CHARACTERIZING THE COOL KOIs. IV. KEPLER-32 AS A PROTOTYPE FOR THE FORMATION OF COMPACT PLANETARY SYSTEMS THROUGHOUT THE GALAXY

By J. Swift, J. Johnson, Timothy Morton, J. Crepp, B. Montet, D. Fabrycky, P. Muirhead. 2012

119 citations recorded by the source corpus.

The Kepler space telescope has opened new vistas in exoplanet discovery space by revealing populations of Earth-sized planets that provide a new context for understanding planet formation. Approximately 70% of all stars in the Galaxy belong to the diminutive M dwarf class, several thousand of which lie within Kepler's field of view, and a large number of these targets show planet transit signals. The Kepler M dwarf sample has a characteristic mass of 0.5 M☉ representing a stellar population twice as common as Sun-like stars. Kepler-32 is a typical star in this sample that presents us with a rare opportunity: five planets transit this star, giving us an expansive view of its architecture. All five planets of this compact system orbit their host star within a distance one-third the size of Mercury's orbit, with the innermost planet positioned a mere 4.3 stellar radii from the stellar photosphere. New observations limit possible false positive scenarios, allowing us to validate the entire Kepler-32 system making it the richest known system of transiting planets around an M dwarf. Based on considerations of the stellar dust sublimation radius, a minimum mass protoplanetary nebula, and the near period commensurability of three adjacent planets, we propose that the Kepler-32 planets formed at larger orbital radii and migrated inward to their present locations. The volatile content inferred for the Kepler-32 planets and order of magnitude estimates for the disk migration rates suggest that these planets may have formed beyond the snow line and migrated in the presence of a gaseous disk. If true, then this would place an upper limit on their formation time of ∼10 Myr. The Kepler-32 planets are representative of the full ensemble of planet candidates orbiting the Kepler M dwarfs for which we calculate an occurrence rate of 1.0 ± 0.1 planet per star. The formation of the Kepler-32 planets therefore offers a plausible blueprint for the formation of one of the largest known populations of planets in our Galaxy.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

1. Timothy Morton
2. D. Charbonneau
3. E. Gaidos
4. J. Johnson
5. A. Mann
6. C. Dressing
7. E. Petigura
8. Andrew W. Howard

In Instrumentation

1. Timothy Morton
2. D. Charbonneau
3. E. Gaidos
4. A. Mann
5. J. Johnson
6. C. Dressing
7. E. Petigura
8. G. Marcy

Citations in the corpus

• STELLAR AND PLANETARY PROPERTIES OF K2 CAMPAIGN 1 CANDIDATES AND VALIDATION OF 17 PLANETS, INCLUDING A PLANET RECEIVING EARTH-LIKE INSOLATION (2015, neutral): “Followup observations may be warranted to search for an additional planet in this system forming a resonant chain, similar to those observed around other stars (e.g., Swift et al. 2013; Campante et al. 2015).”
• A NEARBY M STAR WITH THREE TRANSITING SUPER-EARTHS DISCOVERED BY K2 (2015, background): “Planets transiting M dwarfs offer the best opportunity to study habitability and constrain models of rocky planet assembly and migration (Swift et al. 2013; Hansen 2014) and of planetary atmospheres (Kaltenegger et al. 2011; Rodler & López-Morales 2014).”
• THE OCCURRENCE OF POTENTIALLY HABITABLE PLANETS ORBITING M DWARFS ESTIMATED FROM THE FULL KEPLER DATASET AND AN EMPIRICAL MEASUREMENT OF THE DETECTION SENSITIVITY (2015, background): “Other authors further constrained the properties of particular planet host stars and associated planet candidates by acquiring followup spectroscopic and high resolution imaging observations (Johnson et al. 2012; Muirhead et al. 2012a,b; Ballard et al. 2013; Muirhead et al. 2013; Swift et al. 2013).”
• THE OCCURRENCE RATE OF SMALL PLANETS AROUND SMALL STARS (2013, result): “Our estimate for the occurrence rate of planets with radii between 0.5−4R⊕ and orbital periods shorter than 50 days is 0.90+0.04 −0.03 planets per star, which agrees well with the estimate of 1.0+0.1 −0.1 planets per star calculated by Swift et al. (2013).”
• A STUDY OF THE SHORTEST-PERIOD PLANETS FOUND WITH KEPLER (2014, background): “…some of the more prominent discoveries have been the innermost planets of Kepler-42 (Muirhead et al. 2012) and Kepler-32 (Fabrycky et al. 2012; Swift et al. 2013) and the system Kepler-70, where two very 1 Department of Physics, and Kavli Institute for Astrophysics and Space Research,…”
• The Habitability of Planets Orbiting M-dwarf Stars (2016, background): “Some systems, such as the Kepler-32 five-planet system, have been found orbiting their stars at a fraction of the distance between Mercury and the Sun (Swift et al., 2013b).”
• MOST 1.6 EARTH-RADIUS PLANETS ARE NOT ROCKY (2014, background): “…planets discovered by Kepler formed in situ (e.g, Hansen & Murray 2012; Ikoma & Hori 2012; Chiang & Laughlin 2013), or alternatively acquired their volatiles farther out in the disk and migrated in to their current locations (e.g, Rogers et al. 2011; Swift et al. 2013; Cossou et al. 2014).”
• A STELLAR-MASS-DEPENDENT DROP IN PLANET OCCURRENCE RATES (2014, background): “In a planet-migration context, planets would form farther out, migrate inward through the gas disk, and get trapped at the co-rotation radius instead of falling onto the star (e.g., Swift et al. 2013).”
• Trumpeting M dwarfs with CONCH-SHELL: a catalogue of nearby cool host-stars for habitable exoplanets and life (2014, background): “In comparison, Swift et al. (2013) estimated f = 1.0 ± 0.1 for planets closer than ∼ 0.3 AU, corresponding roughly to 85-day orbits.”
• A Technique for Extracting Highly Precise Photometry for the Two-Wheeled Kepler Mission (2014, background): “…analyses of the frequency of exoplanets around solar mass stars (Howard et al. 2012; Youdin 2011; Fressin et al. 2013), around cool stars (Swift et al. 2013; Morton & Swift 2014), and in their stars’ habitable zones (Dressing & Charbonneau 2013; Petigura et al. 2013; Foreman-Mackey et…”
• THE RADIUS DISTRIBUTION OF PLANETS AROUND COOL STARS (2013, background): “…disks may have much higher surface densities than previously thought (Hansen & Murray 2012; Chiang & Laughlin 2012) or that the observed planets migrated from regions further from their host star where more mass was readily available for assembly (Swift et al. 2013; Raymond & Cossou 2014).”
• EXOPLANET POPULATION INFERENCE AND THE ABUNDANCE OF EARTH ANALOGS FROM NOISY, INCOMPLETE CATALOGS (2014, methodology): “This method is very popular in the literature (Howard et al. 2012; Dong & Zhu 2013; Dressing & Charbonneau 2013; Swift et al. 2013; Petigura et al. 2013a) even though it is not motivated probabilistically.”
• The habitability of Proxima Centauri b. I. Irradiation, rotation and volatile inventory from formation to the present (2016, background): “…can be explained if planetary embryos formed at several AU, migrated inward to the inner edge of the protoplanetary disk and underwent a late phase of collisions (Terquem & Papaloizou 2007; Ida & Lin 2010; McNeil & Nelson 2010; Swift et al. 2013; Cossou et al. 2014; Izidoro & et al. 2016).”
• They are small worlds after all: revised properties of Kepler M dwarf stars and their planets (2015, background): “A full description of the occurrence of planets should include a description of their non-Poisson correlated distribution among stars (Swift et al. 2013; Muirhead et al. 2015; Ballard & Johnson 2016) and the coplanarity of their orbits (Lissauer et al. 2011; Fang & Margot 2012).”
• PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS (2014, background): “In particular, Swift et al. (2013) and Dressing & Charbonneau (2013) find that the average rate of small planets from Kepler is about one per star for periods shorter than 50 days, implying a vast galaxy-wide presence of rocky planets (Morton & Swift 2014).”
• AN ANCIENT EXTRASOLAR SYSTEM WITH FIVE SUB-EARTH-SIZE PLANETS (2015, background): “…multiple-planet systems – characterized by a concentration of dynamically packed planets near 0.1AU – include, e.g., Kepler-11 (Lissauer et al. 2011a), Kepler32 (Swift et al. 2013), Kepler-33 (Lissauer et al. 2012), and Kepler-80 (Rowe et al. 2014), all with at least five planets (Fig.”
• SPECTRO-THERMOMETRY OF M DWARFS AND THEIR CANDIDATE PLANETS: TOO HOT, TOO COOL, OR JUST RIGHT? (2013, background): “…have shown that the occurrence of small planets – including Earth- and super Earthsized planets – increases with decreasing stellar mass (Howard et al. 2012) (although also see Fressin et al. 2013), and that small planets are nearly ubiquitously around late-type stars (Swift et al. 2013).”