By Bobbi Booker
The Book Report II
From Galileo versus Pope Urban VIII to today’s current battle over the
planetary status of Pluto, the path to scientific understanding is not
always rosy. On Friday, more than 300 scientists around the globe
signed a petition protesting against the definition of “planet”
decided by the International Astronomical Union last week (IAU), a
regulating body for information and research in astronomy. That
definition demoted Pluto, leaving the solar system with eight planets.
“What astronomers did this summer really doesn’t have anything to do
with Pluto,” said Derek Pitts, Chief Astronomer and Director of the
Fels Planetarium. “What they did was develop a classification system
for objects that are in our solar system that makes sense. The fall
out is that Pluto’s designation has changed from planet to dwarf
Pluto’s controversial redefinition as a “dwarf planet” by the (IAU) is
based on the fact that Pluto’s orbital path overlaps with other
objects such as asteroids and the planet Neptune.
Arguments over Pluto have raged on since the planet’s 1930 discovery.
Limited information on the distant planet delayed a realistic
understanding of its characteristics. Even with telescopic aid, the
planet is virtually impossible to see. “When I say small and I say
dim, I mean dust speck small and invisible dim,” explained Pitts. “The
only way Pluto is visible is through photography.”
In January, NASA launched its New Horizons spacecraft, the first probe
ever destined for the planet Pluto, its moons and the Kuiper Belt
beyond. The historic mission, traveling at 36,250 miles per hour, will
take more than nine years to reach Pluto in July 2015.
Last year’s discovery of UB313 or “Xena” also put Pluto’s planetary
status on the line. With a diameter of about 1800 miles, UB313 is larger than Pluto (1400 miles) and occupies an orbit well beyond that of Pluto. More objects
like UB313 are expected to be discovered in the future and many in the
astronomical community do not wish to call these bodies planets.
“We start to discover objects beyond Pluto that are bigger than Pluto.
If they should be planets, what do we do about Pluto? Pluto is way out
at the end of the solar system. It’s made of ice, not rock. It’s orbit
is tilted relative to all the other orbits of the solar system and
scientist have agree for at least the last 25 years that it wasn’t
really an original member of the solar system, but a passing object
that was grabbed by the gravitational pull of Jupiter, Saturn, Uranus
and Neptune. So it wasn’t really part of the original planets to begin
In addition to orbiting the sun and being rounded by its own
gravitational field, the IAU definition of a “classical planet”
requires an object to be the sole occupant of its orbit. A dwarf
planet must only meet the first two criteria and cannot be a
satellite. All other bodies in the solar system are referred to as
“small solar system bodies”.
“If we say our solar system is made up of classic planets, then these
other objects that are smaller than planets can be called dwarf
planets. That covers all of those things that are Pluto-sized or
smaller that are round and orbit the Sun.”
The disagreeing scientists have issued a petition that states: “We, as
planetary scientists and astronomers, do not agree with the IAU’s
definition of a planet, nor will we use it. A better definition is
The signers of the petition included NASA scientists, astronomers at
major observatories, university professors and graduate students. The
astronomical union allowed only scientists attending a conference last week in Prague, Czech Republic, to vote.
The group’s definition for a planet specifies three conditions: the
object orbits the sun; it is large enough for its gravity to pull it
into a round shape; and it “has cleared the neighborhood around its
orbit”. The last condition excludes Pluto, because it is located among
many other icy bodies in a ring of debris known as the Kuiper Belt.
“According to a separately developed theory, all the planets in the
solar system are currently placed in their correct order,” said Pitts.
“Pluto is outside of that order. Pluto makes no sense, no matter how
you look at, as a planet.”
According to the IAU’s guidelines we may have lost a planet but gained
a big family of dwarf planets. In other words, our solar system has
just gotten bigger.
“I believe that furor and outcry this summer over Pluto has to do more
with the cultural icon (Pluto, the Disney character) than it has to do
with the planet itself,” mused Pitts.
“You know what, Pluto has no idea. The planet doesn’t care.