description HD 40307 b Overview
HD 40307 b is a radial-velocity exoplanet orbiting the K-type star HD 40307, about 42 light-years away. With a minimum mass of roughly four Earth masses and an orbital period of about 4.3 days, it is the innermost of the three planets reported in the system's original 2008 discovery. Its short orbit places it close to the star and exposes it to far more irradiation than Earth receives.
help HD 40307 b FAQ
How was HD 40307 b discovered?
The planet was detected through stellar radial velocity using the HARPS spectrograph on the ESO 3.6-metre telescope at La Silla. The original three-planet system was announced by ESO on June 16, 2008, while later catalog records cite the 2009 publication. [ESO](https://www.eso.org/public/news/eso0819/)
How long is the orbit of HD 40307 b?
HD 40307 b completes an orbit in about 4.31 days at roughly 0.047 astronomical units from its K-type star. It is the innermost member of the original b, c, and d group. [NASA Exoplanet Archive](https://exoplanetarchive.ipac.caltech.edu/overview/HD%2040307g)
How massive is HD 40307 b?
Its radial-velocity minimum mass is about 4 Earth masses. The planet's radius is not directly known because it is not a confirmed transiting world, so its internal composition cannot be read from the mass alone. [NASA Exoplanet Archive](https://exoplanetarchive.ipac.caltech.edu/overview/HD%2040307g)
What other planets are in the HD 40307 system?
The original HARPS announcement covered HD 40307 b, c, and d, with orbital periods of about 4.3, 9.6, and 20.4 days. Later signals were labeled f and g, but the archive marks g as controversial, so the system's outer-planet history needs that qualification. [NASA Exoplanet Archive](https://exoplanetarchive.ipac.caltech.edu/overview/HD%2040307g)
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