Strange Mini Solar System Found

starexplorer writes "In 1990, Penn State's Alex Wolszczan found the first exoplanets. But he never got much credit from mainstream researchers, because his planets (3 of them, roughly Earth-sized) orbit pulsars and hold no chance for harboring life. Now he's found a 4th object on the outskirts of the system, SPACE.com is reporting. Call it a planet, call it an asteroid, Wolszczan says, but call the setup a dark, eerie twin of the inner half of our solar system. Also in the same story, news of a brown dwarf just 15 times the mass of Jupiter that has a planet-making disk of stuff around it. Together, more problems for astronomers, who still don't have a basic definition for the word planet or a firm idea of what separates planets from stars."

Comments

Planets from stars?

[hobbesmaster]

Someone please correct me if I'm wrong or over generalizing, but planet vs stars: stars have fusion, planets dont. Hence, a gas giant like jupiter is a planet but a brown dwarf is a star (there is SOME fusion going on, or there was in the past).

Planet vs planetoid is another matter altogether... I'd love to know if theres been a 'real' standard proposed - regardless of whether pluto/charon are planets/moon or not.

Re:Planets from stars?

[Scott7477]

As far as a definition I found this:

"Working Group on Extrasolar Planets
Defintion of a "Planet"

POSITION STATEMENT ON THE DEFINITION OF A "PLANET"

WORKING GROUP ON EXTRASOLAR PLANETS (WGESP) OF THE INTERNATIONAL ASTRONOMICAL UNION

Created: February 28, 2001

Last Modified: February 28, 2003

Rather than try to construct a detailed definition of a planet which is designed to cover all future possibilities, the WGESP has agreed to restrict itself to developing a working definition applicable to the cases where there already are claimed detections, e.g., the radial velocity surveys of companions to (mostly) solar-type stars, and the imaging surveys for free-floating objects in young star clusters. As new claims are made in the future, the WGESP will weigh their individual merits and circumstances, and will try to fit the new objects into the WGESP definition of a "planet", revising this definition as necessary. This is a gradualist approach with an evolving definition, guided by the observations that will decide all in the end.

Emphasizing again that this is only a working definition, subject to change as we learn more about the census of low-mass companions, the WGESP has agreed to the following statements:

1) Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.

2) Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed nor where they are located.

3) Free-floating objects in young star clusters with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).

These statements are a compromise between definitions based purely on the deuterium-burning mass or on the formation mechanism, and as such do not fully satisfy anyone on the WGESP. However, the WGESP agrees that these statements constitute the basis for a reasonable working definition of a "planet" at this time. We can expect this definition to evolve as our knowledge improves."

It looks like this is as close as we're going to get.

Re:Planets from stars?

[Rei]

It's not that simple. Do you say "If there was ever a single Dt-Dt reaction, it's a star", or do we require continuous reactions? It's hard to put an exact cutoff on the sequence from planets to main sequence stars.

All of the bodies get some heat from gravitational collapse as they condense. Once you get enough heat and pressure in a small enough area, you can get Dt-Dt fusion; when there is a "significant" amount, it's called a brown dwarf. However, a relatively small amount of hydrogen is deuterium. As it gets hotter and denser, you begin to get other types of fusion, and you end up with a main sequence star.

The planet/moon distinction becomes even harder when you can't tell exactly what's a planet or star. Once we get to some of these "huge jupiters", there will undoubtedly be debates as to whether there is a measurable amount of Dt-Dt fusion going on or not.

semantics

[Anonymous Coward]

semantics seperates planets from stars from asteroids... Our language, not reality...

Stars generate energy

[Man in Spandex]

At least according to Wikipedia

Scientifically, stars are defined as self-gravitating spheres of plasma in hydrostatic equilibrium, which generate their own energy through the process of nuclear fusion.

Using this simple definition, it seems to apply to most stars out there? Correct me if I'm wrong or if the definition provided isn't accurate enough.

Re:Stars generate energy

[YU Nicks NE Way]

That works quite well for objects above about 25 Jovian masses. (In isolation, yadda yadda yadda) At that size, the body is large enough to support sustained thermonuclear fusion of species other than D+D->He3. Such bodies quickly heat up, becoming true red dwarf stars.

Object smaller than about 13 Jovian masses never exhibit any sustained fusion. Those objects are planets if they orbit a star or a stellar remnant. (They are "sub-brown dwarfs" if they don't orbit a star.)

Objects that sit between the 13 and 25 Jovian mass boundaries are in a grey area. They do exhibit sustained fusion, but only of D+D pairs. There isn't much deuterium around, though, so they don't ever heat up very much. Moreover, since they never engage in H+D->T and H+T->He3 fusion, they don't engage in the fusion reactions which are the signature of "real" stars. These are brown dwarfs -- not planets, because they do heat themselves up with fusion reactions, but not stars, either, because they don't fuse H.

Re:TMBG

[Anonymous Coward]

Singing Science Records

The Ballad of Sir Isaac Newton is also not to be missed.