Post on 01-Jan-2016
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PTYS 214 – Spring2011
Homework #7 available for download from the class websiteDue Tuesday, Mar. 29
Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214/
Useful Reading: class website “Reading Material” http://en.wikipedia.org/wiki/Near-Eart_object http://neo.jpl.nasa.gov/stats/ http://users.tpg.com.au/users/tps-seti/swaprock.html
Announcements
Extra Credit Presentation
Sara Cohen
Viktoriya Stoeva
Where did the K/P impactor come from?
Asteroids: small bodies that are made of rock - Located in the Asteroid Belt (between Mars and
Jupiter)
Comets: small bodies made of rock and ice (“dirty snowball”) - Located in the Oort Cloud and in the Kuiper Belt
Inn
er
SS
Ou
ter
SS
Jupiter
Comets Among the oldest bodies in the
solar system
Origin: Kuiper Belt or Oort Cloud (outskirts of the Solar System)
Contain organic material
Very porous objects rich in ices
We do not know a lot about them
First samples: 2006 Stardust Mission! Comet dust resembles asteroid material
Comet Wild 2
A natural experiment: Impact of Comet SL9 Comet Shoemaker-Levy 9 was torn into pieces as a result of a
close approach to Jupiter in July 1992
Discovered in 1993, it collided with Jupiter at a speed of 60 km/s (135,000 mi/hr!) during the third week of July 1994
HST, July 27, 1994
Plumes thousands of km high! Dark “scars” lasted for months
HST, May 1994
Near Earth Objects (NEOs)
Known asteroidsJupiter’s orbit
Mars’ orbit
Ecliptic
Main Belt
Near Earth Objects (NEOs)
NEOs rarely get close to Earth enough to be
considered a major hazard
Asteroids in the neighborhood of the Earth, called
Near Earth Objects (or NEOs)
But the possibility exists!
Peekskill Meteor, 9 Oct. 1992 – 40 seconds of glory!Peekskill Meteor, 9 Oct. 1992 – 40 seconds of glory!
NEOs are potentially hazardous
Peekskill Meteorite
June 30, 1908The Tunguska Event
- The atmospheric shock wave knocked people off their feet and broke windows up to 650 km (400 miles) away
- For few weeks, night skies were so bright that one could read in their light
Early morning:
A big fireball raced through the dawn sky over Siberia (Russia)
It exploded in the atmosphere over the Tunguska region with an estimated force of 1,000 Hiroshima bombs
Tunguska: No crater! 1927: The first expedition to the site found a region of
scorched trees about 50 km across and no crater!
- Most trees had been knocked down pointing away from the center (“ground zero”)
What happened? It was the airburst of a meteor 6 to 10 kilometers above the
Earth's surface
Near ground zero, trees were knocked down by the shock wave produced by a large explosion, similar to the effects observed in atmospheric nuclear tests in the 1950s and 1960s
Alternate Explanation: the Tunguska event is the result of an exploding alien spaceship or an alien weapon going off to "save the Earth from an imminent threat"
No evidence was ever found by UFO sympathizers…
Asteroids Hazard
1 MT= 1 Mton TNT equivalent= 4.21015 J
Bolides (energy <5 MT; D< 30 m ) – no crater Great fireworks display (“shooting stars”), no damage
Small Impact (<15Mt; D< 50 m) – crater ~1 km Damage similar to large nuclear bomb (city-destroyer) Average interval for whole Earth: >1,000 years
Local catastrophes (<10,000 MT; D<250 m) – crater ~10km Destroys area equivalent to small country Average interval for whole Earth: >100,000 years
Global catastrophe (>106 MT; D>1 km) – crater >50 km Global environmental damage, threatening civilization Average interval for whole Earth: >1 million years
Terrestrial Impact Frequency
year
century
million yr
billion yr
10,000 years
100 millionmillion10,00010010.01
Hir
os
him
aTunguska
End-Cretaceous
TNT equivalent yield (MT)
Global catastrophe(for human civilization)
Tim
e Meteor Crater
1 MT= 1 Mton TNT equivalent= 4.1861015 J
Spaceguard Program
D>1 km
Goal: Find 90% of NEAs
with D > 1 km
by the end of 2008
Mar. 16, 2011: 822 discovered
(>85%)
In the United States it is funded by NASA
Comparison with Other RisksStatistical risk of death from impacts: 1 in a million per
year (about 1:20,000 over a lifetime)
Much less than auto accidents, shootings (in U.S.)Comparable with other natural hazards (earthquakes, floods)
It is a different kind of risk! Average interval between major impact disasters is larger
than for any other hazard we face (millions years) A single event can kill millions of people (and other living
things) ! Unique as major threat to civilization (comparable to a
global nuclear war)
Impact cratering is normally regarded as a destructive process, dangerous
for life…
… but is it always that way?
Impacts eject material at high speed
Could an impact eject material into space?
Could it eject rocks with LIFE into space?
Could microbes contained in ejected rocks be ejected
alive?
Nicholson et al. (2009) Bacterial spores survive hypervelocity launch by spallation: Implicatons for lithopanspermia, 27th Lunar Planet. Sci. Conf.
YES!
Near-surface rocks can be ejected at high
speed without serious damage (low shock)
Microbes could be transferred from one large body to another, but they
must survive a host of hazards!
1. Launch
2. Space exposure
3. Landing
Material ejected from planets in large
impacts wanders around the solar
system, rather than traveling directly from
planet to planet
Reaching another planet may take tens of millions of years!
Can life survive this long without
nurishment?
Spore-forming bacteria are tough
Spore-forming bacteria Bacillus Subtilis survived a 6-years spaceflight, experiencing
vacuum, cold, lack of water and radiation
Science 268 (1995) 1060-1064
Dormant microbes may survive for tens of millions of years
(can contamination really be ruled out?)
Some micro-organisms can tolerate a lot of cosmic
radiation, but not much UV, so they have to hide in rocks
Deinococcus Radiodurans
Listed in The Guinness Book of World Records as the world’s
toughest bacterium
Surviving reentry and landing is difficult
…yet meteorites contain fragile organic molecules like amino acids !
So, It is highly probable that viable microbes could be carried from Earth to Mars or vice versa
Quiz Time !