In my book Death from the Skies!, I talk about the many ways our galactic neighborhood can wipe out life on Earth: nearby supernovae, magnetar hissy fits, episodic oscillations of the Sun carrying us into a stream of dangerous intergalactic cosmic rays, and more.
Given that litany of disastrous scenarios, you wish to breathe a momentary sigh of relief that perhaps one of these things can be scratched off the list: the Earth plowing into the galaxy’s spiral arms.
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The Milky Way is a disk galaxy, a flattened circle of stars, gas, and dust. The spiral arms are like traffic jams of material; gravitational speed bumps where gas can pile up and form stars. There aren’t that many more stars in the arms than between them, it’s just where the biggest and brightest tend to be, so they light the place up.
But there are more and denser gas clouds in the arms on average, and every few hundred million years the Sun drifts into and out of these regions. It’s been supposed that wandering into a nebula like this can potentially affect the Earth’s environment. If the dust is dense enough it can block sunlight, cooling the Earth, causing an ice age.
But a new study shows this may not be the case. Universe Today has the details, but basically there appears to be a 140 million year period to changes in Earth’s climate, which was suspiciously close to the period between encounters with our galaxy’s arms. The new study — using actual data of how dense clouds of gas and dust orbit the Milky Way to calculate when our Sun moves into the spiral arms — finds this period does not line up with any galactic goings-on.
Does that mean we’re safe? Well, no. First, all those other impending disasters are still out there, though of course the good news is that they are incredibly rare and basically won’t happen for millions of years (in other words, don’t fret). Second, the period of climate change is still apparently real, it’s just that it’s not tied to the Sun’s orbit around the center of the Milky Way. If it is real, then something must be causing it. We’ve taken one cause off the list, but what else are we missing?
To be honest, I won’t be rushing to edit that chapter in my book just yet. This study looks good, but I’ll wait and see what other scientists say. With another few dozen million years to go, I have plenty of time.
June 29th, 2009 at 7:50 am
Dugg! Yup, there’s one less thing to loose sleep over. Sorta. Climate’s still changing, but at least the spiral arm traffic jam is off the climate change table.
June 29th, 2009 at 7:54 am
Slightly off topic, but does anybody know when astronomers became pretty certain that the Milky Way is a barred spiral? I got the Cosmos series for my birthday this past weekend and I remember thinking that the graphic for the Milky Way galaxy in the first episode was wrong because it wasn’t a barred spiral. Then again, I don’t remember learning that the Milky Way was a barred spiral in high school and I graduated in 1985.
Back on topic: what would roughly be the density of dust needed to decrease the intensity of the sun enough to trigger an ice age? How much would the intensity of the sun needs to decrease in order to trigger an ice age?
June 29th, 2009 at 8:08 am
I just bought the damned book, haven’t even read it yet, and now this is the second retraction? Why don’t you just tell me how it ends, spoiler!
Seriously, though. I enjoy your work and I’m looking forward to reading the book.
June 29th, 2009 at 8:16 am
You wrote a book?
June 29th, 2009 at 8:17 am
140 million year period
That correlates suspiciously closely with how long it’ll take the Senate to approve the Climate Change bill.
June 29th, 2009 at 8:21 am
Reminds me of a novel I read years ago. (google google google) The Genesis Quest by Donald Moffitt. A major plot point is that spiral galaxies cause periodic mass extinctions on all planets within them. Humans avoid extinction by transmitting their genome to a globular cluster, where it’s picked up by starfish aliens. Or something. There’s also a giant space tree called Yggdrasil, I think. I may need to reread that book.
June 29th, 2009 at 8:50 am
Cindy:
According to Wikipedia, astronomers first began to suspect that the Milky Way is a barred spiral galaxy in the 1990s, rather than an ordinary spiral galaxy. Their suspicions were confirmed by the Spitzer Space Telescope observations in 2005, which showed the Galaxy’s central bar to be larger than previously suspected.
June 29th, 2009 at 8:54 am
Hmmm, if the Solar System did happen to wander into a nebula, and chanced upon a newborn star in the vicinity, then most likely the Earth would be cooked due to intense radiation. Am I right?
June 29th, 2009 at 9:37 am
Stone Age Scientist:
Err… no, you only need to worry if the Solar System chanced upon a Gamma-ray burst progenitor — neutron star, magnetar, supernova, etc.
June 29th, 2009 at 10:25 am
I’m sorry to write about something completely apart from the subject but the upper banner belongs to the John Templeton Foundation. I find very “nasty”, sorry for my English, that a blog dedicated to (good) science shows adds about no science at all
June 29th, 2009 at 10:32 am
I like that graphic… “Far out in the uncharted backwaters of the unfashionable western spiral arm of the galaxy lay a small, unregarded yellow star…”
June 29th, 2009 at 11:50 am
“Crucially, [the tapes] could once and for all dispel 40 years of wild conspiracy theories.”
I don’t like the implication “wild conspiracy theories” . Why wild?? prove it.
Ok, background:
I was originally a moon HBer, even though I’m a supposedly educated professor. So I went to Phil’s BAUT forum, got into a huge fight with the scientists there, and guess what, after a long , heated, and very scientific debate, I finally admitted to them I was wrong: I ended debate by listing about 20 things they convinced me proved that Apollo really did land on moon.
I feel on each and every issue, a huge argument like above should occur before someone says it’s a “wild” theory. That is just a ploy to label people as kooky and violates every rule of logic in the book.
June 29th, 2009 at 11:56 am
@ JTerFer,
If you’re using Firefox as your browser, Adblock Plus will block those pesky adverts.
June 29th, 2009 at 5:12 pm
Hmm … So Magnetars may be somewhat more of a threat than we thought and spiral arms somewhat less so … Sounds like swings and roundabouts to me!
@ 6 : 6. treelobsters Says:
Reminds me of a novel I read years ago. (google google google) The Genesis Quest by Donald Moffitt. A major plot point is that spiral galaxies cause periodic mass extinctions on all planets within them. Humans avoid extinction by transmitting their genome to a globular cluster, where it’s picked up by starfish aliens. Or something. There’s also a giant space tree called Yggdrasil, I think. I may need to reread that book.
Yes – great book! Although the aliens aren’t located in a globular cluster but much further away – in the whirlpool galaxy (M51) instead.
Donald Moffitt is an author who write some very impressive “hard SF.” I’ve just finished reading another excellent SF novel of his, The Jupiter Theft (Sphere, 1979) which had astronomer heroes, lots of good astronomy, nicely imagined and cleverly thought out aliens, a very numinous and superluminous premise and way of travelling at relativistic velocities and was also very readable.
Moffitt has also written a sequel to ‘The Genesis Quest’ (Sphere, 1986) called ‘Second Genesis’ (Sphere Books, 1986 – as well) which follows on from the first novel with the same characters. Both are also very good with breath-taklingly big ideas made to sound pretty plausible having been well thought out, good science, scientist heroes that are well characterised and great nicely alien aliens. If you haven’t read them already they’re well worth reading – 8 1/2 to 9 out of ten in my view. He’s a great SF writer – Science Fiction at its best, IMHON .
June 29th, 2009 at 5:30 pm
@ 6 Treelobsters (again) Reminds me of a novel I read years ago. (google google google) ‘The Genesis Quest’ by Donald Moffitt.
Never mind Google – try Wikipedia instead!
See :
http://en.wikipedia.org/wiki/Donald_Moffitt
& http://en.wikipedia.org/wiki/The_Genesis_Quest
& http://en.wikipedia.org/wiki/Second_Genesis
WARNING! WARNING! WARNING! BA BLOG READERS!
There are some SPOILERS there – and *lots* more spoilers on ’The Jupiter Theft’ Wiki entry too!
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The Genesis Quest from Wikipedia, the free encyclopedia
The Genesis Quest is a science fiction novel written by Donald Moffitt first published in 1986, part of a two part series, the conclusion of the story being offered in Second Genesis.
Plot summary
The Genesis Quest gets around the problems involved with intergalactic travel, namely the distance, by avoiding the traditional staple of science fiction, faster than light travel. Instead Moffitt opts for a different tactic, that of having an alien race (The Nar) assemble humans from a stream of genetic information transmitted by radio from the Milky Way Galaxy. The resulting colony of humans spend some time integrated into the Nar society before growing restless, discovering the secret of human longevity, and embarking on the seemingly impossible millennia-long mission of a physical journey back to earth. This epic journey is made in a gigantic space-grown semi-sentient Dyson tree known as Yggdrasil.
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Okay, its safe to look & remain unspoiled (probably) nnnnn- NOW!
Clear skies & good reading to y’all.
June 29th, 2009 at 5:36 pm
That would probably be easier to answer if the processes responsible for glacial periods were known. When I look at an overview (say Wikipedia’s) it is filled with hypotheses (and data) but few if any tests. Maybe geologists know more than that though.
But at least now you can estimate a range of dust densities (or equivalently a sum total range of irradiation/sun spots/greenhouse effect) which doesn’t cause them as previously hypothesized.
June 29th, 2009 at 5:46 pm
Does ruling out the spiral arms periodic threat mean the chances that planet X or ‘Nemesis’ – a solar companion red or brwon dwarf in a very distant perhaps very inclined orbit – are now higher to explain the apparent cycle of mass extinctions?
June 29th, 2009 at 5:57 pm
@ 12. Jeff :
“Crucially, [the tapes] could once and for all dispel 40 years of wild conspiracy theories.”
I don’t like the implication “wild conspiracy theories” . Why wild?? prove it. … I feel on each and every issue, a huge argument like above should occur before someone says it’s a “wild” theory. That is just a ploy to label people as kooky and violates every rule of logic in the book.
Okay first – wrong thread for this comment maybe?
Second – “wild ” to me just implies unlikely, far out , extraordinary, strange, improbable, etc .. & quite often gets applied to serious mainstream SF theories too.
For instance, Einstein’s Relativity and ?Somebody’s?* Quantum mechanics genuinely scientific theories could be (and have both been) described as wild and we don’t call Einstein and ?Whoever?* kooks because of the (accurate) strangeness / bizarreness or wildness.
Thirdly -and lastly, “wild” is an apt and accurate description for almost all coinspiracy “theories”.
Eg. To say the idea that the Earth is hollow, that Venus was ejected from Jupiter as a giant comet & played comic pinball withErath & Mars over recent millennia, that Zeta Reticulan lizard men are really the secret rulers of Earth, etc .. is just “wild” not to mention rather ludicrous and clearly wrong.
No offence intended but if something is wild why should it be called wild?
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* Insert the name of the Quantum Mechanics founding scientist here. I forget who it was – Bohr maybe? Or Dirac? Or Schrodinger… ?
June 29th, 2009 at 6:24 pm
I’d still appreciate a clarification with regard to the comment I posted on the Universe Today article. (I actually created an account in order to ask it.)
In response to Cindy, it was definitely in the mid nineties. I don’t remember the exact year, but I distinctly remember reading about it and realising that some of my childhood astronomy books were out of date. I read about it in one of World Book Encyclopedia’s annual science supplements, which we received from 1994 through 1997.
June 29th, 2009 at 7:09 pm
Since no one seems to have done it yet, I’ll mention Sir Fred Hoyle’s first science fiction novel, The Black Cloud.
June 29th, 2009 at 7:53 pm
@ 19 Adrian Morgan – Okay, I’ll check that out & see what I can say.
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Okay .. Just been there looking and can’t find it – yet – what’s the (sub)forum, username tag, & title please?
@ Coolstar 20 – yes that’s a great hard SF novel too.
June 29th, 2009 at 9:08 pm
@plutonium, I’m talking about the Universe Today article that Phil links to above. At present, there are three comments posted on it. Mine is the second one, pointing out where I find the article unclear and confusing.
June 29th, 2009 at 9:39 pm
Okay. Got it now. I’m not registered for Word Press so I’ll post your comments and answers here if that’s alright with you … (& I sure hope it is! Apologies if not.)
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Adrian Morgan Says: [Word Press -comments on the article linked to above.]
June 26th, 2009 at 6:20 pm
I’m confused. Surely “passing through galactic plane” and “passing between spiral arms” are completely different things, yet this article seems to refer to them interchangeably.
Now I’m not terribly sure of this myself, but my thinking here is that passing through the Galactic plane means rising above and below from the “Galactic equator” which is in a direct line from the “equator” of the Galactic bulge – (Hmm.. Not sure if that makes it clearer …?)
Anyway, I think the spiral arms are also in the midplane of the galaxy but at intervals ie. you have the Galactic plane which is :
Spiral arm-> inter-spiral medium (where the Sun is now) ->Spiral arm -> another interspiral medium -> spiral arm -> etc ..
Given that the number of spiral arms is cited as relevant, it appears to me that this article is really about the cycle of “passing between spiral arms”, and that the conflation between that and “passing through the plane” is an error. (Also note that according to Phil Plait in DFTS page 240, the “passing through galactic plane” cycle is 64 million years.)Could someone clarify these points, please?
Maybe. There does seem to be some ambiguity or potential confusion here.
Anyone else care to clarify this? I’m not sure I quite understand it myself.
July 4th, 2009 at 1:35 am
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