The Earth has reworked itself so many times that geologists seeking to study its earliest days have little left to work with. Catching similar planets in the process of formation, however, could fill in gaps in our understanding, but how hard will it be to spot one at just the right stage? One team of astronomers reached some optimistic conclusions.
The first challenge in observing the birth of an Earth-like planet is to find a star like the Sun but much younger. Most stars form in clusters that gradually disperse, becoming what are called “young moving groups” because the stars that make them up are of the same age and travel similar paths around the galaxy.
Dr Richard Parker of the University of Sheffield studied 10 of these groups within 100 parsecs (326 light-years) of us, seeking members who were previously not recognized as part of the pack. The distance was chosen as a range within which we would have a reasonable chance of detecting a hot young planet with existing technology.
Parker had a team of undergraduates look for the characteristics that identify a star as fitting the criteria for a group. The project gave them a taste of real scientific work usually hard to obtain without a degree, as well as authorship of a paper.
"Observations from the Gaia telescope have helped us to find many more stars in these groups, which enabled us to carry out this study," Parker said in a statement.
Most stars are less massive and considerably fainter than our own, which means planets need to orbit nearby to have prospects of becoming Earth-like. This makes it easier to detect them through the dimming of the star during a transit, or gravitationally induced wobble.
However, very young planets are so hot we should be able to detect their infrared radiation directly, which is how Parker hopes to find them. That's harder if they are close to a faint star than more distant from a brighter one. Consequently, Parker and his young team are particularly interested in stars at least as bright as the Sun.
The worlds the team are seeking are known as magma ocean planets because the constant bombardment from large asteroids and planetesimals creates so much heat, their surface is liquid rock. In The Astrophysical Journal, they present evidence that there are more suitably bright stars in these groups than previously expected, raising the chance of finding a planet.
For three young moving groups, the paper goes further, calculating a probability for finding a magma ocean planet based on reasonable assumptions about the numbers of such worlds and the time-scales over which they are hot enough to find. The best prospect of the three, Beta Pictoris, offers a 71 percent chance of a suitably thorough survey finding a future Earth.