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6 known planets · 174.8 light years

HD 191939

HD 191939 is a yellow star (G9 V) 174.8 light years away, with 6 confirmed planets, 1 of them in the habitable zone. Distances and orbital speeds are to scale; the star and planets are enlarged so you can see them.

Day 0
habitable zone (estimate)planet orbits

Green band: where liquid water could exist on a planet's surface. Drag to turn the system, pinch or scroll to zoom.

The star

The star

HD 191939

Type
G9 V
Surface
≈ 5,348 K
Size
0.94 × the Sun
Mass
0.81 × the Sun
Brightness
0.65 × the Sun
Habitable zone
0.62–1.48 AU

The planets

HD 191939

HD 191939 b

Year
8.88 days
Distance from star
0.0804 AU
Mass
10 Earths
Size
3.4 × Earth
Temperature
≈ 880 K (+607 °C)
Found
2020, transit (Transiting Exoplanet Survey Satellite (TESS))
Too hot
HD 191939

HD 191939 c

Year
28.58 days
Distance from star
0.175 AU
Mass
8 Earths
Size
3.2 × Earth
Temperature
≈ 600 K (+327 °C)
Found
2020, transit (Transiting Exoplanet Survey Satellite (TESS))
Too hot
HD 191939

HD 191939 d

Year
38.35 days
Distance from star
0.213 AU
Mass
2.8 Earths
Size
3 × Earth
Temperature
≈ 540 K (+267 °C)
Found
2020, transit (Transiting Exoplanet Survey Satellite (TESS))
Too hot
HD 191939

HD 191939 e

Year
101.12 days
Distance from star
0.407 AU
Mass
at least 1.1e+02 Earths
Size
13 × Earth
Temperature
≈ 390 K (+117 °C)
Found
2022, radial velocity (W. M. Keck Observatory)
Outside the habitable zone
HD 191939

HD 191939 g

Year
284.00 days
Distance from star
0.812 AU
Mass
at least 14 Earths
Size
3.7 × Earth
Temperature
≈ 278 K (+5 °C)
Found
2022, radial velocity (Multiple Observatories)
In the habitable zone
HD 191939

HD 191939 f

Year
7.9 years
Distance from star
3.71 AU
Mass
at least 2.9 Jupiters
Size
13 × Earth
Temperature
≈ 125 K (-148 °C)
Found
2022, radial velocity (W. M. Keck Observatory)
Outside the habitable zone

Masses found by the wobble method are minimums, because the orbit's tilt is unknown. Temperatures are equilibrium estimates for a bare planet, before any atmosphere.

How we know

The wobble

The planet tugs its star back and forth. Spectrographs measure the tiny shift in the star's light, which gives the planet's year and a minimum mass.

The shadow

The planet passes in front of its star and dims it by a fraction of a percent, every orbit. The dip gives the planet's size and year.

Sources

  1. Planet and star parameters: NASA Exoplanet Archive, Planetary Systems Composite Parameters, retrieved 1 Nov 2026. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with NASA under the Exoplanet Exploration Program.
  2. Position: HYG Database v4.1 (CC BY-SA 4.0).
  3. Habitable zone: a simple estimate from the star's brightness (√L × 0.95 to 1.67 AU), shown as a guide.
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