TOI-5624 f is the fifth and outermost exoplanet discovered in the TOI-5624 system, located approximately 331 light-years from Earth in the constellation Ursa Major.[1] The discovery of the object was officially announced by an international team of astronomers led by Andrea Bonfant in late April 2026.[1]
Artistic depiction of the TOI-5624 system (sizes to scale) compared to Mercury's orbit. TOI-5624 f is the outermost planet in the system, designated as 5624 f
The object is classified as a warm Neptune. Since the planet is not transiting, its radius has not been directly measured.[1][2] The minimum mass, determined by the radial velocity method, is 13.0±3.7M🜨.[1][2] According to numerical modeling of the system's dynamical stability, the planet's true mass cannot exceed 26M🜨, otherwise the system would become unstable over cosmological timescales. It is hypothesized that the planet possesses a massive hydrogen and helium atmosphere or contains a significant fraction of water ice.[1][2]
The planet receives significantly less energy from its star than the inner planets of the system. Its equilibrium temperature is estimated at 478.5 K, which is about 205 °C, assuming an albedo similar to Neptune's Bond albedo.[1][2]
Orbit
As the planet is the outermost of the four other known planets in the system, its orbital period is the longest, at 45.43 days. Its orbit lies at a distance of 0.2366 AU from its host star, which is approximately 60% of Mercury's distance from the Sun.[1][2] Based on the dynamic stability modeling of the system, the orbital inclination of the exoplanet f will be in the range of 60 to 90 degrees.[1][2] The planet itself is in strong dynamical interaction with the planet TOI-5624 e. Their orbital periods are in a 2:1 ratio, leading to significant transit timing variations (TTVs) for the inner planet.[1][2]
In terms of its physical parameters, TOI-5624 f is most similar to Uranus; however, due to its proximity to the star, it is significantly hotter than the ice giants of the Solar System.
1234567891011Bonfanti, A.; etal. (2026-04-21). "The multi-planet system TOI-5624: Four transiting sub-Neptunes with an outer companion revealed by transit-timing variations". arXiv:2604.15035 [astro-ph.EP].
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