Click to expand...
 
"In orbit aroudn THE SUN"

Human egotism strikes again! If it isn't in OUR system, it's not a planet! (granted, we have the term exoplanet for them. But an exoplanet should still be a planet, damn it!)

Would it have killed them to write "A sun" or "A star" instead of "The Sun", just to cover all those questions that will start poping out anyway with each new exoplanet we discover?

Also, giant planets are planets but dwarf planets aren't planets.

These astronomers impress me a lot less than they impress themselves, apparently.
 
That's just the definition for our solar system. I mean, there are several plants we've discovered outside our solar system, and no one's suddenly said they don't count.

And since when do dwarfs count for anything but Christmas and children's movies? It's the racism no one talks about.
 
Status
Not open for further replies.
Back
Top Bottom