'Tenth Planet' found to be a whopper

news@nature.com ^ | 1 February 2006 | Mark Peplow

[neverdem]

Close window

Published online: 1 February 2006; | doi:10.1038/news060130-7

'Tenth Planet' found to be a whopper

Large size of 2003 UB₃₁₃ fuels debate over what is and isn't a planet.

Mark Peplow

2003 UB313 and its moon - currently nicknamed Xena and Gabrielle - take time off from their sword and sorcery shenanigans.© W. M. Keck Observatory

The recently discovered 'tenth planet' of our Solar System is substantially larger than Pluto, astronomers have found.

For many, the discovery that object 2003 UB₃₁₃ is about 3,000 kilometres across will remove any doubt that it deserves to be called a planet.

"Since UB₃₁₃ is decidedly larger than Pluto, it is now increasingly hard to justify calling Pluto a planet if UB₃₁₃ is not also given this status," says Frank Bertoldi, an astronomer at the Max Planck Institute for Radioastronomy in Bonn, Germany, and part of the team that reveals UB₃₁₃'s size in this week's Nature¹.

When astronomer Mike Brown of the California Institute of Technology in Pasadena unveiled 2003 UB₃₁₃ to the world in July 2005, his team was already confident that the new object was at least as large as Pluto, and deserved the status of 'planet'.

But UB₃₁₃'s elongated orbit takes it almost twice as far away from the Sun as Pluto ever gets, making it very difficult to measure its diameter precisely. One clue to its larger size came from the fact that it is slightly brighter than Pluto; a larger mirror would reflect more of the Sun's light. But an alternative explanation could have been that UB₃₁₃ is simply made of a more reflective material than Pluto.

Ice maiden

How does the 'tenth planet' measure up against other bits of the Solar System? Click here to find out.

Using the Institute for Millimetre Radio Astronomy (IRAM) 30-metre telescope in Spain, Bertoldi's team has now studied the radiowaves coming from UB₃₁₃, which reveal how much of the Sun's rays are absorbed and re-radiated as heat. Because very little reflected sunlight is emitted at these wavelengths, the object's brightness in radiowaves depends only on its size and surface temperature.

Based on its enormous distance from the Sun, UB₃₁₃ is calculated to be tremendously cold: a staggering -248 °C. Bertoldi and his colleagues combined this value with their measurements of UB₃₁₃'s radiation to determine its reflectivity and size.

Although this first estimate of 3,000 kilometres may be out by as much as 400 kilometres, this still puts UB₃₁₃ well ahead of 2,300-kilometre-wide Pluto in the size stakes, making it the largest body found in the Solar System since the discovery of Neptune in 1846.

The research also shows that UB₃₁₃ has a reflectivity, or albedo, of about 60%. This is roughly the same as Pluto's, suggesting that the two objects' surfaces are made of very similar materials, such as frozen methane and nitrogen snow. Only a very frosty world could produce an albedo of 60%, says Brown.

Imagine how you'd feel if your baby didn't have a name for seven months.  Mike Brown, Caltech

Brown has also been trying to measure the size of UB₃₁₃ by using the Hubble Space Telescope. Although he released preliminary findings on 25 January at a public meeting at Foothill College in Los Altos Hill, California, suggesting that UB₃₁₃ was just a few percent larger than Pluto, he now says that measurement is wrong. "It was an extremely preliminary estimate," he explains.

A planet with no name

2003 UB₃₁₃ is not the catchiest name, but unfortunately this temporary designation will have to stick until the International Astronomical Union (IAU) decides whether it is indeed a planet that warrants a name from classical mythology.

Since 1992, more than 1,000 similar, albeit smaller, objects have been found in the region around Pluto known as the Kuiper Belt, and astronomers estimate that there may be more than half a million still waiting to be discovered. As more of these icy remnants from the Solar System's birth turn up, Pluto blends into the crowd and its claim to be a unique planet grows slimmer and slimmer.

Some astronomers argue that Pluto should be stripped of its title, to become a Kuiper Belt Object like its orbital fellows. Others suggest that anything larger than Pluto found in the outskirts of the Solar System should also be called a 'planet', which would include UB₃₁₃. "I'd prefer to keep Pluto as a planet, for historical reasons," says Bertoldi.

The IAU set up a committee of 19 top astronomers to come up with a workable definition for a planet that would rule UB₃₁₃ in or out, but in November 2005 the group finally admitted defeat after failing to reach a clear consensus. The IAU has promised action later this year, but Brown is already impatient. "Imagine how you'd feel if your baby didn't have a name for seven months," he says.

Post a comment to this story by visiting our newsblog.

	Top

References

1. Bertoldi F.,

   Altenhoff W.,

   Weiss A.,

   Menten K. M.&

   Thum C. . Nature, 439 . 563 - 564 (2006). | Article |

	Top

Story from news@nature.com:
http://news.nature.com//news/2006/060130/060130-7.html

		© 2004 Nature Publishing Group | Privacy policy

[SunkenCiv]

I think we're getting reports of larger-than-Jupiter worlds and closer-than-Mercury giants because of the limits of the observing technology, which has been improving all the time since the late 1990s, when the first confirmed extrasolar planet was discovered.

The issues raised by these seemingly anomalous systems are real ones, however. :')



http://seds.lpl.arizona.edu/nineplanets/nineplanets/other.html

"Observations of the very nearby Barnard's Star were once thought to be evidence of gravitational effects of planets but they now seem to have been in error."

[presidio9]

They found another 10th planet yesterday?

[Darksheare]

Yes.
And as detection becomes easier and better refined, we may find that our style solar system is more common.
But with Jupiter, Staurn, Uranus, and Nptune in our solar system, how come ours didn't end up mosty toasty like others?
That's probably a question broiling in the backs of some minds at the moment.
(Perhaps our sun was a bit of a stellar oddball and put enough outward pressure to keep things from infalling early on?)

[Darksheare]

Thanks.

[Army Air Corps]

"Seems our solar system is a bit of an oddball."

The more we explore our own backyard, the more weird stuff we discover. Our system is a cornucopia of oddities and unanswered questions.

[Darksheare]

Yeah, What would make it'frosting on the cake' would be to find we are living in a binary star system with a brown dwarf secondary star orbiting our primary star..
That would be something to hear about.

[Army Air Corps]

"What shall we call it? Minerva, Vesta, Diana, Bacchus, Juno, or Vulcan?"



"I do have a preference."

[Paleo Conservative]

Here's a picture from the Hubble space telescope.

[Army Air Corps]

"What would make it'frosting on the cake' would be to find we are living in a binary star system with a brown dwarf secondary star orbiting our primary star."

I'll settle for a stable wormhole. :-)

[SunkenCiv]

My pleasure. Thanks for the link to the Moving Orbits topic. :')

[Termite_Commander]

I say we call it Ceres.

Of course, Ceres was the goddess of motherly love and agriculture (or something), which kinda clashes with a cold, barren, icy rock floating around millions of miles away from the sun...

But in mythology, Ceres is related to Jupiter, Saturn, Neptune and Pluto, so she'd fit in nicely with our current solar system.

[Termite_Commander]

It must be getting late, as I stared at that for about seven seconds, and then began laughing.

My brain is slowing down.

[Ernest_at_the_Beach]

It's just a special place;

[JRios1968]

Here's a picture from the Hubble space telescope.

One of the planet's inhabitants.

[Ernest_at_the_Beach]

2003 UB313 is currently the fifteenth-largest known Solar System object, with a diameter larger than those of Pluto and the neptunian moon Triton, but smaller than those of Earth's Moon and Titan, the largest of Saturn's satellites. Other objects, besides the eight undisputed major planets, that are larger than 2003 UB313 are Jupiter's satellites Callisto, Io, Europa (not pictured) and Ganymede (the largest moon in the Solar System). Behind Pluto, the next-largest known trans-neptunian objects are 2005 FY9, with a diameter of about 1,800 km, and Sedna (1,700 km). A handful more are larger than Ceres, the largest asteroid in the main asteroid belt between Mars and Jupiter. .

[Termite_Commander]

Oh, drat. Ceres already exists?

Now I need to pick out another name.

How tedious!

[neverdem]

Thanks for the link.

[Rastus]

Do they make heavenly body bowling balls? A Ganymede bowling ball would be sweet.

[SunkenCiv]

---

---

[Ernest_at_the_Beach]

It's so lonely out there!