Every day, an average of 45 tonnes of material rain down on Earth from space, primarily as _______.
very small particles the size of a grain of sand
These particles are about the size of a grain of sand.
What is the term for a larger object that hits the Earth, such as an asteroid or comet?
Bolide
The impact of a bolide can have significant consequences.
Define asteroid.
An inactive rocky body orbiting the Sun with a diameter between 1m and 900 km. may be balls of rubble.
The largest discovered asteroid is Ceres (950 km), recently reclassified as a dwarf planet.
Define comet.
A ‘rocky ice’ body up to ~50 km across that can form an atmosphere (coma) and sometimes a tail of dust, gas and ions. ices can vapourise in sunlight.
Ices can vaporize in sunlight.
What is a meteoroid?
A small piece from a comet or asteroid orbiting the Sun, up to 1m across. formed in early history of solar system
Most meteoroids formed early in the history of the solar system.
What is a meteor?
The light phenomena resulting when a meteoroid enters the Earth’s atmosphere and vaporizes (shooting star)
Commonly referred to as a shooting star.
Define meteorite.
A meteoroid (or rarely a small asteroid fragment) that survived its passage through the Earth’s atmosphere and impacted the Earth’s surface
Meteorites provide valuable information about the solar system.
True or false: The impact velocity of most possible impactors is greater than 11,000 m/s.
TRUE
10 - 25 times faster than a bullet from a high velocity rifle
Impact velocity can range from 11 km/s to 25 km/s.
What are the two types of asteroids based on density?
- Stony (density ~3000 kg/m³)
- Nickel-iron (density ~7500 kg/m³)
Most asteroids are found in the Asteroid Belt between Mars and Jupiter.
where is the asteroid belt found?
between mars and Jupiter
Define Near Earth Objects (NEOs).
orbits cross that of Earths (tight orbit)
NEOs have orbits that can cross that of the Earth.
As of the end of 2024, how many Potentially Hazardous Asteroids (PHAs) are known?
2,304
About 8% of the total Near Earth Asteroids (NEAs) are classified as PHAs.
What is the Torino Scale used for?
Assessing the risk posed by likely bolides
It categorizes objects based on their collision probability and potential impact consequences.
What was the impact probability of asteroid Apophis for the year 2029 initially reported as?
1 in 300
This was later revised to 0.004%, effectively no threat.
What happens to smaller bolides (less than 50m) when they enter the atmosphere?
They mostly become so hot that they explode, producing an airburst
This occurs at high altitudes, dissipating energy before reaching the ground.
What was the energy release of the Tunguska event in 1908?
Equivalent to ~100 Hiroshima bombs (1.5 MT TNT)
It flattened trees in an area equivalent to Greater London.
What is the average frequency of a Tunguska-like event?
Every ~1000 years
Such events depend heavily on the location of impact.
What is the impact probability of a surface impact on the Barringer scale in any one year somewhere on Earth?
~ 1:1,000
The Barringer Crater was formed by a bolide that impacted Earth 50,000 years ago.
What are the possible environmental effects of a 1 km impact?
- Darkness due to dust and soot
- Cooling and drop in photosynthesis
- Induction of an ‘Impact winter’
- Ultraviolet Spring due to ozone depletion
These effects would significantly impact food production and could lead to mass starvation.
What was the estimated energy of the Eltanin Asteroid impact?
5 million Hiroshima bombs
The Eltanin Asteroid was approximately 1 km in diameter and struck the Southern Ocean 2.15 million years ago.
The K-Pg impactor, which caused the mass extinction of dinosaurs, was approximately how many kilometers across?
~ 10 km
This impactor created a crater 180 km across and is linked to the extinction of ~75% of all species 65 million years ago.
What are the two approaches to deflecting a bolide?
- Gravity tractor
- Painting to change Yarkovsky effect
These methods aim to alter the orbit of the bolide to avoid collision with Earth.
True or false: Long-period comets have predictable paths and can be deflected easily.
FALSE
Long-period comets have unknown orbits and unpredictable paths, making deflection challenging.
What is the Torino Scale used for?
To assess the impact hazard of near-Earth objects
The scale categorizes the risk of collision with Earth.
