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  • Frequently, presenters must deliver material of a technical nature to an audience unfamiliar with the topic or vocabulary. The material may be complex or heavy with detail. To present technical material effectively, use the following guidelines from Dale Carnegie Training®.   Consider the amount of time available and prepare to organize your material. Narrow your topic. Divide your presentation into clear segments. Follow a logical progression. Maintain your focus throughout. Close the presentation with a summary, repetition of the key steps, or a logical conclusion.   Keep your audience in mind at all times. For example, be sure data is clear and information is relevant. Keep the level of detail and vocabulary appropriate for the audience. Use visuals to support key points or steps. Keep alert to the needs of your listeners, and you will have a more receptive audience.
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  • Seameo qitep pha_dhani

    1. 1. Potential Earth Hazardous Objects Dhani Herdiwijaya Astronomy Research Division, Institute Technology Bandung Email: Course on Earth and Space Science for Sustainable Development, Bandung, 5-11th June 2011
    2. 2. Overview Small Bodies of the Solar System • Comet • Asteroid • Meteoroid NEO and PHA Detection, Characterization, and Mitigation Conclusions
    3. 3. Small Bodies of the Solar System 1
    4. 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. 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. 6. Comets Structure Orbits& Types Oort Cloud vs. Kuiper Belt Famous Comets What message do they convey?
    7. 7. 31
    8. 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. 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. 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. 11. 35
    12. 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. 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. 14. StructureDirty Snowballs
    15. 15. Dust tailIon or plasma tail
    16. 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)
    17. 17. Halley’s comet1986
    18. 18. Halley’s Comet Orbit•Many comets have retrograde orbits
    19. 19. Comet Hale Bopp, 2002
    20. 20. 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.
    21. 21. Comets Demise Comets eventually • breakup into smaller fragments (Comet West below) • evaporate • collide with the sun • collide with other planets
    22. 22. Comets Demise: Sun grazer
    23. 23. Comet Shoemaker-Levy 9 fragments impactJupiter, July 16-22, 1994  ‘Bull’s eye’ on Jupiter larger than Earth; first evidence of water in the jovian atmospher
    24. 24. Comets Demise: Shoemaker-Levy
    25. 25. Asteroids
    26. 26. 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.
    27. 27. Ceres – largest, (1030 km). Namedafter the Roman goddess of theharvest (cereal). Recently named adwarf planet.
    28. 28. Asteroids – rocky leftovers of theinner solar system  Location • Asteroid Belt • Trojan or Lagrange Asteroids • Random Orbits  Types of Asteroids  Minor planets  NEO’s
    29. 29. 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.)
    30. 30. The so-called Main Belt ofasteroids lie between the orbits ofMars and Jupiter, with semi-majoraxes 2.2 to 3.3 AU.
    31. 31. Orbits: Gaps • In the main belt, orbital distances are not distributed evenly.Picture: JPL/SSD Alan B. Chamberlain
    32. 32. 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
    33. 33. 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.
    34. 34. 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.
    35. 35. 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.
    36. 36. 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
    37. 37. 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).
    38. 38. 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).
    39. 39. Picture: David Dunham/IOTA Movie: Rick
    40. 40. 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
    41. 41. 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
    42. 42. Stony AsteroidsGaspra – a typical stony asteroid
    43. 43. Some asteroids are thought to be rubblepiles held together by very low gravity.
    44. 44. Major Asteroids Vesta – smaller (450 km diameter), but much brighter. Barely visible to naked eye. Pallas Juno
    45. 45. Vesta shows signs of having been moltenat one point in its history.
    46. 46. •Surprisingly, this asteroid has its own little moon !
    47. 47. Toutatis – one of the closest ! Toutatis spins on 2 axes.5 km long. Passed just 29 lunar distancesfrom the earth in 2000. 19
    48. 48. Meteoroids – asteroids on acollision … 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.
    49. 49. 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.
    50. 50. •A stony meteorite (hard to find)
    51. 51. •An iron meteorite (easier to find)Where the formation of Iron element occurs ?
    52. 52. Meteoroids were formed inparent bodies (planetessimals) Stonies were formed in the: mantle Irons were formed in the: core
    53. 53. 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
    54. 54. NEO and PHA
    55. 55. 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 Earths 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.
    56. 56. Potentially Hazardous Asteroids Potentially Hazardous Asteroids (PHAs) are defined based on parameters that measure the asteroids 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 cant 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.
    57. 57. How Many Near-Earth ObjectsHave 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
    58. 58. NEO properties and sizePhysical properties Mass Density Porosity Internal structure and composition Surface chemical composition Spin state
    59. 59. 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.
    60. 60. NEO Search and Mitigation StudyMilestones1992 - 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,” whichrecommends the discovery of 90% of NEOs (D > 1 km) within 15 years.2003 – NASA recommends extending             search down to D~140 m 
    61. 61. 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
    62. 62. 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.
    63. 63. 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.
    64. 64. 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.
    65. 65. 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
    66. 66. 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.
    67. 67. ~1/2 mile across; 300,000 years old, W. AustraliaWolfe Creek Also associated with many small iron meteorites
    68. 68. 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
    69. 69. ENVIRONMNETAL EFFECTS IMPACTSCRATER FORMING PROCESSComet 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
    70. 70. ENVIRONMENTAL EFFECTS IMPACTSCRATER FORMING PROCESSComet 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.
    71. 71. 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
    72. 72. 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
    73. 73. 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
    74. 74. 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
    75. 75. 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.
    76. 76. 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
    77. 77. FREQUENCY OF LARGE IMPACTS ANNUAL RISK OF DEATHOver 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.
    78. 78. 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.
    79. 79. 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
    80. 80. 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
    81. 81. 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
    82. 82. 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.
    83. 83. NEO Detection NEO discovery and cataloguing: • Detection and observations: • LINEAR • NEAT • LONEOS • Catalina Sky Survey • Spacewatch • Tracking and threat characterization: • Near-Earth Asteroid Tracking (NEAT) program at JPL • Near-Earth Objects Dynamic Site (NEODyS) in Pisa, Italy
    84. 84. 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.
    85. 85. 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.
    86. 86. EVENTS OF 20TH CENTURYBIGGEST NEAR EVENTSAssessing HazardsHave Torino scale which assesses hazards on a 0 - 10 scale.Enables calm communication about the threats.
    87. 87. NEO Threat Characterization Torino Scale
    88. 88. 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
    89. 89. 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.
    90. 90. 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.
    91. 91. 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.
    92. 92. 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.”
    93. 93. 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
    94. 94. 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.
    95. 95. 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.
    96. 96. 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.
    97. 97. 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.
    98. 98. 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.
    99. 99. 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
    100. 100. 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.
    101. 101. Questions?
    102. 102. 60