Globular Cluster M22

Scientists are mystified by what may be unexpected, wandering, planet-sized objects.

A new image taken by NASA's Hubble Space Telescope implies the presence of these objects. The image is available at http://hubblesite.org/newscenter/archive/releases/2001/20/image/a/.

If confirmed, the new information collected by Hubble's Wide Field and Planetary Camera 2 could yield new insights about how stars and planets formed. The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

In results published this week in the journal Nature, the scientists report six unusual "microlensing" events inside the globular cluster M22. Microlensing occurs when a background star brightens momentarily as a foreground object drifts by. The gravitational field of the object amplifies light from a distant background star in the huge central bulge of our galaxy. The objects believed to cause these events are too dim to be seen directly.

The unusually short period (less than 20 hours) over which these microlensing events occurred indicates that the mass of the intervening objects could be as little as 80 times that of Earth. If confirmed, these bodies would be the smallest celestial objects ever seen beyond our solar system that are not orbiting any star.

Theoretically, these objects might be planets that were gravitationally torn away from parent stars in the cluster. However, they are estimated to make up as much as 10 percent of the cluster's mass -- too numerous to be wandering, "orphaned" planets.

Because these findings are so surprising, the astronomers caution that they must be confirmed by follow-up Hubble observations.

The new Hubble image includes an inset photo showing the entire globular cluster of about 10 million stars. Globular cluster M22 is about 60 light-years wide. A light year equals about 9.5 trillion kilometers (5.9 trillion miles). The image was taken in June 1995 by the Burrell Schmidt telescope at the Case Western Reserve University's Warner and Swasey Observatory on Kitt Peak in Arizona.

Additional information about the Hubble Space Telescope is online at http://www.stsci.edu/hst/. More information about the Wide Field and Planetary Camera 2 is at http://www.stsci.edu/hst/wfpc2.

The Space Telescope Science Institute, Baltimore, Md., manages space operations for the Hubble Space Telescope for NASA's Office of Space Science, Washington, D.C. The Institute is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract with the Goddard Space Flight Center, Greenbelt, Md. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency.