According to NASA, both the existence of our solar system's tail and its general shape have now been confirmed, which... wait – our solar system has a tail?
Yes. Let's bring you up to speed.
One: Our solar system has a tail – a loooong stream of solar particles that astronomers call, awesomely, a "heliotail."
Two: The particles in the heliotail are left behind by a big bubble of sorts called the "heliosphere" – a cosmic orb of solar wind that surrounds our sun and encompasses Earth and all the other planets:
Three: Until a couple days ago, our solar system's hindmost feature was merely an assumption. Astronomers reasoned that a solar system moving through the Universe could be expected to leave bits of itself in a trailing stream, not unlike a meteor leaving bits of itself behind as it blazes through the cosmic firmament. We've seen the heliotails of other stars, but never our own.
Above: The star Omicron Ceti, at far right, hurtles through space. At its leading edge, a curved "bow wave" of solar particles struggle to get out of the way, while a tail of stellar wind material measuring THIRTEEN LIGHT YEARS in length trails behind – Image Credit: NASA/JPL-Caltech/C. Martin (Caltech)/M. seibert (OCIW)
Now we have, with the help of NASA's Interstellar Boundary Explorer, a.k.a. IBEX.
Three years' worth of IBEX imagery were used to observe the tail and map its structure; Universe Today's Nancy Atkinson gives a tidy summary of the process:
IBEX measures the neutral particles created by collisions at the solar system’s boundaries. This technique, called energetic neutral atom imaging, relies on the fact that the paths of neutral particles are not affected by the solar magnetic field. Instead, the particles travel in a straight line from collision to IBEX [which orbits Earth]. Consequently, observing where the neutral particles came from describes what is going on in these distant regions.
“By collecting these energetic neutral atoms, IBEX provides maps of the original charged particles,” said David McComas, lead author on the team’s paper and principal investigator for IBEX at Southwest Research Institute. “The structures in the heliotail are invisible to our eyes, but we can use this trick to remotely image the outermost regions of our heliosphere.”
Here's what IBEX data suggests that outermost region looks like from behind:
The tail, the data suggests, resembles a four-leaf clover. The two side leaves, astronomers believe, are filled with slow-moving particles, while the upper and lower leaves are filled with fast-moving ones. Here's another view:
The farther from the sun these trailing particles get (and the IBEX team says it's still not entirely sure how long the tail actually is), the less like a four-leaf clover they appear, as they are twisted to align not with the magnetic influences of the Sun, but those of the Milky Way.
In a video announcement made on Wednesday (viewable here), the researchers said their findings could be helpful to planetary scientists studying cosmic rays, and complementary to data being beamed back by the Voyager 1 and Voyager 2 probes (the far-flung spacecraft that may or may not have already left the leading edge of the heliosphere).
"These two missions are incredible complementary," said IBEX Principle Investigator Dave McComas. "IBEX is like an MRI — you take an image of the whole body to see what's going on — and the Voyagers are like [highly localized] biopsies."