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Asteroids & Meteorites: The Hazards to Life

Asteroids & Meteorites: The Hazards to Life. 13 March 2018. Asteroids. Apollo. Trojans. Asteroid Belt as viewed from Above. Over 100,000 objects greater than 10 km. now identified in the Main Belt Total mass less than 1% of moon’s mass

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Asteroids & Meteorites: The Hazards to Life

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  1. Asteroids & Meteorites: The Hazards to Life 13 March 2018

  2. Asteroids Apollo Trojans

  3. Asteroid Belt as viewed from Above • Over 100,000 objects greater than 10 km. now identified in the Main Belt • Total mass less than 1% of moon’s mass • Over 100 NEAs greater than 1 km. across are being tracked; probably part of a population of about 2000 • Kirkwood gap (and others) occur in the belt where there are orbital resonances with Jupiter • Asteroids classified by ‘spectral group

  4. Kirkwood Gaps

  5. S Asteroids (‘silicaceous’) • 951 Gaspra 433 Eros (true color) Ida (and Dactyl) • 19 x 12 x 11 km 33 x 13 x13 km 58 x 23 km (1km) • Galileo flyby, 199 NEAR orbit/landing Galileo flyby, 1993 • Grooves, curved near-Earth asteroid, member of Koronis depressions, ridges space weathering family, first ID of (Phobos-like) effects documented asteroid ‘moons’

  6. C Asteroids (‘carbonaceous’) • 253 Mathilde; 66 x 48 x 46 km, visited by NEAR Shoemaker • Surface as dark as charcoal; typical outer belt asteroid

  7. Ida and Dactyl

  8. Itokawa

  9. Hyabusa samples Itokawa

  10. Hyabusa Returns June 2010

  11. Steins 2008

  12. Toutatis Model

  13. Vesta, Ceres, Moon

  14. Dawn Mission at Vesta

  15. Vesta Craters

  16. Asteroids Summary • Solid objects mostly in a belt between Mars and Jupiter • Small bodies much more common than larger ones • Classes similar to meteorites: Stony (S), Carbonaceous (C), Metallic (M) • Bodies and belts shaped by collisions, resonances with Jupiter • Source of meteorites

  17. Meteorites

  18. Chondrite

  19. Achondrite

  20. Martian

  21. Jackson Hole Fireball, August 10, 1972

  22. Hoba Iron • 3m x 2m x 1m; 60+ tons • Found 1920, Namibia • No crater, classified ataxite

  23. Ordinary Chondrites (from S Asteroids?)

  24. Three Views of Vesta • Hubble image, model and color-shaded topography • Largest member of V class of asteroids (vestoids) • Spectral variations consistent with HED meteorites

  25. Meteor showers • Time exposure image, tracking stellar motion • Stars stay still, meteorites make trails

  26. The Peekskill (NY) Fireball

  27. Macroscopic features of the Almahata Sitta meteorite. P Jenniskens et al.Nature458, 485-488 (2009)

  28. Chondrites • Rocky, inhomogeneous, contain round “chondrules” Microscope image

  29. Iron meteorites: from core of differentiated asteroids

  30. Stony-Iron meteorites - the prettiest • Crystals of olivene (a rock mineral) embedded in iron • From boundary between core and mantle of large asteroids?

  31. Sutter’s Mill fell and found in 2012

  32. The main points: Meteorites • Each year the Earth sweeps up ~80,000 tons of extraterrestrial matter • Some are identifiable pieces of the Moon, Mars, or Vesta; most are pieces of asteroids • Meteorites were broken off their parent bodies 10’s to 100’s of million years ago (recently compared to age of Solar System) • Oldest meteorites (chondrites) contain interstellar dust, tiny diamonds made in supernova explosions, organic molecules and amino acids (building blocks of life) • Direct insight into pre-solar system matter, solar system formation

  33. Asteroid Hazard: The Death of the Dinosaurs

  34. Tunguska, Siberia, June 30, 1908 Black and white photos taken during field expedition in 1927; color photo taken in 1990

  35. Potentially Hazardous Asteroid ThreatSize-frequency diagram for impacting objects • ~100 tons of meteroritic dust falls each day • 50 m impactor once per 1000 yr (local effects) • 500 m impactor once per million years (regional effects) • 5 km. impactor once per 100 million years (global effects)

  36. Plot of orbits of known potentially hazardous asteroids, with over 140 meters in size and passing within 7.6 million kilometers of Earth

  37. Potentially Hazardous Asteroids (PHAs) are currently defined based on parameters that measure the asteroid's potential to make threatening close approaches to the Earth. Specifically, all asteroids with an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 au or less and an absolute magnitude (H) of 22.0 or less are considered PHAs. In other words, asteroids that can't get any closer to the Earth than 0.05 au (roughly 7,480,000 km or 4,650,000 mi) or are smaller than about 140 m (~500 ft) are not considered PHAs.

  38. Potentially Hazardous Asteroids

  39. While the chances of a major collision are not great in the near term, there is a high probability that one will happen eventually unless defensive actions are taken. Recent astronomical events—such as the Shoemaker-Levy 9 impacts on Jupiter and the 2013 Chelyabinsk meteor along with the growing number of objects on the Sentry Risk Table—have drawn renewed attention to such threats. NASA warns that the Earth is unprepared for such an event.

  40. Asteroid impact avoidance • Asteroid impact avoidance comprises a number of methods by which near earth objects (NEO) could be diverted, preventing destructive impact events. A sufficiently large impact by an asteroid or other NEOs would cause, depending on its impact location, massive tsunamis, multiple firestorms and an impact winter caused by the sunlight-blocking effect of placing large quantities of pulverized rock dust, and other debris, into the stratosphere.

  41. A collision between the Earth and an approximately 10-kilometer-wide object 66 million years ago is thought to have produced the Chicxulub Crater and the K-T extinction event, widely held responsible for the extinction of most dinosaurs.

  42. Gravity map of buried structure 180 miles across; 65 millions years old Identified in early 1990s with seismic data, after 10 year ‘search’ Chicxulub, Yucatan penninsula, Mexico

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