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Small Bodies in Solar System

Small Bodies in Solar System. Lecture 14. Small chunks of rocks in orbits around the Sun. Asteroids : 2-3.5AU. main belt of asteroid at 2.7AU Asteroids at the outer region have lots of ice  Major source of Earth’s water? Ceres (900km), Pallas and Vesta (500km)  “minor planets”

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Small Bodies in Solar System

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  1. Small Bodies in Solar System Lecture 14

  2. Small chunks of rocks in orbits around the Sun • Asteroids : 2-3.5AU. main belt of asteroid at 2.7AU • Asteroids at the outer region have lots of ice  Major source of Earth’s water? • Ceres (900km), Pallas and Vesta (500km)  “minor planets” • > 100,000 objects with size larger than 1 km. Asteroids ≠ broken up planet total mass of asteroids ≈ Moon’s mass asteroids = debris (remnant) of planet formation

  3. Near Earth Objects (NEOs) : Solar System object whose orbit brings it into close proximity with the Earth. • Congressional mandate to catalog all NEOs that are larger than 1km. • As of 2006, about 20% are still missing… 433 Eros : 33×13km

  4. Trans-Neptunian Objects : small bodies (minor planets and smaller) with orbits lie beyond of Neptune’s (30AU) • 35,000+ objects with size larger than 100km  total mass is comparable to Jupiter’s

  5. Largest Trans-Neptunian Objects

  6. Oort Cloud • Short period comets are originated from Kuiper belt objects and they are more or less close to the Ecliptic plane. • However, long period comets have random inclinations and their orbital sizes are ~10,000 AUs.

  7. Cratering on Planets and Satellites • Impact crators = leave scars on the surface of rocky objects. • Some objects (Mercury, Venus) are heavily cratered than others (e.g., Earth). Why? • Geological activity erased old impact craters! • Geological activity depends on the size of planets!

  8. Cratering and Geologic activity • Smaller objects lose heat faster… • Why? For a given radius, smaller objects have larger ratios of surface area to volume. CPU cooler increased surface area for more efficient radiative cooling

  9. Mercury  smallest  most cratered • Mars  next smallest, cratering is about halfway b/w Earth and Mercury • Venus  slightly smaller than Earth  slightly less cratered than Earth • Earth  geological activity (and small effect from erosion) erased most impact craters (only about 200 are known). Mercury Moon Mars Venus

  10. Magnetic Field • Flow of charged particles create a magnetic field  Dynamo theory • Stronger flow  stronger magnetic field • To have a flow, interior of planets has to be non-solid

  11. Magnetic Fields • Shield against strong solar winds!

  12. Relic Magnetism on Mars In the past, when Mars still had some internal heat, the interior of Mars was molten and created a global magnetism  relic magnetic field on Mars Mercury.. hosts a weak magnetic field (1% strength of Earth’s)  a small fraction of interior is in liquid state. Venus.. although it may still have a molten interior, its slow rotation (243 days) cannot generate strong dynamo effect.

  13. Strong magnetic fields in Jupiter and Saturn • In the solar system, Jupiter has the strongest magnetic field  Jupiter’s rotation is fast (10 hours). • from liquid metallic hydrogen acting like a metal (under 1.4 millon bars of pressure!)

  14. Diversity of the Solar System

  15. Diversity of the Solar System

  16. In summary… Important Concepts Important Terms asteroid belt near-Earth object Kuiper belt : Trans-Neptunian objects Oort cloud Liquid metallic hydrogen • Small objects lose heat faster than larger objects • Dynamo theory • Global magnetic field  internal structure! • Chapter/sections covered in this lecture : sections 7-5 through 7-8

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