Planet Discovered with a Massive Core

helioquake writes "A collaboration of astronomers discovers possible a 'Rossetta Stone' of planetary formation study, reported by San Francisco State Univerity and Subaru Observatory. This new planet, orbiting around G-star like our Sun (HD 149026), weighs roughly equal to that of Saturn, while its size is significantly smaller in diameter. Planetary modeling suggests that the core of the planet alone must have 70 times more mass than Earth, indicating the possible existence of a metallic solid core inside the planet. Just like the rocky planet discovered earlier, the finding of this dense-core planet may lead to better understading of the formation of rockey planets in the Universe."

Comments

Fatal Attraction

[Doc Ruby]

Call me when they discover a giant planet, with a metallic core outside the planet. That's the armored base from which they keep sending us aliens like Ann Coulter and Tom Cruise. Then we just drop magnet-tipped nukes into space, and finally it's safe to watch TV again.

Rockey'n'Roll

[TheStonepedo]

Heavy Metal planets are so Hard Core.

Re:weight

[PaSTE]

Surprisingly, astonomers actually "weigh" the planet by measuring either the planet's gravitational pull on the star, or the star's gravitational pull on the planet (by Newton's 3rd, they are equal). The idea is pretty simple:

1) An object travelling in a circular (or eliptical) orbit requires a certain force toward the center of the focus of the orbit, called centripetal force. It is proportional to the product of the mass times the radius of the orbiting body, and inversely proportional to the square of the period of the orbit.

2) Two massive objects will assert an attractive gravitational force on each other, proportional to the product of their masses, and inversely proportional to the square of the distance between the objects.

All astonomers do is equate one force to another. Astronomers believe that they can calculate the mass of the star by observing the star's apparent brightness, and looking at the star's spectrum to figure out what kind of star it is. Unfortunately, the observed brightness of a star is a function of its distance from Earth, and this measurement has a large degree of error for most stars.

Next, astronomers look at how quickly the star "wobbles" due to the orbit of the planet. This gives a good measure of the period of the planet's rotation.

The final step is to figure out how far the planet is from the star. After entering in all the data, you are left with the mass of the planet being a function of its distance from the star. If you apply some trickery in the form of Kepler's Laws, you can see that the period and radius of an orbit are related.

And that's it! Put all the pieces of the puzzle together, and you have an equation for the mass of the planet. If you are lucky, then the plain of the orbit is end-on when observed from Earth--this allows you to see how much of the star's light is blocked from the eclipsing planet, giving you some measure of the planet's size and composition.