Stars with higher iron content have planets in close orbits
Scientists did not expect stars' elemental compositions to influence evolution of their planetary systems.

Laurel Kornfeld | Apr 19, 2018

Stars with higher than normal iron content tend to have planets in close orbits in contrast to those with lower or normal iron content, which are more likely to have planets in distant orbits, according to a new study presented on Tuesday, January 9, at the American Astronomical Society (AAS) meeting in National Harbor, Maryland.

The study was conducted by astronomers working on the Sloan Digital Sky Survey (SDSS), who analyzed data collected by NASA's Kepler planet hunting mission.

Kepler did not analyze the chemical compositions of the stars it looked at in the hunt for planets. That analysis was done by SDSS's Apache Point Observatory Galactic Evolution Experiment (APOGEE), which has collected spectra of hundreds of stars in the Milky Way.

Stellar spectra reveal the amount of light a star emits at various wavelengths and enable astronomers to measure specific elements within each star and the amounts of each element present.

"All Sun-like stars are mostly hydrogen, but some contain more iron than others," noted Johanna Teske of the Carnegie Institution for Science, who took part in the study.

"The amount of iron a star contains is an important clue to how it formed and how it will evolve over its lifetime."

While scientists expected stars' elemental compositions to impact the stars' evolution, they were surprised to find that stellar composition also impacts the evolution of planetary systems.

This latest study's findings confirm those found in a 2016 study that used less precise stellar spectra from the Chinese Large-Area Multi-Object fiber Spectroscopic Telescope (LAMOST)-Kepler project, in which planets in close orbits were found circling iron-rich stars.

The new study pinned down the orbital periods of planets around iron-rich stars as eight days or less.

Iron-rich stars have only about 25 percent more iron than all other stars. Scientists do not know how or why the former evolve planets in closer orbits or whether their planets actually form further out and subsequently migrate inward.

Answering these questions will require further study of the proto-planetary disks around young stars, from which planets form.



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