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 !