http://www.newscientistspace.com/article/dn7968--distant-solar-system-body-may-be-cigarshaped.html
Distant solar system body may be cigar-shaped
Maggie McKee
New Scientist
08 September 2005
One of the three large new bodies discovered recently in the outer solar
system is spinning so quickly it has stretched into a cigar shape,
according to new observations. If confirmed, the strange shape is sure
to fuel the controversy over what constitutes a planet.
The object, temporarily dubbed 2003 EL61, lies about 51 times farther
away from the Sun than the Earth does, in a ring of rocky bodies called
the Kuiper Belt. It was discovered in July 2005 by a team of Spanish
researchers, who used its apparent brightness to estimate that it might
be larger than Pluto.
But just a day after that group announced its find, another team led by
Mike Brown of the California Institute of Technology in Pasadena, US,
reported that it had also been studying the object and had discovered
a small moon orbiting around it. The moon's orbit revealed the larger
object's mass, which allowed researchers to estimate its width at about
70% that of Pluto, or 1600 kilometres.
Now, however, more observations with a consortium of small telescopes in
Chile suggest the object may actually be about 2000 km - at least in one
dimension. The suggestion comes from observations that reflected
sunlight from 2003 EL61 varies greatly in brightness in a pattern that
repeats once every three to four hours.
The team says more light is reflected when the longer side of the object
is facing the Sun, while less bounces off when the shorter sides are
pointed that way. 2003 EL61 appears to be about twice as long as it is
wide - and shorter still in height. "It takes the shape of a short,
flattened cigar," says team member Chad Trujillo, an astronomer at the
Gemini Observatory in Hawaii, US.
Spotty steel
But Dave Tholen, an astronomer at the University of Hawaii, US, says the
difference in light readings could also be explained if the object
appeared mottled and did not reflect sunlight evenly across its surface.
He points that mottled neighbour Pluto actually shows the second-largest
such "albedo variation" in the solar system, fluctuating in brightness
by 35% during its six-day rotation period.
"You can never completely rule out an albedo variation," Trujillo
acknowledges. But he argues the object's own motion supports the cigar
hypothesis. It spins even faster than the fastest known Kuiper Belt
Object, Varuna, which rotates once every five hours or so. That speed is
necessary to explain how the object keeps from collapsing into a sphere
under its own gravity, as most large objects do.
"It's spinning so fast, it starts elongating out," he told New
Scientist. "It's the weirdest shape ever seen of an object this size,"
says colleague David Rabinowitz of Yale University in New Haven,
Connecticut, US.
If the object does turn out to be elongated, it will heat up an already
contentious debate about how to define a planet. Alan Stern, a planetary
scientist at the Southwest Research Institute in Boulder, Colorado, US,
is on an official committee trying to sort out the issue. But he favours
a definition that limits planets to those objects that directly orbit
stars, are large enough to be round because of their own gravity, but
not so large that they initiate nuclear fusion.
Frozen methane
In related research, Brown's team has also found that the other two
newly discovered large objects in the Kuiper Belt - 2003 UB313 and
2005FY9 - are covered in frozen methane.
Methane vaporises easily if heated, so its presence implies the objects
were not "extremely close to the Sun at any point," says Trujillo. That
will help researchers trace the birthplace of the three newly found
objects. They all lie outside the plane of most other bodies in the
solar system and may have formed around Saturn before being scattered
outward by Neptune.
The research was presented on Thursday at a meeting of the American
Astronomical Society's Division of Planetary Sciences in Cambridge, UK.
______________________________________________
Meteorite-list mailing list
Meteorite-list@meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list
