Kepler-10b (‘Kepler 10’ being the designation for the star and ‘b’ meaning it’s the first planetary companion detected aroudn that star) apparently has both a transit measurement and a radial velocity measurement. This means a direct measurement of its radius and also a direct measurement of its mass. In addition these numbers tell us about its orbit.
So, what we know … it’s 1.4 Earth diameters wide, it masses 4.6 Earth masses and it orbits its star at the absurdly close distance of 3 million or so kilometres. (The Earth, by contrast, averages about 149 million kilometres from the Sun.) So it’s a very reasonable bet that 10b will have a scorchingly hot surface!
In fact, day time temperatures will probably be a couple of thousand degrees. On the planet’s sunward face, the surface will likely be a hemisphere-wrapping sea of molten rock. Presumably the nightside will be cooler, as it faces space, not Kepler-10. So there will possibly be a crust of solid rock on the nightside.
Also, I used ‘night’ and ‘day’ deliberately for these hemispheres. An object this clsoe to its sun is almost certainly tidally locked – that is, it spins in the same time it takes to orbit the star, so that one hemisphere is permanently sun-facing and one pointed forever away.
Kepler-10b is a very, very weird planet. (And that’s the way I like them!)