Has Voyager 1 left the heliosphere? The question is a reminder that the Voyagers are our first interstellar probes; they'll still be returning data when they move into the interstellar medium. The heliosphere is a kind of bubble created by the solar wind from the Sun, that stream of high-speed charged particles constantly blowing into space at roughly 400 kilometers per second. Observing how Voyager 1 makes the transition across the boundary of the heliosphere will provide our first in situ study of interstellar space. Some scientists believe that at roughly 90 AU from the Sun, Voyager 1 has already pushed up against the 'termination shock,' that region where the speed of the solar wind drops to subsonic levels. Now new data studied by French and Finnish researchers indicate that the shape of the heliosphere may be distorted, further complicating the question of just where the true interstellar medium begins. Rosine Lallement and colleagues used data collected by the Solar and...

Our first interstellar mission won't be a long jump to Alpha Centauri or Barnard's Star. In fact, we've already launched not one but several interstellar missions -- the two Pioneer probes, and the two Voyagers that followed them, will all exit the Solar System; i.e., they will eventually cross the boundaries of the heliosphere to emerge into pure interstellar space. Some scientists believe that Voyager 1 is already pushing up against the so-called 'termination shock,' where the speed of the solar wind of gas and charged particles from the Sun drops to subsonic levels. But we need far more information than the Voyagers, with their rapidly fading signals, can tell us. The next mission designed to explore the outer limits of the Sun's influence will be the Interstellar Boundary Explorer (IBEX). Under development at Southwest Research Institute, IBEX is designed to explore how the solar wind interacts with the interstellar medium through which our entire Solar System moves. IBEX won't...

An asteroid called 2004 TP1 came within 13 LD of Earth on November 2 -- LD stands for 'lunar distance,' and is the average distance between the Earth and the Moon (238,855 miles, or 384,401 kilometers). Asteroid 2004 RZ164 will come even closer, at 7 LD on December 8. Both objects are considered Potentially Hazardous Asteroids (PHAs, as acronym-obsessed scientists like to call them). That means they are larger than 100 meters in diameter and come too close to Earth for comfort. 653 Potentially Hazardous Asteroids are now known. We've discussed such objects as perhaps the most significant reason for building up a space-based infrastructure that could ward off a potential strike. A good place to track them is the NASA-sponsored site Spaceweather.com, which bills itself as 'News and Information about the Sun-Earth Environment.' The site likewise tracks solar wind conditions (currently moving at 493.7 kilometers per second, based on data transmitted from the Advanced Composition Explorer...

When it comes to interstellar work, don't forget the Kuiper Belt. Although amateur astronomer Kenneth Edgeworth was the first to predict its existence, the Belt was named for Gerard Kuiper, who analyzed it in 1951. It is a region of thousands (and perhaps millions) of small, icy moons and cometary debris that exists from the orbit of Neptune well into deep space. Our first interstellar missions will be explorations of this area and the vast Oort cloud of comets that may extend as much as a light year out from the Sun. And yes, in a true sense, the Voyager probes could be considered interstellar missions, still reporting data as they move on toward the heliopause. But we may learn a good deal about Kuiper Belt objects by studying the findings of a spacecraft considerably closer, the Cassini Saturn orbiter. Cassini's Ultraviolet Imaging Spectrometer tells us that Phoebe, a tiny world about one-fifteenth the diameter of Earth's moon, is probably itself a Kuiper Belt object that was...

NASA has just announced that it has selected Northrop Grumman Space Technology as the contractor for co-designing its proposed Jupiter Icy Moons Orbiter. JIMO will be designed to orbit and explore three of the most interesting Jovian moons: Callisto, Ganymede and Europa. All three may possess water, organic material and a source of energy, leading to the possibility of some form of life evolving there. Image: The surface of Europa as seen by the Galileo orbiter. Note the crustal blocks on the left that seem to have once broken apart, and then 'rafted' into their current positions. They're evidence of what may be a sub-surface ocean. Credit: Planetary Image Research Laboratory, University of Arizona. Studying these moons closely will involve long periods in orbit around each before moving on to the next target. The propulsion system envisioned here is nuclear electric. NASA's Deep Space 1 spacecraft has already demonstrated the principle, in which electrically charged particles are...

Worth noting in relation to the JIMO story above (and for the broader issue of generating power for deep space probes): "A Power Conversion Concept for the Jupiter Icy Moons Orbiter," by Lee S. Mason (Journal of Propulsion and Power Vol. 20 No. 5, 1 September 2004, pp. 902-910). From the abstract: "An analytical study was performed to compare design options for a reactor power system that could be utilized on a Jupiter Icy Moons Orbiter mission employing nuclear electric propulsion."