Exit Help

Extrasolar Planetary Satellite Integrator Help File

Star & Planet Information

  • HELP. Displays this help screen. To exit, click one of the Exit Help buttons located at the top and bottom of this screen.
  • STELLAR MASS. Specify the mass of the star that the extrasolar planet revolves around in units of Solar masses. Sunlike stars have masses near 1.0.
  • PLANETARY MASS. Specify the mass of the extrasolar planet in in units of Jupiter masses. Extrasolar planets have masses that range from 0.5-10 Jupiter masses.
  • PLANET RADIUS. Specify the radius of the extra-solar planet in Jupiter Radii. This parameter is not known for most extrasolar planets, 1.0 is a good estimate.
  • PLANETARY SEMIMAJOR AXIS. Specify the semimajor axis of the orbit of the extrasolar planet in Astronomical Units (AU). The distance from the Earth to our Sun is 1.0 AU. Extrasolar planets discovered to date range from 0.04 - 3.0AU.
  • PLANETARY ECCENTRICITY. Specify the eccentricity of the orbit for the extra-solar planet. This is a measure of ellipticity which ranges from 0 to 1. A value of 0.0 is a perfect circle, with larger values representing successivly more elongated ellipses.

    Integration Parameters

  • ACCURACY. This number specifies the accuracy of the integration. More accurate integrations take longer and are more prone to run into numerical problems. Accordingly, you want the lowest number which gives an accurate plot. Experiment by following the same orbit at different accuracies and seeing if the output plots are similar.
  • INTEGRATION TIME. Here you specify how many years into the future the orbit should be followed. Be careful in choosing this parameter as it is directly correlated to how long you will wait before seeing a plot! A good strategy is to try a short integration time first to get an idea of how fast the program is.
  • FREQUENCY. This number determines how often a point along the orbit is saved to disk. A larger number yields a more accurately drawn orbit at the expense of plotting time and disk space. You want to choose the largest number that yields a reasonably accurate orbit. Experiment!
  • INTEGRATION LIMITS. These upper and lower limits on the planet-satellite distance allow you to stop the integration once the satellite has wandered into an uninteresting regime. Less than 1.0 planetary radii corresponds to a collision, while greater than several hundred to several thousand radii correspond to a satellite which escapes the planet.

    Initial Conditions

  • INITIAL POSITION. The initial position needs to be specified in spherical coordinates where r is length of the radius vector, θ is the angle between the z-axis and the radius vector, and φ is measured from the x-axis to the projection of the radius vector into the xy plane (see figure). Valid Ranges: r > 0, 0 ≤ θ ≤ 180 degrees, -180 ≤ φ ≤ 360 degrees.
  • INITIAL VELOCITY. The initial velocity is specified in a local coordinate system based on the particle's position. The velocities vr, vθ, and vφ are in the directions that would cause r, θ, and φ to increase (see figure). Since the velocities are normalized to the circular velocity, when the total speed is 1.0, the satellite starts on an initially circular orbit around the planet. The total velocity squared is the sum of the squares of the three velocity components.

  • SUBMIT FORM. Send the parameters that you have chosen to the orbital integration program!
  • LOAD DEFAULTS. Default values are for the first transiting extrasolar planet: HD 209458.
    Exit Help