Exoplanets, here we come!(?) Image: Linshan Feng

Exoplanets, here we come!(?)

Going to Mars seems to be within our reach, but what about visiting exoplanets: planets outside our Solar System? In this article I discuss with former ESA exoplanet expert and Leiden guest professor Malcolm Fridlund about the day humans call another planet home and how to get there.

Any earth-worthy exoplanets out there?

If we want to go to an exoplanet, we first need to know where they are. To find them, astronomers can wield two methods, Fridlund explains. With the first one, named the radial velocity method, you look at how stars move because of the gravitational pull of a planet. The other method makes use of eclipses: “If a planet passes in front of a star, it will eclipse a little bit of the light. Even if the planet is small, as in the case of the earth, it removes 0.01% of the light from the sun when it is passing. If you take Jupiter instead, you are talking about 1% of the light.” This transit method is used by the COROT space telescope, an ESA mission Fridlund has worked on.

“We and other organizations have found about 5000 planetary systems to this day. They are all different: different configurations of the planets, different sizes and different densities.” None of these systems look like our Solar System and our planet. For instance, the first planet found by COROT to have a density similar to earth had a year of only twenty hours. Its small orbit and closeness to its star makes it unsuitable as a visitable exoplanet. It’s simply too hot.

With all these strange planets that don’t resemble our home planet, will we ever find one? “Well, we only started studying these things 25 years ago and now they are taking it more seriously. It’s a hot topic of space research, the search for the holy grail, an earth analogue,” Fridlund explains. “If there are any planets out there like ours, then we will find exoplanets in the next fifty years, I’m certain. But maybe we are unique, that’s something we have to find out.”

And if we find one, how do we get there?

Our current space traveling won’t give us any intergalactic speed tickets. “The spacecrafts that leave the Solar System travel at 50 km/sec, only a small fraction of the speed of light, which is 300.000 km/sec. It would take each of them a hundred or two hundred thousand years to reach interstellar distances, a couple of light years away from the Solar System.” Obviously, with these time scales we will never reach interesting exoplanets before the end of time. If we could travel at 10% of the speed of light, exploring them could become a possibility, Fridlund explains. Then it would take only forty years to reach the nearest star, Proxima Centauri and its planet Proxima Centauri b.

The astronomer speculates that achieving this immense speed is possible. For example, by using atomic power: “In a model called ORION, you detonate two nuclear bombs per second behind a spacecraft. After you detonate 300 of them, your spacecraft is moving at 10% of the speed of light.” Sounds like an interesting idea, why don’t we already use nuclear spacecrafts? “During the cold war governments prohibited detonation of nuclear bombs above ground, this included space.”

Other ways to partially achieve the speed of light are possible, but they take time. “Around ten years ago, ESA received a proposal for a mission to an exoplanet. Its time scales allowed for a hundred years to develop the technology.” Not only large space agencies are curious to explore space. “A Russian billionaire is putting money into finding a way of sending a spacecraft to Proxima Centauri.”

Beside the technical part, our relatively short lifespan set back possible missions as well: “You have to either sleep the whole way, or have generation ships in which the people arriving are not the same as the ones starting the journey or you have to develop immortality.” A piece of cake, right?

WOW Orion WOW Orion
An example of what the nuclear propulsion of the ORION project would look like. Image by Matthew Paul Cushman: https://www.behance.net/gallery/33225347/Cutaway-Illustrations-by-Matthew-Paul-Cushman

Why would we go to an exoplanet?

Even if we could solve all these challenges, why would we go there? It is true that humans have always been adventurous, that’s why you can find us on all continents. But going to an exoplanet, is that out of our reach? “If you compare the effort that went into exploring the earth once upon a time, then of course it is as big as going to the stars. It is just a matter of making it profitable for mankind to do it.”

Ah, yes, the greed of humans, a never-ending story. However, Fridlund isn’t talking about earning money, he means a different kind of profit. “It's a way of ensuring the survival of mankind by putting it in different places. One of these days there will be a meteor coming in that is big enough to wipe us all out, or we do it ourselves or something else happens. Perhaps it will become too hot billions of years into the future, because of the expanding sun. Whatever the reason, we might need to move somewhere else. If we are still here of course.”

Sci-fi fantasy or realistic future?

If given the opportunity, would Fridlund himself go to an exoplanet? “If I could take my loved ones with me, I would probably do it. But it is so far in the future that I could say anything now and I wouldn’t know if I was actually lying to myself.” What the adventurous professor would say yes to in a second? “A 5-minute tourist trip going beyond the Kármán line, currently available for 300.000 euros. If I had the money to spare, say if I won the Nederlandse Staatsloterij or something, then I would go immediately. Just to prove to myself that the earth is really round.”

Visiting or colonizing exoplanets will probably not happen during our lifetime, but with the right technologies and some time it is more than a simple sci-fi fantasy. Fridlund: “We only started looking for exoplanets in the last century and the exoplanet study is becoming more and more active. We are at the beginning of a very exciting period.” Who knows, perhaps our great-grandchildren will go on a school trip to visit nearby exoplanets as if it’s the most natural thing in the world(s).


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