### The 55 Cancri Star System

Forty-one light years from Earth is a star system known to have at least 3 planets. 55 Cancri has two massive planets orbiting it closer than Mercury orbits our Sun. This star system also has a massive planet orbiting it at about the same distance Jupiter orbits our Sun, making this star system somewhat resemble our own solar system.

 Name Mass Semi-major axis (AU) Eccentricity Period (days) 55 Cancri A 0.95 Solar masses -- -- -- 55 Cancri b 0.84 * sin(i) * Jupiter's mass 0.115 0.02 14.653 55 Cancri c 0.21 * sin(i) * Jupiter's mass 0.24 0.34 44.28 55 Cancri d 4.05 * sin(i) * Jupiter's mass 5.9 0.16 5360

The simulation cancri.gsim uses Gravity Simulator to illustrate the 55 Cancri system, and to investigate the dynamical interactions its planets may have on each other. This simulation uses the minimum value for each planets' mass by assuming that i = 90 degrees.

This illustration shows the 55 Cancri System. The two inner planets orbit very close to their star, while the outermost planet orbits from around 6 AU.

This illustration shows the 2 innermost planets in the 55 Cancri System. The inner planet has a very round orbit, while the outer planet has a noticably elliptical orbit.

But how do these orbits change over time? The following illustration shows the 2 innermost planets 48 years later. Notice that the inner planet's orbit no longer appears circular. It now has an eccentricity of almost 0.2. The outer planet's axes have also rotated about 180 degrees.

Gravity Simulator's Auto Save feature created a data.txt file used by Microsoft's Excel Spreadsheet to produce the following graph.

It plots the inner planet's eccentricity as a function of time (years). Notice that the eccentricity of the inner planet's orbit goes through cycles of roughly 100 years. Its eccentricity is ~0.02 at its mimimum and ~0.18 at its maximum.

This graph plots the second planet's eccentricity as a function of time (years). Notice that the eccentricity of the inner planet's orbit goes through cycles of roughly 180 years. Its eccentricity is ~0.2 at its mimimum and ~0.35 at its maximum.