The Kepler telescope has led to the discovery of more than a thousand exoplanets. But there are still several thousand “candidate” planets. An exoplanet can be in candidate status for various reasons. The data may not be solid enough to confirm the planet, or what looks like a planet doesn’t seem to have a stable orbit, or half a dozen other reasons. Sometimes the data might look good, but it’s just…strange.
The color of light we observe from a star depends not only on the color emitted from the star, but also the speed of that star relative to us. From this simple fact we can actually determine a great deal about a star, including the star’s axis of rotation relative to orbiting planets.
As a star forms, a protoplanetary disk also forms, out of which the planets coalesce. Since the protoplanetary disk is generally aligned with the equator of the star, the planets form with that same basic orientation. This is what we see in our solar system and in many exoplanetary systems. But not all systems follow this rule.
The discovery of protoplanetary disks such as this one agree with the nebular hypothesis, which posits that a star and planetary system form together. The star collapses out of a nebula, and it forms an accretion disk around itself, out of which the planets form.
When we started looking for extrasolar planets, Alpha Centauri was high on the list of any astronomer’s inner child. But despite its closeness, finding planets there would be difficult. The orbit of Alpha Centauri B is at an angle relative to us, so there isn’t likely to be any transiting planets that we can detect. That means planets would have to be found by looking at the wobble of the star as the planet orbits it, which is much harder to measure.
We’ve come a long way since the first extra-solar planet was discovered in 1995. Within a decade of that discovery, we will likely identify dozens of earth-like worlds, which is nothing short of amazing.
There are several ways to detect planets, but one of the more interesting methods is known as the transit method. You might remember the transit of Venus, when Venus passed in front of the Sun as seen from Earth. Imagine the same thing happening around a star, where a planet transits that star from our point of view.