An abridged inventory of everything there is in the universe – from rogue planets and exomoons to supernovae, supermassive black holes and the cosmic web.
Navigate our inventory of the universe
PLANETS AND PLANETARY SYSTEMS
We start close to home. Given the vastness of the universe and the number of stars it contains, it would take a peculiarly blinkered view to believe that our solar system, with its ordered retinue of eight planets, is the only such collection of worlds in our galaxy. Only in the past three decades, however, have our telescopes been able to see planets orbiting other stars, known as exoplanets. We have now discovered more than 5000 of them, and most don’t look anything like home.
The surprises with exoplanets started in 1995 with 51 Pegasi b, the first planet to be discovered orbiting a main sequence star, the most common type of star in the galaxy, other than the sun. At about half the mass of Jupiter, but orbiting closer to its star than Mercury does to our sun, it was the first so-called hot Jupiter – a gas giant that orbits scorchingly close to its host star.
We have since found over 1500 hot Jupiters, and the consensus is these planets have migrated in towards their star after forming in a more distant orbit. But while this is a large proportion of the 5000-odd exoplanets found so far, we shouldn’t overestimate how common they are. Most exoplanet detections happen by looking at how a star’s light dips or changes colour as a planet passes in front of it, which biases discoveries towards large, fast-orbiting planets that transit across the face of their star more often. “Hot Jupiter …