Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Formation and Evolution of Planetary Systems: The Search for and Characterization of Young Planets
109
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Despite the revolution in our knowledge resulting from the detection of planets around mature stars, we know almost nothing about planets orbiting young stars because rapid rotation and active photospheres preclude detection by radial velocities or transits and because direct imaging has barely penetrated the requisite range of high contrast and angular resolution. Of the techniques presently under consideration for the coming decade, only space-based astrometry offers the prospect of discovering gas giants (100 to >> 300 Mearth), lower mass systems such as icy giants (10 to 100 Mearth), and even a few rocky, super-Earths 300 Mearth) orbiting stars ranging in age from 1 to 100 Myr. Astrometry will complement high contrast imaging which should be able to detect gas giants (1~10 MJup) in orbits from a few to a few hundred AU. An astrometric survey in combination with imaging data for a subsample of objects will allow a detailed physical understanding of the formation and evolution of young gas giant planets impossible to achieve by any one technique.
rate research
Read More
As part of a national scientific network Pathways to Habitability the formation of planets and the delivery of water onto these planets is a key question as water is essential for the development of life. In the first part of the paper we summarize the state of the art of planet formation - which is still under debate in the astronomical community - before we show our results on this topic. The outcome of our numerical simulations depends a lot on the choice of the initial distribution of planetesimals and planetary embryos after gas disappeared in the protoplanetary disk. We also take into account that some of these planetesimals of sizes in the order of the mass of the Moon already contained water; the quantity depends on the distance from the Sun - close-by bodies are dry, but starting from a distance of about 2 AU they can contain substantial amounts of water. We assume that the gas giants and terrestrial planets are already formed when we check the collisions of the small bodies containing water (in the order of a few percent) with the terrestrial planets. We thus are able to give an estimate of the respective contribution to the actual water content (of some Earth-oceans) in the mantle, in the crust and on the surface of Earth. In the second part we discuss in more detail how the formation of larger bodies after a collision may happen as the outcome depends on parameters like collision velocity, impact angle, and the materials involved. We present results obtained by SPH (Smooth Particle Hydrodynamics) simulations. We briefly describe this method and show different scenarios with respect to the formed bodies, possible fragmentation and the water content before and after the collision. In an appendix we discuss detection methods for extrasolar planets (close to 2000 such objects have been discovered so far).
Stars and planets are the fundamental objects of the Universe. Their formation processes, though related, may differ in important ways. Stars almost certainly form from gravitational collapse and probably have formed this way since the first stars lit the skies. Although it is possible that planets form in this way also, processes involving accretion in a circumstellar disk have been favored. High fidelity high resolution images may resolve the question; both processes may occur in some mass ranges. The questions to be answered in the next decade include: By what process do planets form, and how does the mode of formation determine the character of planetary systems? What is the distribution of masses of planets? In what manner does the metallicity of the parent star influence the character of its planetary system? In this paper we discuss the observations of planetary systems from birth to maturity, with an emphasis on observations longward of 100 $mu$m which may illuminate the character of their formation and evolution. Advantages of this spectral region include lower opacity, availability of extremely high resolution to reach planet formation scales and to perform precision astrometry and high sensitivity to thermal emission.
Recent observations have suggested that circumstellar disks may commonly form around young stellar objects. Although the formation of circumstellar disks can be a natural result of the conservation of angular momentum in the parent cloud, theoretical studies instead show disk formation to be difficult from dense molecular cores magnetized to a realistic level, owing to efficient magnetic braking that transports a large fraction of the angular momentum away from the circumstellar region. We review recent progress in the formation and early evolution of disks around young stellar objects of both low-mass and high-mass, with an emphasis on mechanisms that may bridge the gap between observation and theory, including non-ideal MHD effects and asymmetric perturbations in the collapsing core (e.g., magnetic field misalignment and turbulence). We also address the associated processes of outflow launching and the formation of multiple systems, and discuss possible implications in properties of protoplanetary disks.
The high occurrence rates of spiral arms and large central clearings in protoplanetary disks, if interpreted as signposts of giant planets, indicate that gas giants form commonly as companions to young stars ($<$ few Myr) at orbital separations of 10--300,au. However, attempts to directly image this giant planet population as companions to more mature stars ($> 10$, Myr) have yielded few successes. This discrepancy could be explained if most giant planets form cold start, i.e., by radiating away much of their formation energy as they assemble their mass, rendering them faint enough to elude detection at later times. In that case, giant planets should be bright at early times, during their accretion phase, and yet forming planets are detected only rarely through direct imaging techniques. Here we explore the possibility that the low detection rate of accreting planets is the result of episodic accretion through a circumplanetary disk. We also explore the possibility that the companion orbiting the Herbig Ae star HD~142527 may be a giant planet undergoing such an accretion outburst.
In a previous study, we analysed the spectra of 230 cool ($T_mathrm{eff}$ < 9000 K) white dwarfs exhibiting strong metal contamination, measuring abundances for Ca, Mg, Fe and in some cases Na, Cr, Ti, or Ni. Here we interpret these abundances in terms of the accretion of debris from extrasolar planetesimals, and infer parent body compositions ranging from crust-like (rich in Ca and Ti) to core-like (rich in Fe and Ni). In particular, two white dwarfs, SDSSJ0823+0546 and SDSSJ0741+3146, which show log[Fe/Ca] > 1.9 dex, and Fe to Ni ratios similar to the bulk Earth, have accreted by far the most core-like exoplanetesimals discovered to date. With cooling ages in the range 1-8 Gyr, these white dwarfs are among the oldest stellar remnants in the Milky Way, making it possible to probe the long-term evolution of their ancient planetary systems. From the decrease in maximum abundances as a function of cooling age, we find evidence that the arrival rate of material on to the white dwarfs decreases by 3 orders of magnitude over a $simeq$6.5 Gyr span in white dwarf cooling ages, indicating that the mass-reservoirs of post-main sequence planetary systems are depleted on a $simeq$1 Gyr e-folding time-scale. Finally, we find that two white dwarfs in our sample are members of wide binaries, and both exhibit atypically high abundances, thus providing strong evidence that distant binary companions can dynamically perturb white dwarf planetary systems.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
