For most of history, our Solar System contained the only known planets.
Yet each twinkling point of light — each star — represents a new chance.
Such systems could contain rocky planets, possessing oceans, continents, and — perhaps — life.
In the early 1990s, the first planetary detections around other stars arrived.
As planets orbit their stars, those stars orbit their mutual center-of-mass, creating “wobbles” in their motion.
This stellar wobble, or radial velocity, reveals planetary masses and orbital periods, up to an uncertain inclination angle.
Meanwhile, transiting planets obscure a portion of their parent star’s light.
This periodic dimming reveals a planet’s radius and period; it’s responsible for most presently discovered planets.
Meanwhile, direct imaging and microlensing also reveal exoplanets; their numbers may skyrocket in coming decades.
With 400 billion Milky Way stars, we estimate they contain 1-to-10 trillion orbiting planets, total.
Meanwhile, rogue/orphan planets — ejected and/or formed without parent stars — could be 10-to-10,000 times as numerous.
With ~2 trillion galaxies within our observable Universe, we can extrapolate our Universe’s planetary total.
There are ~1025 planets that orbit stars, with some ~1026-1030 additional starless planets.
With a little luck, we’ll soon find the first extra-solar planet housing extraterrestrial life.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.