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	The impact believed to have caused mass extinctions on Earth 65 million years ago — including the dinosaurs — has been traced to the breakup of the parent of the family of objects associated with the asteroid Baptistina. This 170-kilometer-wide asteroid broke apart 160 million years ago and its fragments later showered the inner solar system. Art by Don Davis

Research spanning the evolution of small bodies, such as:

• Asteroids

• Comets

• Meteoroids

• Dust

to the formation of the planets and satellites like the Moon is performed by space scientists at Southwest Research Institute (SwRI). The ultimate goal is to explore:

• How and when the planet formed

• Why it has water and other conditions suitable for life

• Whether it is possible that other Earth-like planets exist elsewhere

In essence, the exploration of how the solar system came to be is also a way to understand our place in the universe.

The Baptistina Asteroid Family

A particular topic of interest to both scientists and the public is the meteorite impact believed to have wiped out the dinosaurs and other life 65 million years ago. SwRI space researchers traced this impact back to a large breakup event in the main asteroid belt, a region of small bodies between Mars and Jupiter. Approximately 160 million years ago, the 170-kilometer-wide asteroid Baptistina was disrupted when it was struck by another large asteroid. This created a cluster of asteroids with similar orbits (known as the Baptistina family) that gradually spread to a nearby "superhighway" where they could escape the main asteroid belt and be delivered to orbits that cross Earth’s path. The addition of so many new fragments to the inner solar system created an asteroid "shower" that matches up very well with the impact record on both Earth and the Moon over the past 120 million years or so.

The Chicxulub Crater

Close to the peak of this shower, a 10-km asteroid struck Earth and created the 180-km Chicxulub crater on Mexico’s Yucatan Peninsula. Telltale clues from dynamical models, sediment samples and a meteorite from this time period give a 90 percent probability that the object forming the Chicxulub crater was a refugee from the Baptistina family. This work demonstrated that the collisional and dynamical evolution of the main asteroid belt may have significant implications for understanding the geological and biological history of Earth.

Center for Lunar Origin and Evolution

NASA awarded SwRI the Center for Lunar Origin and Evolution (CLOE), one of the first centers of the new Lunar Science Institute. The Moon is a unique extraterrestrial laboratory, because it is the only object that is both relatively accessible and still bears evidence from practically every period of solar system history. CLOE will investigate several lasting mysteries that were uncovered during the historic Apollo program.

	These frames simulate the first 1.2 billion years of solar system history. The orbits of the four giant planets are shown as colored ellipses. The green dots show small comet-like objects. Changes in the orbits of the giant planets cause the smaller objects to scatter widely, some of which strike the inner planets and moons in a "late heavy bombardment."

Late Heavy Bombardment

A key project deals with the intense debate concerning the nature of the lunar impact record in the relatively short interval from 4 to 3.8 billion years ago, commonly referred to as the "Late Heavy Bombardment," or LHB. This phase in lunar history was dominated by large impact events — the remnant lava-filled basins that now shape the dark-colored "man in the moon" design on the lunar surface. Research by staff members suggests the LHB reveals the last and perhaps key phase of planet formation when the solar system may have rearranged itself.

In this model, the giant planets — Jupiter, Saturn, Uranus and Neptune — formed in a much more compact configuration than they have today. Just outside their orbits loomed a massive disk of comets. Gravitational interactions between the planets and the comet disk caused the planets to slowly migrate in space. Computer simulations indicate that, after hundreds of millions of years, Jupiter and Saturn reached orbits where their mutual gravitational kicks became quite pronounced. This triggered an instability that led to a violent reorganization of the outer solar system. Uranus and Neptune were pushed into the comet disk, scattering its members throughout the solar system. Some of these scattered objects then struck, or "bombarded," the planets and moons of the inner solar system.

This model, while radical, is compelling because it can explain many fundamental characteristics of the solar system, from the unusual orbits of the giant planets to the formation of several individual asteroid and comet populations. It also explains why the Moon experienced a barrage of impactors nearly 4 billion years ago. Thus the Moon, and its entire impact history, can be viewed as a "Rosetta Stone" for deciphering the histories of the planets.

For more information about our planetary origins, moon and small body dynamics research capabilities, or how you can contract with SwRI, please contact Robert Grimm, Ph.D., at rgrimm@swri.org or (720) 240-0149.

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Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.

December 28, 2012