Orbit and Mass
Gliese 876 c is in a 1:2:4 Laplace resonance with the outer planets Gliese 876 b and Gliese 876 e: for every orbit of planet e, planet b completes two orbits and planet c completes four. This leads to strong gravitational interactions between the planets, causing the orbital elements to change rapidly as the orbits precess. This is the second known example of a Laplace resonance, the first being Jupiter's moons Io, Europa and Ganymede.
The orbital semimajor axis is only 0.13 AU, around a third of the average distance between Mercury and the Sun, and is more eccentric than the orbit of any of the major planets of our solar system. Despite this, it is located in the inner regions of the system's habitable zone, since Gliese 876 is such an intrinsically faint star.
A limitation of the radial velocity method used to detect Gliese 876 c is that only a lower limit on the planet's mass can be obtained. This is because the measured mass value depends on the inclination of the orbit, which is not determined by the radial velocity measurements. However in a resonant system such as Gliese 876, gravitational interactions between the planets can be used to determine the true masses. Using this method, the inclination of the orbit can be determined, revealing the planet's true mass to be 0.72 times that of Jupiter.
Read more about this topic: Gliese 876 C
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)
“It is strange to contemplate how little sympathy or encouragement the great mass of people have with one who differs from them in tastes, to the extent of desiring an education, while they are content with little or none.”
—Caroline Nichols Churchill (1833–?)