Could Aliens See Us?

One of the most inspiring ventures in the world of astronomy in the 21st century is the increasing discovery of exoplanets. They represent the most extensive effort to find life outside of Earth. So far, we have discovered thousands of planets surrounding other stars, but there is something of a selection bias. Astronomers use a few primary methods: the first is the transit method, and the second is the astrometry method.

Transit involves measuring the dip in light coming from a star, caused by an obstruction of the light from a planet crossing in front of its star relative to the observer. This has a very strong selection bias in several ways. The first is that only planets that cross in front of the star can be detected. This limits the number of possible systems enormously. The second is that only planets that transit somewhat often, meaning only planets that are very close to their host star can be detected.

Astrometry involves measuring the amount of red-shifting or blue-shifting that is present in the starlight, due to the wobble caused by the gravity of the planet while it orbits. This has a heavy selection bias for large planets that orbit close to their host stars.

So I ask the question, “If someone were to look at the sun looking for planets, what would you see?” And the answer, if you were using current methods, is almost nothing. Nearly all of the nearby star systems are not aligned with the sun’s planetary plane, which means they are receiving effectively no information on the orbiting bodies. The few that are lucky enough to be aligned would be able to detect Jupiter if they had a long enough observation, probably using the transit method. None of the other planets would likely be detectable, because they either take much too long to observe three or four orbits, or they are too small to be detected through either method.

In a certain light, this could be seen as quite liberating. Our methods seem so feeble, unable to detect the vast majority of what is almost certainly out there. But, it also means that other, more innovative methods need to be developed if we want to map the universe around us.