Near-Earth Objects (NEOs)

Near-Earth Objects (NEOs)

1. =Solar system object whose orbit brings it into proximity with Earth

   • include:
     • Comets
       • 1. shows coma (due to sublimation of near surface ices by solar radiation)
         • 2. Elliptical orbit
     • Asteroids (Near-Earth Asteroids)
       • 1. doesn't show coma
         • 2. less eccentric orbit than comet

2. Meteor

   • Meteoroids
     • when large meteoroids enter Earth's atmosphere
       • produce bright streaks in the sky
       • such meteors = Fire balls
         • Eg) Peekskill Fireball
         • Eg) 2013 Russian Meteor
           • brilliant fireball over Russia (15 Feb 2013)
             • the meteoroid was an asteroid, with an estimated initial diameter of 20m
               • the object exploded in an ai burst over Chelyabinsk Oblast, generating a bright flash
                 • the explosion generated a powerful shock wave
                   • about 1500 people were injured, all of which were due to indirect effects
                     • mainly from broken glass from winodws that were blown in when the shock wave arrived
                 • The Tungska Event
                   • the object is also believed to have burst in the air
                     • the bursting object's size is estimated to be on the order of 60m~190m
       • a piece of a large meteoroid may survive its passage through the atmosphere & finds its way to the ground
         • =meteorite
     • the more massive meteoroids do make it to Earth's surface
       • => craters
         • Eg) Barringer Crater
           • named in honour of Daniel Barringer (1903) - first to suggest that it was produced by meteoritic impact
           • the best preserved impact crater on Earth
             • created about 50,000 years ago
           • the crater is about 1200m in diameter
             • the meteorite that excavated the crater was a nickel-iron meteorite, about 50m across
         • Eg) Carancas Crater
           • the Caracncas impact (2007) near the village of Carancas in Peru
             • crater = 13m wide
               • impacting meteorite was probably around 1m in diameter

3. It is now generally believed that the mass extinction of the dinosaurs was triggered by a massive impact

   • The meteoroid was 10~15km
     • hurtled into Earth @ Chicxulub on Mexico's Yucatan Peninsula
   • the impact generated a dust cloud that blocked sunlight for a year or less
     • also injected sulfuric acid aerosols into the stratosphere, which reduced sunlight reaching the Earth's surface
       • It would take at least 10 years for those aerosols to dissipate
     • the dust & aerosols inhibited pohotosynthesis
       • causing food chains to collapse both on land & at sea
         • the dinosaurs need a lot of foods to sustain their fast metabolism
           • food chain disruption => they died

4. Frequency of Impacts

   • Inverse r/s b/w he size of the object & the frequency that such objects hit Earth
     • Small Impacts
       • asteroids with a diameter of 4m impact Earth approx 1/year
         • no human is known to have been killed directly by an impact
           • chance of single person born today dying due to an impact = 1/200,000
     • Medium & Large Impacts
       • objects with diameter of roughly 50m strike Earth approx 1 every 1000 years
       • Large collisions - with 5km objects - happen approx once every 20 mn years

5. NEO Program

   • in US, NASA has a congressional mandate to catalogue all NEOs that are at least 1km wide
     • as the impact of such an object would be catastrophic
       • estimated that 93% of the NEAs are larger than 1km & have been found & that only about 70 remain to be discovered
     • Eg) Asteroid 1950 DA
       • more than 1km diameter
       • highest probability of impacting Earth
         • may pass very close to Earth/collide with the Earth in 2880
           • 1/300 chance of hitting the Earth
             • Deflecting an Asteroid
               • Gravity tractor
               • Kinetic Impact
   • WISE = IR-wavelength space telescope (2009)
     • find the NEA by detecting their thermal radiations

Images and files in the map