Abstract:Several small dense exoplanets are now known, inviting comparisons to Earth and Venus. Such comparisons require translating their masses and sizes to composition models of evolved multi-layer-interior planets. Such theoretical models rely on our understanding of the Earth's interior, as well as independently derived equations of state (EOS), but have so far not involved direct extrapolations from Earth's seismic model -PREM. In order to facilitate more detailed compositional comparisons between small exoplanet… Show more
“…Figure 11 displays the position of HD 3167b on the mass-radius diagram compared to the sub-sample of small transiting planets (R R 4 Å ) whose masses and radii have been derived with a precision better than 20%. Theoretical models from Zeng et al (2016) are overplotted using different lines and colors. The precision of our mass determination (∼8%) allows us to conclude that HD 3167b is a rocky terrestrial planet with a composition consisting of ∼50% silicate and ∼50% iron.…”
HD 3167 is a bright (V = 8.9 mag) K0 V star observed by NASA's K2 space mission during its Campaign8. It has recently been found to host two small transiting planets, namely, HD 3167b, an ultra-short-period (0.96 days) superEarth, and HD 3167c, a mini-Neptune on a relatively long-period orbit (29.85 days). Here we present an intensive radial velocity (RV) follow-up of HD 3167 performed with the FIES@NOT, HARPS@ESO-3.6 m, and HARPS-N@TNG spectrographs. We revise the system parameters and determine radii, masses, and densities of the two transiting planets by combining the K2 photometry with our spectroscopic data. With a mass of 5.69±0.44 M ⊕ , a radius of 1.574±0.054 R ⊕ , and a mean density of 8.00 0.98-, HD 3167b joins the small group of ultra-short-period planets known to have rocky terrestrial compositions. HD 3167c has a mass of 8. -, indicative of a planet with a composition comprising a solid core surrounded by a thick atmospheric envelope. The rather large pressure scale height (∼350 km) and the brightness of the host star make HD 3167c an ideal target for atmospheric characterization via transmission spectroscopy across a broad range of wavelengths. We found evidence of additional signals in the RV measurements but the currently available data set does not allow us to draw any firm conclusions on the origin of the observed variation.
“…Figure 11 displays the position of HD 3167b on the mass-radius diagram compared to the sub-sample of small transiting planets (R R 4 Å ) whose masses and radii have been derived with a precision better than 20%. Theoretical models from Zeng et al (2016) are overplotted using different lines and colors. The precision of our mass determination (∼8%) allows us to conclude that HD 3167b is a rocky terrestrial planet with a composition consisting of ∼50% silicate and ∼50% iron.…”
HD 3167 is a bright (V = 8.9 mag) K0 V star observed by NASA's K2 space mission during its Campaign8. It has recently been found to host two small transiting planets, namely, HD 3167b, an ultra-short-period (0.96 days) superEarth, and HD 3167c, a mini-Neptune on a relatively long-period orbit (29.85 days). Here we present an intensive radial velocity (RV) follow-up of HD 3167 performed with the FIES@NOT, HARPS@ESO-3.6 m, and HARPS-N@TNG spectrographs. We revise the system parameters and determine radii, masses, and densities of the two transiting planets by combining the K2 photometry with our spectroscopic data. With a mass of 5.69±0.44 M ⊕ , a radius of 1.574±0.054 R ⊕ , and a mean density of 8.00 0.98-, HD 3167b joins the small group of ultra-short-period planets known to have rocky terrestrial compositions. HD 3167c has a mass of 8. -, indicative of a planet with a composition comprising a solid core surrounded by a thick atmospheric envelope. The rather large pressure scale height (∼350 km) and the brightness of the host star make HD 3167c an ideal target for atmospheric characterization via transmission spectroscopy across a broad range of wavelengths. We found evidence of additional signals in the RV measurements but the currently available data set does not allow us to draw any firm conclusions on the origin of the observed variation.
“…N, V, and E mark the solar system planets. The curves show the mass-radius correlation for compositions ranging from 100% iron to 100% water from Zeng et al (2016). Planet b is likely predominately rocky, and planet c is volatile-rich.…”
Section: Mean-motion Commensurabilitymentioning
confidence: 99%
“…Figure 11 shows HD3167b in comparison with other small exoplanets with masses measured to better than 50% precision; the lines show the composition models of Zeng et al (2016). We randomly draw 100,000 planet masses and radii from our posterior distributions, and compare them to the mass-radius relation of Fortney et al (2007) for pure rock, finding results that are consistent with the models of Zeng et al (2016). Assuming that the planet is a mixture of rock and iron, we compute the iron mass fraction from each random draw using Equation (8) of Fortney et al (2007).…”
HD3167 is a bright (V=8.9), nearby K0 star observed by the NASA K2 mission (EPIC 220383386), hosting two small, short-period transiting planets. Here we present the results of a multi-site, multi-instrument radial-velocity campaign to characterize the HD3167 system. ). We explore the possibility of atmospheric composition analysis and determine that planet c is amenable to transmission spectroscopy measurements, and planet b is a potential thermal emission target. We detect a third, non-transiting planet, HD 3167 d, with a period of 8.509±0.045 d (between planets b and c) and a minimum mass of 6.90±0.71 M Å . We are able to constrain the mutual inclination of planet d with planets b and c: we rule out mutual inclinations below 1°. 3 because we do not observe transits of planet d. From 1°.3 to 40°, there are viewing geometries invoking special nodal configurations, which result in planet d not transiting some fraction of the time.
“…We note that there is additionally a well-known degeneracy in determining the planet's composition from the density. Using the online tool of Zeng et al (2016), we find that the nominal mass of the planet allows for up to about 20 wt% of the planet to be water. Note that this extreme value results in a nearly zero silicate mass fraction, which is highly unphysical, as giant impact simulations show that mantle stripping can produce planets with at most a70% core mass fraction (Marcus et al 2010).…”
Section: Properties Of Gj 1132bmentioning
confidence: 99%
“…The core mass and radius assuming a two-component model (silicate + metal, no water) are determined with the online tool of Zeng et al (2016). Values for the planet properties are given in Table 1.…”
GJ 1132b is a nearby Earth-sized exoplanet transiting an M dwarf, and is among the most highly characterizable small exoplanets currently known. In this paper,we study the interaction of a magma ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the amount of O 2 that can build up in the atmosphere as a result of hydrogen dissociation and loss. We find that the magma ocean absorbs at most ∼10% of the O 2 produced, whereas more than 90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132b from our simulations is a tenuous atmosphere dominated by O 2 , though, for very large initial water abundances,atmospheres with several thousands of bars of O 2 are possible. A substantial steam envelope would indicate either the existence of an earlier H 2 envelope or low XUV flux over the system's lifetime. A steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132b. Further modeling is needed to study the evolution of CO 2 or N 2 -rich atmospheres on GJ 1132b.
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