Epilogue

Abstract

Halfway through the year 2001, NASA announced a new mission to the Solar System’s innermost planet Mercury, for launch in early 2004, and renewed concept studies for a possible mission to Pluto within the same time frame. The novel aspects of both missions remind us that even as the number and variety of planets known to circle other stars continue to mount, we have much to learn about our own Solar System. At the same time, we can be encouraged that astronomers continue to find remnants and parts of other planetary systems that appear to mirror the most salient parts of our own. In February 2001, infrared observations made at the Keck Observatory by UCLA astronomers Christine Chen and Michael Jura indicated that a massive asteroid belt orbits the young (estimated 100 million-year old) star Zeta Leporis, some 21 parsecs away from Earth in the constellation Lepus.¹ Then, in June 2001, the Space Telescope Science Institute (STScI) reported that Hubble observations of microlensing events in the Globular Cluster M22, some 2,600 parsecs away in Sagittarius, picked up the signatures of free-floating planetary-type objects with minimum masses only 80 times that of Earth. As reported in Nature, monitoring 83,000 background stars behind M22 between February and June 1999, the team observed six events in which a background star jumped in brightness by some 50 percent for less than 20 hours. This short brightening of the background star indicates the foreground microlens is being created by a very low-mass object, not unlike an ejected planet. If these observations can be verified, these objects are very likely planets that have been “detached” (or gravitationally ejected or torn) from their orbits around their parent stars. To confirm these events, the team is planning more observations over a continuous seven-day period.²