Is a 'Star Wars' type galaxy possible?

 

 

Remember that scene in Star Wars: A New Hope when Luke and Obi Wan go into the Mos Eisley cantina? The place was full of aliens. Leaning on the bar, arguing, drinking various foaming substances and playing cool, swing music. If you've any sort of interest in science, you'd be like me and go directly into 'go along for the ride' mode. It just isn't probable.

Hang on, though.Our very own Milky Way could contain up to 6 billion (yes, billion with a 'b') 'earthlike planets'. Gosh. Six billion planets that could potentially support life like us. Check it out.

But what does 'earthlike' mean in this context? This report comes from the space telescope Kepler's search for planets orbiting planets like our sun and in the 'Goldilocks' zone. Which means the planet is 'not too hot for liquid water and not too cold'. Kepler can't actually see any of these planets, their presence is surmised from periodic dimming of the sun's light as something passes in front of it and from slight perturbations in the sun's orbit. But scientists can calculate the likely size of the body. For instance, Kepler 22-B is estimated at 2.4 times the size of Earth.

Even so, there's much more to life on Earth than liquid water and reasonable temperature. Rare Earth, a book by Peter Ward and Donald Brownlee, discusses in detail what would be needed to define a planet as an 'earth analog'. Some of the things they list don't readily spring to mind, such as a giant planet like Jupiter acting as a mine sweeper to reduce the amount of debris penetrating to habitable zones to pose a threat to life. We also need that molten metal core inside the Earth to generate a magnetic field which protects us from harmful cosmic rays. Then we need a breathable atmosphere, a year length not too much different from our own, and gravity at least 80% of our own. (Less than that and the planet wouldn't hold atmosphere) but not so massive that we couldn't move around.

We just don't know enough about any of the exoplanets planets to know if they're really 'earthlike'. Venus and Earth are in the habitable zone around our sun. Venus is about the same size as Earth and Mars is half the size. But we won't be setting up a colony on Venus any time soon, and a Mars colony faces a heap of challenges.Mars appears to have lost its atmosphere because its magnetosphere ceased to function. Why that happened is unclear.

Getting back to the cantina scene, we are presented with a number of alien species, all presumably capable of space flight. So what about other life forms on these earthlike planets? Sure, that's possible – but then we come up against the famous Drake equation , which considers variables such as technology and the life span of civilizations. An analogy here on Earth is the Egyptian Empire, which lasted for almost 3,000 years but is now well and truly something from antiquity.

The Drake equation is:

${\displaystyle N=R_{*}\cdot f_{\mathrm {p} }\cdot n_{\mathrm {e} }\cdot f_{\mathrm {l} }\cdot f_{\mathrm {i} }\cdot f_{\mathrm {c} }\cdot L}$

where

N = the number of civilizations in our galaxy with which communication might be possible (i.e. which are on our current past light cone);

and

R_∗ = the average rate of star formation in our Galaxy

f_p = the fraction of those stars that have planets

n_e = the average number of planets that can potentially support life per star that has planets

f_l = the fraction of planets that could support life that actually develop life at some point

f_i = the fraction of planets with life that actually go on to develop intelligent life (civilizations)

f_c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

L = the length of time for which such civilizations release detectable signals into space

On this basis it's quite possible that a civilization developed elsewhere in the Milky Way but disappeared thousands of years ago.

Mind you, Kepler's discoveries are a breakthrough from the time not too many decades ago (maybe only two) when scientists could do no better than to say that our sun was nothing special so other stars would quite probably have planets. The Drake equation dates back to those times. This is such an exciting time to be interested in the universe. I keep getting this feeling that space travel as written in science fiction might not be all that far away. Soon, it seems, we'll have places to visit, too.

I'm not too sure I'll be running auditions for a new cantina scene, though.