Asteroids and Their Characteristics

  • Definition of Asteroids:

    • Remains of planetesimals that were not incorporated into larger planets.

  • Study of Asteroids:

    • Over 800,000 asteroids (precisely 779,736) have been cataloged and their orbits studied.

  • Orbital Patterns:

    • Asteroid orbits are significantly more elliptical compared to the circular or elliptical orbits of planets.
    • Most asteroids travel counterclockwise around the sun.

  • Mass of Asteroids:

    • Total mass of asteroids is about 5% of the moon's mass.
    • There are tens of millions of asteroids smaller than 1 km in diameter.
    • Approximately 250 asteroids exceed 100 km in diameter.

  • Location:

    • The majority of asteroids are found in the asteroid belt situated between Mars and Jupiter.
    • A smaller number of asteroids exist outside this main belt.

  • Notable Asteroids:

    • Vesta:
    • Second largest asteroid visited by NASA's Dawn probe.
    • Has a distinctive difference in crater density between its hemispheres:
      • Northern hemisphere: older and more cratered.
      • Southern hemisphere: younger with fewer craters, home to a 22 km high volcano.
      • Reason for difference: Asteroid collisions.
    • Mathilde:
    • Visited by NEAR (Near Earth Asteroid Rendezvous).
    • Diameter: 60 km, Mass: 10^17 kg.
    • Eros:
    • Another target of NEAR.
    • Mass: 7 x 10^15 kg, density: 2400 kg/m³, numerous impact craters.

  • Kirkwood Gaps:

    • Gaps in the asteroid belt caused by Jupiter's gravitational influence.

  • Safety of Asteroid Belt:

    • Contrary to common beliefs, the asteroid belt is not hazardous; asteroids are typically millions of miles apart.
    • Asteroids can collide at speeds of 2000 mph, but gravity often leads to reassembly of fragments.
    • However, due to instability, asteroid fragments can break apart over time into families that orbit together.

  • Asteroids with Moons:

    • 323 known asteroids have one or more moons (e.g., Ida & Dactyl, Petit-Prince, Romulus, & Remus).

  • Trojan Asteroids:

    • Asteroids that share an orbit with a planet or occupy a LaGrange point.
    • Examples:
    • 9 Trojans with Mars, 1 for Uranus and Earth, 17 for Saturn, and 6,729 for Jupiter.
    • These do not orbit their respective planets but orbit the sun.

  • Potential Threat to Earth:

    • Earth-crossing asteroids pose a risk of collision.
    • Potential for significant damage: A 1 km asteroid could yield destruction equivalent to 100 times all nuclear weapons combined.
    • Lack of clear plans for asteroid impact response suggests that it's not about "if" but "when".

  • Future Implications:

    • Growing interest in Mars as a potential refuge, as expressed by figures like Elon Musk, due to asteroid impact risks on Earth.
    • Current brainstorming for strategies on what to do in case of an asteroid impact on Earth.