PH2 b: Habitable Zone, 283-Day Year
Gas giant around PH2
It is 0.83 times Jupiter's radius, closest in size to Saturn, and 87.1 times Earth's mass, at 0.58 g/cm3, less dense than Earth. A year there lasts 282.53 days, on an orbit 2.2 times Mercury's distance from the Sun. Its equilibrium temperature is 295 K, in the range where liquid water is possible. The host star PH2 runs at 5734 K with 0.97 times the Sun's mass.
The habitability checklist, honestly scored
Inside the habitable zone, computed from the star's luminosity. Yes.
Dense enough to be rock rather than gas, at 0.58 g/cm3. No.
A measured mass, not just a radius. Yes.
A measured temperature rather than one derived from the star. Yes.
Any detection of an atmosphere. Not recorded in the archive.
Radius
9.34 Earth radii
Mass
87.1 Earth masses
Equilibrium temperature
295 K (measured)
One year
282.53 days
Orbit radius
0.8330 AU
Host star
PH2 at 5734 K
Distance
1122 light-years
Starlight blocked
0.812% at each transit
What the dip tells you
How deep the star dims fixes the planet's size relative to it.
Its orbit is noticeably elliptical, eccentricity 0.21, so the starlight it receives changes substantially over one year.
Found by Kepler in 2013. Kepler stared at one patch of sky for four years, which is why so many of its planets have short periods: a planet only counts once you have seen it cross several times.
A transit gives the radius and a separate measurement gives the mass. Having both is what makes a density, and a density is the only clue to composition at this range.
PH2 b 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?
