Planetary Formation and Migration of Hot Jupiters: Possibility of Harboring Earth-Like Planets A. B. Bhattacharya1, S. Mondal2, and B. Raha1 1Department of Physics, University of Kalyani, Kalyani, India 2Department of Physics, Darjeeling Government College, Darjeeling, India International Journal of Research in Sciences Volume 2, Issue 2, July-December, 2014, pp. 16-27 DOA : 26112014, © IASTER 2014, www.iaster.com ABSTRACT Discovery of new exoplanet “hot Jupiters”, with anomalous inflated size, high temperature and low density relative to our solar planetary Jupiter has evoked the exoplanet as prime searching target. In this paper we have critically examined the formation of the family of hot Jupiters with their characteristics emphasizing the characteristics due to location of hot Jupiter as well as the transit timing variations. Possibilities of detectable radio flux with observational limits are focused with some interesting findings. We have further considered the structure and evolution of hot Jupiters besides their atmospheres and associated albedos. Keywords: Exoplanet, Hot Jupiters, Jupiter, Earth-like planet. 1. INTRODUCTION Hot Jupiter, a class of extra solar planets that are being discovered where the planet is really close to the parent star which is only a few stellar radii away and has an orbital period of three days or may be even one and a half days for some cases, while our solar system Jupiter with a fairly cold weather has a very long period of about 12 years orbits at ~5 AU from the Sun. Being close to parent star, temperature of hot Jupiter lies in between 1000 and 2000 K. They have the largest gravitational pull on their stars, so their name in the Doppler method of planet detection is the strongest. In 1995, Michel Mayor and Didier Queloz [1] discovered the first planet and hot Jupiter around a Sun-like star using the radial-velocity technique. They used the spectrum of the star 51 Pegasi for detecting periodic Doppler shifts caused by the planet's gravitational pull on the star. This technique contributed towards finding hot Jupiters around less massive stars. Hot Jupiters have an orbital period of a few days and are much easier to detect than Earth-size planets very far from their stars [2]. In this paper we have first critically examined the formation of hot Jupiters and its characteristics. Possibilities of detectable radio flux from hot Jupiters with observational limits are then focused with some interesting findings. 2. FAMILY OF HOT JUPITERS Until a few decades ago, exoplanets and their solar systems were the matter of theory and assumptions. As our knowledge of the Universe moved from the area of guess work to hard data, we came to see our Sun as one of countless stars. In 1995, first hot Jupiter 51 Peg b was discovered from the spectrum of the star 51 Pegasi to detect periodic Doppler shifts caused by the planet's gravitational pull on the star [1]. 16 International Journal of Research in Sciences Volume 2, Issue 2, July-December, 2014, www.iaster.com Till now more than 415 hot Jupiters have been discovered [2]. Fig. 1 shows an artist's impression of a gas- giant exoplanet transiting across the face of its star. Figure 1 Artist's Impression of a Gas-Giant Exoplanet Transiting Across The Face of its Star [3] Most of the discovered exoplanets have been detected by radial velocity studies of the host star. The second-largest group has been detected through planetary transits. Twenty six planets have been detected by imaging and 12 have been discovered through planet-lens signatures detected during gravitational lensing events in which the host star serves as the primary lens. In 2006 the European Space Agency launched the COROT spacecraft, which was the first satellite used for searching extrasolar planets. The COROT spacecraft has discovered successfully many extrasolar planets. Subsequently, in 2009, NASA has launched Kepler spacecraft which also discovered more than 25 confirmed planets and around 1250 eligible candidates [4]. Both of these missions used the transit method when the planet passing in front of its star, blocking a very small proportion of the starlight [5]. Lensing method provides a potentially important complement to the radial-velocity and transit studies that have already been discovering hot Jupiters. It allows planet discovery even if the central star is too dim for detailed spectral studies and for all orbital inclinations, in contrast to transit studies. Furthermore, lensing provides a direct measure of the lens mass, at least in cases in which the mass of the central star can be determined. Lensing searches for hot Jupiters can be effective for nearby stars [6], allowing detailed follow-up studies. Companions of different hot Jupiters are shown in Table 1 with reference to their distances and associated semi major axis, orbital period as well as the corresponding temperature. Table 1 Hot Jupiters with Companions Semi Orbital Distance Temperature Planet major period M (M ) (pc) p J (K) axis (AU) Porb (days) Sources with eccentricities less than or equal to 0.1 HD 187123b 48.26 0.042 3.10 0.51 1320 HD 209458b 49.63 0.047 3.52 0.69 1316 55 Cnc b 12.34 0.116 14.65 0.84 661 55 Cnc b 12.34 0.240 44.3 0.84 661 HAT-P-13b 214 0.0426 2.91 0.85 1504 ρ CrB b 17.24 0.226 39.84 1.06 - 17 International Journal of Research in Sciences Volume 2, Issue 2, July-December, 2014, www.iaster.com u And e 13.47 5.25 3848 1.06 376 HD 189733b 19.45 0.031 2.22 1.13 1100 υ And b 13.49 0.059 4.62 1.4 1440 Qatar-2b 1.14 0.0215 1.33 2.49 1180 HD 195019b 38.52 0.137 18.20 3.58 - τ Boo b 15.62 0.048 3.31 6.5 6375 Sources with eccentricities greater than 0.1 HAT-P-17b 90.0 0.088 10.3 0.53 707 HIP 14810 d 52.9 1.9 962 0.57 175.6 HD 38529b 39.28 0.131 14.31 0.86 - HIP 14810 c 52.9 0.55 147.73 1.3 327 HAT-P-17c 90.0 2.75 1798 1.400 127.5 HD 217107b 19.72 0.073 7.12 1.85 960 HD 187123c 48.26 4.89 3810 1.990 122.7 HAT-P-31b 354 0.055 5.00 2.2 1325 HD 217107c 19.72 5.27 4210 2.5 111.1 HD 37605b 43.98 3.82 54.23 2.86 414 HD 37605c 43.98 0.261 2720 3.38 116.7 HIP 14810 b 52.9 0.069 6.67 3.9 918 HD 178911 Bb 42.59 0.345 71.48 7.29 470 70 Vir b 22.0 0.484 116.69 7.46 479 HD 114762b 39.5 0.363 83.89 11.68 487 HAT-P-13c 214 1.19 448.2 14.5 276 Recent analysis on Kepler-13Ab (= KOI-13.01) reveled that it is one of very few known short-period planets orbiting a hot A-type star, making it one of the hottest planets currently known. The availability of Kepler data allows measuring the planet’s occultation and phasing curve in the optical range as observed by warm Spitzer at 4.5 μm and 3.6 μm and a ground-based occultation observation in the Ks band (2.1 μm). Day-side hemisphere temperature is obtained as 2750 ± 160 K as the effective temperature of a black body thus showing the same occultation depths as reported [7]. The revised stellar parameters when combined with other measurements, leading to revised planetary mass and radius which can be estimated as, Mp = 4.94-8.09 M J and Rp = 1.406 ± 0.038 R J Kepler mid-occultation time was measured as (34.0 ± 6.9) s earlier than expected based on the mid-transit time and the delay due to light-travel time [7]. 2.1 Planet Jupiter of Sun vis-à-vis hot Jupiter and its Parent Stars Scientists have found that most known exoplanets have many similarities with the Jovian planets in our solar system, such as size, density, and composition. Exoplanets are probably made of hydrogen and helium gas. These planets are very close to the star, they experience a high surface temperature than on the Jovian planets [8]. Table 2 shows comparison between the planet Jupiter of the solar system and "hot Jupiters" as exoplanet. 18 International Journal of Research in Sciences Volume 2, Issue 2, July-December, 2014, www.iaster.com Table 2 Comparative studies between Jupiter and “Hot Jupiters” Dominant Jupiter “Hot Jupiters” Features Appearance Composition Composed primary of H and He Composed primary of H and He Distance and 5 AU from the Sun; orbital period: As closes as 0.03 AU to their stars; Orbit 10475.8 Jupiter solar days orbit as short as 1.2 Earth days Cloud top ~130 K Up to 1300 K temperatures Cloud Clouds of various H compounds Mainly consists of “rock dust” composition Radius 1 Jupiter radius Up to 1.3 Jupiter radii Mass 1 Jupiter mass 0.2 to 2 Jupiter masses Average density 1.33 g/cm3 As low as 0.3 g/cm3 Moons, rings, Present Unknown magnetosphere It appears from the table that the distance of planet Jupiter is much greater than the distance of hot Jupiter from their corresponding parent star while the cloud top temperature of Jupiter is only about one-tenth of that of the exoplanet hot Jupiter.