1. Potential Earth
Hazardous Objects
Dhani Herdiwijaya
Astronomy Research Division, Institute Technology Bandung
Email: dhani@as.itb.ac.id
Training Course on Earth and Space Science for Sustainable
Development, Bandung, 5-11th June 2011

2. Overview
 Small Bodies of the Solar System
• Comet
• Asteroid
• Meteoroid
 NEO and PHA
 Detection, Characterization, and Mitigation
 Conclusions

3. Small Bodies of the Solar
System
1

4. Raw materials
 Comets, asteroids, and meteors are the
remaining leftovers from the formation of
the solar system.
 Their chemical compositions and
distribution yield clues as to how the
solar system formed.
2

5. Small Bodies
Photograph of a meteor entering
 Comet: large and old rocky body Earth’s atmosphere.
 Asteroid: Small rocky body orbiting the Sun.
 Meteoroid: Small particle from a comet or asteroid orbiting
the Sun.
Friction due to the Earth atmosphere
 Bolide:
• Extraterrestrial body that collides with Earth, or
• Exceptionally bright, “fireball” meteor.
 Meteor:
• The streak of light created in the sky when an asteroid enters
Earth’s atmosphere.
 Meteorite:
• Solid remains of a meteoroid that survives atmospheric
passage and lands on Earth’s surface intact.

6. Comets
 Structure
 Orbits& Types
 Oort Cloud vs. Kuiper Belt
 Famous Comets
 What message do they convey?

7. 31

8. Comets Origins
 Primordial gas, dust, and ice frozen in clumps at
the outer limits of the solar system
• Kuiper belt--out to 500 AU
• Oort Cloud--50,000 AU
 Occasionally perturbed into elliptical orbits
approaching the Sun

9. Comet Origins & Orbits
 Kuiper Belt
• Short period comets (return <200 yrs)
• 50 to 200 A.U.
• Several billion comets
• Cometary orbits are more often near the
ecliptic, but may be prograde or
retrograde.
33

10. Comet Origins & Orbits (2)
 Oort Cloud
• Long period comets (return >200 years
or may only pass by sun once)
• Spherical shell of matter up to 2 light
years (65,000 A.U.) in radius.
• Trillions of comets
• Comets may come in from any direction,
with prograde or retrograde orbits.
34

11. 35

12. Comet Structure
 Nucleus
• Water ice, frozen CO , N , methane,
2 2
ammonia, HCN, (CN)2 (cyanogen), amino
acids, sugars all detected.
• Embedded with rocks and dust
• Extremely dark, tarry surface.
 Coma
• Envelope of water vapor and H 2 around
nucleus

13. Comet Structure (2)
 Ion
tail – ionized gas pushed directly
away from the sun by solar wind.
 Dusttail – heavier particles that follow
along behind the path of the comet.
• The dusty path of a comet lingers for
decades, even centuries. When the earth
passes through the dusty path again later, a
meteor shower is produced.

14. Structure
Dirty Snowballs

15. Dust tail
Ion or plasma tail

16. Nucleus of Halley’s Comet
Sunlight causes
Jets of gas
jets of gas to
spew from
the comet’s
nucleus. This
creates the
coma.
Photo by Giotto spacecraft •Dark, tarry organic coating
(ESA)

18. Halley’s comet
1986

19. Halley’s Comet Orbit
•Many comets have retrograde orbits

20. Comet Hale Bopp, 2002

21. Missions to Comets
 There have been 11 past missions to comets,
with 2 current missions.
 Giotto – examined Halley’s comet in 1986.
Photographed the nucleus from a distance of
only 200 km, then continued on to comet
Grigg-Skellerup in 1992.
 Deep Impact – launched a 350 kg copper
impactor into the nucleus of comet 9P/Tempel
1, in July, 2005.
• A 100 m x 25 m crater was created.

22. Comets Demise
 Comets eventually
• breakup into smaller fragments (Comet
West below)
• evaporate
• collide with the sun
• collide with other planets

23. Comets Demise: Sun grazer

24. Comet Shoemaker-Levy 9 fragments impact
Jupiter, July 16-22, 1994
 ‘Bull’s eye’
on Jupiter
larger than
Earth; first
evidence of
water in the
jovian
atmospher

25. Comets Demise: Shoemaker-Levy

26. Asteroids

27. Comets and Asteroids
 Comets:
• Have very eccentric, longer orbit periods.
• Can be more difficult to detect if far from the
Sun.
• Are much less numerous than Near-Earth
Asteroids (NEAs).
• Exhibit jets of volatiles due to heating when in
proximity to the Sun.
 Near-Earth Asteroids:
• Orbits are within region of inner planets.
• No volatiles.
• Very numerous:
• Thousands with mean diameter > 1 km.
• Possibly millions with mean diameter of a few
hundreds of meters or less.

28. Ceres – largest, (1030 km). Named
after the Roman goddess of the
harvest (cereal). Recently named a
dwarf planet.

29. Asteroids – rocky leftovers of the
inner solar system
 Location
• Asteroid Belt
• Trojan or Lagrange Asteroids
• Random Orbits
 Types of Asteroids
 Minor planets
 NEO’s

30. Asteroid belt
 Generally, just outside Mars’ orbit
 2.7 A.U. average distance
 Total mass of all asteroids is
<5% of the earth’s mass (2 to 4 of
our moons.)

31. The so-called Main Belt of
asteroids lie between the orbits of
Mars and Jupiter, with semi-major
axes 2.2 to 3.3 AU.

32. Orbits: Gaps
• In the main belt, orbital distances are not distributed evenly.
Picture: JPL/SSD Alan B.
Chamberlain

33. Asteroid orbit classifications
 Earth-crossing:
• Apollos
• Semi-major axis > 1.0 AU
• Perihelion distance < 1.107 AU
• Atens
• Semi-major axis < 1.0 AU
• Perihelion distance > 0.983 AU
 Mars-crossing:
• Amors
• 1.3 AU > perihelion distance > 1.017 AU

34. Lagrange Asteroids
 Clusters of asteroids co-orbit with the gas
giant planets, 60o ahead and 60o behind the
positions of the planets.
 The clusters are centered on the L4 and L5
Lagrange points (points in space where
Jupiter’s gravitational influence equals the
sun’s gravitation.)
 Jupiter’sLagrange asteroids are known as
the Trojan asteroids.

36. By the Number s
• Ceres, the largest asteroid is just less than 1000
km in diameter.
• Total mass of all asteroids is 3x1021 kg:
= 1/2000 mass of Earth
= 1/20 mass of Moon
• We probably now know all asteroids larger than 25
km across, and 50% of the ones down to 10 km in
size.
• There are an estimated 100,000 asteroids larger
than 1 km in size.

37. Expected Population
• What do we expect in terms of numbers of asteroids of
different sizes?
 More small ones?
 More large ones?
 Equal numbers in each size range?
• Scientists predict that fragmentation processes would
produce equal masses of material in each size range.
• But, a 10 km diameter object has 1000 times the volume
(mass) of a 1 km diameter object.
• So, if there is equal mass in each range, then we expect
1000 times as many objects of 1 km diameter as 10 km
diameter.

38. Asteroid Size Distribution
• In mathematical notation, we
expect the number of objects of a
given diameter D to be inversely
proportional to the volume (cube
of diameter):
Expect: 1
N∝ 3
D
• In fact we find that: 1
N ∝ 2.3
D
• Therefore proportionally more of
the mass in the larger objects.
Picture: Tom Quinn and Zeljko Ivezic, SDSS
Collaboration

39. Sizes and Masses
• Because most of the total mass is contained in the
larger bodies, we can estimate the overall mass of the
main asteroid belt quite well.
• How do we describe average size in the distribution of
this type? Most asteroids are still small, but most of the
mass is in the larger ones.
• Until about 1975, asteroids were mostly unresolved,
star-like points in the sky. We were largely restricted
to:
1. charting their orbits, and
2. measure their rotation rates, by observing
periodic changes in brightness (think of a police
light).

40. Obser ving From Ear th
• Two of the most interesting challenges for asteroid scientists
were to measure:
1. the actual sizes, and
2. the reflectivity.
• One method we can use to determine the size is to watch as
asteroid passing in front of (‘occulting’) a bright background
star.
• If we observe the shadow of the asteroid simultaneously from
various points on the Earth, we can deduce the size and
possibly the shape.
• This technique was first used to measure the size of asteroid 3
Juno on Feb 19th 1958 in Malmo, Sweden (P. Bjorklund and S.
Muller).
• Is this likely to work for very many asteroids?
(about 350 have actually been observed, most in the last 5
years, since Hipparcos).

41. Picture: David Dunham/IOTA Movie: Rick

42. Types of Asteroids
 Asteroid composition classifications:
• Wide variety of spectral classifications, but there are
three main types:
• S-(Stony) type
• Silicaceous, majority of inner asteroid belt
• Iron mixed with iron- and magnesium-silicates
• M-(Metallic) type
• Metallic iron, most of middle asteroid belt
• C-(Carbonaceous) type
• Carbonaceous, 75% of known asteroids

43. Spectroscopy: Composition
• Spectroscopy is also useful in determining composition,
although the spectral features of minerals are much less
sharp than the spectral lines seen in gases (atmospheres).
• This figure shows spectral
data of bright and dark
terrain on asteroid 433
Eros, as measured by the
NEAR spacecraft.
• The spectra are similar in
some respects to primitive
meteorites, but
differences in composition
remain to be explained.
Figure: from Clark et al 2001

44. Stony Asteroids
Gaspra – a typical stony asteroid

45. Some asteroids are thought to be rubble
piles held together by very low gravity.

46. Major Asteroids
 Vesta – smaller (450 km diameter),
but much brighter. Barely visible to
naked eye.
 Pallas
 Juno

47. Vesta shows signs of having been molten
at one point in its history.

48. •Surprisingly, this asteroid has its own little moon !

49. Toutatis – one of the closest !
Toutatis spins on 2 axes.
5 km long. Passed just 29 lunar distances
from the earth in 2000.
19

50. Meteoroids – asteroids on a
collision … with us!
 Meteor – the trail of light & ionized
gas left by a meteoroid
 Meteorite – what’s left of a
meteoroid that hits the Earth.
 Bolide – a fireball or especially
bright meteor.

51. Types of Meteorites
 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.

52. •A stony meteorite (hard to find)

53. •An iron meteorite (easier to find)
Where the formation of Iron element occurs ?

54. Meteoroids were formed in
parent bodies (planetessimals)
 Stonies were formed in the:
mantle
 Irons were formed in the:
core

55. Meteoroids – early planet stuff
 Meteoroids come from the earliest
condensed stuff in the solar
system. They give us the
chemical composition of the
earliest planetissimals.
 Most are about 4.6+ billion years
old ~ the age of solar system

56. NEO and PHA

57. Near-Earth Objects
 Near-Earth Objects (NEOs) are comets and
asteroids that have been nudged by the
gravitational attraction of nearby planets into
orbits that allow them to enter the Earth's
neighborhood within ~ 45 million km of
Earth’s orbit
 Composed mostly of water ice with
embedded dust particles, comets originally
formed in the cold outer planetary system
while most of the rocky asteroids formed in
the warmer inner solar system between the
orbits of Mars and Jupiter.

58. Potentially Hazardous Asteroids
 Potentially Hazardous Asteroids (PHAs) are defined based on
parameters that measure the asteroid's potential to make
threatening close approaches to the Earth. Specifically, all
asteroids with a minimum orbit intersection distance (MOID) of
0.05 AU or less and an absolute magnitude (H) of 22.0 or less
are considered PHAs. In other words, asteroids that can't get
any closer to the Earth (i.e. MOID) than 0.05 AU (roughly
7,480,000 km) or are smaller than about 150 m in diameter
(i.e. H = 22.0 with assumed albedo of 13%) are not considered
PHAs.
 This ``potential'' to make close Earth approaches does not
mean a PHA will impact the Earth. It only means there is a
possibility for such a threat. By monitoring these PHAs and
updating their orbits as new observations become available, we
can better predict the close-approach statistics and thus their
Earth-impact threat.

59. How Many Near-Earth Objects
Have Been Discovered So Far?
 8074 Near-Earth objects have been
discovered.
 829 of these NEOs are asteroids with a
diameter of approximately 1 km or larger.
 1232 of these NEOs have been classified
as Potentially Hazardous Asteroids (PHAs)
(updated May 31, 2011 from http://neo.jpl.nasa.gov)

60. NEO properties and size
Physical properties
 Mass
 Density
 Porosity
 Internal structure
and composition
 Surface chemical
composition
 Spin state

61. Near-Earth Objects (NEOs)
 Asteroids and comets whose orbits are
in close proximity to Earth’s orbit.
• When the phasing is right, such NEOs will
closely approach Earth.
•
Galileo Photograph of Asteroid Gaspra
Potentially Hazardous Asteroids (PHAs) taken October 29st, 1991
have orbits that come to within 0.05 AU of
Earth’s orbit.
 If a NEO’s orbit intersects that of Earth,
a collision is possible.
• Depends on phasing (timing).
• Annual meteor showers are caused by Earth Photograph of Comet Linear
C/2002 T7 [May 2004]
passing through the paths of comets.

62. NEO Search and Mitigation Study
Milestones
1992 - NASA recommends six 2.5 m telescopes with
limiting magnitude = 22 to enable the discovery of 90%
of NEOs larger than 1 km within 25 yrs.
1995 – NASA sponsored “Shoemaker Report,” which
recommends the discovery of 90% of NEOs (D > 1 km)
within 15 years.
2003 – NASA recommends extending
search down to D~140 m

63. The Tidal Wave of PHA Discoveries
 NASA’s report (3/2007) to Congress outlined several
search techniques (optical & space-based IR) that could
carry out the next generation of search.
~50 times the current data flow
~17,000 PHA discoveries
D>140 m (83% complete)
~80,000 PHA discoveries
D>50 m (~40% complete)
≥10 times the current rate
for Earth impactor warnings

64. NEO internal structure
 Monoliths or rubble piles?
• A rubble pile is a non-cohesive (strengthless) asteroid
held together only by gravity.
• Ground observations of spin rates show that most
asteroids are not required to be solid.
• However, this is not conclusive evidence that such
asteroids are in fact rubble piles.
 Solid asteroids are more susceptible to
mitigation techniques that rely on deflection,
particularly impulsive deflection.
 Porous asteroids may be more difficult to
deflect.

65. Craters on the Earth
 Earth’s geologic record (surface
and strata) shows evidence of
many impacts, ranging in size from
small to extinction-level events.
• Most craters on Earth’s surface are
masked by weathering and foliage.
• Shocked quartz is a telltale sign
of an impact site.
• Examples:
• Barringer crater in Arizona
• Chicxulub in the Yucatan
peninsula
• Newly discovered Wilkes Land
crater in Antarctica.

66. Craters on the Earth
 Barringer crater in Arizona:
• ~ 50,000 years ago.
• 55 km east of Flagstaff, near
Winslow.
• 1200 m wide, 170 m deep.
• Caused by a nickel-iron meteorite
~ 50 m in size.
• 2.5 Megaton explosion:
• All life within 4 km killed instantly.
• Everything within 22 km leveled.
• Hurricance-force winds out to 40
km.

67. Craters on the Earth
 Chicxulub crater:
• Cretacious/Tertiary (K/T) boundary extinction
event.
• ~ 65 million years ago
• More than 70% of species made extinct, including the
dinosaurs
• Caused by the impact of a 9 – 19 km diameter NEO in
the Yucatan Peninsula near Chicxulub
Map Showing The Yucatan Location Detailed Enhanced Image Showing Topographic Enhanced Image of the
the K/T Crater Edge 180 km wide, 900 m Deep K/T Crater

68. Craters on the Earth
 Newly discovered Wilkes Land
crater in Antarctica.
• ~ 480 km wide
• Believed to have been
caused by a NEO up to 48
km in mean diameter.
• Likely cause of the Permian-
Triassic extinction 250 million
years ago.
• Confirmation pending.
 If so, the impact killed off most
life on Earth at the time. Ohio State University
• Eventually allowed dinosaurs
to flourish.

69. ~1/2 mile across; 300,000 years old, W. Australia
Wolfe Creek Also associated with many small iron meteorites

70. Simple vs. Complex Craters
 Simple bowl structure
 Diameter is 15-20 times
diameter of impacting
object
 All less than 1-2 miles
across on Earth
 Complex structure with
central peak, peak ring,
or multiple rings
 Melt sheet generated
and thick breccia lens
 Terraced, collapsed
walls; about 10x
impactor diameter

71. 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

72. ENVIRONMENTAL EFFECTS IMPACTS
CRATER FORMING PROCESS
Comet or Asteroid hitting the Earth
3 The release wave
following the shock
wave causes the center
to rise.
4 The fractured walls
slide into the crater
producing wider and
shallower rim.
Outer walls can have a
diameter 100 times the
depth.

73. Periodic Extinction?
 Researchers have found
patterns of periodic
extinction in the fossil
record.
• 62 ± 3 million years
• 140 ± 15 million years
 Cause for some periodic
extinctions may be NEO
impacts.
• NEO impact did cause
the K/T boundary
extinction ~65 million
years ago. Rohde & Muller, Cycles in Fossil Diversity, Letters to Nature, vol. 434, pgs. 208-210

74. Famous “Near Misses”
 Meteoroid 2004 FU 164
 Discovered on 31Mar04
• Crossed Earth’s orbit same night
• 6m in diameter
• Closest approach was 6,400 km
• Closest approach ever recorded
• Would have burned up in the upper atmosphere

75. Famous “Near Misses”
 Aten 2004 FH
 Discovered on 15Mar04
• Crossed Earth’s orbit on 18Mar04
• 30m in diameter
• Closest approach was 43,000 km
• Geosynchronous satellites at 35,790 km
•2 nd
closest approach ever recorded
• Next approach in 2044

76. Famous “Near Misses”
 Apollo 4581 Asclepius (also 1989 FC)
• Discovered on 31Mar89
• Crossed Earth’s orbit on 22Mar89
• 300m in diameter
• Closest approach was 700,000 km
• Missed a direct hit with Earth by 6 hours

77. Apophis
Asteroid 99942 Apophis (previously 2004 MN4)
 Apophis is the Greek name
for the Egyptian God Apep,
who is the God of death,
destruction, and darkness.
 Discovered on 19Jun04 2036 Apophis Collision Event Data
 This asteroid will pass Size 320 - 400 m ¼ mile
within ~ 30,000 km of
Earth’s surface on April 13th, Mass 4.6×1010 kg 130,000 Fully loaded 747
2029. aircraft
 If it passes through a Impact 12.59 km/s 28,000 mph
“keyhole” location in space, Velocity
it will return to impact in Impact 870 Mt 43,500 Hiroshima Bombs
Earth in 2036. Energy (20 Kt each)
• Probability fluctuates as Impact 1/38,000 Comparable to death by
observations are made. Probability snakebite or tornado.

78. Upcoming Events
 29075 (1950 DA)
• Discovered on 23Feb50 then lost until
31Dec00
• 1.1-1.4 km across (About 1/10 size of
K-T object)
• Calculations predict possible impact
on 16Mar2880 (Torino 1) Radar image of 1950
• Highest mathematical probability ever DA by Arecibo
telescope during the
assigned to a known object (1:300)
2002 pass
• Impact will cause cataclysmic
environmental/climatic damage

79. FREQUENCY OF LARGE IMPACTS
ANNUAL RISK OF DEATH
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.

80. Mitigation NEO collisions
 Motivation for studying and learning how
to mitigate NEO collisions with Earth:
• Small but dangerous NEOs collide regularly.
• Large and catastrophic NEOs have collided in
the past and will do so again.
• The ability as a species to save ourselves
from this celestial threat is a true milestone.

81. Mitigation NEO collisions
 Early detection, accurate threat
assessment, and scientific Asteroid Eros Seen During NEAR Mission
characterization are all essential
to mitigation, so these are
motivated also.
• We already want to study NEOs to
advance solar system science and Comet Tempel 1 Stuck During Deep Impact Mission
have deployed spacecraft missions to
do so.
• NEAR
• Deep Impact
• Hayabusa (MUSES-C) Asteroid Itokawa Seen During Hayabusa Mission

82. Systems Engineering
 There is no “silver bullet” solution to the NEO
mitigation problem.
• Each scenario is unique.
• At our current level of knowledge and experience, we
can derive generalized requirements and principles.
• Actual experience gained in practicing on test NEOs
will greatly improve our proficiencies:
• NEO Mitigation
• NEO Science
• NEO Resource Utilization

83. Systems Engineering
 Systems:
• Detection and tracking
• Optical and radar
• Ground- and space-based
• Orbit modeling and impact probability assessment
• Post-processing of observational data
• Spacecraft transponder beacon mission
deployed to NEO
• Physical characterization
• Ground or space observatory data processing
• Spacecraft science mission deployed to NEO
• Mitigation system
• Spacecraft mitigation mission deployed to NEO

84. Systems Engineering
 We need mitigation systems and spacecraft
missions for mitigation.
• Requirements follow from analysis of the general
hazardous NEO scenario.
• Scenario is expressed as a timeline comprised of
events.
• Each event has an associated system.
• Generalized mitigation mission architecture has been
devised and will be presented.
• Requirements drive this architecture.
• The most important requirement is simply this: If a
NEO is on a collision course with Earth, we must
prevent the collision.

85. NEO Detection
 NEO discovery and cataloguing:
• Detection and observations:
• LINEAR
• NEAT
• LONEOS
• Catalina Sky Survey http://www.ll.mit.edu/LINEAR/
• Spacewatch
• Tracking and threat characterization:
• Near-Earth Asteroid Tracking (NEAT) program at JPL
• Near-Earth Objects Dynamic Site (NEODyS) in Pisa,
Italy

86. NEO Characterization
 NEO characterization
• Ground or space observatory systems
• The observational data from these systems can
provide estimates for a NEO’s bulk properties.
• These need to be created.
• Spacecraft science missions
• On-orbit NEO science is the only way to gather
accurate and detailed physical data on the NEO.
• Such information is crucial for effective mitigation
system design.

87. NEO Orbit Characterization
 Orbit propagation and collision detection:
• Knowledge and classification of NEO orbits
• Identification of PHAs
• Determination of collision probabilities
• Ground or space observatories
• Space observatories offer more coverage and
better observations.
• Allows detection and characterization goals to
be met much more swiftly but at higher cost.
• Position accuracies on the order of 100 m and
velocity accuracies on the order of 0.1 mm/s
within a geocentric distance of 2 AU, assuming
a 35 m receiving dish on Earth.

88. 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.

89. NEO Threat Characterization
 Torino Scale
http://impact.arc.nasa.gov/torino.cfm

90. NEO Threat Characterization
 Palermo Scale
 PI 
P = log10 
 P ∆T  - Palermo Scale Value

 B 
PI - Probability of Impact
PB - Annual Background Probability of Impact
for a NEO with Same Kinetic Energy
∆T - Time in Years Before Impact

91. NEO Threat Characterization
 The Torino scale is intended for
communicating impact risk to the general
public.
 The Palermo scale is intended for impact risk
communication within the scientific and
engineering communities.
 Both scales rate threat by cross-referencing:
• Impact energy.
• Probability of impact.

92. NEO Mitigation
 Gravitational keyholes
Small regions in space near Earth defined by the
dynamics between the NEO and Earth such that:
• If the NEO passes through a given keyhole, it will
be placed onto a “resonant” orbit by Earth’s
gravity, causing the NEO to return to collide with
Earth some number of orbits later.
• Example: 7:6 resonance – NEO orbits the sun 6
more times while the Earth orbits 7 more times
and at the end of the 7th Earth orbit, the NEO
collides with Earth.

93. NEO Mitigation Modes
 There are three modes of mitigation:
annihilation, fragmentation, and deflection.
 Annihilation
• Reduction of NEO to vapor or fine-grain dust cloud by
energy application or pulverization.
• Provides the highest assurance that the threat is
permanently eliminated.
• Requires the most energy out of the three modes.
• Energy requirements are generally prohibitive.
• Required technologies are generally unavailable.
• Ultra high-power laser beams.
• Sets of many high-yield explosives.
• Antimatter torpedoes.
• Series of ultra-high energy kinetic impactors.

94. NEO Mitigation Modes
 Fragmentation
• Reduction of NEO to (hopefully) small but not
necessarily negligible pieces.
• Provides assurance that the threat is permanently
eliminated only if the largest fragment is smaller than
the threshold for burning up in Earth’s atmosphere (~
20 – 50 m).
• Least controllable mitigation mode.
• Medium to high energy requirements.
• Examples:
• Properly placed explosives (conventional or nuclear).
• Sufficiently energetic kinetic impactor(s).
• Tungsten bullet “cutters.”

95. NEO Mitigation Modes
 Deflection
• Modification of NEO’s orbit such that it misses Earth
rather than collides.
• Potentially provides the least assurance that the threat
is permanently eliminated.
• Gravitational keyholes.
• NEO still exists.
• Most controllable mitigation mode.
• Low to medium energy requirements.
• Examples:
• Nuclear detonations (surface or standoff).
• Attached thrusters (low or high thrust)
• Solar concentrators
• Gravity tractors

96. 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.

97. NEO Deflection Methods
 Nuclear explosives offer the following advantages:
• No anchoring of equipment to NEO.
• 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.
• 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.

98. 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.

99. 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.

100. NEO Scenario Timeline
A general hazardous NEO scenario has
a timeline associated with it.
• Events ranging from initial detection to Earth
collision, if threat goes unmitigated.
• Analysis indicates steps that will maximize our
chances of successful mitigation.
• Lays foundation for requirements derivation
and mitigation mission planning.

101. NEO Scenario Timeline
 We don’t necessarily want to have pre-built
mitigation systems on standby.
• Collision of dangerous NEOs is a low-frequency event.
• Maintenance costs.
• Uniqueness of NEO scenarios requires custom
designs.
• We can still improve our rapid deployment skills and
develop modular systems that have both mitigation
and other applications.
• NEO Science
• NEO Resource Utilization

102. Conclusions
 Detection and Characterization NEO’s and PHA’s systems
must be maintained, enhanced, and expanded:
• Space-based observatories
• More NEO science missions
• Combine these with mitigation missions for synergy.
• Might even combine with resource utilization
technology test missions for additional
synergy.
• Rapid-deployment beacon mission development.
 Continue and enhance NEO science missions.

103. Questions?
http://www2.jpl.nasa.gov/sl9/image81.html

104. http://www.newscientist.com/data/images/ns/cms/dn8259/dn8259-3_506.jpg
http://www.fli-cam.com/images/comet-liner.jpg
http://www.nasa.gov/images/content/116911main_spitzer-comet-060205-browse.jpg
http://galileo.rice.edu/images/things/comet_1532_apian-l.gif
http://www.astrocentral.co.uk/comet_diagram.gif
http://www.solarviews.com/thumb/comet/comet.gif
http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap14/FG14_06.jpg
http://www.mallorcaweb.net/masm/Aster/astervarios.JPG
http://en.wikipedia.org/wiki/Image:Ceres_Rotation.jpg
http://near.jhuapl.edu/
http://www.isas.jaxa.jp/e/enterp/missions/hayabusa/index.shtml
http://www.daviddarling.info/encyclopedia/N/NEAR.html
http://www.nasa.gov/worldbook/comet_worldbook.html
http://herschel.jpl.nasa.gov/
http://www2.jpl.nasa.gov/
http://nssdc.gsfc.nasa.gov/planetary/
http://www.magma.ca/
http://www.spaceweather.com/
http://solarsystem.nasa.gov/missions/
http://www.hour25online.com/pix/comet-tempel1-orbit_01a.jpg
http://www.cfa.harvard.edu/press/Deep-Impact_lores.jpg
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