On the Luminosity of Young Jupiters

By M. Marley, Jon Fortney, O. Hubickyj, P. Bodenheimer, Jack J. Lissauer. 2006

412 citations recorded by the source corpus.

Traditional thermal evolution models of giant planets employ arbitrary initial conditions selected more for computational expediency than physical accuracy. Since the initial conditions are eventually forgotten by the evolving planet, this approach is valid for mature planets, if not young ones. To explore the evolution at young ages of jovian mass planets, we have employed model planets created by one implementation of the core-accretion mechanism as initial conditions for evolutionary calculations. The luminosities and early cooling rates of young planets are highly sensitive to their internal entropies, which depend on the formation mechanism and are highly model dependent. As a result of the accretion shock through which most of the planetary mass is processed, we find lower initial internal entropies than commonly assumed in published evolution tracks. Consequently, young Jovian planets are smaller, cooler, and several to 100 times less luminous than predicted by earlier models. Furthermore, the time interval during which the young Jupiters are fainter than expected depends on the mass of planet. Jupiter mass planets (1MJ) align with the conventional model luminosity in as little at 20 million years, but 10MJ planets can take up to 1 billion years to match commonly cited luminosities, given our implementation of the core-accretion mechanism. If our assumptions, especially including our treatment of the accretion shock, are correct and if extrasolar Jovian planets indeed form with low entropy, then young Jovian planets are substantially fainter at young ages than currently believed. Furthermore, early evolution tracks should be regarded as uncertain for much longer than the commonly quoted 106 yr. These results have important consequences both for detection strategies and for assigning masses to young Jovian planets based on observed luminosities.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c1736a589a449a01a79dfec75a0826814774ac1e

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Citations in the corpus

MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): PLANETS, OSCILLATIONS, ROTATION, AND MASSIVE STARS (2013, background): “(2) This procedure works well for M down to ∼ 0.1 MJ and over a range of initial radii, allowing the user to choose either a ∼ 1 RJ radius appropriate for a cold planet, to radii ∼ 2–3 RJ appropriate for young or inflated planets (e.g., Marley et al. 2007).”
MASSES, RADII, AND CLOUD PROPERTIES OF THE HR 8799 PLANETS (2012, background): “Of course such theoretical radii have their own uncertainty, including a dependence at young ages—particularly below 100 Myr—on the initial conditions (Baraffe et al. 2002; Marley et al. 2007a; Spiegel & Burrows 2012).”
RESOLVED IMAGES OF LARGE CAVITIES IN PROTOPLANETARY TRANSITION DISKS (2011, background): “Although reassuring, there is little to be learned there, given the uncertainties on the disk viscosities (α) and the luminosities of such low-mass companions (e.g., Marley et al. 2007).”
PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS (2014, background): “On the other hand, “cold start” and “warm start” models (e.g., Marley et al. 2007; Spiegel & Burrows 2012; Mollière & Mordasini 2012; Bodenheimer et al. 2013) follow a core accretion prescription, which assumes significant loss of initial entropy at formation through punctuated energy dissipation…”
Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70 (2018, background): “The planets according to the “hottest” and “coldest” populations have the highest and lowest luminosities, and correspond to the traditional hot and cold start models (e.g. Chabrier et al. 2000; Baraffe et al. 2003; Marley et al. 2007).”
NEAR-INFRARED SPECTROSCOPY OF THE EXTRASOLAR PLANET HR 8799 b (2010, background): “…with degenerate cores cannot reach such small volumes at any point in their 15 Note that the luminosities of HR 8799 b, c, and d do not agree with the luminosities of giant planets formed in the “cold start” models of Marley et al. (2007) and Fortney et al. (2008) for any ages or planet masses.”
Exoplanet Atmospheres: Physical Processes (2010, methodology): “The models used to infer mass have uncertainties especially with initial conditions that correspond to early times (Marley et al. 2007).”
The Gemini Deep Planet Survey (2007, background): “Recent evolution models (Marley et al. 2007) that incorporate initial conditions calculated explicitly for planets formed through core accretion indicate that it may in fact take as much as 10–100 Myr before the planets “forget” their initial conditions; the effect being more important for more…”
ORBITAL MOTION OF HR 8799 b, c, d USING HUBBLE SPACE TELESCOPE DATA FROM 1998: CONSTRAINTS ON INCLINATION, ECCENTRICITY, AND STABILITY (2011, background): “As young giant planets cool down with time, they become less luminous and harder to detect, but the cooling process lasts hundreds of millions of years (Marley et al. 2007).”
Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager (2015, neutral): “A similar though less extreme result – small radii and hence high masses and old ages – is found in several model fits to the HR8799 observations ( 13, 15 16 ), even though high masses are clearly excluded by dynamical stability considerations (e.g. 32 ).”
MAPPING THE SHORES OF THE BROWN DWARF DESERT. II. MULTIPLE STAR FORMATION IN TAURUS–AURIGA (2011, background): “However, more detailed models of planet formation by Marley et al. (2007) and Fortney et al. (2008) suggest that accretion shocks can dispel much of the initial energy, leading to lower internal entropy and initial temperatures.”
CLOUDS AND CHEMISTRY IN THE ATMOSPHERE OF EXTRASOLAR PLANET HR8799b (2011, background): “Given that HR8799b is clearly underluminous compared to the hot-start models and overluminous for the coldstart models (Marley et al. 2007; Fortney et al. 2008), it is unlikely that initial conditions alone are responsible for the offset between the atmosphere-inferred properties and the evolution…”
SPECTRAL AND PHOTOMETRIC DIAGNOSTICS OF GIANT PLANET FORMATION SCENARIOS (2011, background): “…lead to different initial planet properties (such as heat content, radius, temperature, etc.) then there should be observables that, in principle, could be used to determine the mode of formation of giant planets and brown dwarfs (Fortney et al. 2005; Marley et al. 2007; Fortney et al. 2008).”
THE MASS–METALLICITY RELATION FOR GIANT PLANETS (2015, background): “The initial entropy is not important; reasonable initial values typically all converge within a few hundred million years (Marley et al. 2007).”
Synthetic Spectra and Colors of Young Giant Planet Atmospheres: Effects of Initial Conditions and Atmospheric Metallicity (2008, methodology): “In Marley et al. (2007b) and Fortney et al. (2005a) we showed that evolution models that incorporate a core accretion initial condition are significantly less luminous thatour own “hot start” models and those of Baraffe et al. (2003) and Burrows et al. (1997).”
A probable giant planet imaged in the beta Pictoris disk. VLT/NaCo deep L'-band imaging (2008, background): “The validity of these models in the case of young planets formed by core accretion has been recently questionned (Marley et al. 2007) on the basis that te accretion shock might impact the planet initial internal entropy and its subsequent early thermal evolution.”
DIRECT IMAGING OF A COLD JOVIAN EXOPLANET IN ORBIT AROUND THE SUN-LIKE STAR GJ 504 (2013, background): “The hot-start models imply planetary masses (Marois et al. 2008, 2010; Lagrange et al. 2010), while cold-start models cannot reproduce the high observed luminosities (Marley et al. 2007; Spiegel & Burrows 2012).”