description HD 21749 c Overview
HD 21749 c is a transiting planet with a radius estimated at about 0.9 Earth radii and an orbital period of approximately 7.8 days. NASA's TESS mission detected the transit around the K-type star HD 21749, and the planet was announced in 2019 as the mission's first roughly Earth-sized discovery. The same system also contains HD 21749 b, a larger planet on a longer orbit.
help HD 21749 c FAQ
How was HD 21749 c discovered?
NASA's TESS mission detected HD 21749 c through the dip in starlight caused by a transit. The planet was announced in 2019 as one of TESS's first roughly Earth-sized discoveries. [NASA Exoplanet Archive](https://exoplanetarchive.ipac.caltech.edu/overview/HD%2021749%20c)
How long is a year on HD 21749 c?
HD 21749 c orbits its K-type star every 7.79 days at about 0.0695 astronomical units. Its short period places it much closer to the star than Earth is to the Sun. [NASA Exoplanet Archive](https://exoplanetarchive.ipac.caltech.edu/overview/HD%2021749%20c)
How big is HD 21749 c, and is its mass known?
Its estimated radius is about 0.89 Earth radii, but its mass has not been tightly measured. The archive gives an upper limit of roughly 3.7 Earth masses from the available data. [NASA Exoplanet Archive](https://exoplanetarchive.ipac.caltech.edu/overview/HD%2021749%20c)
What is the difference between HD 21749 c and HD 21749 b?
HD 21749 c is the smaller inner planet with a 7.79-day orbit, while HD 21749 b is about 2.6 Earth radii and orbits every 35.6 days. Both planets transit the same K-type star. [NASA Exoplanet Archive](https://exoplanetarchive.ipac.caltech.edu/overview/HD%2021749%20c)
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