Generalized Milankovitch Cycles and Long-Term Climatic Habitability

Abstract

Although Earth's orbit is never far from circular, terrestrial planets around other stars might experience substantial changes in eccentricity. Eccentricity variations could lead to climate changes, including possible "phase transitions" such as the snowball transition (or its opposite). There is evidence that Earth has gone through at least one globally frozen, "snowball" state in the last billion years, which it is thought to have exited after several million years because global ice-cover shut off the carbonate-silicate cycle, thereby allowing greenhouse gases to build up to sufficient concentration to melt the ice. Due to the positive feedback caused by the high albedo of snow and ice, susceptibility to falling into snowball states might be a generic feature of water-rich planets with the capacity to host life. This paper has two main thrusts. First, we revisit one-dimensional energy balance climate models as tools for probing possible climates of exoplanets, investigate the dimensional scaling of such models, and introduce a simple algorithm to treat the melting of the ice layer on a globally frozen planet. We show that if a terrestrial planet undergoes Milankovitch-like oscillations of eccentricity that are of great enough magnitude, it could melt out of a snowball state. Second, we examine the kinds of variations of eccentricity that a terrestrial planet might experience due to the gravitational influence of a giant companion. We show that a giant planet on a sufficiently eccentric orbit can excite extreme eccentricity oscillations in the orbit of a habitable terrestrial planet. More generally, these two results demonstrate that the long-term habitability (and astronomical observables) of a terrestrial planet can depend on the detailed architecture of the planetary system in which it resides.

Debris disks as signposts of terrestrial planet formation

“…However, more detailed modeling of such planets is beyond the scope of the paper and the reader is referred to recent climate modeling papers that include the effects of varying the eccentricity and obliquity (Williams & Pollard 2002Spiegel et al 2009Spiegel et al , 2010Dressing et al 2010).…”

Biomarkers of Habitable Worlds - Super-Earths and Earths

“…Such spectra will be used as part of a big grid to characterize any exoplanets found and influences the design requirements for a spectrometer to detect habitable planets, a grid different international groups are working on (see e.g. , (Segura et al 2003), (Spiegel et al 2010), (Forget & Pierrehumbert 1997), (Cowan et al 2009), (Goldblatt & Zahnle 2011), (Edson et al 2011), (Kitzmann et al 2010), (Domagal-Goldman et al 2011), (Kaltenegger et al 2010c) and references therein). Other geochemical cycles as well as volcanic events can also leave observable features in a planet's atmosphere that can potentially be detectable (see Fig.…”

The debris disk – terrestrial planet connection

“…Indeed, there is a strong anti-correlation between the † These oscillations certainly have important consequences for the planetary climate (Spiegel et al 2010). 05 M⊕) in a sample weighted as 90% from unstable systems and 10% from stable systems.…”