description HD 40307 d Overview
HD 40307 d is one of the planets first identified around the nearby K-type star HD 40307. It was reported in 2008 from radial-velocity measurements and has a minimum mass of about 9.5 Earth masses, placing it in the super-Earth range. In the original three-planet solution, it was the outermost planet and completed an orbit in approximately 20.4 days. Later studies have examined additional planets in the same system.
help HD 40307 d FAQ
What is the orbital period of HD 40307 d?
HD 40307 d completes an orbit in about 20.43 days. Its minimum mass is around 9.5 Earth masses, which places it in the super-Earth mass range by mass even though its radius is not directly measured.
How was HD 40307 d discovered?
It came from radial-velocity measurements of the K-type star HD 40307 and was part of the original b-c-d system report. This technique measures the star's wobble and gives a minimum mass, written M sin i, rather than a guaranteed total mass.
Why is HD 40307 d called a super-Earth if scientists do not know its surface?
Super-Earth describes a mass larger than Earth's and does not mean the planet has an Earth-like surface or atmosphere. HD 40307 d's reported minimum mass is about 9.5 Earth masses, while radial velocity alone does not determine whether it is rocky, icy, or wrapped in gas.
Is HD 40307 d in the habitable zone?
Its 20.43-day orbit is too close to its K-type star for the usual habitable-zone discussion of the system. That discussion centered on the later HD 40307 g signal, which NASA's archive flags as controversial, not on d.
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