Howardites

The answer sheet for the worksheet Delivery: from asteroid families to Earth. Each answer comes with the reason, so it can be used to mark or to go over the questions with the class.

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Answers: Delivery: from asteroid families to Earth

  1. B: CI carbonaceous chondritesThe CI-like nature of Ryugu and Bennu is one of the well-established links.
  2. C: Orbital drift caused by uneven thermal emissionA rotating body re-emits absorbed heat unevenly, producing a small thrust that slowly changes its orbit.
  3. D: They cluster near 470 Myr, when shock reset themShock heating in the break-up reset many argon clocks, so ages cluster close to the Ordovician event.
  4. B: It matches no known meteorite groupÖsterplana 065, from Swedish Ordovician limestone, does not match any known meteorite group.
  5. A: Resonances with Jupiter remove asteroidsResonances with Jupiter pump up orbits there, removing asteroids from those regions.
  6. True (Dynamical modelling and spectroscopy)Combining dynamical models with spectroscopy pointed to a few young asteroid families.
  7. True (Koronis and Karin)The Koronis and Karin families were proposed for H chondrites, and Massalia for L chondrites.
  8. The break-up of the L chondrite parent body (accept any answer with the same meaning)The surge followed the collisional break-up of the L chondrite parent body.
  9. About 466 million years ago (accept any answer with the same meaning)Fossil meteorites and chromite in limestone record the event about 466 million years ago.
  10. Types rare among today's falls were once more common (accept any answer with the same meaning)The mix of meteorite types reaching Earth has changed over time.

Task

Answers will vary. The task comes from the lesson: Plot the cosmic-ray exposure ages of H chondrites as a histogram using values from published compilations. Note the peak around 7 to 8 million years and consider what kind of event could produce it.

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