Hot Jupiters – A Whodunit

Astronomers who collect exo-planets have noticed there are a lot of hot Jupiters out there among the planets discovered so far.  A hot Jupiter, to get the story going, is a planet around the size of Jupiter orbiting its star at a close distance, well inside the radius of the orbit of our planet Mercury, where things get really hot.  Some say it just a result of the selection process of planetary detection, but, being suspicious by nature, my bet is that somebody did it.  There aren't many clues to go on, but in the best Sherlock Holmes tradition, let’s sleuth out what we can.

Who could have done that?  Well, it’s probably not done by remote control, so that means the likely suspect is the space-faring race that is currently living there or at least colonizing that solar system.  Most likely there is only one such group at any solar system, so there’s not much doubt who did it. 

What’s the motive?  Why would they do that?  Well, what would a space-faring race need?  Three things come to mind immediately.  One is energy.  Another is resources, by which we mean materials of various sorts.  The third is a place to live.  You might get all of them by pushing a Jupiter towards its star.

Lots of people interested in mankind’s future think about where to get energy.  For a few decades, since the discovery that the sun’s energy comes from fusion, there has been the concept that someday mankind would be able to control fusion, other than in hydrogen bombs.  Those who think fusion will not be achievable talk about a modest future, running on solar and wind power, with another few renewables thrown in, after we use up the available fossil fuels.  Solar power is of course derived from fusion.  So is wind power, but it has a more complicated series of transformations before the sun’s photons’ energy gets to the windmill’s turbine.  This concentration on one source of fusion power or another seems to be a bit of monomania.  Gravity is a source of energy as well, but our planet doesn't seem to be using much of it anymore, or at least not so obviously.

When the Earth condensed from the effects of gravity, it got hot, and some of the original heat of condensation is probably still around, although the core‘s temperature is thought to be fission generated.  So geothermal energy might have some gravitational energy in it, but not in any obvious way.  However, moving a planet closer to its star clearly is going to generate a lot of energy.  The star is at the bottom of a deep gravity well.  So, one possible motive for moving a gas giant planet nearer its star might be energy extraction.

Resources can be in various kinds.  One sort is minerals, buried in the rocky core of a planet.  We can dig into our planet very easily, but if there was a tremendous atmosphere on it, stripping off some of it might make mining easier.  If a planet gets close to its star, the atmosphere is going to be affected by the stellar wind, and heated up as well, so some of it might escape by thermal effects.  Bringing it down near its star, and waiting a long, long time, might mean that the rocky core could be eventually mined, perhaps only on the cold side of a tide-locked hot Jupiter, but that could still be a lot of minerals.

Another sort of resources is hydrocarbons.  If you wanted a solar powered hydrocarbon factory to be efficient, you could move the hydrocarbons near to the star.  Jupiter’s atmosphere is full of hydrogen and carbon compounds and other Jupiters might have the same mix.  Solar power is pretty weak near our Jupiter’s orbit, but near Mercury’s orbit it is a lot more potent. 

The third thing a space-faring race might want is a right-sized rocky planet in the habitable zone.  If you have a Jupiter occupying that zone, you need to get rid of it.  Alternatively, your Jupiter, or Jupiters, might not be occupying the habitable zone at all, but nothing else is either.   Maybe you can use the motion of the Jupiter toward the star to bring the planet you like into the right zone. 

It just so happens that the three or four things the space-farers might want to obtain by moving a giant planet in closer to its star are the things we like too.  We have a large part of our (primitive) economy engaged in energy capture and transformation.  Another large part is mining resources out of the ground, and hydrocarbon manufacturing based on fossil fuel inputs is also large.  And developing new housing and entire cities takes up another big chunk of our economy.  So, if the space-farers are just like us, only more advanced, they are probably doing the same things we do on a larger scale.

So we know who it might be, and the motive for doing it, but we don’t know how.  There hasn’t been much theoretical work on the engineering of moving planets around in a foreign solar system, so we can’t cite a series of possibilities.  But it probably is being done as cheaply as possible.  Having a large planet fly by the target Jupiter might, if the orbits were cleverly chosen, gradually push it inward toward the star.  The large planet might be put into the right orbit by using a smaller planet, which in turn is being altered by a yet smaller one, down to where we get to an asteroid, which is probably easy to move around by an advanced race.  They would certainly be able to observe the existing orbits, predict them with as much precision as needed, and predict how they would change as well.  This would be a very cheap way to move a Jupiter.

Thus, the whodunit is over.  We have some ideas on who, why and how.  Details like ‘when’, for processes which might take a million years, are not as important as they are to domestic crime-solvers. 

Some people hunt for alien races by listening for some sort of radio signals.  Perhaps hot Jupiters are a better clue.  So, instead of wondering if there are any alien folks out there in the galaxy, we should examine closely what might be the artifacts of their engineering.  This changes the perspective we might have on aliens in general.  The problem of the Great Filter, as it is called, which prevents aliens from visiting Earth is a vastly different problem if we deduce that many of the nearby stellar systems are inhabited or colonized, or at least have been visited in the past when the engineering of orbits was done.  It may well be that the Great Filter doesn’t exist, and the lack of aliens here is simply a matter of timing.  Perhaps we should watch how the orbit of our own Jupiter is changing over very long periods.