2003 Annual Science Report

Virtual Planetary Laboratory (JPL/CalTech) Reporting  |  JUL 2002 – JUN 2003

Chemistry Models for Extrasolar Planets

Project Summary

This year, we have worked on both a coupled photochemical-climate model for Earth-like planets, which is an end-to-end test case for the larger VPL atmosphere model, and chemistry models for extrasolar giant planets.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

This year, we have worked on both a coupled photochemical-climate model for Earth-like planets, which is an end-to-end test case for the larger VPL atmosphere model, and chemistry models for extrasolar giant planets.

The Photochemical-Climate Model for Earth-Like Planets: This model (J. Kasting) has been used to model chemically and radiatively self-consistent atmospheres for Earth-like planets around other stars. Experiments were run (Kasting, Krelove, Segura) for an “Earth” with oxygen levels from the present atmospheric level (PAL), down to 1/100,000th PAL. This time-stepping model was also run to equilibrium to derive atmospheres for the planets around F2V, G2V and K2V stars, and to understand atmospheric conditions during the Earth’s Proterozoic. Figure 1 shows vertical profiles of ozone and temperature for Earth at different oxygen levels. We found that as atmospheric oxygen is removed, the ozone layer descends, and the stratospheric temperature bulge is reduced (via reduced heating from solar ultraviolet (UV) absorption by ozone). However, the ozone column remains appreciable down to 0.01 PAL of oxygen. We also modelled Earth-like planets orbiting K2V and F2V stars. The model atmospheres were also used as input to generate synthetic planetary spectra as described in an associated report.

{{ 1 }}

Extrasolar Jovian Planet Chemistry Models: Atmospheric escape rates are extremely important for understanding a planet’s evolution, and escape rates from young terrestrial planets are believed to be much higher than observed present-day rates. To validate the VPL hydrodynamic escape module for younger planets, we are using observations of “hot Jupiters” as a model validation for high escape rates. For this work, we have developed a one-dimensional (1-D) chemical model for Jovian planets that are extremely close to their parent star (Parkinson). In this environment, they experience high temperatures and UV fluxes, which modify the chemical reactions normally seen in Solar System Jovian planets. For extrasolar hot Jupiters, the formation of hydrocarbons, oxygen chemistry, and hydrodynamical loss is significantly enhanced because of their environment. Because of enhanced photolysis of higher order hydrocarbon species, our model is based only on H2, CO, H2O and CH4. Our two main results are that (a) H is produced largely in the atmosphere through the reactions of OH radicals, and H2 is not sensitive to the exact abundance of CO, H2O, and CH4 and (b) H2O acts as a catalyst and can be produced via the reactions of CO and H2. The modifications to the chemical model to incorporate new chemistry, database modeling, and to couple it to a hydrodynamic escape code are directly applicable to modifications required for the VPL terrestrial planet models.

  • PROJECT INVESTIGATORS:
    James Kasting James Kasting
    Co-Investigator
    Chris Parkinson
    Co-Investigator
  • PROJECT MEMBERS:
    Mark Allen
    Co-Investigator

    Mark Richardson
    Co-Investigator

    Yuk Yung
    Co-Investigator

  • RELATED OBJECTIVES:
    Objective 1.1
    Models of formation and evolution of habitable planets

    Objective 1.2
    Indirect and direct astronomical observations of extrasolar habitable planets

    Objective 7.2
    Biosignatures to be sought in nearby planetary systems