Sirius_Alpha Admin
Number of posts : 4320 Location : Earth Registration date : 2008-04-06
| Subject: KOI-1843.03 - High-density terrestrial planet on a 4.5 hr(!) orbit 16th July 2013, 8:50 pm | |
| The Roche limit for close-orbiting planets: Minimum density, composition constraints, and application to the 4.2-hour planet KOI 1843.03 http://arxiv.org/abs/1307.4080 - Quote :
- The requirement that a planet must orbit outside of its Roche limit gives a lower limit on the planet's mean density. The minimum density depends almost entirely on the orbital period and is immune to systematic errors in the stellar properties. We consider the implications of this density constraint for the newly-identified class of small planets with periods shorter than half a day. When the planet's radius is known accurately, this lower limit to the density can be used to restrict the possible combinations of iron and rock within the planet. Applied to KOI 1843.03, with a radius of 0.6 Earth radii and the shortest known orbital period of 4.245 hr, the planet's mean density must be greater than approximately 7 g/cm^3. By modeling the planetary interior subject to this constraint, we find the composition of the planet must be mostly iron, with at most a modest fraction of silicates (less than approximately 30% by mass).
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Led_Zep SuperJovian
Number of posts : 721 Location : France Registration date : 2011-09-09
| Subject: Re: KOI-1843.03 - High-density terrestrial planet on a 4.5 hr(!) orbit 17th July 2013, 10:46 am | |
| page 4 :
To survive at a period of 4.25 hours, an iron-silicate planet with the measured radius of KOI 1843.03 must be composed of 70% Fe by mass. | |
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Lazarus dF star
Number of posts : 3337 Registration date : 2008-06-12
| Subject: Re: KOI-1843.03 - High-density terrestrial planet on a 4.5 hr(!) orbit 17th July 2013, 1:40 pm | |
| IIRC 70% metallic core is roughly the same proportion as Mercury. - Quote :
- We note in this regard that the planet Mercury, with a mass of 0.055 M⊕ and mean density of 5.4 g cm[sup]−3[/sup[, could not survive in a 4.245 hr orbit.
Extra compression in the more massive planet saves the day? | |
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| Subject: Re: KOI-1843.03 - High-density terrestrial planet on a 4.5 hr(!) orbit | |
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