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Astronomers Say Dying Sun Will Engulf Earth
Posted by
kdawson
on Wed Feb 27, 2008 12:03 AM
from the fire-next-time dept.
from the fire-next-time dept.
iamlucky13 writes "A minor academic debate among astronomers is the final fate of the earth. As the sun ages and enters the red giant stage of its life, it will heat up, making the earth inhospitable. It will also expand, driven by helium fusion so that its outer layers reach past the earth's current orbit. Previously it had been believed that the sun would lose enough mass to allow earth to escape to a more distant orbit, lifeless but intact. However, new calculations, which take into account tidal forces and drag from mass shed by the sun, suggest that the earth will have sufficiently slowed in that time to be dragged down to its utter destruction in 7.6 billion years. "
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Global Warming (Score:5, Funny)
Re:Global Warming (Score:5, Insightful)
Parent
Ah well... (Score:2, Informative)
Re:Ah well... (Score:4, Funny)
My 2c.
Parent
Re:Ah well... (Score:5, Funny)
(/stupid misunderstanding nitpick)
Parent
Maybe (Score:2, Funny)
Ahh, Robert Charles Wilson, you Spin me right round.
Last post (Score:5, Funny)
Re:Last post (Score:5, Funny)
Parent
This is news? (Score:5, Informative)
Re:This is news? (Score:5, Informative)
Parent
Re:This is news? (Score:5, Informative)
Parent
TV isn't the final word (Score:5, Informative)
Therefore the popular notion was thought by many astronomers to be wrong. But in fact, nobody had ever done a really detailed model of the process until the subject of this article. It turns out, the professionals were wrong, and the common folk were correct, if only because we were a couple decades behind the times academically.
If you don't believe me, here's the archived wikipedia page for earth [wikipedia.org] from last Friday. It's since been updated.
Parent
Shell burning, not helium fusion (Score:5, Informative)
Unless there are some revisions in the laws of physics, the nuclear processes throughout stellar evolution are well known based on computer models.
When helium "ash" accumulates in the core, helium fusion is not the next thing that happens. The core starts contracting and heating up, but that lights off H2 fusion in the shell surrounding the core. That phenomenon changes the luminosity and heat transfer rates of the star, causing the outer atmosphere to swell up into the red giant stage.
When shell burning runs its course, again the core contracts and heats up some more, resulting in the helium flash. Based on computer models, the helium flash is a major disruptive event caused by the sudden onset of helium fusion, it does not cause the star to go nova or anything, but it causes the star to change modes as it were, becoming somewhat bluer and smaller, but still more luminous than Main Sequence. From the computer models, it is believed that the upper-righthand HR diagram stars, red giants, are H2 shell burners while the horizontal branch above the Main Sequence represents He core burners.
For a massive enough star, exhaustion of core He will initiate shell He ignition, sending the star back into the red giant range, perhaps as a red supergiant for a massive star.
The red giant phase is only one phase of an evolved star. Everyone just kind of assumed that a star that goes supernova would be a red giant, but it seems like the star that popped off in Supernova 1987a in the LMS was blue.
Parent
Interesting Note (Score:5, Funny)
Re:Interesting Note (Score:4, Informative)
Parent
Come on... (Score:2)
As long as I've been alive, this has been pretty much the inevitable conclusion. Was there a turnaround in the cocaine infested 80s perhaps that we missed, or have since forgotten?
By the way, this is even in New Zealand, waaaaaaay down at the bottom of the globe (not far enough down that we'd be safe from this, however)
Re: (Score:3, Informative)
Uhhh, this isn't news (Score:2, Insightful)
Shit. (Score:5, Funny)
Beer me.
Armageddon (Score:5, Interesting)
Re: (Score:2, Insightful)
In 7.6 bln years time frame there is a 99.9 probability of a massive object hitting Earth and melting the outermost solid shell.
It's certain that it will happen at least 9 times and 90% certain that it will happen 10 times? Or did you mean that there is a 99.9% probability or a .999 probability?
Re: (Score:3, Funny)
Re:Armageddon (Score:5, Insightful)
Where do you get these numbers? They appear suspect. We've gone more than half-a-billion years with *no* impact strong enough to wipe out the primary phyla of animals. That would suggest that mega-impacts are not near as likely as you say.
True, we may be in for some nasty human-ending impacts though, but not necessarily "outer shell melting", at least not the entire shell.
Parent
Didn't realise this was debated (Score:2)
This assumes we really know what powers the sun. (Score:2)
Thermonuclear reactions produce lots of neutrinos. However, the number of those little particles we actually measure and how many we should be measuring if indeed the sun is a giant controlled fusion reactor, is way different. The number we measure is far too sm
Re:This assumes we really know what powers the sun (Score:3, Informative)
Re:This assumes we really know what powers the sun (Score:3, Informative)
the coronal heating problem simply means the mechanism responsible for the increased temperature is a non-equilibrium process. the corona is also a near-vacuum so despite its high temperature there is relatively tiny amount of energy there.
Seems easy enough. (Score:5, Insightful)
Re: (Score:2)
Re:Seems easy enough. (Score:5, Interesting)
Despite the fact that we only have 7.6 billion years to get the computations correct, I have a feeling that we'll be able to get it done right by then. (Either that or evacuate our Dyson Sphere. Whichever comes first.)
Parent
Re: (Score:3, Interesting)
confusion re expanding to earth's orbit vs engulf (Score:5, Informative)
And some of the academic references are actually a decade old: http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html [ohio-state.edu]
Gravity Assist (Score:2, Redundant)
Re:Gravity Assist (Score:5, Funny)
Parent
By that time... (Score:4, Insightful)
At some point (Score:4, Funny)
No problem (Score:4, Funny)
By that time, mankind will be sufficiently advanced to relocate to an outer planet.....like Pluto.
What? Pluto isn't a planet anymore??
Oh No! We're doomed!!
Difficult to imagine... (Score:2)
Out of shear boredom, I decided to do some calculations, using the following (someone please fix my math, if it's wrong):
Avg. distance from Earth to the Sun (according to Wikipedia [wikipedia.org]) = 1.496x10^11 meters
Current mass of the sun (according to Google [google.com]) = 1.9889x10^33 grams
Current Diameter of the sun (according to Google [google.com]) = 1.4x10^9 meters
Volume of a sphere = (4/3)(r^3)
Density = mass/volume
Based on tha
someone ate my pi (Score:2)
Re:Difficult to imagine... (Score:5, Informative)
During the hydrogen burning phase, inert helium gradually builds up in the core and hydrogen becomes less common. This means the core has to contract and become hotter in order to produce enough energy to support itself and the surrounding envelope. The fusion rate depends on the square of the hydrogen density (since you need the hydrogen atoms to collide with each other), so if the hydrogen density goes down, the core has to become hotter and more generally dense in order to maintain the same energy production rate. (This is why stars gradually become more luminous over their main sequence lifetime, as the core actually has to produce more energy in order to support itself in its more compact configuration.)
As a star finishes exhausting its hydrogen, this actually reaches a very extreme configuration where the core becomes much more compact (and much hotter) trying to squeeze out the required energy with very little hydrogen remaining. The total energy being produced by the core (in order to keep itself from collapsing) increases very rapidly at this point, and the larger luminosity will then push the envelope outward, puffing it up. This is why stars expand into red giants, and this is the stage where the Earth will probably be engulfed.
For trivia purposes, the central core eventually runs entirely out of hydrogen and sits there as an inert clump while the upper edges of the core burn hydrogen. When the hydrogen is exhausted for a large enough fraction of the core, the center eventually becomes hot and dense enough to fuse helium into carbon. At this point, the overall luminosity drops again (because the star doesn't need to keep frantically burning just hydrogen to support itself) and the star contracts a bit. The process then starts over again, with a shell of helium fusion surround an inert carbon core that (for stars more massive than the Sun) eventually ignites to fuse into neon, oxygen, etc.
Parent
Re:Difficult to imagine... (Score:4, Insightful)
For empirical evidence, I'll note that one of us sounds like a pedantic nerd with a tweed fetish, while the other is currently modded at +5. Just saying.
Parent
I wouldn't worry about it... (Score:5, Informative)
The Earth will be dead much sooner than that (Score:3, Informative)
This is old news (Score:3, Insightful)
If evolution is a myth... (Score:3, Insightful)
Message from 100 Years into Future (Score:3, Funny)
Re:I don't believe it. (Score:5, Funny)
Uh, it's probably not a problem, probably, but I'm showing a small discrepancy in... well, no, it's well within acceptable bounds again. Sustaining sequence.
Parent
Re: (Score:2, Informative)
Re: (Score:3, Interesting)
Re:Can't wait that long (Score:5, Informative)
Parent