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Meteorites & Asteroids

Meteorites & Asteroids. 23 October 2018. What is a meteorite?.

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Meteorites & Asteroids

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  1. Meteorites & Asteroids 23 October 2018

  2. What is a meteorite? • A meteorite is a solid piece of debris from an object, such as a comet or asteroid, that survives its passage through the atmosphere to reach the surface of a planet. When the object enters the atmosphere, various factors such as friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate that energy

  3. What is a meteor? • It then becomes a meteor and forms a fireball, also known as a shooting star or falling star; astronomers call the brightest examples ”bolides". Meteorites vary greatly in size. For geologists, a bolide is a meteorite large enough to create a crater

  4. As of 2018, there are more than 59,200 well-documented meteorite finds Meteorites are always named for the places they were found

  5. Chondrite

  6. Achondrite

  7. Martian

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

  9. Entry and Impact • As meteoroids are heated during atmospheric entry, their surfaces melt and experience ablation.  • Meteoroids that experience disruption in the atmosphere may fall as meteorite showers • The largest meteorites in a shower are found farthest down-range in the strewn field • Antarctic ice sheets act to concentrate meteorites in certain areas • The largest meteorites leave craters

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

  11. Jackson Hole Fireball, August 10, 1972

  12. 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)

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

  14. The 60-ton, 2.7-metre long Hoba meteorite in Namibia  is the largest known intact meteorite

  15. The 'crater' made by a 61.9-gram Novato meteorite  when it hit the roof of a house on October 17, 2012

  16. NWA 859 iron meteorite showing effects of atmospheric ablation

  17. Ordinary Chondrites (S Asteroids?)

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

  19. What were the processes and products in the early Solar System • Impact features on all planetary surfaces; planets formed by accretion of planetesimals from a turbulent solar nebula • Much mixing of components; completed in 5-10 million years • ‘Residual’ debris forms asteroid belt; Kuiper belt, Oort cloud

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

  21. The Peekskill (NY) Fireball

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

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

  24. Iron meteorites: from core of differentiated asteroids

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

  26. Sutter’s Mill meteorite 2012

  27. 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

  28. Asteroids Apollo Trojans

  29. What are Asteroids? • Asteroids, sometimes called minor planets, are rocky remnants left over from the early formation of our solar system about 4.6 billion years ago. • They are found orbiting the sun between Mars and Jupiter within the main asteroid belt. Asteroids range in size from Vesta—the largest at about 530 kilometers in diameter - to bodies that are less than 10 meters across. 

  30. 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

  31. Asteroid History • Jupiter's massive gravity and occasional close encounters with Mars or another object change the asteroids' orbits, knocking them out of the main belt and hurling them into space in all directions across the orbits of the other planets. Stray asteroids and asteroid fragments slammed into Earth and the other planets in the past, playing a major role in altering the geological history of the planets and in the evolution of life on Earth.

  32. Kirkwood Gaps

  33. Most asteroids are irregularly shaped, though a few are nearly spherical, and they are often pitted or cratered. As they revolve around the sun in elliptical orbits, the asteroids also rotate, sometimes quite erratically, tumbling as they go. More than 150 asteroids are known to have a small companion moon (some have two moons). There are also binary (double) asteroids, in which two rocky bodies of roughly equal size orbit each other, as well as triple asteroid systems The three broad composition classes of asteroids are C-, S-, and M-types.

  34. 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’

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

  36. Ida and Dactyl

  37. Itokawa

  38. Hyabusa samples Itokawa

  39. Hyabusa Returns June 2010

  40. Steins 2008

  41. Toutatis

  42. Vesta, Ceres, Moon

  43. Dawn Mission at Vesta

  44. Vesta Craters

  45. What about M-type Asteroids? 16 Psyche is the largest known M-type asteroid, and is thought to be the exposed iron core of a protoplanet This asteroid may be the remnant of a violent collision with another object that stripped off the outer crust.

  46. Artists' impression of the  Psyche spacecraft

  47. Psyche artist’s conception

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