New Measurements Size Up Distant Dwarf Planet Eris As Pluto's Twin

By Rebecca Boyle Posted 10.27.2011 at 10:59 am 9 Comments

Dwarf Planet Eris Space Telescope Science Institute/Wikimedia

Pluto may not be a fully fledged planet, but at least it’s not the dwarfiest of dwarf planets. Its sibling, Eris, is not as large as astronomers thought, according to a new study. A rare stellar blockage event last year helped astronomers obtain some new measurements of the distant icy world, and they say it is quite dense and it may develop a feeble atmosphere as it moves closer to the sun.

Eris was discovered in 2005 and is partly responsible for knocking Pluto out of the planetary pantheon, because it’s more massive than the object-formerly-known-as-a-planet. It is supremely far away, almost 100 times farther away from the sun than Earth is, so it’s difficult for astronomers to characterize it. Putative measurements have suggested Eris was much bigger than Pluto, as well as more massive, but that turns out not to be the case.

Astronomers led by Bruno Sicardy of the Paris Observatory and the University of Pierre and Marie Curie derived the new measurements after a rare stellar occultation on Nov. 6, 2010. This means the small planet temporarily blocked the light from a background star and cast a wee shadow toward Earth. Astronomers were able to use two separate telescopes to measure the shadow and how long it took for the star to reappear, arriving at a new measurement of the planet’s size. (Astronomers were already pretty sure of its mass because of the way it interacts with its small moon, Dysnomia.)

Eris is 1,445 miles in diameter, just 10 or so miles wider than Pluto, which rings in at 1,432. So it is still bigger, but only a tad. This size relative to its mass also means it must be a dense, rocky world, the astronomers report. Also noteworthy is its greater-than-expected brightness, the astronomers report in the journal Nature. It is covered in a thin shell of methane ice, and is one of the brightest objects in the entire solar system, they say. The team found Eris’ atmosphere is about 10,000 times more tenuous than Pluto’s present atmosphere, and they suggest that it fades away as the planet moves farther away from the sun in its elliptical orbit.

All in all, the occultation event enabled a major leap in scientists’ understanding of large Kuiper Belt objects, said Amanda Gulbis, an astronomer at the Southern African Large Telescope and South African Astronomical Observatory in Cape Town, writing in Nature. “Whether they are called planets or not, there is clearly still much to learn about these distant, icy bodies,” she wrote.

TRAPPIST Observatory: Moonlight over the 60-cm TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) at La Silla, Chile, where one of the Eris occultation light curves was obtained. E. Jehin and V. Chantry

[Nature]

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9 Comments

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cosmic

10/27/11 at 1:02 pm

Planets of any size are just fun and amazing! They always inspire the imagination. It would be wonderful, if sometime in the future through some magical type of new technology we find in our solar system we have 20 or 50 planets. As, long as they are not pumping around like on a billiards table, I think more is better!

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cosmic

10/27/11 at 1:06 pm

'pumping',lol.

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pheonix1012

10/27/11 at 5:41 pm

Do you know what kind of astronomical distances 20 to 50 planets would stretch across? Assuming that they didn't share orbits.

The farthest Kuiper Belt object is already just about 100AU from the sun. Any other worlds further away would be to far to be trapped by the sun's gravitational pull to stay in an orbit.

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cosmic

10/27/11 at 6:17 pm

pheonix1012,
First, space has enough space already. I not think were in danger of running out of room in our solar system for more planets.

Second, as long at the planets play nice and no bumping, causing chaos in our solar system with planet size fragments heading for earth, I am ok with planets sharing orbits.

Third, I want more planets, simply for more things to explorer. I do not believe we will be traveling the next galaxy any time soon you know. It is far more likely we be visiting our own planets.

Forth, ya could not tell I was just kind of wishful thinking; day dreaming; stop being so nit-picky.

Besides, don't you want to explorer our solar system to and all its variety and wonder, too?!

Isn't the our cosmos and our solar system just so COOL!

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drchuck1

10/28/11 at 5:17 am

@cosmic...are you just trolling? there are no hidden planets between the sun and the Kuiper Belt, get a grip on reality! cheers

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cosmic

10/28/11 at 7:57 am

Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its identity was verified later that year.

Eris first considered name was "Lila", after a concept in Hindu mythology that described the cosmos as the outcome of a game played by Brahma.

The name was very similar to "Lilah", the name of Brown's newborn daughter. Brown was mindful of not making his name public before it had been officially accepted. He had done so with Sedna a year previously, and had been heavily criticised. However, he listed the address of his personal web page announcing the discovery as /~mbrown/planet lila and in the chaos following the controversy over the discovery of Haumea, forgot to change it. Rather than needlessly anger more of his fellow astronomers, he simply said that the webpage had been named for his daughter and dropped "Lila" from consideration.

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JediMindset

10/28/11 at 6:34 pm

lol @ cosmic. yes there is also an invisible alien spaceship orbiting pluto. its just so far that we cant see it.

_________________
The people of the world only divide into two kinds, One sort with brains who hold no religion, The other with religion and no brain.

- Abu-al-Ala al-Marri

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cosmic

10/29/11 at 9:22 pm

It was an old time the ancients had visited earth before.
The people were so fearful of us. We could go about our business and take what we need of the planet.

The humans, they helped us in gathering what we need to fuel our ships and bring supplies back to the home world.

It felt good to be back to Earth, closer. "Earth" is it, they call it. We have monitored the planet for thousands of years. We have sent scouts to Earth in recent years in our preparation of our return December 21st 2012.

Oh how the planet will change. We have to be careful. Their technology has grown and is dangerous in many ways as so goes their always persistent fears and war like nature.

We hide now, waiting behind Eris, waiting, and gathering all our ships for our final landing on Earth. Soon this solar system will change, soon.

It will be a new page for my journal and all the planets I visit. This Earth planet and its people, they are different, unique, how will they receive us?

The faithful, the Mayans, we will gather them first; the few tribes that still exist; the true pure tribes live in the mountains. They are few, but we respect the faithful.

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pioneer10

10/31/11 at 10:17 pm

Is Eris current orbital position going to keep it coming closer to the sun for some time? or will it soon reach its closest approach to the suun and begin moving farther away? Either way, a New Horizons type mission would sure provide a neat scientific comparison between the two bodies. Better yet, a probe sent to orbit Eris when it starts to get farther away might give us the chance we missed with Pluto to get an up-close veiw to watch its atmosphere dissipate!

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