Astronomers say Pluto is not a planet (Eight Planets)

Yahoo ^

[Lunatic Fringe]

PRAGUE, Czech Republic - Leading astronomers declared Thursday that Pluto is no longer a planet under historic new guidelines that downsize the solar system from nine planets to eight.

After a tumultuous week of clashing over the essence of the cosmos, the International Astronomical Union stripped Pluto of the planetary status it has held since its discovery in 1930. The new definition of what is — and isn't — a planet fills a centuries-old black hole for scientists who have labored since Copernicus without one.

Although astronomers applauded after the vote, Jocelyn Bell Burnell — a specialist in neutron stars from Northern Ireland who oversaw the proceedings — urged those who might be "quite disappointed" to look on the bright side.

"It could be argued that we are creating an umbrella called 'planet' under which the dwarf planets exist," she said, drawing laughter by waving a stuffed Pluto of Walt Disney fame beneath a real umbrella.

The decision by the prestigious international group spells out the basic tests that celestial objects will have to meet before they can be considered for admission to the elite cosmic club.

For now, membership will be restricted to the eight "classical" planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

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."

Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's.

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.

It was unclear how Pluto's demotion might affect the mission of NASA's New Horizons spacecraft, which earlier this year began a 9 1/2-year journey to the oddball object to unearth more of its secrets.

The decision at a conference of 2,500 astronomers from 75 countries was a dramatic shift from just a week ago, when the group's leaders floated a proposal that would have reaffirmed Pluto's planetary status and made planets of its largest moon and two other objects.

That plan proved highly unpopular, splitting astronomers into factions and triggering days of sometimes combative debate that led to Pluto's undoing.

Now, two of the objects that at one point were cruising toward possible full-fledged planethood will join Pluto as dwarfs: the asteroid Ceres, which was a planet in the 1800s before it got demoted, and 2003 UB313, an icy object slightly larger than Pluto whose discoverer, Michael Brown of the California Institute of Technology in Pasadena has nicknamed Xena.

Charon, the largest of Pluto's three moons, is no longer under consideration for any special designation.

[Getready]

I think that by the standards stated by the leader of the
group(I guess)--you are correct. Neptune has not cleared
Pluto, therefore Neptune is not a planet either.
But maybe Neptune and Pluto haven't been around long enough
for that to happen, maybe at some time in the future, pluto
will be cleared out by Neptune, and have its own even larger
orbit, and maybe less eccentric, and both Neptune and Pluto
will become planets again.

[Bubba_Leroy]

Instead, it will be reclassified in a new category of "dwarf planets," similar to what long have been termed "minor planets."

The term "dwarf" is pejorative and offensive and therefore politically incorrect.

They should call them "differently sized" planets.

[jim_trent]

Has Pluto hired a lawyer yet?

[bobjam]

Three moons, round with an atmosphere- Mercury only has one of those qualities. Any change in status for Pluto should have been put off until the arrival of the New Horizons space probe- then astonomers would be better equipped to make a decision as to what Pluto really is.

I am glad they didn't upgrade Charon to "dwarf planet" as had been discussed. That would have requried upgrades for the Moon, Io, Europa, Callisto, Ganameade, Titan and Triton as well.

[Bubba_Leroy]

Doesn't that mean that Neptune too, the orbit of which must overlap Pluto's is also not a planet? Especially since it's orbit overlaps Pluto's, Neptune has failed to have "...cleared the neighborhood around its orbit."

Yeah, that's the part of the definition that bothers me. I agree that a planet should have sufficient mass for its gravity to force it into a nearly round shape. But the part about clearing its neighborhood is going to make the definition hard to apply, particularly outside of this solar system.

For example, we are doubtlessly going to discover large planets in other solar systems with overlapping orbits, shared orbits and binary planets. This definition would could rule out some massive gas giants from being considered planets.

[jpl]

Oh well, so ends our system's Plutonic relationship.

[bobjam]

In terms of distance from the sun, Pluto overlaps Neptune because for 20 years (1979 to 1999) of its 250 year orbit is is closer to the sun. However, it is important to note that the plane of Pluto's orbit is at an angle to the plane occupied by the other planets and major asteroids.

[calljack]

Well then just what the hell is My Very Educated Mother supposed to Just Serve Up Nine of???
HUH???
WHAT??
TELL ME WHAT!!!

[laker_dad]

They should call them "differently sized" planets.

How about "gravitationally challenged" planets?

[WoofDog123]

"It was unclear how Pluto's demotion might affect the mission of NASA's New Horizons spacecraft, which earlier this year began a 9 1/2-year journey to the oddball object to unearth more of its secrets."

moronic statement. it is on its way and will do the studies it was sent to do. i seriously doubt the course it is on allows any modification, even if it is capable of it.

[RightWhale]

The New Horizons mission statement needs rewritten. It is no longer headed to the outermost planet.

[Gorjus]

Modern "science" is now become the result of one form of an opinion poll or another.

This isn't about science. It's about a definition, and (except when imposed by force) those are always a matter of opinion.

If some of the salient characteristics of Pluto were in dispute scientifically, then it would indeed be bad science to declare as fact what is unproven. But a definition is inherently a declaration, not a matter for data (except to the extent data demonstrate 'natural' distinctions among classes of objects and thus highlight bases for differentiation).

[CougarGA7]

Somebody needs to go get these scientists a date.

If they had just one they would so not care about this.

[Paul Ross]

Artist's rendition of surface view from Pluto

To get an idea of comparative dimensions:

That being the case, I can see some arguing Pluto hardly deserves to be a planet, but the fact is that Pluto is now going to be classified as a planet...just a "Dwarf Planet". I am a bit surprised, as I expected it be re-classified as a "Binary Planet." I.e.,:

Under proposed International Astronomical Union definitions, two planets that orbit each other around a barycenter (or center of mass) between them are a binary planet. Those same definitions would expand the "family" of planets to include Charon, promoting Pluto's large companion from moon to planet and securing the pair's status as the first and (so far) only binary planet in the solar system.

"Binary planet" is a term often used to describe any pair of worlds that are similar in mass. Each orbits the other around a gravitational balance point that is between the two - a location called the center of mass. When one object has a much bigger mass and the objects are far apart then the center of mass is close to the center of the bigger object and the bigger object hardly moves. This is the case of the Earth orbiting the Sun - the Sun's moves only 0.0003 of its diameter due to the gravity of the Earth in its yearly orbit. In the case of Pluto and Charon, separated by 17 Pluto radii, the ratio of their masses is 8:1 so that the center of mass is outside Pluto.

[RightWhale]

Mercury isn't very big either, although it is very bright as seen from earth.

[senorita]

Instead of "My very excellent mother just served us nine pizzas" it will now be "My very excellent mother just served us nachos."

[Sloth]

Mercury is even smaller than Ganymede and Titan.

[colorado tanker]

This definition makes logical sense. I don't think Kuiper objects should be considered planets.

Still, if I'd had a vote (which I don't) I would have voted for Pluto too, for historical reasons and so the public won't think science is too malleable a concept. Besides, it seems cheesy to do this so close to Clyde's death.

[RightWhale]

What is the name of the spacecraft headed to Mercury now? Hermes? Mercury is heavy, mostly iron core.

[Kaylee Frye]

Poor Neptune!!! ;)