About HD 191939 d
HD 191939 d is a rare exoplanet. It lies about 174.8 light-years from Earth, has an equilibrium temperature near 540 K, spans roughly 3 Earth radii and weighs about 2.8 Earth masses.
Crammed into a system of five or more planets.
Rare exoplanet 34 EP
HD 191939 d
RA 302.0256° · Dec 66.8503° · exoplanet
Score breakdown
· 5 badgesRare 46 pts → Epic
- Richly packed system +14
- Multi-planet system +6
- Confirmed exoplanet +5
- Sub-Neptune +5
- Found by TESS +4
Total score 34
12 more points to reach Epic.
Badges
- Confirmed exoplanet · +5
- Sub-Neptune · +5
- Multi-planet system · +6
- Richly packed system · +14
- Found by TESS · +4
Trivia
What makes it special
- Packed system. Crammed into a system of five or more planets.
Could we get there?
- Verdict. Hopelessly far for any craft humanity can build today.
Getting there
- Aboard Voyager 1. ≈ 3.1 million years at Voyager 1's speed (17 km/s).
- Fastest probe ever. ≈ 273 thousand years even at the Parker Solar Probe's 192 km/s.
- At 10% light speed. ≈ 1748 years in a starship at a tenth of light speed.
- Distance. 175 light-years from Earth.
Look-back time
- Look-back time. The light you'd see left around the year 1851.
Saying hello
- Say hello. A radio message and its reply would take 350 years round-trip.
Standing on it
- A year here. A full year lasts just 38.4 Earth days.
By the numbers
- Size. About 3× the width of Earth.
- Volume. About 26.9 Earths could fit inside it.
- Mass. About 2.8× the mass of Earth.
- Your weight. You'd weigh about 0.3× your Earth weight standing here.
- Density. Less dense than water — drop it in a big enough ocean and it would float.
- Temperature. A scorching 267°C on average.
How we found it
- Discovery. Found by Transiting Exoplanet Survey Satellite (TESS) using the transit method.
Cosmic context
- Crowded system. One of at least 6 planets orbiting its star.
Properties
- density gcc
- 0.57
- discovery facility
- Transiting Exoplanet Survey Satellite (TESS)
- discovery method
- Transit
- dist ly
- 174.8486
- eccentricity
- 0.031
- eq temp k
- 540
- insolation
- 14.3
- mass earth
- 2.8
- name
- HD 191939 d
- orbital period days
- 38.353
- radius earth
- 2.995
- sys num planets
- 6
How to see it
Like any astronomical target, HD 191939 d is best seen from a dark site away from city lights, and when it is above the horizon depends on your latitude and the time of year. The visibility panel above works out tonight's viewing window for your saved location.
Why HD 191939 d is a rare exoplanet
HD 191939 d scores 34 points on Spacedle's rarity scale, which places it in the rare tier. Another 12 points would lift it into a rarer tier.
That score comes from 5 science badges — Confirmed exoplanet, Sub-Neptune, Multi-planet system, Richly packed system and Found by TESS — each earned for a real, measurable property of the object. Rarity on Spacedle is never random: the more remarkable an object's astrophysics, the more badges it collects, the higher it scores, and the rarer it ranks.