By Christopher Smeenk
A group of American scientists announced Monday the discovery
of the farthest known object in the solar system.
The object is classified as a planetoid and was named Sedna,
after the Inuit goddess of the sea. Peter Brown, professor
of physics and astronomy at Western, described Sedna as “a
gigantic icy comet or moon.” Because Sedna is too small
to be considered a planet, it is labelled a planetoid, he added.
“Sedna is unusual in a couple of ways,” he said. “One,
its size is greater than anything observed in that region to
date. Two, its orbit is considerably larger than any of the
Michael Brown, an astronomy researcher at the California Institute
of Technology, led the team that discovered Sedna. He described
himself as being “shocked” at finding the planetoid. “This
is the most distant thing ever seen in the solar system,” he
said. “We just didn’t expect to find anything this
He added that Sedna is currently three times farther from
the sun than Pluto. “We could only just barely see it — 100
years in the past or future it would be impossible to see,” he
At approximately 65 per cent the size of Pluto, Sedna is not
large enough to meet planet standards. “There is no good
definition of what is or is not a planet,” he said.
“Our new definition is that to be a planet, you must
be considerably more massive than the things in your vicinity,” he
said, adding by this standard, even Pluto would not be considered
Peter Brown noted that Sedna follows an “extreme elliptical
orbit.” He said it reaches a maximum distance of 130
billion kilometres from the sun, or 1,000 times the average
distance from the Earth to the sun. At perihelion (the closest
a planet gets to its sun), Brown said Sedna is 90 times the
distance between the Earth and sun.
He also said Sedna is suspected to belong to one of two possible
classes of celestial objects: The Kuiper Belt, a disc of objects
beyond Pluto with a roughly circular orbit of the sun, or the
Oort cloud, a collection of comets in the distant reaches of
the solar system.
The planetoid’s strange elliptical orbit may mean it
belongs to the Oort cloud. If so, Peter Brown noted that Sedna
will be the first observational evidence of the Oort belt which
has only been theoretically postulated until now.
“It’s a golden age for astronomy right now,” said
Shantanu Basu, professor of astronomy at Western. “It’s
really the technology that is leading the research right now,” he
said, pointing to telescopes currently under construction that
range up to 50 metres in diameter.