From Dave McComas, IBEX Principal Investigator
Today is the day we have all been waiting for—when the IBEX first heliospheric results and sky maps are unveiled to the scientific community and public audience for the first time! The first results are summarized in five papers published online today by Science Magazine. They chronicle the remarkable discovery of a bright, narrow band of ENA emissions that was totally unpredicted by any previous theories or models and that snakes between the two Voyager spacecraft, but remained totally undetected by either of them. The ribbon appears to be ordered by the external magnetic field in the interstellar medium, which imprints our heliosphere in a very strong, but not yet understood way. In addition, the IBEX team has just published the first ever direct detection of interstellar neutral hydrogen and oxygen, drifting into the heliosphere from the interstellar medium. Together, these truly remarkable observations show just how little we currently understand about the outer reaches of our heliosphere and our place in the galaxy and just how much our Small Explorer mission—IBEX—has to teach us.
Thanks to everyone for your interest in our mission over the years and special thanks to all of the outstanding men and women who have worked so hard to make IBEX such a great success!
What is IBEX 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 can not 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.
How does IBEX collect these particles?
Using two sensors, called IBEX-Hi and IBEX-Lo, the spacecraft measures and counts the ENAs. The scientists can create maps of the boundary using this information. For each small area of the sky, IBEX has measured the number of ENAs coming from that direction.
What do the maps show?
Each of the five maps linked above shows a range of ENA energies, using data collected over the course of six months. In each map, red indicates the highest number of ENAs measured by the spacecraft. Yellow and green indicate lower numbers of ENAs, and blue and purple show the lowest number of ENAs.
Are the ENAs spread evenly across the sky?
No! This is an amazing discovery! There is an arc-shaped region in the sky that is creating a large amount of ENAs, showing up as a bright, narrow ribbon on the maps. Before the IBEX spacecraft was launched, scientists used models to predict the ENA pattern across the sky. These models predicted variations of only tens of percents across the sky—in contrast, IBEX observes variations that are literally hundreds of percents over small angles in the sky. In other words, we are not only seeing ENAs in an unexpected pattern, we are seeing many more ENAs from small regions than we thought we would.
Although the scientists knew the real data would not look exactly as their models predicted, this ribbon feature was a huge surprise to the scientists and was not predicted by any existing models.
More time is needed to fully understand the data. The ribbon appears to be produced by the alignment of magnetic fields outside our heliosphere. These observations suggest that the interstellar environment has far more influence on structuring the heliosphere than anyone previously believed.
Amazingly, an even closer look at segments of the ribbon shows fine details, which suggests that the numbers of ENAs may be significantly enhanced in highly localized regions at the interstellar boundary.
In addition, IBEX has made the first direct observations of other neutral atoms—hydrogen and oxygen atoms drifting in from the interstellar medium, outside the heliosphere.
Why are these maps exciting?
The maps created from IBEX's data provide a new way to look at our home in the galaxy—using particles instead of light. The IBEX results are truly remarkable! What we are seeing in these maps does not match with any of the previous theoretical models of this region. It will be exciting for scientists to review these maps and revise the way we understand our heliosphere and how it interacts with the galaxy. Different conditions can create ENAs, so the scientists' job now is to make new models based on these maps. They will provide a much better picture of how we are affected by our region of the Milky Way galaxy.
How does IBEX's data add to what we previously knew?
Previously, our only direct look at the boundary was in two specific locations through data collected by the Voyager 1 and Voyager 2 spacecraft as they encountered this region of space. The IBEX all-sky maps put the Voyager spacecraft observations in context. Whereas data from the Voyager craft give two pinpoint, “weather station” views of the interstellar boundary region, IBEX provides an all-encompassing “weather satellite” view. The IBEX results show that a lot of the action is happening away from the two Voyagers. We would not have discovered this without IBEX!
Ultimately, why is this information important?
The heliosphere is our home in the galaxy, and understanding how it protects us as we orbit the center of the Milky Way is important as we plan future space travel beyond Earth and think about the conditions surrounding our solar system in the distant past and future.
The heliosphere is like a protective cocoon being inflated in the interstellar medium by the Sun's million mph solar wind. As our Sun orbits the center of the galaxy every 225 million years, it bobs in and out of the disk of the galaxy like a horse on a merry-go-round. As it does this, it passes through areas of the interstellar medium that are more and less dense, causing the heliosphere to change in shape and size. Denser areas can compress the heliosphere, while less dense regions allow the bubble to expand. In addition, the strength of the solar wind varies over the Sun's cycle, “breathing” periodically, also contributing to this.
Understanding how all of these things affect the heliosphere is important so that we can better understand how the heliosphere protects us. It is a crucial layer of protection against dangerous cosmic rays that are harmful to living things. As cosmic rays approach the heliosphere, they are deflected, and the majority of them are not able to pass into the inner solar system. Fortunately, our Earth's magnetic field is usually able to shield life on Earth from the remaining cosmic rays. However, astronauts on deep space missions cannot bring the Earth's protection with them. A recent surge in cosmic ray intensities has been observed by other NASA missions, making it even more important to better understand the heliosphere's ability to shield us from cosmic rays. We must also consider how the heliosphere will protect us in the distant future or how it did protect us in the past. Understanding the heliosphere and how it protects us is part of understanding our home in the galaxy.
What comes next?
IBEX continues to collect data, and a new set of maps will be produced every 6 months. As the Sun and solar wind change over the solar cycle, these changes may be reflected in the quantity of particles detected and the direction from which they are detected. Stay tuned—much more is in store for IBEX!
Go to the Public Data Page for access to research-level data from the IBEX mission.
Go to the journal Science for access to the newly published papers.