TOI-4468 c is a sub-Neptune, a planet between Earth and Neptune in size, that orbits just outside a hot Jupiter. It is about 3.1 times Earth's width and circles its star, an orange dwarf about 1,200 light-years away, every 7.01 days, while its giant sibling, TOI-4468 b, orbits closer in, every 2.77 days.
A team led by Joseph Livesey reported both planets in 2026, using data from NASA's TESS satellite and ground-based telescopes, which caught the planets crossing in front of the star, and from the NEID spectrograph, which measured the star's wobble. The giant's mass came out clearly from that wobble. TOI-4468 c's did not, so the team confirmed it statistically instead, showing with ground-based observations that its signal is far more likely to come from a planet than from anything else. The NASA Exoplanet Archive's mass of about 10 Earth masses is therefore an estimate, not a measurement.
Its existence is the system's main puzzle. TOI-4468 c is a close outer companion to a hot Jupiter with no inner one, a layout the team calls unique among known systems. They argue it means the system never passed through a gravitational resonance that tilts companions' orbits in comparable systems, a clue to how hot Jupiters arrive at their tight orbits. TOI-4468 c receives about 83 times the light Earth gets from the Sun, according to the archive, far too much for liquid water.