Asteroid Impact Mitigation: Why? How? When?

Transcription

1 Asteroid Impact Mitigation: Why? How? When? Simon Green Planetary and Space Sciences School of Physical Sciences, The Open University Milton Keynes, UK.

2 Why. should we care?

3 Impacts everywhere? Physical evolution of Solar System bodies is driven by impacts of comets and asteroids NASA (Apollo 16) NASA/JPL-Caltech/Space Science Institute 3

4 Impacts on Earth Barringer crater 1.2 km ~ y Popigai ~100 km 36 My Manicouagan ~100 km 214 My NASA S.F. Green Vredefort Dome ~300 km ~2 By NASA Wolf Creek 875 m < 0.3 My NASA LPI 4 LPI, V.I. Sharpton

5 Mass Extinctions Species loss: 85% 75% 95% 75% 75% LPI, David Kring 5

6 Iridium Layer Nature.ca, David Kring Shocked quartz Lawrence Berkeley Laboratory USGS 6

7 Chicxulub ~ 300 km multi-ring crater [Athena Review Vol. 2, no.1] ~ 30 km deep ~12 km diameter impactor Age 66 Ma ~ km 3 of ejecta 7

8 1908: Tunguska Airburst at ~5-10 km Over 2000 km 2 damage ~ 50 m asteroid CIA/B.D. Bryant Leonid Kulik expedition

9 15 February 2013 Near miss predicted 2012 DA 14 ~30 m Impact unpredicted: Chelyabinsk ~17 m asteroid Reuters P Chodas (NASA JPL) E. Guido/ N. Howes/ Remanzacco Observatory Константин Кудинов Kyodo/AP 9

10 How often do they hit? Interval (y) Chelyabinsk Megaton TNT 1 Estimated casualties 0 Tunguska thousand Barringer 10 thousand 500 thousand 1 million 1 billion Mass extinction event 100 million 6 billion 10

11 How... can we deflect an asteroid?

12 Not like this 12

13 Find the next Impactor Potentially Hazardous Asteroids (PHAs) Minimum orbit Intersect Distance (MOID) < 0.05 AU (7.5 million km) Diameter > 100 m A. Fitzsimmons GOOD NEWS Many search programmes Under a 1000 NEAs with D > 1 km Almost all found BAD NEWS Estimated ~ NEAs with D > 100 m and ~5000 PHAs Only around 25% of PHAs known We haven t tested any mitigation method PanSTARRS1 13

14 First observed impactor Catalina Sky Survey 1.5m Mt. Lemmon, Arizona 2008 TC TC 3 Catalina Sky Survey, University of Arizona 19 hours later Richard Kowalsky & Ed Beshore A. Fizsimmons, H. Hsieh, S. Duddy Image courtesy: EUMETSAT Peter Jenniskens (SETI institute/nasa Ames) 14

15 Impact Hazard Number < H Impact interval / years Diameter (km) Greatest risk from ~ m objects Discovered objects 15

16 Relevant asteroid properties Orbit Size, shape Mass, density Structure Monolith or rubble pile? Spin properties Periods: seconds-many days Composition Observations required: Remote Spacecraft?? (sample return) 16

17 Space missions 1 Ceres 950 km Dawn km 4 Vesta 530 km Dawn

18 Space missions Asteroid Missions 100 km Ceres 950 km Dawn Toutatis km Chang e Vesta 530 km Dawn

19 Space missions 10 km 9969 Braille Deep Space 1, 1999 Dactyl (243 Ida I) Galileo, Toutatis Chang e 2, 2003 Itokawa Hyabusa, Steins Rosetta, Annefrank Stardust,

20 Slow push: Gravity Tractor Pros No physical interaction with asteroid High degree of control Technology ready Astrium/NEOShield project Cons Requires decades warning time Only suitable for small (<~300 m) targets Station keeping in complex gravitational field 20

21 Impulse: Kinetic Impactor Pros Simple concept Impact targeting already tested Cons Requires ~decade warning time Not suitable for larger impactors Uncertain response dependent on asteroid properties 21

22 Kinetic Impactor: Momentum transfer Conservation of momentum M V = m v impact m M v sc 22 V

23 Kinetic Impactor: Momentum transfer Change in Momentum of asteroid M V = m v sc + m ejecta v ejecta M V = b m v sc v ejecta m ejecta M b is momentum multiplication factor Values from 1 (no ejecta) to >5, depend on v V

24 Some simple calculations 100 m asteroid, mass 1 million tonnes Require orbit position change of km to safely miss Earth Gravity Tractor: Spacecraft mass: 5 tonnes Hover distance of 200 m from asteroid centre Ion engine with specific impulse of N s kg -1 Gravitational force: F = G M m/r 2 = N Momentum change required: M DV = F t 10 9 x (10 7 /t) = t Time required t = >35 years DV = 9 mm s -1 Fuel required 0.9 tonnes 24

25 Some simple calculations 100 m asteroid, mass 1 million tonnes Require orbit position change of km to safely miss Earth Kinetic impactor: Spacecraft mass: 5 tonnes Impact speed: 5 km s -1 Momentum enhancement: b = 2 Speed change DV = b (m/m) v sc = 2 (5000/10 9 ) 5000 = 5 cm s -1 Time required t = 6.3 years 25

26 Blast Deflection Buried/surface or stand-off Pros Suitable for shorter warning times Suitable for large impactors Cons Politically sensitive Cannot be tested under current space law Uncertain response dependent on asteroid properties Neoshield project 26

27 Credit: Tim Warchocki (adapted from National Research Council Final Report: Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies ). 27

28 Other methods Ion Beam Shepherd Laser Ablation Mirror bees University of Strathclyde Bryan Christie Design Astrium/NEOShield project Surface thrusters Mass Driver ejection of mass Electrostatic charge deflection Light Tug light absorption Yarkovsky effect 28

29 When... do we need to try?

30 30

31 Apophys Discovered: 19 June 2004 during close approach to Earth Diameter ~350 m Close approach in 2029 Impact probability rose to 1 in 37 (Torino scale level 4) Then fell to zero Possible impact in 2036 Torino scale level 1 Then also fell to zero Possible impact in 2068, probability 1 in Why? 31

32 Impact probabilities View from asteroid along its trajectory Low probability of impact Position uncertainty ellipse In b-plane Impact probability 1 0 Time 32

33 Impact probabilities View from asteroid along its trajectory Increasing probability of impact Position uncertainty ellipse In b-plane Impact probability 1 0 Time 33

34 Impact probabilities View from asteroid along its trajectory Increasing probability of impact Position uncertainty ellipse In b-plane Impact probability 1 0 Time 34

35 Impact probabilities View from asteroid along its trajectory High probability of impact Position uncertainty ellipse In b-plane Impact probability 1 0 Time 35

36 Impact probabilities View from asteroid along its trajectory Certain impact Position uncertainty ellipse In b-plane Impact probability 1 0 Time 36

37 Impact probabilities View from asteroid along its trajectory Position uncertainty ellipse In b-plane Impact probability 1 Miss 0 Time 37

38 Impact probabilities View from asteroid along its trajectory keyholes Position uncertainty ellipse In b-plane Impact probability 1 Miss 0 Time 38

39 Lots of studies A Global Approach to Near-Earth Object Impact Threat Mitigation HAMMER: Hypervelocity Asteroid Mitigation Mission for Emergency Response 39

40 AIDA Asteroid Intercept and Deflection Assessment AIDA = DART + AIM

41 AIDA target (65803) Didymos 2003 November Phase P orbit = 11.9 h Arecibo, November 2003 Primary rotational lightcurve (time-axis stretched) Range (15 m/pixel) Doppler frequency (0.3 Hz/pixel) Phase P orbit = 11.9 h 41

42 AIDA target (65803) Didymos Didymain D = 800 m 11.9 h orbit Didymoon 2.26 h Tidally locked? D = 160 m 1.18 km 42

43 Comparison with Deep Impact Comet 9P/Tempel vs. Didymos 160 m 800 m ~ 6 km/s DART ~ 350 kg 10 km/s Deep Impact 370 kg 6.5 km Predicted Didymoon orbit period change of 4 minutes 43

44 NASA DART mission continues Launch: Dec 2020 May 2021 Arrival: 7 October 2022 Deflection test on Didymoon (to 10%) Imaging before impact Ground-based observation support Status: In Phase B 44

45 ESA Hera mission proposed Launch: October 2023, backup Oct 2024 Arrival: Jul-Sep 2026 Didymoon mass Crater properties Binary asteroid science Interplanetary Cubesats Small JAXA Impactor? scaling laws MASCOT+ lander? Status: Funded for Phase B Decision for continuation Oct

46 Coming soon NEA Sample Return missions to primitive asteroids: Hayabusa 2 Arrival at (162173) Ryugu (~800 m) July 2018 OSIRIS-Rex Arrival at (101955) Bennu (~500 m) August 2018 Bennu shape model Michael C Nolan/Arecibo Observatory 46

47 (not ) The End 47

48 Effects of large Impacts K/T boundary type event: >1000 km radius immediate ignition radius Ballistic ejecta ignites vegetation over entire globe If ocean impact - global scale tsunami Global storms and high speed winds Dust loading: Nuclear winter for months or years If ocean impact water loading of atmosphere heats atmosphere Acid rains turn upper 100m of ocean acid enough to dissolve shell Ozone layer depletion and mutagens in atmosphere 48