= Solution
The continuum <exoplanet transit photometry> depth is approximately the opaque projected area ratio, assuming a corrected or negligible <limb darkening> contribution:
$$
D_0=\left(\frac{R_p}{R_s}\right)^2=0.01,\qquad R_p=0.1R_s.
$$
For a Sun-sized host, \b[$R_p\simeq6.96\times10^7\,\mathrm m\simeq R_J\simeq11R_\oplus$]. The natural size analogue is <Jupiter>, not <Earth>.
The expected bulk constituent is \b[<molecular hydrogen>], with <helium> next most abundant for a retained <primary planetary atmosphere>. The <water> band detects a strong trace absorber; it does not imply that <water> is the dominant gas. This interpretation assumes a conventional H/He <gas giant>; the measured radius by itself is not a measurement of mass or composition.
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