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Our future, our universe, and other weighty topics

Saturday, August 2, 2014

Is Kepler-78b a Sign of Astronomical Engineering?

For decades astronomers have expected to one day find some sign of what is called astronomical engineering. Astronomical engineering is engineering on an astronomical scale, produced by a civilization. Astronomers have reasoned that since there are so many solar systems in our galaxy where life could evolve, we would expect that civilizations would have arisen on many planets, and that we would also expect to see evidence of large-scale activities by such civilizations. Such astronomical engineering projects might consist of a movement or manipulation of planets or asteroid belts, or the creation of huge artificial structures in space. One popular idea about astronomical engineering is that extraterrestrial civilizations might create a sphere around their sun to capture all its energy, a sphere known as a Dyson sphere.

Efforts to detect a Dyson sphere have come up short, but there may be a space discovery that offers possible evidence of astronomical engineering: the discovery of Kepler-78b, the “planet that shouldn't exist.”

Kepler-78b is a planet orbiting the star Kepler-78, a G-class star like the sun, located about 400 light-years away. The strangest thing about the planet is the location of its orbit. The planet orbits its star at a distance of about 900,000 miles, which is about the diameter of the sun and other G-class stars. This is an orbit which places the planet more than 30 times closer to its sun than the planet Mercury is to our sun. Scientists assume that the planet is some kind of lava world too hot for life to exist on it.

Scientists are baffled by how a planet of this size could exist in this orbit, and the Science Daily article on the discovery is entitled Lava World Baffles Astronomers: Planet Kepler-78b 'Shouldn't Exist.' The article says: “When this planetary system was forming, the young star was larger than it is now. As a result, the current orbit of Kepler-78b would have been inside the swollen star.” It then quotes astronomer Dimitar Sasselov as saying this about the planet: "It couldn't have formed in place because you can't form a planet inside a star. It couldn't have formed further out and migrated inward, because it would have migrated all the way into the star.” Sasselov therefore calls the planet “an abomination.”

But there is one way to explain this strange planet: by imagining that it is part of an astronomical engineering project started by a civilization living on some planet revolving around the sun-like star Kepler-78. Such a civilization may have moved the planet from a more distant orbit to its current orbit very close to the sun it orbits. The planet may have originally been a much larger planet (possibly a gas giant planet like Neptune or a frozen super-Earth several times larger than our planet). The planet may have been deliberately moved to the orbit close to its star, for the sake of stripping off its outer layers, and leaving behind an inner rocky metallic core. Such an astronomical engineering project may have been started for the sake of creating a gigantic mining target, a million-year source of metals and minerals to be exploited. Another possibility is that the astronomical engineering project may have been started with the goal of creating a new Earth-like habitable planet in the Kepler -78 solar system.

How to Move a Planet

Before considering such possibilities, we must ask: is it reasonable to imagine that an extraterrestrial civilization would be able to reposition planets in its solar system? Certainly when imagining such a civilization we should allow the possibility that they might have god-like powers of engineering. Such a civilization might be many thousands (or possibly even millions) of years more advanced than ours. Considering how much technical progress our civilization has made in the past hundred years, if we imagine an extraterrestrial civilization that mastered atomic power thousands of years ago, we should imagine that such a race would be able to do almost anything that is technically feasible.

When I wrote a blog post last year on this topic (entitled Is Mystery Planet Kepler-78b the Work of Intelligent Planet Movers?), I suggested the idea that a highly advanced civilization could move a planet in its solar system by causing asteroids to crash into the planet (and using asteroids as projectiles that might cause moons of a planet to crash into the planet). But it turns out there is a more sophisticated technique for moving planets. In 2001 three scientists wrote a scientific paper entitled Astronomical engineering: A strategy for modifying planetary orbits. The scientists describe how we could move our planet farther away from the sun by creating an accelerated mass stream that moves in a loop traveling between Earth and the planet Jupiter. The mass stream would consist of one or more asteroids or other massive objects. Jupiter would act as a gravitational slingshot to greatly accelerate the mass stream. The same technique could be used to move a planet closer to a sun. The accelerated mass stream would travel in a loop between the planet to be moved and the sun.

how to move a planet

As the highly accelerated asteroids pass by the planet, there is a transfer of angular momentum that causes the planet to be moved. Imagine if you are standing in a field and your friend runs towards you at high speed, looping around you before running away. If you grab your friend's coat edge as he is whizzing by, you will feel a little tug pulling you in one direction (and the faster your friend was moving, the greater the tug you would feel). Similarly, matter passing by a planet at high speed causes a little gravitational and angular momentum tug that can pull a planet in a particular direction. Given enough repetitions, sufficient speed, and sufficient mass in the matter passing by, this can be enough to gradually change the orbit of a planet.

So it seems that using techniques such as these scientists have described, an extraterrestrial civilization would definitely be able to move around planets in its own solar system. Changing a planet's orbit requires simple old Newtonian physics, not any far-out science fiction assumptions such as space warps or space-time wormholes. 
Why Move a Planet to an Orbit Very Close to a Sun?

But why would such a civilization want to move a planet very close to its sun? There are two possible motives:
  1. Kepler-78b might have been moved very close to its sun in order to heat up and “strip off” the outer layers of the planet, leaving behind a metallic rocky core that could be a mining target, a source of metals and minerals that might last for millions of years.
  2. Kepler-78b might have been moved very close to its sun in order to heat up and “strip off” the outer layers of the planet, leaving behind an Earth-sized metallic rocky core intended to be moved to another orbit in the habitable zone of the Kepler-78 solar system. This may be part of a massive astronomical engineering project to create a second habitable planet in this solar system.
To explain both of these ideas, I must explain the idea of layer stripping. Planets such as Neptune, Jupiter, and Saturn are believed to be composed of different layers. For example, we see below a diagram showing the layers of Neptune. The outer layers are gases and frozen material. But the core is a rocky metallic core about the size of Earth. A similar diagram could be made of a frozen super-Earth planet with a mass five times greater than Earth, except that the proportions and element mixtures would be different.

layers of Neptune
Layers of Neptune (Credit: NASA)

Now what would happen if such a planet were to be moved very, very close to its sun, to the same distance that Kepler-78b is (a distance equal to about the diameter of the sun)? It would be like placing a big snowball with a rock at its center next to a big fire – the heat would strip off the outer layers, leaving only the rock remaining. All the gaseous and frozen layers of the planet would get so hot that they would steam off into space, like steam escaping from a boiling soup pan. What you would have left is a rocky metallic core about the size of the Earth – which exactly matches the description of Kepler-78b.

One possibility is that an extraterrestrial civilization will use Kepler-78b purely as a mining target, a source of metals and minerals. In such a case they might extract metals and minerals from the planet in its current orbit. Or they might later move the planet farther away, and then exploit its resources. It might be easier to mine the planet once it had been moved to a cooler location.

Another possibility is that extraterrestrials living in this solar system might later move Kepler 78b to an orbit in the habitable zone of their solar system, using the same simple technique they used to move the planet close to the sun. Their intention might be to create a new habitable planet in their solar system, a future home where they can live. They might have decided on such a massive astronomical engineering project after using up all the land and resources of their home planet, due to population growth.

Someone might object that Kepler-78b has been called a “lava world,” so such a planet would not be suitable as a future home for extraterrestrials living in the Kepler-78 solar system. But we're not actually sure that Kepler-78b is a lava world. There have been no measurements of the planet's temperature. The assumption that it is a lava world is based on the assumption that the planet has been in its current location for millions of years. But what if the planet had been moved to its location fairly recently, as part of an astronomical engineering project? In such a case it might not be a lava world. Imagine if the planet was in a particular stage of this “layer stripping” process when most of the gas and frozen layers had been stripped off, but there still remained a layer of ice a few miles thick. If such a planet were then moved to the habitable zone of the Kepler-78 solar system (the "Goldilocks zone" that is neither too hot nor too cold), it would be a rocky planet with oceans or seas, which could easily become habitable.

Gathering Support for These Ideas (Or Ruling Them Out)

Further scientific work may provide additional reasons for believing in these hypotheses, or such work may rule out these speculations. We do not know yet how many planets are in the Kepler-78 solar system. Kepler-78b is the only planet yet to be discovered there. But due to limitations in our planet detection techniques, it is perfectly possible that there is an undiscovered Earth-like planet in the habitable zone of this solar system. If such a planet were to be discovered (possibly by the forthcoming James Webb Space Telescope), it would make the ideas I have discussed seem more plausible (although it would not prove them true). If, on the other hand, astronomers were to conclude with high likelihood that there are no habitable planets in the Kepler-78 system, that would rule out the ideas discussed here.

There is also one way scientists might prove correct the ideas discussed here (or something close to them). We might point our radio telescopes to the Kepler-78 system, and listen for radio signals. If we were to detect such a radio signal, it would lend great credence to the ideas discussed here.