Charles Redmond Headquarters, Washington, D.C. February 23, 1990 (Phone: 202/453-1547) Pete Waller Ames Research Center, Moffett Field, Calif. (Phone: 415/694-5091) RELEASE: 90-29 PIONEER 11 PASSES NEPTUNE'S ORBIT, LEAVES SOLAR SYSTEM Pioneer 11 today will cross the orbit of Neptune and become the fourth spacecraft to leave the solar system, providing a coda to humanity's first major planetary explorations. Pioneer 11 will join Pioneer 10 and Voyagers 1 and 2 in searching for the heliopause, the point at which the Sun's electromagnetic influence gives way to the galaxy's influence. As it crosses Neptune's orbit, Pioneer 11 will be 2.8 billion miles from the Earth. Neptune's orbit currently marks one measure of the expanse of the solar system because, for the next 12 years, Pluto's eccentric orbit carries it inside Neptune's path. Some scientists refer to the heliopause as the edge of the solar system. By that definition, all four spacecraft are still within the solar system. Launched in 1973, Pioneer 11 provided scientists with their closest view of Jupiter, passing within 26,600 miles of the cloud tops in December 1974. The close approach and the spacecraft's speed of 107,373 mph, by far the fastest speed ever reached by a man-made object, hurled Pioneer 1.5-billion miles across the solar system toward Saturn. Before reaching Saturn in 1979, Pioneer 11 reached an inclination of 17 degrees above the solar equatorial plane, high enough to illuminate the true character of the sun's magnetic field. Now 780 million miles above the ecliptic plane where most of the planets orbit the sun, the spacecraft recently showed that many of the solar cosmic rays in the heliosphere originate outside the Sun's atmosphere in the interstellar gas, the space between the stars. - more - - 2 - Pioneer 11 flew to within 13,000 miles of Saturn and took the first close-up pictures of the planet. Instruments located two previously undiscovered small moons and an additional ring, charted Saturn's magnetosphere and magnetic field and found its planet-size moon, Titan, to be too cold for life. Pioneer 11, which will traverse interstellar space in the same direction as the Sun moves, continues to return good data, but in 3 years, operating the radio transmitter and scientific instruments simultaneously will be difficult, says NASA Project Manager Richard Fimmel. Technical adjustments may extend the craft's life through 1995. Pioneer 10, with a stronger power supply, may return data through the year 2000, which would extend its original 30-month design life to 28 years. In June 1983, Pioneer 10 made history by becoming the first human artifact to leave the solar system, travelling in the direction opposite Pioneer 11's path. Today, Pioneer 10 will be 4.5 billion miles from Earth. Returning data to Earth at the speed of light requires 6 hours, 36 minutes. Pioneer 10 continues to search for the heliopause for very long-wavelength gravity waves that would further understanding of Einstein's Theory of Relativity and for evidence of a 10th planet. The Pioneers are managed by the Ames Research Center, Mountain View, Calif., for NASA's Office of Space Science and Applications. The spacecraft were built by TRW Space & Technology Group, Redondo Beach, Calif. - end - TO: MDS/PRA Group 1615 L Street, N.W. - Suite 100 Washington, D.C. 20036 DATE & TIME: FEBRUARY 23, 1990 3:00pm ORDERED BY: Edward Campion NASA Headquarters/LMD 400 Maryland Avenue, SW Washington, DC 20546 PHONE: 202/453-8400 PROJECT TITLE: Release No: 90-29 PRINT ORDER: 2215 PRINTING: Camera Ready, lst pg on NASA logo, other pages plain ENCLOSE & MAIL: Release of 2 pages MAIL DATE: FEBRUARY 26, 1990 EXTRA COPIES: Deliver specified quanities to locations below: 50 copies 275 copies 75 copies -------------------- ------------------- ----------------- National Press Club NASA Mailroom NASA Newsroom 13th floor newsrack NASA Headquarters NASA Headquarters National Press Building 600 Independ. Ave, SW 400 Maryland Ave, SW 529 14th Street, NW Room A16 Room 6043 Washington, DC 20045 Washington, DC 20546 Washington, DC 20546 MEDIA SUMMARY OPTION: Name-by-name media summary - 1 copy CLIENT COMPUTER LISTS: Run the following: LS-CA, LS-FA, LS-GA*27E, LS-KA TYPE OF RELEASE & PIX: General news X 21:T-23:T PUT ADDRESSING ON: Self-mailer MEDIA SELECTION: END OF ORDER FORM END OF TRANSMISSION