62 million year extinction cycle

There was an article in a recent Science News about the relation between
the motion of the solar system in the Milky Way and mass extinctions on
Earth. As the solar system moves, it bobs up and down relative to the
plane of the Milky Way. That bobbing apparently takes about 62 million
years. When the solar system is on the side closer to Virgo, it is
exposed to more radiation and cosmic rays from Virgo and this is what
they say causes the cycle of mass extinctions on Earth.

Questions:
(1) Where are we presently in the 62 million year cycle? I.e. when was the
last mass extinction of this cycle?
(2) How fast are we actually moving towards Virgo and how quickly
should the radiation levels increase as we do?
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

On Jun 10, 2:04 pm, Allan Adler wrote:
There was an article in a recent Science News about the relation between
the motion of the solar system in the Milky Way and mass extinctions on
Earth. As the solar system moves, it bobs up and down relative to the
plane of the Milky Way. That bobbing apparently takes about 62 million
years. When the solar system is on the side closer to Virgo, it is
exposed to more radiation and cosmic rays from Virgo and this is what
they say causes the cycle of mass extinctions on Earth.

Questions:
(1) Where are we presently in the 62 million year cycle? I.e. when was the
last mass extinction of this cycle?
(2) How fast are we actually moving towards Virgo and how quickly
should the radiation levels increase as we do?



What kind of a cycle is it? I know about 26000 years around the
galactic plane...
This star could wipe out Earth someone wrote and all the gama
bursts...
http://chandra.harvard.edu/photo/200...ta_opt_900.jpg

boson boss writes:

What kind of a cycle is it? I know about 26000 years around the
galactic plane...

OK, we're thinking of the Milky Way as a big merry-go-round and the
solar system as one of the horses. On some merry-go-rounds, including
this one, the horses move up and down as they go around. Our horse
takes 62 million years to start in the plane, move up as far as it goes,
move down as far as it goes and then move back up to the plane.

In addition to my other questions, how far up and down does our horse go?
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

Allan Adler wrote:
There was an article in a recent Science News about the relation between
the motion of the solar system in the Milky Way and mass extinctions on
Earth. As the solar system moves, it bobs up and down relative to the
plane of the Milky Way. That bobbing apparently takes about 62 million
years. When the solar system is on the side closer to Virgo, it is
exposed to more radiation and cosmic rays from Virgo and this is what
they say causes the cycle of mass extinctions on Earth.

This seems awfully surprising to me. What kind of "radiation" are
they claiming changes? I don't see what small amounts of interstellar
material would be blocking. The column density through the Galactic
plane is only of order 10^20 H atoms per cm^2. Is there a reference
to a published article?

Questions:
(1) Where are we presently in the 62 million year cycle? I.e. when was the
last mass extinction of this cycle?

Has there been a mass extinction since the C-T boundary?

(2) How fast are we actually moving towards Virgo and how quickly
should the radiation levels increase as we do?

From my trusty _Astrophysical Quantities_, the Sun's motion towards
Virgo is about 7 km/s. According to NED, Sgr A* has a Galactic
latitude of -0.046 degrees. If the Galactic coordinates correctly
define the plane and the galactocentric distance is 8.5 kpc, that
would put the Sun about 7 pc north of the plane.

As I say, though, I'm suspicious of the whole idea.

Steve Willner writes:

This seems awfully surprising to me. What kind of "radiation" are
they claiming changes? I don't see what small amounts of interstellar
material would be blocking. The column density through the Galactic
plane is only of order 10^20 H atoms per cm^2. Is there a reference
to a published article?

First of all, the article I'm asking about appeared in the Apr.21, 2007
issue of Science News (vol.121, number 16). It is entitled, "Northern
exposu the inhospitable side of the galaxy?". It mentions a forthcoming
article Medvedev in Astrophys. J.
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

In article . com,
boson boss wrote:

snip

What kind of a cycle is it? I know about 26000 years around the
galactic plane...

You're probably thinking of lunisolar precession, which has a period of
about 26 ka -- and has to do with the 'wobble' of the Earth's equatorial
plane, not the solar system's position WRT the galactic plane. The Sun's
orbit around the Galaxy is thought to take more than two hundred mlllion
years, so we cross the galactic plane at intervals of somewhat over 100
Ma.

--
Odysseus

Odysseus writes:

In article . com,
boson boss wrote:
snip What kind of a cycle is it? I know about 26000 years around the
galactic plane...

You're probably thinking of lunisolar precession, which has a period of
about 26 ka -- and has to do with the 'wobble' of the Earth's equatorial
plane, not the solar system's position WRT the galactic plane. The Sun's
orbit around the Galaxy is thought to take more than two hundred mlllion
years, so we cross the galactic plane at intervals of somewhat over 100
Ma.

The article said 62 million years was the period of the extinction cycle and
the period of the motion above and below the galactic plane. I think that
means that, assuming your figure of about 200 million years is correct for
the galactic orbit of the sun, that the sun crosses the galactic plane 6
times in each orbit around the Milky Way.

I guess there is no reason to assume that the period of the sun around the
Milky Way and the period of the sun above and below the galactic plane have
to be commensurate, nor that the sun has to return to the place in the
Milky Way where it started (even ignoring the fact that the Milky Way is
changing too). So, it is conceivable that in some orbits around the Milky
Way, the sun could actually cross the galactic plane 7 times. If we take
the figures 200 million and 62 million literally, that would happen roughly
every 600 million years.
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

Allan Adler wrote:
I guess there is no reason to assume that the period of the sun around the
Milky Way and the period of the sun above and below the galactic plane have
to be commensurate...

They aren't. I've long since forgotten what the actual values are,
and a quick check doesn't find them, but they are independent. The
vertical period depends on the local mass density of the disk, whereas
the orbit period depends on the Galactic mass interior to the Sun's
orbit and on the orbit radius. In both cases, the mass distribution
is important. This is unlike the simple situation with spherically-
symmetric mass distributions.
nor that the sun has to return to the place in the
Milky Way where it started

It doesn't. Orbits are not closed.

"AA" == Allan Adler writes:

AA There was an article in a recent Science News about the relation
AA between the motion of the solar system in the Milky Way and mass
AA extinctions on Earth. As the solar system moves, it bobs up and
AA down relative to the plane of the Milky Way. That bobbing
AA apparently takes about 62 million years. When the solar system is
AA on the side closer to Virgo, it is exposed to more radiation and
AA cosmic rays from Virgo and this is what they say causes the cycle
AA of mass extinctions on Earth.

See astro-ph/0602092, URL: http://lanl.arxiv.org/abs/astro-ph/0602092 .

AA Questions:
AA (1) Where are we presently in the 62 million year cycle? I.e. when
AA was the last mass extinction of this cycle?

I don't see anything obvious in their paper, other than the statement
that the Sun is about 10 pc above the Galactic plane and moving away
from it. This suggests that we are moving toward a peak height above
the plane.

AA (2) How fast are we actually moving towards Virgo and how quickly
AA should the radiation levels increase as we do?

There are some figures in their paper, but they suggest that the
Galaxy is falling toward the Virgo cluster at about 300--500 km/s.


--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

When the Sun moves in its orbit in the Milky Way, what exactly is it
orbiting around and why? What kinds of general statements can be made
about the orbits of the other stars in the Milky Way? For example, are
there some basic classifications of orbit types? If so, how typical is
the Sun's orbit?

The same questions apply as well to other galaxies.

What would be a good book or article to read on stellar orbits in galaxies?

When the Sun moves in its orbit, it bobs up and down in the equatorial plane
of the Milky Way. Why does it do that? If, for comparison, we look at the
orbit of the Earth in the solar system, is there any comparable bobbing
motion?
--
Ignorantly,
Allan Adler
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.