
Sun's galactic journey linked to mass extinctions (2013) - DrScump
http://www.abc.net.au/science/articles/2013/10/02/3857090.htm
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vivekd
I remember Stephyen Jay Gould wrote an essay caleed the "cosmic dance of
Shiva" where he talked about how the fossil record suggests that mass
extinction events at regular intervals of 20 something million years. He wrote
that since it would be difficult to find a terrestrial explanation for an
extinction event at regular intervals, so it made sense to look at factors
from outer space. This could be the sort of missling link in Gould's theory.

I can't find a non-paywalled version of Goud's article but here is another one
talking about mass extinctions at regular intervals

[http://www.theatlantic.com/science/archive/2015/11/the-
next-...](http://www.theatlantic.com/science/archive/2015/11/the-next-mass-
extinction/413884/)

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DrScump
Full paper, with some illustrations (free):

[http://saj.matf.bg.ac.rs/187/pdf/043-052.pdf](http://saj.matf.bg.ac.rs/187/pdf/043-052.pdf)

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mirimir
The authors seem to assume that there's a spiral arm pattern that rotates
coherently. What's the evidence for that?

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benjoffe
It's believed that the spiral arms are quasi-static and that the stars move in
and out of these regions of higher density.

See:
[https://en.wikipedia.org/wiki/Density_wave_theory](https://en.wikipedia.org/wiki/Density_wave_theory)

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mirimir
Yes, that's what I vaguely recalled. But we don't have enough observations to
test that hypothesis. I wonder, through, whether alternate-path gravitational
lensing could provide enough snapshots of some other galaxy to be useful.

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marcosscriven
I really don't understand how the solar system can orbit the galaxy faster
than the spiral arms and be in accordance with Kepler's 2nd law?

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egjerlow
It is better to view the spiral arms as 'transient' in the same way you would
view a momentary queue in traffic - although the jam itself moves slowly or
not at all, the individual cars that make it up move through the jam and
eventually exit on the other side.

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marcosscriven
Interesting: "Measurements in the late 1960s showed that the orbital velocity
of stars in spiral galaxies with respect to their distance from the galactic
center is indeed higher than expected from Newtonian dynamics but still cannot
explain the stability of the spiral structure."

[https://en.wikipedia.org/wiki/Spiral_galaxy#Origin_of_the_sp...](https://en.wikipedia.org/wiki/Spiral_galaxy#Origin_of_the_spiral_structure)

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stephengillie
Wasn't the higher than expected orbital velocity among the first evidence of
dark matter?

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rusanu
Rubin-Ford effect

[https://en.wikipedia.org/wiki/Vera_Rubin#Galaxy_rotation_pro...](https://en.wikipedia.org/wiki/Vera_Rubin#Galaxy_rotation_problem_and_Dark_matter)

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yelnatz
Welp, we're about to enter one of the arms.

It's been nice knowing you guys.

~~~
JumpCrisscross
> _Summed over the entirety of its orbital path over the last 500 Myr, based
> on the new weighted symmetrical model, we find that the Sun has spent ∼60%
> of its time in the spiral arms_

This is a statistical observation. In any case, do you have a source for your
assertion?

[http://saj.matf.bg.ac.rs/187/pdf/043-052.pdf](http://saj.matf.bg.ac.rs/187/pdf/043-052.pdf)

~~~
yelnatz
My prediction is based on their newly weighted symmetrical model given at
figure 2.

All previous extinction events are when the sun is in the galaxy arms, and we
are currently entering one of them.

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JumpCrisscross
Pardon me. Could you point me to a source showing we are entering one of them?

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yelnatz
[http://i.imgur.com/u69Qd6Y.png](http://i.imgur.com/u69Qd6Y.png)

Yellow dot is where we are right now, as you can see we are entering one of
the black lines.

6 blue dots represent the known mass extinctions, they all lie on black lines.

5 orange dots represent proposed new mass extinction events proposed in the
paper.

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DrScump
Here's a great interview by John Batchelor (free podcast):

[https://audioboom.com/boos/4073570-mass-extinction-and-
the-s...](https://audioboom.com/boos/4073570-mass-extinction-and-the-
structure-of-the-milky-way-jonti-horner-m-d-filipovic-e-j-crawford-n-f-h-
tothill)

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basicplus2
not sure this is new... if I remember correctly our galaxies arms rotate along
their length and cross each other every (approx) 140 million years which
disturbs our kuiper belt which dislodges numerous items which rain down
destruction on earth approx 70 million years later, so Jupiter mops up most
but not all.

