Episode for August 9th, 2023 Download

Throughout the course of this podcast, we’ve established the idea that there are a lot of exoplanets in our universe. Some are big, some are small, some are close to their stars, others are very far away. One thing we haven’t said much about though is just how far away they all are.

Many people feel that it’s very important for humanity’s long term survival that we become a multiplanet species. Traveling to and possibly even inhabiting other planets in our solar system is not only possible with our current levels of technology, but compared to going to the stars, it’s downright easy.

But what about traveling to exoplanets? Can we reach the stars?

With the way things are now with our rocket technology, it’s not looking good. Let’s use traveling to the closest exoplanet to us as an example. How long would it take to get to Proxima Centaui b?

To get anywhere in the galaxy at anything resembling a reasonable time, we need to go fast - some fraction of light speed would be best. Proxima Centauri is 4.3 light years away, so even the fastest thing we know about - light - takes years to get there. So far, the fastest spaceship we have ever built is the New Horizons Probe and it’s going along at 58,000 kilometers per hour. At that speed, it would take roughly 80,000 years to get to Proxima Centauri b. The Voyager 1 and II probes are also going fast, they aren’t heading toward Proxima b, but they are going really fast too, 61,000 and 55,000 kilometers per hour respectively.

So if they were pointed at Proxima b, then we’re looking at about 80,000 years for the Voyager probes too.

More recently, the Parker Solar Probe managed speeds of 700,000 kilometers per hour at closest approach around the Sun, but it did that at very short intervals. Still that’s .06% the speed of light, so we’re getting there, but it wasn’t sustainable for long distance stellar flight.

We’ll need to do a lot better than that if we want to get to the closest exoplanet to us in any reasonable amount of time. Chemical rockets, the kind we’re using right now, won’t get anywhere near fast enough and are very problematic because we need to carry all that fuel with us as we go, and that reduces efficiency a lot.

Fusion rockets are very promising, but we don’t have any of those yet. Still, if we could use the energy of fusing Helium-3 isotopes and Deuterium we might be able to reach sustained speeds on order of the Parker Solar Probe of 0.06% the speed of light and arrive at Proxima b in about 25,000 years.

The sweet spot would be if we could somehow attain speeds of about 10% the speed of light. If we could do that, then travel to Proxima b, 4.3 light years away would take 44 years or so. That’s well within a normal human lifespan.

Slightly less appealing but still remarkable would be if humanity could achieve 1% light speed. It would still take 436 years to reach our closest exoplanet, but one can imagine technologies, like cryogenics, that might help us get through the journey intact.

Space is big, there’s no doubt about it. And looking at the big picture, that’s probably a good thing. Still, it would be nice if we could figure out technologies that can get us to appreciable percentages of light speed to cover these vast interstellar distances in reasonable times. Of course, we might discover new physics that allows us to traverse the galaxy, but for now we are confined by relativity and technologies that keep us well below light speeds and the distant exoplanets out of our reach.