Nearby Star May Have More Planets Than Our Solar System

The Bad Astronomer writes "HD 10180 is a near-twin of the Sun about 130 light years away. It's known to have at least six planets orbiting it, but a new analysis of the data shows clear indications of three more, for a total of nine! This means HD 10180 has more planets than our solar system. And whether you think Pluto is a planet or not, all nine of these aliens worlds have masses larger than Earth's, putting them firmly in the 'planet' category."

Yes, but...

[mmullings]

So, how many of you saw HD 1080i

Re:mass?

[meglon]

It's because it hasn't cleared it's neighborhood of other objects (not including it's moons). Pluto is basically one of the largest objects in a debris disk. Had it accreted that disk, we'd still call it to planet.

Re:mass?

[Anonymous Coward]

The current IAU definition is (c/o Wikipedia)

The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:
(1) A "planet"[1] is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.
(2) A "dwarf planet" is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape[2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.
(3) All other objects[3], except satellites, orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".
Footnotes:
1 The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2 An IAU process will be established to assign borderline objects into either "dwarf planet" and other categories.
3 These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
The IAU further resolves:
Pluto is a "dwarf planet" by the above definition and is recognised as the prototype of a new category of trans-Neptunian objects.

Pluto fails because it hasn't cleared its orbit.

Many people don't like the definition for many reasons. Among them, that what constitutes a "clear" orbit is not specified and is arbitrary (no planet has an orbit 100% free of other objects), that the point of 'hydrostatic equilibrium' is also unspecified and arbitrary, and that it only applies to the Solar System ("The Sun" is in there).

More Great Work from Kepler

[physburn]

NASA's Kepler mission has so far found 2300 potential planets outside the solar system, and the mission has been extended to past 2016. Way to go Kepler!

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Extra Solar Planets [feeddistiller.com] Feed @ Feed Distiller [feeddistiller.com]

Re:mass?

[Mal-2]

Yes, there is a 5-order-of-magnitude gap in our solar system, but there are other systems, and they may have celestial bodies that fall within that gap, so clearer terms might be useful.

Since we don't yet know the composition of these other systems (though I think most would grant they should exist), shouldn't the defining be similarly deferred? Make the definition as useful as it needs to be now, tighten it up later when it's clearly inadequate. It's an imperfect process, but it worked before and it will work again (Pluto controversy notwithstanding). "Planet" is a name for a class of objects, and perhaps overly broad, but right now it usefully defines what we know. When we know more, we'll muck with the definition to fit.

Re:HD 10180 Nearby?

[rachit]

I don't think any object that no human being can visit in their lifetime without defying the laws of physics can be truly said to be "nearby".

You *can* visit it in your lifetime without violating the laws of physics, its just that you cannot visit it in the lifetime of the people observing you from Earth.