Impact Scars and Space Debris

Impact Scars on the Moon

• these scars show evidence of a collision
• shortly after the planets formed (until around 3.9 billion years ago), asteroids/ comets collided frequently with the Moon and the Earth
• Moon has no plate tectonics, water or life
  • craters are preserved here

Space Debris

• space debris include:
  • $asteroids:$ small, rocky objects
  • $comets:$ frozen dust, ice, and rock
  • $meteoroids:$ asteroids and comets that orbit the sun
  • $meteors:$ a “shooting star”
  • a meteoroid enters the Earth’s atmosphere and vaporizes
  • $meteorites:$ a meteoroid that hits the Earth’s surface
  • can be rocky or metallic

Asteroids

• 3 large asteroids: ceres (590 miles diameter), Vesta (326 miles), and Pallas (319 miles)
• >200 with diameters >62 miles
• around 1000 with diameters >19 miles
• millions with diameters >0.62 miles
• most are located in the asteroid belt between Mars and Jupiter
• some have orbits that intersect the Earth’s orbit
  • $Apollos:$ >1000 mountain-sized asteroids

Comets

• frozen dust, ice, and rock (“dirty snowballs”)
• release gas and dust as they travel through space
• most are >10 miles in diameter
• $short-period comet:$ completes its orbit in <200 years
  • Kuiper Belt near Neptune
• $long-period comet:$ completes its orbit in >200 years
  • about 1 trillion in the solar system
  • orbit far out of our solar system