:INFO
Ice giant around Kepler-51
It is 0.87 times Jupiter's radius, closest in size to Saturn, and 7.6 times Earth's mass, at 0.05 g/cm3, less dense than Earth. A year there lasts 130.19 days, on an orbit 1.3 times Mercury's distance from the Sun. Its equilibrium temperature is 381 K, hotter than any desert. The host star Kepler-51 runs at 6018 K with 1.04 times the Sun's mass.

:JOURNEY
Kepler-51 from the inside out
1 0.251 AU
2 0.384 AU
3 0.509 AU

:STATS
[icon:TARGET] Radius | 9.70 Earth radii
[icon:CHART] Mass | 7.6 Earth masses
[icon:FIRE] Equilibrium temperature | 381 K (measured)
[icon:CLOCK] One year | 130.19 days
[icon:BOLT] Orbit radius | 0.5090 AU
[icon:STAR] Host star | Kepler-51 at 6018 K
[icon:USERS] Distance | 2557 light-years
[icon:TRENDING_DOWN] Starlight blocked | 0.893% at each transit

:COUNTER
0.05 g/cm3: less dense than cork

:TIMELINE
🔭🪐📅
2012-01-01 | Kepler-51 b, Kepler-51 c
2014-01-01 | Kepler-51 d

:CHECKLIST
Where this planet stands on each testable criterion
[ ] Inside the habitable zone. No.
[ ] Dense enough to be rock rather than gas, at 0.05 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.

:PATH
What a crossing measures
The fraction of starlight blocked sets the radius against the star's.

:NOTE
Found by Kepler in 2014. Kepler's method needed repetition, not brightness. It could find small planets around faint stars, provided they came round quickly enough to be seen twice.

:NOTE
Kepler-51 has 4 known planets. Systems like this are the ones where architecture can be studied instead of guessed at.

:NOTE
The size came from a crossing, the mass did not. That pairing is uncommon and it is what lets anyone say whether this is rock or gas.

:LINK
https://exoplanetarchive.ipac.caltech.edu/overview/Kepler-51%20d
NASA Exoplanet Archive: every published measurement of this planet