Back in 2003, the team that developed IBEX sat down to consider the questions that the mission would be designed to answer. What did we want to find out using IBEX? Four major questions came out of those discussions. One of those questions had to do with how the material between the stars, called the "interstellar medium," interacted with the outer reaches of the boundary of our Solar System. In January, we announced new science results from the IBEX mission that highlighted detections of neutral atoms of hydrogen, helium, oxygen, and neon drifting in from the interstellar medium, outside our heliosphere. Those observations showed that the neutral atoms were coming from a slightly different direction and a slightly lower speed than had been found previously by the Ulysses spacecraft. Using that new information and combining it with improved inferences of the local interstellar magnetic field strength, we are announcing that one of our major questions has been at least partially answered: the bow shock, a region where the interstellar density was thought to discontinuously jump up as it tries to avoid colliding with our heliosphere, does not, in fact, exist. These results are now available in a new paper published online in the May 10, 2012 issue of Science Express.

It is too early to know all of the implications of this for our heliosphere. Decades of research have explored scenarios that included a bow shock. Those models now have to be redone using the latest IBEX results. Already, we know there are likely implications for how charged particles and galactic cosmic rays propagate around and sometimes enter the Solar System, which is relevant for human space travel, and I am excited to see what future repercussions this research will have. There is a lot to think about in these results, but I am so pleased with the contributions to the study of the structure of our Solar System and its boundary that IBEX has already made! I want to especially thank IBEX team members from the University of New Hampshire, University of Alabama in Huntsville, Moscow State University, Space Research Centre of the Polish Academy of Sciences in Warsaw, and the University of Bonn in Germany for making this paper possible. Go IBEX!

Our Solar System is composed of several parts. Our Sun emits a "wind" of material outward in all directions, at typically about a million miles (1.6 million kilometers) per hour. As the solar wind streams away from the Sun, it races out toward the space between the stars. We think of this space as "empty" but it contains traces of gas, dust, and charged, or "ionized," gas – together called the "interstellar medium." The solar wind blows against this material and clears out a cavity–like region in the ionized gas. This cavity is called our "heliosphere." Our entire heliosphere, which contains our Sun, the planets, and everything else in our Solar System, is moving through the interstellar medium.

The most simple explanation is that the boundary of our Solar System is formed at the location where the solar wind streaming outward meets the interstellar medium. The distance at which this occurs is about 10–15 billion miles, or 16–24 billion kilometers, from the Sun in the direction in which our Solar System is traveling. Scientists thought that if our Solar System was traveling fast enough, the pressure of our heliosphere plowing through the interstellar medium material would cause that material to greatly slow down and pile up in front of our heliosphere, forming a "bow shock," in a similar fashion to how air piles up in front of a supersonic jet forming a sound wave shock or "sonic boom."