ast202: the universe: contents, origin, evolution and ...mischak/teaching/universe/fs2017/... ·...

Origin of oceans and waterworlds

AST202: The Universe: Contents, Origin, Evolution and Future

https://water.usgs.gov/edu/gallery/global-water-volume.html

Nadia Boppart & Sascha Hablützel 21.03.2017

Ocean forming Origin of H2O Introduction Waterworlds Summary

Some facts ¾ 71 % of the Earth’s surface is covered by oceans

• compared to other terrestrial planets in our solar system

¾ Earth: ME = 6.0 * 1024 kg ¾ Oceans: MOce = 1.37 * 1021 kg (0.023 wt%) ¾ With other water reservoirs and Earth mantel &

core mass fraction does not exceed 2 wt% • Other water reservoirs: M = 5 * 1020 kg

Where did the water come from?

(Genda, 2016; Mottl et al., 2007) https://water.usgs.gov/edu/gallery/global-water-volume.html [changed]

Ocean Other reservoirs Drinking water


Oceans have existed since the very early stage of the Earth’s history

¾ The oldest pillow lavas was formed at 3.7-3.8 Ga • characterized by pillow-shaped masses

→ formed when hot lava flows into water and cools rapidly

¾ Hadean zircon (ZrSiO4; mineral) have high oxygen isotope values • produced by low-temperature interactions

between rocks and liquid water • Zircon has an ages of 3.91 to 4.28 Ga

(Appel et al., 1998; Mojzsis et al., 2001; Wilde et al., 2001)

Hidenroi, 2016


H2O is abundant in our solar system ¾ Hydrogen / Oxygen are the most / the third most abundant element in the

universe ¾ In the protoplanetary disk there were numerous H2O molecules

• 2-3 times the mass of the rocks and iron

¾ Distance to the central star (e.g. sun) is the most important factor determine the stability of liquid water on a planetary surface • If orbiting close to a star all liquid water will be vaporized due to the runaway greenhouse

effect of water vapor → Earth with no greenhouse gases would have a temperature of -15 °C and be fully covered with ice

The adequate distance from the sun and a suitable amount of

greenhouse gases in the atmosphere have made Earth habitable

(Anders & Ebihara, 1982; Kasting et al., 1993; Petigura & Marcy, 2011)


Three stages to build up a planet ¾ Planets are formed in a protoplane-

tary disk (nebular disk) around a star

(Armitage, 2011)

Star

Jovian planet region Terrestrial planet region

* Not part of the presentation


Three stages to build up a planet ¾ Formation of rocky / icy

planetsimal by accretion of dust particles • Snowline = boundary between

condensation and vaporization of H2O

(Armitage, 2011; Cuzzi et al., 2008; Genda et al., 2015)

Star




Three stages to build up a planet ¾ Planetsimal collisions produce

proto-planets • rocky Mars-sized within the terrestrial

planet region • Icy protoplanets within the Jovian planet

region

(Tanaka & Ida, 1997)

Star




Three stages to build up a planet ¾ Icy planetsimal forming outer

planets by either attract nebular gas or not

¾ Giant impacts forming terrestrial planets • collisions among rocky protoplanets

(Agnor et al., 1999; Chambers & Wetherill, 1998; Kokubo & Genda, 2010; Mizuno, 1980; Pollack et al., 1996)

Star



Hidenroi, 2016 [changed]


Star

Planetsimals with surface Oceans

¾ Recent models suggest that snow line moves with time, and so may have been temporarily located inside 1 AU

¾ Rocky protoplanets might have had surface oceans • Therefore the building Earth had already small amounts of water

¾When planet grows to lunar size (~1023 kg) water will begin to degas • a significant steam atmosphere was formed

→ followed by the formation of oceans

Earth would have originated as wet planet

(Kasting et al., 1993; Matsui, 1986; Oka et al., 2011; Sasselov & Lecar, 2000; Zahnle et al., 1988)



Comets as an external source of water

¾ Gravitational disturbance of the asteroid belt region by Jupiter • large fraction of asteroids is ejected

→ Some of which collide with Earth

¾Migration of Uranus & Neptun result in the scattering of icy planetesimals • number of these bodies have entered the terrestrial planet region

→ Considered to be responsible for the late heavy bombardment around 4 Ga

¾ Comets consist of 80 wt% of water • the accretion of these objects could only provide 1% of Earth’s mass

→ high noble gas concentration would significantly affected the noble gas budget on Earth

Amount of water supplied to Earth by comet is likely been minor

(Dauphas, 2003; Gomes et al., 2005; Morbidelli et al., 2000)



Carbonaceous chondrites

¾ The idea based on the late-veneer hypothesis • Originally proposed to explain the excessive concentration of highly siderophile elements

(HSEs) in the Earth’s mantle → Ru, Rh, Pd, Re, Os, Ir, Pt and AuCarbonaceous chondrites and comets have ~ 5 wt% and 80 wt% water, respectively, the

accretion of these objects to provide only 1% of Earth’s mass is sufficient ot have contributed the present ocean mass

¾ The relative abundance of HSEs in the Earth’s mantle is similar to that in carbonaceous chondrites

¾ 80 wt% Carbonaceous chondrites consist of water

Amount of water supply is sufficient to make up the present ocean mass

(O’Neill & Palme, 1998)



Star Nebular gas ¾ Protoplanetary disk (nebular disk) will gravitationally attract the

surrounding gas • generating a hydrogen-rich atmosphere

¾ Oxygen and hydrogen would have formed water molecules on the planetary surface • supplied from oxides in the Earth’s interior

¾ Under the assumption of a magma ocean and a large quantity of hydrogen a mass comparable to that of the present Earth’s oceans would result Generation of water by gravitationally attracted hydrogen-rich nebular

atmosphere

(Hayashi et al., 1979; Mizuno, 1980; Pollack et al., 1996)



D/H ratios as a hunt for the origin of water

¾ Ice grains are highly enriched in deuterium (D/H ratio ~10-2) • synthesized in the interstellar medium through ion-molecule reactions

¾ After the entrance into the protosolar nebula ice grains get vaporized • D/H ratio was lowered through isotopic exchange with molecular hydrogen

¾ Later decreasing temperature lead to new condensed microscopic icy grains • with decreasing D/H ratios the closer they were to the Sun

D/H ratio in various planetary materials can give

exceptional insights into the origin of Earth’s water

(Brown & Millar, 1689)

http://www.differencebetween.info/sites/default/files/images/heavy-water.jpg


D/H ratios as a hunt for the origin of water ¾Model predict D/H ratio at Earth’s distance ~ 0.8 * 10-4

• ratio on Earth is 1.56 *10-4

Terrestrial water must have been imported from the coldest regions of the solar system

(Brown & Millar, 1689)

Star

decreased increased D/H ratio

Hidenroi, 2016 [changed]


D/H ratios as a hunt for the origin of water

Earth’s oceans were likely supplied by carbonaceous chondrites

(Dauphas, 2003; Hidenroi, 2016; Morbidelli et al., 2000)

Earth-forming planetesimals Protosolar nebula Carbonaceous chondrites (meterorites) Comets

Theory Earth would have originated as wet planet

Gravitational attraction of hydrogen-rich nebular

atmosphere

Formed beyond the orbit of Jupiter and then moved

inward to the Earth

Disturbance of asteroid belt by Jupiter lead to colliding

asteroids

D/H ratio (10-4) ? ~ 0.17 * 1.56 1.3-1.7 ~ 2 * 1.56

Result Too very small amount of water currently on Earth

inconsistent with some geochemical constraints

observed in Earth

Amount of water supply is sufficient to make up the

present ocean mass

Amount of water supply is to minor, noble gas budged

would be significantly affected


Why are our oceans salty?

¾ Rocks ¾ Erosion by acid rain

• carbon dioxide is dissolved

¾ Ions created and transported to oceans ¾ Increase in concentration over time ¾ Sodium and Chloride make up to 90% of

the «salty» Ions

(oceanservice.noaa.gov)

http://static7.depositphotos.com/1028580/780/i/950/depositphotos_7800909-stock-photo-eroded-stones-in-the-black.jpg



Waterworlds – how would it be?

¾ Entirely covered by water ¾ Double the size of our Earth ¾Metallic core (8000 km diameter) ¾Mass up to 6 x denser than our Earth ¾ Depth up to 25 times bigger than our

oceans ¾ Dense atmosphere ¾ High pressure!

(www.spacesciencejournal.de)

http://www.spacesciencejournal.de/Astrobiologie/real_waterworld.html


Water – States of matter

¾ Ice under water - high pressure up to 5000 km width

https://upload.wikimedia.org/wikipedia/commons/thumb/3/34/Phase-diag2.svg/350px-Phase-diag2.svg.png


Stable Climates in Waterworlds

¾ globally ice covered: < -28,15 °C ¾ cold and damp: -3.15 °C - 16.85 °C ¾ hot and moist: 76.85 °C - 276.85 °C ¾ very hot and dry: > 626.85 °C

No stable climate exists for 16.9⪅TS ⪅76.9 °C or 276.9⪅ TS ⪅676.9 °C

(Goldblatt, 2015)


Discovery

¾ Provided its sun is cooler than ours and the angle to us is right: EDDINGTON telescope can measure the weakened shine of sunlight up to planets having at least half the radius of our planet (like Mars)

http://www.esa.int/var/esa/storage/images/esa_multimedia/images/2003/04/artist_s_impression_of_eddington2/

9767387-3-eng-GB/ Artist_s_impression_of_Eddington_node_full_image_2.jpg

http://www2.astro.psu.edu/users/rbc/a1/lec32_f5. jpg


Take home message

¾ Oceans have existed since the very early stage of the Earth’s history ¾ Earth’s oceans were likely supplied by carbonaceous chondrites ¾ Origin of the Earth’s water is not so simple if other geochemical

constraints are considered • Xe/Kr ratio on Earth are much lower than that in any of the C. chondrites

¾ There is no evidence of live and habitability on waterworlds ¾ Some technical progress is necessary


Summary as a video

Where Did Earth's Water Come From? https://www.youtube.com/watch?v=_LpgBvEPozk



References ¾ Agnor, C. B., Canup, R. M., & Levison, H. F. (1999). On the character and consequences of large impacts in the late stage of

terrestrial planet formation. Icarus, 142(1), 219-237. ¾ Anders, E., & Ebihara, M. (1982). Solar-system abundances of the elements. Geochimica et Cosmochimica Acta, 46(11), 2363-

2380. ¾ Appel, P. W., Fedo, C. M., Moorbath, S., & Myers, J. (1998). Recognizable primary volcanic and sedimentary features in a low-

strain domain of the highly deformed, oldest known (∼ 3.7–3.8 Gyr) Greenstone Belt, Isua, West Greenland. Terra Nova, 10(2), 57-62.

¾ Armitage, P. J. (2011). Dynamics of protoplanetary disks. Annual Review of Astronomy and Astrophysics, 49, 195-236. ¾ Chambers, J., & Wetherill, G. (1998). Making the terrestrial planets: N-body integrations of planetary embryos in three

dimensions. Icarus, 136(2), 304-327. ¾ Cuzzi, J. N., Hogan, R. C., & Shariff, K. (2008). Toward planetesimals: Dense chondrule clumps in the protoplanetary nebula. The

Astrophysical Journal, 687(2), 1432. ¾ Dauphas, N. (2003). The dual origin of the terrestrial atmosphere. Icarus, 165(2), 326-339. ¾ Genda, H. (2016). Origin of Earth’s oceans: An assessment of the total amount, history and supply of water. Geochemical Journal,

50(1), 27-42. ¾ Genda, H., Fujita, T., Kobayashi, H., Tanaka, H., & Abe, Y. (2015). Resolution dependence of disruptive collisions between

planetesimals in the gravity regime. Icarus, 262, 58-66.


References ¾ Goldblatt, C. (2015). Habitability of waterworlds: runaway greenhouses, atmospheric expansion, and multiple climate states of

pure water atmospheres. Astrobiology, 15(5), 362-370. ¾ Gomes, R., Levison, H. F., Tsiganis, K., & Morbidelli, A. (2005). Origin of the cataclysmic Late Heavy Bombardment period of the

terrestrial planets. Nature, 435(7041), 466-469. ¾ Hayashi, C., Nakazawa, K., & Mizuno, H. (1979). Earth's melting due to the blanketing effect of the primordial dense atmosphere.

Earth and Planetary Science Letters, 43(1), 22-28. ¾ Kasting, J. F., Whitmire, D. P., & Reynolds, R. T. (1993). Habitable zones around main sequence stars. Icarus, 101(1), 108-128. ¾ Kokubo, E., & Genda, H. (2010). Formation of terrestrial planets from protoplanets under a realistic accretion condition. The

Astrophysical Journal Letters, 714(1), L21. ¾ Matsui, T. (1986). Evolution of an impact-induced atmosphere and. Nature, 319, 23. ¾ Mizuno, H. (1980). Formation of the giant planets. Progress of Theoretical Physics, 64(2), 544-557. ¾ Mojzsis, S. J., Harrison, T. M., & Pidgeon, R. T. (2001). Oxygen-isotope evidence from ancient zircons for liquid water at the

Earth's surface 4,300 Myr ago. Nature, 409(6817), 178-181. ¾ Morbidelli, A., Chambers, J., Lunine, J., Petit, J., Robert, F., Valsecchi, G., & Cyr, K. (2000). Source regions and timescales for the

delivery of water to the Earth. Meteoritics & Planetary Science, 35(6), 1309-1320. ¾ Mottl, M. J., Glazer, B. T., Kaiser, R. I., & Meech, K. J. (2007). Water and astrobiology. Chemie der Erde-Geochemistry, 67(4), 253-

282.


References ¾ O’Neill, H. S. C., & Palme, H. (1998). Composition of the silicate Earth: implications for accretion and core formation. The Earth’s

Mantle: Composition, structure and evolution, 1. ¾ Oka, A., Nakamoto, T., & Ida, S. (2011). Evolution of snow line in optically thick protoplanetary disks: effects of water ice opacity

and dust grain size. The Astrophysical Journal, 738(2), 141. ¾ Petigura, E. A., & Marcy, G. W. (2011). Carbon and oxygen in nearby stars: keys to protoplanetary disk chemistry. The

Astrophysical Journal, 735(1), 41. ¾ Pollack, J. B., Hubickyj, O., Bodenheimer, P., Lissauer, J. J., Podolak, M., & Greenzweig, Y. (1996). Formation of the giant planets

by concurrent accretion of solids and gas. Icarus, 124(1), 62-85. ¾ Sasselov, D., & Lecar, M. (2000). On the snow line in dusty protoplanetary disks. The Astrophysical Journal, 528(2), 995. ¾ Tanaka, H., & Ida, S. (1997). Distribution of planetesimals around a protoplanet in the nebula gas. Icarus, 125(2), 302-316. ¾ Wilde, S. A., Valley, J. W., Peck, W. H., & Graham, C. M. (2001). Evidence from detrital zircons for the existence of continental

crust and oceans on the Earth 4.4 Gyr ago. Nature, 409(6817), 175-178. ¾ Zahnle, K. J., Kasting, J. F., & Pollack, J. B. (1988). Evolution of a steam atmosphere during Earth's accretion. Icarus, 74(1), 62-97.


Websites ¾ https://de.wikipedia.org/wiki/Ozeanplanet [visited: 18.03.2017] ¾ http://oceanservice.noaa.gov/facts/whysalty.html [visited: 07.03.2017] ¾ http://www.spacesciencejournal.de/Astrobiologie/real_waterworld.html [visited: 18.03.2017]

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