An international group of astronomers decided to downgrade Pluto’s status as a planet to something else at a meeting in Prague last August when a much larger rock was found nearby. The discovery even lead the group to question what exactly constituted a planet.
The International Astronomical Union (IAU) was reviewing several newly discovered objects near the former planet to determine their planet worthiness, and to decide whether or not they as well should be considered planets, comets, asteroids, or something else entirely.
These objects, along with Pluto, belong to the Kuiper Belt, an area in space beyond Neptune, now the outermost fully recognized planet, and filled with what are primarily small, icy bodies.
Cal State Northridge’s Donald E. Bianchi Planetarium invited Dr. Amanda Mainzer from the Jet Propulsion Lab (JPL) to campus two weeks ago to explain the IAU decision in more detail. Mainzer is a voting IAU member and attended the Prague meeting in 2006.
In her lecture, “The Planet Club: Why Pluto got Kicked Out, and Why Earth is So Special,” Mainzer said everything was running smoothly for Pluto when the new objects were being discovered near the planet. Their discovery even sparked interest among other astronomers to study this region of the solar system and uncover more of its mysteries.
But this caused a problem when astronomers discovered a substantially large object there in 2003. Appropriately named after the Greek goddess of discord because of the controversy it caused, Eris was found to be larger than Pluto, challenging its classification as a planet.
Eris’ discovery created a divide within the astronomical community, with one side arguing to allow Pluto to keep its planetary status and with another side calling for it to be assigned another classification. It challenged the definition of the word “planet” itself, as the solar system would have been expanded if other large Kuiper Belt objects were also deemed planetary bodies. To resolve the dilemma, the IAU crafted a new definition they thought would appease everyone.
“A body needs to have sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium,” Mainzer said was the first feature an object must possess in order for it to be considered a planet under the IAU’s proposed definition.
In other words, these objects must be so massive that their own gravity crushes and shapes them into a round or somewhat round shape, similar to the shape of the Earth.
These astronomers also required that “the object has to orbit a star, our Sun, and it cannot be a satellite to a planet.” But this requirement would have expanded the solar system by about 200 more planets, including Eris, and objects dubbed Ceres and Charon.
Since this did not solve the initial problem of having to classify too many objects as planets, IAU astronomers decided to add a third requirement to their working definition.
“The object must clear out its neighborhood in order to be dominant along with the rest of the newly discovered objects,” Manzier explained how the problem was solved.
This angered many who favored Pluto as a planet. To appease them, the astronomical group came up with the term “dwarf planet” to classify Pluto, Eris and similar objects.
But many astronomers are still not content with the latest IAU definition of a planetary body, a sentiment that could cause another controversy such as Eris sometime in the future.
“This new definition of a planet is now well stated. We need a better definition, particularly the last part,” said Dr. Jan Dobias, Bianchi Planetarium program coordinator.
“The reason is that a planet has to clear its orbits,” said Dobias, who is also an astronomer. “Other planets like Earth, Jupiter and Neptune may not have done so yet.”
Mainzer, like Dobias, questions the definition’s clarity because astronomers do not know a lot about Pluto’s position in space, as it is so far away and still being explored, she said.
Pluto’s status as a “dwarf planet” may change as new information develops in the summer of 2015, when the unmanned NASA New Horizons spacecraft reaches the former planet. New Horizons Web site shows that the craft was a week away from Jupiter as of last Thursday.
There could be many more mysteries waiting to be uncovered in space, which becomes more feasible as interest in the stars continues and technology progresses. But sometimes discoveries create conflict amongst those who have different points of view about them.
CSUN’s Bianchi Planetarium hosts events every other Friday of the month for anyone who wishes to explore in further detail what astronomers have found in space thus far.
Tickets can be purchased in advance at the Associated Students Ticket Office or at the Planetarium Box Office, which opens 30 minutes before each event. The next event is March 9 at 7:30 p.m. and features stars and constellations visible in the sky in the winter.
All planetarium events are followed by telescope viewing via the campus stellar observatory, if the weather is clear. Telescope viewing is free for all wishing to attend.