arXiv subjects

A. Aitta

Publications and source records attributed to A. Aitta.

6 recordsLinked to original sources

arXiv2018

Interior structure of Mars and other rock-and-iron planetary bodies

Here it is shown how to find the interior structure of a variety of rock-and-iron planetary bodies by using the rock density and some aspects of the core density as known for the Earth and using a convection principle for the iron-rich core. Convection minimizes both the density and temperature gradients inside the core fluid. This is achieved if the density of the core fluid is close to pure iron melting density at the core-mantle boundary, and the density has the smallest value possible for iron-rich melt at the inner core boundary. The critical iron densities for both pure iron and iron with maximal light impurities were previously obtained utilizing Landau's theory of first order phase transitions with the most reliable experimental scaling. The planetary interior density is found by iteratively calculating the gravity and pressure in small radial steps. Moment of inertia factors are also calculated and agree well for the bodies for which we have accurate measurements: Moon, Mars and Mercury. Calculations are also made for the exoplanets Kepler-78b, K2-229b and Kepler-10b. All show iron-rich liquid in their cores. The lighter, solar objects are without an inner core, but the heaviest two exoplanets have a pure iron innermost core inside the inner core. The parameter range for a growing inner core in the radius-mass plane is calculated. The magnetic field following the growth of an inner core protects life on Earth, and similarly for exoplanets. This guides the selection of exoplanets to study in the search for life.

astro-ph.EP↗

arXiv2015

Internal structure of Pluto and Charon with an iron core

Pluto has been observed by the New Horizons space probe to have some relatively fresh ice on the old ices covering most of the surface. Pluto was thought to consist of only a rocky core below the ice. Here I show that Pluto can have an iron core, as can also its companion Charon, which has recently been modelled to have one. The presence of an iron core means the giant impact origin calculations should be redone to include iron and thus higher temperatures. An iron core leads to the possibility of a different geology. An originally molten core becomes solid later, with contraction and a release of latent heat. The space vacated allows the upper rock layers to flow downwards at some locations at the surface of the core, and some of the ice above the rock to descend, filling the spaces left by the rock motion downwards. These phenomena can lead to the forces recently deforming the icy surface of Pluto, and in a lesser way, of Charon.

astro-ph.EP↗

arXiv2009

Tricritical Points and Liquid-Solid Critical Lines

Tricritical points separate continuous and discontinuous symmetry breaking transitions. They occur in a variety of physical systems and their mathematical models. A tricritical point is used to determine a liquid-solid phase transition line in the pressure-temperature plane [Aitta, J. Stat. Mech., 2006]. Excellent experimental agreement has been obtained for iron, the material having the most high pressure data. This allows extrapolation to much higher pressures and temperatures than available experimentally. One can predict the temperature at the liquid-solid boundary in the core of the Earth where the pressure is 329 GPa. Light matter, present as impurities in the core fluid, is found to generate about a 600 K reduction of this temperature.

cond-mat.stat-mech↗

arXiv2008

Light matter in the core of the Earth: its identity, quantity and temperature using tricritical phenomena

Light elements in the iron-rich core of the Earth are important indicators for the evolution of our planet. Their amount and distribution, and the temperature in the core, are essential for understanding how the core and the mantle interact and for modelling the geodynamo which generates the planetary magnetic field. However, there is a longstanding controversy surrounding the identity and quantity of the light elements. Here, the theory of tricritical phenomena is employed as a precise theoretical framework to study solidification at the high pressures and temperatures where both experimental and numerical methods are complicated to implement and have large uncertainties in their results. Combining the theory with the most reliable iron melting data and the Preliminary Reference Earth Model (PREM) seismic data, one obtains the solidification temperature at the inner core boundary (ICB) for both pure iron and for the alloy of iron and light elements in the actual core melt. One also finds a value of about 2.5 mole% for the amount of light matter. In addition, the density of both solid and liquid pure iron at its melting temperature is found. This allows one to obtain the density of the light matter and thus to identify it to be MgSiO3.

physics.geo-ph↗

arXiv2007

Iron melting curve with a tricritical point

Solidification as a first order phase transition is described in the Landau theory by the same equation as tricritical phenomena. Here, the solidification or melting temperature against pressure curve is modelled to end at a tricritical point. The model gives the phase transition temperature's dependence on pressure up to the quadratic term with a definite expression for the coefficients. This formula is expected to be generally valid for pure materials having melting curves with dT/dP approaching zero at very high P. Excellent experimental agreement is obtained for iron, the material having the most high pressure data which rather accurately determines the value of the coefficient defining the curvature. The geophysically interesting iron solidification temperatures at the Earth's core pressures are obtained. In addition, the general formulae for entropy change, latent heat and volume contraction in solidification are found and calculated for iron as functions of pressure and temperature.

cond-mat.stat-mech↗

arXiv2002

An Fe-Si-Ni solidification model of the Earth's layering

The physical process creating layered structure in planetary rocky bodies is considered here to be multicomponent solidification. This is a unified alternative approach to the present interpretations where each layer is reasoned and matched individually. The Earth's solidification is modelled using the ternary phase diagram Fe-Si-Ni. The four cotectic concentrations and the four corresponding seismic discontinuity radii have been used to show that the silicon concentration as a function of the distance R from the centre of the Earth can be modelled by C(Si) = G(R/Re)(R/Re) where G = 0.583, Re is the Earth's radius and the Ni/Fe ratio is 0.072. Earth would have up to 13 chemically different layers. This model predicts that there are three to four chemically slightly different sublayers in the D" layer and two boundaries in the inner core at radii 870 km and 1050 km. The observed hemispheric asymmetry in the inner core could follow if the Ni-concentration slightly varies locally. Although this model can account for all the layers using only three elements it can not, of course, match the full chemistry of the real Earth.

physics.geo-ph↗