TRANSITS AND OCCULTATIONS OF AN EARTH-SIZED PLANET IN AN 8.5 hr ORBIT

Sanchis-Ojeda, Roberto; Rappaport, S.; Winn, Joshua N.; Levine, Alan M.; Kotson, Michael C.; Latham, David W.; Buchhave, Lars A.

doi:10.1088/0004-637x/774/1/54

Cited by 154 publications

(137 citation statements)

References 46 publications

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“…The final parameters are (R pl /R star ) 2 Figure 2. These values are compatible with the previous estimate that was not constrained by ρ star [6].…”

Section: Methodssupporting

confidence: 93%

“…Transit parameters are crucial to estimate the planet radius, which in turn affects our ability to estimate the composition of the planet. These parameters were measured previously with the discovery of Kepler-78b 6 . In that study the impact parameter b was nearly unconstrained because the 30 min average of the Kepler long-cadence data cannot resolve the transit ingress time.…”

Section: Methodsmentioning

confidence: 99%

“…Aside from this additional constraint, our transit analysis is similar to the one in [6]. In brief, we analyzed the Kepler long-cadence data from Q1 through Q15 (a total of 3.7 years of nearly continuous observations) to construct a filtered, phase-folded light curve with a final cadence of 2 minutes.…”

Section: Methodsmentioning

confidence: 99%

“…Kepler-78 is young active star, as demonstrated by the large stellar flux variations observed with Kepler. A previous study 6 measured P rot = 12.5 ± 1.0 days using a Lomb Scargle periodogram of the photometry. Inspection of the RVs measured over one month indeed show some repeatability with a timescale of ~12-13 days, a sign that starspots are also inducing a large RV signal (see Extended Data Figure 3).…”

Section: Methodsmentioning

confidence: 99%

“…Kelper-78b is a member of an emerging class of planets with orbital periods of less than half a day 6,16,17 . Another member is KOI 1843.03 (refs.…”

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confidence: 99%

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A rocky composition for an Earth-sized exoplanet

Howard

Sanchis-Ojeda

Marcy

et al. 2013

Nature

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Planets with sizes between that of Earth (with radius R ⊕ ) and Neptune (about 4 R ⊕ ) are now known to be common around Sun-like stars 1,2,3 . Most such planets have been discovered through the transit technique, by which the planet's size can be determined from the fraction of starlight blocked by the planet as it passes in front of its star. Measuring the planet's mass-and hence its density, which is a clue to its composition-is more difficult. Planets of size 2-4 R ⊕ have proven to have a wide range of densities, implying a diversity of compositions 4,5 , but these measurements did not extend down to planets as small as Earth. Here we report Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b, which orbits its host star every 8.5 hours (ref. 6). Given a radius of 1.20 ± 0.09 R ⊕ and mass of 1.69 ± 0.41 M ⊕ , the planet's mean density of 5.3 ± 1.8 g cm -3 is similar to the Earth's, suggesting a composition of rock and iron.Kepler-78 is one of approximately 150,000 stars whose brightness was precisely measured at 30-minute intervals for four years by the NASA Kepler spacecraft 7 . This star is somewhat smaller, less massive, and younger than the Sun (Table 1). Every 8.5 hours the star's brightness declines by 0.02% as the planet Kepler-78b transits (passes in front of) the stellar disk. The planet's radius was originally measured 6 to be 1.16 !!.!" !!.!" R ⊕ . The mass could not be measured, although masses >8 M ⊕ could be ruled out because the planet's gravity would have deformed the star and produced brightness variations that were not detected.We measured the mass of Kepler-78b by tracking the line-of-sight component of the host star's motion (the radial velocity, RV) due to the gravitational force of the planet. The RV analysis is challenging not only because the signal is expected to be small (~1-3 m s -1 ) but also because the apparent Doppler shifts due to rotating starspots are much larger (~50 m s -1 peak-to-peak). Nevertheless the detection proved to be possible, thanks to the precisely known orbital period and phase of Kepler-78b that cleanly separated the timescale of spot variations (P rot ≈ 12.5 days) from the much shorter timescale of the planetary orbit (P ≈ 8.5 hours). We adopted a strategy of intensive Doppler measurements spanning 6-8 hours per night, long enough to cover nearly the entire orbit and short enough for the spot variations to be nearly frozen out.We measured RVs using optical spectra of Kepler-78 that we obtained from the High Resolution Echelle Spectrometer (HIRES) 8 on the 10-m Keck I Telescope. These Doppler shifts were computed relative to a template spectrum with a standard algorithm 9 that uses a spectrum of molecular iodine superposed on the stellar spectrum as a reference for the wavelength scale and instrumental profile of HIRES (Supplementary Table 1). Exposures lasted 15-30 minutes depending on conditions and produced RVs with 1.5-2.0 m s -1 uncertainties. The time series of RVs spans 38 days, with large velocity offsets between nights ...

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“…The final parameters are (R pl /R star ) 2 Figure 2. These values are compatible with the previous estimate that was not constrained by ρ star [6].…”

Section: Methodssupporting

confidence: 93%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

“…Kelper-78b is a member of an emerging class of planets with orbital periods of less than half a day 6,16,17 . Another member is KOI 1843.03 (refs.…”

mentioning

confidence: 99%

See 3 more Smart Citations

A rocky composition for an Earth-sized exoplanet

Howard

Sanchis-Ojeda

Marcy

et al. 2013

Nature

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191

157

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The structure of terrestrial bodies: Impact heating, corotation limits, and synestias

2017

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During accretion, terrestrial bodies attain a wide range of thermal and rotational states, which are accompanied by significant changes in physical structure (size, shape, pressure and temperature profile, etc.). However, variations in structure have been neglected in most studies of rocky planet formation and evolution. Here we present a new code, the Highly Eccentric Rotating Concentric U (potential) Layers Equilibrium Structure (HERCULES) code, that solves for the equilibrium structure of planets as a series of overlapping constant‐density spheroids. Using HERCULES and a smoothed particle hydrodynamics code, we show that Earth‐like bodies display a dramatic range of morphologies. For any rotating planetary body, there is a thermal limit beyond which the rotational velocity at the equator intersects the Keplerian orbital velocity. Beyond this corotation limit (CoRoL), a hot planetary body forms a structure, which we name a synestia, with a corotating inner region connected to a disk‐like outer region. By analyzing calculations of giant impacts and models of planet formation, we show that typical rocky planets are substantially vaporized multiple times during accretion. For the expected angular momentum of growing planets, a large fraction of post‐impact bodies will exceed the CoRoL and form synestias. The common occurrence of hot, rotating states during accretion has major implications for planet formation and the properties of the final planets. In particular, the structure of post‐impact bodies influences the physical processes that control accretion, core formation, and internal evolution. Synestias also lead to new mechanisms for satellite formation. Finally, the wide variety of possible structures for terrestrial bodies also expands the mass‐radius range for rocky exoplanets.

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