Talk:HD 149026 b

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[edit] Density

How can this planet have a density of 5428 kg/m³? Earth's density is of 5515 kg/m³, so that would make it more of a rocky planet than a gas giant. Futhermore, if this planet is 36% of Jupiter's mass and 72% of Jupiter's Radius, that would make: m= 6.8350e+026 kg, and r=48469150 m (using Jupiter's polar radius, I don't really know what a "Jupiter radius" is exactly, as Jupiter is not a perfect sphere), leading to a volume of 4.7696e+023 m³ (assuming it's a sphere) Therfore the density of the planet HD 149026 b should be 1433 kg/m³, higher than Jupiter's 1326.

This source, http://www.extrasolar.net/planettour.asp?StarCatId=normal&PlanetId=304, indicates that its density is "1.4 times that of water", so similar to the 1443 kg/m³ that I calculated. This other source, http://www.journals.uchicago.edu/ApJ/journal/preprints/ApJ64021.preprint.pdf, states that its density is 1180 +/30 kg/m³. Which is what you would get if you use Jupiter's Equatorial radius. But then you would get a lower density than Jupiter, contradicting the statement that HD 149026 b is very dense for a gas giant.

Since I'm not too sure about the volume, I won't change the page, but the 5428 density seems way off.

Any thoughts on this? And anyone know the value used for Jupiter radius? There are two different radius on the Jupiter entry. AtikuX 03:43, 23 July 2007 (UTC)

Hi, good catch- my girlfriend also noticed this error. The 5428 kg/m^3 density is WAY off, and listed with a ridiculous number of significant digits. It is true that this object is of roughly the same density as Jupiter, however it is unexpectedly dense for objects of this mass, and it is much more dense than other known objects of this mass (eg, Saturn). This density requires a huge core, which is the somewhat puzzling thing. I've changed the density to 1,400 kg/m^3 to match your calculation (which appears to be consistent with the given mass and radius), and to more properly reflect the uncertainty. Unexpect 04:07, 24 August 2007 (UTC)

I speculated that the average density for Saturn-mass planets are between 1000-1100 kg/m^3. I don't agree that this planet be exceptionally dense. Saturn is unique as it have density of around 700 kg/m^3. BlueEarth 22:12, 24 August 2007 (UTC)

Answer: In July, a planet with the largest core ever discovered was announced. The planet, HD 149026 b, orbits the star HD 149026, and has a core that is estimated to be 70 Earth masses, accounting for two-thirds of the planet's mass.