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Investigating the Near-Earth Object Population

Investigating the Near-Earth Object Population. William Bottke Southwest Research Institute. When people think about “asteroids”, they mostly do not picture this:. They think of this…. Or this…. “Killer Asteroid,” National Geographic Television, 2004. Hazards From Asteroid Impacts.

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Investigating the Near-Earth Object Population

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  1. Investigating the Near-Earth Object Population William Bottke Southwest Research Institute

  2. When people think about “asteroids”, they mostly do not picture this:

  3. They think of this…

  4. Or this… “Killer Asteroid,” National Geographic Television, 2004

  5. Hazards From Asteroid Impacts Leonid Meteor Shower Tunguska, 1908 Peekskill Meteorite Chicxulub, 65 Million Years Ago Jupiter Impacts 1994 Huge Extremely Rare Smallest Most Frequent

  6. Environmental Consequencesof Small Impacts

  7. A Better Way to Think About Asteroids is This…

  8. Meteorites are from Asteroids • Meteorites are hand-samples of asteroids (and possibly comets) that have survived passage through our atmosphere to reach Earth. • Properly analyzed, these objects can tell us about planet formation processes and evolution in the solar nebula. Ordinary Chondrite Iron Meteorite

  9. Fossils of Formation ~106 objects with diameters D > 1 km between Mars and Jupiter

  10. NEOs are the “Middlemen” Between Meteorites and Main Belt Asteroids Near Earth Objects NEOs Meteorites Asteroid Belt Jupiter Family Comets

  11. Some NEO Science Questions • NEO orbit and size distributions? Compositions? Internal structures? • How are NEOs replenished over time? By what populations? • How do NEOs physically evolve? What does this tell us about planetesimal evolution? • How are NEOs connected to meteorites? Where did their parent bodies originate? • Did NEO deliver water to the Earth? • How has the NEO impact rate on the terrestrial planets changed with time? Itokawa Eros Geographos To answer these questions, we need the most accurate model of the NEO population possible.

  12. How Do Near-Earth Asteroids Get Here? (Part 1) Asteroid Collision Asteroid Belt Near Earth Objects Jupiter Family Comets

  13. Collisions in the Asteroid Belt • Asteroids strike one another and create ejecta. • Most fragments are ejected at low velocities (V < 100 m/s). Sample references: Benz and Asphaug (1999); Michel et al. (2001); Durda et al. (2004)

  14. How Do Near-Earth Asteroids Get Here?(Part 2) Asteroid Collision Dynamical Escape Asteroid Belt Near Earth Objects Jupiter Family Comets

  15. Yarkovsky Effect Allows Fragments to Reach “Escape Hatches” Very Elongated Koronis family • Observed • Model Elongation of Orbit Very Circular Distance From Sun (Closer) (Further) Bottke et al. (2001)

  16. What Happens to Them Along the Way? En route to the inner solar system (and Earth), lots of strange things can happen to NEOs…

  17. Asteroid Collisions Create Fragments! Far view Close up • The fragments can be very different from one another, implying different origins and evolution histories.

  18. Sunlight Causes Fragments to Spin Up! Spin-Up and Disruption of a Contact Binary by YORP • Absorbed and reemitted sunlight can change asteroid’s spin rate! • This effect can produce strange shapes and even binary asteroids! Walsh and Richardson (2007)

  19. Planetary Encounters Can Pull Them Apart! Disruption of an NEO During Close Pass with Earth • Gravitational (tidal) forces from Earth can pull the asteroid apart! • These effects can also produce asteroid satellites! Richardson, Bottke, and Love (1998); Walsh and Richardson (2006)

  20. How Can Arecibo Radar Help Us Obtain the Properties and Geologic Context of NEOs? • Direct determination of how sunlight (Yarkovsky and YORP thermal effects) affects evolution of NEOs: • This helps us understand the timing of asteroid breakups, the evolution of the fragments over time, and where they will go in the near future. • NEO physical properties • Precise shapes and spin rates for NEOs. • Detection of NEOs with satellites. • NEO crater histories and surface properties. • NEO orbital/composition distributions • These parameters provide critical clues about NEO origins and evolution.

  21. Exploring Near Earth Objects OSIRIS mission to return samples from “1999 RQ36”. • Another way to determine the context of meteorites is to use spacecraft to return samples from an NEO.

  22. Radar Provided Unparalleled Knowledge of 1999 RQ36 • Radar provided RQ36’s approximate shape, size, spin properties, surface properties, and precise orbit, all which were critical for mission planning.

  23. NEOs are the “Middlemen” Between Meteorites and Main Belt Asteroids • Rocks and sediments in a riverbed yield information on the types of material found upstream.

  24. NEOs are the “Middlemen” Between Meteorites and Main Belt Asteroids Eros Itokawa • Rocks and sediments in a riverbed yield information on the types of material found upstream. • NEOs and meteorites tell us about the nature and evolution of bodies in the main asteroid and Kuiper belts.

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