GOAL

1
GOAL 1 LEARN HOW THE SUNS FAMILY OF PLANETS
AND MINOR BODIES ORIGINATED.

• M. Wadhwa
• M. Abbas
• G. Blake
• J. Chambers
• W. Hubbard
• K. Lodders

2
Introduction

• Our solar system was born about 4.6 billion
  years ago when the collapse of a cloud of gas and
  dust resulted in the formation of a nascent Sun
  surrounded by an accretion disk. Subsequently,
  condensation and coalescing of materials in the
  disk formed solid aggregates that became the
  building blocks of the major and minor solar
  system bodies including the planets and their
  moons, asteroids, Kuiper-belt objects and comets.
  Many of the characteristics of our solar system,
  and the bodies within it, were established during
  the first billion years or so if its history.
  This is also the period during which life emerged
  on Earth, and possibly in other places in the
  solar system. However, processes active since
  this earliest epoch have either overprinted or
  erased much of the record of conditions and
  processes in the early solar system, making it
  extremely challenging to decipher this record.
  Nevertheless, this record is still well preserved
  in the physical and chemical characteristics of
  some solar system materials, such as the oldest
  rocks on the Earth, Moon and Mars, primitive
  asteroidal meteorites, and comets. Moreover,
  novel approaches involving theoretical modeling,
  computer simulations and experiments, as well as
  astronomical observations of other newly born
  star systems, allow us to probe through the
  depths of time to better understand the
  conditions and processes occurring in the
  earliest history of our own solar system.

3
OBJECTIVE 1 Understand conditions in the solar
accretion disk and processes marking the initial
stages of planet formation

• Investigation 1a Chemical and isotopic
  compositions of primitive meteorites and their
  components Blake.

4
OBJECTIVE 1 Understand conditions in the solar
accretion disk and processes marking the initial
stages of planet formation

• Investigation 1b Physical, chemical and isotopic
  characteristics of comets and KBOs Blake.

5
OBJECTIVE 1 Understand conditions in the solar
accretion disk and processes marking the initial
stages of planet formation

• Investigation 1c Theoretical modeling of nebular
  dynamics to account for the physical and chemical
  characteristics of primitive solar system
  materials and astronomical observations of
  accretion disks Lodders.
• Lodders The history of the solar nebula - the
  gaseous accretion disk surrounding the Sun during
  its birth plays a central role in understanding
  the origin of the solid and gaseous planets as
  well as the other small bodies in the solar
  system. Accretion disks observed around other
  young stars can provide snapshots of the physics
  and chemistry that also must have been ongoing
  when our solar system formed. Although currently
  disk observations may not yet have the spatial
  resolution necessary for detailed studies, such
  observations will give valuable tests for
  dynamical models of planet formation around young
  stars.
• The gas and dust from an interstellar molecular
  cloud went through various processes in the solar
  nebula and resulted in the formation of the Sun
  and planets. Several questions about these
  processes are still lingering unanswered. What
  are the time scales for photochemical and
  thermochemical reactions involving the compounds
  which influenced the opacity and hence the energy
  transport and mixing processes within the solar
  nebula? What is the influence of magnetic field
  driven turbulence on dynamical mixing of gas and
  dust in accretion disks? How much unprocessed
  interstellar cloud material remains in primitive
  objects such as comets and Kuiper-Belt Objects
  located in the outer solar system, and how much
  was preserved in the asteroid belt from where
  most primitive meteorites originate? What
  compounds of the life-sustaining elements carbon,
  oxygen and nitrogen were inherited by the solar
  nebula from the interstellar medium? The
  questions about the carbon and oxygen containing
  compounds are of renewed interest because recent
  spectroscopic analyses of the solar photosphere
  indicate that these elements are almost a factor
  of two less abundant in the Sun and in the
  overall solar system than previously thought.
• The relatively recent observations of gas giant
  planets quite close to a central star in other
  solar systems suggest that planets may form at
  some distance from the central star and then
  migrate inwards toward the star. By analogy, such
  processes may also have played a role in the
  solar system. If so, the gravitational tug from
  the migration of large, massive gas-giant planets
  could have influenced the accretion history
  (e.g., late accretion of volatile-rich
  planetesimals) of the terrestrial planets.

6
OBJECTIVE 1 Understand conditions in the solar
accretion disk and processes marking the initial
stages of planet formation

• Investigation 1d Theoretical modeling and
  experimental obervations of the processes
  involved in the initial stages of planet
  formation Abbas.
• Chambers modifications by Hubbard and Abbas
  The formation of planets involves a number of
  steps with different physical and chemical
  processes occurring at each stage. For the rocky
  planets, early stages involved interactions
  between dust grains and diffuse, turbulent gas in
  a microgravity environment. Later stages involved
  high speed collisions between large solid bodies
  and gravitational interactions during near
  misses. Giant planets such as Jupiter are mostly
  composed of gas but a large solid core may have
  been necessary to trigger their formation. Such
  cores would have formed in the same way as the
  rocky planets. The ice-rich giant planets Uranus
  and Neptune may be the incomplete cores of
  hydrogen-rich giant planets similar to Jupiter
  and Saturn, suggesting that the Suns primordial
  gas nebula was too tenuous or already lost when
  Uranus and Neptune formed. Gravitational
  interactions between growing planets and the
  Sun's protoplanetary nebula played a big role in
  determining the current configuration of the
  planetary system. Theoretical simulations of
  these processes and of the rate of migration of
  primordial giant planets, as affected by the
  nebula, will help us to understand the present
  and past architecture of our solar system and
  extrasolar planetary systems. However,
  theoretical models need to be based on
  observations and experimental data.
• Interpretation of observations of emissions from
  dust grains as well as modeling of the
  protoplanetary disk processes is based on
  radiative transfer models that involve
  experimental measurements of the optical
  properties. These measurements include complex
  refractive indices, and extinction properties or
  opacities of the analogs of dust grains in the
  protoplanetary disk, in particular in the
  infrared and the UV spectral regions. The dust
  grains in the disk are generally charged, and the
  grain charge influences the grain dynamics,
  grain-grain and grain-gas interactions, grain
  coagulation and evolution. Experimental
  investigations of grain charging processes by
  photoemission (photoelectric yields of micron to
  submicron size dust grains), collisions with gas
  phase electrons, and by triboelectric and contact
  charging processes are needed to provide more
  realistic information to understand and model the
  processes involved. In addition, experimental
  investigations of the growth and sticking
  efficiencies of dust grains by studying
  condensation processes of volatile gases on dust
  grains will provide valuable information for
  studies of the growth of dust grains in the early
  stages. Thus, studying dust grain sticking and
  collisions in a turbulent, low pressure gas and
  in microgravity will provide an important
  foundation for our understanding of the early
  stages of planetary growth and essential ground
  truth for computational models of planet
  formation. The processes involved in collisions
  between large solid bodies and the dispersal or
  reaccumulation of fragments can best be
  understood by observing these processes and their
  outcome in the modern asteroid belt and planetary
  ring systems. The asteroid belt bears the scars
  of many energetic collisions in its history.
  Flybys, orbiting spacecraft and sample return
  missions will tell us much about the outcome of
  violent collisions between asteroids as well as
  the gentler collision that allowed these bodies
  to accumulate from dust grains and small solids.
  Our limited understanding of planetary migration
  can be enhanced using constraints based on the
  modern orbital arrangement and chemical makeup of
  the main-belt, Trojan and Kuiper-belt asteroids.
  Current theories of planet formation infer that
  chance played an important role in determining
  the shape of the Solar System. For this reason,
  continuing efforts to detect and characterize
  extrasolar planets will improve our understanding
  of the processes involved by determining the
  range of possible outcomes.

7
OBJECTIVE 2 Learn about the earliest processes
occurring on the surfaces and interiors of
planets and minor bodies

• Investigation 2a Physical and chemical
  characteristics of asteroids and their
  relationship to meteorites ?.

8
OBJECTIVE 2 Learn about the earliest processes
occurring on the surfaces and interiors of
planets and minor bodies

• Investigation 2b Studies of ancient rocks on the
  Earth, Moon and Mars Wadhwa.
• Wadhwa The earliest processes occurring in the
  inner solar system have left their imprint on the
  rock record on the terrestrial planets.
  Unfortunately, rocks on the Earth older than
  about 3.5 billion years have been almost
  completely eradicated by processes such as
  impact, weathering, tectonics and biological
  activity. Nevertheless, although rare, there are
  still localities where rocks and minerals that
  preserve a record of the first billion years of
  Earth history may be found and petrologic,
  chemical and isotopic investigations of these
  materials can help us to understand the
  environment on the early Earth and the processes
  that shaped it. Unlike the Earth, the Moon still
  retains a substantial record of the formation of
  the Earth-Moon system. The latest computational
  models indicate that the Moon was formed by the
  energetic impact of a Mars-sized body into the
  early Earth. The Apollo and Luna samples and
  lunar meteorites are helping to elucidate some of
  this early history, but the limited regions of
  the Moon sampled by these materials restricts
  their ability to address some fundamental
  questions. For example, we still have only
  limited constraints on how the impact flux varied
  in the region of the Earth-Moon system during the
  first billion years of solar system history, even
  though this issue has important implications on
  questions relating to the environment on the
  early Earth and the timing of emergence of life
  on this planet. The South Pole-Aitken basin on
  the Moon, one of the largest impact structures in
  solar system, exposes materials from the deep
  crust and possibly the upper mantle, and provides
  an opportunity to sample materials unlike those
  that have been previously available. Moreover,
  impact melts from this structure would provide
  the opportunity to obtain a precise age of the
  basin-forming event. The ancient highlands of
  Mars also preserve a record of the earliest
  processes occurring on that planet. Remote
  analyses by spacecraft and detailed studies in
  state-of-the-art laboratories on Earth of
  returned samples of ancient Mars rocks will be
  invaluable towards a better understanding the
  earliest conditions and processes on the
  terrestrial planets.

9
OBJECTIVE 2 Learn about the earliest processes
occurring on the surfaces and interiors of
planets and minor bodies

• Investigation 2c Interior structure and
  chemical-isotopic compositions of the deep
  atmospheres of the giant planets and comparison
  with characteristics of exoplanets Hubbard.
• Lodders In our solar system, most of the
  planetary mass is in Jupiter, Saturn, Uranus, and
  Neptune. Still, their deep atmospheric
  composition as well as the interior structure
  remains poorly known. How much water do they
  contain? What is the cloud-layer structure in the
  gas-giant planets? How big are their deep cores
  and if their cores indeed exist, how and when did
  these cores form? Information on the isotopic
  composition of C, N, O, and the noble gases is
  another desired diagnostic tool to understand
  giant planet formation and evolution.
  Self-consistent models for the formation and
  evolution of all giant planets require better
  observational data of the chemical and physical
  properties that only can be provided by
  spacecraft missions. The Galileo Mission to
  Jupiter showed us that that entry-probe
  measurements can lead to valuable results but
  reliable in-situ measurements of the abundances
  of methane, ammonia, water, the noble gases,
  compounds containing elements such as e.g.,
  sulfur and phosphorus, are required for all outer
  planets to build a solid base for models of giant
  planet formation in the outer solar system.
• Hubbard We now have our first measurements of
  atmospheric compositions in giant planets
  orbiting other stars. Interpretation of these
  measurements depends on many poorly understood
  processes such as cloud formation, deep
  convection and local weather, and effects of
  irradiation from the parent star. The same
  processes are at work in the atmospheres of our
  own giant planets. Some hot exoplanets may even
  have observable silicate clouds analogous to
  those thought to be buried deep in the
  atmospheres of our own giant planets, together
  with more easily observable water vapor.
  Definitive measurement of Jupiters deep water
  abundance is needed to understand the formation
  processes for giant planets, and will soon be
  needed for comparison with exoplanet
  measurements. While the highly successful
  Galileo probe gave us our first look at Jupiters
  atmospheric chemistry, it did not reach high
  enough pressures to definitively measure water, a
  key tracer of Jupiters formation.
  Interpretation of the probe data was complicated
  by local meteorology, and at the deepest levels,
  the probes interior temperature was far higher
  than planned. The available Jupiter probe
  abundance results are a puzzling combination of
  some values that are higher than expected (e.g.,
  noble gases that are indicative of
  low-temperature enrichment processes) and some
  that are much lower than expected (e.g., the
  noble gas neon). However, the probe confirmed an
  important result from interior modeling studies,
  namely that Jupiters envelope is enhanced in
  elements heavier than hydrogen and helium. The
  next step in experimentally understanding these
  results is to probe Jupiters atmosphere again,
  preferably at locations that have varying
  meteorology, as well as to deeper levels, say to
  about 100 bars. Similarly, it is essential to
  make comparable measurements in the atmospheres
  of our other three giant planets. New revisions
  of abundances of the elements carbon and oxygen
  in the Sun itself are upsetting the paradigm for
  the interior structure of the Sun and its helium
  abundance, and it is certain that comparable
  measurements in our giant planets and extrasolar
  giant planets will lead to far-reaching and
  revolutionary changes in our understanding of
  planetary formation and evolution.