What did the universe’s first planets look like?
We think that the first generation of stars didn’t form planets. These stars were very unstable and likely developed in a short time very strong winds, violent pulsations and eventually exploded. All of these processes contributed to releasing new chemical elements that formed in the interior of these stars in the nearby gas, changing forever the chemical composition of the universe.
The information we’ve collected so far indicates that gaseous giant planets are normally found orbiting metal-rich stars, while small rocky planets can be found both around metal-rich and very metal-poor objects. The current explanation for this is that larger gaseous planets would need larger cores to form, and in the discs of metal-poor stars there may not be enough heavy elements.
For these reasons we believe the first planets in the universe were likely small rocky systems. This is also supported by the properties of the oldest planetary systems discovered so far. These are compact groups of small rocky planets orbiting around stars that are about 13 billion years old. Dr Elena Sabbi is NIRSpec branch manager at the Space Telescope Science Institute, Baltimore, Maryland