37th DPS Meeting, 4-9 September 2005
Session 25 Planet and Satellite Formation
Oral, Tuesday, September 6, 2005, 2:00-3:50pm, Law LG19

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[25.05] Young Jupiters are Faint

M. Marley, J. Fortney (NASA - ARC), O. Hubickyj (UCSC)

The early evolution of young extrasolar giant planets is of considerable interest. EGPs are brightest--and most easily detectable--when they are young. However traditional planet evolution models, which progress from arbitrarily hot and extended initial states, are unreliable at young ages. Despite modelers' impassioned caveats, the lack of alternatives has led various tabulations of model luminosities for young planets to be routinely used to plan observations and estimate detectability of these objects at ages of less than twenty or so million years. This model shortcoming led our group to produce the first self-consistent evolutionary calculations for one to several Jupiter-mass planets including all stages of formation, accumulation, and subsequent cooling. Our calculations include the accretion of an approximately ten Earth mass core followed by the subsequent rate-limited flow of nebular gas onto that core. After the total planet mass reaches the final mass accretion is terminated and the planet begins to cool adiabatically, as in standard cooling sequences. Since the evolutionary calculation begins with a planet that has been self-consistently brought to its initial state, we believe the behavior at young ages is more reliable than previous computations. We find that while our total luminosity agrees well with other models at ages in excess of about 30 million years, at younger times our predicted luminosity is substantially--by up to a factor of two or mor--lower. This result implies that extrasolar giant planets around very young stars may be substantially more difficult to detect than expected. Equivalently, very low masses assigned to recently detected young objects may be substantially too small. We will present our evolution calculations as well as model spectra and photometry of young EGPs.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.