Extraordinary Claim: the Earth Formed Volatile Free

United Theory of Planet Formation (I): Tandem Regime

Authors:

Ebisuzaki et al

Abstract:

We have obtained a steady-state, 1-D model of the accretion disk of a protostar taking into account the magneto-rotational instability (MRI). We find that the disk is divided into an outer turbulent region (OTR), a MRI suppressed region (MSR), and an inner turbulent region (ITR). The outer turbulent region is fully turbulent because of MRI. However, in the range, r_{out} (= 8 - 60 AU) from the central star, MRI is suppressed around the midplane of the gas disk and a quiet area without turbulence appears, because the degree of ionization of gas becomes low enough. The disk becomes fully turbulent again in the range r in (= 0.2 - 1 AU), which is called the inner turbulent region, because the midplane temperature become high enough (\gt 1000 K) due to gravitational energy release.

Planetesimals are formed through gravitational instability at the two distinct sites, outer and inner MRI fronts (the boundaries between the MRI suppressed region (MSR) and the outer and inner turbulent regions), because of the radial concentration of the solid particles. At the outer MRI front, icy particles grow through low-velocity collisions into porous aggregates with low densities. They eventually undergo gravitational instability to form icy planetesimals. On the other hand, rocky particles accumulate at the inner MRI front, since their drift velocities turn outward due to the local maximum in gas pressure. They undergo gravitational instability in a sub-disk of pebbles to form rocky planetesimals at the inner MRI front.

The tandem regime is consistent with the ABEL model, in which the Earth was initially formed as a completely volatile-free planet. The water and other volatile elements came later through the accretion of icy particles by the occasional scatterings in the outer regions.

Potential Meridional Transport in Atmospheres of Terrestrial Exoplanets Based on Earth and Mars

Meridional Transport in the Atmospheres of Earth and Mars

Author:

Soto

Abstract:

As we continue to discover terrestrial exoplanets, many with orbital and planetary characteristics drastically different from anything encountered in our solar system, we are likely to encounter 'exotic' atmospheric transport processes. As an example, we show an analysis of meridional transport from simulations Mars. These simulations provide insight into the differences in meridional transport between Earth and Mars, particularly through the role of a condensation flow. The differences between Earth and Mars are a reminder that there may be a wide variety of meridional transport processes at work across the range of observed terrestrial planets.

The Jupiter's Driving Role in Earth's Orbital Evolution

The role of Jupiter in driving Earth's orbital evolution: an update

Authors:

Horner et al

Abstract:

In the coming decades, the discovery of the first truly Earth-like exoplanets is anticipated. The characterisation of those planets will play a vital role in determining which are chosen as targets for the search for life beyond the Solar system. One of the many variables that will be considered in that characterisation and selection process is the nature of the potential climatic variability of the exoEarths in question.

In our own Solar system, the Earth's long-term climate is driven by several factors - including the modifying influence of life on our atmosphere, and the temporal evolution of Solar luminosity. The gravitational influence of the other planets in our Solar system add an extra complication - driving the Milankovitch cycles that are thought to have caused the on-going series of glacial and interglacial periods that have dominated Earth's climate for the past few million years.

Here, we present the results of a large suite of dynamical simulations that investigate the influence of the giant planet Jupiter on the Earth's Milankovitch cycles. If Jupiter was located on a different orbit, we find that the long-term variability of Earth's orbit would be significantly different. Our results illustrate how small differences in the architecture of planetary systems can result in marked changes in the potential habitability of the planets therein, and are an important first step in developing a means to characterise the nature of climate variability on planets beyond our Solar system.