Pluto: The Biggest Dwarf Planet?

by Katie Bowell, Curator of Cultural Interpretation

New Images of Pluto from the Hubble Space Telescope

Pluto’s had a tough couple of years, hasn’t it? First Eris showed up. An object in our solar system thought to be larger than Pluto, the 2005 discovery of the dwarf planet brought Pluto’s status as a planet into question (in that regard, Eris’ name is quite appropriate: “Eris” was the Greek goddess of discord and strife). Then in 2006, the International Astronomical Union (IAU) declared that Pluto would be reclassified as a “dwarf planet.”

But now, a little bit of good news.

Last month astronomers were able to measure Eris by watching it pass in front of a star (learn more about how they measured Eris here).

By measuring how long the star disappeared behind Eris, a measurement that corresponds to Eris’ size, astronomers now believe that Eris may be no larger than 1,454 miles across. Pluto is believed to be 1,456 miles across. So is Pluto 2 miles wider? Maybe.

The size of both dwarf planets is still being explored, and with measurements so close, the winner of this size contest will likely be debated for quite some time.

However, even if Pluto is bigger than Eris, that doesn’t mean a promotion back to full planet status. Pluto still hasn’t “cleared out” its orbit, joining or consuming the smaller objects in its orbit, one of the three requirements for “planethood” established by the IAU. Pluto’s also in a neighborhood full of similarly-sized bodies, and so its dwarf status is still solid. But after five years of beat downs and demotions, if Pluto does turn out to be the largest dwarf planet, that’s still something to celebrate.

For more on the Pluto planet debate, watch PBS’s The Pluto Files.

Science at home: The Pluto Files

by Katie Bowell, Curator of Cultural Interpretation

PBS.org

I suspect that someday, when I’m not yelling at the neighborhood kids to get off my lawn, I’ll gather them ’round and tell them how, when I was their age, Pluto was a planet.

The demotion of Pluto from full planet status in 2006 surprised me, and I will admit to a pang of sadness upon realizing that my mnemonic device of “My Very Excellent Mother Just Served Us Nine Pizzas” would no longer work (“My Very Educated Mother Just Said Uh-oh, No Pluto?”). However, I didn’t begin to imagine just how much Pluto’s removal from our Solar System roster would upset the public and divide the scientific community.

Tomorrow, March 2nd, PBS premiers The Pluto Files, the inside story to “the rise and fall of America’s favorite planet” based on Neil deGrasse Tyson’s book of the same name. If the program is anything like it’s preview, it should be a funny and interesting look at the little planet that was.

In addition to the program, PBS has released several short videos interviewing major news broadcasters on their opinion of Pluto and Neil deGrasse Tyson. Watch the clip below to hear Brian Williams proclaim that Tyson is not the boss of the Solar System, or him.

So, whatever happened to Pluto, anyway?

by Jason Wolvington, Associate Director, Discovery Science Center

I’m still bitter.

OK, so maybe “bitter” isn’t the right word. Heartbroken? Disappointed? It’s probably more that I’ve always known Pluto as a planet, and so that’s how it always will be in my mind. That’s legit, right?

Actually, no … it’s not.

Back in August 2006, at a meeting of the International Astronomical Union, astronomers made a final decision about the definition of a planet. For an object to be considered a “planet,” it needs to meet these three requirements:

• It must orbit around the Sun.
• It must have enough mass and gravity to pull itself into a nearly-round shape, called hydrostatic equilibrium.
• It needs to have “cleared out” its orbit, meaning it has to have joined with or consumed all smaller objects in its orbit.

From this, Pluto meets only 2 of the 3 requirements – it has not “cleared out” the neighborhood of its orbit. Simply put, Pluto is just one object within the Kuiper Belt, a large collection of celestial bodies similar to an asteroid belt. And wiithin the Kuiper Belt, there are several objects, some of which are even larger than Pluto. So Pluto is not a classified as a planet anymore, just another object in the Kuiper Belt. Make sense?

So what does this mean? In a nutshell, it means that science is doing its job.

Science is a way of seeking to understand our natural world, through observation, experiments, and analysis. Science relies on examining evidence and interpreting its findings through logic; it is tested, repeated, and verified. A scientific theory is a well-substantiated explanation for a set of phenomena that has been tested and verified.

And that’s the key: while scientific theories may be well-supported by evidence, they can be modified or replaced as new evidence appears. Science changes – and it should! – as new discoveries are made.

A perfect example: for thousands of years, people believed the Earth was stationary – and flat! – located at the center of the universe. It wasn’t until scientists such as Copernicus, Galileo, Kepler, and Newton – using a combination of advances in mathematics and developments in telescope optics – developed a new understanding of astronomy and physics that led to new discoveries. You know, things like correctly recognizing that the Earth revolves around the Sun, and that all other planets are ruled by the same physical laws as the Earth.

And that’s what happened to our now non-planet Pluto. As scientific discoveries were made, science adapted … and the Solar System now has 8 planets. It’s not so much that Pluto was demoted, but rather scientific thought refined the classification of what constitutes a planet. And unfortunately, Pluto no longer meets the requirements.

Pluto is now considered a dwarf planet, along with Ceres, Eris, Haumea, and Makemake,  all found in the Kuiper Belt. Will it someday regain its planetary status? Perhaps. But with dwarf planet Eris being larger than Pluto, we may have to adjust from the current 8 planets to 10.

And that would just be crazy, right?!

Postscript: It’s only appropriate that we pay homage to Venetia Phair, who, as an astronomy-loving 11-year old in 1930, proposed the name “Pluto” for the newly-discovered “Planet X.” She passed away on April 30th, at the age of 90.