During its first five years, IBEX has made some astounding discoveries
Image Credit: NASA's Goddard Space Flight Center
IBEX
discovered a giant ribbon at the edge of the solar system, an anomaly
that has now been determined to be a reflection where solar wind
particles heading out into interstellar space are reflected back into
the solar system by a galactic magnetic field. Image Credit: NASA/IBEX. View larger
IBEX
found that Energetic Neutral Atoms, or ENAs, are coming from a region
just outside Earth's magnetopause where nearly stationary protons from
the solar wind interact with the tenuous cloud of hydrogen atoms in
Earth's exosphere.Image Credit: NASA's Goddard Space Flight Center. View larger
A
recent mapping of the heliotail shows it has two lobes of slower
particles on the sides, faster particles above and below, with the
entire structure twisted, as it experiences the pushing and pulling of
magnetic fields outside the solar system.Image Credit: NASA's Goddard Space Flight Center. View larger
IBEX has found that there's more oxygen in our solar system than there is in the nearby interstellar material. Image Credit: NASA's Goddard Space Flight Center. View larger
Launched on Oct. 19, 2008, the Interstellar Boundary Explorer, or
IBEX, spacecraft, is unique to NASA's heliophysics fleet: it images the
outer boundary of the heliosphere, a boundary at the furthest edges of
the solar system, far past the planets, some 8 million miles away.
There, the constant stream of solar particles flowing off the sun, the
solar wind, pushes up against the interstellar material flowing in from
the local galactic neighborhood.
IBEX is also different because it creates images from particles
instead of light. IBEX, scientists create maps from the observed neutral
atoms. Some are of non-solar origin, others were created by collisions
of solar wind particles with other neutral atoms far from the sun.
Observing where these energetic neutral atoms, or ENAs, come from
describes what's going on in these distant regions. Over the course of
six months and many orbits around Earth, IBEX can paint a picture of the
entire sky in ENAs.
During its first five years, IBEX has made some astounding discoveries.
Mapping the Boundaries
In its first year, IBEX scientists created the first-ever all-sky map
of the heliosphere's boundary, where the influence of the solar wind
diminishes and interacts with the interstellar medium. The most
startling finding is that the map was not uniform or symmetrical, but
shows a bright ribbon of energetic neutral atoms snaking through it.
During its second and third years, IBEX showed that the heliosphere's
boundaries changed more rapidly than expected, with variations as short
as six months. Additional sets of all-sky maps showed the evolution of
the interstellar boundary region: the mysterious ribbon feature at the
nose, of the heliosphere – in the front as it moves through space –
evolved. Also, a knot-like feature spread and diminished. This
variation over time is challenging scientists to try to understand how
the heliosphere can change so rapidly.
ENAs Near Earth
Because IBEX is orbiting Earth, it also can look back toward Earth's
neutral-atom environment and so has provided the first ENA images of the
magnetosphere from the outside.
Nearby, IBEX has scanned the moon, as well. The moon has no
atmosphere or magnetosphere, so the solar wind slams unimpeded into its
surface. IBEX observations showed that the moon creates a backscattered,
neutral solar wind: about 10 percent of the impinging solar-wind
protons bounce off the lunar surface, becoming ENAs as they do.
The Heliosphere: Looking Ahead and Looking Behind
Measurements by IBEX announced in 2012 show the influence of the
heliosphere on the local interstellar medium is different than expected.
Previous models showed a boundary ahead of the heliosphere, outside the
influence of the sun: a shock formed by the entire heliosphere pushing
through the interstellar material around it. IBEX data suggests that
there is no bow shock preceding the heliosphere's movement through
space.
IBEX also offered up the first observations of the heliotail. If our
eyes could see particles and we looked straight down the tail we would
see an unexpected shape a little like a four-leaf clover. The two side
leaves are filled with slow moving particles and the upper and lower
leaves with fast ones.
Into the Galaxy
Much further away, IBEX also provided information about the local
galactic environment. It made the first direct measurements of neutral
hydrogen, oxygen, and neon coming into the heliosphere from the
interstellar medium. The measurements show that the composition of the
current galactic neighborhood is different than that of the sun and the
solar system. This puzzle may mean that the sun has moved out of the
region where it formed, or that some of the oxygen has been captured by
dust in interstellar space.
IBEX also found that the speed of the galactic wind registered around
52 thousand miles per hour. By comparing this wind to previous results
from other missions over the last 40 years, scientists believe that the
direction of the wind has changed by about 7 degrees in the last four
decades. While the cause of this shift is unknown, it may be telling us
something about changing conditions as we move through our region of the
Milky Way.
IBEX is a NASA Heliophysics Small Explorer mission. The Southwest
Research Institute in San Antonio, Texas, leads IBEX with teams of
national and international partners. NASA's Goddard Space Flight Center
in Greenbelt, Md., manages the Explorers Program for the agency's
Science Mission Directorate in Washington.
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