Voyager has reached that point were the solar wind drops to zero and islikely flowing sideways. We will shortlybe exiting the heliosheath and entering interstellar space and will get ourfirst data. Now we will know the temperaturefor sure.
Voyager has been very successful and of course has made the argument forsending out a lot of additional probes to fully map the whole extended systemin multiple directions. It has taken itthirty three years to approach the end of the zone of influence of the sun.
It also shows us just how far the influence of the solar wind protects theOort cloud in particular.
This year we are getting a welcome blast of data regarding the sun inparticular. We are a long way yet frommapping the whole system, particularly in regards to the magnetic fields, butthe number of probes is increasing rapidly now.
Voyager Reaches Interstellar SpaceAs Solar Wind Slows To Zero
Launched on Sept. 5, 1977, Voyager 1 crossed the termination shock inDecember 2004 into the heliosheath. Scientists have used data from Voyager 1'sLow-Energy Charged Particle Instrument to deduce the solar wind's velocity.
The 33-year odyssey of NASA's Voyager 1 spacecraft has reached a distant pointat the edge of our solar system where there is no outward motion of solar wind.
Now hurtling towardinterstellar space some 17.4 billion kilometers (10.8 billion miles) from thesun, Voyager 1 has crossed into an area where the velocity of the hot ionizedgas, or plasma, emanating directly outward from the sun has slowed to zero.Scientists suspect the solar wind has been turned sideways by the pressure fromthe interstellar wind in the region between stars.
The event is a majormilestone in Voyager 1's passage through the heliosheath, the turbulent outershell of the sun's sphere of influence, and the spacecraft's upcoming departurefrom our solar system.
"The solar windhas turned the corner," said Ed Stone, Voyager project scientist based atthe California Institute of Technology in
"Voyager 1 is gettingclose to interstellar space." Pasadena, Calif.
Our sun gives off astream of charged particles that form a bubble known as the heliosphere aroundour solar system. The solar wind travels at supersonic speed until it crosses ashockwave called the termination shock. At this point, the solar winddramatically slows down and heats up in the heliosheath.
Launched on Sept. 5,1977, Voyager 1 crossed the termination shock in December 2004 into theheliosheath. Scientists have used data from Voyager 1's Low-Energy ChargedParticle Instrument to deduce the solar wind's velocity.
When the speed of thecharged particles hitting the outward face of Voyager 1 matched the spacecraft's speed, researchers knew that the netoutward speed of the solar wind was zero. This occurred in June, when Voyager 1was about 17 billion kilometers (10.6 billion miles) from the sun.
Because the velocitiescan fluctuate, scientists watched four more monthly readings before they wereconvinced the solar wind's outward speed actually had slowed to zero.
Analysis of the datashows the velocity of the solar wind has steadily slowed at a rate of about 20kilometers per second each year (45,000 mph each year) since August 2007, whenthe solar wind was speeding outward at about 60 kilometers per second (130,000mph). The outward speed has remained at zero since June.
The results werepresented at the American Geophysical Union meeting in
. San Francisco
"When I realizedthat we were getting solid zeroes, I was amazed," said Rob Decker, aVoyager Low-Energy Charged Particle Instrument co-investigator and senior staffscientist at the Johns Hopkins University Applied Physics Laboratory in Laurel,Md.
"Here wasVoyager, a spacecraft that has been a workhorse for 33 years,showing us something completely new again."
Scientists believeVoyager 1 has not crossed the heliosheath into interstellar space. Crossinginto interstellar space would mean a sudden drop in the density of hotparticles and an increase in the density of cold particles.
Scientists are puttingthe data into their models of the heliosphere's structure and should be able tobetter estimate when Voyager 1 will reach interstellar space. Researcherscurrently estimate Voyager 1 will cross that frontier in about four years.
"In science,there is nothing like a reality check to shake things up, and Voyager 1provided that with hard facts," said Tom Krimigis, principal investigatoron the Low-Energy Charged Particle Instrument, who is based at the AppliedPhysics Laboratory and the Academy of Athens, Greece.
"Once again, weface the predicament of redoing our models."
A sister spacecraft,Voyager 2, was launched in Aug. 20, 1977 and has reached a position 14.2billion kilometers (8.8 billion miles) from the sun. Both spacecraft have beentraveling along different trajectories and at different speeds.
Voyager 1 is travelingfaster, at a speed of about 17 kilometers per second (38,000 mph), comparedto Voyager 2's velocity of 15 kilometers per second(35,000 mph). In the next few years, scientists expect Voyager 2 to encounterthe same kind of phenomenon as Voyager 1.