# Determination of the size, mass, and density of exomoons from photometric transit timing variations - Astrophysics

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Abstract: Precise photometric measurements of the upcoming space missions allow thesize, mass, and density of satellites of exoplanets to be determined. Here wepresent such an analysis using the photometric transit timing variation($TTV p$). We examined the light curve effects of both the transiting planetand its satellite. We define the photometric central time of the transit thatis equivalent to the transit of a fixed photocenter. This point orbits thebarycenter, and leads to the photometric transit timing variations. The exactvalue of $TTV p$ depends on the ratio of the density, the mass, and the size ofthe satellite and the planet. Since two of those parameters are independent, areliable estimation of the density ratio leads to an estimation of the size andthe mass of the exomoon. Upper estimations of the parameters are possible inthe case when an upper limit of $TTV p$ is known. In case the density ratiocannot be estimated reliably, we propose an approximation with assuming equaldensities. The presented photocenter $TTV p$ analysis predicts the size of thesatellite better than the mass. We simulated transits of the Earth-Moon systemin front of the Sun. The estimated size and mass of the Moon are 0.020Earth-mass and 0.274 Earth-size if equal densities are assumed. This result iscomparable to the real values within a factor of 2. If we include the realdensity ratio (about 0.6), the results are 0.010 Earth-Mass and 0.253Earth-size, which agree with the real values within 20%.

Author: ** A. Simon, K. Szatmary, G.M. Szabo**

Source: https://arxiv.org/