Muted Features in the JWST NIRISS Transmission Spectrum of Hot-Neptune LTT 9779 b
The Astrophysical Journal Letters(2024)
摘要
The hot-Neptune desert is one of the most sparsely populated regions of the
exoplanet parameter space, and atmosphere observations of its few residents can
provide insights into how such planets have managed to survive in such an
inhospitable environment. Here, we present transmission observations of LTT
9779 b, the only known hot-Neptune to have retained a significant
H/He-dominated atmosphere, taken with JWST NIRISS/SOSS. The 0.6-2.85μm
transmission spectrum shows evidence for muted spectral features, rejecting a
perfectly flat line at >5σ. We explore water and methane-dominated
atmosphere scenarios for LTT 9779 b's terminator, and retrieval analyses reveal
a continuum of potential combinations of metallicity and cloudiness. Through
comparisons to previous population synthesis works and our own interior
structure modelling, we are able to constrain LTT 9779 b's atmosphere
metallicity to 20-850x solar. Within this range of metallicity, our retrieval
analyses prefer solutions with clouds at mbar pressures, regardless of whether
the atmosphere is water- or methane-dominated – though cloud-free atmospheres
with metallicities >500x solar cannot be entirely ruled out. By comparing
self-consistent atmosphere temperature profiles with cloud condensation curves,
we find that silicate clouds can readily condense in the terminator region of
LTT 9779 b. Advection of these clouds onto the day-side could explain the high
day-side albedo previously inferred for this planet and be part of a feedback
loop aiding the survival of LTT 9779 b's atmosphere in the hot-Neptune desert.
更多查看译文
关键词
Exoplanets,Hot Neptunes,Exoplanet atmospheres,Planetary atmospheres
AI 理解论文
溯源树
样例
生成溯源树,研究论文发展脉络
Chat Paper
正在生成论文摘要