Open thread, Oct. 24 - Oct. 30, 2016

MrMind

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If it's worth saying, but not worth its own post, then it goes here.

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Any insights about the following calculation?

If 100 km size body will fall on the Sun it would produce the flash 1000 times stronger than the Sun’s luminosity for 1 second, which would result in fires and skin burns for humans on day side of Earth.

The calculation is just calculation of energy of impact, and many “ifs” are not accounted, which could weaken consequences or increase them. Such body could be from the family of Sun grazing comets which originate from Oort cloud. The risk is not widely recognized and it is just my idea.

The basis for this calculation is following: Comets hit the Sun with speed of 600 km/s, and mass of 100 km size body (the comets of this size do exist) is 10e18 kg, so the energy of impact is 3.6x10e29 J, while Sun’s luminosity is 3x10e26 W.

Wouldn't most of the energy go into mechanical deformation of the comet and the sun, rather than EM radiation?

6Pfft10y

It sounds pretty spectactular! I found one paper about comets crashing into the sun, but unfortunately they don't consider as big comets as you do--the largest one is a "Hale-Bopp sized" one, which they take to be 10^15 kg (which already seems a little low, Wikipedia suggests 10^16 kg.) I guess the biggest uncertainty is how common so big comets are (so, how often should we expect to see one crash into the sun). In particular, I think the known sun-grazing comets are much smaller than the big comet you consider. Also, I wonder a bit about your 1 second. The paper says, [...] If a lot of the energy reaching the Earth comes from the prompt radiation, then it should arrive in one big pulse. On the other hand, if the comet plunges deep into the sun, and most of the energy is absorbed and then transmitted via thermal conduction and mass motion, then that must be a much slower process. By comparison, a solar flare involves between 10^20 and 10^25 J, and it takes several minutes to develop.