[meteorite-list] Defining 'Planet': Newfound World Forces Action

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Aug 2 13:58:47 2005
Message-ID: <200508021757.j72HvbU19021_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/050802_planet_definition.html

Defining 'Planet': Newfound World Forces Action
By Robert Roy Britt
space.com
02 August 2005

"The word planet is simply not a scientific word, it is a cultural word."
- Mike Brown, leader of the "10th planet" discovery team

The claim Friday that a 10th planet has been discovered in our
solar system has set off a fresh round of debate and international talks
aimed at defining the most vexing term in astronomy: the word planet.

A formal proposal could come within a week or two. But some astronomers
see no easy resolution.

Now, the guy who stirred the latest dust is trying to snuff the whole
debate by repositioning planet as a cultural term that no longer has any
scientific meaning.

"Scientists have for the most part not yet realized that the term planet
no longer belongs to them," says Caltech's Mike Brown, who led the
discovery of the new larger-than-Pluto object.

Brown's new view comes after contemplating six years of mostly fruitless
scientific arguments that began when the public became outraged over a
rumor that scientists planned to demote Pluto, a rumor rooted in the
fact that some astronomers had already stopped calling Pluto a planet by
the late 1990s.

"I finally realized the mistake we astronomers had been making all
along," Brown told SPACE.com yesterday . "The word planet is simply not
a scientific word, it is a cultural word. Once you get over that trap
the rest becomes easy."

The problem

At the heart of the problem is small world that should never have been
called the ninth planet when it was found 75 years ago.

Pluto is small, its orbit very noncircular, and it travels 17 degrees
outside the main plane of the solar system where the other planets roam.
In recent years, several other round worlds at least
half as big as Pluto have been found on similar offbeat paths, including
two announced last week in addition to 2003 UB313, whose orbit is
inclined a whopping 45 degrees.

Most astronomers view all of them, Pluto included, as members of the
Kuiper Belt (other terms are used,
too, to describe the increasingly complex outer solar system).

The newfound object, temporarily named 2003 UB313, is perhaps 1.5 times
the diameter of Pluto and appears to have a similar surface rich in
frozen methane. So Brown called it the 10th planet in a hastily arranged
teleconference with reporters Friday evening.

NASA, which funded the research, appeared to endorse the label by using
Brown's terminology in its official press release.

But yesterday, NASA's Paul Hertz said, "It's not NASA's job to decide
what is and what is not a planet." Hertz, chief scientist in the
agency's Science Mission Directorate, acknowledged the task falls to the
International Astronomical Union (IAU).

"We anticipated there would be a difference of opinions," Hertz said in
a telephone interview.

Wildly different, it turns out.

If 2003 UB313 is a planet, one argument goes, then so are those other
round things out there. So the new kid on the block would have to go to
the back of the line, numerically. It might be No. 12 or No. 24,
depending on whose scheme you like.

Proposal soon?

Efforts to craft an official definition have dragged on for years.

The IAU, responsible for nomenclature of all things beyond Earth, has
been mulling a planet definition since at least 1999. An IAU Working
Group specifically set up to develop a recommendation has been stalled
for the past six months.

But most of the dozen members in the group were "exchanging a lot of
email this weekend," said Alan Stern of the Southwest Research
Institute, who is on the committee.

The members have said they "want to get something done, pronto," Stern
told SPACE.com. He said it's possible a proposal could be finalized in a
week or two and made public. Still, group members have clearly different
ideas goals in mind.

A synopsis of Stern's thinking:

A planet is a body that directly orbits a star, is large enough to be
round because of self gravity, and is not so large that it triggers
nuclear fusion in its interior.

"I think there's a consensus moving in this direction," Stern said.

The actual definition will, at least, be more complex than that. Stern
favors calling the smaller objects dwarf planets, for example. Other
astronomers prefer the term minor planet. Another term bandied about is
Kuiper Belt planets. Some don't like the idea of applying the planet
label at all.

Let there be 8

Brian Marsden, who is also on the IAU Working Group and who runs the
Minor Planet Center where data on objects like these end up, says a
simple definition like Stern's makes sense from a theoretical point of view.

If adopted, the wording would bring our solar system's tally of known
planets to about two dozen, Marsden said.

-----------------------------------------------------------------------------

A Revolution

A swarm of small worlds discovered in recent years is remaking our view
of the solar system, astronomers agree. Pluto, once an oddball, is now
thought to be one of many round objects out there.

"It's really a revolution," says Alan Stern of the Southwest Research
Institute. "We are finding out just how quaint our view of the solar
system was."

Improved technology promises more discoveries. Some astronomers won't be
surprised if something as big as Mars, or even Earth, is found way out
there but still bound to the Sun. So far, only a fraction of objects
thought to be in the Kuiper Belt, beyond Neptune, have been found.

Stern, who is managing NASA's New Horizon's mission to Pluto, points out
that there is a billion times more space in our solar system beyond the
Kuiper Belt compared to inside that region.

"Hold onto your hat," he said. "It's just going to get more bizarre."

--Robert Roy Britt

---------------------------------------------------------------------------

But practically speaking, Marsden, who expects it will take "somewhat
more than a week or two to come up with a policy," prefers another approach.

"The only sensible solution is to accept that the solar system contains
the eight planets known a century or so ago," Marsden said via email,
"and to add new members only if they are larger than, say, Mars -- or
maybe even the Earth."

(Stern and others contend that such large worlds indeed await discovery.)

The discovery of 2003 UB313 presents "the best chance to resolve the
problem," Marsden said. "I doubt that all astronomers will be happy with
the outcome, but I would hope that what is decided is enough of a
compromise that most of them are."

Forget science

Mike Brown yesterday attempted to shift the whole debate away from science.

In Brown's mind -- and he admits to changing it recently -- Pluto is too
enshrined in our culture, from place mats to postage stamps, to strip it
of planethood.

"Some astronomers have rather desperately attempted to concoct solutions
which keep Pluto a planet, but none of these are at all satisfactory, as
they also require calling dozens of other objects planets," Brown wrote
on his web site this week. "While people are perhaps prepared to go from
nine to 10 planets when something previously unknown is discovered, it
seems unlikely that many people would be happy if astronomers suddenly
said, 'we just decided, in fact, that there are 23 planets, and we
decided to let you know right now.'"

Brown's team is taking a stand.

"We declare that the new object, with a size larger than Pluto, is
indeed a planet," Brown wrote. "A cultural planet, a historical planet.
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 advises the public to "ignore the distracting debates" of the scientists.

It seems clear the IAU Working Group plans to ignore Brown, at least
insofar as they expect to forge a scientific definition.

Yet no matter what the group comes up with, you can bank on at least one
more year of debate. For a definition to be made official, it must be
voted on at an IAU General Assembly meeting. The next one is in Prague
in August, 2006.


============================================================================


http://news.bbc.co.uk/1/hi/magazine/4737647.stm

Farewell Pluto?
By Alexis Akwagyiram
BBC News
August 2, 2005

The discovery of a new planet in our Solar System could have an
unintended consequence - the elimination of Pluto in the list of planets
everyone has in their heads. Is it time to wave this distant, dark piece
of rock farewell?

To the casual observer, the announcement that scientists have identified
a tenth planet orbiting the Sun is primarily of importance to few people
other than science teachers and schoolchildren.

But, on closer examination, the revelation may have more far-reaching
consequences for the way in which we think about space.

At around 3,000km across, 2003 UB313 - as it has been named - is the
largest object found in our Solar System since the discovery of Neptune
in 1846.

--------------------------------------------------------------
PLANETS MNEMONICS
My Very Excellent Mother Just Sent Us Nine Pizzas
My Very Earnest Mother Just Served Us Nine Pickles
Matilda Visits Every Monday, Just Stays Until Noon, Period
--------------------------------------------------------------

And it is thought to be larger than Pluto, whose status as the furthest
planet from the Sun has been enshrined in accepted thought since it was
identified in 1930.

But this could all change.

Technological advances have enabled astronomers to find more minor
planets, stars, asteroids and comets.

And in the late 1960s scientists found that Pluto's size had been
over-estimated.

It was first thought to be around as large as Earth, whereas accepted
thought now suggests that the planet's mass is only around a fifth of
the moon's.

"Today, the world knows that Pluto is not unique. There are other
Plutos, just farther out in the Solar System where they are a little
harder to find," says David Rabinowitz of Yale University, who was among
the astronomers who discovered 2003 UB313 two years ago.

His point is echoed by Professor Mark Bailey, director of Armagh
Observatory in Northern Ireland.

"Increasingly, objects are far away and there are objects which are of
comparable size to Pluto, so if you think of Pluto as a planet then you
should refer to those objects as planets," he says.

He estimates that there could be tens of thousands of objects beyond
Neptune in the Solar System region known as the Kuiper belt, many of
which may be larger than Pluto.

The discovery of 2003 UB313 comes soon after it was announced that 2003
EL61 had been found.

And a number of distant objects around the same size of Pluto have been
found in recent years, including Quaoar (found in 2002) and Sedna
(detected in 2004).

It is widely accepted that the struggle to provide an adequate
definition of a planet is the crux of the problem.

"Originally a planet was a wandering star. Then it was something that
moved across the sky. Then it was something that revolved around the
Sun. The criterion about when it should be called a planet is something
that is changing over time," says Prof Bailey.

"I'm sure we will continue to discover more and more objects of
comparable size which will continue to challenge established thought
about planets."

'Size does matter'

Dr Brian Marsden, director of the International Astronomy Union's minor
planet centre, believes the simplest way to resolve the confusion is to
reject Pluto's claim to being a planet on the grounds that "size does
matter".

Instead he says people should accept that "we have eight planets and
only an object bigger than Mars could be considered to be a planet in
the future".

He argues that the disruption that would be caused to accepted thought
would, ultimately, provide a more accurate understanding of space.

"School text books concentrate too much on the idea that Pluto is the
ninth planet. Teaching should stress that there are hundreds of
thousands of much smaller objects. Knowing a mnemonic and naming the
planets is not science."

But not everyone believes science has the right, or influence to turn
accepted thought on its head.

"Our culture has fully embraced the idea that Pluto is a planet and
scientists have for the most part not yet realised that the term planet
no longer belongs to them," says Michael Brown, one of the astronomers
who discovered 2003 UB313.

His conclusion is simple: "From now on, everyone should ignore the
distracting debates of the scientists. Planets in our solar system
should be defined not by some attempt at forcing a scientific definition
on a thousands-of-years-old cultural term, but by simply embracing
culture. Pluto is a planet because culture says it is.

"It is understandably hard for scientists to let go of a word that they
think they use scientifically, but they need to."

He considers 2003 UB313 to be a planet in a "cultural" and "historical"
sense, adding: "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.

"We scientists can continue our debates, but I hope we are generally
ignored."
Received on Tue 02 Aug 2005 01:57:37 PM PDT