NASA Astrobiology Institute (NAI)

1. Detection of Super-Earths Using Transit Timing Variation Method

   Project Investigators: Eric Agol, Nader Haghighipour

   Summary

   Jupiter-like planets may orbit their parent stars in very close distances and reduce their brightness by blocking some of their lights. A second planets with a mass several times more than the Earth in such systems can disturb the orbit of the Jupiter-like planet and causes its transit to occur at different times. By measuring the time between these transit we can determine the size and orbit of the perturbing planet.

   Astrobiology Roadmap Objectives:

   • Objective 1.2: Indirect and direct astronomical observations of extrasolar habitable planets

   Project Progress

   Short-period terrestrial-class and Super-Earth 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 close-in Jovian-mass planetary companions. The latter, also known as the TTV method, is particularly efficient in detecting small close-in planets in resonant orbits. Haghighipour and collborator Eric Agol from the University of Washington, started an an expansive project on the study of the capability of the TTV method in detecting close-in Super-Earth objects. They and have identified regions of the parameter-space for which such planets will produce strong TTV signals. Haghighipour has also studied the effects of interior and exterior mean-motion resonancces on the detectability of Super-Earths, and has been able to show that for a tidally locked Jovian body, a Super-Earth planetary companion has a greater chance of detection if it has a long-term stable orbit with a low eccentricity and a low inclination (figure 1). Two of Haghighipour’s student have also been involve din this project. The results of their studies indicate that low-order mean-motion resonances, such as 1:2 and 1:3 resonances, cause strong enhancements in TTV signals and present most probable configurations for the detection of Super-Earth objects. Trojan planets in 3 to 10 day orbits and with eccentricities ranging from 0 to 0.15 will also have a high probability for detection especially around M dwarfs.

   
   

   Graph of stability for an Earth-size planets in a
   transiting system. The central star is Sun-like.
   The transiting planet (not shown here) is Jupiter-like in a 3-day circular
   orbit at 0.0407 AU. The circles
   correspond to the values of the semimajor axis and eccentricity
   of the Earth-like planet at the beginning of each simulation. The orange
   dotted lines show the boundaries of the unstable region for an Earth-size
   planet. The red
   circles present conservative regions of the stability of a
   terrestrial-class object.

   Cross-Team Collaborations

   In this project, I am collaborating with Eric Agol from University of Washington(modeling transit timing variations in resonant orbits), Steinn Sigurdsson from Penn State (dynamics and formation of close-in Earth-like planets), and Lisa Kaltenegger from Harvard (atmosphere and spectra of habitable Super-Earths). These collaborations have helped the initial conditions of the related compuational simulations to be physically meaningful.

Publications

Capen,S. & Haghighipour, N. (2009) DetectabilityOf Low‐Mass Trojan Planets In Transiting Systems Using Transit Timing Variation Method. BAAS, submitted,