[Paris Observatory] An international team, including scientists from the Paris Observatory – PSL at the Time-Space Laboratory, has spent ten years studying an exceptional planetary system comprising at least six planets with long orbital periods, the outermost of which reaches as far as Mars’s orbit. Such a rare system offers a new window into understanding the diversity of planetary systems.
The planets in the HIP 41378 system pass in front of their star (transit method), requiring an almost perfect alignment with Earth. However, only one out of every 200 systems like HIP 41378 has this configuration. The HIP 41378 system is therefore a rare gem that allows us to study planets with orbits comparable to those of the planets in the Solar System.
Five planets in the system were first discovered in 2015 by the Kepler telescope, but their nature and orbits remained poorly understood.
Understanding this system required a decade of observations using instruments located primarily in Chile, which measured variations in the star’s velocity caused by the planets (radial velocity method).
HIP 41378 thus becomes one of the first multiple systems in which long-period planets have been well characterized. It consists of three inner planets smaller than Neptune and three outer planets, which are low-density and can reach the size of Saturn. A seventh, more distant planet has yet to be confirmed.
Among the exoplanets, HIP 41378 f is particularly intriguing: its extremely large radius, given its mass, defies planetary formation models. One hypothesis, currently being studied at the LTE as part of the WRAPS project (“Where do Rings Appear in Planetary Systems?”), suggests that this planet is actually surrounded by highly inclined, opaque rings, giving it the appearance of a larger planet (see Figure).
Read the original article: A decade of monitoring the HIP 41378 planetary system: Masses and orbital periods of six planets and a planet candidate, Astronomy & Astrophysics No. 710, A275, 2026.
Astrobiology, exoplanet,
