Fauxpocalypse is a work of fiction, and focuses mainly on human reactions. But, for those who are interested, we set out some of the possible science behind it.
Is it a bird? Is it a plane? No it’s a…
Two months after that, the story broke in the popular press. “Killer Asteroid Headed Towards Earth” the headlines screamed―which made the astronomers cringe, because of course it wasn’t an asteroid, it was a comet. But that’s the media for you.
– p.1, Fauxpocalypse!, Misha Burnett
So, what is the difference? NASA defines an asteroid as “…a relatively small, inactive, rocky body orbiting the Sun “, whereas a comet is “… a relatively small, at times active, object whose ices can vaporize in sunlight forming an atmosphere (coma) of dust and gas and, sometimes, a tail of dust and/or gas.” (http://neo.jpl.nasa.gov/faq/).
So the differences are:
orbit: asteroids have a relatively stable orbit (mostly between the orbits of Mars and Jupiter) whereas comets follow a longer path;
frozen gases: asteroids do not have atmospheres, whereas comets are wrapped in a cloud of gas.
Grijalva arrives unexpectedly and boils with gases, so is a comet.
Could a comet actually collide with Earth?
Between 16th and 22nd July 1994, pieces of Comet P/Shoemaker-Levy 9 collided with Jupiter. So, if a comet loses enough ice, it can change path and collide with planets. Cometary collisions are not just events from the formation of the galaxy, they are happening now.
Wouldn’t a comet burn up in the atmosphere?
Comets are defined by their frozen gases, so when it entered the atmosphere it would definitely start to lose mass rapidly. However, comets are not only ice; they also contain solid matter.
In 2001 a survey of Comet Borrelly by NASA discovered the surface was completely dry and very hot, similar to many asteroids. This shell of dust and rock was permeable enough for the frozen gases below the surface to form a coma, but also insulated them.
So, like a bully’s evil snowball, a comet could be could be just enough frozen matter to hold a ball of rocks together.
Even investigation of the impact site does not rule out a significant portion making it to the surface. The 1996 survey of the Aorounga craters in Chad concluded they could be caused by either a comet or an asteroid (http://www2.jpl.nasa.gov/sl9/news80.html). So – while deeper investigation of minerals in the area will identify the likely type of object by the presence or absence of gases or metals – the physical force exerted by either can be comparable.
By starting volume, an asteroid would cause more damage; but both are only small compared to planets. Even after losing mass to atmospheric friction, a comet has the potential to cause immense damage.
The immediate effect of a planetary impact could include:
- thermal radiation: the massive release of energy will cause a fireball
- seismic effects: depending on the size and type of impact, earthquakes could be noticeable at a great distance
- tsunami: even if the impact does not occur in water, seismic effects could cause tidal waves
- air blast: the vast quantities of air displaced by the objects passage and by the impact will produce both wind and noise
- ejecta: solid debris will be blasted into the sky, falling a great distance from the impact point
The longer term effects could include:
- Change in planetary orbit: an impact of enough force could alter the Earth’s orbit, changing the length of the days and seasons; or at an extreme, moving the planet out of the Goldilocks zone needed for a viable ecosphere.
- Changes in climate: the massive plume of vapour and debris sent up by impact will change both the visual and chemical properties of the atmosphere. This could lead to a radical change in temperatures, and the reduction or even loss of the ozone layer (http://www.livescience.com/8825-asteroid-strike-force-humans-twilight-existence.html).
Fauxpocalypse does not give the exact impact point, size, angle of entry, or composition of Comet Grijalva, so it is impossible to say what the exact effects would be. However, using the average depth of the Pacific, and the most likely atmospheric entry figures of 45 degrees at a speed of 51 km/s, a 10km object composed entirely of ice could cause the following effects:
|Distance||1,000 km||20,000 km (approx on the other side of Earth)|
|Changes in Orbit||Less than 1/20 degree in the tilt of Earth’s axis and does not shift the orbit noticeably.
The collision might change the length of the day of up to 1.47 milliseconds.
|Changes in Climate||Chlorides and bromides injected into the atmosphere by a 1 km object striking the Pacific Ocean would raise daytime UV levels above human safe limits for most of the planet for 2 years.
No calculations were available for a 10 km object.
|The fireball appears 22.1 times larger than the sun and is 64 times brighter.
Clothing, paper, wood, and vegetation ignite.
Flesh suffers third degree burns.
|The fireball is below the horizon. There is no direct thermal radiation.|
|Richter Scale Magnitude: 9.7 (This is greater than any earthquake in recorded history)
Mercalli Scale Intensity at 1000 km:
Dishes, windows, doors disturbed; walls make cracking sound.
Sensation like heavy truck striking building.
Standing motor cars rocked noticeably.
|Mercalli Scale Intensity at 20000 km:
Not felt except by a very few under especially favourable conditions.
|Tsunami||Tsunami wave amplitude is between: 228 m and 457 m.||Tsunami wave amplitude is between: 11.4 m and 22.8 m.|
|Peak Overpressure: 191,000 Pa
Max wind velocity: 277 m/s
Sound Intensity: 106 dB (May cause ear pain)
Multi-storey wall-bearing buildings will collapse and wood-frame buildings will almost completely collapse.
Highway truss bridges will collapse.
Glass windows will shatter.
Up to 90 percent of trees blown down; remainder stripped of branches and leaves.
|Peak Overpressure: 1650 Pa
Max wind velocity: 3.85 m/s = 8.62 mph
Intensity: 64 dB (Loud as heavy traffic)
|Ejecta||Average Ejecta Thickness: 5.72 cm
Mean Fragment Diameter: 1.27 mm
|Little rocky ejecta reaches this site; fallout is dominated by condensed vapour from the projectile.|
So, even if Grijalva were almost entirely ice (a rock-laden impact would be more destructive) massive fires followed by extensive flooding would probably kill most of the unprepared within a day. While people outside the initial blast radius, who sheltered above sea-level could survive, the loss of the ozone layer could make the Earth’s surface only accessible at night for decades.
A comet larger than any science has discovered, that was also at the low end of gas by volume, is (thankfully) not a high probability; but Grijalva is a possibility.