FIGURE 8 Comparison of the size of a collision on Jupiter to size of Earth. SOURCE: Heidi Hamel, presentation to the workshop on Sharing the Adventure with the Public—The Value and Excitement of “Grand Questions” of Space Science and Exploration, November 9, 2010. Jupiter: Courtesy NASA, ESA, H. Hammel (Space Science Institute), and the Jupiter Impact Team. Earth: Courtesy of NASA.

in which the planets orbit the Sun. Some KBOs are in columns and clusters in resonant orbits with Neptune: “For every two times Neptune goes around, the Kuiper belt goes around three times. They are locked in a dance,” Hammel explained. Pluto is one of these objects, and there are more than 300 objects just like it. That structure developed when the giant planets migrated, sweeping up the tiny objects and locking them into orbital resonances.

The discovery of exoplanets beginning in 1995 is “what sent Humpty Dumpty over the edge,” with 490 exoplanets discovered to date. Everything she learned in graduate school about planetary formation, she said, is “out the window.” So the question is how to put Humpty Dumpty back together again.

Hammel showed a series of seven slides that explained the current theory of how solar systems form, starting with a collapsing cloud of gas and dust that forms a star, leading to clumps of dust grains sticking together and getting angular momentum that turn them into disks that grow into planestismals that stick together and become protoplanets that collide with one another to form planets and then gas attaches to the larger ones. Finally, the planets get redistributed.

“It’s complex and it’s messy. Lots of whooshing and crashing,” Hammel exclaimed, adding that all of this knowledge has developed during her career. “In 5 or 10 years, they’ll tell you a completely different story. That’s just the nature of science,” she added.

Our solar system itself is still a “work in progress” with massive impacts on Jupiter, for example. She provided a number of examples, including a series of images of a recent collision between Jupiter and a comet or asteroid that she took using the Hubble Space Telescope. “I try to people-ize this,” she said, by showing what the impact site would have been like on Earth (Figure 8). It would be a “biosphere-

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