[meteorite-list] Density of iron at high pressure

[Carl Agee]

Eric is right, this high density can be explained by the effect of
very high pressures on pure solid iron in a planet 1.6 times the
diameter of the Earth . Of course, nothing is pure in nature, so there
is presumably Ni, Co, S, O, and C in the mix. The light elements
offset the dense iron. If there are high temperatures in the planet,
then thermal expansion offsets volume decrease by the pressure to some
extent. How did this iron rich planet form? Perhaps similar to
Mercury, which may have lost most of its silicate mantle in an early
giant impact.

Dense planets of gold, lead, and uranium are ruled out simply based on
the abundance of the elements in the universe. Or else this is the
largest ore deposit in the neighborhood! :)

What would be really interesting is to know the density distribution
in this planet, which cannot be determined without knowing its moment
of inertia.

Carl Agee

Sterling wrote:

<A planet of 75% iron with a 25% crust of Tungsten would have a
density of 11, and I suppose that if everything less refractory than
tungsten had boiled away, you could get such a planet...>

Those densities are for items sitting on your desk. The iron core of
earth has a density of almost 13gm/cm^3 out to 1000km. Over the next
2000km the density drops to around 11gm/cm^3. I would imagine if this
planet is 1.6 times the diameter of earth the 11+gm/cm^3 would extend
even farther from the center. Additionally if most of the lighter
elements have boiled away leaving a mostly iron and refractory element
sphere, the 11+gm/cm^3 could comprise a significant portion of the
sphere with the center being very dense. In other words it probably
doesn't need an exotic mix to get to this density. The core of a gas
giant boiled away (as Sterling mentioned) to the iron and refractory
elements would probably do just fine.

-- 
Eric Olson
610 W. Moore Rd
Tucson AZ 85755

--
Carl B. Agee
Director and Curator, Institute of Meteoritics
Professor, Earth and Planetary Sciences
MSC03 2050
University of New Mexico
Albuquerque NM 87131-1126

Tel: (505) 750-7172
Fax: (505) 277-3577
Email: agee at unm.edu
http://epswww.unm.edu/iom/pers/agee.html