Kepler-51 c: Less Dense Than Cork
Ice giant around Kepler-51
It is 0.80 times Jupiter's radius, closest in size to Saturn, and 4.0 times Earth's mass, at 0.03 g/cm3, less dense than Earth. A year there lasts 85.31 days, on an orbit 1 times closer to its star than Mercury is to the Sun. Its equilibrium temperature is 439 K, hotter than any desert. The host star Kepler-51 runs at 6018 K with 1.04 times the Sun's mass.
Kepler-51 from the inside out
Orbit
/
Planet
Radius
9.00 Earth radii
Mass
4.0 Earth masses
Equilibrium temperature
439 K (measured)
One year
85.31 days
Orbit radius
0.3840 AU
Host star
Kepler-51 at 6018 K
Distance
2557 light-years
Starlight blocked
0.769% at each transit
0.03g/cm3: less dense than cork
What you get from the shadow
The fraction of starlight blocked sets the radius against the star's.
Kepler-51 has 4 known planets. Systems like this are the ones where architecture can be studied instead of guessed at.
Found by Kepler in 2012. 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.
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.
