Catastrophes in the Solar System

Tunguska Event (1908)

• more than 100 years before Chelyabinsk, large explosion caused by another meteorite occurred over Tunguska, Siberia

• Blast flattened almost 1000 square miles of forest (size of majority city)

• No impact crater, object exploded in atmosphere

• Energy released comparable to that of large nuclear weapon

What effect do collisions with small (<1km) meteorites cause + ex.

Only local effects

Ex. Chelyabinsk and Tunguska events

Size of impact craters

10-15 times the size of meteorites that produced them

If an asteroid that was half a mile in diameter hit Earth, approximately how big would the impact craters be

Between 5-7 miles

Collision with large (>1km) meteorite effects

Severe, global consequences, mostly due to debris

• impact large enough to cause mass extinction only occur several or tens of millions of years

Watch what happened immediately after the dinosaurs went extinct

Yessir

Consequences of an impact with a an object greater than or equal to 1km object

• impact causes massive explosions producing intense heat, shock waves, global earthquakes, and tsunamis

• Dust and debris from the crater injected high into the atmosphere, blocking sunlight

• Global cooling (impact winter) lasting months to years

• Worldwide fires and acid rain

• Major disruption of photosynthesis and climate

• Widespread ecosystem collapse and mass extinctions

What are we doing about impacts?

1998, NASA began the Spaceguard Survey with the goal to discover and track earth-approaching asteroids greater than 1km in diameter

• we have fewer smaller ones to detect because they are harder to see

Watch How does nasa spot a near earth asteroid video

Yes maam

We find a potential threat. Now what?

NASA established a wide range of centers and offices to develop strategies with potential impactors

• CNEOS

• PDCO

Planetary Defense

• Search, Detect, and Track

  • Space based and ground based observations, IAWN

• Characterize (what is it?)

• Plan and coordinate (if it hit us, what would we do? Who is responsible?)

  • Meet once a year for once a week to come up with solutions for potential problems

• Mitigate

• Assess

DART (double asteroid redirection test)

Took an asteroid that is actually two asteroids surrounding each other (Didymos and Dimorphos), sent DART to hit the little one (Dimorphos) to see how much it would change the orbit

• chose the ones rotating around each other cause easier to measure how the orbit changes

• DART had to self navigate because light takes time to travel, so if we move the stick, by the time the signal reaches DART, it would be too late

Watch defending the planet: NASA’s DART mission

Alrighty

NASA’s DART mission

• first real planetary defense experiment designed to test asteroid deflection

• Launched in 2021, collided with Dimorphos in 2022 (Moon of Didymos), neither of which threaten earth

• Impact shorted Dimorphos’ orbital period by 32 minutes

• Demonstrated a kinetic impact can alter an asteroid’s motion (key for future earth protection)

• Follow up studies showed ejecta and boulders carried significant momentum, providing insights into impact physics

Watch solving asteroid mysteries | Hera planetary defense mission

Waho

ESA’s Hera Mission

• European Space Agency’s follow up to DART

• Launched Oct 2024, en route to Didymos/Dimorphos binary asteroid system

• Rendezvous with system in late 2026, with planned detailed observation of Dimorphos

• Will make impact crater, measure mass, internal structure, and geometry of both bodies

• Carries two CubeSats to investigate surface properties and evolve the binary dynamics

• Hera’s data will help scientists understand momentum transfer and refine deflection models for planetary defenses (how momentum is transferred from space craft to asteroid)

Why does the moon have so many more craters than earth

Earth has certain features that either mitigate the impacts or erase them after they happen

What features does earth have to mitigate impacts/erase them after they happen

• earth has an atmosphere

• Erosion (Winds, water, erase craters)

• Volcanism (spewing lava erases craters)

• Plate tectonics (surface of earth is constantly going under and coming back out, cleared when it comes back out)

Age of land and impact crater sites

Since the land is newer, it doesn’t have the same chance/time to get hit by objects

Four main hypotheses of where moon came from

1. Fission hypothesis

2. Sister hypothesis

3. Capture hypothesis

4. Giant impact hypothesis

Fission hypothesis

Earth spun so fast that it spun off the moon

• fallen out of favor because not possible

Sister hypothesis

Earth and moon formed simultaneously

• could be possible, but if they are formed from the same material then why are they not the EXACT same composition?

Capture hypothesis

Earth captured the moon (orbits weren’t quite circular, then the moon came by and captured it with its gravity)

• less likely because why does the outer part of the moon have similar composition to earth?

Giant impact hypothesis

Moon formed from the debris of a collision between the proto-earth and another protoplanet

Clues that moon is from the earth

Composition of moon is very similar to earth’s mantle, but moon lacks the metal core that the earth has

What is the most likely explanation for the origin of the earth

Moon formed from the debris of a collision between the proto-earth and another proton-planet

Steps of giant impact hypothesis

• during middle to late stages of earth’s accretion, about 4.5 billion years ago, a Mars sized body impacted the earth

• The giant impact quickly propelled a shower of debris from both the impacted and earth into space

• Impact sped up earth’s rotation and tilted earth’s orbital plane

• Earth reformed as largely molten body

• Moon aggregated from the debris

• Ancient moon rocks brought back by the Apollo astronauts support the impact hypothesis

Collisions help explain…

Things that may seem to contradict the solar nebula hypothesis

Things that contradict solar nebula hypothesis

• earth has a large moon, unlike most terrestrial planets, so it was most likely created by a giant impact

• Some planets seem to rotate in the opposite direction

• Earth (a terrestrial planet) have water: water and other hydrogen compounds possibly brought to terrestrial planets by impact of icy planetesimals

What other hazards are there in the solar system

The sun

Characteristics of the sun

• a star!

• 93 million miles away from earth (much closer than other stars but still very far)

How far is the sun? In context?

• a modern commercial jetliner would take more than 17 years to travel from earth to the sun

• A manned spaceship, like the ones that took astronauts to the moon, would take more than two years

• Light travels at the ridiculously fast speed of 186,000 miles/sec. Even then, light takes 8 minutes 19 seconds to make the trip from the sun to the earth

Diameter of sun compared to earth

Diameter of sun is 109 times the diameters of earth (can stack 109 earths to reach height of the sun)

How many earths can fit inside the sun

1,300,000