Terrestrial (Rocky) Planet Discovered

KilgoryTrout writes "A 'super-Earth' planet was identified in orbit around mu Arae, a star 50 light years away. It orbits at 2 AUs and surface gravity is 14gs. Two gas giants have been detected in orbit about the star. Space.com's article suggests that it is a failed gas giant's rocky core."

Comments

Interesting for different reasons:

[hoggoth]

This is very interesting, however it isn't the most "Earthlike" planet found yet. There are three planets generally ignored by scientists because they are dead and orbit a neutron star. However they are Earth sized and there is a possibility that in the distant past they may have harbored life.

It would be monumental to find evidence that life on Earth isn't a singleton freak accident, even if we found it on worlds that could never harbor life again.

2AU?

[thhamm]

found a bit more here:

http://www.eso.org/outreach/press-rel/pr-2004/pr-2 2-04.html

cant find anything about the 2AU. is that possible? 2AU radius and 10day period?

Re:2AU?

[Wubby]

RTA. The nearby gas giant is at 2AU. The rocky planet is within that orbit, and therefore going faster.

Wrong numbers

[Euphonious Coward]

It says the super-earth is so close to its star that it orbits in 10 days. A nearby gas giant is orbiting at 2 AU. Also, they say the mass is 14 times that of Earth. That would imply a surface gravity of 14G only if it was the same size as
Earth, which could only happen if it were made out of uranium or something.

I guess a radius 2.4 times that of Earth, if it's made of the same stuff, or less if it has more iron and less silicates.

Re:Wrong numbers

[Euphonious Coward]

Assuming radius is 14 ** (1/3) = 2.41 times Earth's, and it's made of the same materials, then surface gravity should be 14 / (2.4 ** 2) = 2.41G also.

Probably it's denser, and radius is smaller, and surface gravity is higher, maybe 3 or 4G, but not 14G.

Re:Is there an astrophysicist in the house?

[elendel]

This being slashdot, post has an error - the planet in question is not 2AU away, rather the other planet in the system is. Quoth the aricle:

"the planet had to form inside the orbit of the larger planet in the system, which orbits the star about twice as far as Earth is from the Sun."

The article is a little short on info, but states of the discovered plane "It completes its tight orbit in less than 10 days" so we can assume it is much closer to the sun.

How you could get 14 Gs

[Engineer-Poet]

The average density of Earth is about 5.5 g/cc, while the surface rocks average 3.5 g/cc. There are two reasons for this:

1. The Earth's core is made largely of iron, which is much denser than rock.
2. The core matter is compressed by the pressure of the overlying material.

If you took Earth and doubled its size with no other changes, you'd have a surface gravity of about 2 G. If you tripled the diameter of the core at the expense of the mantle (more metals in the star, more metals in the planet), you'd increase the density of the mantle zone from ~4 g/cc to 8-10 g/cc; this would give you 6-9 G at the surface. Factor in some additional compression due to the overlying mass, and I could see 14 G surface gravity.

Still doesn't hold a candle to Mesklin.

Cross-checked numbers

[Engineer-Poet]

It goes something like this:

1. The star's temperature yields its luminosity, and indirectly its mass.
2. The Doppler shift and period of the wobble yields the planet's mass as a fraction of the star.
3. The amount of light blocked by the planet yields its area, and thus its size.
4. From size, you can calculate volume. Density = mass/volume.

If the star is close enough and the planet heavy enough you can cross-check the wobble using astrometry.