Water in Exoplanets: Can we learn from our Solar System? Fred Ciesla Department of the Geophysical Sciences The University of Chicago

Gerard Kuiper

What about Life?

Water = Habitability

Mystery of Earth s Water Earth is 0.05-1% water by mass Planetary materials at 1 AU are expected to have been totally dry. Question: What was the source of Earth s water? Should we expect similar sources to be available for extrasolar planets?

An Artist s View

Large, nearby disks can be resolved Always large scales are probed (0.1 to hundreds of AU) Only Certain Disk Regions are Observable: Different Wavelengths/Technique probe different disk regions Optical/infrared: only disk surface AU Mic Debris Disk

An Astronomer s View

A Planetary Scientist s View

Comets

Asteroids

Chondrites as Primitive Bodies

Formation of the Earth

The Snow Line Solids: 100% Rock Solids: 40% Rock 60% Ice Water exists as vapor Water exists as solid ice

The Snow Line Solids: 100% Rock Solids: 40% Rock 60% Ice Water exists as vapor Water exists as solid ice T~160 K

The Snow Line Solids: 100% Rock Solids: 40% Rock 60% Ice Water exists as vapor Water exists as solid ice T~160 K Habitable Zone: 273-373 K (approximately)

Temperatures in the Solar Nebula Two sources of heat: Internal dissipation during disk evolution Irradiation from the Sun

Structure of our Solar System

Structure of our Solar System Snow Line Minimal Water Abundant Ice

Possible Water Carrier: Comets

Possible Water Carrier: Comets As planets accreted from asteroid and comet-like planetesimals, could the Earth have accreted materials from beyond the snow line?

Possible Water Carrier: Comets As planets accreted from asteroid and comet-like planetesimals, could the Earth have accreted materials from beyond the snow line? Probability of comet from beyond Jupiter hitting the Earth is very low: 10-6 under optimistic assumptions. In order to get 0.05% of Earth s mass (water content) as being from comets, that means ~500 Earth masses of comets were needed as ammunition.

Deuterium As a Fossil Hydrogen (H) is the most abundant element Deuterium (D) has an abundance 100,000 times below that of hydrogen (relic from big bang) at low temp. (T < 50 K) chemistry favors transfer of D as opposed to H if T < 50 K then HDO/H2O > D/H if T > 50 K then HDO/H2O = D/H

D/H Ratios in the Solar System 10-3 D/H 10-4 10-5

D/H Ratios in the Solar System 10-3 D/H 10-4 10-5 Any water on this line formed at T > 50 K

D/H Ratios in the Solar System 10-3 Formed at least in part at T < 50 K D/H 10-4 10-5 Any water on this line formed at T > 50 K

D/H Ratios in the Solar System 10-3 Formed at least in part at T < 50 K D/H 10-4 10-5 Any water on this line formed at T > 50 K Earth water (SMOW) partially formed at very low temperatures - T < 50 K

Carbonaceous Chondrites 1-10% water by mass Water is locked up in hydrated silicates and clays Form from the reaction of anhydrous rock and liquid water D/H Ratio matches Earth s Parent bodies appear to be largely relegated to the outer asteroid belt Roughly 2.5-4 AU

Water Ice at Late Times

Water Ice at Late Times Chondrite Formation Period

Water delivery from Wet Asteroids

Mystery Solved? While these models produce planets that are Earth-like they do not produce planets that are Mars-like.

A More Dynamic Origin (I)

A More Dynamic Origin (II)

A More Dynamic Origin (III)

A More Dynamic Origin (IV)

A More Dynamic Origin (V)

A More Dynamic Origin (V) Earth s water brought in by objects formed in the giant planet region! Comets again?

New Comet Data 10-3 D/H 10-4 10-5

Seriously...Really New!

So...where are we? Our story for the formation of the solar system is evolving. The origin of Earth s water remains a mystery. There are many theories, all of which have their merits. Can we say anything about Extrasolar Planets?

What Would this Mean for Planets around Other Stars?

Lower Mass Stars: More Common, Less Luminous 0.6 M

Important Questions How is water locked up into planetesimals? Why does the water abundance in planetesimals vary with location in the manner that it does? How do the different water delivery mechanisms operate around different stars? If we want to think about habitability, how much water do we need? Impacts climate, plate tectonics, geologic activity of planet, ability of life to form/sustain

Getting Answers... Probe the 0.1-10 AU region of protoplanetary disks around young stars to characterize the physical and chemical environments in which planets form. Characterize the ices that exist in disks and how they vary with location. Where is the snow line in disks around stars of different types? Identify the planetary architecture of solar systems outside of our own.

Observing Extrasolar Planets The chemical composition of a planet and its atmosphere reflects the influences of: Chemical and physical processes in the protoplanetary disk Accretionary processes Planetary Differentiation Atmosphere-condensed phase-crustal interactions Geologic Activity Photochemical Processes (Stellar Irradiation) Biologic Activity

Optimism and Pessimism

Changes in Stellar Luminosity M Lifetime of Protoplanetary Disks and Duration of Planetesimal Formation 0.6 M 0.2 M

Trying to tell...