March 3, 1999

The Search for Extrasolar Planets

Disk of dust (pale greenish color) surrounding star 55 Cancri. The star itself is not visible. Its bright, blinding light is blocked by a mask, seen as the round, red ring in the middle of this image. The horizontal and vertical lines are artifacts introduced by the telescope.

Image Credits: David E. Trilling and Robert H. Brown, University of Arizona. The image was taken at NASA's Infrared Telescope Facility (IRTF) on Mauna Kea, HI.

The above image shows a disk of dust surrounding 55 Cancri, a star similar to the Sun but with slightly less mass. It is located in the constellation Cancer, the Crab, at a distance of 44 light-years from Earth. It is also one of nearly 20 stars known to possess planets.

Like most of the planets discovered to date, the one that revolves around 55 Cancri is quite massive and has a very small orbit. The planet's mass is estimated to be 0.8 times that of Jupiter. Its orbit is nearly circular and has a radius of only about 0.11 times the Sun-Earth distance. That corresponds to about 10 million miles, or a little more than a quarter of the distance from the Sun to Mercury. The planet orbits the star every 14.6 hours.

The unusual feature about 55 Cancri is that it possesses both a planet (there may actually be more than one) and a dust disk. The disk has been measured to extend at least 40 Sun-Earth distances from the central star, but it is probably much larger. The composition of the dust is similar to that of Pluto, other small, icy bodies, and dust debris that orbit in the outer fringes of our solar system, and are collectively known as Kuiper belt objects.

The discovery of both a planet and a circumstellar disk similar to our Sun's Kuiper belt circling 55 Cancri suggests that our solar system may not be unique. There probably exist other, perhaps many other, such systems in our galaxy.

If this conjecture is correct, the questions arise: "How many planetary systems exist in our and other galaxies?" "How many of these planets possess conditions suitable for the origin of life?" "On how many planets has life evolved past the single-cell stage into multi-celled organisms?"

At present, scientists cannot answer such questions. However, more powerful, Earth-orbiting telescopes now on the drawing board, such as NASA's Terrestrial Planet Finder, may give us the first tentative answers to some of them by the second decade of the next century.

More Cool Stuff

We obtained the above image and information about 55 Cancri from a release by the University of Arizona News Services:

http://science.opi.arizona.edu/lasso.acgi?-database=science.fp3&-layout=Fields& -response=%2f%7escience%2fcurrentdetails.htm&-recid=34267&-search

Excellent starting points for learning more about the rapidly evolving field of searching for extrasolar planets are brought to you by scientists at the San Francisco State University, the University of Arizona, and the Observatoire de Paris:

http://www.physics.sfsu.edu/~gmarcy/planetsearch/planetsearch.html
http://www.public.asu.edu/~sciref/exoplnt.htm
http://wwwusr.obspm.fr/departement/darc/planets/encycl.html

For information about the Sun's Kuiper belt, go to our Observation of the Week of September 26, 1996, "Billions of Icy Bodies Beyond Neptune":

http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960925/ob960925.html

NASA's future mission to search for and study extrasolar planets orbiting nearby stars, the Terrestrial Planet Finder (TPF), is described at:

http://tpf.jpl.nasa.gov/

As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the space sciences:

Jet Propulsion Laboratory (JPL) sponsors Telescopes In Education (TIE), a project that focuses on providing the tools students need to make hands-on discoveries in astronomy and astrophysics.

http://tie.jpl.nasa.gov/tie/

Other LTP sites that are dedicated to space science can be found at:

http://learn.ivv.nasa.gov/education/topics/space_sci.html