There is solid evidence that NASA’s Voyager 1 spacecraft has become the first manmade object to reach interstellar space, more than 11 billion miles distant and 36 years after it was launched, claiming an iconic place in in the history of space exploration.
For several months, the relative position of Voyager 1 has stirred something of a scientific debate because there remains some lingering evidence of the nearby heliosphere beyond the heliopause.
A short history of Voyager's historic journey
Even though Voyager 1 has passed into interstellar space, it does not mean that its journey is over, says Bill Kurth, UI research scientist and co-author of the Science paper.
“Now that we’re on the outside, we are learning that interstellar space isn’t a bland region,” Kurth says. “Rather, there are variations in some of Voyager’s measurements that may be due to the nearby presence of the heliosphere. So, our attention is turning from crossing the boundary to understanding what is going on outside,” he says.
At age 36, Voyager 1 is the most distant human-made object at more than 11.6 billion miles from the sun, or about 125 astronomical units.
“At that distance it takes more than 17 hours for a radio signal to travel from the spacecraft to one of NASA’s Deep Space Network antennas. The signal strength is so incredibly weak that it takes both a 230-foot and a 110-foot-diameter antenna to receive our highest resolution data,” Gurnett says.
Launched Sept. 5, 1977, Voyager 1 completed flybys of both Jupiter and Saturn and is currently moving outward from the sun at about 3.5 AU per year. A sister spacecraft, Voyager 2 was launched Aug. 20, 1977, on a flight path that took it to encounters with Jupiter, Saturn, Uranus, and Neptune. At present, Voyager 2 is still inside the heliosphere about 103 AU from the sun and traveling outward at about 3.3 AU per year.
The sounds of the electron plasma oscillations heralding Voyager’s entry into interstellar space and other sounds of space can be heard by visiting Gurnett’s website.
Elsewhere, astronomers using the National Science Foundation's (NSF) Very Long Baseline Array (VLBA) and Green Bank Telescope (GBT) spotted the faint radio glow from NASA's famed Voyager 1 spacecraft -- the most distant man-made object.
According to NASA's Jet Propulsion Laboratory (JPL), the VLBA imaged the signal from Voyager 1's main transmitter after the spacecraft had already passed beyond the edge of the heliosphere, the bubble of charged particles from the Sun that surrounds our Solar System.
Using NASA's Deep Space Network, JPL continually tracks Voyager and calculates its position on the sky, which is known as the ephemeris. Since the VLBA has the highest resolution, or ability to see fine detail, of any full-time astronomical instrument, NRAO astronomers believed they could locate Voyager's ephemeris position with unprecedented precision. This is unrelated to Voyager's distance from the Sun or position relative to the heliosphere.
The initial observations, which were made on February 21, placed Voyager very near, but not precisely at its predicted location. The difference was a few tenths of an arcsecond. An arcsecond is the apparent size of a penny as seen from 2.5 miles (4 kilometers) away. The second observations on June 1 produced similar results.
"It is possible that these observations are at the milliarcsecond [one-thousandth of an arcsecond] level, or better," said NRAO scientist Walter Brisken, who led the observations with the VLBA. At 11.5 billion miles -- Voyager's approximate distance at the time of the initial observations -- one milliarcsecond would be roughly 50 miles across.
Voyager's main transmitter shines at a feeble 22 watts, which is comparable to a car-mounted police radio or -- in visible light -- a refrigerator light bulb. Though incredibly weak by the standards of modern wireless communications, Voyager's signal is astoundingly bright when compared to most natural objects studied by radio telescopes.
"The ability to pinpoint the location of Voyager and other spacecraft is critical as we explore the inner Solar System and beyond," said Brisken. "The NRAO's VLBA has the capability to do this vital task with unprecedented precision."
Voyager 1, which was launched in 1977, is now headed away from the Sun at a speed of about 38,000 miles per hour.
In a remarkably sensitive complementary observation, the NRAO's Green Bank Telescope (GBT), which is the world's largest fully steerable radio telescope, easily detected Voyager's signal, picking it out from the background radio noise in less than one second.
"Voyager is the first man-made object to penetrate the interstellar medium, and we really want to be able to receive the data from this new frontier," said NRAO scientist Toney Minter, who oversaw the Green Bank observations. "This information will provide many clues about how the interstellar medium behaves and how the Sun interacts with it."
The Daily Galaxy via NRAO and http://now.uiowa.edu/