Gadget by The Blog Doctor.

Sunday, December 26, 2010

Voyager 1

Voyager 1 was launched 33 years ago on September 5, 1977. Voyager 1 flew past Jupiter and Saturn producing many photographs and observations. Some or the photographs can be seen at this link. (Voyager 2 used the alignment of the planets to also visit Uranus and Neptune.)

Voyager 1's tasks were not complete after its groundbreaking observations at Jupiter and Saturn. When it was beyond the Saturn system, Voyager 1 was turned around and took pictures of all of the planets, including the iconic Pale Blue Dot photo of Earth - for details see this post.

Voyager 1 is still making important contributions to our understanding of the Solar System, as it maps the details of its large scale structure. The graphic below shows the major elements of the Sun's System. For details on the Helioshpere, Heliopause, Termination Shock, Heliosheath and Bow Shock see this link.

The notes below are from this source. Reference to the graphic above will assist in understanding the description.

PASADENA, Calif. – The 33-year odyssey of NASA's Voyager 1 spacecraft has reached a distant point at the edge of our solar system where there is no outward motion of solar wind.

Now hurtling toward interstellar space some 17.4 billion kilometers (10.8 billion miles) from the sun, Voyager 1 has crossed into an area where the velocity of the hot ionized gas, or plasma, emanating directly outward from the sun has slowed to zero. Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind in the region between stars.

The event is a major milestone in Voyager 1's passage through the heliosheath, the turbulent outer shell of the sun's sphere of influence, and the spacecraft's upcoming departure from our solar system.

"The solar wind has turned the corner," said Ed Stone, Voyager project scientist based at the California Institute of Technology in Pasadena, Calif. "Voyager 1 is getting close to interstellar space."

Our sun gives off a stream of charged particles that form a bubble known as the heliosphere around our solar system. The solar wind travels at supersonic speed until it crosses a shockwave called the termination shock. At this point, the solar wind dramatically slows down and heats up in the heliosheath.

Launched on Sept. 5, 1977, Voyager 1 crossed the termination shock in December 2004 into the heliosheath. Scientists have used data from Voyager 1's Low-Energy Charged Particle Instrument to deduce the solar wind's velocity. When the speed of the charged particles hitting the outward face of Voyager 1 matched the spacecraft's speed, researchers knew that the net outward speed of the solar wind was zero. This occurred in June, when Voyager 1 was about 17 billion kilometers (10.6 billion miles) from the sun.

Because the velocities can fluctuate, scientists watched four more monthly readings before they were convinced the solar wind's outward speed actually had slowed to zero. Analysis of the data shows the velocity of the solar wind has steadily slowed at a rate of about 20 kilometers per second each year (45,000 mph each year) since August 2007, when the solar wind was speeding outward at about 60 kilometers per second (130,000 mph). The outward speed has remained at zero since June.

The results were presented today at the American Geophysical Union meeting in San Francisco.

"When I realized that we were getting solid zeroes, I was amazed," said Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator and senior staff scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "Here was Voyager, a spacecraft that has been a workhorse for 33 years, showing us something completely new again."

Scientists believe Voyager 1 has not crossed the heliosheath into interstellar space. Crossing into interstellar space would mean a sudden drop in the density of hot particles and an increase in the density of cold particles. Scientists are putting the data into their models of the heliosphere's structure and should be able to better estimate when Voyager 1 will reach interstellar space. Researchers currently 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 1 provided that with hard facts," said Tom Krimigis, principal investigator on the Low-Energy Charged Particle Instrument, who is based at the Applied Physics Laboratory and the Academy of Athens, Greece. "Once again, we face the predicament of redoing our models."

So after travelling for 33 years at about 15 Km/second Voyager 1 is 17.4 billion kilometers from Earth, which is about 2.7 times the average distance to Pluto (from the Sun. It is the most remote human-made object. This sounds impressive but when viewed in interstella terms it has travelled only 0.0017 light-years.

The nearest star to our sun is Proxima Centauri, which is 4.2 light years away. At its current speed, Voyager 1 it would take until the year 84,000 A.D. to get to our nearest star, if it were traveling in the right direction. (It isn't.)

So much for interstellar travel.

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