Notes from Day 2 of 2011 IAA Planetary Defense Conference. Follow twitter feed for more information:
Day 2 (Tuesday 10 May 2011) Session 3
Potentially Hazardous Objects: Recent Progress
- P. Michel
Cote d'Azur Observatory
Physical Properties of NEOs that inform mitigation
For all mitigation concepts needs size/mass, rotational properties, and shape
For kinetic impactor and nuclear concepts:
needs surface and subsurface properties and internal structure if disruption is the goal
Most NEOs are rubble piles
very small asteroids have fast spin
material properties may involve microporosity
- Amy Mainzer
NEOWISE: A new infrared views of the NEOs and the Solar System
NEOWISE PI at JPL
Wide Field Infrared Survey Explorer (WISE), astrophysics mission
40 cm in diameter, solid hydrogen cryostat
expected life of 10 months, surveyed entire sky two times
4 imaging channels
525 km LEO circular orbit
lots of coverage of data over poles
2009 Dec 14 launch Delta II
thermal infrared for asteroids gives physical parameters
get diameters quite accurately and albedos
NEOWISE funded by NASA Planetary Science, archive and store exposures to public, created an archive of individual objects and tool for accessing moving objects
WISE moving Object Pipeline (WMOPS) derived from PS MOPS
Survey began in Jan 14 and started delivering Tracklets in March to MPC
Needed to see objects five times to say it was detected
157K objects observed, 34K objects
585 NEOS observed, 135 discoveries (including 17 PHAs)
1500 Trojans, 123 comets observed, 20 discovered , 20 centuars and SDOs
NEOWISE will not meet congressional mandate
NEO orbits for ~2 weeks before uncertainty becomes large for follow-up
Amateurs helped in follow up
NEO Science: get orbital distribution
carrying out thermal model of objects
used NEATM model
diameter can be determined to +/- 10%, albedo to +/- 20%
Survey biases need to be understood
run items through simulated surveys to determine size and albedo of NEOs
First data release: 14 April 2011 (57% of WISE data first pass) final data release: March 2012
NEOWISE is proof of concept for larger NEO survey, NEOCam
Near Earth Object Camera (real asteroid mission)
Discovery Mission Proposal in 2006/2010
Study NES and asses risk
detect and characterize 2/3 of all PHOs < 140 m in 4 years
NEOCam selected for 2011 Discovery selection for technology development
Q: hope for additional discoveries in data
A: yes, could potentially find new objects after data analysis, more things in database coupled with follow-up
excess of high inclination NEOs - WISE could potentially answer question on high inclination NEOs
- Lance Benner
Radar Tracking and Near Earth Object Characteristics
JPL, uses data to provide shape models and physical models, rotation characteristics
cumulative presentation from multiple people, including Steve Ostro (worked with him from 13 years)
radar can spatially resolve objects 4 meter resolution, exceeds any ground or space-base optical telescope, estimate 3D shapes, proxy for spacecraft missions, identify binary and ternary objects (2/3 of such objects identified by radar)- can estimate mass and bulk density, can back out albedo, improve orbits, very precise and can shrink drastically for new NEOs, 1E8 doppler precision, radar ranging can improve orbits can reduce uncertainties by
Arecibo: 305m (within 20 deg, can see 1/3 of sky, 1 MW of power, can see objects double of Goldstone, 7.5 meter/pixel), Goldstone: 70m (2nd most sensitive radar, fully steerable, sees 80% of sky, 4 meter/pixel), higher complimentary
Status of Arecibo: NASA funding of $2M annually started in 2010, observatory will stay open, NEO radar program is expanding significantly, radar offline for several months due to equipment problems (equipment problems, results of insufficient maintenance perhaps, missed many targets), at least through June or longer (transmitter system got wet because of seal), new generators: resume transmitting 900 kW at regular basis (5-6 years ago, get 700 Kw, one year ago got 100 kW), higher science return, requesting three times as many asteroid targets as three years ago, two new klystrons,
Goldstone: new 4 meter chirp resolution, 5x finer than previous resolution of 18.75 meter resolution (over one year ago) - also 7.5/15/30 m resolutions
Offline from March - Nov 2010 for scheduled maintenance, some people doing repairs caused damage, pointing problems since Dec. 2010, return to regular service in June 2011, tracking problem last week, work is underway to increase priority of radar
272 NEos observed (20-30 detected annual, ~5% of what could be done), have observed 2 meter object (smallest object seen)
EPOXI Mission target flyby of rComet Hartley 2, also Hayabusa mission support
2010 JL33 (2 km object), Dec. 12 observation from Goldstone
Have made shapes for 30 objects from 272 NEOs observed
If have 3D shape then can do other things
Have observed Yarkovsky effect by radar ranging of Golevka
YORP effect detected for multiple objects
New 3.75 meter resolution (2010 AL30, diameter of 30m), spatially resolve tiny NEAs, up to 5x radar astrometry, finer shape and surface detail
- Emel'yanenko
Institute of Astronomy, RAS (russian Federation)
Orbital Distribution of NEOs
Feb. 18, 2011: 7665 NEOs (q<1.3 AU)
- A. Milani
1999 RQ36 Impact Risk Monitoring the Long Term Yarkovsky Effect
Univ. of Pisa
Have ebeen doing routine work for 12 years for assessing NEO impact monitoring
Goal was to obtain follow up observations.
May 5, 2011: 310 risk files (asteroids with known impacts in 80-100 years), 317 in NEODyS-1, 369 in JPl SENTRY, 359 in SENTRY version 2
why different and why such a long list?
Risk File: list of potential risks and impact probability over time
2010 RF12: next TC3 type object in 2095 (small)
What is the impact probability that is appropriate to give to the decision makers. If want to get to from 10-7 to 10-9 in terms of impact probability calculation - need $750K of extra computers, practical impact of impact probability confidence level
91 NEAs with H<25, 198 H >25 have been lost
What is the meaning of lost NEAs with VIs?
two largest asteroids 2010 AR85 and 2010AU118 are extinction level events that WISE found but no one else has found them
Follow-up system does not work (list remains polluted) with dangerous asteroids we cannot remove, these discoveries of VIs that are lost has not contributed to reducing risk
system is not working because of this
Q (Alan Harris): Vi created to make where one has to look for impact
A: Problem is that there are many orbits one as to look at (too many) 5000 VIs, requires significant "negative" surveys
- Steve Chesley
Asteroid Impact Hazard Assessment Over Long Time Intervals
new title: Asteroid Impact Hazard Assessment and Yarkovsky Effect
JPL
developed SENTRY system
Italian, California, Hawaiian NEO "Mafias"
two case studies: Apophis and 101955 (1999RQ36)
Apophis has stiff integration in 2029 (scatters) and poor Yarkovsky knowledge - short term prediction issues
RQ36 smoother dynamics - long term prediction case study
Apophis impact probability updated: improved data treatment, astrometry updates
Apophis update: new keyhole appears for 2068
2036 keyhole is 7 sigma away
new Keyhole in 2068 2m across
Yarkovsky target plane uncertainties: 190km from astrometry and 500 km from Yarkovsky, thus now it is important
don't know parameters for Apophis Yarkovsky (conductivity, density, diameter, obliquity)
put distribution on above four parameters - get semi-major axis drift rate distribution - add that into trajectory, Yarkovsky skews towards keyhole
putting uncertainties on probabilities
2036 potential impact is not ruled out (more than 3 sigma away, IP = 4X10-6 impact probability)
reasonable to expect 2036 impact to be ruled out soon, 2068 is likely o persist longer, recent data in March 2011 on Apophis but does not change data - such a good orbit so new information has not changed situation
1999 RQ36
target of OSIRIS ReX mission (0.5 km)not hazardous now but 150 years from now potential for impact, have radar and other data
RQ36 has 1 in 1800 impact probability in year 2182, really? Arecibo observations should reduce uncertainty in semi-major axis drift rate, fractal structure that makes it difficult to rule out possibilities of impact, see more into the fractal structure as more observations,
- Peter Veres
The Search for Earth Impacting Asteroids by Pan-STARRS
Comenius University (Slovenia) - post doc at Hawaii in future
Feb. 28, 2010 Slovakia
May 4, 2011, meteorite fall in Poland
How efficient would PS1 be for finding an impactor
Survey simulation for Pan-STARRS from 2011-2013
pop of 130K impactors in simulation
after 4 years of observation 10% chance of finding 2008 TC2 analogue in 4 years, large impactors identified within 2 years
ATLAS telescope (2 telescopes, 100 km distance from each, each has 4 scopes, to see parallex, potential to find objects that are close and small, might cover entire sky)
- Paul Chodas
Keyholes as Providers of Deflection Leverage
phrased "keyholes"
How pre-impact close approaches impact deflection strategy
Apophis 2029 close approach, how typical is keyhole scenarios
keyhole started in 1999, B. Marsden proposed future years
how far does a keyhole go?
Apophis close approach scenario is very rare, has very high leverage for close approach
dynamics of close approach when thinking about mitigation missions
Jabbas: big fat area in the pre-impact b-plane at which the close approach produces a compression on the Line of Variations, 15 to 60 lunar distances, jabba widths are less than 1 lunar distance but they can be as wide as several million km
25% of impactors have keyholes reducing deflection within 25 years of impact: interesting
fly-by anomaly not modeled for asteroids (have seen for S/C)
folding does not change impact probability per se but moves into future
not really a fractal, MOIDS get off the Earth - finite expression of fractal, partial view of infinite view, limited view of chaos
