We present analytic estimates of the fractional uncertainties on the mass, radius, surface gravity, and density of a transiting planet, using only empirical or semi-empirical measurements. We first express these parameters in terms of transit photometry and radial velocity (RV) observables, as well as the stellar radius R _⋆, if required. In agreement with previous results, we find that, assuming a circular orbit, the surface gravity of the planet (g _p ) depends only on empirical transit and RV parameters, namely the planet period P, the transit depth δ, the RV semi-amplitude K _⋆, the transit duration T, and the ingress/egress duration τ. However, the planet mass and density depend on all these quantities, plus R _⋆. Thus, an inference about the planet mass, radius, and density must rely upon an external constraint such as the stellar radius. For bright stars, stellar radii can now be measured nearly empirically by using measurements of the stellar bolometric flux, the effective temperature, and the distance to the star via its parallax, with the extinction A _V being the only free parameter. For any given system, there is a hierarchy of achievable precisions on the planetary parameters, such that the planetary surface gravity is more accurately measured than the density, which in turn is more accurately measured than the mass. We find that surface gravity provides a strong constraint on the core mass fraction of terrestrial planets. This is useful, given that the surface gravity may be one of the best measured properties of a terrestrial planet.

我们仅使用经验或半经验测量，对过境行星的质量、半径、表面重力和密度的部分不确定性进行分析估计。如果需要，我们首先用_凌日光度和径向速度 (RV) 可观测值以及恒星半径R _⋆表示这些参数。与之前的结果一致，我们发现，假设一个圆形轨道，行星的表面重力（g _p）仅取决于经验凌日和 RV 参数，即行星周期P、凌日深度δ、RV 半振幅K _⋆中转时长T和入口/出口时长 τ。然而，行星的质量和密度取决于所有这些量，加上R _⋆。因此，关于行星质量、半径和密度的推断必须依赖于诸如恒星半径之类的外部约束。对于明亮的恒星，现在可以通过使用恒星热通量、有效温度和通过视差到恒星的距离的测量几乎凭经验测量恒星半径，消光度为A _V 是唯一的自由参数。对于任何给定的系统，行星参数都有可达到的精度等级，因此行星表面重力比密度更准确，密度比质量更准确。我们发现表面重力对类地行星的核心质量分数提供了很强的约束。这很有用，因为表面重力可能是类地行星的最佳测量特性之一。