Debate has been raging
about whether Pluto should continue to have the status of a Planet! The
International Astronomical Union (IAU) General Assembly, on 24 August 2006,
has decided to make a new category - the Dwarf Planet and put Pluto into
this new category.
Astronomical Union (IAU) - which has the naming rights to space objects
- has a working group considering the definition of a "planet". But some
would say that the vote to demote Pluto, on the last day of the General
Assembly when most Astronomers had departed, meant that
not truly representative" of the IAU.
Under the new ruling, the
IAU defines a planet as "a celestial body that is in orbit around the
sun, has sufficient mass for its self-gravity to overcome rigid body
forces so that it assumes a nearly round shape, and has cleared the
neighbourhood around its orbit".
Because Pluto does not meet the last criterion (its orbit cuts into that
of Neptune), the IAU demoted it to 'dwarf planet' status. The decision
leaves the solar system with only eight planets - Mercury, Venus, Earth,
Mars, Jupiter, Saturn, Uranus and Neptune.
Alan Stern, the lead scientist on NASA's robotic New Horizons mission,
now on its way to Pluto, and several astronomers of the Johns Hopkins
University in the US, were among those who do not approve the new
Johns Hopkins said in a statement that several of its astronomers
described the IAU's decision as a "muddled" ruling "that is unlikely to
settle ongoing debates over how to define a planet and whether the term
should apply to Pluto".
According to BBC News, NASA's Stern slammed Pluto's demotion saying "it
is impossible and contrived to put a dividing line between dwarf planets
and planets". (Source:
Indo-Asian News Service, 28th August 2006)
Basri, an astronomer at the University of California - wants to increase the
number of planets to 12! Professor Basri's definition: a planet must orbit a
star, not another planet, and it must be round. That means it must be 700K
in diameter, when gravity moulds it into a sphere, or bigger. Smaller
objects are potato-shaped. All the accepted planets are round.
Professor Basri says
that a planet can't be bigger than 13 times the mass of Jupiter. Because
such objects generate heat and light, they should be called stars. But Geoff
Marcy, a member of the Anglo-Australian planet search team at Siding Springs
telescope says other factors need to be taken into account, including how
the planet was formed.
Professor Ross Taylor, at the
Australian National University, has removed Pluto from planet status in
their textbooks (reported
back in 2003!)
Pluto is now classified as a Dwarf Planet - Is this the
Frances Moore, Managing Director, WebQuest Direct