Recent news on the debate over Pluto's planethood

November 29, 2010
Credit: NASA-JPL-Caltech

Earlier this month, Eris -- the distant world first discovered by Caltech's Mike Brown and colleagues back in 2005, paving the way for the eventual demotion of Pluto from planet to dwarf planet -- passed fortuitously in front of a faint star in the constellation Cetus.

That passage, or occultation, allowed the first direct measurement of Eris's size. And it produced a surprising result that reignited—in the media, at least—the debate over Pluto's planethood: Eris and Pluto are, within the uncertainties, essentially the same size.

But since Eris is 27% more massive than Pluto, Eris is substantially denser. The two objects, once thought to be slightly differently sized twins, are in fact very different.

But does this really mean that Pluto's demotion was unjustified?

Certainly not, Brown says. Pluto was not demoted simply because it was thought to be smaller than Eris, he explains, so even though the two are now known to be essentially the same size, the logic behind keeping both of them out of the planetary club remains the same. What is different, he says, is how much more interesting this discovery makes Eris.

"When we first discovered Eris, we thought it was just a slightly larger copy of Pluto. Finding a slightly larger copy doesn't teach you much more than the original, so even though Eris was always important to the public, it never garnered that much attention from astronomers, " Brown says.

"Now that we know it has a substantially different composition from , weare scrambling to figure out ways to understand how a planetary system can produce such seemingly different objects out of what is supposed to be the same material."

Explore further: Pluto-Charon origin may mirror that of Earth and its Moon

More information: Read more about these new observations in Brown's blog, "Mike Brown's Planets."

Related Stories

Pluto-Charon origin may mirror that of Earth and its Moon

February 2, 2005

The evolution of Kuiper Belt objects, Pluto and its lone moon Charon may have something in common with Earth and our single Moon: a giant impact in the distant past. Dr. Robin Canup, assistant director of Southwest Research ...

Kuiper Belt Moons Are Starting to Seem Typical

January 11, 2006

In the not-too-distant past, the planet Pluto was thought to be an odd bird in the outer reaches of the solar system because it has a moon, Charon, that was formed much like Earth's own moon was formed. But Pluto is getting ...

NASA to send spececraft to Pluto

January 16, 2006

NASA is all set to launch its $700-million New Horizons spacecraft from Cape Canaveral in Florida on a nearly nine-year journey to Pluto.

Astronomers Measured Mass of Largest Dwarf Planet

June 18, 2007

Aptly named after the Greek goddess of conflict, the icy dwarf planet, Eris, has rattled the general model of our solar system. The object was discovered by astronomer Mike Brown of Caltech in the outer reaches of the Kuiper ...

Plutoid chosen as name for solar system objects like Pluto

June 11, 2008

Almost two years after the International Astronomical Union (IAU) General Assembly introduced the category of dwarf planets, the IAU, as promised, has decided on a name for transneptunian dwarf planets similar to Pluto. The ...

Picking Planets from Potatoes

April 26, 2010

New research indicates that there may be many more dwarf planets similar to Pluto in our solar system than previously thought. Studying these distant objects can help astrobiologists understand the basic properties of our ...

Recommended for you

A blue, neptune-size exoplanet around a red dwarf star

November 25, 2015

A team of astronomers have used the LCOGT network to detect light scattered by tiny particles (called Rayleigh scattering), through the atmosphere of a Neptune-size transiting exoplanet. This suggests a blue sky on this world ...

The hottest white dwarf in the Galaxy

November 25, 2015

Astronomers at the Universities of Tübingen and Potsdam have identified the hottest white dwarf ever discovered in our Galaxy. With a temperature of 250,000 degrees Celsius, this dying star at the outskirts of the Milky ...

Aging star's weight loss secret revealed

November 25, 2015

A team of astronomers using ESO's Very Large Telescope has captured the most detailed images ever of the hypergiant star VY Canis Majoris. These observations show how the unexpectedly large size of the particles of dust surrounding ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.