Gliese 876 D - Orbit and Mass

Orbit and Mass

Gliese 876 d is located in an orbit with a semimajor axis of only 0.0208 AU (3.11 million km). At this distance from the star, tidal interactions should in theory circularize the orbit; however, measurements reveal that it has a high eccentricity of 0.207, comparable to that of Mercury in our solar system.

A limitation of the radial velocity method used to detect Gliese 876 d is that only a lower limit on the mass can be obtained. This is because the measured mass value also depends on the orbital inclination, which in general is unknown. However, models incorporating the gravitational interactions between the resonant outer planets enables the inclination of the orbits to be determined. This reveals that the outer planets are nearly coplanar with an inclination of around 59° with respect to the plane of the sky. Assuming that Gliese 876 d orbits in the same plane as the other planets, the true mass of the planet is revealed to be 6.83 times the mass of Earth.

Models predict that, if its non-Keplerian orbit could be averaged to a Keplerian eccentricity of 0.28, then tidal heating would play a significant role in the planet's geology to the point of keeping it completely molten. Predicted total heat flux is approximately 104-5 W/m2 at the planet's surface; for comparison the surface heat flux for Io is around 3 W/m2. This is similar to the energy it receives from its parent star of about 40,000 W/m2.

Read more about this topic:  Gliese 876 D

Famous quotes containing the words orbit and, orbit and/or mass:

    Words can have no single fixed meaning. Like wayward electrons, they can spin away from their initial orbit and enter a wider magnetic field. No one owns them or has a proprietary right to dictate how they will be used.
    David Lehman (b. 1948)

    The Fitchburg Railroad touches the pond about a hundred rods south of where I dwell. I usually go to the village along its causeway, and am, as it were, related to society by this link. The men on the freight trains, who go over the whole length of the road, bow to me as to an old acquaintance, they pass me so often, and apparently they take me for an employee; and so I am. I too would fain be a track-repairer somewhere in the orbit of the earth.
    Henry David Thoreau (1817–1862)

    The best reason why Monarchy is a strong government is, that it is an intelligible government. The mass of mankind understand it, and they hardly anywhere in the world understand any other.
    Walter Bagehot (1826–1877)