Science Escape 8 -- Hmmmm . . . Where to Go? Where to Go? (Part 4)
Okay, I lied. I will not wrap up our view to our stellar neighbors in this essay. Because this time we have something special.
So, let’s get Sirius!
Sirius AB (binary star system--8.6 light years away)
The next stop on our journey is the Sirius star system. This system is directly west of us if you consider our galactic center to the southeast, and is also at about the same level up/down in three dimensions. This system is pretty unique, and consists of two rather young stars--a white/blue main sequence star that is verging on being a small giant (Sirius A), and a small white dwarf star (Sirius B). On average these two stars orbit each other at about the distance that Uranus is from the Sun.
This has been a very, very dynamic and young system. The Sirius system is only about 225 million years old.
The Two Stars
Sirius A is the brightest star in our sky. Taking a look at the illustration below, you can start to see why! At about 1.7 times the diameter of our Sun, and about twice the Sun’s surface temperature (17,400 degrees Fahrenheit versus 9,900 degrees Fahrenheit), it’s a monster star! It burns so hot it emits light in the white to almost blue range, whereas our Sun is solidly in the yellow range.
Courtesy of Dave Jarvis (http://www.davidjarvis.ca/) via Wikipedia and the Creative Commons 3 license.
Its neighbor, Sirius B is an amazing white dwarf. With a excruciating surface temperature of 45,000 degrees Fahrenheit, it has a diameter of about 92% of the Earth’s diameter, but its mass is about equal to the Sun’s mass. Sirius B is one of the most massive white dwarfs known.
Sirius B was a blue giant star for about 100 million years--larger than Sirius A is today. Sirius B gradually expanded into a red giant as its hydrogen was fused away, and it then fused helium until that was exhausted. With nothing left to fuse, the star collapsed 124 million years ago into the white dwarf it is today.
White dwarf stars no longer fuse anything, but they are some of the hottest bodies in the universe. Gradually, over hundreds of millions of years, they cool until there is nothing left but a cold, burned out cinder.
Within a billion years, Sirius A will follow the course that Sirius B laid down. It will eventually expand into a red giant as its hydrogen is exhausted. It will then burn all its helium and collapse into a white dwarf.
Now, it may come as a surprise to some, but I’m actually a raging evil corporatist (shhhhh . . . don’t tell anyone!). I love exploiting resources--and I’ve been looking for planets to plunder and strip mine to my heart’s desire! I think I’ve finally found a prime system to pillage--and that would be Sirius.
Sirius A not only is huge and hot--it is chock full of metals. For example, there is 7.5 times the concentration of iron in Sirius A than in our Sun, meaning that any planets we find there would also be loaded with iron. Other heavy elements would likely also be in greater concentrations in the Sirius system than in our system. This means we might also find ample supply of Cobalt, Nickel, Copper, Tin, Platinum, Gold, Lead, Unobtainium, Uranium, and Plutonium, among other useful and commercially exploitable materials.
So, free marketeers rejoice! We may have found a place that will provide ample resources to construct our space colonies and fleets of spaceships.
The Planetary Problem
However, there is one catch. You might recall that Sirius B went red giant not so long ago, and even before that time, the orbits of the two very large stars were so close they would have disrupted orbits of any planets orbiting just one of them.
So, unless there are planets or asteroids orbiting both stars, chances are that there are almost no planets towards the center of the system. Even smaller asteroids might be scarce.
A search for larger planets orbiting both stars has so far come up empty.
Also, the changing stars and short length of time the system has been existence (225 million years) makes the chances for finding life there almost nil. Sirius B going red giant undoubtedly baked or entirely swallowed most planets in the area.
Also, here on Earth we have not found evidence of any life (even single-cell life) before the Earth was 500 million years old. So the chances of finding any kind of life at Sirius, which is only about half that age, are exceedingly low.
So, take heart all you bleeding-heart lefties and whack-a-doodle eco-lovers! If we corporatist despoilers ever do make it to Sirius to exploit its resources, there is probably nothing there to kill to make you wring your hands in anguish!!!
The Spacecraft Timescale Paradox
To sail our spacecraft using a light sail to Sirius at 20% the speed of light would take 43 years. However, there is a problem. If we want to exploit potential metal-rich planets in the system, we don’t want to just make a fly-by of the type intended by Breakthrough Starshot. We want to slow down and stay!
When you’re traveling at 20% the speed of light, slowing down is a huge problem! You’re actually traveling about 196,363 times the speed of a speeding bullet from a handgun! You’ve used laser light to speed you up to that incredible velocity. But, what can slow you down?!? All you’ve got is a sail, and no lasers at the other end.
Well, you can use the light and solar wind of the star at the other end to slow you down! And this is exactly what the plan would be.
However, it would still take a long time. Speeding yourself up with focused laser light is efficient. Slowing yourself down with unfocused starlight is not so efficient.
One study was done using spacecraft traveling at 12.5% the speed of light as a basis. For Alpha Centauri A, at that speed it would take 35 years to conduct a flyby mission like Breakthrough Starshot. But actually slowing down, getting into a long gravitational parking orbit, and stopping would take 101 years total. Uggh! That’s enough to make a capitalist shudder when only thinking short-term to next quarter’s financials!!
However, Sirius presents a unique case.
Because of the large size of Sirius, using the method to slow down that is outlined above, this star system actually presents us with the BEST CASE scenario (from a timescale perspective) for traveling to a star system and staying there. Traveling through the Sirius system Breakthrough Starshot style would take us 68 years at 12.5% the speed of light.
However, traveling to Sirius A and staying would take a mere 69 years because of the larger size of the star. More light, more solar wind, more stopping power! There is no other star system that we could stop at more quickly.
I’m not sure whether traveling at 20% light speed would be better or worse as far as time to travel. Going faster probably requires much more time to slow down. If any nerds here have the mathematical prowess to figure this out via the article below, it’d be much appreciated (PDF warning--may load slowly)!
Well, my friends, Sirius is indeed a fascinating star system. A resource-rich system where you can slow down and stop quickly. Truly, this could be a major focus for our interstellar travels. It depends on what we are primarily looking for (interstellar life? an Earth-like planet to colonize? resources?).
In the next Science Escape, we’ll wrap up our interstellar trip!
(PS--some of the above was snark.)
Sources (not cited above):