论文标题
潮气通货膨胀可与核心积聚相协调
Tidal Inflation Reconciles Low-Density Sub-Saturns with Core Accretion
论文作者
论文摘要
虽然太阳系在天王星和土星的大小之间没有行星，但我们当前的系外行星人口普查包括几十个具有良好质量和半径的行星。这些子折叠表现出多种多样的密度，范围为$ 0.1-3 \ \ rm {g \ cm}^{ - 3} $。当简单地建模为岩石岩心上的氢/氦信封时，这种密度的多样性转化为行星包络分数的多样性，$ f_ \ rm {env} = m_ \ rm {envy}/m_p $从〜$ 10 \％至〜$ 50 \ $ 50 \％$。带有$ f_ \ rm {env} \ sim50 \％$的行星通过核心 - 核核酸造成的巨型行星形成的传统模型构成了挑战，当$ m_ \ rm {envy} \ sim m_ m_ m_ m_ \ rm {core {core} $时，核心 - 核中的积聚了巨型行星。在这里，我们表明，在考虑到潮汐加热之后，其中许多明显的$ f_ \ rm {env} \ sim50 \％$行星比看起来不那么富含信封。我们提出了一个新的框架，用于建模亚湿内部内部，该内部融合了由于潮汐而引起的包膜通胀，该潮汐是由观察到的非零偏心率以及潜在的倾斜驱动的。因此，当我们将模型应用于已知的子托恩时，我们将比无潮汐估计值低。我们提出了K2-19 B的案例研究，这是一个中等偏心的亚星期。忽略潮汐，K2-19 B似乎具有$ f_ \ rm {env} \ sim50 \％$，在失控的阈值附近pres依；通过包括潮汐，我们找到$ f_ \ rm {env} \ sim10 \％$，解决张力。通过对$ 4-8 \ r _ {\ oplus} $行星的系统分析，我们发现大多数（但不是全部）类似的包络行星具有$ f_ \ rm {envy} \ sim10 \％\％-20 \％$的$ f_ \ rm {envy} \ sim10 \％$。因此，许多亚质量可以理解为经历了严重半径膨胀的亚北极，而不是单独的对象。潮汐半径通胀可能在其他大小的行星类别中起重要作用，包括超低密度木星大小的行星，例如黄蜂-107 b。
While the Solar System contains no planets between the sizes of Uranus and Saturn, our current exoplanet census includes several dozen such planets with well-measured masses and radii. These sub-Saturns exhibit a diversity of bulk densities, ranging from ~$0.1-3\ \rm{g\ cm}^{-3}$. When modeled simply as hydrogen/helium envelopes atop rocky cores, this diversity in densities translates to a diversity in planetary envelope fractions, $f_\rm{env}=M_\rm{env}/M_p$ ranging from ~$10\%$ to ~$50\%$. Planets with $f_\rm{env}\sim50\%$ pose a challenge to traditional models of giant planet formation by core-nucleated accretion, which predict the onset of runaway gas accretion when $M_\rm{env}\sim M_\rm{core}$. Here we show that many of these apparent $f_\rm{env}\sim50\%$ planets are less envelope rich than they seem, after accounting for tidal heating. We present a new framework for modeling sub-Saturn interiors that incorporates envelope inflation due to tides, which are driven by the observed non-zero eccentricities, as well as potential obliquities. Consequently, when we apply our models to known sub-Saturns, we infer lower $f_\rm{env}$ than tides-free estimates. We present a case study of K2-19 b, a moderately eccentric sub-Saturn. Neglecting tides, K2-19 b appears to have $f_\rm{env}\sim50\%$, poised precariously near the runaway threshold; by including tides, we find $f_\rm{env}\sim10\%$, resolving the tension. Through a systematic analysis of $4-8\ R_{\oplus}$ planets, we find that most (but not all) of the similarly envelope-rich planets have more modest envelopes of $f_\rm{env}\sim10\%-20\%$. Thus, many sub-Saturns may be understood as sub-Neptunes that have undergone significant radius inflation, rather than a separate class of objects. Tidal radius inflation likely plays an important role in other size classes of planets including ultra-low-density Jupiter-size planets like WASP-107 b.
