Tatooine's Double-Sunset a Common Sight

anthemaniac writes "Thirty years ago, Luke Skywalker beheld something that scientists are just now realizing is likely quite common in the universe: double sunsets. Astronomers have long known that binary star systems are common. And models suggested that planets could form in these systems, even though there's a double-tug of gravity on the material that would have to form a planet. Observations from NASA's Spitzer telescope, show that binary systems are just as likely to be surrounded by planet-forming debris disks are are lone stars."

Comments

This just in

[Clever7Devil]

Quantum systems also likely to be surrounded by debris.

Force, not tug

[140Mandak262Jamuna]

It is the FORCE of gravity, not tug. Not when you are talkin' about the Pod Race Capital of the universe. At a stretch you could call the Millenium Falcon a tug, but not what gravity exerts.

Re:Force, not tug

[winkydink]

Seems to me like somebody is feeling the tug of pedantry.

Two suns in the sunset?

[OriginalArlen]

could be the human race is run...

Great

[eviloverlordx]

More places for hives of scum and villainy!

I love this movie!

[blhack]

Any k-paxian could have told you this.
its common knowledge to them.

Planetary Orbit?

[MrSteveSD]

How would the planet orbit them though?

Would it have to be far enough away so they appeared as one, or go into some crazy chaotic close orbit?

Re:Planetary Orbit?

[Lars T.]

How would the planet orbit them though?

Would it have to be far enough away so they appeared as one, or go into some crazy chaotic close orbit? Look at the image in TFA. Either the stars are closer than 3 AU, then the planet(s) circle around them both, or they are farther away than 50 AU, then the planet(s) circle one of them (it doesn't mention if there could be planets about both, but IMHO that's also possible). In between, no planets will form.

Re:Planetary Orbit?

[cswiger]

There are two stable possibilities: where the two stars orbit each other fairly closely (ie, 0-4 AU from the article, IIRC), and planets then orbit the common center of gravity formed by these two stars...or where one star has a very distant orbit, which is so far that it doesn't disrupt planets close in to the bigger primary.

If the second binary star is in a medium-sized orbit (ie, somewhere between where Jupiter and Pluto are in our system), it seems to be the case that this disrupts the planet-forming disk of gas so much that no planets are likely to form.

If you want to see a full list of all known exoplanets, go here: http://exoplanets.org/planets.shtml
The column marked "a (AU)" is orbital radius, where 1 AU is the earth's distance from the sun.

Re:Planetary Orbit?

[Anonymous Coward]

Planets and stars technically orbit each other, strange as that may seem when you say it out loud. In the case of the earth and the sun, they both swing around a common center of gravity. Because of the huge difference in mass however, this center is still located within the body of the sun.

Picture a long board with an anvil at one end and a small paperweight at the other. If you were to find the balance point between the two, it would certainly a lot closer to (perhaps underneath) the anvil. That stars revolve around this balance point produces a noticeable wobbling effect for each planet that circles it. In fact, this is one way in which scientists can guess if a star has planets in its system: by looking for this wobble.

With regard to binary systems, it would of course (as other posters have noted) depend how far apart the stars are and how close the planet in question is to either of them. Picture a mobile for a decent analogy. If you get two stars close enough together and a planet far enough away, the planet would likely calmly orbit the center of gravity common to the two stars and the planet.

Re:Planetary Orbit?

[Mattsson]

The bigger question would be:
Is it possible to create an orbit around a binary system where a planet has a stable enough environment for harboring life?

It wasn't thirty years ago...

[xxxJonBoyxxx]

Thirty years ago, Luke Skywalker beheld something that scientists are just now realizing is likely quite common in the universe: double sunsets.

Luke didn't see the sunset thirty years ago - he saw it "A Long Long Time Ago (in a Galaxy Far Far Away)..."

I can't believe I'm posting to a Star Wars item...feel like I need to take a shower now.

Two is Better than One

[AaxelB]

Trilling and his team looked for disks in 69 binary systems between 50 and 200 light-years away from Earth. All the stars are more massive and younger than our middle-aged Sun.

Better endowed and younger, eh? And you can have two at once? Maybe we'd better rethink our exclusive orbit with our Sun... After all, we just keep going in circles.

what about a double-sunset + life?

[dmoen]

Planets may be common in binary systems, but what about planets that support life?

One of the reasons that Earth can support life is that the distance between the earth and the sun remains close to a constant for the duration of Earth's orbit around the sun, so the Earth receives a fairly constant amount of solar energy. This means, for example, that the temperature doesn't go down to -200 in the winter and up to +800 in the summer.

But in a binary system, I would imagine that orbits that provide a constant amount of solar energy in the Earth-normal range would be less likely to occur. (What would such an orbit look like when there are 2 suns?) Are there any astrophysicists out there that can comment on this?

Doug Moen

Re:what about a double-sunset + life?

[stratjakt]

"life" isn't as delicate as we've once thought, it can be supported in extreme environments, and doesnt even have to be carbon based - on this planet.

Sure planets could support "life". What you're asking is, could they support you? Maybe not.

Earths precarious orbit and presense of the water and the particular temperature make it suitable for our type of life - or is it the other way around, did life suit itself to the rock we happen to be stuck on?

Re:what about a double-sunset + life?

[aldheorte]

I think it would be wrong to assume that the Sol and Earth arrangement is even the most suitable spot for our kind of life. Maybe, especially if you live in a Mediterranean environment, you think the planet is near perfect, but if you live at higher or lower latitudes or directly on the equator in desert or high humidity rainforest hothouse environments, you'll find extremes and seasonal differences brutal. Think of what an organism in even middle latitudes faces: 100 degree 100% humidity summers with ocassional -20 degree arid dips with bone-chilling wind-chill (although most organisms probably aren't as affected by this as us of the hairless ape variety). All this happening on a yearly basis. This suggests to me that life could readily take purchase on binary or trinary systems with large periodic differences in insolation (solar heating) at least at some latitudes of the planet they are on.

So, the Earth is great, but probably only 5% (totally pulled off the top of my head, if someone wants to do an analysis of temperate high production areas, be my guest) of it or so is 'perfect' for our kind of life. Could the universe do better? Most likely. Also, stars all differ in size and temperature. 1AU might not be the optimal from even our sun (it is clearly not at optimal since its orbit is not perfectly circular and the sun goes through heating and warming cycles that result in measurable differences in energy output received on Earth, suggesting that orbit and distance could be improved for more constant energy transfer) and differences in suns could make planets at many distances quite habitable for our kind of life.

Probably of importance to whether a planet can bear life is the stability of its periodic insolation and tidal changes. Fortunately, solar systems are generally paragons of stability (it's a delicate balance, if they were not, they would quickly come apart) and orbit a shared center in sum as well as engaging in complex checks and balances that lead to synchronization of phenomena (see tidal locking). Therefore, it's quite likely that many planets in the universe have stable periodic fluctuations and if they do, even if those fluctuations are severe, some life will be able to evolve to survive it.

Re:what about a double-sunset + life?

[arminw]

.....Therefore, it's quite likely that many planets in the universe have stable periodic fluctuations.......

The mass and distance of the sun and earth are very critical and cannot be changed very much. Making a smaller sun means the earth would need to be closer. At some point, the earth could no longer rotate independently, but its rotation would be the same as its orbit, such as Mercury. That would preclude life, since one side would be very hot and the other extremely cold. Too massive of an earth would retain poisonous gases such as methane and ammonia. Venus is that way. A smaller planet would mean the loss of water into space. Mars is such a planet.

Putting the earth farther away would necessitate a bigger sun. Large stars go through larger swings of energy output than living systems can tolerate. The spectrum of the sun and the chemical binding energies of photosynthesis are well matched to each other. A red giant would not make a very efficient energy source for living things. The mass, chemical composition, rotation rate and other factors have to be "just so" in order for a planet to have life. If you would factor all this together, you would realize that our planet is unique and very special, a very carefully designed spaceship indeed.

Re:what about a double-sunset + life?

[mrbiggenes]

I am not an astrophysicist, but there is some good information at the following link regarding the Alpha Centauri system (which is basically a dual-star system if you discount the temporary incursion of the Proxima Centauri red dwarf star):

http://www.solstation.com/stars/alp-cent3.htm

Seems the most important factor is not the duration of energy that two stars give, but whether liquid water can exist. Even though Alpha Centauri A and B range between 11 and 35 AU from each other, habitable planets that have liquid water could exist within one or two AU of each star (both stars even have decent light for photosynthesis to occur), and planetary orbits would be stable within a few AU of each star. Granted, there might be long time periods when you don't get a "night" because there are stars on either side of you, but I think that would just be a matter of whatever life arose there adapting to conditions.

Why do we have to drag Republicans into this?

[xxxJonBoyxxx]

hives of scum and villainy

Why do we have to drag the White House into every science discussion we have on SlashDot?

Alaska - already on a planet with two suns

[Lockjaw]

http://www.northernlatitude.com/images/FEB02-sundo g_parks_hwy.jpg

Sundog

[XanC]

Neat picture! Doesn't have anything to do with latitude, though; it's the ice crystals in the clouds. http://en.wikipedia.org/wiki/Sundog

500 A.U. only _relatively_ tight

[StefanJ]

500 A.U. is more than 10 times the orbital radius of Pluto.

Remember the inverse square rule:

A companion star even 40 A.U. far out would be just an especially bright star. If it had the same luminosity as the Sun, it would appear 1/1600 as bright (.0625%).

The Tatooine scenario is still romantic fiction: Stars close enough to appear in the sky together as visible disks would probably be close enough that planets in orbit around them to have strange orbits.

Re:500 A.U. only _relatively_ tight

[MichaelSmith]

500 A.U. is more than 10 times the orbital radius of Pluto.

Brings to mind the time when I was about 12 or so and I got my hands on a 40 power telescope. With Alpha Centauri in the field changing to the higher magnification resolved the binary pair for the first time, and they are only 80 AU apart, IIRC. Doing that gives a fantastic feeling of depth. You can feel how far away it is.

In other space news...

[bluemonq]

...scientists have come to the conclusion that *that's* no moon.

Helliconia got it right...

[kale77in]

if a binary system had two stars the size of our sun, then being far enough away for gravitational and seasonal stability would also mean being too far away for liquid water to exist. At least one star would have to be very large in a binary system for this to work.

Helliconia by Brian Aldiss had a striking ternary system with a small star (with an inhabited planet) orbiting a binary system, giving a 1,500-year long mega-season that gave it regularly-occuring ice-ages.

That seems quite viable, but it illustrates some of the extra threats to life in that situation. I would suspect that extra stars would lead to more planetary comet/asteroid collisions, owing to more variable gravity effects on outer-system objects like their Oort cloud.

Old news

[Sigma 7]

Mercury has a double sunset - with the same sun setting twice without going over the sky: http://www.time.com/time/magazine/article/0,9171,8 36746,00.html.

This was discovered sometime in 1967.

doubles common

[rubycodez]

right, binary star systems no big deal and they could have planets. But those trinary systems, that's a whole different matter, every 22 years the habitable planets around them really, really suck. Unless you're a darkness loving carnivorous boogey-creature, then it's happy hour.

Re:Defenders of the Indefensible

[geekoid]

"...20 years to build the Deathstar ..."
Haliburton.

"Luke found Leia such a "Turn-me-on Hot Chicky Mamma ooooh yeah""

Let's see:
Teenager, in a small confined space with 2 droids, a wookie, and old man, a pirate and a princess.

It was either the princess or the pirate.

Re:Lagrangian

[Hognoxious]

Yes, but only during the day.