Astronautics Professor Mike Gruntman has been focused on the science objectives of NASA’s Interstellar Boundary Explorer spacecraft program since long before IBEX’s launch in October, 2008 — in fact, he and a small number of other scientists proposed its key experimental approach and instrumentation more than 25 years ago.
Now, a year after its launch, IBEX has sent back a flood of information about the edge of solar system, where the sun's solar wind collides with the surrounding interstellar medium, at a distance of 10-14 billion miles. IBEX obtained the first ever deep space sky map of this region by imaging fluxes of the energetic neutral atoms (ENAs).
Gruntman first began speculating on what might be found out at the edge of the sun's realm in 1979, when he was in his 20s. Very few people then thought that actual measurements would ever be possible – it was believed that because heliospheric ENA fluxes would be too weak to detect, and the space environment is particularly hostile to such measurements.
In 1982, he published a paper on the concept of a sensor remotely sampling energetic neutral atoms that might be carried on a spacecraft. It took more than twenty years to develop the fundamentals of the new experimental and instrumental techniques enabling detection of ENAs in space.
He was among a small core group of scientists who proposed this mission in the late 1990s. NASA selected the mission in 2005 in a competition as part of the Small Explorer program.
IBEX spacecraft and image. Credit: Adler/SwRI
NASA recently summarized the most recent IBEX results, achieved thanks to the work of Gruntman and others:
"The sky map was produced with data that two detectors on the spacecraft collected during six months of observations. The detectors measured and counted particles scientists refer to as energetic neutral atoms.
"The energetic neutral atoms are created in an area of our solar system known as the interstellar boundary region. This region is where charged particles from the sun, called the solar wind, flow outward far beyond the orbits of the planets and collide with material between stars. The energetic neutral atoms travel inward toward the sun from interstellar space at velocities ranging from 100,000 mph to more than 2.4 million mph. This interstellar boundary emits no light that can be collected by conventional telescopes.
"The new map reveals the region that separates the nearest reaches of our galaxy, called the local interstellar medium, from our heliosphere -- a protective bubble that shields and protects our solar system from most of the dangerous cosmic radiation traveling through space.
"NASA released the sky map image Oct. 15 in conjunction with publication of the findings in the journal Science. The IBEX data were complemented and extended by information collected using an imaging instrument sensor on NASA's Cassini spacecraft. Cassini has been observing Saturn, its moons and rings since the spacecraft entered the planet's orbit in 2004.”
Theissue of Science includes three papers on which Gruntman is a co-author. In additon to the Viterbi School and Southwest Research, institutions collaborating on IBEX include Los Alamos, Applied Physics Laboratory, Lockheed Martin, the University of New Hampshire, Bern University and many others.