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."