October 19, 2012 marks exactly four years since the launch of the IBEX spacecraft. On that same date in 2008, the many in the team and I watched from Dulles, Virginia as IBEX was carried into space by a Pegasus rocket launched from Kwajalein, an atoll in the middle of the Pacific Ocean. It was a tense day, but in the end, everything worked out just fine and IBEX was safely in its initial orbit around Earth. In the last weeks of December, we were elated when IBEX began detecting energetic neutral atoms (ENAs) coming from the boundary of our Solar System. Little did we know that day the amazing discoveries that were in store for us. In October 2009, IBEX’s first science results were released, highlighting the surprising and completely unexpected "IBEX Ribbon," an arc–shaped region in the sky that is producing many more ENAs than was expected. During the past three years, we also have detected neutral atoms from outside our heliosphere as they make their way to Earth’s region of our Solar System, and we have discovered ENAs coming from the surface of our Moon and from regions just outside and inside Earth’s magnetosphere. Most recently, we announced that there is no bow shock for our heliosphere, a complete paradigm shift from what was thought before. To date, scientists have already published 100 papers related to this small but remarkable mission — what an incredible scientific harvest!

And the science hits just keep on coming for IBEX… This month, a major update has been published in the Astrophysical Journal Supplement Series assembling, correcting, and validating the first three years of IBEX data, including new boundary region maps, identification of a strong candidate for the source of the IBEX Ribbon, and the first complete set of ENA sky maps using data from the IBEX–Lo sensor. All of these data have been posted on the IBEX website and provided to NASA’s data repository, so the entire science community can and should be using these new data for future studies. This is such an amazing time for the study of our Solar System’s last frontier, and we are beginning to unravel its mysteries. Please read on for more of the revolution in the understanding of our heliosphere. Go IBEX!

IBEX studies energetic neutral atoms. The boundary of our Solar System emits no light, so information about it cannot be collected by conventional telescopes. Charged particles, such as protons and electrons, stream off of our Sun at high speed; this wind of particles is called the "solar wind." The solar wind heads outward, far past the planets. Billions of miles from the Sun, the solar wind particles interact with material between the stars, called the "interstellar medium." This interaction process creates energetic neutral atoms (ENAs), which are particles with no charge that move very fast. Because these particles have no charge, they are not affected by magnetic fields and travel in a straight line in the direction they were moving when they became neutral. Some of the ENAs happen to be moving inward and travel back through the Solar System toward Earth where IBEX can detect them. IBEX provides the only way we currently have of studying the entire boundary of our Solar System all at once.

IBEX contains two ENA sensors, IBEX–Hi and IBEX–Lo. Each sensor detects different ENA energies, and the energy levels of the two sensors overlap so they can be checked against one another, which is important to make sure that the data are valid.

The IBEX Ribbon
The first all–sky maps of ENAs coming from our Solar System’s boundary showed something expected and something else completely surprising. There are ENAs coming from various parts of the sky, in somewhat similar patterns as the scientists thought they would see. 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, which has subsequently been called the IBEX Ribbon.