Transcript Hazardous Near-Earth Asteroids: To Defend or Not?

Hazardous Near-Earth
Asteroids: To Defend or Not?
Clark R. Chapman
Southwest Research Inst.
Boulder, Colorado, USA
“Astrobiology Societal Issues Workshop”
SETI Institute, Mountain View CA
Evening Panel: 9 February 2009
Sizes and Impact Frequencies
of NEOs
Smallest, most
frequent
Leonid meteor
shower
“NEOs” = Near
Earth Objects.
Peekskill meteorite
Huge,
extremely rare
Tunguska, 1908
K-T mass extinctor, 65 Myr ago
SL9
hits
Jupiter
1994
What Do We Know About the
Impact Hazard?
 How many asteroids and comets there are of
WE KNOW THIS…
various sizes in Earth-approaching orbits (hence,
impact frequencies are known).
 How much energy is delivered by an impact (e.g.
the TNT equivalence, size of resulting crater).
 How much dust is raised into the stratosphere
and other environmental consequences.
 Biosphere response (agriculture, forests, human
beings, ocean life) to environmental shock.
 Response of human psychology, sociology,
political systems, and economies to such a
catastrophe.
Impacts of Practical Concern
• Mass extinction events are too improbable to worry about
• Meteorites do minor damage, are a minuscule fraction of the
hazard from “falling objects”
 Statistical mortality rate once
Spaceguard Survey is
complete in a couple years
 Current rate (many hundreds/
year) will be down to a couple
hundred per year, mainly by
removing threat of “Global”
impactors > 2 km diameter
 Dominant threat will remain for
“Tunguskas,” for which there
is a several-% chance this
century that one will strike and
kill hundreds or thousands of
people.
 Thus Tunguskas and their
smaller cousins will dominate
public interest in the impact
hazard.
Worldwide Deaths (Annual)
Death Threat from Impacts, by Asteroid
Diameter and Location of Impact
(For nominal case)
Global
Land
Tsunami
Asteroid Diameter (km)
How the mortality
will diminish from the three kinds
of impacts as the Spaceguard
telescopic searches continue
Consequences of a Large, Rare
Civilization-Threatening Impact
 Total destruction in near-crater zone

Destruction zone 30 times the size of the asteroid
 Tsunami (“tidal waves”)

Inundation of shores of impacted ocean
 Stratospheric dust obscures sun

Sudden global climate change threatens agriculture
 Widespread fires

Re-entering ejected material broils Earth’s surface
 Poisoning of the biosphere

Sulfates, nitric acid, ozone layer destroyed
 Earthquakes

Modest effects compared with everything else
Consequences from Small,
Likely Impacts
“9/11”
 Damage & casualties are at most
like a minor natural disaster (e.g.
tornado, wildfire)
 Public and national over-reaction
after 9/11 (stock market, homeland
security hysteria, Iraq war) could be
replicated by a modest but
unexpected impact disaster.
 An otherwise harmless but brilliant
OVER KASHMIR? OVER ISRAEL? HOW
WOULD THE GENERALS RESPOND?
bolide (fireball) could be mistaken
for an atomic attack, causing a
dangerous response.
 Even sensational journalism or a
mistaken prediction about a
possible future impact can be
disruptive.
The Impact Hazard in Perspective
* Unlike most natural disasters, we can predict
an NEO impact…and warn.
* Unlike any other natural disaster, we can
deflect the NEO, so the impact doesn’t happen.
 Most effects are individually familiar (fire,
wind, falling debris, seismic shaking…)
Meteorite punctured
roof in Canon City, CO


Disaster responders face nothing truly alien
Synergy of many different effects in 1sr 10 min.
 Warning versus no warning (time and location)



Deaths and injuries are dramatically reduced with warning
Property damage can be lessened somewhat with warning
Even with no warning, people can reduce exposure by taking
cover (within seconds to minutes) if they have been educated
to recognize what’s happening (Indian Ocean tsunami analogy)
 Impact disasters: local/regional versus global


Like Katrina, earthquakes, or wars, unaffected
people can provide emergency response…
…But NOT if the consequences are global
The Spaceguard Survey…Now
and Prospective
Kitt Peak Natl. Observatory
LSST
LINEAR, New Mexico
 Spaceguard Survey: 1998 to
2008, find 90% of NEAs >1
km diameter (85% complete
as of 2009)
 Congress ordered NASA to
find 90% of NEAs >140 m by
2020
Deflect an Asteroid so it
Misses the Earth
 Most threatening
Kinetic Impactor
Gravity Tractor
Stand-off
Nuclear
Blast
NEOs are small.
One can be
deflected either (a)
by a “Gravity
Tractor” (GT) or (b)
by striking it with a
“kinetic impactor”
(like Deep Impact),
then “trimmed” by
a GT
 If an NEO is very
big or there is
short warning
time, only a
nuclear device
would be powerful
enough to work
Apophis: To Tell or Not to Tell…


In what was a 1-chance-in-37 that
it would hit in 2029, extreme
destruction would occur within a
corridor near the blue line
You can hardly imagine a line
crossing more geopolitically
sensitive, densely populated
areas.
Population Density
Apophis now has
1-in-45,000 chance
of passing thru a
keyhole in 2029,
then striking
somewhere on
path-of-risk on
April 13, 2036
There was hot debate about
whether to release the
possible impact points after
they were calculated on Dec.
24th 2004. NASA officials,
scientists argued we should
wait for perhaps a year. But
withholding information from
the public violates riskcommunication principles!
Societal Issues
 NEO impacts: are they an Astrobiological issue?
 NEOs affected the origin and evolution of life on Earth
 NEOs currently present a “potential hazard to our home planet”
 NEOs could well affect the (probably distant) “future of life on Earth”
 Big impacts raise philosophical concerns (end of civilization)
 Small impacts are a largely unrecognized element of the field of
“natural hazards”: public fears/perceptions, political response
 Deflection toolbox:


Smallest NEOs: do we deflect (at great cost) or let them hit? (We can
always mitigate, evacuate, undertake usual disaster response.)
Largest, most dangerous, but most unlikely NEOs >1 km require nuclear
technique: Do we use it? Should we even discuss it and research it?
 “All-hazards” approach to natural disasters should include NEOs.
There’s no national or international responsibility (yet).
 Unusual international political, military, legal issues: being
addressed by ASE input to UN (COPUOS)
What’s Happening Now…
 The National Research Council is doing a
study of the NEO hazard, including detection
and mitigation: the Shapiro Committee’s
report is due by Dec. 2009
 The Association of Space Explorers’ report
“Asteroid Threats: A Call for Global Response”
will be presented to the United Nations
(COPUOS) later this month concerning
protocols and a management structure for
an international approach to the NEO impact
hazard
 The next Planetary Defense Conference
(sponsored by the International Academy of
Astronautics) will be in Granada, Spain, 2730 April 2009
Comet McNaught
433 Eros
Numbers of Small NEOs
Known and to be Discovered
Incremental numbers: 0.5 mag. Intervals centered on listed mag. and size.
H
Diam. (km)
17.75
22.02
24.26
25.36
27.75
29.26
1.0
0.14
0.05
0.03
0.01
0.005
Data courtesy A. Harris (June 2007)
Known Now
No. % of Tot.
SG1 (goal)
No. % of Tot.
SG2 (goal)
No. % of Tot.
234
162
147
85
17
6
280
450
1200
640
200
30
333
4000
80000
2 million
400000
200000
59
3.5
0.09
0.01
1e(-6)
3e(-8)
83
9
0.6
0.08
1e(-5)
3e(-7)
98
83
40
20
2
0.2
 The discovery rate for 10 m NEAs may go up 2000 times!
 By the end of SG2, we will know nearly half of Tunguska-class NEAs.
 We will then be tracking 2 million 30 m objects; any threatening one
will demand attention, even if impact damage might be minimal.
 Think of the implications for meteoroids research: a quarter-million
known objects 5 m in size!
How Important is NEO Threat? We’ve
Many Other Things to Worry About!
9/11
Source: John Pike
NEO impact similar to this
Mortality
Source: Johnfrom
Pike Twentieth Century Catastrophes
Public Perception
 An impact disaster has never
been experienced in recorded
history.
Odds of a “Royal Flush” (1 in
649,739) are like chances of a 1.5
km-wide asteroid striking next year!
 The tiny chances combined with
huge consequences are difficult
for people to comprehend (e.g.
building in floodplains…or hoping
to win the lottery).
 The impact hazard is “dreadful”
and “apocalyptic”…hence
people may over-react.
 Scientific/mathematical
illiteracy prevails.
You’re kidding! I
was struck twice
by lightning, too!
How Well do we Plan for and Respond to
Other Disasters?
Guatemala, Hurricane Stan
Hurricane Katrina
Indian Ocean Tsunami
Kashmir Earthquake
Comparing NEO Impacts and
Climate Change
NEO Impact
Climate Change
Similarities…
Similarities…
• They can potentially affect the globe
• Global warming is planetary in scale
• Asteroids can be deflected to miss Earth
• Society can reduce greenhouse gases
Dissimilarities…
Dissimilarities…
• Global effects within 2 hours, global
climate change within months
• Timescale for major changes: about one
century
• Extremely unlikely to happen this century
• Actually underway right now
Will an NEO Destroy
our World?
Alabama, 1954
 The NEO hazard helps us contemplate
the most extreme environmental
disaster and put the lesser, more likely
ones into context…
 …and to distinguish between societal
issues and true catastrophes.
 Many threats to society and our lives
(flu, war, famine…even global
warming) are here today.
 Asteroids are in our future…as places
to travel to, as fuel stations for a
spacefaring civilization.
Arecibo radar
(Pat Rawlings, SAIC)
Asteroid Itokawa
The Torino Scale (to communicate
seriousness of predicted NEO impacts)
 Astronomers tried to learn from other risk
communicators and developed a color-coded scale.
 Official scale: the words (for TS = 0 – 10, 1 dimension)
 TS is a simplification of the Palermo Scale, based on
energy, probability, how far in future (3 dimensions).
 Designed pedagogically to illustrate unlikelihood of
catastrophe: nearly all cases would be TS=0 or TS=1.
 Adopted by IAU in 1999, used by most news media.
 Homeland Security Terrorism scale became a joke.
 Behind-the-scenes arguments about T.S., but it’s OK.
 Then in Dec. 2004 Apophis blew it away: TS = 4!
Chances of Dying from Selected
Causes (for U.S.A.) (Chapman/Morrison 1994)
Reduced risk
thanks to
Spaceguard
since 1998
By terrorism
(much due to
Sept. 11th)
9/11