by Kyoko Hasegawa
Thursday, February 28, 2008
Scientists at a Japanese university said Thursday they believed
another planet up to two-thirds the size of the Earth was orbiting
in the far reaches of the solar system.
The researchers at Kobe University in western Japan said
calculations using computer simulations led them to conclude it was
only a matter of time before the mysterious "Planet X" was found.
"Because of the very cold
temperature, its surface would be covered with ice, icy ammonia
and methane," Kobe University professor Tadashi Mukai, the lead
researcher, told AFP.
This illustration released by Kobe
University shows a planet - half the size of Earth - which is
believed to be in the outer reaches of the solar system.
researchers at Kobe University have said that their theoretical
calculations using computer simulations
lead them to conclude it
was only a matter of time before the long-awaited "Planet X" was
The study by Mukai and researcher
Patryk Lykawka will be published in the April issue of the
US-based Astronomical Journal.
"The possibility is high that a yet
unknown, planet-class celestial body, measuring 30 percent to 70
percent of the Earth's mass, exists in the outer edges of the
solar system," said a summary of the research released by Kobe
"If research is conducted on a wide scale, the planet is likely
to be discovered in less than 10 years," it said.
Planet X - so called by scientists as it
is yet unfound - would have an oblong elliptical solar orbit and
circle the sun every thousand years, the team said, estimating its
radius was 15 to 26 billion kilometers.
The study comes two years after school textbooks had to be rewritten
when Pluto was booted out of the list of planets.
Pluto was discovered by the American astronomer Clyde
Tombaugh in 1930 in the so-called
Kuiper belt, a chain of icy
debris in the outer reaches of the solar system.
In 2006, nearly a decade after Tombaugh's death, the International
Astronomical Union ruled the celestial body was merely a dwarf
planet in the cluttered Kuiper belt.
The astronomers said Pluto's oblong orbit overlapped with that of
Neptune, excluding it from being a planet. It defined the solar
system as consisting solely of the classical set of Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
The team noted that more than 1,100 celestial bodies have been found
in the outer reaches of the solar system since the mid-1990s.
"But it would be the first time to
discover a celestial body of this size, which is much larger
than Pluto," Mukai said.
The researchers set up a theoretical
model looking at how the remote area of the solar system would have
evolved over the past four billion years.
"In coming up with an explanation
for the celestial bodies, we thought it would be most natural to
assume the existence of a yet unknown planet," Mukai said.
"Based on our hypothesis, we calculated how debris moved over
the past four billion years. The result matched the actual
movement of the celestial bodies we can observe now," he said.
He was hopeful about research by Kobe
University, the University of Hawaii and Taiwan's
National Central University.
"We are expecting that the ongoing
joint celestial observation project will eventually discover
Planet X," Mukai said.