What is the geophysical evolutionary history of terrestrial planets of different sizes and compositions?
What are the consequences for astrobiology!
Explanation: Geophysical evolution of a terrestrial planet will be a major control on its climate, atmospheric composition, and surface volatile inventory. Terrestrial planets (and moons) are expected to range in size, composition, magnetic, gravitational, and orbital parameters. Understanding how such bodies evolve over timescales of billions of years will allow us to understand the conditions to be expected on them.
Justification (why do we care): Understanding the geophysical evolution of the planets will allow us to understand critical aspects of potential habitability from a fundamental perspective.
High Level Geophysical Questions
! How does the Earth work? ! What can we learn from comparative planetology? ! What are the properties of planets in stellar HZs? ! What are the properties of Earths & Super Earths around other stars? ! What are the properties of rocky terrestrial moons in gas giant HZs? ! What can be learned from “Super-Ios” around other stars? ! Are there geophysical consequences for planets around non-Sol class stars?
Solar Energy Inner Solar System! & Around Gas Giants Radiation Sputtering & Meteorite Gardening
What is the composi-on of an Exoplanet? low C/0
Earth
Solar C/O
high C/O
Bond et al., 2010
! The Earth’s Solid Inner Core formed ~1 Gyr ago ! Changed the evolution of the magnetic field with time ! Strange coincidence that the time for the inner core to form is comparable to the main sequence lifetime of the sun!
Figure from P. Driscoll (UW)
Earth with different amounts of Radiogenic Heating
Young et al., submiEed
Rc/Rp = ratio between core radius & planet radius.
remnant magnetism
Earth Rc/Rp = 0.5 Intrinsic strong dipole magnetic field
Hopelessly confusing picture Induced magnetic field Intrinsic dipole magnetic field Induced magnetic field
Consequences? Magnetic fields? Differentiation? Core heat longevity?
remnant magnetism
Rc/Rp = 0.7 NO magnetic field
Intrinsic weak dipole magnetic field
Internal heat loss occurs both by conduction AND by convection of interiors………
Mars
Thin lithospheres produce shallow convection where lithospheric slabs are continually created and consumed as they shift about driven by gravity, as on Earth… But what about other “styles” of interior? Can they also produce a recycling mechanism over geological time that can sustain habitability?
Titan
Inner rocky core Liquid layer Outer ice rock crust
Tidal Heating of Super-Earths of VB* 10 (0.08 solar mass star) HZ -‐>
Tidal Venus
Tidal Earth
*Van Biesbrock’s Star (a Red M Dwarf)
Venus Barnes et al., 2013 Barnes & Heller, 2013
Earths
Density Case 1: Planet with the density of Neptune
Gravity Geophysical Considerations ! Effects on Tectonics? ! Effects on Orogeny? ! Effects on Weather Patterns? Consequences ! Effects on Hydrology? ! Effects on Weathering Processes? ! Effects on Depth of Critical Zone? ! Effects on Organisms?
Mass and density were defined as the first two columns, then radius calculated from there (using required volume for mass and density). Surface gravity calculated using the radius of the planetary case, then put in terms of gE for perspective.
Hansen & Boston, 2014, work in progress
Important Questions How does the Earth work? ! How does Plate Tectonics work? ! ! ! !
How does the carbon cycle operate? Why is the Earth ~50/50 land/water? How did Earth evolve from a magma ocean through runaway greenhouse into plate tectonics? What is the Urey ratio (radiogenic heating/other heating)?
What can we learn from comparative planetology in the Solar System? ! ! ! !
Why are Earth and Venus so different, yet so similar? Why does Venus have no magnetic field? What causes differences between stagnant lid/plate tectonics/ advective volcanism? How do tectonics on icy satellites operate?
What can be learned from “super-Ios”, “exo-Enceladus’s”, etc. around other stars’ gas giants? ! If actively outgassing, can we observe the volcanic species? Water vapor? Etc. ! !
Are they proxies for planets in the HZ? Can we distinguish evaporated (i.e. having lost a significant volatile envelope) worlds from those that are primordially rocky?
Important Questions What are the geophysical properties of planets in exoplanet HZs that have significant consequences for astrobiology? ! Are they carbonate or silicate? – depends on properties of disk and formation ! ! ! ! ! ! ! ! !
How do metallic silicates affect evolution of super-Earths? For low-mass stars, how does tidal heating affect interiors? How does synchronous rotation affect dynamo? How much radiogenic heating is available? Can we classify planets based on the properties of the planetary system? How important is history for current properties? How does stellar composition map to planetary composition? How do “water world” interiors operate? How do very dry (but habitable) planet interiors operate?
What is the geophysical evolutionary history of ...
Inner Solar System. Radiation Sputtering. & Meteorite Gardening. Inner Solar System. & Around Gas Giants. Core Formation. Accretionary Heating. Solar Energy.
Some of these host species show the same disjunct distribution patterns observed in T. acutifolius, particularly in the dry seasonal forests of South America. (Prado and Gibbs 1993). The differentiation of the two clades of T. acutifolius recovered i
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