Picking Planets from Potatoes

Apr 26, 2010
In space, objects tend to conform to one of five shapes: (clockwise from left) spheres, dust, potatoes, halos and disks. Credit: Lineweaver, Norman and Chopra

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 solar system and the effects that dwarf planets might have on other celestial bodies, such as Earth.

When Pluto was discovered in 1930, it was considered to be the ninth planet of our . Since that time, astronomers have discovered similar icy objects in that far-distant orbital region of the Sun known as the . Many astronomers questioned whether Pluto should be grouped with worlds like and , and in 2006 this debate led the International Astronomical Union (IAU), the recognized authority in naming heavenly objects, to formally re-classify Pluto as a .

New research from The Australian National University has further reduced the status of Pluto by suggesting there are many more dwarf planets in the solar system than previously thought.

ANU astronomers have published results that would reclassify what it is to be a dwarf planet, increasing the number of Pluto’s fellow travellers by a factor of ten.

The IAU classifies objects in the solar system into three groups: planets, dwarf planets, and small solar system bodies. When they demoted Pluto from planet to dwarf planet, the IAU stated the solar system is composed of eight planets, five dwarf planets and thousands of small solar system bodies orbiting the Sun.

Charley Lineweaver and Marc Norman from the ANU Planetary Science Institute looked at how spherical the icy moons in our solar system are, and recalculated the size of objects at the boundary between dwarf planets and small solar system bodies.

Previous estimates have classified icy objects with radii larger than 400 km as dwarf planets. The new research suggests that this radius should be closer to 200 km, which would increase the number of objects classified as dwarf planets to roughly 50.

The Kuiper belt is a ring of icy material located outside the orbits of the planets in our solar system. Image Credit: NASA

The boundary between dwarf planets and small solar system bodies is based on whether the object is round or not.

“Small solar system objects are irregularly shaped, like potatoes,” Lineweaver said. “If an object is large enough that its self-gravity has made it round, then it should be classified as a dwarf planet. We calculated how big rocky objects (like asteroids) have to be, and how big icy objects (like the moons of the outer planets and objects farther out than Neptune) have to be, for their self-gravity to make them round. For icy objects we found a ‘potato radius’ of roughly 200km - about half as large as the roughly 400km radius now used to classify dwarf planets."

“The boundary between dwarf planets and small solar system bodies is somewhat arbitrary, but is based on the concept of hydrostatic equilibrium, or how round an object is," Lineweaver added. "Whether the self-gravity of an object is strong enough to make the object round depends on the strength of its material. That is why strong rocky objects need to have a radius of roughly 300km before they turn from lumpy, potato-shaped bodies into spheres, while weaker icy objects can be spheres with a radius of only roughly 200km.”

Lineweaver and Norman’s paper "The Potato Radius: a Lower Minimum Size for Dwarf Planets" will be published in the Proceedings of the 9th Australian Space Science Conference, eds W. Short and I. Cairns, and is available online.

Studying dwarf planets and objects in the Kuiper Belt can help astrobiologists get a better picture of how our solar system formed and how it was able to support habitable worlds like Earth. Some scientists also believe that impactors that have struck Earth in the past, such as comets, could have originated from this mysterious region of the solar system. Studying Kuiper Belt objects can help astrobiologists understand the likelyhood of such objects entering into collision-course orbits with Earth in the future.

Explore further: Raven soars through first light and second run

Related Stories

Astronomers Measured Mass of Largest Dwarf Planet

Jun 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 ...

Tiny Brown Dwarf's Disk May Form Miniature Solar System

Feb 09, 2005

Using the Spitzer Space Telescope, a team of astronomers led by Kevin Luhman (Harvard-Smithsonian Center for Astrophysics) has discovered a protoplanetary disk around a surprisingly low-mass brown dwarf. This remarkable finding ...

Kuiper Belt Moons Are Starting to Seem Typical

Jan 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 ...

Solar systems around dead Suns?

Apr 20, 2009

(PhysOrg.com) -- Using NASA’s Spitzer Space Telescope, an international team of astronomers have found that at least 1 in 100 white dwarf stars show evidence of orbiting asteroids and rocky planets, suggesting ...

White dwarf and ultra-cool dwarf keep their distance

Apr 18, 2007

Scientists from the University of Hertfordshire have discovered a rare binary system consisting of a white dwarf, a Sun-like star that has reached the end of its life, and an ultra-cool dwarf, which is the smallest kind of ...

Recommended for you

Raven soars through first light and second run

16 hours ago

Raven, a Multi-Object Adaptive Optics (MOAO) science demonstrator, successfully saw first light at the Subaru Telescope on the nights of May 13 and 14, 2014 and completed its second run during the nights ...

How can we find tiny particles in exoplanet atmospheres?

Aug 29, 2014

It may seem like magic, but astronomers have worked out a scheme that will allow them to detect and measure particles ten times smaller than the width of a human hair, even at many light-years distance.  ...

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

paulo
3.7 / 5 (3) Apr 27, 2010
"The Potato Radius"
that is the best title for a paper ever.
laurele
1 / 5 (4) Apr 27, 2010
Adding more dwarf planets is in no way another demotion for Pluto. The reason is that in spite of the controversial IAU decision, dwarf planets are planets too. Dr. Alan Stern, who coined the term, intended it to refer to a subclass of planets large enough to be in hydrostatic equilibrium (pulled into a round shape by their own gravity) but not large enough to gravitationally dominate their orbits. He never intended dwarf planets to be designated as not planets at all. And he said he anticipates there being hundreds of these small planets in our solar system.
Titto
5 / 5 (1) May 04, 2010
Would be interesting to see some of the latest WISE findings?