1. 1 Near-Earth objects – a threat for Earth? Or: NEOs for engineers and physicists Lecture 7 – From orbits to impact warnings Dr. D. Koschny (ESA) Prof. Dr. E. Igenbergs (LRT) Image credit: ESA

2. 2

3. The b-plane The ‘b-plane’ (body plane) is the plane going through the center of the Earth and perpendicular to the incoming velocity vector of the asteroid outside the sphere of influence

4. Apophis flyby geometry Uncertainty as known before 2011

5. Apophis b-plane Before March 2011

6. D. Bancelin (2011) Keyholes for Apophis in the b-plane Image: http://www.billfrymire.com/gallery /keyhole-clouds- opportunity.jpg.html

7. The concept of keyhole maps 7

8. A keyhole map 8 Farnocchia et al., Icarus 2013 Image: http://www.billfrymire.com/gallery /keyhole-clouds- opportunity.jpg.html Position knowledge: 7 km… but without Yarkowsky 

9. A keyhole map 9 Predicted 3-sigma orbit uncertainty at 2029 flyby, with Yarkowsky Farnocchia et al., Icarus 2013, IEEE 2015 Image: http://www.billfrymire.com/gallery /keyhole-clouds- opportunity.jpg.html

10. Another way of showing it 10 Farnocchia, IEEE 2015 Δξ 2029 (km) PDF (km -1 ) 2036 2068 Keyhole width (km) gravity-only w/ Yarkovsky

11. And the conclusion: From Farnocchia and Chesley 2015: We are safe until 2060. After that we don’t know – needs observations after the 2029 fly-by.

12. When do I want to deflect an asteroid? Head-On Impact Deflection of NEAs: A Case Study for 99942 Apophis, Planetary Defense Conference 2007, 05-08 Mar 2007, Wash. DC. See http://www.doom2036.com/P2-3-- Dachwald.pdf

13. Typical evolution of an impact threat Example – a quick run-through through a simulation we did with German and Swiss representatives of their emergency response agencies

14. ESA UNCLASSIFIED – For Official Use SSA-NEO Detlef Koschny, Gerhard Drolshagen SSA-NEO Segment Emergency response workshop ESOC, Darmstadt, 24+25 Nov 2014 A simulated asteroid impact threat over Germany and Switzerland

15. Introduction We step through a fictive case of a small asteroid impact At different key points we present the facts… … and discuss the envisages response We’ll start 4 weeks before the potential impact, and simulate 5 key points in time (30 days, 26 days, 5 days, 3 days, 1 hour after) in ~1.5 hour sessions Points for thought Which information do you think you would require as an emergency response agency? What would you do with the information? What would you expect the Space Agency to be doing at each step? Whom should we give information, which information? How will the public respond? We explain a bit of background – to make you aware of the uncertainties

16. Setting the scene – Real situation ESA’s Optical Ground Station (OGS)

17. Setting the scene - Real situation Asteroid 2014QN266 – discovered in Aug 2014 by ESA’s OGS telescope http://neo.ssa.esa.int Search for object ‘2014QN266’, click on ‘orbit visualization’ Positions for 13 Mar 2027

18. Physical properties http://neo.ssa.esa.inthttp://neo.ssa.esa.int – Search for NEO ‘2014QN266

19. Our fictive case Object hasn’t been observed for quite some time and ‘lost’ Rediscovered with large telescope on 13 Feb 2027 Was ‘lagging behind’ on orbit Possible impact 13 Mar 2027

20. T0 – 26 days TO-30 DAYS

21. T0 – 30 days Orbit uncertainty as seen from the asteroid Available information: Astrometric (position) measurements Impact probability: 20 % Size estimate: 12 m - 38 m (based on brightness) Mass estimate: 900 t – 200000 t Velocity: 12.5 km/s Energy estimate: 7. 10 13 J (17 kt TNT) to 1.6. 10 16 J (3.7 Mt TNT) (warning: ‘kt TNT’ may not be an adequate description)

22. What is a ‘kt TNT’? Unit for energy release in explosions 1 ton TNT = 4.184 GJ = energy released in the detonation of a metric ton of TNT (Trinitrotoluene) Hiroshima bomb: 15 kt TNT (63 TJ) Be careful – an asteroid airburst puts more energy into the ground as an explosion https://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_an d_Nagasaki#/media/File:Atomic_bombing_of_Japan.jpghttps://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_an d_Nagasaki#/media/File:Atomic_bombing_of_Japan.jpg, CC BY- SA 3.0)

23. Possible effects 12-m fragile object will break apart in atmosphere – comparable to Sudan 2008 event Bright fireball Meteorites (< 1 kg) found on ground Strewn field a few km in size 5 cm

24. Possible effects 40-m stony object – comparable to Tunguska 1908 Fireball much brighter than Sun (1000 times?) Shockwave flattens trees and structures tens of km away Heat wave Seismic effects

25. Possible effects 40-m iron object – a bit smaller than Arizona Crater (50000 A.D.) Impact crater, 1.3 km in diameter Shock- and heat waves emanating from impact location Affects ~hundreds of km

26. Discussion How should we react? Do you care? Who would need to know? Which information would need to be distributed, and to whom? Reaction of the public (if any)?

27. T0 – 26 days TO-26 DAYS

28. T0 – 26 days Available information: More astrometric (position) measurements Impact probability: 60 % Size estimate: 12 m - 38 m (based on brightness) Mass estimate: 900 t – 200000 t Velocity: 12.5 km/s Energy estimate: 7. 10 13 J (17 kt TNT) to 1.6. 10 16 J (3.7 Mt TNT)

29. Discussion How should we react? Do you care? Who would need to know? Which information would need to be distributed, and to whom? Reaction of the public (if any)?

30. T0 – 10 days T0-5 days

31. Spectroscopic observations Can only be done on brighter objects Allows a rough estimate of the material

32. Spectroscopic observations Our object: X-class Can be M (metallic, 10-20 % reflectivity) E (rocky, >30 % reflectivity) P (organic-rich, <10 %)

33. T0 – 10 days Available information: More astrometric (position) measurements + spectral observations Impact probability: 100 % Centered around Switzerland – Germany and covering Spain - Russia Size estimate: 17 m - 38 m (based on brightness and spectral class) Mass estimate: 7800 t – 87000 t Velocity: 12.5 km/s Energy estimate: 6.1. 10 14 J (146 kt TNT) to 6.9. 10 15 J (1.6 Mt TNT)

34. Effects If organic-rich: Tunguska-like event If metallic: maximum size 20 m Bright fireball, 100 times brighter than the sun Shockwaves from airburst – comparable to the Chelyabinsk event (overpressure 500 Pascal) over 20 km diameter Possibly one large crater with 300 m diameter, resulting shockwave, heat wave Or several smaller craters, tens of meters in diameter, over an area of 10 km. Velocities around 3 km/s (still hypervelocity)

35. Discussion How should we react? Do you care? Who would need to know? Which information would need to be distributed, and to whom? Reaction of the public?

36. T0 – 5 days TO-10 DAYS

37. T0 – 5 days Available information: More astrometric (position) measurements + spectral observations Impact probability: 100 % Centered around Lake Constance – Bavarian Forest Size estimate: 17 m - 38 m (based on brightness and spectral class) Mass estimate: 7800 t – 87000 t Velocity: 12.5 km/s Energy estimate: 6.1. 10 14 J (146 kt TNT) to 6.9. 10 15 J (1.6 Mt TNT)

38. Discussion How should we react? Do you care? Who would need to know? Which information would need to be distributed, and to whom? Reaction of the public?

39. T0 – 3 days T0-3 DAYS

40. Radar observations Currently only done with US-based Goldstone and Puerto-Rico based Arecibo radar Can ‘image’ asteroids up to a few Mio km distance Very precise size/shape information Constrains composition TIRA (radar system close to Bonn) could do it

41. T0 – 3 days Available information: More astrometric (position) measurements + spectral observations + radar Impact probability: 100 % Centered around Lake Constance – Augsburg Size estimate: 17 m (based on radar) Material must be iron (based on radar) Mass estimate: 18330 t Velocity: 12.5 km/s Energy estimate: 1.4. 10 15 J (340 kt TNT)

42. T0 – 2 days Available information: More astrometric (position) measurements + spectral observations + radar Impact probability: 100 % Centered around Lake Constance – Augsburg Size estimate: 17 m (based on radar) Material must be iron (based on radar) Mass estimate: 18330 t Velocity: 12.5 km/s Energy estimate: 1.4. 10 15 J (340 kt TNT)

43. Effects Bright fireball, 100 times brighter than the sun Shockwaves from airburst – comparable to the Chelyabinsk event (overpressure 500 Pascal) over 20 km diameter Possibly one large crater with 100 m diameter, resulting shockwave, heat wave Or several smaller craters, tens of meters in diameter, over an area of 10 km. Velocities around 3 km/s (still hypervelocity) Hitting Lake Constance: Effects not clear – mini-’Tsunami’? Shikote Alin: 7 m metallic object Chelyabinsk – 18 m stony object

44. Discussion How should we react? Do you care? Who would need to know? Which information would need to be distributed, and to whom? Reaction of the public? Hourly updates – more precise impact location

45. ESA UNCLASSIFIED – For Official Use SSA-NEO T0 + 1 hour What finally happened

46. T0 + 1 hour Object broke apart 3 main impacts 5 m object close to Friedrichshafen => 30 m crater, shock wave with overpressure of 10 kPa - Levels structures in the near vicinity 3 m object in Lake Constance - 1 m flooding 8 m object in St. Gallen => 50 m crater, shock wave with overpressure of 30 kPa - Levels everything up to about 1 km distance

47. Discussion How should we react? Do you care? Who would need to know? Which information would need to be distributed, and to whom? Reaction of the public?

48. Excel sheet with computations

49. ADDITIONAL INFORMATION And what did we learn?

50. ESA should actively inform Emergency Response Agencies and political entities about impact threats with > 1 % impact chance within the next 50 years. ESA has to focus on factual information. Recommendations on how to react will be done by the emergency response agencies. There is no need to provide frequent information if no new information is available. However, ESA should say when they expect new information to become available. ESA should provide information on the expected ground damage to emergency response agencies. Information of the impact location and potential damage zones is of highest importance for civil protection. Impact zone and expected ground damage information should, at least initially, only be shared with political entities and emergency response agencies. ESA should provide information after the impact.

51. Current process @ ESA Defined in ‘NEO information plan’ Impact warning When a credible impact threat occurs 1 %, 50 years Affects our assets Information release A predicted close flyby or hit of a small object which may generate interest in the public Impact prediction for another planet or the Moon Procedure to follow for an ‘impact warning’ Validation of prediction via independent system Publish orbit info on internet (as usual) Calculate impact zone, estimate energy release, publish Calculate impact effects on ground, give best and worst cases Prepare information for political entities, emergency response agencies, and the media/public (orbit prediction, position measurements, impact probabilities, impact time, size/mass estimate…) Distribute this information as ‘impact warning’ Update information regularly, coordinate with other entities After impact: Confirmation of precise time/location, estimation of size and energy release, have a ‘lessons learned’ debriefing

52. Summary We have learned what the b-plane, a keyhole, and a keyhole map is We saw some examples for Apophis We understand the uncertainties in the orbit predictions We went through an example exercise with emergency response agencies and saw how the information about an imminent impact would evolve We heard how ESA is distributing this information

53. 53 Orbits – Tasks Compute the velocity of the Earth Use the JPL Horizons system to get the Earth’s state vector at spring equinox What is the given position/velocity? Does it match your expectations? Make a sketch of the geometry. G = 6.67. 10 -11 N m 2 kg -2 M = 1.99. 10 30 kg