We have studied the UV radiation in the range 180 to 330 nm emitted by several stars with planetary systems, in order to determine the constraints on the habitable zones posed by the radiation levels. The observations were taken from the International Ultraviolet Explorer (IUE) and the Hubble Space Telescope (HST) satellites database. The stellar sample was chosen to cover the range of what are usually called solar-type stars, from late F to K stars. We found that the planets discovered around Epsilon Eridani and 16 Cyg B are within both the optical and UV habitable zones.

The first extrasolar planetary system was discovered around the pulsar PSR B1257+12, and the planets therein remain the lowest mass exoplanets known (with one whose mass is of order a lunar mass). Pulsar planetary systems will remain the only extrasolar planetary systems within which terrestrial-mass planets can be detected for the near future, and multiple pulsar planetary systems would provide strong circumstantial evidence that terrestrial-mass planets are ubiquitous, and possibly information about the formation of terrestrial-mass planets. We summarize two searches for planetary or proto-planetary systems around pulsars. The first is a series of infrared observations of millisecond pulsars in which the objective is to detect (proto-planetary) disks. The second uses a genetic algorithm—a function optimization method based on evolutionary processes in the natural world—to search for the signatures of planetary perturbations in pulse timing data.

The Advanced Camera for Surveys was installed on the Hubble Space Telescope in March 2002. The instrument science team will search for planets using direct imaging with the ACS coronagraph and with precise astrometric and photometric measurement of suitable stars and disks. The camera is operational and performing to expectation.

We report on our ongoing imaging efforts to detect brown dwarfs orbiting solar-type stars and other brown dwarfs. We study the properties of brown dwarf companions as a function of primary mass. Our results indicate that the frequency of brown dwarf companions around solar-type stars for separations larger than about 40 AU is non-negligible. The frequency of brown dwarf binaries is about 20%. There is a dearth of brown dwarf binaries with separations larger than ∼20 AU. We propose that brown dwarf systems are a scaled down version of stellar systems, which probably form via triggered collapse of small molecular cores.

The time during which the temperature of a terrestrial-like planet remains in the liquid water range during the fading of its parent brown dwarf is calculated as a function of brown dwarf mass and planetary semimajor axis using recent models for brown dwarf evolution and two criteria for habitable zone width. Durations of habitability range from 0.5–2 Gyr at a brown dwarf mass of 0.03 M⊙ to 2–10 Gyr at a brown dwarf mass of 0.07 M⊙ for planets within a few Roche radii.

Brown dwarfs have masses intermediate to stars and planets, but their atmospheres can span planetary plasma conditions as they cool over time. They are more directly observable than the currently known extra-solar planets. In this paper, we provide a brief summary of the atmospheric properties of brown dwarfs, and apply this knowledge to predict the thermal and spectral properties of extra-solar planets.

We discuss how the process of star formation across the spiral arms of galaxies functions as an ecosystem. The carbon abundance plays a crucial role in both its self-regulation and evolution.

NASA and ESA are currently undertaking mission studies for space-based observatories designed to search for life on other worlds. To optimize the designs of these missions, and to ultimately interpret the data sent back by them, we need to recognize habitable worlds and to discriminate between planets with and without life based only on remotely-sensed information. This paper provides an overview of the characteristics we would look for on an extrasolar terrestrial planet that might indicate habitability or the presence of life. It also describes a new NASA Astrobiology Institute research project to develop an innovative suite of modeling tools to simulate the environments and spectra of extrasolar planets. These modeling tools will constitute a Virtual Planetary Laboratory, which will be used to explore the plausible range of atmospheric compositions and globally-averaged spectra for early Earth and for plausible terrestrial planets both with and without life. Products of this research will provide an improved basis for recommending spacecraft and instrument characteristics, as well as search strategies required to remotely sense the signs of life in the atmosphere or on the surface of another world.

The homochirality of biological molecules — the almost exclusive use of L-amino acids and D-sugars — is a fundamental property of life, but its origin poses a problem. Recent work has shown an excess of the L enantiomer in amino acids in the Murchison and Murray meteorites, supporting the model, first proposed by Rubenstein et al. (1983) of an extraterrestrial origin for homochirality. This paper discusses the evidence for extraterrestrial chiral asymmetry, the processes which could have led to such asymmetry, and the possible relevance for the origin of biological homochirality on Earth.

The origin of homochirality is one of the longest-standing puzzles in understanding the origins of life. In the laboratory, illumination by circularly polarised UV radiation (asymmetric photolysis) is an effective means of producing an enantiomeric excess in an otherwise racemic mix of chiral molecules. In the natural world, however, it has proven difficult to identify a suitable source of Circularly Polarised Light (CPL). Recent observations of L-excesses of 2–9% for a number of α-methyl amino acids in the Murchison meteorite and our discovery of large degrees of CPL in some star forming regions has added weight to the suggestion that the origin of homochirality is extra-terrestrial. Here we report initial modelling of the production of that CPL.

Terrestrial biochemistry is based upon chiral (handed) molecules, of which only one of the two possible hands is predominantly employed. This biomolecular “homochirality”, may be a universal “signature” of life. Along with all living organisms, plant leaves are constructed from arrays of chiral molecules of a single hand. Through the development of a new spectroscopic approach, Diffuse Reflectance Circular Dichroism in the UV-visible wavelength regions, we have detected this chirality non-invasively from non-specular light scattered by leaves. The characteristic spectra are sensitive to plant species and leaf age/health. The technique may provide a means of remote sensing the state of flora and, at closer range, an indicator of living organisms for interplanetary landers.

In searching for a terrestrial source of circular polarization that could be an agent for homochirality, I have re-discovered earlier work by Ivanoff & Waterman (1958) showing that total internal reflection of sunlight scattered by water or suspended particles can, in calm shallow waters such as tidal pools, yield a degree of circular polarization >10% in favourable directions. A terrestrial source would have the distinct advantage over an astronomical source that the perilous journey to the planetary surface is eliminated. The relative viability of this mechanism is compared with the widely discussed astronomical mechanism of Bailey et al. (1998).

A search for biologically significant molecules in the interstellar medium (ISM) is currently being undertaken with the Australia Telescope Compact Array (ATCA) of the CSIRO Australia Telescope National Facility (ATNF) at millimetre wavelengths. The search includes several chiral molecules, and glycine, the simplest amino acid. Some first results from this search are presented here.

Interstellar dust grains are vectors for cosmic carbon and other biogenic chemical elements. They deliver carbon to protoplanetary disks in various refractory phases (amorphous, graphitic, etc.), and they are coated with icy mantles that contain organic molecules and water. The nature of the organics present in and on the dust appears to be closely related to physical conditions. Complex molecules may be synthesized when simple ices are irradiated. Astronomical observations show that this occurs in the vicinity of certain massive protostars, but it is not known whether our Solar System formed in such a region. Organic matter does not survive cycling though diffuse regions of interstellar space; any organics delivered to the early Earth must have originated in the parent molecular cloud, or in the solar nebula itself. A key question is thus identified: What was the star-formation environment of the Solar System? Possible constraints are briefly discussed.

The results of a submillimetre wavelength spectral line survey between 455.1 – 507.4 GHz of the Orion-KL hot cloud core are reported. 254 lines were detected, and are associated with 30 different molecular species or their isotopomeric variants. Apart from the abundant diatomic rotors such as CO and CS, the spectrum is dominated by SO, SO2 and CH3OH and large organic molecules such as (CH3)2O, CH3CN, C2H3CN, C2H5CN and HCOOCH3 which make up ∼ 72% of the total number of lines; unidentified lines ∼ 13%; and other lines the remaining ∼ 15% of the total. Rotational temperatures and column densities derived using standard rotation diagram analysis techniques were found to range from 70 – 600 K, and 1014 – 1017cm2 respectively.

Molecular cloud cores are often found to contain regions with high abundances of organic molecules such as formaldehyde, methanol, ethanol, dimethyl ether, and methyl formate. First we will review the status of observations of these molecules in a number of sources and discuss some of the limitations of present techniques. Then we will discuss systematic factors involved in the conversion of column densities into fractional abundances and introduce an independent method of calibrating that conversion. Finally we will present recent results from high spatial resolution observations of W3(OH).

Infrared spectroscopic observations of the circumstellar envelopes of AGB and post-AGB stars have identified a variety of inorganic grains including amorphous silicates, crystalline silicates, silicon carbide, carbonates, corundum, spinels and possibly rutiles. Isotopic studies of meteorites have also identified similar species of presolar origin. The existence of aromatic and aliphatic features in the spectra of post-AGB stars suggests that organic compounds in solid-state form are made during the post-AGB phase of stellar evolution. These features show similarity with the IR spectra of kerogen, which is also found in meteorites. These grains therefore represent an important link between stars and the solar system.

Recent developments in infrared spectroscopy have made possible the detection of the stretching and bending modes of organic molecules in space. Infrared emission bands of the C-C and C-H stretching and bending modes of aromatic compounds have been widely observed in carbon-rich planetary nebulae, the descendents of carbon stars. Infrared spectra of the transition objects between carbon stars and planetary nebulae, called proto-planetary nebulae, have shown definite signatures of a variety of aliphatic side-groups attached to aromatic rings. This suggests that molecular synthesis is actively ongoing in the circumstellar environment and the chemical nature of these compounds evolve over time scales as short as several hundred years.

Understanding the organic chemistry of molecular clouds, particularly the formation of biologically important molecules, is fundamental to the study of the processes which lead to the origin, evolution and distribution of life in the Galaxy. Determining the level of molecular complexity attainable in the clouds, and the nature of the complex organic material available to protostellar disks and the planetary systems that form from them, requires an understanding of the possible chemical pathways and is therefore a central question in astrochemistry. We have thus searched for prebiologically important molecules in the hot molecular cloud cores: Sgr B2(N-LMH), W51 e1/e2 and Orion-KL. Among the molecules searched: Pyrimidine is the unsubstituted ring analogue for three of the DNA and RNA bases. 2H-Azirine and Aziridine are azaheterocyclic compounds. And Glycine is the simplest amino acid. Detections of these interstellar organic molecular species will thus have important implications for Astrobiology. Our preliminary results indicate a tentative detection of interstellar glycine. If confirmed, this will be the first detection of an amino acid in interstellar space and will greatly strengthen the thesis that interstellar organic molecules could have played a pivotal role in the prebiotic chemistry of the early Earth.

We used the BIMA Array to observe CO and CS molecules in Comet Hale-Bopp (C/1995 O1) during the 1997 apparition. A spur-like structure around the cometary nucleus is observed. These molecular spurs may be attributed to gas or dust jets. Using Haser model, we find the theoretically predicted CO scale length agrees well with observations. A large fraction of CO is sublimated directly from the nucleus, with the remaining CO coming from icy dust grains in cometary coma. The [CO/H2O] abundance ratio of Hale-Bopp is consistent with that of icy dust grains in star forming regions. We conclude that Hale-Bopp was likely formed at the stage when there were still ample of icy grains in Solar Nebula; therefore, abundances of parent molecules in a comet may reflect the primordial chemical composition of the Nebula.