The discovery was made by a team of astronomers using a high-resolution spectrograph and the ESO's 142-inch (3.6-meter) telescope at the La Silla Observatory in Chile. Using a high-precision technique that enables them to detect miniscule variations in the relative speed of stars, astronomers are able to detect variations caused by the push and tug of orbiting planets. More than five years of observation turned up a minute wobble in the motion of iota Hor b's host star, which the team was able to verify as the influence of a planetary companion.

Measurements of the wobble have shown that Iota Hor b orbits its host star once every 320 days. It travels in a slightly elliptical orbit that stretches from 117 million kilometers to 162 million kilometers from its sun. If the planet revolved in the same orbit around Earth's Sun, its path would stretch from just outside the orbit of Venus to just outside Earth's orbit.

The discovery of iota Hor b marks the first time a European Southern Observatory instrument has found an extra-solar planet. Astronomers at the observatory plan to continue watching the system to learn more about the host star, its age, and any more companion planets it may have.