Origins, Worlds, and Life A Decadal Strategy for Planetary Science and Astrobiology 2023-2032 (2022) / Chapter Skim
Currently Skimming:
2 Tour of the Solar System: A Transformative Decade of Exploration
2 Tour of the Solar System: A Transformative Decade of Exploration
Pages 28-96
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 29... ...
Because of its orbit close to the Sun, Mercury has experienced more intense impact bombardment than anywhere else in the solar system, and impactors strike the surface at an average velocity at least three times that of the Earth-Moon system. However, in contrast to the expectation of a heavily cratered surface, PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-2
|
From page 34... ...
Using estimates of the impact flux and composition of planetesimals, models of the rate of accretion of materials to Earth tend to predict formation ages for the Moon that are substantially younger than other methods -- as much as ~100 million years after the formation of the solar system. Determining the formation time of the Moon is PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-7
|
From page 36... ...
If these features are confirmed to be related to recent eruptions, the occurrence of such young volcanism implies that the lunar mantle was warmer than previously thought, and/or that heterogeneous or localized concentrations of radioactive elements allowed for small-scale eruptions to continue late into lunar evolution. In addition, silicic volcanism appears to be more prevalent PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-9
|
From page 37... ...
Terrestrial ground-based monitoring of the Moon has also captured impact flashes associated with impacts, and direct observations of the dusty ejecta from small impacts seen by LADEE. Integrating these observations has led to a revised picture of the rate at which the uppermost surface of the Moon is gardened, and emphasized the importance of high frequency, small PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-10
|
From page 39... ...
Whereas previous data were ambiguous as to the form in which hydrogen is present, results from Moon Mineralogy Mapper data confirm for the first time that at least some polar H is present as H2O. Numerical modeling indicates that volatiles are also thermodynamically stable beneath the surface in areas of temporary sunlight near the lunar poles, and in micro-cold traps at higher PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-12
|
From page 40... ...
LADEE also confirmed the presence of argon-40 and helium, found neon in comparable PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-13
|
From page 42... ...
Later PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-15
|
From page 44... ...
That same mission saw short-lived, highly localized increases in surface temperature in regions of the planet interpreted with Magellan data to be where the crust has pulled apart; some of the most concentrated areas of volcanic activity on Earth are in such rift zones. And Pioneer Venus recorded a dramatic reduction in the abundance PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-17
|
From page 45... ...
Venus Express found that the largest PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-18
|
From page 46... ...
And no magnetometer-equipped mission has flown sufficiently close to or landed on the planet to determine if the crust preserves any record of an ancient Venus dynamo. Establishing whether the planet once generated its own magnetic field would help us PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-19
|
From page 48... ...
. Another discovery was the magnetization of the Venus PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-21
|
From page 49... ...
Venus has a particularly critical role to play in guiding our interpretations of exoplanet data, because although Venus-analog worlds will likely be one of the most common classes of planets observed by Webb, they may also be one of the most difficult types of world to interpret correctly if they, too, possess a global cloud layer that blocks the bulk of the atmosphere from view. To understand the chemical signatures of gases and aerosols detected in the atmospheres of those planets, then, we will need to understand the PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-22
|
From page 51... ...
It is the only PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-24
|
From page 53... ...
, for certain times of the year over parts of the planet. Temperature PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-26
|
From page 54... ...
Although we have known about dust storms for over a century, improved observations and continuous monitoring over the last decade have resulted in greater understanding of how they begin and evolve, and of annual patterns in when and where they occur. Global PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-27
|
From page 55... ...
. When these ice deposits were emplaced, whether they represent a one-time deposition or a PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-28
|
From page 56... ...
Recent advances in three-dimensional climate modeling have confirmed that CO2 and H2O alone are insufficient to warm early Mars, even with a much thicker early atmosphere. However, two recent approaches have demonstrated the viability of PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-29
|
From page 60... ...
Curiosity was also able to characterize daily, as well as seasonal, timescales PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-33
|
From page 61... ...
More dynamic activity occurs on Mars today than was previously known, including migrating sand dunes, recurring slope lineae formation, changing ice landforms, methane PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-34
|
From page 63... ...
As the giant planets grew, they traded angular momentum with the gas disk, allowing them to move to new locations. As a consequence, small bodies from the terrestrial planet and giant planet zones were injected into the asteroid belt.
|
From page 64... ...
Antarctica continues to be a major collection area for discovering new extraterrestrial samples, with (right) the experimental dust collection station collecting interplanetary dust PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-37
|
From page 65... ...
FIGURE 2.19 The orbits of the most distant trans-Neptunian objects in the solar system are shown. The magenta orbit is one possible orbit for a distant, as-yet undiscovered, giant planet that dynamical PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-38
|
From page 66... ...
In particular, Rosetta monitored the comet's evolution during its closest approach to the Sun and beyond, providing new insights into the geologic features, surface properties, active PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-39
|
From page 68... ...
In the last decade, there have been multiple new studies investigating an alternate origin for the martian moons -- formation from a giant impact into Mars. Giant impacts have been recognized as important events across the solar system, including with the PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-41
|
From page 69... ...
and will return with at least several hundred grams to Earth in PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-42
|
From page 70... ...
Constraints on the strength of such forces have been estimated by astronomical observations of active asteroids, buttressed by in situ measurements from the Hayabusa2 and OSIRIS-REx missions. These two missions have further expanded our insight into rubble pile bodies by providing our first direct estimate of PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-43
|
From page 71... ...
This event was identified using lunar impact spherules returned by the Apollo astronauts and the calculated PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-44
|
From page 72... ...
As analytical techniques continue PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-45
|
From page 74... ...
There are many similarities among the giant planets: all appear to have interiors dominated by a large, dense core; deep, dynamic hydrogen/helium atmospheres; multiple satellites, some of which suffer additional heating by tidal dissipation to have subsurface oceans; multiple rings that interact with small moons; and substantial magnetospheres. The Galileo, Cassini, and Juno missions have shown that the interior structures of gas giants, Jupiter and Saturn, are far more interesting and complex than expected, and have advanced our understanding of their atmospheres, magnetospheres, satellite, and ring systems.
|
From page 77... ...
In addition, the deep interiors of the giant planets serve as natural laboratories for materials at high-pressures and temperatures, as a result, constraining the interiors of the outer planets is also of interest to the high-pressure physics community. Finally, the planets in the solar system serve as prototypes for exoplanetary science.
|
From page 78... ...
Knowledge of the fluxes and heat transport mechanisms within the outer planets can reveal information not only on their evolution and structure, but also on the link between the atmosphere and deep interior. The existence and nature of the magnetic fields provide important observational constraints on the present-day interior structure and dynamics of the outer planets.
|
From page 79... ...
Understanding the magnetic fields of the giant planets is not only crucial for putting constraints on the composition, but also on the heat transport mechanisms within the planets and the interplay between rotation, interior, and dynamics. Magnetospheres Jupiter's magnetosphere -- sphere of influence of its magnetic field -- is the largest planetary structure in the solar system, 10 times the volume of the Sun and stretching out past the orbit of Saturn.
|
From page 80... ...
Satellite systems can also preserve the non-gaseous composition of the planets and solar nebula in the region they formed. The satellite systems of the giant planets reveal four very different outcomes of planet formation processes and the subsequent dynamical evolution that can modify or disrupt them, as recorded in their surface features and crater populations.
|
From page 81... ...
Triton appears to be a near twin of Pluto but has experienced a very different dynamic and geologic history. Astrobiological Potentials of Giant Planet Moons Three key ingredients required to support life on Earth are liquid water, source(s)
|
From page 82... ...
Those in closer orbits are being studied by Hubble, and soon James Webb Space Telescope, to understand what their atmospheres are made of. This makes comparison with the detailed studies of our own giant planets especially valuable.
|
From page 83... ...
. Increased seasonal storms PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-56
|
From page 84... ...
(2019) : 1046-1051, DOI: 10.1126/science.aat3760 OCEAN WORLDS AND DWARF PLANETS In addition to Earth, we have identified over 20 worlds throughout the solar system that may once have had or currently support large liquid water oceans.
|
From page 85... ...
In the following subsections, the committee describes major discoveries made in the past decade and list outstanding questions in planetary sciences and astrobiology associated with ocean moons of the giant planets and dwarf planets found in both the inner and outer solar PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-58
|
From page 86... ...
Ocean Moons Among the confirmed ocean worlds are the Jovian satellites Europa and Ganymede, as well as the Saturnian satellites Enceladus and Titan. Candidate ocean worlds, where ocean presence is not confirmed but available evidence can best be interpreted as due to an ocean, include Jupiter's satellite Callisto, Saturn's satellite Dione, and Neptune's satellite Triton.
|
From page 87... ...
. Perhaps relatedly, pockets of liquid water, from which the plume material may be sourced, may be perched within the ice shell above the subsurface ocean.
|
From page 89... ...
Determining if Titan's ocean is interacting with its rocky core would provide a key constraint on the habitability of large ocean worlds both within and beyond the solar system. Global high-resolution imaging and topography would allow us to use Titan's surface and climate system as a natural laboratory; for instance, to study how planetary-scale PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-62
|
From page 90... ...
Ganymede and Callisto Initial studies of Ganymede's ocean suggested that a layer of high-pressure ice, likely sandwiched between the rocky core and subsurface ocean, would significantly limit water-rock interaction, and hence limit the ocean's habitability potential. Recent modeling work, however, suggests that not only is exchange PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-63
|
From page 91... ...
suggest that tidal energy could maintain a subsurface ocean to PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-64
|
From page 92... ...
As a result, these two dwarf planets have been studied intensively, and both are now also regarded as candidate ocean worlds (see below)
|
From page 95... ...
Exploration of the Ice Giant Systems, Uranus and/or Neptune, remains a priority and would provide an opportunity to confirm the presence or absence of subsurface oceans on the larger Uranian satellites and Triton. A Titan orbiter would provide critical context to extend Dragonfly's regional exploration to global-scale, while a lake probe would provide in situ exploration of an environment inaccessible to Dragonfly and directly assess the potential habitability of the liquid PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-68
|
From page 96... ...
doi:10.1146/annurev-astro-081817-051935 PREPUBLICATION COPY – SUBJECT TO FURTHER EDITORIAL CORRECTION 2-69
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.