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Renyu Hu

Publications and source records attributed to Renyu Hu.

129 records · Page 8Linked to original sources
arXiv2012

Theoretical Spectra of Terrestrial Exoplanet Surfaces

We investigate spectra of airless rocky exoplanets with a theoretical framework that self-consistently treats reflection and thermal emission. We find that a silicate surface on an exoplanet is spectroscopically detectable via prominent Si-O features in the thermal emission bands of 7 - 13 μm and 15 - 25 μm. The variation of brightness temperature due to the silicate features can be up to 20 K for an airless Earth analog, and the silicate features are wide enough to be distinguished from atmospheric features with relatively high-resolution spectra. The surface characterization thus provides a method to unambiguously identify a rocky exoplanet. Furthermore, identification of specific rocky surface types is possible with the planet's reflectance spectrum in near-infrared broad bands. A key parameter to observe is the difference between K band and J band geometric albedos (A_g (K)-A_g (J)): A_g (K)-A_g (J) > 0.2 indicates that more than half of the planet's surface has abundant mafic minerals, such as olivine and pyroxene, in other words primary crust from a magma ocean or high-temperature lavas; A_g (K)-A_g (J) < -0.09 indicates that more than half of the planet's surface is covered or partially covered by water ice or hydrated silicates, implying extant or past water on its surface. Also, surface water ice can be specifically distinguished by an H-band geometric albedo lower than the J-band geometric albedo. The surface features can be distinguished from possible atmospheric features with molecule identification of atmospheric species by transmission spectroscopy. We therefore propose that mid-infrared spectroscopy of exoplanets may detect rocky surfaces, and near-infrared spectrophotometry may identify ultramafic surfaces, hydrated surfaces and water ice.

astro-ph.EP↗
arXiv2010

Transport of First Rocks of The Solar System by X-winds

It has been suggested that chondrules and calcium-aluminum-rich inclusions (CAIs) were formed at the inner edge of the protoplanetary disk and then entrained in magnetocentrifugal X-winds. We study trajectories of such solid bodies with the consideration of the central star gravity, the protoplanetary disk gravity, and the gas drag of the wind. The efficiency of the gas drag depends on a parameter $η$, which is the product of the solid body size and density. We find that the gravity of the protoplanetary disk has a non-negligible effect on the trajectories. If a solid body re-enters the flared disk, the re-entering radius depends on the stellar magnetic dipole moment, the disk's gravity, the parameter $η$, and the initial launching angle. The disk's gravity can make the re-entering radius lower by up to 30%. We find a threshold $η$, denoted as $η_t$, for any particular configuration of the X-wind, below which the solid bodies will be expelled from the planetary system. $η_t$ sensitively depends on the initial launching angle, and also depends on the mass of the disk. Only the solid bodies with a $η$ larger than but very close to $η_t$ can be launched to a re-entering radius larger than 1 AU. This size-sorting effect may explain why chondrules come with a narrow range of sizes within each chondritic class. In general, the size distributions of CAIs and chondrules in chondrites can be determined from the initial size distribution as well as the distribution over the initial launching angle.

astro-ph.EP↗