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IBEX
 
September 30, 2010
From Dave McComas, IBEX Principal Investigator
IBEX PI Dave McComas
Last month, we updated everyone on IBEX’s exciting observations of energetic neutral atoms (ENAs) produced via solar wind collisions with our Earth’s magnetosphere. Right on the heels of that, we have even more amazing news: our second set of heliosphere maps is here and they show some more really surprising changes! The ENA “ribbon” that we saw in the first maps is still clearly visible, but now we have seen variations in the ribbon in the six months between the first and second set of maps. This is remarkable, as we had no idea that changes could occur on such a short timescale. Read on for more details or see our just published paper for all the nitty-gritty. Other fantastic studies by the IBEX Science team are underway, so stay tuned for even more amazing discoveries in the coming months!
Science Update – “Ribbon” Changes Over Time
What has IBEX been studying?

At the boundary of our Solar System, the interactions between solar wind particles and interstellar medium particles create Energetic Neutral Atoms (ENAs) - particles with no charge that move very fast. Some of the ENAs happen to be traveling in just the right direction so that they move inward through the Solar System toward Earth where IBEX can collect them. In this way, IBEX is a special kind of “telescope.” This region emits no light and so information about it cannot be collected by conventional telescopes. Instead, IBEX measures these inward-traveling particles. IBEX provides the only way we currently have of studying the entire edge of our Solar System all at once.

The first all-sky maps of ENAs coming from our Solar System’s boundary showed something expected and something completely surprising. There are ENAs coming from various parts of the sky, in somewhat similar patterns as the scientists thought they would see prior to IBEX’s launch. However, what was unexpected is an arc-shaped region in the sky that is creating a huge amount of ENAs, showing up as a bright, narrow ribbon on the maps. Right now, the science team is trying to figure out what is causing this ribbon and how distant the region is that produces these ENAs.

In addition, we are not only seeing ENAs in an unexpected pattern, we are seeing many more ENAs from the ribbon as compared to the rest of the sky. The pattern of ENAs coming from other parts of the sky is essentially “dominated” by the ENA ribbon. There are so many more ribbon ENAs that the ribbon is the main feature seen in the first set of IBEX maps, even though ENAs from other parts of the sky are in that data, too.

What has IBEX been doing since the first set of maps was released?
While the scientists have been studying data from the first set of Solar System boundary maps, the IBEX spacecraft has been orbiting Earth & collecting data for the second set of maps. The new maps are now available!
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The maps on the left represent the first six months of ENAs that the IBEX spacecraft collected between December 25, 2008 and June 18, 2009. The maps on the right represent the second six months of ENAs that the IBEX spacecraft collected between June 18, 2009 and December 10, 2009.

Credit: SwRI/IBEX Team

Has anything changed between the first & second sets of maps?

The large-scale structure is generally stable between the two sets of maps, meaning the overall sky pattern of ENAs and the ribbon are still there. However, there are some remarkable changes that show that the region producing the ribbon is also evolving over this short six month timescale.

In the time period for the second set of maps, IBEX saw lower numbers of ENAs coming various parts of the sky, including the region that is producing the ribbon. The scientists are not yet sure why, but it may have something to do with the lower amount of solar wind that has been flowing outward for the past several years.

With ENAs coming from a supposed billion-mile thick region and traveling back toward Earth at different speeds, IBEX mission scientists had expected that any highs and lows in intensity arising from within that zone would be hopelessly smeared out in the spacecraft’s all-sky maps. We are elated by the variations and changes seen so far by IBEX. These early results hint that the solar wind and the interstellar medium might be interacting in a thinner layer than many imagined.

Next, at higher energies in the first maps, we saw a bright “knot” of ENAs in the upper left (northern) portion of the ribbon. Below, the map cutout at the top shows the knot region from the first set of maps, and the middle one shows the same region in the second set of maps. Red, orange, and yellow colors indicate regions emitting higher numbers of ENAs; green and blue colors indicate lower numbers of ENAs.

Map

Credit: McComas, et al. (2010), Journal of Geophysical Research

In the second cutout, do you see the much smaller bulge of red and the greater use of yellows and greens in our map? The use of those colors in the map tells us that the knot area emitted fewer ENAs during the time period of the second set of maps. The knot seems to have spread out a bit, as well. The red outline has been added to help you see this area a little more easily.

What does this mean?

Not only did IBEX see the ribbon, but we have seen it evolve over time. This is very exciting, and the scientists are very surprised! The team thought that we might detect small changes in the numbers of ENAs gradually over many years, but not over the course of only 6 months. “These observations show that the interaction of the Sun with the interstellar medium in our neighborhood of the Milky Way galaxy is far more dynamic and variable than anyone envisioned,” says Dave McComas.

In the past, space physicists did not have a clear idea of what to expect along the boundary where the Sun’s own magnetic bubble, the heliosphere, meets the material flowing between the stars, the interstellar medium. Even though the solar wind travels outward at roughly a million miles per hour, it still takes about a year for the solar wind particles to reach our heliosphere’s edge. Also, the zone where solar wind particles and interstellar medium particles interact is believed to be several billion miles thick. Finally, the ENAs that happen to travel toward Earth take another six months to many years to complete the trip, depending on their direction and energy.

With ENAs coming from a supposed billion-mile thick region and traveling back toward Earth at different speeds, IBEX mission scientists had expected that any highs and lows in intensity arising from within that zone would be hopelessly smeared out in the spacecraft’s all-sky maps. We are elated by the variations and changes seen so far by IBEX. These early results hint that the solar wind and the interstellar medium might be interacting in a thinner layer than many imagined.

What’s next?

Getting more data from IBEX will help the scientists start to narrow down their set of hypotheses about what is creating the ribbon ENAs, how distant this region is, and how thick it is.

The scientists have put forth several models, but none of them can fully explain the data that we have collected so far. There may even be a combination of processes occurring, which some of the scientist teams are exploring.

What else will IBEX see? Stay tuned!

Where can I learn more?
These results are outlined in a paper released by the Journal of Geophysical Research. Check it out!
In addition, you can go to the Students section of this website for more explanations of terminology, and go to the Planetaria section for related downloadable educational materials.
Go to the Public Data Page for access to research-level data from the IBEX mission.
NASA Principal Investigator: Dave McComas
E/PO Lead: Lindsay Bartolone
Webmasters: Wendy Mills & Georgina Avalos
Last Updated: 22 NOVEMBER 2010
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