Multi-planet system
TOI-178
Six planets in a precise resonance chain — orbital ratios like a cosmic clock.
- Planets
- 6
- Distance
- 204.5 ly
- Host
- K-type
About TOI-178
Discovery
TOI-178 was first flagged by TESS and characterized in detail by Leleu et al. 2021 (A&A) using CHEOPS, HARPS, and ESPRESSO — revealing six planets in a precisely tuned Laplace resonance chain around a K-dwarf 62 parsecs away.
Why it matters
TOI-178's outer five planets are locked in a 2:4:6:9:12 resonance chain — a fragile orbital configuration that almost certainly formed by smooth disk migration and has survived undisturbed for billions of years.
Current research
The system is a benchmark for testing migration and tidal-evolution models, and for studying how planet density varies across resonance chains — TOI-178's planets do not vary monotonically with distance.
Comparable to
A cosmic metronome: six planets whose orbits tick in interlocking small-integer ratios, like a perfectly tuned music box.
System geometry
At a glance
- Hostname
- TOI-178
- Spectral type
- K
- Distance
- 204.5 ly · 62.70 pc
- Stellar mass
- 0.65 M☉
- Stellar radius
- 0.66 R☉
- Luminosity
- 0.136 L☉
- Effective temp
- 4316 K
- Confirmed planets
- 6
- Habitable zone
- 0.350 – 0.505 AU
Top-down orbital diagram
Orbits to scale within this system. Dashed green = habitable-zone edges.
Planet positions are illustrative (evenly spaced in phase). For live motion see the 3D scene.
The planets
6 confirmed.
Rocky world
TOI-178 b
- Orbit
- 0.026 AU
- Period
- 1.91 days
- Radius
- 1.20 R⊕
- Mass
- 0.96 M⊕
- Eq. temperature
- 1040 K
- Eccentricity
- 0.000
- Discovered
- 2021 · Transit
Sub-Neptune
TOI-178 c
- Orbit
- 0.037 AU
- Period
- 3.24 days
- Radius
- 1.75 R⊕
- Mass
- 4.64 M⊕
- Eq. temperature
- 873 K
- Eccentricity
- 0.000
- Discovered
- 2021 · Transit
Sub-Neptune
TOI-178 d
- Orbit
- 0.059 AU
- Period
- 6.56 days
- Radius
- 2.69 R⊕
- Mass
- 5.20 M⊕
- Eq. temperature
- 690 K
- Eccentricity
- 0.007
- Discovered
- 2021 · Transit
Sub-Neptune
TOI-178 e
- Orbit
- 0.078 AU
- Period
- 9.96 days
- Radius
- 2.30 R⊕
- Mass
- 3.48 M⊕
- Eq. temperature
- 600 K
- Eccentricity
- 0.000
- Discovered
- 2021 · Transit
Sub-Neptune
TOI-178 f
- Orbit
- 0.104 AU
- Period
- 15.23 days
- Radius
- 2.42 R⊕
- Mass
- 5.63 M⊕
- Eq. temperature
- 521 K
- Eccentricity
- 0.000
- Discovered
- 2021 · Transit
Sub-Neptune
TOI-178 g
- Orbit
- 0.128 AU
- Period
- 20.72 days
- Radius
- 2.94 R⊕
- Mass
- 4.40 M⊕
- Eq. temperature
- 470 K
- Eccentricity
- 0.000
- Discovered
- 2021 · Transit
Compared to our Solar System
Each row shows the closest Solar-System analog by radius (log-space). Earth is pinned at the bottom as the constant frame of reference.
| Planet | Radius (R⊕) | Mass (M⊕) | Orbit (AU) | Period (days) | Eq temp (K) | Solar analog |
|---|---|---|---|---|---|---|
| TOI-178 b | 1.20 | 0.96 | 0.026 | 1.91 | 1040 | Earth |
| TOI-178 c | 1.75 | 4.64 | 0.037 | 3.24 | 873 | Earth |
| TOI-178 d | 2.69 | 5.20 | 0.059 | 6.56 | 690 | Neptune |
| TOI-178 e | 2.30 | 3.48 | 0.078 | 9.96 | 600 | Neptune |
| TOI-178 f | 2.42 | 5.63 | 0.104 | 15.23 | 521 | Neptune |
| TOI-178 g | 2.94 | 4.40 | 0.128 | 20.72 | 470 | Neptune |
| Earth (reference) | 1.00 | 1.00 | 1.000 | 365.25 | 255 | — |
Research status
◇ JWST observation status
No JWST programs are currently targeting planets in this system. The system may be observed in future cycles or by upcoming missions (Ariel, HWO, Roman).
Discovery timeline
- 2021
6 planets: b, c, d, e, f, g
via Transit
If you liked this
Other systems in the same theme:
Kepler-90
8 planets · 2766.6 ly · G2V
Eight known planets — first system to tie our solar system's count.
HR 8799
4 planets · 134.5 ly · A5
Four giant planets directly imaged at infrared — orbiting a young A-type star.
Kepler-11
6 planets · 2108.1 ly · G2V
Six tightly packed planets — all closer to their star than Mercury is to ours.
Experience it
See TOI-178 in interactive 3D
Fly through the system, click any planet, watch orbits play out at 100× speed.
▶ Launch 3D scene