NASA Astrobiology Institute (NAI)

1. Formation and Detection of Hot-Earth Objects in Systems with Close-in Jupiters

   Project Investigators: Eric Agol, Nader Haghighipour

   Summary

   The time of the transit of a planet can be altered by the perturbation of other (planetary) objects in the system. These alterations can be used to identify the presence of the perturbing bodies and are much larger when the perturber and the transiting object are in mean-motion resonances. This project is on mapping the parameter-space of a system of a hot-Jupiter and a terrestrial planet to identify regions where the tererstrial planet will produce the largest transit timing variations.

   Astrobiology Roadmap Objectives:

   • Objective 1.1: Models of formation and evolution of habitable planets
   • Objective 1.2: Indirect and direct astronomical observations of extrasolar habitable planets

   Project Progress

   Short-period terrestrial-mass objects are predicted to be captured into near mean-motion resonant orbits with migrating giant planets. These objects are potentially detectable via transit photometry of their host stars, or the measurement of the variations of the transit-timing due to their Jovian-mass planetary companions. The detectability of these objects requires their long-term stability implying that to determine the prospects of their detection, it is necessary to develop a detailed understanding of the interactions between close-in terrestrial and Jovian planets, and the region of their parameter-space for which a terrestrial-class object will be dynamically stable. We have carried out extensive numerical simulations of the dynamical evolution of a short-period Earth-like object in the vicinity of a close-in giant planet, and have identified the ranges of its orbital parameters for which the system is stable. Our results indicate that for a tidally locked Jovian body, a terrestrial-class object can be stable on low eccentricity (< 0.2) and low inclination (< 15 deg.) orbits (Figure 1).

   
   

   The region of stability (shaded areas) of an Earth-like object in the system with a hot-Jupiter. As shown here, a terrestrial-class planet with low inclination and eccentricity can have a stable orbit in low-order mean-motion resonances, where the TTV signals are strong.

   We have also been able to identify regions where a terrestrial planet can be in stable 1:2 or 1:3 mean-motion resonances with the giant planet. As shown in Figure 2, the synthetic transit timing variations of a giant planet in such systems have large amplitudes. Our simulations also indiate that regions may exist in the vicinity of unstable mean-motion resonances, where a super-Earth object can maintain its orbit for a long time and produce strong signals detectable by the transit-timing variations method (Figure 2).

   
   

   TTV signals corresponding to 2:3 and 1:2 mean-motion resonances between an Earth-like planet and a hot-Jupiter. As shown here, the amplitudes of the signals are high implying that an Earth-like object has a higher chance of being detected through the TTV method when in such resonances.

Publications

Haghighipour, N.  (2008).  The Prospects of Detecting Super-Earth Planets via the Transit Timing Variation Method.  Ascona Workshop on Planet Formation.  Ascona,Switzerland.