# HD 110067

HD 110067 is a star with six known sub-Neptune exoplanets (b, c, d, e, f, g) with radii ranging from 1.94 R$_⊕$ to 2.85 R$_⊕$. The planets orbit the host star in a rhythmic orbital resonance. The star, and related planetary system, is located 105 light-years away in the constellation Coma Berenices.
HD 110067 is part of a wide triple star system, along with the spectroscopic binary system HD 110106.

## Description

HD 110067, located 105 light-years away in the constellation Coma Berenices, is orbited by six known sub-Neptune exoplanets (b, c, d, e, f, g) with radii ranging from 1.94 R$_⊕$ to 2.85 R$_⊕$, and with densities (and solid cores) similar to that of gas giants in the Solar System. None of the planets in the planetary system were found to be in the habitable zone for life as we know it.

## Discovery

The two innermost exoplanets orbiting HD 110067, a bright K0-type star, were first detected by the TESS (NASA) space telescope, using the transit method, in 2020. The remaining four exoplanets were later confirmed in 2023 as a result of additional observations using the CHEOPS (European Space Agency) space telescope.

## Scientific importance

On 29 November 2023, an international team of astronomers, led by Rafael Luque, astronomer from the University of Chicago, published a review of the discovery in the journal Nature entitled, "A resonant sextuplet of sub-Neptunes transiting the bright star HD 110067". According to Luque, "It’s like looking at a fossil: The orbits of the planets today are the same as they were a billion years ago."
Further study of the HD 110067 planetary system may provide a better understanding of how the pattern of the planetary orbits in the Solar System arose, which once may have begun harmoniously, but later turned chaotic. The result, possibly, of a passing star or planet or some other astronomical object capable of disrupting the nascent harmonic orbital dynamics. Additionally, further studies of the system, including compositional studies of the planetary interiors and atmospheres, may also provide a better understanding of the conditions that potentially may support life.

## Planetary system

Six known sub-Neptune exoplanets (b, c, d, e, f, g) with planetary radii ranging from 1.94 R$_⊕$ to 2.85 R$_⊕$ from HD 110067, the host star. All planets are smaller than Neptune and have large atmospheres. The star and related planetary system are located 105 light years away, in the constellation Coma Berenices. Masses of all six of the planets in the system range from 3.9 M$_⊕$ (mass of Earth) to 8.5 M$_⊕$. All of the planetary orbits in the HD 110067 system are closer to their star than distance between the planet Mercury and the Sun.
The planets orbit the host star in synchronized rhythms of orbital resonance (a rare 1 percent of such systems in the Milky Way galaxy have this symmetry): the innermost planet orbits three times for every two times for the next planet out – a so-called 3:2 resonance; this same 3:2 resonance also applies to the second and third planet, as well as to the third and fourth planet; whereas the fourth planet orbits four times for every three times for the fifth planet out – in a so-called 4:3 resonance; additionally, the penultimate fifth planet orbits the sixth planet out in this same 4:3 resonance. Further, the innermost planet completes six orbits in exactly the same time the outermost planet completes one orbit.
The resonance ratio for the entire system is 54:36:24:16:12:9. The resonance period is ~492 d$_⊕$ (Earth-days).
The HD 110067 planetary system :
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
| b | 5.69+1.78 −1.82 M$_🜨$ | 0.0793±0.00096 | 9.113678(10) | — | 89.061±0.099° | 2.200±0.030 R$_🜨$ |
| c | < 6.3 M$_🜨$ | 0.1039±0.0013 | 13.673694(24) | — | 89.687±0.163° | 2.388±0.036 R$_🜨$ |
| d | 8.52+3.31 −3.25 M$_🜨$ | 0.1362±0.0017 | 20.519617(40) | — | 89.248±0.046° | 2.852±0.039 R$_🜨$ |
| e | < 3.9 M$_🜨$ | 0.1785±0.0022 | 30.793091(12) | — | 89.867±0.089° | 1.940±0.040 R$_🜨$ |
| f | 5.04+1.89 −1.94 M$_🜨$ | 0.2163±0.0026 | 41.05854(10) | — | 89.673±0.046° | 2.601±0.042 R$_🜨$ |
| g | < 8.4 M$_🜨$ | 0.2621±0.0032 | 54.76992(20) | — | 89.729±0.073° | 2.607±0.052 R$_🜨$ |