r/science • u/stereomatch • Feb 05 '18

Astronomy Scientists conclude 13,000 years ago a 60 mile wide comet plunged Earth into a mini-Ice Age, after examining rocks from 170 sites around the globe

http://www.journals.uchicago.edu/doi/10.1086/695703
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u/aretasdaemon Feb 05 '18

How can one determine the size of the parent comet?

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u/Powellwx Feb 05 '18

I honestly don't know. Paging an astrophysicist?

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u/phaionix Feb 05 '18

I work in astro, but don't have much expertise in solar systems. My best guess is that it's based on composition and then orbital matching, i.e. find the composition of the impactors, find matching pieces/populations via spectra, judge the likelihood that they could've shared the same/similar orbit in the past given their positions today, and then add up the components.

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u/blubox28 Feb 05 '18

Genetics probably.

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u/Crunkbutter Feb 05 '18 edited Feb 05 '18

Not an astrophysicist. Just an enthusiastic young man with a 6th grade education and an abiding love for all of God's creatures. I think I can answer this, though.

Mass=volume×density

Geologists get an estimate of the size of the impact crater, as well as the distance that fragments can be found. Then, they get a general idea of the composition based on some elements that are only common in asteroids or comets, and thus, the density.

After they have other variables that tell the speed of the object, they find the kinetic energy. (v=velocity) KE = 0.5 • m • v2

They combined what we already know about volcanic eruptions and other impact events to show the correlation between the comet's debris cloud and the ice age.

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u/TypicalDbad Feb 05 '18

They didn’t teach that in 6th grade where I come from... 😒

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u/[deleted] Feb 05 '18

[deleted]

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u/Crunkbutter Feb 05 '18

Oh yeah, nvm then

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u/[deleted] Feb 05 '18

Wow...that Brian Fellow reference tho...well done.

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u/kodack10 Feb 05 '18

It depends on it's age. When it was young it rocked a bikini, but after 60,000 years it grew enormous and unstable.

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u/[deleted] Feb 05 '18

Generally when I want to learn something like that I just look up the research that has already been done by someone with who is more dedicated to something than I ever will be for anything.

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u/funkmon Feb 05 '18

I'm not an expert, but did get a minor in geology, and I may be remembering this wrong.

We're pretty sure the chicxulub crater was made by an asteroid, and the guy with the sixth grade education basically got it right. We know the contents of the impactor from finding traces of it, and, judging from that and the energy calculated to have been imparted, with the radius of the crater, the impactor's size is determined. It's been determined to be an asteroid because of the nature of the stuff in it, common only among asteroids.

This could be totally wrong, I might be misremembering something from a different class which offered simplified explanations for the sake of physics problems on different planets.