Which star is orbited by the ultra-short-period planet 55 Cancri e?

The ultra-short-period planet 55 Cancri e orbits the star 55 Cancri.

The system lies about 41 light-years away in the constellation Cancer. 55 Cancri is a Sun-like star, also known as Copernicus, and it hosts multiple known planets. The innermost of them, 55 Cancri e, is a super-Earth that circles its star in less than a day—about 17.7 hours—making it an ultra-short-period planet.

Because 55 Cancri e passes in front of its star, astronomers can measure its transit and estimate its size. Its mass is also constrained through the star's gravitational wobble. Those measurements show a world much more massive than Earth but smaller than Neptune. The planet is intensely heated, and observations have investigated whether it has a changing atmosphere or a surface dominated by molten rock.

The designation can cause confusion. “55 Cancri” names the host star, while the lowercase letter “e” identifies one particular planet in that system. The star is sometimes called Copernicus, but “55 Cancri e” remains the standard planet designation used in catalogs and scientific discussions. It is not the same object as a planet orbiting Gliese 876, Epsilon Eridani, or Tau Ceti.