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At least 649 records · Page 36Linked to original sources
PubMed2000

Detection of Planetary Transits Across a Sun-like Star.

We report high-precision, high-cadence photometric measurements of the star HD 209458, which is known from radial velocity measurements to have a planetary-mass companion in a close orbit. We detect two separate transit events at times that are consistent with the radial velocity measurements. In both cases, the detailed shape of the transit curve due to both the limb darkening of the star and the finite size of the planet is clearly evident. Assuming stellar parameters of 1.1 R middle dot in circle and 1.1 M middle dot in circle, we find that the data are best interpreted as a gas giant with a radius of 1.27+/-0.02 RJup in an orbit with an inclination of 87&fdg;1+/-0&fdg;2. We present values for the planetary surface gravity, escape velocity, and average density and discuss the numerous observations that are warranted now that a planet is known to transit the disk of its parent star.

Journal Article↗
PubMed2000

Correcting Radial Velocities for Long-Term Magnetic Activity Variations.

We study stars in the Lick planetary survey for correlations between simultaneous measurements of high-precision radial velocities vr and magnetic activity (as measured in an SIR emission index from Ca ii lambda8662). We find significant correlations in approximately 30% of the stars. After removing linear trends between SIR and vr, we find that the dispersion in vr in these stars is decreased by an average of 17%, or approximately 45% of the dispersion above the measurement noise. F stars and less active stars with variable Ca ii H and K lines are the most successfully corrected. The magnitude of the slope of the SIR versus vr relations increases proportional to vsini and (excepting M dwarfs) tends to decrease with decreasing Teff. We argue that the main cause of these effects is modification of the mean line bisector shape brought on by long-term, magnetic activity-induced changes in the surface brightness and convective patterns. The correlations can be used to partially correct vr data for the effects of long-term activity variations, potentially permitting study of planets around some (higher mass) younger stars and planets producing smaller stellar reflex velocities.

Journal Article↗
PubMed2001

NASA's new Mars Exploration Program: the trajectory of knowledge.

NASA's newly restructured Mars Exploration Program (MEP) is finally on the way to Mars with the successful April 7 launch of the 2001 Mars Odyssey Orbiter. In addition, the announcement by the Bush Administration that the exploration of Mars will be a priority within NASA's Office of Space Science further cements the first decade of the new millennium as one of the major thrusts to understand the "new" Mars. Over the course of the past year and a half, an integrated team of managers, scientists, and engineers has crafted a revamped MEP to respond to the scientific as well as management and resource challenges associated with deep space exploration of the Red Planet. This article describes the new program from the perspective of its guiding philosophies, major events, and scientific strategy. It is intended to serve as a roadmap to the next 10-15 years of Mars exploration from the NASA viewpoint. [For further details, see the Mars Exploration Program web site (URL): http://mars.jpl.nasa.gov]. The new MEP will certainly evolve in response to discoveries, to successes, and potentially to setbacks as well. However, the design of the restructured strategy is attentive to risks, and a major attempt to instill resiliency in the program has been adopted. Mars beckons, and the next decade of exploration should provide the impetus for a follow-on decade in which multiple sample returns and other major program directions are executed. Ultimately the vision to consider the first human scientific expeditions to the Red Planet will be enabled. By the end of the first decade of this program, we may know where and how to look for the elusive clues associated with a possible martian biological record, if any was every preserved, even if only as "chemical fossils."

Mars↗
PubMed2004

Hypersaline microbial systems of sabkhas: examples of life's survival in "extreme" conditions.

Life and living systems need several important factors to establish themselves and to have a continued tradition. In this article the nature of the borderline situation for microbial life under heavy salt stress is analyzed and discussed using the example of biofilms and microbial mats of sabkha systems of the Red Sea. Important factors ruling such environments are described, and include the following: (1) Microbial life is better suited for survival in extremely changing and only sporadically water-supplied environments than are larger organisms (including humans). (2) Microbial life shows extremely poikilophilic adaptation patterns to conditions that deviate significantly from conditions normal for life processes on Earth today. (3) Microbial life adapts itself to such extremely changing and only ephemerally supportive conditions by the capacity of extreme changes (a) in morphology (pleomorphy), (b) in metabolic patterns (poikilotrophy), (c) in survival strategies (poikilophily), and (d) by trapping and enclosing all necessary sources of energy matter in an inwardly oriented diffusive cycle. All this is achieved without any serious attempt at escaping from the extreme and extremely changing conditions. Furthermore, these salt swamp systems are geophysiological generators of energy and material reservoirs recycled over a geological time scale. Neither energy nor material is wasted for propagation by spore formation. This capacity is summarized as poikilophilic and poikilotroph behavior of biofilm or microbial mat communities in salt and irradiationstressed environmental conditions of the sabkha or salt desert type. We use mainly cyanobacteria as an example, although other bacteria and even eukaryotic fungi may exhibit the same potential of living and surviving under conditions usually not suitable for life on Earth. It may, however, be postulated that such poikilophilic organisms are the true candidates for life support and survival under conditions never recorded on Planet Earth. Mars and some planets of other suns may be good candidates to search for life under conditions normally not thought to be favorable for the maintenance of life.

Bacteria↗
PubMed2002

The astrophysics of crowded places.

Today the Sun is in a relatively uncrowded place. The distance between it and the nearest other star is relatively large (about 200,000 times the Earth-Sun distance!). This is beneficial to life on Earth; a close encounter with another star is extremely unlikely. Such encounters would either remove the Earth from its orbit around the Sun or leave it on an eccentric orbit similar to a comet's. But the Sun was not formed in isolation. It was born within a more-crowded cluster of perhaps a few hundred stars. As the surrounding gas evaporated away, the cluster itself evaporated too, dispersing its stars into the Galaxy. Virtually all stars in the Galaxy share this history, and here I will describe the role of 'clusterness' in a star's life. Stars are often formed in larger stellar clusters (known as open and globular clusters), some of which are still around today. I will focus on stars in globular clusters and describe how the interactions between stars in these clusters may explain the zoo of stellar exotica which have recently been observed with instruments such as the Hubble Space Telescope and the X-ray telescopes XMM-Newton and Chandra. In recent years, myriad planets orbiting stars other than the Sun--the so-called 'extrasolar' planets--have been discovered. I will describe how a crowded environment will affect such planetary systems and may in fact explain some of their mysterious properties.

Journal Article↗
PubMed2005

Reasoning from unfamiliar premises: a study with unschooled adults.

A long tradition of research initiated by Luria in the 1930s has established that unschooled adults perform poorly on reasoning tasks. Particularly when the premises are unfamiliar, they adopt an inappropriate empirical bias. However, recent findings show that young children with little or no schooling reason competently if prompted to think of the unfamiliar premises as pertaining to a distant planet. We tested two groups of adults: illiterate, unschooled adults and adults with limited schooling. Both groups received problems that included either a premise with unknown content or a premise contradicting their everyday experience. When given a minimal prompt, both groups manifested the customary empirical bias. By contrast, when explicitly prompted to think of the unfamiliar premises as pertaining to a distant planet, they reasoned accurately and appropriately justified their conclusions in terms of the supplied premises.

Adolescent↗
PubMed2001

Extraterrestrial intelligence? Not likely.

The possibility that there exist extraterrestrial creatures with advanced intelligence is considered by examining major events in mammalian, primate, and human evolution on earth. The overwhelming evidence is that the evolution of intelligence in creatures elsewhere who have the capability to communicate with us is vanishingly small. The history of the evolution of advanced forms of life on this planet is so beset by adventitious, unpredictable events and multiple contingencies that the evolution of human-level intelligence is highly unlikely on any planet, including earth.

Animals↗
PubMed2005

Disks around stars and the growth of planetary systems.

Circumstellar disks play a vital evolutionary role, providing a way to move gas inward and onto a young star. The outward transfer of angular momentum allows the star to contract without breaking up, and the remnant disk of gas and particles is the reservoir for forming planets. High-resolution spectroscopy is uncovering planetary dynamics and motion within the remnant disk, and imaging at infrared to millimeter wavelengths resolves disk structure over billions of years of evolution. Most stars are born with a disk, and models of planet formation need to form such bodies from the disk material within the disk's 10-million-year life-span.

Journal Article↗
PubMed2006

Global mineralogical and aqueous mars history derived from OMEGA/Mars Express data.

Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Activité (OMEGA) instrument on the European Space Agency's Mars Express spacecraft provides new information on Mars' geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet's history (the "phyllocian" era) are found in the oldest terrains; sulfates were formed in a second era (the "theiikian" era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the "siderikian") is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.

Aluminum Silicates↗
PubMed1999

A search for companions to nearby brown dwarfs: the binary DENIS-P J1228.2-1547

Hubble Space Telescope imaging observations of two nearby brown dwarfs, DENIS-P J1228.2-1547 and Kelu 1, made with the near-infrared camera and multiobject spectrometer (NICMOS), show that the DENIS object is resolved into two components of nearly equal brightness with a projected separation of 0.275 arc second (5 astronomical units for a distance of 18 parsecs). This binary system will be able to provide the first dynamical measurement of the masses of two brown dwarfs in only a few years. Upper limits to the mass of any unseen companion in Kelu 1 yield a planet of 7 Jupiter masses aged 0. 5 x 10(9) years, which would have been detected at a separation larger than about 4 astronomical units. This example demonstrates that giant planets could be detected by direct imaging if they exist in Jupiter-like orbits around nearby young brown dwarfs.

Journal Article↗
PubMed1999

The origin of chaos in the outer solar system

Classical analytic theories of the solar system indicate that it is stable, but numerical integrations suggest that it is chaotic. This disagreement is resolved by a new analytic theory. The theory shows that the chaos among the jovian planets results from the overlap of the components of a mean motion resonance among Jupiter, Saturn, and Uranus, and provides rough estimates of the Lyapunov time (10(7) years) and the dynamical lifetime of Uranus (10(18) years). The jovian planets must have entered the resonance after all the gas and most of the planetesimals in the protoplanetary disk were removed.

Journal Article↗
PubMed2000

Discovery of young, isolated planetary mass objects in the final sigma Orionis star cluster.

We present the discovery by optical and near-infrared imaging of an extremely red, low-luminosity population of isolated objects in the young, nearby stellar cluster around the multiple, massive star final sigma Orionis. The proximity (352 parsecs), youth (1 million to 5 million years), and low internal extinction make this cluster an ideal site to explore the substellar domain from the hydrogen mass limit down to a few Jupiter masses. Optical and near-infrared low-resolution spectroscopy of three of these objects confirms the very cool spectral energy distribution (atmospheric effective temperatures of 1700 to 2200 kelvin) expected for cluster members with masses in the range 5 to 15 times that of Jupiter. Like the planets of the solar system, these objects are unable to sustain stable nuclear burning in their interiors, but in contrast they are not bound to stars. This new kind of isolated giant planet, which apparently forms on time scales of less than a few million years, offers a challenge to our understanding of the formation processes of planetary mass objects.

Journal Article↗
PubMed2000

Planetary science. A dripping wet early Mars emerging from new pictures.

The latest images from the Red Planet, a sampling of which is shown on page 1927, are suggesting that water ponded across its equatorial region eons ago, just when life might have been emerging. Although the authors offer more than one interpretation, the one they prefer has the sediments laid down beneath broad lakes and shallow seas at a relatively clement time in the planet's history. The geologic implications of the pictures plus supportive signs from earlier missions mean that these possible lake sediments will be prime candidates for NASA missions seeking signs of past life on Mars.

Atmosphere↗
PubMed2000

Teleconvection: remotely driven thermal convection in rotating stratified spherical layers.

We report the discovery of a convective phenomenon found to occur in a rotating spherical system in which an inner convectively unstable fluid layer is bounded by a corotating outer convectively stable fluid layer. Although convection is thermally driven in the unstable interior, the resulting convective motions concentrate primarily in the stable outer region. This phenomenon, which we term teleconvection, suggests that fluid motions observed at the "surface" of a planet (such as Jupiter's alternating zonal winds) may be driven by an energy source located deep inside the planet.

Journal Article↗
PubMed2002

Measurement of microbial activity in soil by colorimetric observation of in situ dye reduction: an approach to detection of extraterrestrial life.

BACKGROUND: Detecting microbial life in extraterrestrial locations is a goal of space exploration because of ecological and health concerns about possible contamination of other planets with earthly organisms, and vice versa. Previously we suggested a method for life detection based on the fact that living entities require a continual input of energy accessed through coupled oxidations and reductions (an electron transport chain). We demonstrated using earthly soils that the identification of extracted components of electron transport chains is useful for remote detection of a chemical signature of life. The instrument package developed used supercritical carbon dioxide for soil extraction, followed by chromatography or electrophoresis to separate extracted compounds, with final detection by voltammetry and tandem mass-spectrometry. RESULTS: Here we used Earth-derived soils to develop a related life detection system based on direct observation of a biological redox signature. We measured the ability of soil microbial communities to reduce artificial electron acceptors. Living organisms in pure culture and those naturally found in soil were shown to reduce 2,3-dichlorophenol indophenol (DCIP) and the tetrazolium dye 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt (XTT). Uninoculated or sterilized controls did not reduce the dyes. A soil from Antarctica that was determined by chemical signature and DNA analysis to be sterile also did not reduce the dyes. CONCLUSION: Observation of dye reduction, supplemented with extraction and identification of only a few specific signature redox-active biochemicals such as porphyrins or quinones, provides a simplified means to detect a signature of life in the soils of other planets or their moons.

Bacteria↗
PubMed1996

The modification of human society by natural systems: discontinuities caused by the exploitation of endemic species and the introduction of exotics.

Drastic reductions in Earth's biodiversity, old growth forests, top soil, clean water and air, and truly wild areas are occurring during a period when discussions of sustainable growth and sustainable production are becoming common. Using such terms as sustainable growth and sustainable production rather than the more accurate sustainable use of the planet leaves the impression that, with a little more skill, society can continue its present practices indefinitely. A number of explanations are possible for this desire to maintain two conflicting beliefs (i.e., severe environmental destruction occurs but society can continue its basic practices indefinitely): 1) the idea that a technological solution can be found for every problem; 2) an addiction to present behavioral norms, which is so strong that the consequences of continuing such behavior are irrelevant; and 3) the concept that, while human society can alter natural systems to suit its own needs, natural systems are incapable of altering human society. This last issue is the focus of this discussion: if human society eliminates all species on the planet that are incapable of tolerating human society's present practices, the only species remaining will be those that human society is unable to control successfully or eliminate; these species are called pests. Another hypothesis could be stated: a world of pests that human society cannot control effectively will inevitably reshape human society through disease and famine, technological breakdown, and interference with domesticated and wild species upon which the integrity of human societal structure depends.

Animals↗
PubMed2002

Nulling interferometry without achromatic phase shifters.

In the infrared wavelength region, a typical star is approximately a million times brighter than the planet that surrounds it, which is a major problem when we attempt to detect exoplanets in a direct manner. Nulling interferometry is a technique that one can use to solve this problem by attenuating the stellar light and enhancing that of the planet. Generally, deep nulling is achieved by use of achromatic phase shifters (APSs). Unfortunately, the technology needed to build these APSs is not yet fully developed. We show that deep nulling can also be achieved by using delay lines only. We investigate the nulling depth as a function of the width of the wavelength interval and the number of telescopes. We also show that we can obtain nulling depths of less than 10(-6), which are required for exoplanet detection. Furthermore, we investigate the properties of the transmission map and make a comparison between our system and an APS system.

Journal Article↗
PubMed2004

Systematic errors in nulling interferometers.

Nulling interferometers combine on-axis suppression with high angular resolution, making them ideal instruments for the direct detection of faint planets close to their parent star. Analysis is developed to show that it is systematic errors, resulting from fluctuations in the null depth, that drive the instrument performance. A second-order combination of amplitude and phase errors is the dominant contributor. In the calculated example, the detection of an Earthlike planet around a Sunlike star at 15 pc requires that the arms of the interferometer must be phased to within approximately 1.5 nm and have their amplitudes matched to approximately 0.1%.

Journal Article↗