The catalog of known exoplanets passed a milestone this year that would have been unthinkable when the first one was confirmed three decades ago: confirmed planets are now counted in the thousands, with candidate lists an order of magnitude larger and growing faster than the literature can name them.
How you find a planet you cannot see
Almost none of these worlds have been photographed. The census runs on inference: transits — the hundredth-of-a-percent dimming as a planet crosses its star — and radial velocity, the wobble of a star being tugged by an orbiting companion. The newest survey instruments automate both at industrial scale, monitoring hundreds of thousands of stars with the photometric stability to catch Earth-sized silhouettes against Sun-like ones.
- Transits: the dimming method, best for finding small planets
- Radial velocity: the wobble method, best for weighing them
- Atmospheric spectroscopy: the next decade's main event
What the statistics already say
The demographic findings are robust even as individual worlds remain mysterious: planets outnumber stars in our galaxy; small planets are the norm, not the exception; and the most common planet type in the catalog has no analogue in our own solar system — worlds between Earth and Neptune in size, a class the theorists are still arguing about.
The decade ahead
The frontier has moved from detection to characterisation. The next generation of instruments is built to read atmospheres — sniffing the light that filters through alien skies for the chemical signatures of chemistry, weather and, in the dreaming version of the field, biology. The habitable-zone candidates are already queued. The instrument time is booked. The next decade of astronomy is, quite literally, scheduled around the question.