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Atmospheric Heating from Meteorite Impact

  1. Jul 24, 2017 #1
    I am proposing a collision between Earth and the Centaur 10199 Chariklo (a.k.a. 1997 CU26). For the actual collision information I used the "Impact Earth" web site from Purdue University. This is the data I used:

    10199 Chariklo (a.k.a. 1997 CU26)
    Diameter:
    248 ± 18 km (334 x 266 x 172 km)
    Density: 3.493 g/cm3
    Mass: 2.23E+20 kg

    Angle of Impact: 45°, from east to west
    Impact Velocity: 23 km/s (51,450 mph)
    Location of Impact: 14.032281°N, -158.039055°W
    Water Depth: 2,076 meters (6,810 feet)

    The following "spoiler" are the results of the impact from various locations on Earth. I've included the results for those who are interested, but my question pertains to the information not being provided by the Purdue University "Impact Earth" web site.

    Results of the Impact Globally
    Energy before atmospheric entry: 7.38 x 1027 Joules = 1.76 x 1012 Megatons of TNT

    The Earth is not strongly disturbed by the impact and loses negligible mass.

    The impact does not make a noticeable change in the tilt of Earth's axis (< 0.05°). Because the impact strikes from east to west at a 45° angle 14° north of the equator, it causes an increase in the length of the day, slowing Earth's rotation by 28.7 seconds. The impact does not shift the Earth's orbit noticeably.

    The crater opened in the water has a diameter of 1,500 km (928 miles).
    Transient Seafloor Crater Diameter: 912 km (566 miles)
    Transient Seafloor Crater Depth: 322 km (200 miles)
    Final Seafloor Crater Diameter: 2,220 km (1,380 miles)
    Final Seafloor Crater Depth: 3.01 km (1.87 miles)

    The crater formed is a complex crater. The volume of the target melted or vaporized is 46 million cubic km (11 million cubic miles). Roughly half the melt remains in the crater, where its average thickness is 70.5 km (43.8 miles ).

    The earthquake will be felt world-wide with a magnitude of 12.8. The time the seismic waves arrive varies from location to location, but not the magnitude of the earthquake. The earthquake will last for several minutes, and the aftershocks (greater than magnitude 5.0) will be felt for weeks afterward. The tsunamis will continue for days after the impact, gradually diminishing.

    Results of the Impact from Honolulu, Hawaii – 806.86 km (501.36 miles)
    The earthquake will arrive approximately 2.69 minutes after impact. Just 7.8 seconds after the seismic shaking the entire State of Hawaii will be entirely engulfed within the fireball.

    Thermal Exposure: 5.32 x 1012 Joules/m2
    Duration of Irradiation: 14.1 hours
    Radiant flux (relative to the sun): 105,000

    The ejecta will arrive approximately 7.28 minutes after the impact. The State of Hawaii is beneath the continuous ejecta deposit.

    Average Ejecta Thickness: 11.8 km (7.3 miles)
    Mean Fragment Diameter: 6.53 cm (2.57 inches)

    The air blast will arrive approximately 40.8 minutes after impact.

    Peak Overpressure: 329 million Pascals; 3,290 bars; 46,800 psi
    Maximum wind velocity: 14,600 m/s (32,700 mph)
    Sound Intensity: 170 dB

    The entire State of Hawaii is within the crater formed by the impact, and in less than an hour after impact ceases to exist.

    All of the forests along the entire Pacific coast, from Alaska to Chile and from Siberia to Australia, are ignited by the thermal radiation.

    Results of the Impact from San Francisco, California – 4,389.37 km (2,727.43 miles)

    The fireball appears 126 times larger than the sun.

    Time for maximum radiation: 2.82 minutes after impact
    Visible fireball radius: 2,440 km (1,520 miles)
    Thermal Exposure: 9.8 x 1010 Joules/m2
    Duration of Irradiation: 14.1 hours
    Radiant flux (relative to the sun): 1,940

    The major seismic shaking will arrive approximately 14.6 minutes after impact, 11.78 minutes after the fireball appears.

    The ejecta will arrive approximately 23.3 minutes after the impact, 8.7 minutes after the seismic shaking begins. There will be a fine dusting of ejecta with occasional larger fragments.

    Average Ejecta Thickness: 73 meters (240 feet )
    Mean Fragment Diameter: 734 microns (28.9 thousandths of an inch)

    The air blast will arrive approximately 3.69 hours after impact.
    Peak Overpressure: 6.83 million Pascals; 68.3 bars; 970 psi
    Maximum wind velocity: 2,090 m/s (4,670 mph)
    Sound Intensity: 137 dB

    The tsunami waves begin to arrive approximately 8.55 hours after impact. The tsunami wave amplitude is between 354 meters (1,160 feet) and 707 meters (2,320 feet).

    Results of the Impact from New York City, New York – 8,516.84 km (5,292.12 miles)

    The major seismic shaking will arrive approximately 28.4 minutes after impact.

    The ejecta will arrive approximately 47.9 minutes after the impact, 19.5 minutes after the earthquake begins. There is a fine dusting of ejecta with occasional larger fragments.

    Average Ejecta Thickness: 10 meters (32.8 feet )
    Mean Fragment Diameter: 127 microns (4.99 thousandths of an inch)

    The fireball is below the horizon. There is no direct thermal radiation.

    The air blast will arrive approximately 7.17 hours after impact.
    Peak Overpressure: 1.53 million Pascals; 15.3 bars; 217 psi
    Maximum wind velocity: 961 m/s (2,150 mph)
    Sound Intensity: 124 dB

    The impact-generated tsunami wave arrives approximately 16.6 hours after impact. Tsunami wave amplitude is between 182 meters (598 feet) and 364 meters (1,200 feet).

    Results of the Impact from London, England – 12,400.42 km (7,705.27 miles)

    Little rocky ejecta reaches London. The fallout is dominated by condensed vapor from the projectile.

    The fireball is below the horizon. There is no direct thermal radiation.

    The major seismic shaking will arrive approximately 41.3 minutes after impact.

    The air blast will arrive approximately 10.4 hours after impact.

    Peak Overpressure: 666,000 Pascals; 6.66 bars; 94.6 psi
    Maximum wind velocity: 606 m/s (1,360 mph)
    Sound Intensity: 116 dB (may cause ear pain)

    The tsunami waves begin to arrive approximately 24.1 hours after impact. The tsunami wave amplitude is between 125 meters (410 feet) and 250 meters (821 feet).

    While "Impact Earth" provided valuable information, it did not answer a question I had concerning atmospheric heating. The thermal radiation from the resulting fireball would be sufficient to ignite all the forests around the Pacific Coast, but just how far would 7.38 x 1027 Joules of energy spread beyond the horizon?

    I have attempted to look up the information, but I get conflicting results. Some claim there would be significant atmospheric heating, others claim there would be a cooling of the Earth due to the debris in the atmosphere.

    According to the simulator "Universe 2" (which I do not consider a credible source on climate issues) depicts the collision increasing the atmospheric temperature in excess of 5,000°C within the first 72 hours after impact, then diminishing over a ~90 day period before returning back to normal. Needless to say, such temperatures would not only boil off all the oceans, but also turn the entire surface of the planet molten.

    Which is what brings me to the Physics Forum. What better place to get an answer to how much atmospheric heating - world-wide - an impact of this size would cause?

    Sources:
    Global climatic effects of atmospheric dust from an asteroid or comet impact on Earth - Global & Planetary Change, Volume 9, Issues 3-4, December 1994, Pages 263-273
    An experimental assessment of the ignition of forest fuels by the thermal pulse generated by the Cretaceous–Palaeogene impact at Chicxulub - Journal of the Geological Society, March 2015
     
  2. jcsd
  3. Jul 25, 2017 #2

    mfb

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    2016 Award

    Staff: Mentor

    A few rough estimates: If the whole surface of Earth is heated to 5300 K, it emits the full impact energy within 4 days. Assuming no process adds significant energy to the impact energy, it can't stay that hot for longer than 4 days.

    The initial temperature will depend on how much energy is deposited where. everything into the atmosphere certainly doesn't work. Everything into the oceans is more than sufficient to boil them (2200 J/g).
    If a significant part of the energy goes into the atmosphere, the atmosphere will escape and the remaining surface could be quite hot. If a large part is distributed evenly over the oceans, we get a lot of water vapor, but it won't be hot enough to escape. It won't reach 5300 K either. It could be that the surface gets really hot, but then the boiling oceans reduce the temperature quickly.
     
  4. Jul 25, 2017 #3
    Not to worry, I did not take Universe 2 seriously. As you say, all that energy is not going to be deposited in just one location. That impact energy is going to be distributed between the atmosphere, the ocean, and the land it impacts, and while there will certainly be global effects, a lot of that energy is also going to be reflected back into space in a giant plume.

    Temporarily vaporizing much of the Pacific Ocean seems plausible. There will be indirect thermal radiation effects felt beyond the horizon, there is no doubt about that. While the air blast may traverse the globe (probably several times), it does not seem likely that the indirect thermal radiation effects would travel that far, but I could be wrong. I would like to know just how far the indirect thermal radiation would travel beyond the horizon. Knowing this, or at least having a rough estimate, would help assess the damage to the ozone layer world-wide and how much nitrogen is scorched out of the atmosphere.

    Based upon the wind speeds "Impact Earth" provides, even as far away as London, it is hard to imagine how more than 10% of the trees on the planet would remain standing. I lose trees on my property in 100 mph winds, and we are talking 13 times that speed in London. I don't think there are many high rises in New York City that can withstand 2,150 mph either. The Purdue University web site does not give a duration for these wind speeds, but I do not think it is unreasonable to assume the winds would last as long as the duration from the irradiation of the blast - 14.1 hours.

    Would not the speed of the winds contribute the to distribution of the indirect thermal radiation? While the indirect thermal radiation would diminish quickly, the blast wave arrives on the other side of the planet in under 12 hours. It seems plausible that the initial air blast, and the subsequent winds that follow, would contain residual heat - but roughly how much heat, and what would be the consequences of 14.1 hours under such heat?
     
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