Found 51 talks archived in Planetary systems
AbstractShort-lived nuclides (SLNs) were incorporated to the solar nebula at the time of condensation of the first minerals from the vapor phase. The study of the isotopic ratios preserved in primitive meteorites provides clues on the stellar sources that produced these SLN, being supernovae and Asymptotic Giant Branch stars (AGBs) candidates. On the other hand, stellar grains were also preserved in primitive meteorites and Interplanetary Dust Particles (IDPs). Their survival demonstrates that the solar nebula was not so hot as first researchers proposed in the 60s. Interestingly, the available stellar grain abundances in primitive meteorites (chondrites) depend of the physico-chemical processes suffered by their parent bodies: metamorphism, aqueous alteration, etc. An evaluation of the primordial presolar grain abundances in the protoplanetary disk at the time these materials formed would allow a comparison with the derived from theoretical models. For gaining insight on these processes we should study the most primitive meteorites (the chondrites), but also even more pristine materials arrived from comets, particularly these captured in the stratosphere as IDPs, or collected from 81P/Wild 2 comet by Stardust (NASA) spacecraft.
AbstractDue to their orbits, near-Earth asteroids (NEAs) have been considered the most evident parent bodies of meteorites. Dynamical models show that NEAs come primarily from the inner and central parts of the Main Belt (MB), and they reach their orbits by means of gravitational resonances (mainly ?6 and 3:1). This part of the MB is dominated by spectral types S and Q, also the most common spectral types among the NEA population (~60%), and correspond to objects composed of silicates. Their reflectance spectra show very characteristic absorption bands that can be used to infer their mineralogical composition applying different methods of analysis. Those absorption bands are also present in the spectra of the most abundant class of meteorites (~80%), the ordinary chondrites (OC). In order to better understand the connection between MB asteroids, NEAs and OCs, we undertook a spectroscopic survey of asteroids between 2002 and 2007, using the telescopes and instrument facilities of "El Roque de los Muchachos" Observatory, in the Canary Islands. The survey contains visible and near-infrared spectra (0.5 - 2.5 µm) of a total of 105 asteroids. We have applied a method of mineralogical analysis based on spectral parameters to our sample of NEAs, and also to a sample of 91 MBs and 103 OCs obtained from different databases. We have found some significant compositional differences between NEAs, MBs and OCs. The most remarkable one is that NEAs compositionally differ from the whole set of OCs, and show a more olivine-rich composition, similar to what it is found for LL chondrites (only 8% of the falls). This result suggests that S type NEAs are not the immediate precursors of ordinary chondrites, as it was believed. We consider the size of the objects as the key factor to explain this difference. NEAs are km-sized objects, while meteorites are meter tocm sized objects. Combining the information obtained from the dynamical models and the drift in semimajor axis of the smaller objects due to their thermal intertia (Yarkovsky effect), we set out a possible scenario for the formation and the transport routes of NEAs and meteorites that could explain this compositional difference in a plausible way.
AbstractOf the 342 planets discovered so far orbiting other stars, 58 'transit' the stellar disk, meaning that they can be detected by a periodic decrease in the starlight flux. The light from the star passes through the atmosphere of the planet, and in a few cases the basic atmospheric composition of the planet can be estimated. As we get closer to finding analogues of Earth, an important consideration toward the characterization of exoplanetary atmospheres is what the transmission spectrum of our planet looks like. Here we report the optical and near-infrared transmission spectrum of the Earth, obtained during a lunar eclipse. Some biologically relevant atmospheric features that are weak in the reflected spectrum (such as ozone, molecular oxygen, water, carbon dioxide and methane) are much stronger in the transmission spectrum, and indeed stronger than predicted by modeling. We also find the fingerprints of the Earth's ionosphere and of the major atmospheric constituent, diatomic nitrogen (N2), which are missing in the reflected spectrum. Our results indicate that the technique of transit spectroscopy of rocky planets may be a very powerful tool for exoplanet atmospheric characterization, and is likely to provide the first detection of a habitable exobiosphere.
AbstractThere is a multitude of photochemical processes occurring in a planet's atmosphere. Some of these processes occur with an excess of energy and lead to products in the form of excited atoms, molecules and ions.In specific cases, these gases radiate at wavelengths that range from the UV to the NIR. Solar light is the ultimate cause of these airglow emissions, but traditionally one distinguishes between the day airglow (dayglow), and the night airglow (nightglow). The contribution of the Sun to the excitation of the emitting gas is more immediate in the day glow than in the nightglow. The airglow makes it possible to remotely investigate the chemical kinetics, energetic balance and dynamics of a planetary atmosphere. In the talk, I will go over some of the air glow missions that are known to exist in the atmospheres of the Earth, Mars and Venus. The examples illustrate some of my recent work, and include theoretical modelling and the interpretation of observational data. There is a long record of contributions to the nightglow from observations carried out at ground-based telescopes. I will briefly comment some of these.
AbstractSuperWASP is the UK's leading extra-solar planet detection program, having detected 22 of the 52 transiting planets known to date. This stems from the instruments ability to image ~500 square degrees every 60sec down to 16th mag (equivalent to the whole visible sky every 20 minutes). Recent experiments have shown that the data from SuperWASP can be reduced with 1 min of it being obtained and with further software development we will be able to identify transient sources within minutes of their observation. Detailed analysis of SuperWASP-N data has shown many populations of transient objects, including rapidly variable objects, which seem to correspond to extremely faint objects in the Sloan survey. Spectroscopy of these objects has proved challenging.
Comets may have played an important role in depositing the organic matter that, between 4,6 and 3,6 billion of years ago, allowed the formation of life on the primordial Earth. Nowadays, many complex organic molecules are routinely observed in the gaseous component of the comae by radio and near-IR observations. However a large quantity of organic matter may be under the form of solid, either as organic grains or organics embedded in silicate grains. The Giotto mission to the 1P/Halley comet revealed for the first time the in-situ presence of organic grains, that accounted for almost 50% of the mass of organic matter in its coma. Remote detection of these organic grains in other comets is very difficult because they rapidly sublimate under the solar radiation and their spectroscopic signatures are hidden within those of the refractory cometary dust. In this talk I will give a short review on the organic matter in comets, I will describe a method for detecting organic grains in comets and I will present recent results.
AbstractRed Dwarf (dM) stars are the most numerous stars in our Galaxy. These faint, cool, long-lived, and low mass stars make up > 80% of all stars in the Universe. Determining the number of red dwarfs with planets and assessing planetary habitability (a planet’s potential to develop and sustain life) are critically important because such studies would indicate how common life is in the universe. Our program - "Living with a Red Dwarf" addresses these questions by investigating the long-term nuclear evolution and magnetic-dynamo coronal and chromospheric X-ray to Ultraviolet properties of red dwarf stars with widely different ages. The major focus of the program is to study the magnetic-dynamo generated X-ray-Ultraviolet emissions and flare properties of red dwarf stars from youth to old age. Emphasized are how the stellar X-UV emissions, flares & winds affect hosted planets and impact their habitability. We have developed age-rotation-activity relations and also are constructing irradiance tables (X-UV fluxes) that can be used to model the effects of X-UV radiation on planetary atmospheres and on possible life on nearby hosted planets. Despite the earlier pessimistic view that red dwarfs stars are not suitable for habitable planets - mainly because their low luminosities require a hosted planet to orbit quite close (r <0.3 AU) to be sufficiently warm to support life. Our initial results indicate that red dwarf stars (in particular the warmer dM stars) can indeed be suitable hosts for habitable planets capable of sustaining life for hundreds of billion years. Some examples of red dwarf stars currently known to host planets are discussed.
The role of asteroids and comet impacts on the origin of Earth’s water and organic molecules is reviewed. Earth is believed to have formed dry, and magma oceans probably destroyed any primordial organics on Earth. The oldest clear evidence for water on Earth is about 3.85 Ga, right after the “Late Heavy Bombardment” (LHB). Asteroid and comet impacts during the LHB probably contributed significantly to Earth’s water and organic inventory. Evidence for this contribution is found in the D/H isotopic ratios of meteorites and comets. The abundance and variety of organic solids in asteroids and comets also point at a significant contribution to the organic inventory of the early Earth. However, the pieces of this puzzle do not all fit into a neat picture and several questions remain unanswered.
AbstractThe Infrared Spectrograph (IRS) on Spitzer has observed more than 120 asteroids, several Centaurs and Kuiper Belt objects (KBOs), and satellites of the giant planets. The asteroid sample includes objects from near-Earth space, through the Main Belt, and into the Jupiter Trojan swarms. Asteroids from all taxonomic classes have been observed, as have several binary and multiple component systems. The diameters of these targets range from a few hundred meters to a few hundred kilometers. On the whole, IRS has provided a broad sample of emissivity spectra of small Solar System bodies. The largest emissivity features detected are at the 10% level and are confined to the more primitive asteroid classes. Significant spectral variation is apparent among the IRS asteroid sample. Some of the dust observed in the close environment of other stars likely comes from asteroid collisions, so asteroids in the Solar System are proper mineralogical analogs. As capabilities continue to improve, direct observations of small body populations in other systems and inter-comparisons between systems will foster significant insights into the formation and evolution of planetary systems. The Solar System occupies a unique role by its accessibility and the detail to which it can be studied. While the IRS data are a good start, there is much to be learned from a larger set of mid-infrared spectra (e.g., from JWST and SOFIA). In this talk, I will present an overview of the IRS observations of small Solar System bodies, with a few representative objects highlighted for detailed discussion.
Radar observation of near-Earth asteroids (NEAs) reveal the size, shape, spin characteristics of the population of small bodies near the Earth. Although spacecraft missions may give higher resolution images, they are infrequent and expensive. Only through ground based observations can we hope to understand the diverse population of NEAs. Radar imaging reveals surface features and shape at up to 7.5-m resolution. We see a surprising variety of object shapes, which tells us about their formation and evolution. Binary NEAs are easily detected using radar regardless of viewing geometry, the characteristics of which have led to new ideas about NEA evolution and internal structure. Craters and other surface concavities are often visible in radar images, unlike lightcurve-based shape models. Although opportunities to observe comets with radar are rare, more than ten comet nuclei have been detected to date, three with high resolution imaging. Radar observations have played an important role in a number of key areas in small body science, some of which will be discussed in this talk.