The Earth-Moon system has often been characterized as having some characteristics of a “double planet” system. It is demonstrated that while the orbital barycenter of the Earth-Moon pair lies inside the radius of the Earth, the Moon does meet all three requirements of the IAU definition for “planet” and therefore the Moon can correctly be identified as the Solar System’s 9 planet. In order to a...

For centuries, our knowledge of planetary systems and ideas about planet formation were based on a single example, our solar system. During the last thirteen years, the discovery of ≃ 170 planetary systems has ushered in a new era for astronomy. I review the surprising properties of extrasolar planetary systems and discuss how they are reshaping theories of planet formation. I focus on how mult...

According to Paracelsus (1493-1541) everything from this planet is poison, only the dose makes the poison to be harmless. Even the essential elements for life support are toxic for all organisms in high amounts. Mercury, cadmium, metalloid arsenic and lead were responsible for poisoning and death of many humans and life forms from this planet for centuries. Cadmium forms different compounds tha...

Any planetary system with two or more giant planets may become dynamically unstable, leading to collisions or ejections through strong planet–planet scattering. Following an ejection, the other planet is left in a highly eccentric orbit. Previous studies for simple initial configurations with two equalmass planets revealed two discrepancies between the results of numerical simulations and the o...

We present evidence that stars with planets exhibit statistically significant silicon and nickel enrichment over the general metal-rich population. We also present simulations which predict silicon enhancement of planet hosts within the context of the core-accretion hypothesis for giant planet formation. Because silicon and oxygen are both α-elements, [Si/Fe] traces [O/Fe], so the silicon enhan...

Almost half of the stellar systems in the solar neighborhood are made up of multiple stars. In multiple-star systems, planet formation is under the dynamical influence of stellar companions, and the planet occurrence rate is expected to be different from that for single stars. There have been numerous studies on the planet occurrence rate of single star systems. However, to fully understand pla...

Ribas and collaborators have recently proposed that an additional, ∼ 5 M ⊕ planet orbits the transiting planet host star GJ 436. Long-term dynamical interactions between the two planets leading to eccentricity excitation might provide an explanation for the transiting planet's unexpectedly large orbital eccentricity. In this paper we examine whether the existence of such a second planet is supp...

Correlations between stellar properties and the occurrence rate of exoplanets can be used to inform the target selection of future planet-search efforts and provide valuable clues about the planet-formation process. We analyze a sample of 1266 stars drawn from the California Planet Survey targets to determine the empirical functional form describing the likelihood of a star harboring a giant pl...

Most of the first-discovered extrasolar multi-planet systems were found to lie close to dynamically unstable configurations. However a few observed multiplanet systems (e.g. HD 74156) did not show this trait. Those systems could share this property if they contain an additional planet in between those that are known. Previous investigations identified the properties of hypothetical planets that...

Ribas and collaborators have recently proposed that an additional, ∼ 5 M ⊕ planet orbits the transiting planet host star GJ 436. Long-term dynamical interactions between the two planets leading to eccentricity excitation might provide an explanation for the transiting planet's unexpectedly large orbital eccentricity. In this paper we examine whether the existence of such a second planet is supp...