Ribbon Changes Over Time

The Sun traveling through the Galaxy happens to cross at the present time a blob of gas about ten light-years across, with a temperature of 6-7 thousand degrees kelvin. This so-called Local Interstellar Cloud is immersed in a much larger expanse of a million-degree hot gas, named the Local Bubble. The energetic neutral atoms (ENA) are generated by charge exchange at the interface between the two gaseous media. (Source: SRC/Tentaris,ACh/Maciej Frolow) [A model of the Galaxy] suggests that the boundary between the Local Cloud and the Local Bubble might be not within a few light years from the Sun, as it was believed earlier, but within just a thousand of astronomical units, a thousand-fold closer. This might mean that the Solar System could enter the million-degree Local Bubble cloud as early as the next century. Such clouds are of very low density, much lower than the best vacuum obtained in the Earth labs. Once in, the heliosphere will reform and may shrink a little, the level of cosmic radiation entering the magnetosphere may rise. -- Physics.org: The IBEX Ribbon: Are we in for a new era in the Sun's voyage through the Galaxy? ~ ~ ~ "Ribbon" Changes Over Time By Dave McComas, IBEX Principal Investigator, NASA 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! 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 "> The maps above (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 ">"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. "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. Where can I learn more?Go to the Public Data Page for access to research-level data from the IBEX mission. Students can go to this section of NASA's website for more explanations of terminology, and go to the Planetaria section for related downloadable educational materials. Highlights from the paper released by the Journal of Geophysical Research: The evolving outer heliosphere: Large-scale stability and time variations observed by the Interstellar Boundary Explorer: o In this study we compare the second set of sky maps to the first in order to assess the possibility of temporal changes over the six months between views of each portion of the sky.o An interesting feature revealed in the combined maps is the clear extension of the ribbon toward a complete ring compared to what can be seen in the individual sets of sky maps.o While the large-scale structure is generally stable between the two sets of maps, there are some remarkable changes that show that the heliosphere is also evolving over this short timescale.o The overall reduction in the knot emissions are substantial, with roughly one fourth to one third less emission observed over six months.o The overall reduction in flux at both poles is clear and represents a decrease of ~10-15% over six months across the entire energy range from ~0.5-6 keV.o We conclude that departures of differences between the two sky maps of more than ~10% are most likely due to real changes in the outer heliosphere and not modulation of ENAs propagating back through the solar wind.~ ~ ~ The red 3D surface outside the heliopause is where the LISM field is most stressed by draping about the heliopause. Source: Comparison of Interstellar Boundary Explorer Observations with 3D Global Heliospheric Models. Schwadron, et al., Science 326, 959 (2009); published online 15 October 2009 (10.1126/science.1180906). Related: Time Off For Research "Local Fluff" Could Cause TEOTWAWKI Future May Rely on a Ribbon