Inconstant Sun

November 1, 2006 8:39 AM

I'm working on a short story, a sort of parallel to Inconstant Moon by Larry Niven, that involves the Sun going nova, and its effects on Earth's last minutes/hours/days. I'm starting to wonder if his description of what would happen if the Sun went nova is 100% accurate, so I'd like to pick it apart. Secondarily, what would happen if the sun turned into a red giant, instead?

Okay: The Sun goes nova. In the story, it basically cooks the light side of the earth, while a steam-storm rushes over the terminator to the dark side of the earth, steaming everyone alive within a relatively short period of time.

My thoughts: If the Sun were to go nova, the central mass that holds us in orbit would lessen, and our orbital distance from the Sun would increase. Would we move out of the way of the bulk of matter being ejected from the sun? How long would it take for climate to change? Would we crash into our moon? Other satellites? When would we die, and from what?

If the Sun were to shift into a red giant, that also involves a significant loss of mass. It's commonly held that the Sun would just envelop and scorch the Earth, but I again wonder: Wouldn't the loss of mass cause our orbital distance to increase? Is it possible that we'd orbit the now red giant Sun in such a way as to continue life on Earth?

posted by Merdryn to science & nature (29 comments total)

For the second: Not fast enough. We'd be turned into fissionable material long before our orbital distance increased.

For the first: It's more likely that we'd be microwaved alive by the radiation before we had to deal with steam clouds or anything else.
posted by SpecialK at 8:42 AM on November 1, 2006

Our sun will never go nova. That happens to white dwarves and truly massive stars. Our sun will turn into a red giant.

Solar Evolution and the Distant Future of Earth [pdf]
posted by Zed_Lopez at 8:50 AM on November 1, 2006

(Charles Stross's "Iron Sunrise" opens with a pretty good description of what would happen with a sudden nova event. The planet's first warning was when their sun monitoring sattelites suddenly went offline, and there was no way to get the word out -- and nowhere to run to -- before everyone died.)
posted by SpecialK at 8:52 AM on November 1, 2006

It's worth noting that the nova in Stross' book was artificially generated, but Zed's point is true and I overlooked it.
posted by SpecialK at 8:53 AM on November 1, 2006

Zed: I didn't ask.
posted by Merdryn at 8:59 AM on November 1, 2006

A spherical object exerts the same gravity on something beyond it regardless of its density. The mass loss only affects the orbit of the Earth when the mass has passed the Earth's orbit.

Unless the mass loss is highly anisotropic and goes out along the poles (which wouldn't happen in a remotely natural event, not that there will be a natural event, but... well... it wouldn't happen alright?) then stuff is going to hit the Earth before the orbit is affected.

You'd likely end up in an elliptical orbit anyway, so you'd probably get scorched sooner or later.
posted by edd at 9:02 AM on November 1, 2006

At the end of Niven's story, doesn't the lead character determine that in fact, the sun didn't go nova? Instead, he theorizes a catastrophic solar flare.
posted by bluejayk at 9:16 AM on November 1, 2006

It looks like Zed's link provides a scientific explanation for what will happen to the Earth when the Sun transitions to a red giant. That sounds very much like the question you asked.
posted by justkevin at 9:22 AM on November 1, 2006

No. He gave the situation ("The Sun goes nova") and asked what would happen. He's not asking if it could happen or not.
posted by Memo at 9:24 AM on November 1, 2006

edd: It seems to me that if the sun underwent an instantaneous mass loss, we'd end up in an elliptical orbit, but with perihelion at the sun-earth distance when the event occurred. So you'd probably freeze rather than get scorched. And, of course, all bets are off if the sun has not only lost mass but also become some other kind of star.

Incidentally, with regard to the second question, stars don't just suddenly become red giants. There's a long period of brightening that our sun will undergo before becoming a red giant, so the earth is likely to become a much warmer, much less pleasant place to live long before it gets enveloped by the sun.
posted by dseaton at 9:40 AM on November 1, 2006

Well, according to this paper the Earth would completely evaporate in a matter of days, well before any change in its orbit could have much mitigating impact. It further speculates that the moon's increased brightness would increase temperatures on the nightside by thousands of degrees fairly quickly.
posted by justkevin at 9:52 AM on November 1, 2006

A supernova releases a lot of energy and the blast wave would most likely knock Earth out of orbit as well as instantly "washing" away the entire atmosphere at the speed of light. When a star goes supernova it even affects other star systems nearby.
posted by JJ86 at 11:14 AM on November 1, 2006

If the Sun were to shift into a red giant, that also involves a significant loss of mass. It's commonly held that the Sun would just envelop and scorch the Earth, but I again wonder: Wouldn't the loss of mass cause our orbital distance to increase? Is it possible that we'd orbit the now red giant Sun in such a way as to continue life on Earth?

You're talking about a process that takes thousands of years.
posted by Steven C. Den Beste at 11:28 AM on November 1, 2006

For the record, bluejayk is right: the Sun doesn't actually go nova in "Inconstant Moon". You can (and should) read the story here if you're interested.
posted by Johnny Assay at 11:52 AM on November 1, 2006 [1 favorite]

There is always a point in scienc fiction writing where you must ignore reality. The premise (sun going nova, simply boiling off the atmosphere slowly) is that point here. The question is really about the fallout of such an event, whether or not that event is what a real supernova would be like. So, to answer the questions:

"Would we move out of the way of the bulk of matter being ejected from the sun? How long would it take for climate to change? Would we crash into our moon? Other satellites? When would we die, and from what?"

No we wouldn't. As folks mentioned, the orbit only changes when the mass enclosed by our orbit changes, in other words, only after we get hit by all the mass.

The climate would change basically instantaneously. A steam storm boiling everyone alive is climate change in action.

The earth moon interaction would be unchanged, except if one or the other was blown off its orbit by whatever nova shockwave type thing you want to employ. And then, crashing is a matter of orientation....Say the nova happens during a solar eclipse and you can have the moon shielding the earth from the blast but crashing into it instead.

In your example of a steam storm scorching everything we'd die at that point. In a "real" nova that somehow happened to our sun we'd die about 8 minutes after it happened, the light travel time from earth to sun.
posted by Shutter at 12:28 PM on November 1, 2006

Just to clarify some terms, "going nova" refers to becoming a red giant. "Going supernova" is a big explosion, but it's physically impossible for our sun to do that. (It is much too small.)

The transition to red giant isn't something that happens in minutes, or even in years. It's a very slow process in human terms, which is only really fast by comparison to the entire lifespan of the star. Our sun will burn for about another 5 billion years, of which the last few hundred million will be spent as a red giant (before collapsing again into a white dwarf, after which it will coast forever on the energy of past glory but won't create much new energy).

When the sun becomes a red giant, it will expand out to past the orbit of Mars. But before its surface gets anywhere near Earth, all life will already be gone as a result other earlier effects.
posted by Steven C. Den Beste at 12:32 PM on November 1, 2006

This being science fiction, you could cause the sun to go supernova by dropping a moon-sized body made of antimatter into it. (Coming up with such a body and controlling its orbit to guarantee a collision is left as an exercise to the student.)
posted by Steven C. Den Beste at 12:34 PM on November 1, 2006

Hmn, would it be antimatter, or would a planet-sized chunk of iron do? I think that's what the Eschaton did in "Iron Sunrise".
posted by SpecialK at 12:57 PM on November 1, 2006

Just to clarify some terms, "going nova" refers to becoming a red giant.

Huh? No, it doesnt! A nova is caused by white dwarf accretion disks. A red giant is a transitory phase at the end of a hydrogen-burning lifetime in regular stellar evolution.

I'm curious: Are you just making stuff up...or?
posted by vacapinta at 1:03 PM on November 1, 2006

The best answer to all of your questions is really

"Yes, if it's important to the plot that it happen that way."

Otherwise the answers are likely something like:

Would we move out of the way of the bulk of matter being ejected from the sun?

Not without a big fucking rocket.

How long would it take for climate to change?

Seconds.

Would we crash into our moon?

No.

When would we die, and from what?

When: very very quickly.
From what: massive radiation input, shit resulting from massive radiation input. More immediately, people would die from the destruction of their brain or anoxia, because those are the only two ways to die.

Is it possible that we'd orbit the now red giant Sun in such a way as to continue life on Earth?

No.

Just to clarify some terms, "going nova" refers to becoming a red giant.

No, that's just normal stellar evolution. A nova is a massive burst of radiation from a degenerate-matter dwarf orbiting a still-fusing star. The parasite dwarf sucks hydrogen from the "parent" star, and every so often it builds up a thick enough layer of hydrogen to briefly fuse.
posted by ROU_Xenophobe at 1:05 PM on November 1, 2006

Hmn, would it be antimatter, or would a planet-sized chunk of iron do? I think that's what the Eschaton did in "Iron Sunrise".

(1) The iron bomb wasn't a big fuck-off sized piece of iron. It manipulated spacetime so that the core of the star burned itself down to a core of iron, and then the star imploded into a supernova.

(2) That wasn't the Eschaton, it was the Space Nazi Slaves of the Other Thing.
posted by ROU_Xenophobe at 1:09 PM on November 1, 2006

It's sci fi. Don't get caught up in the technical stuff. It's boring. Characters with real behaviors and emotions is what makes a great story. See Spaceship Radio #44 for a podcast story along a similar vein to your idea. It's completely unrealistic but still a good story.
posted by chairface at 1:36 PM on November 1, 2006

So, during the quite long transition to red giant, would the sun's size catch up to our orbit? Would our orbit even change? It appears, from posts so far, that it wouldn't, but there must be a loss of mass on its way to red giant stage, right?

This is quite fascinating to me. :)

@chairface: The story I'm writing is meant as more of an exercise than something I'd write for consumption by others. It's a forced constraint I'm using to, in reality, help with a different writing block I'm experiencing.
posted by Merdryn at 2:19 PM on November 1, 2006

there must be a loss of mass on its way to red giant stage, right?

Sort of. Right now the Sun loses *googles* 4--5 million tons/second in fusion.

But the process of turning into a red giant isn't one of losing mass. IIRC, it's from shifting from hydrogen fusion to helium fusion. This is hotter at the core, which makes the Sun expand. But expansion also cools the surface of the sun from white-hot to red-hot.
posted by ROU_Xenophobe at 2:33 PM on November 1, 2006

Off topic:

I followed Johnny Assay's link to the original Inconstant Moon story and was immediately struck by this line:

When the first commercials came on I got up to reheat some coffee. Commercials came in strings of three and four, going on midnight. (my emphasis)

Old sci-fi can be so quaint.
posted by hifimofo at 3:07 PM on November 1, 2006

Old sci-fi can be so quaint.

For that, you can't beat "The sky was the color of a television tuned to a dead channel."

Somebody -- MacLeod or Stross IIRC -- went and used that in one of their books... the perfect, pure blue of a television...
posted by ROU_Xenophobe at 3:42 PM on November 1, 2006

Merdryn: You're absolutely right. The Sun is expected to lose almost half its mass during its red giant phase, and the Earth's orbit will expand in inverse proportion to the Sun's mass, so it will end up at almost 2 AU. The Earth may well escape being engulfed by the Sun, though life won't be pleasant (Pluto might be habitable, though.) See this paper for a stellar evolution model that discusses the future of the Sun.
posted by lukemeister at 3:53 PM on November 1, 2006

dseaton: yeah, my thinking too about the perihelion. The logic behind the scorching rather than freezing was that if it's going to do the red giant thing then the luminosity is going to go up lots, so the closest approach is going to be lots hotter.
posted by edd at 4:53 PM on November 1, 2006

@lukemeister: WONDERFUL find there!
posted by Merdryn at 5:03 PM on November 1, 2006