With excitement building over what everyone hopes will be a January launch of the New Horizons mission to Pluto and Charon, astronomers have found yet another tool for studying the distant worlds. They're taking advantage of a rare alignment in which Charon, Pluto's moon, passes in front of a star. Such an event has been observed only once, some 25 years ago, and with less capable instrumentation. We'll know a lot more about the results of the July 10-11 occultation in September, when they're presented at the 2005 meeting of the American Astronomical Society's Division of Planetary Sciences meeting, to be held in Cambridge, England. There, scientists from MIT and Williams College will report on observations taken with four telescopes located at various sites in Chile. Remarkably, the team was able to muster more than 100 square meters of telescope surface facing Charon, a number that represents a '...noticeable fraction of the world's total telescope area,' according to an MIT news...

Designing a mission to interstellar space is a long-term process. Indeed, NASA's early work on the concept dates back to studies like the Interstellar Precursor Mission developed at the Jet Propulsion Laboratory in 1977, and the later Thousand Astronomical Unit mission, both designed to penetrate as far as 1000 AU into nearby interstellar space. These two missions were envisioned as operating with nuclear-electric propulsion, though solar sails were also under consideration. An early driver for this work was the conference "Missions Beyond the Solar System," held at JPL in 1976. We have yet to develop a fixed interstellar precursor probe design, but the concept continues to evolve. NASA's last interstellar probe review (1999) was based on solar sail technology, but solar thermal, nuclear thermal and nuclear electric propulsion have remained on the table. Now another interesting propulsion alternative has surfaced, using low-thrust but continuous propulsion delivered by a...

The New Horizons mission to Pluto and Charon is on schedule. The spacecraft is now completely assembled and has undergone a comprehensive performance test of its own systems and its seven instruments, according to principal investigator Alan Stern. The first of the major flight mission simulations began at the end of April; this will be followed by another run of performance tests, with environmental testing beginning in mid-May. Eying the January 2006 launch window, NASA plans a readiness review at the end of May. Image: Pluto and Charon are primary targets for this first targeted Kuiper Belt mission. Credit: Johns Hopkins University Applied Physics Laboratory. Stern's contributions to the New Horizons site at Johns Hopkins University's Applied Physics Laboratory are a great way to keep up with the mission's progress. In the latest, Stern recalls how New Horizons got its name: ...as I waited for a streetlight to change near the intersection of Foothills and Arapahoe and looked west...

The so-called 'Pioneer Effect' continues to trigger study. Both Pioneer 10 and 11, as discussed in these pages back in November, have shown changes in their expected trajectories since they moved 20 AU beyond the Sun. In fact, since 1980 radio signals from the Pioneers have been slowly shifting to shorter wavelengths, which seems to imply a slight but interesting deceleration. This has led to at least one proposal for a mission to investigate the Pioneer effect. Both Galileo and Ulysses data have been examined for evidence of a similar effect; while Galileo's data were too limited for use, Ulysses did show a provocative, though extremely slight, change to its own acceleration (though at a much smaller distance from the Sun). Now a new paper notes the difficulties in measuring the Pioneer anomaly, and discusses a way of using asteroids and comets to measure gravitational effects in the outer Solar System. The paper is by computer scientists Gary Page and John Wallin (George Mason...

With the Jupiter Icy Moons Orbiter (JIMO) on hold, NASA is talking to the European Space Agency about a possible joint mission to Europa. A BBC story reports that a prime driver for ESA is the need to use radioisotope thermal generators (RTGs) on the mission, a power source with which the Europeans have little experience. RTGs are needed on missions to the outer planets because they increase the power available to the spacecraft, allowing for a wider range of experiments with more sophisticated instruments. Solar panels remain an option in Jupiter space, but aren't nearly as effective. The other driver, of course, is the recent success of the Cassini/Huygens combined mission, whose stunning images of the Saturnian system and data from the Titan descent and landing have many scientists now thinking of Europa. The moon's cracked ice seems to have been shaped by tidal forces from Jupiter, with reason to believe that an ocean of liquid water might be found beneath an ice crust tens of...

January 11 to February 14, 2006 marks the launch window for NASA's New Horizons mission to Pluto and the Kuiper Belt. At the moment, New Horizons is in pieces, or as principal investigator Alan Stern puts it in an update on the mission, it's in "...boards, boxes and a spacecraft bus on the cleanroom floor at the Johns Hopkins Applied Physics Laboratory..." The high-gain antenna is being checked, and the main computer system installed. According to Stern: The bird also received a guidance, navigation and control software load, and the first testing of the autonomy system (that provides for fault protection) has taken place. Coming soon to the spacecraft are the redundant flight computer, the gyros and the Ralph remote-sensing package. We are now approaching the time - only weeks away - when the last avionics box goes on the spacecraft and New Horizons is dressed in thermal blankets for environmental testing in a large vacuum chamber at NASA Goddard Space Flight Center. New Horizons...

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...