Apophis:%20the%20End%20of%20the%20World%20is%20Nigh?

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Apophis the End of the World is Nigh?

• Mark Kidger
• INSA y Herschel Science Centre

2
Over the last 25 years awareness of the asteroid
threat has increased rapidly. Hollywood has
brought the danger to the public notice.
3

• But some big, tough, action man always saves the
  day and destroys the nasty asteroid, even if NASA
  have only 2 weeks warning to do it!

4
The evidence that the extinction of the dinosaurs
is linked to a huge impact in Yucatan is now
regarded as almost conclusive.
5
The K-T boundary layer of grey clay, rich in
iridium is found all around the world.This layer
is from Gubbio (Italy).
6
A gravity map reveals a large (gt100km) crater in
the ocean floor off the coast of Yucatán (Mexico)
dated at 65Myr old.
7
Some scientists suggest though that the impact
may only have been the et tu Brute after the
eruption of the Deccan Traps supervolcano.
8
In a period of just 30 000 years, a 600-m depth
of lava outflowed from this structure in
India.It was part of a 2-3x106km3 release of
lava from a 5x105km2 area over some 2 Myr.
9
Could the human race go the same way as the
dinosaurs?If there is a threat, how should it be
communicated?
The fate of the dinosaurs has focussed public
concern on the question
When will I be able to get that HSpot Manual
update done now?
10
With the exception of Io, every solar system body
that we have looked at has impact craters on its
surface. These reveal the violent history of the
solar system.
11
The relatively small number of fresh, young
craters shows that the impact rate at present is
very low, especially compared to the early
history of the solar system.
12
However, craters such as the Barringer Crater in
Arizona
13
or Wolf Creek, in Australia, show that
significant impacts still happen.
14
However, its as well to mention that, however
impressive it looks, unlike many lunar craters,
the Arizona crater can barely seen from space
15
Asteroid surveys show that there are still some
dinosaur-killers in near-Earth space, like the
one that produced the Manicouagan crater in
Quebec.
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Manicouagan is 100km in diameter and was formed
about 214 millon years ago by an asteroid around
7km in diameter.
Stereo view
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The impact would have caused severe destruction
over a 2000km diameter.
18
The largest Potentially Hazardous Asteroid (PHA)
(4953) 1990 MU is also approximately 7km in
diameter and is a high velocity impactor,
although of no immediate threat to the Earth in
the next few millennia.
19
If we take a long-term view, the even larger
(933) Eros (maximum diameter 35km) will probably
impact in the next 100 million years or so.
20
If proof is needed that impacts still happen,
2008 will mark the centenary of the Tunguska
event.
21
Trees were blown down up to 15km away and people
blown off their feet 50km away.
22
Tunguska was an airburst at about 8km altitude,
greatly increasing its destructive force, which
was probably about 3-4Mt (as opposed to the 30Mt
usually found in books and articles, which would
only be a valid value had it been a groundburst).
23
It was probably caused by an object about 40-m in
diameter, similar to Idas moon, Dacyl.
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The Asteroid Threat Significant or overstated?

• In December 2004 the Tenerife Science Museum
  hosted a very singular conference.
• A multidisciplinary group of 50 experts in such
  diverse fields as geology, astrophysics,
  volcanology, medicine, insurance, strategic
  planning and tsunamis met to discuss the impact
  threat.

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The meeting was held under the auspices of the
ICSU the International Council of Science. It
was organised by the President of the
International Geological Union Peter Bobrowsky
(top) The General Secretary of the
International Astronomical Union Hans Rickman
(bottom) Participation was by strict invitation
and included representatives of organisations
such as UNESCO.
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• The aim was to discuss all aspects of the
  asteroid threat
• The near space inventory
• The evidence for historical impacts
• The consequences of an impact
• The societal implications of announcing an
  impact threat
• The medical capacity to respond to an impact
• Etc.

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The Nature of the Impact Risk

• Risk is strongly dependent on size.
• Objects larger than 1km diameter
• Potential global consequences
• Objects 100-m to 1km
• Potential regional consequences
• Objects 40-m to 100-m
• Potential local consequences
• Land impact consequences
• Blast wave, firestorm, nuclear winter from dust.
• Sea impact consequences
• Tsunami, changes in ocean currents, climate
  change.

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Just 3 weeks later, the Asian tsunami showed the
effects of even a small (2-m) tidal wave
29
Some 80 000 people died from the effects of a
tsunami perhaps one twentieth of the height of
that expected from a moderate sea impact.
Before
After
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On November 1st 1755 Lisbon was largely destroyed
by a tsunami. Many of the worlds largest cities
are on the coast and the many of the most
vulnerable members of society live in the poorest
and most exposed coastal housing.
31
Much industrial activity and nuclear power
generation is situated on vulnerable coasts too.
This leads to enormous concern about the effects
of possible impact tsunami.
But
32
However, evidence was presented that the tsunami
threat from ocean impacts may have been greatly
overstated. Some studies have suggested that the
short wavelength of impact tsunami means that
they will decay rapidly, particularly when
crossing continental shelf, and are not capable
of crossing large distances while remaining
destructive.
33
Other evidence was presented that suggested that
the threat of nuclear winter from a land impact
has also been greatly overestimated. The amount
of dust launched into the high atmosphere may be
only a tiny fraction a few percent of what
has been suggested previously.
34

• The estimated frequency of small impacts like the
  Tunguska event has recently been reduced by a
  factor of 10 from 1 per 100 years to 1 per 1000
  years.
• This would make even another small, Tunguska-like
  impact extremely unlikely in the next few
  decades.
• Larger events that would be a threat to humanity
  would be even less likely.
• The principal threat would be the background from
  high-velocity Oort Cloud comet impacts
  (intrinsically unpredictable and with usually
  little warning).

35
It was suggested, by some delegates at the
Tenerife meeting, that other catastrophic events,
such as the collapse of La Palma, might be a more
severe long-term danger than asteroid impacts.
36

• However, not everyone agrees with this risk
  assessment.
• At present, even the optimists accept that we
  only know about two-thirds of the impact risk.

• Even the deepest planned surveys in the future
  will only be complete for 300-m diameter objects.
• And, just 3 weeks after the meeting, the most
  dangerous object known to date was found.

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The Threat

• As of today, there are 139 asteroids on the JPL
  current impact hazard list.
• Only 5 of these have been observed recently (i.e.
  in the last 2 months).
• In many cases the orbit is based on a very short,
  poorly observed arc.

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• The total probability is 1 that one of the 139
  asteroids will impact in the next century.

39

• However, about 70 of that risk comes from just
  2000 SG344 and 2006 JY26 estimated to be about
  40-m and 7-m diameter respectively. Such small
  objects will normally explode in the atmosphere
  and not reach the surface.

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• The immediate impact risk from 100-m diameter or
  larger bodies
• 26 asteroids have 679 impact solutions between
  2009 and 2106.
• Total impact probability 1.38x10-4 (1 in 7250).
• Median impact energy 640Mt.

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• The first predicted potential impact is by 2004
  XY130
• Very low impact probability on April 18th 2009
• 500-m diameter
• Impact energy about 3000Mt
• But
• Based on an orbit from observations covering just
  2 days in December 2004.

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The 5 most dangerous asteroids in the next
century
Years No. Impacts Tot. Prob. d (km) vimpact (km/s) Eimpact (Mt) PE (Mt)
1979 XB 2056-2101 3 3.30E-07 0.685 27.0 3.79E04 1.25E-02
99942 Apophis 2036-2037 2 2.20E-05 0.25 12.6 4.05E02 8.91E-03
1998 HJ3 2100-2104 3 2.10E-07 0.694 26.6 3.82E04 8.03E-03
2004 XN44 2013-2102 18 2.90E-07 0.73 17.3 1.89E04 5.49E-03
1994 WR12 2054-2102 134 1.00E-04 0.11 14.9 4.79E01 4.79E-03
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What is (99942) Apophis?

• Discovered June 19th 2004 from Kitt Peak
  (Arizona).
• Designated 2004 MN, it was observed only on June
  19th 20th.
• It was then lost until December.

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• It was recovered on December 18th 2004 by the
  Australian amateur Gordon Garradd.
• It was later named Apophis for the Egyptian
  serpent god of destruction.
• Apophis passed 14.4 millon km from the Earth on
  December 21st 2004.
• Then

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On December 23rd 2004, JPL and the University of
Pisa broke the news of a possible Earth impact on
April 13th 2029, with an unusually high
probability.
46
The impact probability reached as high as 1 in
40. This was by far the highest impact
probability ever detected. No asteroid had ever
reached 2 on the Torino threat scale Apophis
reached 4 and came close to 5 (threatening).
47
The Apophis Threat File

• Estimated diameter 400 metres
• Impact velocity 12.6km/s
• Explosive force 1500 Mt
• Equivalent to 80 000 times the Hiroshima bomb.

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Probable impact point the North Atlantic Ocean.
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An impact of Apophis in these conditions would
have excavated a crater in the water 7.8km in
diameter and 2.7km deep.
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By one estimate the impact tsunami would be 100m
high. It would still be 10 metres high after
crossing the Atlantic.
51
On December 27th Apophis was located in images
taken at McDonald Observatory (Texas) in March
2004.
These eliminated an impact solution, for 2029,
but confirmed that Apophis would make an
exceptionally close pass.
52
The current miss distance is calculated to be 34
660km from the centre of the Earth.
It will be an easy naked-eye object crossing the
sky southeast to northwest over several hours.
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But the new observations showed a new impact
solution.

• A gravitational deflection of the orbit could
  lead Apophis to an impact on April 13th 2036.

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• There is a keyhole at a miss distance around 37
  000km, at which a pass through a corridor of
  ?100m would lead to an impact 7 years later.

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• Radar observations have fixed the position and
  velocity of Apophis with great precision and
  given size and shape information.
• But there continues to be a possible error of
  /-1000km in the 2029 miss distance.
• As a result there is still a 1 in 45000
  probability of Earth impact in 2036.
• This is still by far the highest current impact
  probability for a large asteroid.

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• In case of impact it would probably be in the
  North Pacific, but there is a risk from the North
  Atlantic to Siberia.
• Even though Apophis seems to be smaller than
  first thought, the impact tsunami would be at
  least 50 metres high.
• Hundreds of millions of people would have to be
  evacuated from coastal regions of the Pacific Rim
  and Pacific islands.

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What does a 1 in 45 000 risk mean?

• 1 in 45 000 is approximately the chance of
  winning the Gordo in the Spanish Christmas
  lottery by buying 2 tickets.
• Not a chance many people would bet on.
• But, someone always ends up winning.
• It is estimated that, for an American citizen,
  the risk of dying from an asteroid impact is
  about the same as that of dying in a terrorist
  attack.
• But, is the 1 in 7250 risk of an impact
  equivalent to a 650Mt explosion in the next
  century really so low as to be ignored safely?
• 1 in 7250 is a far larger risk than that from
  living alongside a nuclear power station.

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What can we do?

• On January 9th 2013 Apophis will make a
  relatively close pass to the Earth.
• Measures of its position and, in particular,
  radar measurements will refine the orbit with far
  greater exactitude.
• If there is still an impact risk, a radio buoy
  could be dropped on the surface of the asteroid
  by an automated probe.
• The radio signal could be used to determine the
  orbit with sufficient precision to confirm or
  deny a 2036 impact and to determine the potential
  impact point with precision.
• If there is STILL an impact risk, there would be
  23 years to decide and implement strategies to
• Avoid an impact or, if unavoidable,
• To limit the resulting damage.

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Impact Mitigation

• Hollywood movies suggest sending a large
  muscleman with a big bomb.
• Not a very effective solution.
• Breaking an asteroid into several, slightly
  smaller pieces will probably make it more
  dangerous, not less!
• A small force, applied 20-30 years before impact
  is far more effective.
• We only need to alter the trajectory such that at
  impact date the asteroid will have shifted by
  6000km.
• Simple solutions such as painting the sunward
  hemisphere white and allowing radiation pressure
  to change the orbit are low-tech, but very
  effective.
• Creating directed outgassing, for example using a
  powerful laser to heat the surface, would be a
  possible alternative.

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(29075) 1950 DA Danger for our descendants

• On Feb. 23rd 1950 Carl Wirtanen discovered what
  appeared to be just another asteroid.
• It was observed for 17 days and then lost.
• On Dec. 31st 2000 it was rediscovered.

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• The orbit crosses the Earths orbit.

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• Radar observations from Goldstone (California) in
  March 2001 showed that
• It is 1.1km in diameter
• It is almost spherical
• It has a rotation period of 2.1 hours and
• It could hit the Earth on March 16th 2880.

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The impact probability may be as high as 1 in 300.
The deciding factor is the effect of thermal
reemission on solar heating depending on how the
pole is orientated this force will direct itself
one way or another.
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What would the effects of an impact be?

• Velocity 17.6km/s.
• Impact energy 70 000Mt.
• A land impact would make a 16km crater.
• There would be a total destruction zone of
  approximately 250km.
• But, in the sea, 600km from the east coast of the
  USA

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Ward Asphaug (2003, Geophys J. Int, 153,
F6-F10). 1950 DA impact modelling.
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Their findings contradict the suggestion that an
impact tsunami would have a short lifetime and
would collapse quickly. 15 hours after impact off
the coast of New England a tsunami nearly 25-m
high would hit the west coast of the British
Isles. It would take 2.5 hours to build up. The
Atlantic coast of the Iberian Peninsular would be
hit by a tidal wave 15-20 metres high.
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How to Protect the Earth?

• The danger of an impact in any year is very
  small.
• Current estimates predict a Tunguska event
  every 1000 years.
• You have to be very unlucky to suffer an impact.
• But, the possible consequences are so grave that
  it is foolish to ignore the risk.
• The first step is the NASA-led inventory of
  near-Earth space.
• All potential impactors need to be found and
  tracked.
• If we find an object that may impact in 20-30
  years time, there are mitigation strategies.