Published : Saturday, October 6, 2018 | 5:06 AM
NASA’s Voyager 2 spacecraft, built by engineers at the Jet Propulsion Laboratory in Pasadena and launched in August 1977, is showing signs it is about to exit the heliosphere – the vast protective bubble around the sun and the planets – to become the second man-made object to enter interstellar space, the region between stars.
Voyager 1, launched in September 1977, exited the heliosphere in August 2012, but about three months before that, it began detecting an increase in the rate of cosmic rays hitting the spacecraft – just like Voyager 2 is detecting now.
Cosmic rays are fast-moving particles that originate outside the solar system. Some of these cosmic rays are blocked by the heliosphere, so mission planners have been expecting that Voyager 2 will detect that increased cosmic ray activity as the spacecraft approaches and crosses the boundary of the heliosphere.
Since late August, the Cosmic Ray Subsystem instrument on Voyager 2 has measured about a five percent increase in the rate of cosmic rays hitting the spacecraft compared to early August, a JPL statement said. The probe’s Low-Energy Charged Particle instrument has detected a similar increase in higher-energy cosmic rays.
Voyager 2 is a little less than 11 billion miles – about 17.7 billion kilometers – from Earth, or more than 118 times the distance from Earth to the Sun.
Since 2007 the probe has been traveling through the outermost layer of the heliosphere, dominated by solar material and magnetic fields. Voyager scientists have been watching for the spacecraft to reach the outer boundary of the heliosphere, known as the heliopause.
“We’re seeing a change in the environment around Voyager 2, there’s no doubt about that,” said Voyager Project Scientist Ed Stone, based at Caltech in Pasadena. “We’re going to learn a lot in the coming months, but we still don’t know when we’ll reach the heliopause. We’re not there yet – that’s one thing I can say with confidence.”
The twin spacecraft were both built by JPL engineers. Launched by NASA from Cape Canaveral, Florida, the Voyagers were originally designed to conduct closeup studies of Jupiter and Saturn, Saturn’s rings, and the larger moons of the two planets.
To accomplish their two-planet mission, the spacecraft were built to last five years. But as the mission went on, and with the successful achievement of all its objectives, mission scientists and engineers at JPL saw it was possible to have them do additional flybys of the two outermost giant planets, Uranus and Neptune.
The engineers used remote control programming to endow the Voyagers with greater capabilities than they had when they left Earth – and so their two-planet mission became four, their five-year lifetimes stretched to 12, and now they have been out in space nearly 37 years.
Between them, Voyager 1 and 2 have explored all the giant outer planets of the solar system, 48 of their moons, and the unique systems of rings and magnetic fields those planets possess. The information they have returned to Earth has revolutionized the science of planetary astronomy, helping to resolve key questions while raising intriguing new ones about the origin and evolution of the planets in the solar system.
JPL continues to operate both spacecraft for NASA’s Heliophysics System Observatory, managed by the Heliophysics Division of the Science Mission Directorate in Washington.