Ever since the dawn of human consciousness, skywatchers have been mystified by "wandering stars." These are the five visible planets circling our Sun. It was thought they influenced earthly affairs and allowed for future predictions through the pseudoscience of astrology. But real astronomers asked: where did the planets come from?
In the late 18th century, Immanuel Kant and Pierre-Simon Laplace hypothesized that the planets condensed out of a disk of dust and gas encircling the newborn Sun. This was based on the observations that the planet's orbits are co-planar, and they all move in the same direction, like a spinning phonograph record. In essence, their orbits are the residual skeleton of the long-vanished disk. But astronomers had to wait 200 years before the first telescopic evidence was collected that supported Kant and Laplace's conjecture. With the Infrared Astronomical Satellite (IRAS), they found a puzzling excess of infrared light from warm dust around the bright blue star Vega in the summer constellation Lyra. This was interpreted as a disk of planet-forming material. Observations with IRAS discovered that such disks are common around young stars. Vega was the first clue.
Teams of astronomers have now used the combined power of the Hubble and James Webb Space Telescopes to revisit the legendary Vega disk. Hubble sees debris the size of smoke particles, and Webb traces roughly sand-grain-sized particles. The big surprise is that there is no obvious evidence for one or more large planets plowing through the disk like snow tractors. This is common around other young stars. However, the Vega disk looks almost as smooth as a pancake, with no signs of planets. Vega is forcing astronomers to rethink the range and variety among planetary systems around other stars. The disk architecture apparently plays out differently around other star systems. Hubble and Webb are showing us that the starry sky is all about unanticipated diversity when it comes to planetary construction yards.
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