A unique and unexpected structure has been recently revealed by NASA's Interstellar Boundary Explorer (IBEX) spacecraft.
Researchers have long theorized that, like a comet, a "tail" trails the heliosphere, the giant bubble, in which
our solar system resides, as the heliosphere moves through interstellar space.
The first IBEX images released in 2009 showed an unexpected ribbon of surprisingly high energetic neutral atom (ENA)
emissions circling the upwind side of the solar system. With the collection of additional ENAs over the first year
of observations, a structure dominated by lower energy ENAs emerged, which was preliminarily identified as the heliotail.
Click on image to enlarge
Other stars show tails that trail behind them like a comet’s tail. Scientists used NASA’s Interstellar Boundary Explorer to confirm that our solar system has one too. From top left and going counter clockwise, the stars shown are: LLOrionis; BZ Cam; and Mira.
Image Credit: NASA/HST/R.Casalegno/GALEX
However, it was quite small and appeared to be offset from the downwind direction, possibly because of interactions
from the galaxy's external magnetic field.
As the next two years of IBEX data filled in the observational hole in the downwind direction, researchers found a
second tail region to the side of the previously identified one.
The IBEX team reoriented the IBEX maps and two similar, low-energy ENA structures became clearly visible straddling
the downwind direction of the heliosphere, indicating structures that better resemble "lobes" than a single unified tail.
"We chose the term 'lobes' very carefully," says Dr. Dave McComas, IBEX principal investigator and assistant vice
president of the Space Science and Engineering Division at Southwest Research Institute.
"It may well be that these are separate structures bent back toward the downwind direction. However, we can't say
that for certain with the data we have today."
This data from NASA’s Interstellar Boundary Explorer shows what it observed looking down the solar system’s tail. The yellow and red colors represent areas of slow-moving particles, and the blue represents the fast-moving particles.
Image Credit: NASA/IBEX
The team adopted the nautical terms port and starboard to distinguish the lobes, as the heliosphere is the "vessel"
that transports our solar system throughout the galaxy.
IBEX data show the heliotail is the region where the Sun's million mile per hour solar wind flows down and
ultimately escapes the heliosphere, slowly evaporating because of charge exchange.
NASA/IBEX Provides First View of the Solar System's Tail
The slow solar wind heads down the tail in the port and starboard lobes at low- and mid-latitudes and, at
least around the Sun's minimum in solar activity, fast solar wind flows down it at high northern and southern latitudes.
Solar Neutral Particles
This animation shows a neutral solar particle's path leaving the sun, following the magnetic field lines out to the
heliosheath. The solar particle hits a hydrogen atom, stealing its electron, and we follow it until we see it hit
one of IBEX's detectors. Credits: NASA/Goddard Space Flight Center
"We're seeing a heliotail that's much flatter and broader than expected, with a slight tilt," says McComas.
"Imagine sitting on a beach ball. The ball gets flattened by the external forces and its cross section is oval
instead of circular. That's the effect the external magnetic field appears to be having on the heliotail."
The IBEX spacecraft uses two novel ENA cameras to image and map the heliosphere's global interaction, providing
the first global views and new knowledge about our solar system's interaction with interstellar space.
"We often think we know what we're going to study in science, but the work sometimes takes us in unexpected
directions," says McComas. "That was certainly the case with this study, which started by simply trying to
better quantify the small structure incorrectly identified as an 'offset heliotail.'
The heliotail we found was much bigger and very different from what we expected."
The paper is published today in the Astrophysical Journal.
For more information about IBEX science and mission, visit: