Smallest Planet Outside Our Solar System Found

mikkl666 writes "Following the recent story about the discovery of the youngest planet outside our solar system, Spanish researchers now report that they found the smallest exoplanet observed so far. The planet, known as GJ 436c, was found by analyzing distortions in the orbit of another, larger planet, and its radius is only about 50 percent greater than the Earth's. The scientists are confident that their new method will lead to a series of further discoveries: 'I think we are very close, just a few years away, from detecting a planet like Earth.' You can also reference the the original paper online for further details."

Comments

The article is wrong

[Geoffrey.landis]

The article seems to be wrong. Smaller planets have been discovered orbiting pulsars. Check out PSF 1257+12a for a small planet.

What they mean to say is that this seems to be the lowest mass planet found orbiting a main-sequence star.

It's also annoying that the press release quotes the radius of the planet (which cannot be measured, and is only an approximation based on guesses at density), when what they actually measured is the mass. Planetary densities vary widely; they have no idea what the radius is.

Re:The article is wrong

[Falkkin]

Yes, I wish we could score the article -1, Wrong. This is the smallest exoplanet discovered "around a Sun-like star". More details on this and previous discoveries can be found at the Bad Astronomy blog:

http://www.badastronomy.com/bablog/2008/04/10/no-its-not-the-smallest-exoplanet-found/

Re:The article is wrong

[CheshireCatCO]

You got it. Phil Plait (aka, The Bad Astronomer) ranted about this today.

Re:The article is wrong

[j1m 5n0w]

From the article:

With a mass about five times greater than Earth's, it is the smallest planet yet discovered outside the solar system

From wikipedia article on Gliese 581c:

Using the known minimum mass of the previously detected Gliese 581 b, and assuming the existence of Gliese 581 d, Gliese 581 c has a mass at least 5.03 times that of Earth. The mass of the planet cannot be very much larger than this or the system would be dynamically unstable.

It seems like it may be a little premature to assume that the new planet is the smallest, even when comparing to planets around main-sequence stars.

I agree the radius is probably a made up number.

Scientist: "Assuming a density similar to earth's, the radius of the planet would be 50% greater than Earth's."

Science reporter: "The planet's radius is 50% greater than Earth's."

Re:planet definition

[4D6963]

what is the minmum possible size/mass of a planet according to the new definition of 'planet'?

I don't know about that (well I do know but you could just look it up) but if a planet 4.7 times as heavy and 50% bigger than Earth was considered too small/lightweight to be considered a planet I'd seriously consider packing my bags and moving to a real planet like Uranus (to live in an airship of some sort that is, I'm very aware that you can't actually stand on Uranus, thank you!).

Re:planet definition

[Ragzouken]

It's more to do with the planet clearing its own orbit of debris rather than size, I think.

It's not really confirmed...

[Plamadude30k]

I (and a group of people) am actually researching this system myself. We observed a transit of GJ436b on March 30, and we're reducing the data now. I'd like to point out, however, this paper is NOT a discovery article. I read it in February (before it was published), and I've got it on my desk right in front of me. Basically, it PREDICTS that there MIGHT be a planet of said radius and mass in an orbit about twice as far out as GJ436b (a transiting hot neptune), but it also says that more study is needed to confirm the existence of this planet. What my study was trying to do was to show that there's a change in GJ436b's orbit caused by this new theoretical planet. So far, things look promising, but we haven't confirmed anything yet.

In reality...

[Tatarize]

According to the IAU definition a planet needs to orbit around the Sun. No exoplanet is really a planet. Though the question depends a lot on what it's made of. It needs to be at hydrostatic equilibrium and fairly round (this is easier fluids and gases) and it needs to have cleared it's area.

Lets say it needs to be about the size of mercury and sweep the question under the rug as frankly a ball of water the size of a basketball, if the only object orbiting a star, would qualify as a planet.