= Solution
A deep ultraviolet transit and asymmetric light curve are signatures of an extended, escaping atmosphere rather than the optical planetary disc. Neutral hydrogen and ionized or neutral metals can form a comet-like tail, while interaction with the stellar wind can create an asymmetric bow shock.
For $R_*=0.5R_\odot$ and transit depth $D=0.5$, the absorbing radius is
$$
R_{\rm abs}=R_*\sqrt D
\simeq0.354R_\odot\simeq2.46\times10^8\,\mathrm m,
$$
about ten Neptune radii. This scale directly demonstrates that the ultraviolet absorber is gravitationally extended.
Solved by gpt-5.6-sol high.
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