A team of U.S. and French scientists, led by a SwRI researcher, has been working to understand the population of asteroids and comets which can potentially strike the Earth. They find that an armada of asteroids and comets, nearly 1000 strong, all roughly a kilometer in diameter or larger, present a potential hazard to life on Earth. Their observational and computer-based study will better quantify the likelihood of future catastrophic collisions with Earth, while also helping observational astronomers to improve their search for hard-to-find asteroids and comets that might pose a threat to the planet.

Division 15 researchers, in collaboration with colleagues at the University of Arizona's Lunar and Planetary Laboratory, examined the environmental consequences of large asteroid impacts by mapping the trajectories of material ejected from the impact crater responsible for the extinction of the dinosaurs 65 million years ago. Post-impact wildfires were ignited across the world by the re-entry heating of debris lofted above the atmosphere in the impact vapor plume.

Global map of the regions of the world 65 million years ago that were heated by atmospheric re-entry of impact debris to the point of igniting even wet vegetation. These are the areas where massive wildfires are expected to have occurred.

Division 15 scientists are studying the relationship between the Sun's complex, ever- changing magnetic field and the ultrahot (million-degree) plasma of the solar corona. The work, funded by NASA, uses a ground-breaking SwRI-developed technique called "fluxon analysis" to solve problems that are inaccessible to more conventional techniques. It will ultimately enable forecasting of solar coronal mass ejections, the largest explosions in the solar system.

Solar data from the SOHO spacecraft showing measured magnetic field at the solar surface over a sunspot, and extrapolated magnetic field lines in the corona above the surface.

As part of the Division's emphasis on the study of planetary origins, scientists investigate the earliest history of the Earth and other planets. Division scientists use sophisticated numerical hydrodynamic models to simulate collisions between planet-sized objects, believed to have been typical in the late stages of planet formation in our solar system. Recently, Smooth Particle Hydrodynamic (or SPH) simulations have been utilized to demonstrate for the first time the type of impactor capable of accounting for the Earth- Moon system in the so-called "Giant-Impact" hypothesis for lunar origin. Division scientists also apply SPH methods to the origin of the Pluto-Charon binary planet pair, and to the formation of asteroid satellites.

SwRI scientists are developing models for the formation of the large satellites of Jupiter and Saturn. These satellites –which are each thousands of kilometers in size —hold important clues to the processes that affected giant planet formation in our solar system, as well as for the formation of giant planets around other stars. A current emphasis is determining the types of formation environments that would allow the long-term survival of the satellites while also accounting for their basic compositional features, e.g., the mass fraction of rock vs. ice inferred from a satellites' bulk density.

SwRI scientists participated in the historic NEAR Shoemaker mission, which orbited the large (34 km long) near-Earth asteroid Eros from 14 February 2000 to 12 February 2001, when it was soft-landed on the asteroid. Images taken from orbit, during low altitude flyovers, and during the landing, revealed unexpectedly few small craters, enormous numbers of house-sized boulders, and remarkable flat terrains, whimsically dubbed "ponds" (there is no water on the asteroid). Measurements by NEAR's infrared spectrometer and other instruments imply that it is probably made of so-called "LL chondrite" material, similar to LL chondrite meteorites. The NEAR Shoemaker Science Team held its final meeting in SwRI's Boulder offices in July 2001.

Unexpected surface features were found on the small, Earth- approaching asteroid Eros, when the NEAR spacecraft obtained these close-in images. Flat "pond- like" regions, with sharply bounded edges, continue to perplex NEAR scientists (including SwRI members of the NEAR Science Team) since such small asteroids surely lack near-surface water.

SwRI scientists continue their pioneering work in the search for moons of asteroids with ground based telescopes, using "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. SwRI scientists made the first discovery of a moon of an asteroid from Earth-based observatories in 1998. This year, they have discovered a new class of object -- a double asteroid, where both objects are of similar size (rather than a large asteroid with a small moon). Currently, theorists are baffled about the origin of such pairs. 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.

SwRI scientists have been selected to participate in the first spacecraft mission to the planet Mercury since 1975. The Mercury Surface, Space Environment, Geochemistry, and Ranging Mission (MESSENGER) will carry 7 instruments into orbit around the closest planet to the Sun. To be launched in 2004 for arrival in 2009, it will study Mercury's shape, interior, magnetic field, and surface. SwRI scientists will study Mercury's surface geology.

The Galileo Millennium Mission continues to collect data on Jupiter's four largest satellites: Io, Ganymede, Callisto, and particularly Europa. One of the prime objectives is to study the surface of Europa to determine whether there is a liquid water ocean beneath its icy crust. SwRI scientists are studying the cratering records on each of these surfaces to learn about the ages of the surfaces and the populations of impactors that form the craters.

SwRI scientists are working on a tool capable of automatically detecting and categorizing craters in images of planetary surfaces. This tool, developed in collaboration with JPL machine vision engineers, addresses a crisis in planetary image data analysis: the current inventory of NASA imagery exceeds what a human can expect to process --- by a factor of thousands --- and the problem is expected to get worse as more missions return data. Measurement of the crater sizes and distributions are the only means available for determining the ages and histories of surface regions on bodies in the solar system, short of returning a sample to the Earth.

SwRI astrophysicists reported results of a study showing that perhaps as many as half of the most massive stars in nearby galaxies were born in "field" regions, far from the crowded stellar clusters generally assumed to be the primary cradles of such stars. This result, if verified by further observations, would require revisions of the standard models of star formation and change our views of the evolution of galaxies.

Institute scientists and their international collaborators discovered the first binary Trans- neptunian object (TNO). TNOs are asteroid like objects that orbit in the far outer reaches of our solar system (perhaps as far as 100 times more distant from the Sun than is the Earth), and are believed to be the left over debris from the formation of the solar system. TNOs are incredibly faint (some are more than 100 million times fainter than can be seen with the unaided eye), requiring large telescopes and sophisticated detectors for detailed study. Using telescopes around the world as well as the Hubble Space Telescope, the research team has found this TNO to actually contain two objects orbiting each other with a separation of 40,000 km.

SwRI scientists have established the Triton Watch program, which uses the internet to bring together amateur and professional astronomy observers from around the world in a collaborative effort to monitor changes in Triton, the largest moon of the planet Neptune.

SwRI scientists helped organize the Third Hot Star Workshop in Boulder, Colorado. This meeting was attended by 110 international scientists, who discussed the earliest phases of the birth of massive stars (stars that are 10 to over 100 times the mass of the Sun).

The SwRI-built ALICE ultraviolet spectrometer for the ESA-NASA Rosetta comet mission completed all of its testing and calibration activities and was delivered to the spacecraft contractor in July. ALICE was the first of three U.S. instruments to be delivered; among the other two U.S. instruments is the Ion Electron Spectrometer (IES), also built by SwRI.

SwRI researchers reported the first-ever detection of a noble gas in any comet. The discovery revealed that comet Hale-Bopp, which the SwRI team observed with an ultraviolet spectrograph in 1997, may have been formed much farther out in the solar system than previously expected. A new and more powerful rocket spectrograph is now being built by SwRI with NASA funding to follow up on this discovery by observing fainter comets in 2002 and 2003.

A SwRI-Johns Hopkins Applied Physics Laboratory team was selected to lead one of two design studies for NASA's hoped-for Pluto Kuiper Belt mission.

Research scientists in Division 15 have initiated two projects to conduct experimental studies of solar system accretion physics in the microgravity environment. These studies, funded by JPL and SwRI culminated in a series of 80 zero-G research parabolas during two flights aboard the NASA KC-135 reduced gravity aircraft in April 2001. These flights tested equipment and techniques for more extensive future Space Shuttle or International Space Station experiments now on the drawing board.

SwRI scientists are developing computer models of the early climate of Mars in order to understand how liquid water may once have flowed on its surface. These models are the first to incorporate the greenhouse effects of both gases and of carbon dioxide clouds that may have existed in the early Martian atmosphere. Coupling the effects of exchanges of gases with the surface, the evolution of polar caps, and the loss of gases to space, these models may ultimately reveal if and how Mars was hospitable to life early in its history.

SwRI researchers have been studying the climate effects of large comet impacts on the planet Venus. They find that very large comets, by injecting significant quantities of water (a greenhouse gas) into the atmosphere, can trigger substantial global warming on Venus.

SwRI scientists at Division 15 spent seven nights in May at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii, imaging the dark side of Venus in infrared light. By tracking cloud features from night to night, the SwRI investigators are constructing a movie of the cloud motions, and deriving wind speeds and patterns in the Venus atmosphere at the base of the lower clouds.

The patchiness of the lower clouds of Venus is shown in this raw image, backlit by intense thermal radiation from the hot lower atmosphere.