Ever since we started finding exoplanets in the 1990s, folks have wondered if our system is normal or not. Do other solar systems store their rocky worlds near their suns? Is it typical to have Jupiters and Saturns farther out? Understanding these questions takes time and technology. To confirm the existence of a planet, we really need to wait for it to complete an orbit, and the farther from the Sun an object is, the longer it will take. Jupiter’s orbit is twelve Earth years long, and Saturn’s is 29! Pluto… Well, we haven’t actually seen Pluto complete an orbit yet. It was discovered in 1930 and will take 248 years to orbit.
To really understand what is going on, a survey of a large set of stars is required, and this is where the California Legacy Survey comes in. This survey is looking at 719 sunlike stars and is trying to identify the pulls and pushes of orbiting planets reflected in the stars’ motions. This 30-year-old project has released data on fifteen new planets that join its catalog of 177 worlds.
While not sensitive enough to detect distant ice giants like Uranus or Neptune, this survey does see gas giants, and it finds that gas giants are most often found with orbits between the size of Earth’s orbit and 10 Earth orbits. This shows our solar system is pretty typical in its planetary placement, at least in comparison to other systems we can see. With more time, and more sensitive instruments, we’ll be able to see more distant planets and a wider range of planet masses.
This is a reminder that astronomy is a long game, and sometimes the experiments and spacecraft started by one generation are completed by future generations.
Caltech press release
“The California Legacy Survey I. A Catalog of 177 Planets from Precision Radial Velocity Monitoring of 719 Nearby Stars over Three Decades,” Lee J. Rosenthal et al., to be published in The Astrophysical Journal Supplement (preprint on arxiv.org)