This artist's concept shows NASA's two Voyager spacecraft exploring a turbulent region of space known as the heliosheath, the outer shell of the bubble of charged particles around our sun. Image via NASA/JPL-Caltech
Is the Voyager 1 spacecraft about to go where no Earth-created object has gone before? It has been 36 years since Voyager 1 packed its scientific equipment and headed off into space. This week, US space agency NASA gave astronomers something tantalising to chew upon – the spacecraft would appear to be edging closer to becoming the first human-made object to travel into interstellar space.
Not everyone would agree with NASA’s prediction, but more on that later.
Planet-trotting
Voyager 1 and its twin spacecraft, Voyager 2, rocketed off into space in 1977. They have since been planet-trotting, taking in such stellar sights as planets Jupiter, Saturn, Uranus and Neptune.
In 1990, the two spacecrafts changed track and set their sights on interstellar space. Their immediate goal now is to leave the heliosphere.
The spacecrafts have also been measuring the size of the heliosphere during their mission, with this data being beamed back to scientists on the ground.
Interstellar journey …
So, what does this all this interstellar babble mean exactly? According to NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, data from Voyager 1 shows that the spacecraft is now more than 18bn km (11bn miles) from the sun before it crosses the solar bubble and heads into interstellar space.
This is the region of space beyond the Earth’s atmosphere and between star systems within a galaxy.
NASA has this week published its research findings using Voyager data in the journal Science.
This data, the agency said, gives new insights on the last region the spacecraft will cross before it leaves the heliosphere – also known as the bubble around our sun – and enters interstellar space.
Image depicting Voyager. Image via NASA/JPL
Magnetic highway
The three research papers featured in Science describe how Voyager 1’s entry into a region called the “magnetic highway” has enabled simultaneous observations of the highest rate so far of charged particles from outside the heliosphere and the disappearance of charged particles from inside the heliosphere.
It would appear that scientists have seen two of the three signs of Voyager 1’s arrival at interstellar space – these are charged particles disappearing as they zoom out along the solar magnetic field, and cosmic rays from far outside zooming in.
They are missing one last sign, however. They need to detect an abrupt change in the direction of the magnetic field as this would indicate the presence of the interstellar magnetic field.
“This strange, last region before interstellar space is coming into focus, thanks to Voyager 1, humankind’s most distant scout,” said Ed Stone, Voyager project scientist at California Institute of Technology in Pasadena.
“If you looked at the cosmic ray and energetic particle data in isolation, you might think Voyager had reached interstellar space, but the team feels Voyager 1 has not yet gotten there because we are still within the domain of the sun’s magnetic field,” explained Stone.
Voyager and its scientific equipment load. Image via NASA/JPL
Translating the data
The papers that feature in Science this week home in on observations made from May to September 2012 by Voyager 1‘s cosmic ray, low-energy charged particle and magnetometer instruments.
Some additional charged particle data obtained through April of this year has also been added to the research mix.
Apparently, Voyager 2 is about 15bn km (9bn miles) from the sun and still inside the heliosphere. On 25 August last year, Voyager 1 was recorded as being about 18bn km (11bn miles) away. This was when the spacecraft appeared to have reached the aforementioned magnetic highway.
NASA said this is also known as the depletion region or a connection to interstellar space.
For the first time in this region, scientists said the data from Voyager 1 enabled scientists to detect low-energy cosmic rays that originate from dying stars.
“We saw a dramatic and rapid disappearance of the solar-originating particles. They decreased in intensity by more than 1,000 times, as if there was a huge vacuum pump at the entrance ramp onto the magnetic highway,” said Stamatios Krimigis, the low-energy charged particle instrument’s principal investigator at the Johns Hopkins University Applied Physics Laboratory in Maryland, US.
“We have never witnessed such a decrease before, except when Voyager 1 exited the giant magnetosphere of Jupiter some 34 years ago,” Krimigis added.
Other charged particle behaviour observed by Voyager 1 point to how the spacecraft is still in transition phase before it makes the leap into the interstellar medium, NASA said.
Scientists do not know exactly how far Voyager 1 has to go to reach interstellar space. They estimate it could take several more months, or even years, to get there.
JPL built and operates the spacecraft, while California Institute of Technology in Pasadena manages JPL for NASA.
All images courtesy of NASA and JPL
