Post by Quadibloc Post by Lynn McGuire
Because it is their job ?
Because Congress gave them the job some 20 plus years ago? The concern
This is all true enough.
However, it's easy enough to see why someone might infer a paranoid conspiracy
theory about NASA keeping a secret about a deadly asteroid about to hit Earth in
a few years from current efforts to deal with this threat.
only if you’re insane.
Post by Quadibloc
No dinosaur-killer asteroid has hit the Earth in several thousand years of
human civilization. So, obviously, there's no rational reason to expect one to
hit us in the next few thousand years either.
actually, no it doesn’t. the odds of something big slapping the planet are
not affected by past events, or at least not in that way. And sopmething a
lot smaller than a dino-killer would be quite sufficient to make a mess. The
boys at Imperial College, London, and Purdue Uni, West Lafayette, have a nice
little site https://impact.ese.ic.ac.uk/ImpactEarth/ which can be used to
simulate various impacts. I did a run with a small rock:
"Distance from Impact:100.00 km ( = 62.10 miles )
Projectile diameter:500.00 meters ( = 1640.00 feet )
Projectile Density:3000 kg/m3
Impact Velocity:35.00 km per second ( = 21.70 miles per second )
Impact Angle:45 degrees
Target Density:2500 kg/m3
Target Type: Sedimentary Rock"
I used a diameter of only 500 metres, and used a density of 3 tons/cubic
metre, a.k.a. rock and a relative velocity of 35 km/s, a.k.a. probable impact
velocity given the velocity in orbit of the Earth and the velocity in orbit
of an Oort object entering the inner system. Not that 35 km/s is on the low
side, total impact velocities of double that are quite possible, and note
that kinetic energy goes up by the square of the velocity; something moving
twice as fast would have four times the energy. Note also that the angle of
impact makes a difference; too low, and the projectile burns up, or breaks up
and then burns up, in the atmosphere, while too steep and the object treats
the atmosphere as a solid and explodes.
"Energy before atmospheric entry: 1.20 x 1020Joules=2.87 x 104 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during
the last 4 billion years is 3.0 x 105years"
This is the base kinetic energy, prior to atmospheric entry.
"The projectile begins to breakup at an altitude of 65600 meters = 215000 ft
The projectile reaches the ground in a broken condition. The mass of
projectile strikes the surface at velocity 34.4 km/s = 21.3 miles/s
The impact energy is 1.16 x 1020Joules = 2.77 x 104MegaTons.
The broken projectile fragments strike the ground in an ellipse of dimension
1.08 km by 0.762 km"
This is the energy on impact. Note that the object slows from 35 km/s to 34.4
km/s on the way down. Note that the object starts to break up. An object of
lower density (comets are mostly water ice, density 1 ton/cubic meter) would
break up at a higher altitude and might not make it all the way down,
depending on angle of entry. An object of higher density (an iron meteor,
density around 8 tons/cubic meter) will both make it down in one piece and
not lose as much velocity.
"Crater shape is normal in spite of atmospheric crushing; fragments are not
nt)Diameter:8.4 km ( = 5.21 miles )
Transient Crater Depth:2.97 km ( = 1.84 miles )
iameter:11.1 km ( = 6.92 miles )
Final Crater Depth:611 meters ( = 2010 feet )
The crater formed is acomplex crater
The volume of the target melted or vaporized is 0.729 km3= 0.175 miles3
Roughly half the melt remains in the crater, where its average thickness
is13.2 meters ( = 43.2 feet )."
the crater would be normal, and would be 11.1 km in diameter. Note that this
means that if the object hit an urban area, kiss that urban area buh-bye,
"Time for maximum radiation:284 millisecondsafter impact
Visible fireball radius:8.96 km ( = 5.57 miles )
The fireball appears20.4times larger than the sun
Thermal Exposure:4.97 x 106Joules/m2
Duration of Irradiation:2.11 minutes
Radiant flux (relative to the sun):39.2
Effects of Thermal Radiation:
Much of the body suffers third degree burns
Deciduous trees ignite
Above are the thermal radiation effects at 100 km, the distance I specified.
Note that the blast is causing serious burns and fires at a range of 100 km.
If this object landed in Central Park in New York, then New York City is
gone, and New Jersey and Connecticut are going to feel real pain.
"The major seismic shaking will arrive approximately 20 secondsafter impact.
Richter Scale Magnitude:7.6
Mercalli Scale Intensity at a distance of 100 km:
VI. Felt by all, many frightened. Some heavy furniture moved; a few instances
of fallen plaster. Damage slight.
VII. Damage negligible in buildings of good design and construction; slight
to moderate in well-built ordinary structures; considerable damage in poorly
built or badly designed structures; some chimneys broken."
Above are the seismic effects, at 100 km range. Kiss any trailer parks
goodbye. Properly constructed buildings may be on fire, but won’t have
damage due to the initial shock.
"The air blast will arrive approximately5.05 minutesafter impact.
Peak Overpressure:58100 Pa = 0.581 bars = 8.24 psi
Max wind velocity:112 m/s = 250 mph
Sound Intensity:95 dB(May cause ear pain)
Multistory wall-bearing buildings will collapse.
Wood frame buildings will almost completely collapse.
Glass windows may shatter.
Glass windows will shatter.
Up to 90 percent of trees blown down; remainder stripped of branches and
Oops. Here’s the secondary blast. We got trouble in River City. Those
burning buildings which didn’t have much damage from the initial shock are
now collapsed. Add Pennsylvania to the areas which will feel pain.
Remember, this is a small rock, moving relatively slowly. Bigger, faster,
rocks will be much worse. I had it hit sedimentary rock; a water impact would
have been much worse. A water impact would generate tsunamis, and the wave
from a water impact near New York would cross the Atlantic.
Post by Quadibloc
Given that, unless NASA knows something it's not telling us, research to
find ways to deflect incoming asteroids is _obviously_ a complete waste of money.
Hence, because our government never wastes money on useless projects just
because they're in some influential Congressman's district, clearly NASA knows
something it's not telling us.
Given the destruction that even a small rock can do, taking precautions is a
Good Idea (™).
Post by Quadibloc
As it happens, though, a large asteroid-sized comet is heading for
the Sun at this moment. It won't get any closer than the orbit of Saturn...
but for it to be coming this far in from where it was, 'way out in the Oort
Cloud, not the Kuiper Belt, means that it's really just luck that it isn't heading
in to hit the Earth.
Maybe we are currently heading into a dustier part of the galaxy where incoming
bodies will be a bit more common than they have been in the last while. That
I could accept.
all we need is one...