Early last week I wrote an article about how new data from Voyager 1 shed light on the structure of the Sun’s heliosphere and solar wind. Just a few days after that, researchers announced evidence of Earth’s own space wind!

Scientists proposed the existence of a space wind surrounding Earth about 20 years ago, but direct detection has eluded scientists until now.

Earth is surrounded by a magnetic field that encloses our magnetosphere. The plasmasphere is the inner part of that magnetosphere, and it looks a giant donut made of electrically-charged particles called (as its name suggests) plasma.

The Sun’s magnetic activity can accelerate plasma toward Earth, which impacts our magnetosphere. During such solar storms, we have observed plumes of material transfer between the plasmasphere and the outer magnetosphere, but researchers also proposed the existence of a steady flow of plasma that occurs around the clock. After years of theoretical work, Iannis Dandouras of the Research Institute in Astrophysics and Planetology in Toulouse, France, has directly detected this wind in data from the European Space Agency’s Cluster spacecraft.

Dandouras measured the properties of charged particles in the plasmasphere to find that the forces governing plasma motion exist slightly out of balance, forming a steady wind.

“After long scrutiny of the data, there it was, a slow but steady wind, releasing about one kilogram of plasma every second into the outer magnetosphere. This corresponds to almost 90 tons every day. It was definitely one of the nicest surprises I’ve ever had!” said Dandouras.

Don’t worry, the plasmasphere won’t evaporate away: it also refills. Dandouras reassured everyone that “due to the plasmaspheric wind, supplying plasma—from the upper atmosphere below it—to refill the plasmasphere is like pouring matter into a leaky container.”

Michael Pinnock, Editor-in-Chief of Annales Geophysicae, recognizes the importance of the new result. “It is a very nice proof of the existence of the plasmaspheric wind. It’s a significant step forward in validating the theory. Models of the plasmasphere, whether for research purposes or space weather applications (e.g. GPS signal propagation) should now take this phenomenon into account.”

We can even apply our understanding of Earth’s plasmaspheric wind to other places. Why wouldn’t another planet such as Jupiter or Saturn experience the exact same phenomenon? The Solar System could be a very windy place!

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA

How large is the heliosphere? The region of interstellar space dominated by the Sun? The Voyager 1 spacecraft has a partial answer: much larger than expected!

The heliosphere, composed of the sun’s magnetic field and a high-velocity stream of charged particles called the solar wind, creates an enormous bubble around our solar system. The charged particles move at about a million miles per hour, only slowing down when they near the region where the pressure of interstellar gas dominates. We thought Voyager 1, our farthest spacecraft, had arrived at edge of the heliosphere, but there is something fishy about Voyager 1’s new data.

Launched in 1977, the twin spacecraft Voyager 1 and Voyager2 have both entered an area called the heliosheath, where the solar wind slows, even though they’re headed in different directions away from the Sun. Voyager 1 lies farthest away, 11 billion miles from Earth, and at this distance it encountered a “magnetic highway.” Here the Sun’s magnetic field connects with the interstellar magnetic field, allowing for an exchange of charged particles between inside and outside the heliosphere.

Voyager 1 measured the highest rate of change so far between incoming and outgoing particles. “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 Laurel, Maryland. In this same region, scientists first detected the low-energy cosmic rays that originate from dying stars.

This should indicate that the spacecraft has reached interstellar space, except scientists have not yet seen the final indicator: an abrupt change in the direction of the magnetic field.

“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,” said Edward Stone, Voyager project scientist at the California Institute of Technology in Pasadena.

So how much farther does Voyager 1 need to travel until it reaches interstellar space? Scientists estimate several months or even years until Voyager 1 experiences a change in magnetic field direction. For now, they have named this strange zone the heliosheath depletion region. Catchy, eh?

Stay tuned for more Voyager discoveries from the edge of interstellar space!

Alyssa Keimach is an astronomy and astrophysics student at the University of Michigan and interns for the Morrison Planetarium.

Image: NASA/JPL-Caltech