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A study of four years’ worth of spectrometer data has revealed details of a “hot Jupiter” exoplanet named CI Tau b, which has formed around a star that is only two million years old. Previous theories of planetary formation say that giant planets like Jupiter tend to form over a period of ten million years or more.

The study included a detailed analysis of the mass and brightness of CI Tau b, as well as the carbon monoxide content of its atmosphere. Astronomers Christopher Johns-Krull of Rice University and Lisa Prato of Lowell Observatory presented the findings at a meeting of the American Astronomical Society on June 10.

Prato said that the exoplanet’s rapid orbit around its host star was very helpful for analysis of the spectral lines that reveal clues about the planet’s chemical makeup. CI Tau b orbits its host star once every nine days.

“Many of the spectral lines that are in the planet are also in the star,” Prato said. “If both the planet and star were stationary, their spectral lines would all blend together, and we wouldn’t be able to tell what was from the star and what was from the planet. But because the planet rapidly orbits the star, its lines shift back and forth dramatically. We can subtract out the star’s lines and see only the lines from the planet. And from those, we can determine how bright the planet is, relative to the star, which tells us something about how it formed.”

This helps the astronomers pin down its size and brightness. The research team behind this study says that the host star’s young age and CI Tau b’s may challenge current models of planetary formation.

Rice University Ph.D. student Laura Flagg, the lead author of the study, said, “CI Tau’s age gives a tight constraint for putting models to the test: Can they produce a planet this bright and this massive in so little time?”

One theory holds that planets like CI Tau b could form so quickly due to a “hot start” in which gravitational instabilities in the star system could accelerate the formation of giant planets. Prato called the young “hot Jupiter” planet a good test for competing planetary formation theories.

“At about 2 million years old, CI Tau b is by far the youngest hot Jupiter directly detected,” she said.

The spectrometer data used to study CI Tau b came from McDonald Observatory’s 2.7-meter Harlan J. Smith Telescope and Lowell Observatory’s 4.3-meter Discovery Channel Telescope. A preprint of the study paper can be found on arXiv.