10th Planet in Solar System Discovered?

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BBC News

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I don't like the name, Sedna

 

And didn't they think they found a new planet like 10 years ago anyway?

[Swift Terror 0]

From Space.com:

 

 

In the same week that the planetary community learned a mission to Pluto has been approved, a hot debate has re-ignited over whether the small world deserves planetary status at all.

 

This time the argument is fueled by a newly proposed definition for planets that would instantly boost the solar system's tally to 12 or more by including one large, round asteroid and at least two faraway and icy brethren of Pluto.

 

The intellectual argument is civil yet laced with terms like "arrogant" and "embarrassment," pitting researchers within the same institution against each other.

 

The core of the problem is this: The International Astronomical Union (IAU), charged with categorizing objects in space, can define everything from an asteroid to a star but has no definition for a planet. Officials never needed one until new discoveries in recent years highlighted the inadequacy and a stark debate began

 

 

An IAU statement admits to having "never officially defined what constitutes a planet." Furthermore, the IAU used "historical practice in accepting the eight planets that were known when the IAU was created and accepting Pluto as the ninth when it was discovered (in 1930) not long after the formation of the IAU."

 

For two years, Gibor Basri of the University of California, Berkeley, has been working on a formal definition of planets to propose to the IAU. In Basri's scheme, made public today, there are at least 12 planets known right now, and the tally would quickly rise beyond two dozen as more discoveries are made.

 

Most of these additional small worlds, some roughly half the size of Pluto, orbit at the fringes of our solar system in a region called the Kuiper Belt.

 

Bigger controversy

 

On the other end of the planet spectrum, another controversy swirls around what to call huge objects found orbiting other stars. That area of otherworldly indecision is equally gray if not more so and involves what to call dozens of newfound worlds.

 

David Letterman waded into this big-planet flap back in April of 2001 when famed planet hunter Geoffrey Marcy appeared on the Late Show. Their exchange, over a newly detected ball of gas 17 times more massive than Jupiter but not self-illuminating like a star, illustrates the state of scientific affairs.

 

Marcy: "We don't know what to call it. Is it a planet? Is it a star? Is it something in between? We're befuddled."

 

Letterman: "Well, what the hell are we going to do?"

 

Marcy: "We're screwed."

 

Letterman: "Run for your life, everybody."

 

Astronomers are not running from the planet definition debate. But after many months of intense discussion, no agreements have been reached on where to draw the lines at either end of the size spectrum.

 

Adding planets

 

Many astronomers do agree Pluto should never have been called a planet. It is only 1,430 miles (2,300 kilometers) wide, smaller than Earth's Moon. It travels an elongated orbit that also dips above and below the plane of Earth's orbit by 17.1 degrees. By the late 1999, as observations were revealing Kuiper Belt Objects (KBOs) that approached the size of Pluto, controversy grew. The flap reached a peak when diminutive Pluto received a unilateral demotion when the Hayden Planetarium in New York City chose not to include it in a new display of planets.

 

Some astronomers now speculate that a KBO as big or larger than Pluto might soon be discovered. What would we call it? Planet No. 10?

 

"It's something of an embarrassment that we currently have no definition of what a planet is," Basri said. "People like to classify things. We live on a planet; it would be nice to know what that was."

 

Basri would like to accommodate Pluto and those who can't fathom its demotion. He proposes that the murky lower limit for planet-hood get set at a diameter of about 435 miles (700 kilometers). That's roughly the bulk needed to allow gravity to shape an object into a sphere, depending on density. Smaller objects -- both asteroids and comets -- tend to look like potatoes or bell peppers.

 

If the size cutoff were accepted, two KBOs -- named Varuna and Quaoar -- would become instant planets. More would surely be added to the list each year as new discoveries are made. More than 600 KBOs have been detected so far, but researchers extrapolate the limited sky surveys done so far to estimate there are about 100,000 of them bigger than 62-miles (100 kilometers). Enough larger KBOs exist to grow the solar system's planet count, based on Basri's definition, to two dozen within two years, according to estimates.

 

The asteroid Ceres would also have to be reclassified as a planet under Basri's plan. At 930 kilometers (580 miles) wide the Texas-sized rock was the first asteroid ever discovered back in 1801. At the time, some astronomers thought it was a planet, until other asteroids were discovered. Like most other asteroids, Ceres orbits the Sun in a belt between Mars and Jupiter.

 

Pluto: Just a rock

 

Basri said he would be surprised if the IAU has not adopted a definition along the lines of his idea within a decade.

 

Other astronomers will be surprised if the IAU does formally increase the planet count.

 

Berkeley researchers Imke de Pater and Eugene Chiang would prefer simply to toss Pluto clear out of the planet picture and go back to eight. It’s just a big rock, they say, the largest of the KBOs. In fact, Pluto's orbit, like those of other KBOs, is controlled by Neptune's gravitational presence. Pluto is yanked around the sun twice for every three trips made by Neptune. Astronomers call this an orbital resonance of 3:2.

 

The Kuiper Belt, interestingly, is seen as a comet reservoir, a swarm of objects that formed together in non-planetary manner, each object standing to be kicked toward the inner solar system at any time to become a comet.

 

"I would say a planet is a body in orbit about a star, but not forming part of a larger swarm, like the asteroids in the asteroid belt or the Kuiper Belt Objects," de Pater said. "A planet also would have to be in a stable orbit for a few billion years -- it shouldn't be a KBO in transit to becoming a comet."

 

The middle road in the argument, which is winning so far, goes like this: Pluto is a planet, and the public would be confused and even upset to change that. Leave it as the ninth and final planet, but scientifically keep in mind that it's a KBO and don't otherwise increase the count of planets in our solar system.

 

The larger argument

 

Around other stars, the definition of a planet gets even murkier. An IAU working group has come to some agreements. A planet is something that orbits a star but does not, like a moon, orbit another planet.

 

That definition has proved inadequate in the face of new discoveries.

 

In recent years, astronomers have found dozens of gas giant planets that are much more massive than Jupiter. Though they are not quite heavy enough to jumpstart the thermonuclear fusion that powers a real star, these gargantuan objects strain the definition of planets as we once knew them.

 

Confusion results in part because astronomers had, back in the mid-1990s, agreed on a loose definition for middleweight objects called brown dwarfs. These failed stars are not massive enough to ignite hydrogen, but they do radiate more than Jupiter. No mass cutoff was set to distinguish between large planets and small brown dwarfs.

 

Basri suggests it be set at 13 times the mass of Jupiter, or roughly 4,000 Earth masses. Anything bigger can cause deuterium to fuse in the object's core, generating the sort of heat and low-level light typically associated with brown dwarfs.

 

Geoffrey Marcy, the Letterman guest and co-discover of that 17-Jupiter-mass object, disagrees with Basri. Marcy, who also works at the University of California, Berkeley, says an additional factor must be considered: How did the object form?

 

If a large object condenses into being at the same time a companion star forms, then the object might be called a brown dwarf, Marcy suggests. But if the object forms later, out of the detritus of star formation (as did all the planets in our solar system) then it deserves consideration as a planet, regardless of mass.

 

Marcy thinks it's too early to commit to any firm taxonomy.

 

"It's way too early to define a planet," Marcy said. "No one would have predicted 10 years ago that we'd have any extrasolar planets. Even though we have now found more than 100 of them, these are still the early days in planet hunting."

 

One of Marcy's colleagues, Debra Fischer, also at Berkeley, agrees that there is more to learn before firm definitions are set. She worries that a quick resolution to the debate could set astronomers' up for a repeat of the definition problems they face today.

 

"It's a little arrogant, I think, for us to imagine that we understand what the full spectrum is going to shake out to be," Fischer said. "Are we really in the ultimate position right now where we should redefine things, because it freezes it in again?"

 

Fischer said drawing sharp lines could cause trouble in a decade or two.

 

"Let's admit that at either end, the high-mass end and low-mass end, this has been completely arbitrary, and that some things don't fit with our classification scheme."

 

Basri disagrees

 

Basri stands his ground.

 

"It's like saying we shouldn't define what a star is until we understand all about star formation and weird binary stars, and so on," Basri said. "If we define a planet based on the basic observable properties of these objects, people can later apply all sorts of adjectives to them as they are understood better, without changing what they are basically talking about."

 

Alan Boss, who chairs the IAU Working Group on Extrasolar Planets to which Basri plans to submit his proposal, thinks Nature should decide.

 

Boss, an extrasolar planet theorist at the Carnegie Institution of Washington, shared his personal views with SPACE.com, making clear that his thoughts do not represent the IAU. Boss' views are in line with what Marcy and Fischer expressed.

 

"It would be nice to name things based on how they formed," Boss said, "even though that is the hard way to go about it." In the end, he said, "it would be best to group things together based on how Nature makes them, because that will probably tell us more about how they formed."

 

Boss said it might turn out that sun-like stars typically have companions with masses up to 20 times that of Jupiter, but seldom anything more massive. If that were true, "then I would be tempted to let Nature make the decision for us and call all those objects planets."

 

Regarding Pluto, Boss brings us right back to where we started.

 

"It seems clear to me, based on what we know about the present solar system, that there are only eight planets, and several populations of generally smaller objects."

 

Pluto is unlikely to be officially delisted as a planet, most experts agree. A suggestion along those lines generated a public outcry back in 1999, prompting the IAU to issue a press release stating its regret that "incomplete or misleading" press reports on the status of Pluto "appear to have caused widespread public concern." The statement went on to assure that "no proposal to change the status of Pluto as the ninth planet" had been made within the IAU.

 

When NASA's New Horizons probe visits Pluto and the Kuiper Belt in 2015, it will almost surely become crystal clear -- if it hasn't already before then -- that Pluto the planet is also just a common rock, very unplanetlike in most astronomers' eyes, roaming in a sea of planetary wannabes.

[Styles 0]

It's baffling really how something that should be so exciting and interesting like space exploration is so incredibly boring and apathetic...

[Guest Stunt Granny]

Yeah, unless it's full of monsters that we can eat or use for fuel, I don't care.

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woohoo...