This Solar System is Lopsided

If you ever felt things were a little off-kilter, now we know why:

 The Voyager 2 spacecraft, which has been traveling outward from the Sun for 31 years, has made the first direct observations of the solar wind termination shock, according to a paper published in the July 3 issue of the journal Nature.

At the termination shock the solar wind, which continuously expands outward from the sun at over a million miles per hour, is abruptly slowed to a subsonic speed by the interstellar gas.

Shock waves in the thin, ionized gas — called plasma — that exists in space are similar in some respects to the shock waves produced by an airplane in supersonic flight. Shock waves in space are believed to play an important role in the acceleration of cosmic rays, which are very energetic atomic particles that continually bombard Earth.

The most energetic cosmic rays, which are potentially hazardous to astronauts, are believed to be produced in intense shock waves caused by supernova explosions — immense stellar explosions that occur in massive stars toward the end of their lives.

The termination shock is believed to be responsible for the origin of less energetic cosmic rays called "anomalous cosmic rays." The recent observations at the termination shock are expected to help physicists understand how cosmic rays are produced by the turbulent fields that exist in such shocks.

Gurnett said,"There is no way for us to make direct measure of a super nova shock, so the Voyager 2 measurements at the termination shock provide us the best opportunity in the foreseeable future to understand how cosmic rays are produced by supernova cosmic shocks."

Here’s a summary of the electric field amplitudes in the Voyager-1 1.78 kHz and 3.11 kHz PWS spectrum analyzer channels from 1992 to present: 

 

So what does all that mean?

You can dig into the scientific analysis here. Or, NASA’s Jet Propulsion Laboratory provides a lay explanation, as well as a much better picture:

 

This artist’s rendering depicts NASAs Voyager 2 spacecraft as it studies the outer limits of the heliosphere – a magnetic ‘bubble’ around the solar system that is created by the solar wind. Scientists observed the magnetic bubble is not spherical, but pressed inward in the southern hemisphere, according to recent data published as part of a series of papers in this week’s (July 3, 2008) Nature. These findings help build up a picture of how the sun interacts with the surrounding interstellar medium.

Having crossed the termination shock and the edge of our solar system, Voyager now continues on; in five to seven years, it may have something equally profound to tell us about deep space.

Meanwhile, NASA’s Stereo Mission (which we blogged about here and here) has created its first images of the edge of the solar system, and its findings are equally interesting and helpful in understanding what happens at the point where the solar system meets interstellar gas:

 

 NASA’s sun-focused Solar Terrestrial Relations Observatory, or STEREO, twin spacecraft unexpectedly detected particles from the edge of the solar system last year. …

From June to October 2007, sensors aboard both STEREO spacecraft detected energetic neutral atoms originating from the same spot in the sky, where the sun plunges through the interstellar medium.

Mapping the region by means of neutral, or uncharged, atoms instead of light "heralds a new kind of astronomy using neutral atoms," said Dr. Robert Lin, professor of physics at the University of California, Berkeley and lead for the suprathermal electron sensor aboard the STEREO spacecraft…..

The results, reported in the July 3 issue of the journal Nature, clear up a discrepancy in the amount of energy dumped into space by the decelerating solar wind. The solar wind was detected when Voyager 2 entered the heliosheath.

Researchers determined that the newly discovered population of ions in the heliosheath contains about 70 percent of the dissipated energy from the solar wind, exactly the amount unaccounted for by Voyager 2’s instruments. The Voyager 2 results also are reported in the July 3 issue of Nature.

The Berkeley team concluded that these energetic neutral atoms were originally ions heated up in the termination shock area that lost their charge to cold atoms in the interstellar medium and, no longer hindered by magnetic fields, flowed back toward the sun and into the sensors aboard STEREO.

Would it be a bad holiday pun to call all of this a shocking discovery?

Indeed it would be a bad pun. But now it’s done.

Enjoy the Fourth!