Alejandro García

Piedras del Cielo
Alejandro García
Universidad de los Andes
Bogotá, Colombia
Charla Pública, AdeLA 2014
Planetario de Santiago, Chile, 30 de septiembre de 2014
ADeLA2014
Astronomía Dinámica en
Latino-América
Colombia
z
Bogotá
BOG-SCL
4247 km
Colombia
Bogotá
8'000.000 hab.
Departamento
de Física
Grupo de
Astronomía
http://fisica.uniandes.edu.co
Motivación
Distribución de Impactos en la Tierra
Distribución de Impactos en la Tierra
Distribución de Impactos en la Tierra
KNOWN IMPACTS ON THE EARTH
METEOR CRATER ARIZONA
Classic meteorite crater, 1 km wide, 185 m deep.
Known to to be a meteorite crater for the following reasons:
1 Steep sides and closed, 2 Rim uplifted and tilted away from center
3 inverted piles of rock found outside the crater, 4 large blocks of limestone
found outside crater, 5 Crater has 265 m of shattered rock, 6 Numerous
pieces of nickel-iron found in the area and 7 High P/T rocks including fused
sandstone and shatter cones.
30 m diameter meteorite about 50,000 years ago.
KNOWN IMPACTS ON EARTH
THE CRETACEOUS/TERTIARY BOUNDARY EVENT
Chicxulub structure
Around world at K/T boundary found
large amounts of Iridium.
Rare on Earth. Common in meteorites.
Suggested meteoritic collision with
the Earth.
Evidence suggested came down in the
Caribbean.
Circular gravity anomaly off the tip of
the Yucatan Peninsula.
PMEX had drilled exploratory holes in
the area which had encountered
shattered rock and glasses
Geophysical surveys shoed circular
structures at depth.
Seismic data showed an inner and
outer ring of 80 and 195 km
diameter.
Gravity and magnetic structures show
some opening to the North west.
Suggests a 10 km asteroid slammed
into the Earth at a 20 - 30 degree
angle 64.98 Ma
ENVIRONMNETAL EFFECTS IMPACTS
CRATER FORMING PROCESS
Comet or Asteroid hitting the Earth
Large meteorites form complex craters
1
incoming meteoroid hits earth at
speeds as high as 30km/sec
2
Impact shock creates high P & T
that vaporizes most of the crater
rock and the meteoroid
ENVIRONMENTAL EFFECTS IMPACTS
CRATER FORMING PROCESS
Comet or Asteroid hitting the Earth
1
The release wave following the
shock wave causes the center to
rise.
1
The fractured walls slide into the
crater producing wider and
shallower rim.
Outer walls can have a diameter 100
times the depth.
ENVIRONMENTAL EFFECTS IMPACTS
PROBLEMS FOR LIFE FROM IMPACTS
Impact of K/T asteroid had major effects on surface temperature.
First, a fireball and hot gases that lasted many hours. Second, temperatures
dropped to winter conditions as dust and ash blocked out sunlight. Third,
after dust settled C02 remains aloft creating greenhouse warming of 10o C.
Also have major 300 m tsunami and a huge steam bubble.
EVENTS OF THE TWENTIETH CENTURY
COMET EXPLOSION
Tunguska, Siberia 30 June 1908
Strange event in unpopulated Siberia.
Massive fireball exploded 8 km above
ground.
Produced very bright light in northern Europe.
Found all the trees in a 30 x 30 km area
knocked down.
No impact crater or even broken ground. 30 to
50 m meteorite exploded above ground.
Expedition in 1958 found evidence of melted
iron and silica rich rock.
If over Washington do tremendous damage.
30 de junio de
1908
1921
EXPEDICIÓN
Distribución de Impactos en la Tierra
574 REGISTROS EN CHILE
EVENTS OF THE TWENTIETH CENTURY
BIGGEST NEAR EVENTS
Meteor/Asteroid diameter, crater size and life
Beyond 100 m diameter meteoroids have a devastating effect on life
EVENTS OF 20TH
CENTURY
BIGGEST NEAR EVENTS
Assessing Hazards
Have Torino scale which assesses
hazards on a 0 - 10 scale.
Enables calm communication about the
threats.
Escala de Torino
FREQUENCY OF LARGE IMPACTS
Over 2000 NEO’s. 25-50% will
eventually hit the earth.
Average time between impacts is
100,000 years.
Risk being killed by impact is 1 in
20,000. High because a huge
number of people 1.5 Billion will be
killed in an impact.
ANNUAL RISK OF DEATH
Asteroids
●
●
●
●
All planets and moons have
been modified chemically and
geologically.
Where do you look for a piece
of the original “stuff” of the
solar system?
Asteroids and comets.
Small objects
– Little internal heat, little to no geological activity.
– Little gravity, little to no atmosphere.
Orbits
1. Asteroid belt.
2. Same as Jupiter, but
separated by 60º Trojans
3. Elliptical orbits that pass
Earth
• Earth-crossing asteroids:
– Near-earth asteroids
(NEAs)
– Near-earth
objects (NEOs)
Asteroid sizes
●
How big are they?
– Largest (Ceres) is 940 km in diameter
– Three larger than 500 km
– About a dozen larger than 250 km
– Number increases rapidly with decreasing size
●
Total volume of all asteroids ~ much smaller than moon.
Asteroid Encounters
●
fly-bys of asteroids:
– Gaspra by Galileo in 1991
– Ida by Galileo in 1993
– Mathilde by NEAR in 1999
●
orbiters:
– Eros by NEAR in 2000
– Itokawa by Hayabusa in 2005
Eros
Eros
Itokawa
Density
●
Calculate Density
●
Rock ( ~ 3g/cm3) vs. metal (~7g/cm3).
●
Solid vs. rubble pile.
●
Ida = 2.6 g/cm3
●
Eros = 2.4 g/cm3
●
Itokawa = 1.9 g/cm3
●
Mathilde = 1.5 g/cm3
●
Eugenia = 1.12 g/cm3
Meteorites
Primitive
Processed: stony-iron
Processed: iron
Peekskill Meteorite oct 1992
Copyright – Anne Arundel (1992)
http://www.youtube.com/watch?v=B17TmSSb5aI
Peekskill Meteorite oct 1992
$125 por gramo
Forming Doublets
●
●
●
●
Random impacts (unavoidable)
Very oblique impacts, ricochet (Messier,
Messier A)
Endogenic crater formation (volcanoes,
collapse pits, etc.)
Atmospheric break-up, explosion
(Henbury)
●
Tidal break-up (Shoemaker-Levy 9)
●
Spatially clustered secondaries
●
Impact of binary asteroid or comet
Physical Properties of
Decameter-scale Asteroids
http://www.oosa.unvienna.org/oosa/e
n/COPUOS/stsc/wgneo/index.html
Systems Engineering Approach to
the Mitigation of Hazardous NearEarth Objects (NEOs)
Brent William Barbee, M.S.E.
Emergent Space Technologies, Inc.
July 11th, 2006
NEO Deflection Methods
●
Deflection is the preferred mode of mitigation.
– Most practical mitigation mode, given current and foreseeable
technology.
• Energy requirements are tractable for a wide range of
NEOs.
– Most controllable, generally.
• With practice we can develop proficiency and learn
the pitfalls.
– This is absolutely critical if we are to be prepared.
NEO Deflection Methods
●
Deflection has its difficulties:
– Rubble piles or highly porous NEOs.
– Some proposed deflection systems are very challenging
to implement due to:
•
•
•
•
Anchoring to NEO surface.
Complex proximity operations about NEO.
NEO spin state.
Long periods of operation on orbit in hostile space environment.
– Higher probabilities of failure.
– All proposed systems are currently untested.
NEO Deflection Methods
●
Some possible deflection systems:
– Gradual
• Solar concentrators
• Attached low-thrust thrusters
• Gravity tractor
– Impulsive
• Kinetic impactors
• Attached high-thrust thrusters
• Nuclear explosives
– Standoff blast
– Surface blast
NEO Deflection Methods
●
Nuclear explosives offer the following advantages:
– NEO spin state not a factor.
– No anchoring of equipment to NEO.
– No long operation on orbit.
– Highest available energy density.
• High capability for imparting momentum to a NEO.
– High energy density equates to easier launch from Earth.
• Multiple launches are more feasible.
NEO Deflection Methods
– High momentum transfer performance:
• Can adequately deflect larger NEOs than other
methods even with limited warning time.
– Technology is currently available.
– Puts former weapons of mass destruction to a use that benefits all
humankind.
– Deflection is relatively controllable through proper positioning of the
device prior to detonation.
NEO Deflection Methods
●
Nuclear explosive disadvantages:
– Untested.
– Required rendezvous and proximity operations are challenging in
some cases.
– Requires special packaging inside launch vehicle to ensure
containment in the event of launch vehicle failure.
– Danger of inadvertently fragmenting NEO in an undesirable fashion.
NEO Deflection Methods
– Sensitive to NEO physical properties.
• In the absence of good knowledge of NEO physical
properties, the system must be over-designed.
– Requires amendment of the “Nuclear Test Ban Treaty” (1963).
– Public fear and misunderstanding.
– Political tensions.
NEO Deflection Methods
●
Standoff nuclear detonation:
– Nuclear device of proper yield is
placed at the optimal detonation
coordinates.
• Optimal distance from NEO
surface.
• Optimal orientation of imparted
impulse vector.
– Neutrons from the explosion
penetrate 10-20 cm into NEO
surface, superheating a thin shell of
NEO material.
– Material blows off and imparts
momentum to NEO.
NEO Detection
●
NEO discovery and cataloguing:
– Detection and observations:
•
•
•
•
•
LINEAR
NEAT
LONEOS
Catalina Sky Survey
Spacewatch
http://www.ll.mit.edu/LINEAR/
– Tracking and threat characterization:
• Near-Earth Asteroid Tracking (NEAT) program at JPL
• Near-Earth Objects Dynamic Site (NEODyS) in Pisa, Italy
NEO Detection
Catalina Sky Survey
NEO Detection
NEO Threat Characterization
●
Palermo Scale
P=log 10
PI
P B ΔT
( )
- Palermo Scale Value
P I - Probability of Impact
Background Probability of Impact
P B- Annual
for a NEO with Same Kinetic Energy
ΔT - Time in Years Before Impact
Tipos de Meteoritos
• Types – just like asteroids!
– stony (incl. carbonaceous chondrites)
– irons & iron / nickel (90% / 10%)
– stony-irons (a combination of
materials)
– the type of meteorite tells you where it
came from.
61
•Meteoritos rocosos (difíciles de encontrar)
62
•Meteoritos ferrosos (fáciles de encontrar)
63
•Meteoritos carbónicos
64
•Meteoritos ferro-rocoso-cristalinos
65
Los meteoroides se formaron en
cuerpos mayores (planetesimales)
Rocosos se forman en el manto
Ferrosos se forman en el núcleo
66
Los meteoroides provienen de la
materia condensada más temprana en
el sistema solar. Ellos nos dan la
composición química de los primeros
planetisimales.
La mayoría tienen una edad ~ 4.6
millones de años.
67
Cinturón de Asteroides
En general, a las afueras de la órbita
de Marte, 2.7 a.u. distancia media.
La masa total de todos los asteroides
es <5% de la masa de la Tierra.
68
4
69
5
Clases de Asteroides
• S – Rocoso (Stony)
• C – Carbonaceo (Carbonaceous)
(asteroides rocosos con superficies
oscuras y cavidades interiores)
• M – Metálicos (Metallic) (poco
frecuentes)
70
8
Asteroides Rocosos
Gaspra – a typical stony asteroid
71
9
Se piensa que algunos asteroides son
Pilas de escombros que se mantienen
unidas debido a su baja gravedad.
72
10
Vesta
P=5.3h
73
12
Asteroides mayores
• Vesta – más pequeño (R=250 km), pero
mucho más brillante. Apenas visible a
simple vista.
• Pallas
• Juno
74
14
Toutatis - uno de los más cercanos!
Toutatis gira sobre 2 ejes.
De 5 km. Pasó tan sólo a 29 distancias lunares
de la tierra en 2000.
75
19
Comet Shoemaker-Levy 9 broke into a
series of fragments before impacting
Jupiter. (1994)
The ‘fireball’
from each
impact was
larger than
the earth.
76
39
An atmospheric “scar” left by the impact
of Shoemaker-Levy 9. These faded after
several weeks.
77
40
http://www2.jpl.nasa.gov/sl9/image81.html
79
46
80
47
Comet particles
trapped in the
aerogel (a light
silicon gel).
81
50
Misión Rosetta
• Rosetta – launched 2004 to comet 67P/Churyumov-Gerasimenko. Rosetta
will fly along with the comet for 2 years as it approaches the sun, beginning
in 2014. It also has a small lander which will explore the comet’s nucleus.
• http://sci.esa.int/where_is_rosetta/
82
52
Asteroid observations
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
ASTEROIDS
# Observations of 1980 Tezcatlipoca at OHP
# Two nights: 25/07/2006 (63 frames), 30/07/2006 (55 frames)
# Telescope: 1.20 cm
# Detector: CCD TK1024
# Filter: R
# Exposure time: 120 s
PHYSICAL CHARACTERIZATION OF ASTEROIDS: PHOTOMETRY
ASTEROIDS
# Selected reference stars and asteroid (1980
Tezcatlipoca)
LOWELL OBSERVATORY
LONEOS Schmidt telescope
Detección NEO's
http://www2.jpl.nasa.gov/sl9/image81.html
Detección NEO's
http://www2.jpl.nasa.gov/sl9/image81.html
Detección
Detección/ Falsos +
Detección
ESO/
PARANAL
Detección
Gaia
Detección
ALMA
Preguntas
http://www2.jpl.nasa.gov/sl9/image81.html