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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."
could be the human race is run...
Everything I needed to know about life, I learnt from Blake's Seven
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?
"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?
I don't need no instructions to know how to rock!!!!
http://www.northernlatitude.com/images/FEB02-sundo g_parks_hwy.jpg
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.
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.
http://michaelsmith.id.au
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.
.....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.
All theory is gray
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.htmSeems 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.