Ironduke

What's a Planet?

New riddles beyond the solar system

Ron Cowen

"I found a planet!" Caltech astronomer Mike Brown remembers exclaiming during a phone call he made to his wife early in 2005. Little did he know that he'd have to eat his words just 18 months later. Brown had found an outer–solar system object heavier than Pluto, so it seemed reasonable to call the object the tenth planet.

But last August, the International Astronomical Union approved the first formal definition of a planet since the Greeks coined the term some 2,000 years ago. Pluto, got the boot, and Brown's proposed tenth planet, a body now called Eris, was disqualified.

The group of astronomers decided to call Pluto and Eris "dwarf planets"—a class that the scientists say is separate from the solar system's eight official planets. That decision remains controversial, although many astronomers say that there's merit in the demotion. Both Pluto and Eris are considerably smaller than the first eight planets discovered. These two orbs ought to be grouped with the swarm of other icy objects in the Kuiper belt, a region beyond Neptune that may contain millions of such bodies, Brown says.

Although Pluto's planethood is etched in cultural memory—and on lunch boxes, on postage stamps, and in textbooks—knowledge about the solar system has skyrocketed since the body's discovery in 1930.

"The new definition essentially corrects an astronomical mistake from 76 years ago and shows that astronomy can move forward in the face of new information about the solar system," Brown wrote recently on his blog (http://www.gps.caltech.edu/~mbrown/eightplanets/). But even as scientists and the public grapple with Pluto's demotion, new findings from beyond the solar system are eroding the meaning of planet.

Over the past few years, astronomers have found several extrasolar objects that by weight would qualify as planets, yet they lack what would seem to be the most basic of planetary prerequisites—a parent star. Many of these free-floating orphans are surrounded by disks of dust and gas with enough mass to coalesce into their own miniature solar systems. One of the orphans, which some researchers call planemos, may even have a planetary-mass object orbiting it.

The discoveries are blurring the line between planets and stars—and may bring about a revolution in thinking about planets that goes far beyond the Pluto debate.

Read more here: http://www.sciencenews.org/articles/20061202/bob8.asp

Firral

Interesting article. Though I already heard about "star" which is similar to a planet more. Probably it has not proved to be true, but in system of 61 constellations the Swan, except for two stars the third object has been found out. It influenced in the weight, movement of a double star. By calculations, it was twice the greater weight, than the Floodlight. Because of the weight it could not be a star though and for a planet was too big.

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omon

let's call, it plantar

Firral

Yes, as it while exists only in mathematical calculations on a paper. But this "planet" (if it exists) is very similar to a class of planets-giants (type of the Neptune or Saturn) so theoretically the probability of its existence is very great.
Recently has appeared a lot of such " the calculated planets " at other stars. To us remains only it hopes that really planets, and that besides planets-giants, these stars have also smaller planets from firm substance.

1010011010

If some visiting alien looked at our solar system it would note a small object whipping about very close to the sun, two similar-mass objects further out (one with liquid water- mark for later colonization), another smaller one further from that, a big smear of rocky debris, a big radiant gas giant, a smaller but more radiant gas giant with pretty rings, and a middling gas planet further yet still. And a bunch of ice and other crap scattered further out.

There's no reason to pick one piece of that vast bunch of ice and other crap and say "I shall call him... Pluto. He shall be a planet."

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Trooth

"What's a planet?"

A bijou plan?

I'll get my coat.

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omon

i always tought that a planet is a celestial body that reflects light from stars and isn,t burning. A star is celestial body that burns gives off light and heat.so if a planet is very large it is still not qualified to be a star no matter how big it is. is it right?

1010011010

Jupiter, Saturn, and Neptune all radiate more energy than they receive from the sun. It's not visible "light", mind you, but restricting the radiation to an arbitrary couple hundred nanometer band because it's what pigments in our retina respond to would be stupid.

I'd settle for a body massive enough to have become spherical under the force of its own gravitation, in orbit around a star, and significantly larger than other objects in the system. Pluto isn't a planet by the last condition.

dalem

"significantly larger than other objects in the system."? Which objects? Pluto's pretty darned big compared to the vast majority of objects orbiting the sun.

I would go with a body that is alone in its orbit (except for satellites) and set a minimum mass figure of some sort - probably right around Pluto's mass.

-dale

ArmchairGeneral

Um, you missed one.

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gunnut

Pluto reacts...

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omon

yea but stars don'r revolve around planets, planets revolve around stars. is it always the case, or just our solar system only?

gunnut

That's by definition (planets revolve around stars).

If a planet has enough mass to ignite, then the body it orbits definitely has enough mass to be at least brilliant.

There are binary, even trinary star systems, where multiple bodies revolve around a central point due to their offsetting gravitational pulls on one another.

Some binary systems have a massive body and a much smaller body, still a star because the nuclear reaction is self-sustaining, orbiting around it.

omon

thanx man, i had no idea there are binary, even trinary star systems.

there are billions of star systems here, pics like this tell us how small we realy are in the space. our own earth is probably as huge as uneverse compare to microbs, bacteria, atoms and malecules. damn i won't be surprised if enitre uneverse is a small part of someting bigger.

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Trooth

OK, i skip read this thread. However isn't the moon on dangerous ground as well as Mickey's dog?

When the moon was "discovered" it was the only other lump of rock. However now that we have discovered dozens of "moons" isn't our lunar friend our twin planet? It just so happens the centre of orbit of our pair is within the Earth, but compared to other moons our lunar partner is considerably more massive?