December 1999

Newly Discovered Planet Thought to Orbit Two Stars

Gravity simulation According to an article just published in the journal Nature, the discovery of what appears to be a massive planet orbiting two stars instead of the usual one has opened the possibility of more planetary systems than previously recognized by scientists.

The possible planet is thought to be about three times the mass of Jupiter and about seven astronomical units from the binary star. Jupiter, in contrast, is 5.3 astronomical units from our sun. It takes the planet 20 to 30 Earth years to circle the two stars.

The planet was discovered using a technique called gravitational microlensing, first proposed by Albert Einstein over a half century ago. The technique looks at the way light bends around distant stars.

There are other possible explanations for the phenomenon observed by the scientists, and therefore they are careful to claim the "possibility" of a new planet. The team hopes to use the Hubble Space telescope to test their findings.

Read about the discovery: Astronomers find evidence of first planet orbiting a pair of stars

Learn about the Problem

First you should look at Kepler's laws for the orbits of planets in our own solar system.

Then you can look at other orbits to gain a basic understanding of known systems.

The possibility that the path of light could be bent by the gravity of a large object was raised by Einstein in the 1930s, and this effect was observed soon afterward. Because we normally think of glass or plastic lenses as "bending light," any massive object that bends light rays is called a "gravitational lens." You can learn about how a lens bends light in the following two activities:

Think about the Problem

  • Sketch a picture of how you think the planet's orbit looks around the two stars. Mark the center of mass on the sketch.
  • Do Kepler's laws need to be reconsidered to accommodate a binary star system?

For the Teacher: Extending the Problem

Students who want to learn more about binary stars can read a brief description at Eclipsing Binary Stars. This site includes additional technical information about topics such as modeling light curves.

Students with a strong background in physics may want to learn more about gravitational microlensing. They can consult the following sites for information:

Students who are interested in other stellar phenomena should enjoy the following sites that introduce phenomena such as quasars, pulsars, supernovae and black holes:

Students who have questions related to space can take advantage of the following NASA services:

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