From NASANews@luna.osf.hq.nasa.govTue Dec 12 11:05:07 1995
Date: Fri, 1 Dec 1995 20:29:23 -0500
From: NASA HQ Public Affairs Office <NASANews@luna.osf.hq.nasa.gov>
To: press-release-com@mercury.hq.nasa.gov
Subject: Galileo Crosses Boundary into Jupiter's Environment

Douglas Isbell 
Headquarters, Washington, DC        December 1, 1995 
(Phone:  202/358-1753) 
 
Franklin O'Donnell 
Jet Propulsion Laboratory, Pasadena, CA 
(Phone:  818/354-5011) 
 
RELEASE:  95-215 
 
GALILEO CROSSES BOUNDARY INTO JUPITER'S ENVIRONMENT 

     NASA's Galileo spacecraft radioed confirmation late 
this week that it has entered Jupiter's environment, 
crossing over the boundary from interplanetary space into 
the giant magnetic cocoon around Jupiter called the magnetosphere. 
      
     "With the spacecraft now in the magnetosphere, we begin 
our first direct measurements of the Jupiter system," said 
Galileo Project Manager William J. O'Neil at NASA's Jet Propulsion
Laboratory (JPL), Pasadena, CA.   
 
     Data from Galileo's magnetometer confirmed that the 
spacecraft passed the milestone on Nov. 26 at a distance of 
about six million miles (nine million kilometers) from 
Jupiter's cloud tops, scientists announced today. 
 
     After a six-year voyage through the Solar System, 
Galileo is less than a week away from taking up permanent 
residence around Jupiter.  On Thursday, Dec. 7, Galileo's 
previously deployed atmospheric probe will plunge into 
Jupiter's cloud tops at 5:56 p.m. EST and descend into the 
giant planet on a parachute. 
 
     Overhead, the Galileo spacecraft itself will collect 
and record data radioed from the probe during the 40- to 75-
minute probe mission.  At 8:19 p.m. EST, an hour after the 
probe mission is completed, Galileo will begin to fire its 
onboard rocket to slow down and allow itself to be captured 
into orbit around Jupiter to begin a two-year mission of 
closeup studies of Jupiter's large moons, the planet itself, 
and continuous measurements of the magnetosphere. 

     Jupiter's magnetosphere is like a giant bubble around 
the planet.  A shock wave -- called "bowshock" after the 
wave that builds before the bow of a ship -- exists where 
the magnetosphere faces the stream of charged particles 
flowing outward from the Sun, called the solar wind.  As the 
solar wind flows around Jupiter, the magnetosphere tapers 
off like a wind sock, with the whole invisible structure 
moving in response to buffeting by the solar wind. 

     Galileo scientists said they first saw signs of the 
bowshock on Nov. 16, but the bowshock apparently moved back 
and forth in response to alternate gusts and waning of the 
solar wind.  "As the solar wind velocity increased, the 
shock moved inside the position of the spacecraft leaving 
Galileo again in the solar wind," said Dr. Margaret Galland 
Kivelson of the University of California at Los Angeles, the 
principal investigator on Galileo's magnetometer experiment. 
 
     This crossing and recrossing of the shockwave happened 
several times, she said, between the first shock encounter 
on  Nov. 16, when the spacecraft was about nine million 
miles (15 million kilometers) from Jupiter, and Nov. 26 when 
Galileo finally crossed the main bowshock at 1 p.m. EST at 
about six million miles out from Jupiter's cloud tops.   
 
     The magnetometer science team also found the first 
direct evidence that the jovian magnetosphere was either 
unaffected or had recovered in the aftermath of last year's 
impact of Comet Shoemaker-Levy with Jupiter.  Some 
scientists had theorized that the magnetosphere might have 
been modified signficantly by the violent impact, but that 
appears not to be the case, according to data from Galileo. 
 
     Meanwhile, Galileo engineers report that work has been 
completed on the spacecraft's tape recorder to assure its 
readiness for recording data during Thursday's atmospheric 
probe descent.  Final fine-tuning of the spacecraft's flight 
path is scheduled for this Saturday, Dec. 2.
 
     Two Internet home pages exist to provide information on 
the atmospheric probe, Galileo orbiter spacecraft, mission 
operations and science returns.  The Galileo Project home 
page may be accessed at http://www.jpl.nasa.gov/galileo.  A 
home page sponsored by the atmospheric probe team at NASA 
Ames Research Center, Mountain View, CA, may be accessed at  
http://ccf.arc.nasa.gov/galileo_probe/. 

NOTE TO EDITORS:  A press briefing prior to the probe 
mission and Galileo's Jupiter orbit-entry will be held at 
JPL on Dec. 7 at 4 p.m. EST, and a follow-up briefing will 
be held at 9:45 p.m. EST.  Both events will be carried live 
on NASA Television.
 
	NASA Television is available through the Spacenet 2 
satellite, transponder 5, channel 9, 69 degrees West 
longitude, frequency 3880 MHz, audio subcarrier 6.8 MHz, 
horizontal polarization. 

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