Division scientists studied Jupiter's faint ring system using the Cassini spacecraft's ISS instrument. By observing the ring over a range of angles and wavelengths, they measured the size, shape, and composition of the tiny dust grains making up the rings. Knowing the properties of these grains will enable them to model physical processes within the ring, and answer fundamental questions about the ring system's origin and history. Cassini flew past Jupiter en route to its arrival at Saturn on July 1, 2004.

Division 15 scientists continued their leading involvment in New Horizons, an exciting scientific investigation to obtain the first close look at Pluto-Charon, a binary planet, and then multiple Kuiper Belt Objects (KBOs). Owing to their fundamental relationship to understanding our solar systems origin and evolution, a Kuiper BeltPluto flyby was the top priority in the National Research Councils Decadal Survey of Solar System Exploration.

New Horizons seeks to learn more about the surfaces, atmospheres, interiors and space environments of Pluto, Charon and KBOs by using imaging, visible and infrared (IR) spectral mapping, ultraviolet (UV) spectroscopy, radio science, and in situ plasma sensors. Scheduled for launch in 2006, New Horizons could fly through the Pluto-Charon system as early as 2015. Over a 150-day period it would conduct the first spacecraft reconnaissance of these worlds, then continue into the Kuiper Belt for further encounters.

The solar physics group at Divsion 15's Boulder office won both a three-year grant from NASA and a SwRI Presidential IR grant to build and launch a suborbital rocket payload. The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) is slated to fly in the summer of 2006. It will accumulate over 3500 ultraviolet solar spectra in just six minutes of space flight, identifying magnetic disruptions, waves, and winds above the Sun's surface.

The solar physics group also recently demonstrated machine vision software capable of simultaneously identifying and tracking 10,000 magnetic poles on the churning surface of the Sun. This is a milestone in the ongoing effort to understand our star's strange, ultra-hot atmosphere, which is thought to be heated by magnetic induction effects.

SwRI scientists completed a high-altitude airborne search for vulcanoids, a population of small, asteroid-like bodies that may orbit the Sun interior to the orbit of the planet Mercury. Any vulcanoid asteroids that might exist in that region would present planetary scientists with a sample of condensed material from the early inner solar system, and could help in our understanding of Mercury's cratering record. But such small objects so close to the Sun are exceedingly difficult to search for with ground-based instruments because of their relative faintness in the bright twilight sky so near the Sun.

To overcome these difficulties, SwRI astronomers took to the air with NASA research pilots in six flights aboard a NASA F/A-18B Hornet jet aircraft, flying to an altitude of 49,000 feet to achieve far darker twilight sky conditions than are ever possible on the ground. There, thousands of search images of the vulcanoid zone obtained with SwRI's SWUIS-A astronomical imaging system verified the benefits of high-altitude observations, although in the end that search turned up no vulcanoids larger than about 30 kilometers across. SwRI's search for vulcanoids continues in January 2004, with a flight to even higher altitudes (and, therefore, even darker twilight conditions) aboard a sub-orbital sounding rocket launched from the White Sands Missile Range in New Mexico.

Also of interest to astrobiology were new theoretical studies performed by division 15 scientists of the longevity of oceans on the planet Venus. Preliminary results suggested that Venus may have retained oceans for a significant part of its early history.

Division scientists reported in Nature on the potential importance of deep atmospheric circulations forced by topography on Mars' climate system. The circulations may also be responsible for a large amount of atmospheric dust recycling, a process which helps to maintain Mars' backgroud atmospheric dust concentration, and may explain the origin of elevated atmospheric dust layers.

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SWRI researchers continued their research into asteroid collisions. This movie illustrates what might happen when two asteroids collide. The impact simulation is part of a matrix of 150 simulations, with varying impactor angles, velocities, and diameters, conducted at SwRI in close collaboration with JPL. In this simulation, the diameter of the Basalt target body is 100 kilometers, the impact angle is 45 degrees, the relative velocity is 7 kilometers per second, and the diameter of the Basalt impactor is 14 kilometers. Similar impacts appear to be extremely efficient producers of binary asteroid systems. The result of this impact was 119 particles in a stable orbit about the remnant, as well as 632 escaping binary systems. View movie (warning: large)

SwRI scientists continue their pioneering work in the search for moons of asteroids, using a new optical technology on ground-based telescopes, called adaptive optics. This revolutionary technique removes the blurring caused by the Earth's atmosphere and will allow us to see faint moons close to bright asteroids. In addition, SwRI scientists are now using the Hubble Space Telescope to search for moons around particularly faint, small asteroids. SwRI scientists made the first discovery of a moon of an asteroid from Earth-based observatories in 1998, and have now discovered two-thirds of the known asteroid moons in the main asteroid belt. Discoveries of such moons allows scientists to study the composition, structure, and origin of the asteroids, something which can otherwise be done only by spacecraft. Their work continues to provide surprises --- the satellites appear to be grouped into different classes that the scientists believe is related to their method of formation.

[The figure below shows a small moon (at the 4:00 position) around asteroid (121) Hermione, discovered by SwRI scientists in September 2002 at the world's largest telescope, the Keck in Hawaii. The asteroid is about 210 km in diameter, while the moon is about 13 km across. It orbits the asteroid about every 4 days at a distance of about 1000 km.

To better understand the origin of these asteroid satellite systems SwRI scientists have conducted an extensive series of numerical simulations to model the formation of asteroid satellites as a result of impacts between asteroids. A 3-dimensional smooth-particle hydrodynamics (SPH) code models impacts between colliding asteroids; the outcomes of the SPH models then passed to N-body simulations, which follow the evolving trajectories of the ejecta fragments to search for the formation of satellite systems. Many of the 161 simulations conducted so far seem to produce satellite systems qualitatively very similar to observed systems in the main asteroid belt.

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In addition to the direct scientific results, the suite of simulations provides a baseline for measuring the performance of JPL-developed Directed Learning tools. Requiring as few simulation runs as possible, the Directed Learning tools determine the location and shape of regions of interest within the multidimensional input parameter landscape - combinations of parameters where the formation of asteroid satellite systems is optimized.

SWRI researchers recentlyfound that sunlight can have a surprisingly important effect on the spins of small asteroids. Their study shows that sunlight absorbed and reemitted over millions to billions of years can spin some asteroids up so fast that could potentially fly apart. In other cases, it can nearly stop them from spinning altogether. There are even weird cases when the effects of sunlight, when combined with the gravitational tugs of the planets, slowly force asteroid rotation poles to point in the same direction. The results of this study indicate that sunlight may play a more important role at determining asteroid spin rates than collisions.

SWRI astronomers took monthly infrared spectra of Neptune's moon Triton to "catch it in the act" of surface changes, based on reported changes in color changes in the visible and ultraviolet. This program exercises the Infrared Telescope Observatory's new remote observing abilities, ushering in a new era in astronomy.

Work in the astrobiology field continued in the department. This included a study of how bodies like Pluto and the KBOs would evolve topossessing organic-rich oceans when the Sun goes red giant in the distant future. This work also explored how many red giants now in existence may possess far flung habitable zones just like this.

Division scientists recieved an award from the NSF Major Research Instrumentation Program to build a suite of four next-generation high-speed portable telescope and camera systems which will be used to understand small bodies in the outer solar system through stellar occultations.

Researchers in the Department continued to study the evolution of comets using observatories like HST, FUSE, and Chandra. Work also continued toward understand the processes that affect comets while in storage in the Oort Cloud and Kuiper Belt; a major review on this topic was published in Nature. (download)

Division researchers recently reported results on two binary stars that present puzzling questions for stellar structure and evolution models. One is a double supergiant binary that cannot simply be explained as an evolutionary state of a binary, but may initially have been a triple star system. In that scenario, the more massive star of the now binary system is the product of the merger of a star that was four times the mass of the Sun and another that was twice the mass of the Sun . The second system is a binary consisting of two massive stars in physical contact with one another. The new results, based on photometry and high resolution spectroscopy, give very accurate masses and radii for the stars and show that the orbital period has not changed in 30 years.