space science astrophysics voyager solar_system
Does New Data Suggest Voyager’s Exit from Solar System?

by Michael Keller

NASA released new data current through Oct. 4 that seems to show the environment around the Voyager 1 spacecraft has drastically changed. Is it possible that the craft, now more than 18.3 billion km from Earth and the farthest human-made object, has already left the solar system?

The above graph shows that since September the craft’s instruments have sensed a major, sustained drop in the low-energy charged particles released by the sun that reach it.

During the same period, Voyager’s cosmic ray detector has recorded a steady rise in higher-energy charged particles originating from outside the solar system. This detector can also detect the output of large solar flares.

Here is the 2011 six-hour averages for low-energy particles coming from the sun for comparison:

And the low-energy particles emanating from the sun from January to August 2012:

Here’s the 2011 six-hour averages for higher-energy particles coming from outside the solar system:

And the high-energy particles for January to August 2012:

Astrophysicists are considering three key factors to determine when Voyager 1 has officially left the solar system: the sun’s charged particles that reach the craft, the amount of high-energy cosmic rays that reach it, and the direction of magnetic fields around it.

No word yet from NASA on whether these numbers mean what they seem to mean, nor have the the experts released findings from their magnetic field investigation. They expect magnetic field lines to change direction when Voyager crosses into interstellar space.

Merav Opher, a Boston University astronomer and NASA Heliophysics Guest Investigator, says the Voyager team needs to analyze the magnetic field data before it can come to any conclusions about whether the craft has entered interstellar space.

“The canonical standard model says that the magnetic field inside the solar system is east-west,” Opher says in an interview with Txchnologist. “As you leave the solar system there is no reason for the magnetic field to be like that; you will see a north-south component.”

But two factors confound the process.

First, Opher and Voyager colleague Jim Drake at the University of Maryland have been arguing in recent years that the magnetic field data would become more complicated around the heliopause, the theoretical boundary in space where the solar wind’s strength is balanced out by those of other stars.

“I think the correct statement is we don’t think the transition from inside to outside [the solar system] will be on and off like that,” Opher says.

The second factor is the advanced age of Voyager’s instruments. The magnetometer responsible for picking up magnetic fields on Voyager I is already at its detection threshold and the data is difficult to analyze (in fact, there are only a few people who can do it for the Voyager team).

Opher believes the Voyager team might meet next month to discuss the situation.

But keep your champagne corked for the moment, she cautions: “I think it’s going to take a long time for the team itself to come to a consensus.”

Images: courtesy NASA Goddard Space Flight Center Voyager Cosmic Ray Subsystem.

(via and Houston Chronicle’s SciGuy)

Michael Keller is the Managing Editor of Txchnologist. His science, technology and international reporting work has appeared online and in newspapers, magazines and books, including the graphic novel Charles Darwin’s On the Origin of Species. Reach him at

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