A new idea for SETI

I was just reading an article about the “space parasol” idea. That’s the concept of placing a sunshade at the Earth-Sun L1 point¹ to intercept perhaps 2% of the solar flux before it reaches Earth. This would counter the projected temperature changes on Earth due to a green-house effect.

It struck me there is more to it than that. It is known the Solar Constant² has risen slowly over the aeons of our star’s life and will continue to do so. At some point in our distant future we will have no choice but to either move our planet further outwards, abandon it for a new home or build sunshades. The evolution of the solar system gives us absolutely no choice in the matter. We will be forced to take complete control of the energy balance of Earth or else we and all other life will be on our way to extinction.

I’m confident our “greens” will by then have mutated into “browns” who will believe we should allow events to run their natural course from parched bare rock to parched bare rock.

Whether we take up the reigns of control now or our descendant species do so millions of years from now is not relevant to the purpose of this article however. Somewhere in the Universe there are civilizations which have faced the choice already. Some of them will have chosen to control the stellar flux on their home world.

We have two methods of detecting extrasolar planets currently. One is by the doppler effect caused by a stars’ dance about the changing center of gravity of its’ planetary system; the other is by watching the light curve for dips due to planets passing across their star’s disk from our perspective.

It is quite possible for us to see doppler effects without seeing eclipses. It happens if the plane of the alien solar system is tilted with respect to us such that planets never pass directly between us and their star. This is the most likely scenario.

But what if we were to see the opposite effect? What if we see a significant dip in the light curve at predictable intervals and yet do not see any doppler effect?

I’ll expand on this for those who have not said “Aha!” yet.

It should take a fairly significant sized body to make a dip we detect: almost certainly one with a disk size from which we would infer a substantial, Jupiter class, mass. Such an object would almost certainly cause alternating redward and blueward doppler shifts of the stars spectral lines as it orbits the star. If that is not the case, we have an anomaly. An object in orbit about its’ star which is large enough to block substantial light and yet is very low mass relative to its’ size should strike one as very odd.

It could be a parasol built by intelligent life.

¹ = Lagrange points are where the gravity between two bodies creates a “balance” point such the pull from each tends to keep the object where it is. The Earth-Sun L1 point is on a line directly between and a couple million miles inwards. You can either read about it or calculate it yourself.

² = The Solar Constant is the average total energy flux at Earth orbit, currently about 1.37 kw/m^2 flat on to the Sun. It is reasonably constant over a human lifetime but is not constant in the long term. The Sun was hotter in its’ earliest years until it stabilized somewhat cooler than it is now. It has slowly grown hotter and will continue to do so for billions of years to come. Life will be impacted long before our star leaves the Main Sequence in the far future. At that time it will expand to red gianthood and will become large enough to absorb or at best turn Earth into an orbiting cinder.