We need to learn everything we can about the solar wind. A stream of charged particles moving at 500 kilometers per second and more, it may one day provide the push for fast missions to the outer Solar System and beyond. Magnetic sail concepts like Robert Winglee’s Mini-Magnetospheric Plasma Propulsion (M2P2) would operate by injecting plasma into a magnetic field to create the sail, which is actually a huge magnetic bubble. And because such a sail is not a physical structure, sail diameters of hundreds of kilometers are possible.

Riding the solar wind, a sail like this would sharply reduce travel time to Jupiter and beyond, and it’s possible to imagine future versions pushed not by the solar wind but particle beams — now we’re talking interstellar. Take the concept a step farther and you’ve produced, as physicists Dana Andrews and Robert Zubrin first deduced, an ideal method of braking upon arrival into a destination solar system. After the long cruise, an interstellar spacecraft inflates a new magnetic bubble and uses the star’s solar wind to slow down.

We’re a long way from such advanced concepts, but the sooner we get down to testing magsail concepts in space, the better. And as to the solar wind itself, new information has come in from the University of Leicester, where scientists have uncovered a strong correlation between it and the way auroras form around the poles of Jupiter. The work focuses on measurements taken by the Hubble Space Telescope and compares them to simultaneous readings from Cassini as the spacecraft flew past Jupiter in December of 2000 and early 2001.

Image: This composite image gives an indication as to the location of Jupiter’s auroras. Only the northern auroras are shown but, like at Earth, the auroras occur at both northern and southern poles. Credit: John Clarke, Denis Grodent, ESA and NASA.

As presented at the Royal Astronomical Society’s April 4 meeting, the argument is this: the solar wind imparts substantial amounts of energy to Jupiter, causing processes of aurora formation on some parts of the planet that are surprisingly like those on Earth. Previously, it had been assumed that Jupiter’s auroras were entirely the result of the planet’s rapid spin and a constantly replenished stream of plasma coming from the Jovian moon Io.

But read carefully, and note the emphasis on the polar auroras in this comment from Jonathan Nichols, who presented these results at the meeting:

“The argument is certainly not cut and dried. Previous work by our group has shown that Jupiter’s main auroral oval is not caused by the same type of processes that cause the Northern Lights on Earth. However, this new study shows that the auroras located polewards of the main ovals are directly linked to the strength with which the solar wind is blowing, which means that Earth-like processes are causing these polar auroras. Surprisingly, we’ve also found that the main oval also shows a direct correlation to solar wind strength, which is completely the opposite result to the one we were expecting from our predictions.”

Comparable work by Sarah Badman (also performed at Leicester), contrasting Hubble and Cassini data during the latter’s approach to Saturn, corroborates the idea that the release of solar wind energy that has built up in the planet’s magnetic field is the cause of its auroras. This picture is similar to that of Earth, where charged particles from the solar wind interact with air molecules inside Earth’s magnetosphere, releasing spectacular light shows like the Northern Lights, whose intensity and duration are dependent on changing solar wind conditions.