Finding & Reaching a Beta World
I did a LOT of research for Tangled Planet. This is the first of three posts on how I used some of it in the book.
DISCLAIMER! I have stretched, tweaked and in some places rabidly mauled the current tech in my book – the second half of science fiction is the fiction part, after all. Astrophysics shouldn’t be allowed to get in the way of a good story.
Finding a Planet for Settlement
Because planets in other solar systems (exoplanets) are tiny (relatively speaking!), they’re tricky to spot. The main ways in which we discover the existence of a planet around a distant star are through transit photometry or Doppler spectroscopy.
Transit photometry is looking at the small drop in brightness of a star as a planet passes in front of it, like a teeny, tiny version of an eclipse – or holding up a grain of sand in front of the sun. We can measure regular dips in the light coming from a star, and get quite a bit of information about the planets that must be in orbit around it.
Doppler spectroscopy is based on observing differences in the colour of light that reaches Earth from a distant star. The gravity of a sun keeps a planet in orbit around it, but the gravity of a planet also has an effect on the star it orbits. This effect is very small, but we can measure it due to the fact that it makes a star appear to ‘wobble’ slightly, causing slight changes in the colour of its light. That’s why Doppler spectroscopy is sometimes known as the ‘wobble method’.
These methods tell us the planets exist, but amazingly, we can find out an awful lot more from just that little bit of data. We might be able to work out the size of a planet (or its minimum size, at least), and its distance from the star. We can use our knowledge of how solar systems form and use spectroscopy – analyzing the light that reflects off a planet – to get an idea of what the planet is made of.
For a planet to be a possible candidate for life, it has to be within the ‘Goldilocks Zone’ (or the circumstellar habitable zone, if you’re being boring). Not too close or it’ll be boiling hot, or too far as it’ll be frozen. And for humans to settle, it has to be a terrestrial planet – one made of rock.
I put Beta Earth about 30 light years from Earth. We have found terrestrial exoplanets within the Goldilocks Zone much closer (such as Proxima Centuri B, only 4.2 light years away, Ross 128b at 11 light years and Wolf 1061b at 13.8 light years), but being within the Goldilocks Zone does not mean they are likely to be suitable for humans.
We evolved for the exact environment of Earth, and small variations in atmosphere, temperature or geothermal activity could make a planet deadly to us. We may need a star like our sun (a main-sequence, G-type star) to thrive, and without major genetic modifications, we would certainly need an atmosphere, a geologically active planet, gravity close to 1G (which is the gravity of Earth), favourable weather systems and a range of temperatures similar to our own planet before bioengineering could begin. We don’t know how many (if any!) exoplanets have such conditions. There is also some debate on whether a moon is necessary (I went back and forth on giving Beta a moon – but eventually went without).
So, I put Beta at around 30 light years. There are hundreds of stars within this distance (with more being discovered), 19 of which are G-type. It’s optimistic to imagine that one of those would have a planet that could be livable for us, but it’s possible. There are countless planets still to be discovered. After all, 30 years ago, we had not confirmed a single exoplanet, and now we know of 3,588 (at the time of writing this – and it keeps going up).
With current technology it would take around 350,000 years to get to Beta, so I had to look into theoretical propulsion systems.
When my story opens my starship, the Venture is already at its destination – and the main propulsion system is offline and being cannibalized for its parts. However, I still needed to have an idea of what it was and its potential speed, in order to work out how long their journey had been. A solar sail would likely be too slow for interstellar travel, and an Bussard Ramjet too unwieldy, but there are other rocket-powered possibilities such as a nuclear pulse rocket, or an antimatter rocket. With steady acceleration that could be withstood by the crew, these could (once a LOT of major issues are resolved) reach 10% of the speed of light (or perhaps more). So I have worked with the assumption that it would, under ideal conditions, take the crew 300 years to reach Beta (but that doesn’t allow time for acceleration/deceleration, and I felt that delays en route would be inevitable, so I made their journey closer to 400 years).
At the planet, they would need another form of propulsion to power their shuttle between the surface and the Venture in orbit, because nuclear pulse would result in deadly fallout for miles around the launch zone, and antimatter propulsion would be incredibly dangerous. So they have an advanced version of a VASIMR rocket – using highly efficient nuclear power generated in orbit to ionize (convert) a fuel into plasma (a highly energized state of matter, like a gas).
I have been absurdly optimistic on fuel generation and use in all my planning – because producing the amount of fuel necessary for interstellar travel is one of the major hurdles to any future voyage to another solar system – and even once you’ve produced that fuel, you need a spacecraft large enough to carry it, as well as any passengers.
This wouldn’t be much of an issue for my crew. If you travel at one tenth of the speed of light it would actually take about 99.4% of the amount of time that passes on Earth. So, if you traveled for 400 years at one tenth of the speed of light, for people back on Earth, just over 402 years would have passed since the launch of the Venture.
But as you get closer to the speed of light, time slows down for you a lot more. When you are speeding along at about as close to light speed as you could be expected to get, time goes about 10 billion times slower for you, than for people left on Earth. This is fascinating to me, as it means that you could reach the end of the observable universe in a single human life time – about 45 years in fact, if you could just get a ship that went fast enough, and found a way not to crash into practically everything along the way. Of course, while you were traveling, everyone you know would die and the Earth would be swallowed by the sun, which would also die. Plus the universe appears to be accelerating, so you could only reach the edge of the observable universe, not the ultimate end of it.
It would all be a bit of a downer, really.
Anyway, all that research told me that since time dilation would not work its magic and the flight would take about 400 years, my crew either had to be in suspended animation or the Venture had to be a generation starship.
Which leads us to next week’s blog post, which will be: Using Science To Create a New World – Part 2: Surviving En Route to a Beta World.