Voyager 1 is continuing to push through the outer edge of our known solar system in what is arguably one of the greatest adventures in the history of mankind. The spacecraft has travelled farther than any man-made object ever has, and soon Voyager 1 will cross the boundary of our solar system and venture into deep space, sending data back across the heavens to us here on Earth as it travels through interstellar space like something out of the television series Star Trek.
Launched in 1977 on a Titan IIIE rocket from Cape Canaveral Air Force Station in Florida, the spacecraft is currently speeding through the cosmos at over 38,000 miles-per-hour. Voyager 1, as of June 24, 2012, is over 11 billion miles away from the sun. The distances Voyager 1 has covered are so vast that astronomers do not actually measure them in miles, but in Astronomical Units – or AU. One AU is the average distance between the Earth and Sun, about 93 million miles. Voyager 1 is over 120 times further from the sun than Earth is, and clearing over 3 AU every Earth year (365 days). At these distances, radio signals from Voyager 1 take over sixteen hours to reach researchers here on Earth, and the round-trip light time from the sun is over thirty-three hours.
These distances alone do not suggest Voyager 1 is on the verge of leaving our solar system, but the data received from the spacecraft about the environment it is cruising through point to the fact that the sun is having less influence as Voyager 1 pushes further out into space. One of the telltale signs that Voyager 1 is on the verge of crossing into interstellar space is the number of cosmic rays hitting the spacecraft, and that number continues to climb as Voyager ventures further away.
“The latest data from Voyager 1 indicate that we are clearly in a new region where things are changing quickly,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. “This is very exciting. We are approaching the solar system’s final frontier.”
That “final frontier” Stone refers to is an area on the edge of our solar system called the heliosheath – a zone that marks the outer boundary of our solar system still dominated by the Sun’s magnetic field and particles contained in the solar wind. Although astronomers don’t know exactly just how wide the heliosheath is, and therefore can’t pinpoint exactly where the border between our solar system and interplanetary space is, they can see changes in the environment become more dramatic as Voyager 1 approaches the border - known as the heliopause.
“From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering,” said Stone. ”More recently, however, we have seen a very rapid escalation in that part of the energy spectrum. Beginning on May 7, 2012, the cosmic ray hits have increased five percent in a week and nine percent in a month.”
In addition to a sharp rise in the detection of cosmic rays from deep space, Voyager 1 has also seen the supersonic solar wind being held back from further expansion by the interstellar wind – instruments on the spacecraft show solar wind speeds have dropped from 150,000 mph to zero as of last spring. That interaction is a characteristic environment of the “termination shock” phase, where influence from interstellar wind slows our sun’s solar winds to subsonic speeds and large changes in plasma flow direction and magnetic field orientation occur.
VIDEO: Voyager spacecraft set to enter interstellar space. Credit: ScienceAtNASA
Voyager 1 crossed through the termination shock phase and began its voyage through the heliosheath in December of 2004. Now, eight years later, data from Voyager 1 about its space environment point to the inevitable crossing of mankind’s first spacecraft from our solar system into interstellar space happening sooner rather than later. Over the last several months the spacecraft has also seen energetic particles from the solar system decline by nearly 50%, while the detection of high-energy electrons from interstellar space has increased 100 fold.
Although Voyager 1 is still in an environment dominated by the sun’s magnetic field and particles contained in the solar wind, researchers expect to see the spacecraft exit the heliosphere sometime between now and 2015. When that occurs, big changes are expected to be seen in the data sent back to Earth. For example, energetic particles from the sun will be few and far between, and the magnetic field around Voyager 1 will change direction from that of the sun’s magnetic field to that of the unexplored magnetism of interstellar space.
Although traveling slower, and thus lagging behind its cousin Voyager 1, Voyager 2 is currently traversing the solar system on a course which will eventually see it leave the solar system as well. Both spacecraft are reported to be in good health, and have enough power and thruster fuel to operate until at least 2020, possibly until 2025.
The Voyager spacecraft should provide better data regarding what the space between stars and solar systems is like in a way no other spacecraft has ever been able to, simply because no spacecraft has ever actually travelled there. Originally Voyager 1 and 2 were to explore the gas giant planets in the outer solar system – Voyager 2 is still the only spacecraft to have ever visited Uranus and Neptune. Their current mission, the Voyager Interstellar Mission (VIM), aims to extend our exploration beyond the solar system.
“When the Voyagers launched in 1977, the Space Age was all of 20 years old,” said Stone. “Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it. ”
Voyager 1 is not heading towards any particular star, and will not even come “close” to one for 40,000 years, when the spacecraft will pass within 1.6 light years (almost 10 trillion miles) of a star in the constellation Camelopardalis. Voyager 2 will pass within 4.3 light years (25 trillion miles) of the brightest star in the sky, Sirius, 296,000 years from now.