Notes from Day 2 of 2011 IAA Planetary Defense Conference. Follow twitter feed for more information:
Day 2 (Tuesday 10 May 2011) Session 4
Impact Consequences and Education
- Longo, G.
"Consequences of the Tunguska Impact and their Interpretation"
more than 100 theories of Tunguska event
many expeditions, 1991 Italian expedition to collect wood samples
new map obtained of 1908 treefall
from final traj. azimuths: single body trajectory or multiple bolide formed by two bodies
New hypothesis: Tunguska bolide underwent fragmentation or was a double body (perfers double body)
example crater to look at Carancas Crater
Lake Cheko: something perhaps under bottom of lake (reflection) (historical evidence refers to lake Cheko but not lake Cheko)
Several surviving trees have in 1908 an inclination toward the lake
Before 1908 think there was a forest before at the current lake location
Would like to drill to bottom of Lake Cheko - do not have the money to drill (but have plan), hopefully in the next decade can drill
http://www-th.bo.infn.it/tunguska
Q: Good to scrape enough particles (take logs apart), if get enough cromium could do isotopic analysis - could prove extraterrestrial nature
A: Have nanograms of particles in tree resin: possible consequence of body but cannot confirm (need to drill to bottom of Lake Cheko)
- Martin Mueller
"Creating Awareness" of the Impact Hazard
Univ. of Eichstaett-Ingolstadt
geographer
meteorite impact and their influence on human society are part of geography curriculum
interviews with experts and surveys of youth in Germany
Results:
the interest in meteorite impacts is above the expected average
both boys and girls are equally interested (not expected since boys more interested in natural disasters)
the interest is much higher in the 5th grade than in the 11th grade
for students, the issue of meteorites impacting today and consequences of a large impact are of highest interest (than pure natural science)
the more complex the concepts are they then are more in the way scientists think (perhaps specific to Germany)
students gather their knowledge from school and TV/movies
students do no know "nuclear winter"
students unaware of asteroid/comets
students do not know a single crater by name
most students are unaware of the geological timescale (missing a deep time framework)
two fundamentally different concepts could be identified" "hot stone in Earth orbit"
Have developed a website called CRATER with online calculator
central aim of future educational activities, covered best in geography classes
- Gritsevich, M.
"New Classification Scale for Impact Consequences"
MSU, University of Helsiknki (Russian Federation)
more reliable scale
non-dimensional parameters for asteroid entry
alpha: aerobraking efficiency
beta: fraction of KE to effective destructive enthalpy
u = meteorite rotation
- Mark Boslough
Airburst Warning and Response
looking at modeling airburst less as a point source, effects on ground greater than as point burst, policy implications of where community should go
LAA (low altitude airburst), talking referring to Harris event/mag chart and how difficult to visualize, reason airburst has gained interest is that larger objects have been mostly found
Two types of airbursts (Tunguska free fall and Libyan Desert glass)
nuclear airburst is a bubble, but asteroid energy is carried downward
Type 1 Tunguska airburst: fireball in sky, blast wave hitting ground
Type 2: fireball all the way to the ground
Kind Tut's scarab dung beetle - carved out of Libyan desert glass (referring to Anders Sandberg reference to searching for academic terms)
1908 Tunguska airburst 5 megatons (also trees potentially unhealthy so lower wind speeds could caused damage)
uncertainty quantification required
IPCC likelihood Scale - refer back to this for impact threat
politically relevant time scale is a decade (think in decade times of scales)
not paying attention to public concerns
probability of biggest impact in a decade - number of people - total number
integrates to 1363 (1409) deaths/year
current assessed threat = 126 (152) deaths/year
Future (after next survey) = 5 (17) deaths/year
point (non-point) values
we are going to be so successful that we will put ourselves out of business (for the next hundred years) - good news for humanity and bad news for this community
relative threat from airburst is increasing
100 Mt will dominate threat after current survey
mitigation should focus on small (~100m) NEOs
probability of an airburst in the next decade is about 1% (1 in a 1000 event) - Tunguska like
Probability that asteroid >140 m will be discovered in the next decade is on a collision course in the next century is about 0.1%
we are ~10 times more likely to save lives by reducing imminent impactors in the next survey
Evac plan needs to include uncertainty in size
NRC report: death lunge recommendation: next dangerous event is an airburst from <50m object, not a crater forming event
Proposed Bucharest style Airburst scale from 1 to 5
Research and Entertainment: TC3
Who would be willing to fund to witness the next TC3.
- G. Gisler, "Calculation of Impact of a Small Asteroid on a Continental Shelf"
should not call asteroid tsunami's tsunamis
what is the smallest size asteroid we need to defense against (200 m asteroid)
in Granada advocated: that is Apophis was targeting middle of Pacific because let it fall, well instrument with assets, to understand effects
of the ~200 recognized impact craters worldwide, very few are in the ocean (most on shelf)
tsunami deposits would be a sign of deep water impact
diameter of asteroid has to be 1/5 of depth of water
doing a continental shelf impact simulation, 200 m asteroid into a 100 m + 100 m sediment layers, 526 MT, used sage code with 1.5 m resolution using 200K of CPUs for 165 seconds of physical time
sediment-laden storm surge washes ashore with sand-blasting winds
Atmospheric effects from cont shelf are worse than impact tsunami, damage by blast wave and hot, fast winds
sediment laden surge is similar to powerful tropical storm
sediment on the shelf i lofted and then propelled by winds
propagation distance: 200 m impact (do not want to be 100km-200 km distance)
hydrocarbon finds craters on shelf (propitiatory data): lots more impacts on shelf
shelves are ideal for collapse and get most of tsunami like events
- Dragos Isvornau
"Dynamics of Tsunamis Generated by Asteroid Impact in the Black Sea"
- Verant, J.L
The protective role of Earth's atmosphere against the threat of asteroids"
