[meteorite-list] And the winner is-- Plutoid!

[Darren Garrison]

http://www.space.com/scienceastronomy/080611-plutoid-planets.html

Pluto Now Called a Plutoid
By Robert Roy Britt
Senior Science Writer
posted: 11 June 2008
10:30 am ET

Updated 2:00 p.m. ET

Pluto's years-long identity crisis just got more complex today.

The International Astronomical Union has decided on the term "plutoid" as a name
for Pluto and other objects that just two years ago were redefined as "dwarf
planets."

The surprise decision is unlikely to stem ongoing controversy and confusion,
astronomers say.

Sidestepping concerns of many astronomers worldwide, the IAU's decision, at a
meeting of its Executive Committee in Oslo, comes almost two years after it
stripped Pluto of its planethood and introduced the term "dwarf planets" for
Pluto and other small round objects that often travel highly elliptical paths
around the sun in the far reaches of the solar system.

"Most of the people in astronomy and planetary science community had no idea
this was going to come out," said Hal Weaver of the Johns Hopkins University
Applied Physics Laboratory. Weaver called the new definition "sort of outdated,
outmoded, archaic."

A meeting in August at the Applied Physics Laboratory is slated to debate the
entire topic of defining planets. Meanwhile, other astronomers said the new
definition needed more definition or that it might simply not be used.

"This seems like an unattractive term and an unnecessary one to me," said David
Morrison, an astronomer at NASA's Ames Research Center who, in 2006, said the
IAU's actions on Pluto have created major rifts among astronomers.

The new definition

The name plutoid was proposed by the members of the IAU Committee on Small Body
Nomenclature (CSBN), accepted by the Board of Division III and by the IAU
Working Group for Planetary System Nomenclature (WGPSN), and approved by the IAU
Executive Committee at its recent meeting in Oslo, according to a statement
released today.

Here's the official new definition:

"Plutoids are celestial bodies in orbit around the sun at a distance greater
than that of Neptune that have sufficient mass for their self-gravity to
overcome rigid body forces so that they assume a hydrostatic equilibrium
(near-spherical) shape, and that have not cleared the neighborhood around their
orbit."

In short: small round things beyond Neptune that orbit the sun and have lots of
rocky neighbors.

The two known and named plutoids are Pluto and Eris, the IAU stated. The
organization expects more plutoids will be found.

"Rather than resistance to 'plutoid,' I think we'll just be hearing groans,"
said Stephen J. Kortenkamp, senior scientist at the Planetary Science Institute
in Tucson.

Controversy continues

One IAU leader recognizes it is adding to an ongoing controversy.

The IAU has been responsible for naming planetary bodies and their satellites
since the early 1900s. Its decision in 2006 to demote Pluto was highly
controversial, with some astronomers saying simply that they would not heed it
and questioning the IAU's validity as a governing body.

"The IAU is a democratic organization, thus open to comments and criticism of
any kind," IAU General Secretary Karel A. van der Hucht told SPACE.com by email
today. "Given the history of the issue, we will probably never reach a complete
consensus."

Van der Hucht said the new designation is not a further demotion for the
once-favorite planet of grade-school children: "Pluto is now the prototype of a
very interesting category of outer solar system bodies."

IAU Division III President Edward L.G. Bowell of the Lowell Observatory said the
ruling stems from unfinished business from the forging of a planet definition in
2006. Bowell said there is no agreed-upon way to define "dwarf planet" yet, so
"officers of the IAU thought it would be a good idea to adopt alternative
criteria that would at least allow those large bodies to be named as though they
were dwarf planets."

It remains to be seen whether astronomers will use the new term.

"My guess is that no one is going to much use this term, though perhaps I'm
wrong," said Caltech astronomer Mike Brown, who has led the discovery of several
objects in the outer solar system, including Eris. "But I don't think that this
will be because it is controversial, just not particularly necessary."

Brown was unaware of the new definition until the IAU announced it today.

"Back when the term 'pluton' was nixed they said they would come up with another
one," Brown said. "So I guess they finally did."

Reactions were not all negative, however.

"It seems like a reasonable decision to me, and given the excitement generated
by New Horizons [a NASA probe headed for Pluto], it's in everyone's interest to
favor the largest Kuiper belt objects with their own categorical designation,"
said Gregory Laughlin, a University of California, Santa Cruz extrasolar planet
researcher.

"The only fly in the ointment that I can envision is if a plutoid larger, than,
say, Mars is detected," Laughlin points out. "In that case, I think we'd see a
big flare-up of the what-is-a-planet debate."

More debate coming

The dwarf planet Ceres (which used to be called an asteroid, and before that was
called a planet!) is not a plutoid as it is located in the asteroid belt between
Mars and Jupiter, according to the IAU. Current scientific knowledge lends
credence to the belief that Ceres is the only object of its kind, the IAU
stated. Therefore, a separate category of Ceres-like dwarf planets will not be
proposed at this time, the reasoning goes.

Weaver, the Johns Hopkins researcher, has helped organized a meeting, planned
earlier this year for Aug. 14-16 at Johns Hopkins University Applied Physics
Laboratory, that aims to bring astronomers of varying viewpoints together to
discuss the controversy.

"We're not trying to slam the IAU, it's just that we also don't want to lead
people to the idea that there's a handful of people who decide where science
should go," Weaver said today. The meeting is designed to "address this question
in terms of a scientific conference." He said no votes will be taken at the
meeting. Rather, it's a time to "sit back and take stock of everything we've
learned in the past couple of decades."

The term plutoid joins a host of other odd words -- plutinos, centaurs,
cubewanos and EKOs -- that astronomers have conjured in recent years to define
objects in the outer solar system, whose appearance seems to grow more complex
every year.

Kortenkamp wonders if "plutoid" isn't just one more confusing term in the cosmic
lexicon.

"So Pluto is a Kuiper belt object, a plutino (the unofficial but nearly
universally accepted name for objects in the 2:3 resonance with Neptune), a
dwarf planet, and now also a plutoid?" he said. "If the IAU is trying to make
things more clear, I think it needs to try again. This is just another layer of
confusion that will feed the "pluto is a planet" camp at the [Johns Hopkings]
meeting."

Kortenkamp also thinks the new defiinition leaves Ceres up in the air: "And this
"-oid" classification doesn't apply to Ceres?" he asks. "Okay, so does that
means we continue calling Ceres an ASTERoid?"

Asked if Ceres remains a dwarf planet and is not an asteroid, Bowell, the IAU
official, said: "I think so!"