From Dave McComas, IBEX Principal Investigator
Much has been happening with the IBEX spacecraft since our last update in January. We continue to collect data for our sets of heliosphere maps, and our scientists have been using that data to discuss, debate, and model the various hypotheses that we have for the cause of the "ribbon" feature seen in our first set of maps. IBEX has also made some very important new observations of the space environment much closer to home, which we have highlighted below. IBEX and its instruments continue to work extremely well, and we'll be telling you about the next outer heliospheric sky maps very soon, but just to let you in on the big news - IBEX is observing time evolution in the heliosphere's interstellar interaction! Anyway, we'll be post that new information soon and we continue to look forward to even more fantastic results—GO IBEX!
Science Update—Observing Earth's Magnetosphere
As charged particles from the Sun travel outward, they crash into the Earth's magnetosphere, which is a kind-of magnetic "bubble" that surrounds our planet. Now, an IBEX scientist team has used IBEX observations to understand how the process works.
What is IBEX seeing?
As the solar wind streams outward from the Sun at a million miles per hour (1.6 million kilometers per hour), the solar wind protons and electrons pile up along the outer boundary of Earth's magnetosphere, called the "magnetopause". These charged particles are shocked, heated, and slowed almost to a stop before getting diverted sideways. A few of those charged particles interact with neutral atoms in the very outer reaches of our atmosphere about 35,000 miles (56,000 kilometers) from the surface of the Earth. This extremely low-density region of our atmosphere, called the "exosphere", extends beyond Earth's protective magnetic field. The solar wind charged particles exchange electrons with our exosphere's neutral particles, and the solar wind particles become neutral in the process. Now, they are no longer affected by Earth's magnetic field and fly off in whatever direction they were going when they became neutral. Because some of these particles happen to be traveling in the direction of the IBEX spacecraft and its sensors, IBEX can detect them. Just like our heliosphere boundary, our magnetosphere boundary does not give off light that we can detect, so we must use particle sensors like those of IBEX to study regions like this.
Go to our Graphics page for a diagram of this process.
What is going on here?
The area where the exosphere and solar wind interact most heavily produces the most ENAs. But don't think that this region is a dense wall of material—IBEX data shows that there are only about 8 particles per cubic centimeter at the highest amounts. Thanks to IBEX's exquisitely sensitive particle detectors, though, even this tenuous area of space can be studied.
The new IBEX map shows that the ENAs are created in greater numbers at the magnetosphere boundary in the direction pointing toward the Sun and thin out at locations away from this point. Red and yellow colors in the map above show areas with the most ENAs; green and blue colors show areas with the least ENAs
Earth's magnetic boundary isn't shaped like a sphere. Instead, it has a teardrop shape that is closest to Earth at its nose (pointing toward the Sun) but farther away everywhere else. So at locations well away from the centerline, even fewer of the exosphere's hydrogen atoms are hanging around to interact with the solar wind. Where the exosphere is least dense, the least number of ENAs are created.
Was IBEX designed to make these observations?
Well, yes and no.
IBEX's main goal is and has always been to measure the energetic neutral atoms created at our Solar System's boundary when the solar wind streaming outward rams into the interstellar medium, which is the gas and dust between the stars. Because the IBEX spacecraft is in orbit around the Earth, though, it is unavoidable that Earth is periodically in the view of the extremely sensitive IBEX-Hi and IBEX-Lo particle detectors. The team has taken advantage of the fact that while IBEX spins and its sensors sweep around, it is able to examine Earth's magnetosphere.
IBEX has made the first images of the interaction between the solar wind and the Earth's magnetosphere. "These are fantastic first images of the important region where the solar wind piles up as it deflects around the Earth's magnetic field," says Dave McComas. "It is particularly satisfying that we were able to use a spacecraft built for a different purpose to unwrap a mystery that has long eluded us."
These key observations were made in March and April 2009 when its detectors could scan the region directly in front of the magnetopause. During some of the March observations, the European Space Agency's Cluster 3 spacecraft was positioned just in front of the magnetopause, where it measured the number of deflected solar-wind protons directly. "Cluster played a very important role in this study," said Lockheed Martin's Stephen A. Fuselier, lead investigator for the IBEX-Lo sensor. "It was in the right place at the right time."
Why is this region important to study?
"Without the Earth's magnetosphere, the highly energetic charged solar wind particles could strip away some of Earth's atmosphere," said Dr. Fuselier. "The exchange of electrical charges between the solar wind and the outer reaches of the Earth's atmosphere is one of the causes of atmospheric loss, but the Earth's magnetosphere blocks the solar wind from penetrating close to the planet. IBEX is becoming an important tool for studying this important protective process."
Where can I learn more?
The interaction between the solar wind and the Earth's magnetosphere that creates this charge exchange process is detailed in a paper — "Energetic Neutral Atoms from the Earth's Subsolar Magnetopause" — published recently in Geophysical Research Letters.
Go to the Public Data Page for access to research-level data from the IBEX mission.