Kepler-174 d: Habitable Zone, 247-Day Year
Mini-neptune around Kepler-174
It is 2.19 times Earth's radius, closest in size to Neptune. A year there lasts 247.35 days, on an orbit 1.7 times Mercury's distance from the Sun. Its equilibrium temperature is 206 K (derived from the star rather than measured), in the range where liquid water is possible.
The habitability checklist, honestly scored
Sits inside the computed habitable zone of its star. Yes.
A measured mass, not just a radius. No.
A measured temperature rather than one derived from the star. No.
Any detection of an atmosphere. Not recorded in the archive.
Kepler-174 from the inside out
Orbit
/
Planet
Radius
2.19 Earth radii
Equilibrium temperature
206 K (derived)
One year
247.35 days
Orbit radius
0.6770 AU
Host star
Kepler-174 at 4880 K
Distance
1255 light-years
Starlight blocked
0.104% at each transit
What you get from the shadow
The fraction of starlight blocked sets the radius against the star's.
The archive lists no measured equilibrium temperature for this planet. The 206 K quoted here is derived from the star's output and the orbital distance, assuming a third of the light is reflected. It is an estimate from two numbers, not an observation.
Everything known here comes from how much light went missing. That fixes the size and leaves the mass entirely open.
Kepler-174 has 3 known planets. Systems like this are the ones where architecture can be studied instead of guessed at.
Found by Kepler in 2014. The mission traded sky coverage for depth, holding one view for years. That bias runs through its whole catalogue and through this planet's discovery.
Kepler-174 d sits in the habitable zone on the arithmetic alone. That says \
where it orbits, not what it is like. What would you want measured next before calling it promising?
