Statistical Research on Characteristics of Exoplanets

Progress of Theoretical Physics Supplement, 2005

We review the observed properties of exoplanets found by the Doppler technique that has revealed 152 planets to date. We focus on the ongoing 18-year survey of 1330 FGKM type stars at Lick, Keck, and the Anglo-Australian Telescopes that offers both uniform Doppler precision (3 m s −1 ) and long duration. The 104 planets detected in this survey have minimum masses (M sin i) as low as 6 M Earth , orbiting between 0.02 and 6 AU. The core-accretion model of planet formation is supported by four observations: 1) The mass distribution rises toward the lowest detectable masses, dN /dM ∝ M −1.0 . 2) Stellar metallicity correlates strongly with the presence of planets. 3) One planet (1.3 MSat) has a massive rocky core, MCore ≈ 70 M Earth . 4) A super-Earth of ∼ 7 M Earth has been discovered. The distribution of semi-major axes rises from 0.3 -3.0 AU (dN /d log a) and extrapolation suggests that ∼12% of the FGK stars harbor gas-giant exoplanets within 20 AU. The median orbital eccentricity is e = 0.25, and even planets beyond 3 AU reside in eccentric orbits, suggesting that the circular orbits in our Solar System are unusual. The occurrence "hot Jupiters" within 0.1 AU of FGK stars is 1.2±0.2%. Among stars with one planet, 14% have at least one additional planet, occasionally locked in resonances. Kepler and COROT will measure the occurrence of earth-sized planets. The Space Interferometry Mission (SIM) will detect planets with masses as low as 3 M Earth orbiting within 2 AU of stars within 10 pc, and it will measure masses, orbits, and multiplicity. The candidate rocky planets will be amenable to follow-up spectroscopy by the "Terrestrial Planet Finder" and Darwin.

Int. J. Fundam. Phys. Sci, 2021

The discovery of extrasolar planets outside our solar system and around other stars is now well underway. In the presented paper, calculations of some physical properties for confirmed exoplanets have been done. We have estimated physical properties such as the semi-major axis for potentially habitable exoplanets, the mass of planets by applying Kepler's third law around the mass of solar, Jupiter, and Earth-mass, stellar luminosity, habitability zone for the inner center and outer regions, radial velocity amplitude, planetary equilibrium temperature (PET) or effective radiation emission temperature and planet density. The massradius (MR) relationship of planets was investigated for potentially habitable exoplanets of three different groups of extrasolar planets: Subterran (Mars-size), Terran (Earth-size), and Superterran (Super-Earths or Mini-Neptunes); introduced in PHL, and found well coefficient values for each group. The minimum and maximum values for the mass and radius of exoplanets have been selected from 0.1 < < 10 ⊕ and 0.4 < < 2.5 ⊕. The same MR relationship has also estimated the same properties for a larger number of confirmed exoplanets with a mass and radius of 0.1< M < 100 ⊕ and 0.4 < < 15 ⊕ , respectively, resulting their classification within 7 groups of mass and radius, with good coefficient values for each group. This is a new, possible cataloging that may need more effort for concluding a better understanding of the properties and varieties of the exoplanets.

The Astrophysical Journal, 2014

We study the masses and radii of 65 exoplanets smaller than 4R ⊕ with orbital periods shorter than 100 days. We calculate the weighted mean densities of planets in bins of 0.5 R ⊕ and identify a density maximum of 7.6 g cm −3 at 1.4 R ⊕ . On average, planets with radii up to R P = 1.5R ⊕ increase in density with increasing radius. Above 1.5 R ⊕ , the average planet density rapidly decreases with increasing radius, indicating that these planets have a large fraction of volatiles by volume overlying a rocky core. Including the solar system terrestrial planets with the exoplanets below 1.5 R ⊕ , we find ρ P = 2.43 + 3.39 (R P /R ⊕ ) g cm −3 for R P < 1.5R ⊕ , which is consistent with rocky compositions. For 1.5 ≤ R P /R ⊕ < 4, we find M P /M ⊕ = 2.69 (R P /R ⊕ ) 0.93 . The RMS of planet masses to the fit between 1.5 and 4 R ⊕ is 4.3 M ⊕ with reduced χ 2 = 6.2. The large scatter indicates a diversity in planet composition at a given radius. The compositional diversity can be due to planets of a given volume (as determined by their large H/He envelopes) containing rocky cores of different masses or compositions.

2004

We describe the motion of planetesimals in the protoplanetary nebula in terms of a fractal and irreversible process. As a consequence the equation of dynamics can be transformed to take a Schrödinger-like form. Its solutions yield a planetesimal distribution showing peaks of probability for particular values of conservative quantities such as the energy and the Runge-Lenz vector. After accretion, this results in expected probability peaks of the semi-major axis distribution at a n = (GM/w 2)n 2 , and of the eccentricity distribution at e = k/n, where k and n are integer numbers, M is the star mass and w is a constant having the dimension of a velocity. The current observational data support these predictions in a statistically significant way, in terms of a constant w = 144.7 ± 0.5 km/s which is common to the inner solar system and to the presently known extrasolar systems.

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2014

Proceedings of the National Academy of Sciences, 2013

The hundreds of exoplanets that have been discovered in the past two decades offer a new perspective on planetary structure. Instead of being the archetypal examples of planets, those of our Solar System are merely possible outcomes of planetary system formation and evolution, and conceivably not even terribly common outcomes (although this remains an open question). Here, we review the diverse range of interior structures that are known to, and speculated to, exist in exoplanetary systems-from mostly degenerate objects that are more than 10 times as massive as Jupiter, to intermediatemass Neptune-like objects with large cores and moderate hydrogen/helium envelopes, to rocky objects with roughly the mass of the Earth.

2000

Prior to discovery of extrasolar planets, the overwhelming majority of planetary research focused on explaining the properties of our own Solar System, sometimes in considerable detail. The discovery of extrasolar planetary systems revealed an unexpected diversity of planetary systems that has revolutionized planet formation theory. A strong program of theoretical research is essential to maximize both the discovery potential and the scientific returns of future observational programs, so as to achieve a deeper understanding of the formation and evolution of planetary systems. We outline three broad categories of theoretical research. Detailed studies of specific planetary systems can provide insights into the planet formation process ( §2.1). This approach is particularly effective for multiple planet systems with strong dynamical constraints (e.g., high precision radial velocity (RV) and/or astrometric measurements). Second, theorists can test planet formation models by comparing their predictions to the observed exoplanet population ( §2.2). This approach benefits greatly from wide planet surveys sensitive to a broad range of planets and stars. Finally, detailed modeling of specific physical processes is essential to understand planet formation and the origin of our solar system ( §2.3). Dynamical research plays an important role in analyzing observations for a wide range detection methods ( §3) and contributes to understanding the Earth's place in the universe and the potential for Earth-like life beyond our solar system ( §4). In this white paper, we suggest how to maximize the scientific return of future exoplanet observations ( §5).

The Astrophysical Journal, 2013

The rapid growth in the number of known exoplanets has revealed the existence of several distinct planetary populations in the observed mass-period diagram. Two of the most surprising are, (1) the concentration of gas giants around 1AU and (2) the accumulation of a large number of low-mass planets with tight orbits, also known as super-Earths and hot Neptunes. We have recently shown that protoplanetary disks have multiple planet traps that are characterized by orbital radii in the disks and halt rapid type I planetary migration. By coupling planet traps with the standard core accretion scenario, we showed that one can account for the positions of planets in the mass-period diagram. In this paper, we demonstrate quantitatively that most gas giants formed at planet traps tend to end up around 1 AU with most of these being contributed by dead zones and ice lines. In addition, we show that a large fraction of super-Earths and hot Neptunes are formed as "failed" cores of gas giants-this population being constituted by comparable contributions from dead zone and heat transition traps. Our results are based on the evolution of forming planets in an ensemble of disks where we vary only the lifetimes of disks as well as their mass accretion rates onto the host star. We show that a statistical treatment of the evolution of a large population of planetary cores initially caught in planet traps accounts for the existence of three distinct exoplantary populations-the hot Jupiters, the more massive planets at roughly orbital radii around 1 AU orbital, and the short period SuperEarths and hot Neptunes. There are very few evolutionary tracks that feed into the large orbital radii characteristic of the imaged Jovian planet and this is in accord with the result of recent surveys that find a paucity of Jovian planets beyond 10 AU. Finally, we find that low-mass planets in tight orbits become the dominant planetary population for low mass stars (M * ≤ 0.7M ⊙), in agreement with the previous studies which show that the formation of gas giants is preferred for massive stars.

2013

Aims. We explore the relations between physical and orbital properties of planets and properties of their host stars to identify the main observable signatures of the formation and evolution processes of planetary systems. Methods. We used a large sample of FGK dwarf planet-hosting stars with stellar parameters derived in a homogeneous way from the SWEET-Cat database to study the relation between stellar metallicity and position of planets in the period-mass diagram. We then used all the radial-velocity-detected planets orbiting FGK stars to explore the role of planet-disk and planet-planet interaction on the evolution of orbital properties of planets with masses above 1M Jup. Results. Using a large sample of FGK dwarf hosts we show that planets orbiting metal-poor stars have longer periods than those in metal-rich systems. This trend is valid for masses at least from ≈10M ⊕ to ≈4M Jup. Earth-like planets orbiting metal-rich stars always show shorter periods (fewer than 20 days) than those orbiting metal-poor stars. However, in the short-period regime there are a similar number of planets orbiting metal-poor stars. We also found statistically significant evidence that very high mass giants (with a mass higher than 4M Jup) have on average more eccentric orbits than giant planets with lower mass. Finally, we show that the eccentricity of planets with masses higher than 4M Jup tends to be lower for planets with shorter periods. Conclusions. Our results suggest that the planets in the P-M P diagram are evolving differently because of a mechanism that operates over a wide range of planetary masses. This mechanism is stronger or weaker depending on the metallicity of the respective system. One possibility is that planets in metal-poor disks form farther out from their central star and/or they form later and do not have time to migrate as far as the planets in metal-rich systems. The trends and dependencies obtained for very high mass planetary systems suggest that planet-disk interaction is a very important and orbit-shaping mechanism for planets in the high-mass domain.

Solar System Research, 2010

After the discovery of more than 400 planets beyond our Solar System, the characterization of exoplanets as well as their host stars can be considered as one of the fastest growing fields in space science during the past decade. The characterization of exoplanets can only be carried out in a well coordinated interdiscipli nary way which connects planetary science, solar/stellar physics and astrophysics. We present a status report on the characterization of exoplanets and their host stars by reviewing the relevant space and ground based projects. One finds that the previous strategy changed from space mission concepts which were designed to search, find and characterize Earth like rocky exoplanets to: A statistical study of planetary objects in order to get information about their abundance, an identification of potential target and finally its analysis. Spectral analysis of exoplanets is mandatory, particularly to identify bio signatures on Earth like planets. Direct charac terization of exoplanets should be done by spectroscopy, both in the visible and in the infrared spectral range. The way leading to the direct detection and characterization of exoplanets is then paved by several questions, either concerning the pre required science or the associated observational strategy.