Participants and abstracts.

Invited speakers:
Pawel Artymowicz, Stockholm Obs., Sweden * abstract
Alan Boss, CIW, DTM, USA,* abstract
Adam Burrows, U. Arizona, USA * abstract
Mark Harrison, RSES, ANU, Australia, abstract
Ray Jayawardhana, U. Michigan, USA* abstract
Laurie Leshin, Arizona State U., USA * abstract
Doug Lin, UC Lick Observatory, USA* abstract
Jonathan Lunine, LPL, AZ, USA* abstract
Kevin McKeegan, UCLA, USA* abstract
Frank Shu,  National Tsing Hua U., Taiwan, * abstract

Contributed talks:
Francies Albarede, Ecole Normale Sup. de Lyon, France
Yuri Amelin, Geological Survey of Canada, *,abstract
Martin Asplund, RSAA, ANU, Australia, abstract
Jeremy Bailey, AAO, Australia, * abstract poster 1 poster 2
Victoria C. Bennett, RSES, ANU, Australia *
Mike Bessell, RSAA, ANU, Australia, *
Brad Carter, U. of S. Queensland, Australia * abstract
Geoff Davies, RSES, ANU, Australia* abstract
Ulyana Dyudina, RSAA, ANU, Australia* abstract
Justin Freeman, RSES, ANU, Australia*, abstract
Andrew Glikson,RSES, ANU, Australia*, abstract
Karl E. Haisch Jr., U. Michigan, USA,*abstract
Peter Holden,RSES, ANU, Australia*
Masahiko Honda, RSES, ANU, Australia* abstract
Trevor Ireland, RSES, ANU, Australia* abstract
Ing-Guey Jiang, Astronomy, National Central U., Taiwan* abstract
Warrick Lawson , UNSW@ADFA, Australia*, abstract
Kurt Liffman, CSIRO and Monash U., Australia*,abstract
Charley Lineweaver, UNSW, Australia*,abstract
Sarah Maddison, Swinburne U., Australia*, abstract poster abstract
Rosemary Mardling, CSPA, Monash U., Australia * abstract
Franklin Mills, RSPhysSE,ANU, Australia*f abstract
Keiji Misawa, Nat. Inst.Polar Res., Japan,n*
Louis Moresi, Monash U., Australia* abstract poster abstract
James Murray, Swinburne U., Australia*
Marc Norman,RSES, ANU, Australia* abstract
Allen Nutman, RSES,ANU, Australia* abstract
Andrew Prentice, Monash U., Australia* abstract
Penny D. Sackett, RSAA, ANU, Australia*
Thomas Sharp, Arizona State U., USA,* poster abstract
Therese Schneck, Consulting Civil Engineer,France *?,poster abstract
Robert G. Smith,UNSW@ADFA, Australia*f abstract
Dave Stegman. Mathematical Sci., Monash U., Australia* abstract
Ross Taylor, Geology, ANU, Australia *, abstract
Mark Wardle, Macquarie U, Australia,*f abstract
David Wark, Monash  U., Australia * abstract
Peter Wood, RSAA, ANU, Australia*? abstract
Chris Wright, ADFA, UNSW, Australia *f abstract
Li-Chin Yeh, National Hsinchu Teachers College, Taiwan *f, abstract
Williaml Zealey,U. of Wollongong, Australia* abstract
Students:
Daniel Bayliss, MSO, ANU, Australia* abstract
Adrian Brown, Macquarie U, Australia* abstract
Andres Carmona,ESO Garching.,Heidelberg U., Germany* poster abstract
Marie Gibbon, Monash U., Australia n*
Daniel Grether, UNSW, Australia, poster abstract
Antti Kallio, RSES, ANU, Australia n*
Gareth Kennedy, Monash U., Australia*f abstract
A-Ran Lyo, ADFA, Australia, * poster abstract
Marco M. Maldoni, UNSW@ADFA, Australia,* poster abstract
Charles Morgan, Monash U., Australia* abstract
Craig O'Neill, U. Sydney, Australia, * abstract
Dr. John Patten, unaffiliated student, Australia, *
Kala Perkins, SRES, ANU, Australia, n*?
Tamara Rogers, U. Santa Cruz, USA,*  poster abstract
Raquel Salmeron, U. Sydney, Australia,* abstract
Patrick Scott, MSO, ANU, Australia, n*
Robert Smalley, U. NSW, Australia, n
Christine Thurl, MSO, ANU, Australia, n*
Miguel de Val Borro, Stockholm U., Sweden, * title only abstract
David Weldrake, RSAA, ANU, Australia, n *

*- I have the complete registration, no more action needed
*f-payment and registration is faxed, no more action needed
*?-registration information is there but the payment information is missing
n-not presenting


Yuri Amelin (1),  Alexander Krot (2) and Eric Twelker (3).
1) Geological Survey of Canada, 601 Booth St., Ottawa, ON, Canada, K1A 0E8, yamelin@NRCan.gc.ca,
2) Hawai'i Institute of Geophysics and Planetology, SOEST, University of Hawai'i at Manoa, Honolulu, HI 96822, USA, sasha@higp.hawaii.edu,
3) Juneau, AK  99803, USA, twelker@alaska.net.

Duration of the chondrule formation interval: a Pb isotope study.

       Chondrules are among the earliest solid objects that formed in the solar system.
We have  determined the ages of chondrules from several carbonaceous chondrites using the Pb-Pb isochron method. High precision Pb isotope dates are obtained for three silicate clasts (large chondrules) from the CBa (Bencubbin-like) chondrite Gujba. Additional analyses of chondrules from the CV3 chondrite Allende allowed to improve precision of the age. The summary of precise Pb-Pb ages of chondrules from primitive chondrites is shown below:

Meteorite                                             Pb-Pb isochron age, Ma         Comment
Allende (CV3)                                      4566.7±1.0                             this study
Acfer 059 (CR2)                                  4564.7±0.7                             Amelin et al. (2002)
Gujba (CBa)                                         4562.7±0.5                             this study

       From these data, we deduce that the period of chondrule formation started simultaneously with, or shortly after the CAI formation [4567.2±0.6 Ma (Amelin et al., 2002)], and continued for at least 4.0±1.5 m.y. If the dates of the chondrules reflect their timing of formation, then there were probably a variety of processes occurring over at least 4-5 m.y. that we now combine under the umbrella name of "chondrule formation".  More high-precision Pb-Pb and extinct nuclide dating, as well as geochemical and petrologic studies of chondrules from primitive meteorites, will be  required to understand individual processes of chondrule formation.

Pawel Artymowicz
Stockholm Univ.

"Migration of bodies in disks: Timescales and unsolved problems"

Solid bodies with size ranging from dust to planets are present in  protoplanetary disks, with which they couple via processes involving gas drag, radiation pressure, and gravitational torques of several types (due to Lindblad and corotational resonances).  As a result, several size-dependent migration modes exist, operating on timescales shorter than the lifetime of the disks. Theory of migration studies the role of mobility in accumulation of solids, origin of the orbital distance distribution of extrasolar planets, and the ring-like appearence of some circumstellar dust disks.  This talk presents an overview of the underlying physics, timescales, and the outcomes of migration in the scenarios of planetary system formation.  We discuss in some detail a newly discovered, fast migration mode of protoplanets (timescale ~1000 yr), dependent on corotational torques (tentatively named type III).
 
Martin Asplund
RSAA, ANU, Australia

The solar chemical composition

The chemical composition of the Sun is one of the fundamental reference points in astronomy to which all other cosmic objects are anchored. It is therefore crucial to have as accurate element abundance estimates as possible, not the least for a proper understanding of star and planetary formation. I will review the current status of our knowledge of the solar chemical composition determined from solar spectroscopy, in particular in view of new 3D hydrodynamical models of the solar atmosphere. These more realistic models have recently caused substantial downward revisions of the solar C, N and O abundances by almost a factor of two. Implications of this and a comparison with the meteoritic evidence will be briefly discussed.

Jeremy Bailey
AAO, Australia

Evolution of Terrestrial Planet Atmospheres
Time when the process started in the solar system:  -4.5 byr
Time when it ended:   still continuing

The planets Venus, Earth and Mars have developed very different atmospheres over 4.5 billion years of evolution, although we suspect that their early atmospheres may have been quite similar. Mars has a very thin (7 mbar) and dry atmosphere of mostly CO2. The Earth's 1 bar atmosphere is predominantly nitrogen and oxygen with very low CO2 content, and Venus has a 90 bar atmosphere of mostly CO2 in which a runaway greenhouse effect has heated the planets surface to 720K. I will review some of the processes which have
operated on the three planets to control the evolution of their atmospheres, and discuss issues including the "early faint Sun" problem, "snowball Earth" events and the rise of oxygen in the Earth's atmosphere.

Jeremy Bailey (1,2),  Sarah Chamberlain (2),  Malcolm Walter (2) and David Crisp (3)
(1)  AAO   (2) Australian Centre for Astrobiology, Macquarie University
(3)  Jet Propulsion Laboratory, Caltech


Poster: IR Observations of Mars during the August 2003 opposition

    We present some preliminary results of observations obtained during the very favourable opposition of Mars in August 2003 using the UIST instrument on the United Kingdom Infrared Telescope (UKIRT) at Mauna Kea, Hawaii. We obtained narrow band images which we believe are probably the sharpest ever obtained with a ground-based telescope, as well as spectral scans of the disk at a range of near-IR wavelengths and resolving powers. The observations include absorption features due to atmospheric gases, CO2 ice at the south pole, and water ice clouds in the north. We can use the CO2 band strength to image the distribution of surface atmospheric pressure and hence topography.
    The data may be used to search for absorption features due to hydrated clay minerals, carbonates and sulphates which might provide evidence for the past presence of surface water.

Jeremy Bailey (1),  Phil Lucas (2), Jim Hough (2) and Motohide Tamura (3)
(1)  Anglo-Australian Observatory and Australian Centre for Astrobiology
(2)  University of Hertfordshire
(3)  National Astronomical Observatory, Japan

Poster: Direct Detection of Extrasolar Planets by Polarimetry
Despite the detection of more than 100 extrasolar planets by the radial  velocity method, no extrasolar planet has yet been seen directly by its emitted or reflected light. Detections by spectroscopic techniques have so far been unsuccessful while photometric detection requires accuracies which are beyond current ground-based photometry.
    However, we believe that planets orbiting close to their stars (Hot Jupiters) might be detected by means of the polarization of the light scattered from their atmospheres. While the resulting polarization of the combined light of the planet and star is small, polarization measurements can in principle be made with very high sensitivity since polarimetry is a  differential measurement and is not limited by the stability of the Earth's atmosphere as photometry is.
    We have designed and built a stellar polarimeter which should be capable of achieving the required sensitivity. The instrument is now being tested, and on a 4m or larger telescope should be capable of detecting the polarization signature of bright hot Jupiter systems such as Tau Boo, Upsilon And or 51 Peg.


Daniel Bayliss, Ulyana Dyudina, Penny Sackett
RSAA, ANU, Australia

Modeling of Reflected Light from Extra Solar Planets with Eccentric Orbits
An extra solar planet will shine by reflecting light from its parent star.  As the planet orbits the star the amount of light reflected will vary as the phase of the planet changes with respect to the observer, resulting in a light curve with a periodicity equal to the orbital period of the planet.  We model the reflected light from extra solar planets at different phases based the reflective properties of Jupiter and Saturn obtained by the Pioneer space probes.  Since a large proportion of the known extra solar planets display highly elliptical orbits, our models include changes in angular velocity and orbital distance resulting from such elliptical orbits.  Current Earth based photometry is limited to a precision of about 100ppm of the parent's stars luminosity due to atmospheric extinction.  However new space photometers, such as MOST and Kepler, are expected to have precisions down to less than 10ppm. At these new sensitivities the light curves from many known extra solar planets should be detectable.  These light curves should give us information not only on the size and orbital properties of the planet, but also on atmospheric  particle size, cloud cover, and the presence of rings.  We discuss the likelihood of these properties being extracted from the light curves with the data from space and earth based instruments in the next 5-10 years.

Alan Boss
Carnegie Institution

''The Formation of Giant Planets''
 
[All times relative to formation of the protosun and solar nebula]

Time core accretion started: 0 Myr
Error bar: 0 Myr
Time core accretion finished: 5 Myr
Error bar: 2 Myr

Time disk instability started: 0 Myr
Error bar: 0.1 Myr
Time disk instability finished: 0.1 Myr
Error bar: 0.1 Myr

  Two very different mechanisms have been proposed for the formation of the gas and ice giant planets. The conventional explanation for  the formation of gas giant planets, core accretion, presumes that a gaseous envelope collapses upon a roughly 10 Earth-mass, solid core that was formed by the collisional accumulation of planetary embryos orbiting in the solar nebula. The more radical explanation,  disk  instability, hypothesizes that the gaseous portion of the nebula underwent a gravitational instability, leading to the formation of  self-gravitating clumps, within which dust grains coagulated and settled  to form cores. Core accretion appears to require several million years or more to form a gas giant planet, implying that only long-lived disks would form gas giants. Disk instability, on the other hand, is so rapid (forming clumps in thousands of years), that gas giants could form in even the  shortest-lived disks. Core accretion has severe difficulty in explaining the formation of the ice giant planets, unless two extra protoplanets are  formed in the gas giant planet region and thereafter migrate outward.
  Recently, an alternative mechanism for ice giant planet formation has been  proposed, based on observations of protoplanetary disks in the Orion: disk instability leading to the formation of four gas giant protoplanets with cores, followed by photoevaporation of the disk and gaseous envelopes of the protoplanets outside about 10 AU by a nearby OB star, producing ice giants. In this scenario, Jupiter survives unscathed, while  Saturn is a transitional planet.

Adrian Brown
Dept of Earth and Planetary Sciences, Macquarie University

 "Evidence for the earliest Hydrothermal System on Earth in the East Pilbara Granite-Greenstone Terrane"

Time  when the process you  describe started in the solar system: 3.45 Gy
The error bar on the start time: 100 My
Time when this process ended: 3.46
The error bar on the end time: 100 My

The East Pilbara Granite Greenstone Terrane is a well preserved Archaean succession of domical granite batholiths surrounded by thick greenstone synclinoria. The North Pole Dome region in postulated to be a granite dome predominantly covered by greenstones of the Warrawoona Group. Following intrusion of the granite and eruption of the felsic Panorama Formation around 3.45 Gya, it is hypothesized that a hydrothermal event took place, utilising the felsic magma conduits to propel water to the palaeosurface, thereby creating an epithermal hydrothermal deposit at Miragla Creek. The alteration caused by this event is in the process of being mapped using airborne hyperspectral sensing as part of a three year PhD project. It provides an opportunity to examine one of the earliest hydrothermal events in the history of the Earth.

The 600 sq. km hyperspectral dataset was captured in October 2002 and covers the wavelengths from 400 to 2400 nm at 5m resolution. Mapped litholgies so far include sericite, chlorite and pyrophyllite alteration zones, along with a serpentine-rich komatiite flow at the base of the Apex Basalt. These will be discussed and implications of the event, including its possible links with putative stromatolite structures within the 3.42 Gyr Strelley Pool Chert, which overlies the Panorama Formation.

Adam Burrows
 U. Arizona

Direct Detection of Extrasolar Giant Planets

Over the past eight years we have seen the number of known extrasolar giant planets (EGPs) grow from 1 in 1995 to more than 110 today.  However, these epochal discoveries outside our solar system have been made using indirect techniques.  In order to truly characterize their physical and chemical nature, more direct detection of the light of the planets themselves is necessary.  To this end, NASA and ESA have embarked upon an ambitious plan of direct planet measurement that includes projects with the KIA, LBTI, VLTI, SIM, GAIA, Kepler,  COROT, MOST, MONS, WISE, JWST, and the Spitzer Space Telescope.      
    I will review theoretical calculations of the atmospheres, spectra, and evolution of irradiated EGPs as a function of  mass, age, orbital separation, eccentricity, primary star, and composition.  Moreover, I will describe EGP albedos and orbital phase functions, as well as transit physics. The predictions I summarize are predominantly to inform the numerous direct discovery campaigns being planned for the next decade.  
 
Andres Carmona
European Southern Observatory. Garching. & Heidelberg University. Heidelberg. Germany

Poster: Observational studies of gas in circumstellar disks around YSO
Time when the process you describe started in the solar system: 0
The error bar on the start time: -
Time when this process ended: 5 Myr (?)
The error bar on the end time: 1 Myr

Circumstellar disks around young stellar objects (YSO), where the process of planet formation is thought to take place, consist nearly 99% of gas. However, until the present, a great part of the observational effort in understanding YSO's disks has been focused on the study of the dust. It is well known that dust causes
the bulk of infrared continuum radiation, as well as strong infrared spectroscopic features. Interesting insights on the physics of the disks has been consequently obtained even at low spectroscopic resolution. Unfortunately, dust does not provide kinematic information that allow the detailed study of the dynamics of the disk. Indeed dust observations don't permit a direct measure of the mass distribution as a function of the
distance to the star.On the theoretical arena, recent studies of planet formation focused principally on the study of the dynamics of the gas in the circumstellar disk. It appears that observational work aimed to study the gas is
necessary and fundamental for constructing a more accurate picture of the planet formation process. Specifically, gas studies are vital to constrain and observationally test theoretical scenarios proposed about
giant planet formation and migration in particular.Gas has weaker features, so observationally harder to study. However with gas it is possible to obtain kinematic information. Only advanced technology allowing extremely high spectral resolution would permit to resolve the weak spectral features associated with circumstellar gas.
Only 8m class telescopes are able to provide the high angular resolution required to spatially resolve the disks around a close stellar objects.The ESO-VLT capabilities combined with a new generation of high
resolution infrared spectrometers (VISIR and CRIRES) will allow astronomers for the first time to study the gas and the dynamics circumstellar disks. However, even with the best instrumentation available, to be able to resolve the disks and perform detailed gas studies, young, close, ^Óbig^Ô and bright, stellar objects are required. Young intermediate mass stars Herbig Ae/Be appear to be the more suitable targets for effectuating this new and challenging research.

Brad Carter
USQ www.usq.edu.au/users/carterb

The Anglo-Australian Planet Search
Time when the process you describe started in the solar system: 3Gyr (2 Gyr ago)
The error bar on the start time: 1 Gyr
Time when this process ended: 5 Gyr
The error bar on the end time: 1 Gyr
(The above figures represent the fact that the exoplanets to be
discussed are mature objects thought to be several billion years old to
roughly solar age or perhaps older)

The Anglo-Australian Planet Search (AAPS) is currently surveying about 250 generally solar-type stars in the southern sky, to detect orbiting planets using stellar reflex motion. Precision Doppler measurements of stellar radial velocity are made with the Anglo-Australian Telescope (AAT) equipped with an echelle spectrograph and an iodine absorption cell. The spectrograph point spread function and wavelength calibration are derived from the iodine line spectra, resulting in a long term precision of 3 metres per second. Because the magnetic activity of young stars produces a jitter that affects precision radial velocity measurements, the target stars selected are older than 3 Gyr and their planets are "mature" objects. The AAPS has revealed more than a dozen planet candidates with minimum mass ranging from 0.2 to 10 times the mass of Jupiter, and an additional four planet candidates have been confirmed. For the most part the exoplanets detected are in eccentric or close orbits that are in marked contrast to our solar system. Nevertheless, a recent result is the detection of a planet orbiting the
star HD70642 that suggests a planetary system architecture similar to our own.

      
Geoff Davies
Research School of Earth Sciences, Australian National University

Stratifying the Earth
Time  when the process started : Magma ocean: during Mars-sized impact, late stage of accretion, say 30 Ma after meteorite formation (4.56 Ga).
The error bar on the start time: 15 Ma
Time when this process ended: 5000 years later
The error bar on the end time: 3000years
OR
Time  when the process started : Removal of excess accretional heat from Earth's interior:  late stage of accretion, 30 Ma after meteorite formation (4.56 Ga).
The error bar on the start time: 15 Ma
Time when this process ended: 400 Ma later (4.2 Ga)
The error bar on the end time:  200 Ma

    The Earth's iron core probably began to segregate when the Earth was about half grown, and would then have kept pace with the growth of the Earth, assuming Earth formation lasted a few to a few tens of millions of years.
    A magma ocean would freeze out in thousands of years, even if it were hundreds of kilometers deep, unless there was a dense, opaque early atmosphere to keep the surface hot.  Thus a global magma ocean is only likely to have occurred after giant impacts, and then only briefly.  Transient magma seas or lakes would have formed after lesser large impacts.
    Basaltic crust would have begun to form as soon as melting began, during the later stages of accretion, and this would continue to the present day through mantle convection.  Relatively thick basaltic crust (10-50 km) would have been forming as the Earth approached its final size, and would have persisted through the early phase of internal heat dissipation.  The mantle strongly self-limits thermally at higher temperatures.
     The excess internal heat left from accretion would be removed by mantle convection over a few hundred million years.  Thereafter the internal temperature would have slowly declined as the main radioactive heat sources (U, Th, K) decayed by a factor of about 4.
    Much of the early basaltic crust may have been subducted and settled to the bottom of the mantle because under pressure it becomes denser than the mantle.  It could have formed a layer 100-1000 km thick, which could explain early geochemical depletion of "incompatible" elements in the upper  mantle.
    Continental crust, closer to granitic composition, apparently accumulated only slowly during the first billion years, more rapidly for the next billion years, and then more slowly again.

U. Dyudina(1), P.Sackett(1), D. Bayliss(1), L Dones(2), H. Throop (2), A. Del Genio(3), C. Porco(4), S. Seager(5)
(1)Mount Stromlo Obs., Australian National University
(2)Southwest Research Institute, Boulder, USA
(3)NASA Goddard Institute for Space Studies, NY, USA
(4)Space Science Institute, Boulder, USA
(5)DTM, Carnegie Institute at Washington, USA

Disk-averaged phase light curves of extrasolar Jupiter and Saturn.
Time  when the process you  describe started in the solar system: 10^6 y
The error bar on the start time: ranges from 10^5 to 10^6 y
Time when this process ended:continuing
The error bar on the end time:n/a

    We predict how the remote observer would see the brightness of the giant planets vary as they orbit the star. The prediction is based on our empirical model of Jupiter, Saturn, and Saturn's rings reflectivity. The planets' and rings' surface reflectivity and the phase angle dependence of the reflectivity is derived from Pioneer and Voyagers spacecraft observations. We model the planets and the rings at different planets' obliquities and different viewing geometries. We derive the disk-averaged brightness of the planet and rings  depending on the  orbital inclination and eccentricity.
    Back-scattering effect of the real atmosphere makes the planet appear several times brighter than Lambertian sphere at full phase. The rings make the planet appear several times brighter at some geometries. A planet with rings produces complicated non-symmetric light curve as it orbits the star and changes phase. The brightest point on the curve may be different from the full phase geometry. This asymmetry together with a specific shape of the light curve may allow to detect rings in the precise photometry observations.
    We will discuss detectability of extrasolar planets and the rings around the planets using their phase light curves.

J. Freeman (ANU), L. Moresi (Monash University) and D. May (VPAC, Monash University)

Stagnant Lid Convection with a Water Ice Rheology

Numerical investigations of thermal convection with strongly temperature dependent Newtonian viscosity (diffusion creep) and extremely large viscosity contrasts have demonstrated the existence of three convective regimes. These are the small viscosity contrast regime, transitional regime and the stagnant lid regime. The strong temperature dependence of water ice suggests that convection operating within the mantle of an icy satellite should be within the stagnant lid regime. We study the evolution into the stagnant lid regime with a water ice rheology by solving the equations of thermal convection for a creeping fluid with the Boussinesq approximation and infinite Prandtl number. The viscosity is non-Newtonian (dislocation creep). We fix the Rayleigh number at the base (Ra₁) to be 1 X 10⁴ and systematically increase the viscosity contrast (as determined by (Delta T) over the region from Delta \eta = 1 to 10¹⁴. The transition to the stagnant lid regime occurs at a viscosity contrast greater than 10⁴ for Newtonian viscosity convection, whilst non-Newtonian viscosity convection accommodates the stagnant lid regime at larger viscosity contrasts.
    For a stress exponent, n, equal to 3, the stagnant lid regime is achieved at a viscosity contrast greater than 10⁸. Dislocation creep of water ice is characterized by a larger stress dependence (n=4) than silicates (n=3), and with this water ice rheology, the stagnant lid regime is attained at a viscosity contrast greater than 10¹⁰.

Andrew Glikson
RSES, ANU

Early terrestrial maria-like impact basins: mineralogy and chemistry of early Precambrian asteroid impact ejecta, Pilbara and  Transvaal, may imply existence of large oceanic impact basins on the early Precambrian Earth.

Asteroid impact fallout units, consisting of microkrystite (impact condensate) spherules and microtektites, increasingly allow the deciphering of the early impact history of Earth. In a paper of key importance, B.M. Simonson, D. Davies, M. Wallace, S. Reeves, and S.W. Hassler, (1998, Iridium anomaly but no shocked quartz from Late Archie microkrystite layer: oceanic impact ejecta?, Geology, 26:195-198) point out the likely oceanic (mafic-ultramafic) crustal source of early Proterozoic impact ejecta in the Pilbara Craton, Western Australia. Studies of mainly chloritic microkrystite spherules from the Barberton greenstone belt, Transvaal, are consistent with a mafic derivation of impact condensates (Lowe et al., 1989; Byerly and Lowe. 1994; Shukloyukov et al., 2000; Kyte et al., 2003; Lowe et al., 2003). Recent field and geochemical studies of Archaean to early Proterozoic impact units in the Pilbara Craton (Glikson and Vickers, 2003) lend support to Simonson et al.'s (1998) suggestion, on the following basis:
    [1]  Siderophile element (Ni, Co), ferroan elements (Cr, V) and Platinum Group Element (PGE) patterns of least-altered microkrystite (impact-condensate) spherules and microtektites from Archaean and early Proterozoic impact fallout in the Pilbara Craton (northwestern Australia) and the Kaapvaal Craton (Transvaal) (Table 1) indicate a mafic/ultramafic composition of impact target crust.
    [2]  No shocked quartz grains are observed in the impact fallout units.
    Estimates of asteroid and crater sizes based on (a) Mass balance calculations of asteroid masses based on the flux of Iridium and Platinum as measured from impact fallout units, and (b) spherule size-frequency distribution using the method of Melosh and Vickery (1991), provide evidence for asteroids several tens of kilometer in diameter (Byerly and Lowe,1994; Shukloyukov et al., 2000; Kyte et al.; Glikson and Vickers, 2003) and consequent oceanic (sima crust-located) impact basins with diameters on a scale of several hundred kilometers.
    The implications of these observations for the nature of the early Earth are inconsistent with strict uniformitarian geodynamic models based exclusively on plate tectonic processes. It is suggested the evolution of the early crust represents the combined effects of mantle-driven convection, modified plate tectonic regimes, and large extraterrestrial impacts which triggered deep faulting and adiabatic mantle melting. The latter resulted, in turn, in a feedback mechanism which temporally and spatially controlled the onset and loci of long term dynamic plate tectonic patterns.
    A picture emerges of a post-3.8 Ga early Precambrian Earth, i.e. postdating the Late Heavy Bombardment of 3.9-3.8 Ga, which consisted of sialic (SiAl-dominated) continental nuclei composed of multiple superposed greenstone-granite cycles interspersed within extensive tracts of simatic (SiMg-dominated) oceanic crust. The latter included maria-like impact basins on scales of up to several hundred kilometer, i.e. similar in size to the lunar Mare Crisium impact basin (~3.2 Ga; Ds ~ 400 km) or even Mare Serenitatis (Ds ~ 600 km).

References: Byerly, G.R., Lowe, D.R., 1994, Geochim. Cosmochim. Acta, 58, 3469-3486; Glikson, A.Y., Vickers, J., 2003, Geol. Surv. West Aust. Report;
Kyte, F.T., Shukloyukov, A., Lugmair, G.W., Lowe, D.R., Byerly, G.R., 2003, Geology, 31, 283-286; Lowe, D.R., Byerly, G.R., Asaro, F., Kyte, F.T.,
1989, Science 245, 959-962; Lowe, D.R., Byerly, G.R., Kyte, F.T., Shukloyukov, A., Asaro, F., Krull, A., 2003, Astrobiology, 3, 7-48; Melosh, H.J.,
Vickery, A.M., 1991, Nature, 350, 494-497; Shukolyukov, A., Kyte, F.T., Lugmair, G.W., Lowe, D.R. and Byerly, G.R. (2000), Springer, Berlin, pp.
99-116; Simonson, B.M., Davies, D., Wallace, M., Reeves, S., Hassler, S.W., 1998, Geology, 26, p. 195-198;

Karl E. Haisch Jr
University of Michigan

'Circumstellar Disk Evolution in Young Stellar Clusters"

Time when the process you describe started in the solar system: 200,000 yr
The error bar on the start time: 100,000 yr
Time when this process ended: 6 Myr
The error bar on the end time: 1 Myr

We report the results of the first sensitive infrared and millimeter continuum surveys of the young clusters NGC 1333, NGC 2071, NGC 2068, and IC 348 to obtain a census of the circumstellar disk fractions in each cluster. Our observations reveal that the variation in the fraction of detected millimeter sources from cluster to cluster is similar to the variation in the fraction of infrared sources for these clusters, implying that the inner and outer disks are coupled.
In addition, we conclude that our published estimation of disk lifetimes (t ~ 6 Myr) from infrared excesses provides accurate upper limits to the lifetimes of massive outer disks. This is the timescale for essentially all the stars in a cluster to lose their disks, and should set a meaningful constraint for the planet building timescale in stellar clusters. The implications of these results for current theories of planet formation are discussed.



Masahiko Honda
Research School of Earth Sciences, The Australian National University

The origin and evolution of planetary atmospheres - implications from noble gases

Time the formation of the terrestrial atmosphere started: unknown
Time the formation of the terrestrial atmosphere finished: 100 Ma relative to the formation of solar system
Error bar: 40 Ma

The differences in noble gas elemental abundances between the Earth's atmosphere and the solar abundances lead to the recognition that the Earth's atmosphere was formed secondarily by extensive degassing of volatiles from the Earth's interior, rather than by directly acquiring a primary atmosphere from the surrounding solar nebula.
    Models of degassing of volatiles from the Earth based on the differences of 40Ar/36Ar ratios in the Earth's atmosphere (=295.5; 40Ar produced from the decay of radioactive isotope 40K in the Earth and 36Ar is primordial) and in mantle-derived samples (>40,000) suggest that the Earth atmosphere was formed during a short period within ~100 million years of the formation of the solar system; namely by catastrophic degassing. Excess 129Xe, relative to the atmospheric 129Xe/130Xe ratio, observed in mantle-derived samples is believed to be attributable to the radioactive decay of the extinct nuclide 129I (half life 16 million years) once present in the Earth; this requires that the Earth's atmosphere must have separated from the mantle before all the 129I had decayed (another powerful argument in favour of early catastrophic degassing of the Earth).
    The observation of primordial solar neon, distinctly different from present-day atmospheric neon, in mantle-derived samples implies that the Earth's atmosphere has not evolved in a closed system.  This can be explained by postulating that isotope fractionation occurred in the Earth's atmosphere as a consequence of hydrodynamic-escape processes, possibly associated with the rupture of the Moon, or, that volatile-rich meteoritic material accreted at a late stage in the Earth's formation.
    Similarities between the noble gas elemental abundances of the atmospheres of the terrestrial planets (Venus, Earth and Mars), and between the neon isotopic compositions of the Earth's atmosphere and Mars-derived meteorites, suggests that insights to the formation of the Earth's atmosphere may be generally applicable to the atmospheres of the other inner "terrestrial-type" planets.


T. M. HARRISON
Research School of Earth Sciences, Australian National University, Canberra, A.C.T. 2601 AUSTRALIA

The Mission to Really Early Earth: When Did Conditions Appropriate for Life Emerge?
Start Time:  4.38 Ga
Error Bar on start time: ±0.01 Ga
End Time:   4.0 Ga
Error Bar on end time:  ±0.0 Ga

Recent work confirms that >3.83 Ga biomass is the most likely source of light carbon in graphitic inclusions from West Greenland thus raising the possibility that life originated during the Hadean Eon (~4.5-4.0 Ga), a period for which there is no known rock record. If so, how can we determine when the necessary ingredients for life, notably liquid water, first appeared? Provided sufficient quantities can be obtained, detrital zircons as old as ~4.4 Ga from the Jack Hills, Western Australia, offer the prospect of unprecedented insights into surface environmental conditions during the Hadean. An ion microprobe age survey of 21,500 Jack Hills zircons (~4 milligramm each) has yielded ~1000 between 4.0 to 4.38 Ga which have been used in a variety of studies to assess the earliest evolution of the atmosphere, hydrosphere, and continental lithosphere. delta¹⁸O_SMOW values and inclusions within Jack Hills zircons indicate that they formed by both subduction-related melting and anatexis of clay-rich protoliths within ~200 m.y. of planetary accretion.  Single zircon Xe isotopic analyses document a terrestrial Pu/U ratio of 0.0035±0.0005. One implication of this near chondritic value is that mantle-derived Xe isotopes cannot be interpreted in terms of the age of the atmosphere in a straightforward manner – such the 4. 4 Ga model age based on 129Xe systematics. ¹⁷⁶Hf/¹⁷⁷Hf and ¹⁴²Nd/¹⁴⁴Nd studies are underway to assess the presence and extent of Hadean continental crust. Because Jack Hills zircons carry intrinsic remenant magnetism, experiments are planned that could constrain the timing of geodynamo activation.  Our results to date challenge the view that continental and hydrosphere formation were frustrated by meteorite bombardment and basaltic igneous activity until ~4 Ga.  Rather, they suggest the existence of terrestrial continental crust and a mature, liquid-water-mediated sedimentary cycling system operating within it as early as ca. 4.3 Ga.

Trevor Ireland
RSES, ANU, Australia

Solidification of the Solar Nebula:  A primer for astronomers

Our solar system is the only planetary system for which we have a solid record of processes existant during formation.  The gravitational collapse of a molecular cloud results in a planetary system similar to the current configuration in less than 10 million years.  The earliest solid phases available (refractory inclusions) bear startling resemblances to the mineralogy of direct solar condensates.  Chondrules, subspherical  olivine-pyroxene inclusions, are a major component of the commonest stony meteorites (chondrites) and formed within a few million years of refractory inclusions.  Acondrites, essentially volcanic meteorites from planetary bodies formed about 8 Myr later.  Planetary bodies continue to evolve over longer periods (10-100 Myr) through stochastic impacts and internal differentiation

Ing-Guey Jiang
Institute of Astronomy, National Central University, Taiwan

The Eccentricity Outburst and Resonance Sweeping
Time when the process started in the solar system: 0 Myr
The error bar on the start time: 0.9 Myr
Time when this process ended: 1.0 Myr
The error bar on the end time: + 1.0 Myr, - 0.9 Myr

The dynamics of asteroids within planetary systems is studied and the role of proto-stellar discs is discussed.
We found that the orbital eccentricities of test particles  near the resonant region can be amplified siginificantly.
The disc depletion could lead to the migration of resonant region, which would definitely affect the resulting observed dynamical properties of the asteroid belts for any planetary systems in general.

Ray Jayawardhana
University of Michigan

Timescales of Disk Evolution and Planet Formation

Most newborn stars are surrounded by disks of dust and gas. It is out of these disks that planetary systems form. Studies of disk evolution can provide valuable insight into the timescales and processes of planet formation. Recent observations at infrared and millimeter wavelengths of young stars spanning a range of ages suggest that their (inner) dusty disks evolve relatively rapidly, on timescales of 10 million years or less. I will review the current evidence and discuss the constraints on planet formation models.

Gareth Kennedy
 Monash U., Australia

The Influence of a Binary Companion on Planetary Formation

The timescale for terrestrial planets, or giant planet cores, to form by accretion depends on the balance between excitation in the early planetesimal disk caused by self-gravitational interactions, and de-excitaton caused by inelastic collisions. However, since approximately 48% of local galactic field stars have binary companions, we investigate the disruption of this balance when a binary companion is included. The method used to study this problem removes the effect of the interaction between planetesimals, thus allowing the "tidal stirring" effect on the disk caused by the binary to be examined. A summary of results will be given from computer simulations investigating additional excitation caused by a binary companion, and the implications for planetary formation.

Warrick Lawson
UNSW@ADFA, Australia

Long-lived accretion in nearby T Tauri stars
Time when the process started in the solar system: 0 Myr
The error bar on the start time: 0.9 Myr
Time when this process ended: 1.0 Myr
The error bar on the end time: + 1.0 Myr, - 0.9 Myr

The nearest young stellar populations share a kinematic origin with the nearest OB-star population (the Oph-Sco-Cen association) and have inferred ages of 5-15 million years. These stars are prime targets for all early stellar and planetary evolution issues, including the issue of circumstellar disk longevity. Optical/infrared study finds a small fraction of these stars still possess inner disks and are undergoing active disk-star accretion at 10 Myr, a timescale comparable to that demanded by planet formation theory to grow Jovian planets to near their final masses.

Laurie A. Leshin(1) and Steven J. Desch(2)
(1)Geological Sciences/Meteorite Center, (2)Physics and Astronomy, Arizona State University

Making Waterworlds:  The Importance of 26Al

In order to understand the possibility of discovering life elsewhere, we seek to explore factors that affect the likelihood of forming "waterworlds" like the Earth in other solar systems.  Here, we consider the effect of the astronomical setting of a forming solar system, and specifically its effect on the abundance of the short-lived radioisotope 26Al.  If the source of 26Al in our solar system and others is a nearby supernova, the essentially random distance to the supernova explosion sets a solar system's initial abundance of 26Al.  Recent models for the delivery of water to the forming terrestrial planets indicate that most of Earth's water was carried in by hydrated asteroids.  In solar systems with more initial 26Al, asteroids would be drier, and dry Earths would result. In fact, solar systems with less 26Al than our own are more likely, and this could result in much wetter Earths.  Clearly this is only one factor that could affect the habitability of an extrasolar Earth, but it demonstrates the need to bring together astronomers, planetary scientists, and geoscientists to consider which factors are likely to be the most critical to forming and sustaining life.

Kurt Liffman
Monash University & CSIRO

Particle Size Sorting in the Solar Nebula
Time  when the process you  describe started in the solar system: 2 Myr
The error bar on the start time: 1 Myr
Time when this process ended: 7 Myr
The error bar on the end time:+ 3Myr, - 5 Myr

We wish to examine size sorting of chondrules and metal grains within the context of the jet flow model for chondrule/CAI formation. In this model, chondrules, CAIs, AOAs, metal grains and related components of meteorites are formed in the outflow region of the inner most regions of the solar nebula and then ejected, via the agency of a  bipolar jet flow, to outer regions of the nebula.
We wish to see if size sorting of chondrules and metal grains occurred in the outflow formation region or after the particles had left the outflow and were moving above or into the solar nebula.

Doug Lin
UC Lick Observatory, USA

The ubiquity of planets and the diversity of planetary systems.
Based on the core-accretion scenario, we consider the emergence of planetesimals, growth of cores, accretion of gas, and migration of gas giants in an evolving protostellar disks.  We outline the condition which lead to the dynamical architecture of our own Solar System. We discuss the mass and period distribution of gas giant planets and show their dependence on the metallicity of their host stars. Based on these results we infer the time scale for gas giant planet formation is a few Myr and that for terrestrial planets and ice giants is a few times longer.

Charles Lineweaver
UNSW, Australia

Galactic prerequisites for the formation of other Earths
(I will be talking about a paper by Lineweaver, Fenner and Gibson that will appear in Science Magazine on Jan 2, 2004.)