METEO 466 Planetary Atmospheres

Reading for this week 1.Habitable Planet, Chapters Chambers, EPSL (2004) –Available from class website on Angel 3.Grad students (ABIOL 574) only –Tsiganis et al., Nature (2005) –Gomes et al., Nature (2005) –Walsh et al., Nature (2011)

The nine planets of the Solar System Ref.: J. K. Beatty et al., The New Solar System (1999), Ch. 2. eight No Pluto!

Gas giants Ice giants Terrestrial planets Solar System planet types

Our home planet, Earth Earth is by far the most interesting planet because it harbors life, including us Planets with liquid water on or beneath their surfaces are possible homes for carbon-based life

Special properties of H 2 O Strong dipole moment has several useful consequences –Good solvent for polar molecules –Hydrogen bonding in DNA –High heat capacity  helps moderate climate on planets (like Earth) with large oceans –The solid is less dense than the liquid, i.e., ice floats! All of this leads to the concept of the habitable zone around stars…

The (liquid water) habitable zone

Question: Why is Earth’s climate stable? Possible answers: 1.Stabilizing, largely abiotic feedback processes (e.g., carbonate-silicate cycle) 2.Stabilizing biotic feedback processes (the Gaia hypothesis) 3.Because we were lucky (the Rare Earth hypothesis)

The Gaia Hypothesis James Lovelock Earth’s climate is regulated by (and for?) the biota Lynn Margulis ( )

Gaia—The Greek goddess Gaia is Mother Earth. She is from whom everything comes, but she is not quite a divinity, because she is Earth. She bore the Titans as well as monsters like the hundred armed men, and some of the Cyclopes - others were sons of Poseidon. She was the daughter of Chaos, and the mother of all creatures (according to some). She was the first and the last, and wanted all of her children, no matter what. She was primarily spoken of as a Mother of other Gods, rather than having her own myths.

The Rare Earth hypothesis Earth is “lucky” in a number of respects Life itself may be commonplace, but complex life, i.e., animal life, is rare in the universe Do we believe this? Copernicus/Springer-Verlag (2000)

We will look at these questions. However, we’ll also do a tour of the Solar System on the way to see what our neighboring planets, and particularly their atmospheres and climates, are like…

Venus UV image (false color) from the Galileo spacecraft Planet is nearly featureless in the visible 93-bar, CO 2 -rich atmosphere Surface temperature: 730 K Practically no water Very high D/H ratio (~150 times Earth’s value) Image courtesy of NASA

Venus as seen by Magellan Image made using synthetic aperture radar (SAR)

Earth topography Earth’s topography shows tectonic features such as midocean ridges

Earth topography Earth’s topography shows tectonic features such as midocean ridges and linear mountain chains

Mars from HST (Hubble Space Telescope) Mars is small –½ Earth’s radius –1/10 th Earth’s mass Thin CO 2 -rich atmosphere (~6-8 mbar) Mean surface temperature: 218 K (  55 o C) Polar caps of frozen H 2 O and CO 2 From: NASA Planetary Photojournal

MARS PATHFINDER Twin peaks view Today, the surface of Mars is a frozen desert

Courtesy of NASA Nanedi Vallis (from Mars Global Surveyor) ~3 km River channel But there are lots of fluvial features on the heavily cratered southern highlands  Mars was wet early in its history, and it may have been warm, as well

Mars Science Laboratory (MSL, Nov ) MSL will assess whether Mars ever was, or is still today, an environment able to support microbial life. Other rovers found evidence for highly acidic water, which may have been present as the warm, wet period ended Courtesy of Joy Crisp

Jupiter (with Io and Europa) 318 Earth masses (M  ) solar masses (M  ) –Smallest star is 0.08 M , or 80 M Jup Nearly solar in composition –Dominantly H and He Long-lived dynamical features (The Great Red Spot)

Europa (from Galileo) 2 nd -most of the 4 Galilean moons Tidally heated  liquid beneath its icy shell How thick is the ice? –And what lies beneath it? Courtesy: NASA Planetary Photojournal

New evidence for liquid water on Europa (Nov 16, 2011) Galileo probe has discovered what appears to be a body of liquid water the volume of the North American Great Lakes locked inside the icy shell of Jupiter’s moon Europa.

Saturn (from Voyager 1) The ringed planet Rings appear to be dynamically unstable –How and when did they form? Has an interesting moon…

Titan (from Voyager 2) Largest moon in the Solar System Atmosphere is 15 times as dense as Earth’s –1.5 bar surface pressure –93 K surface temperature Haze is thought to form from photolysis (and charged particle irradiation) of CH 4

Lakes on Titan? Image taken by the Huygens Probe, launched from the Cassini spacecraft (January, 2005)

Titan shoreline?

Titan specular reflection (glint) Picture (from the Cassini spacecraft) published Dec. 23, 2009 This is the first direct evidence for (filled) liquid lakes on Titan specular-reflection-titan-lakes-.html

Our Solar System has only 8 planets, so our knowledge of planets in general has been limited up until fairly recently but Astronomers are now finding planets around other stars…

Currently known exoplanets V E J exoplanet.eu

Radial velocity (Doppler) method The pull of the planet on its host star makes the star wobble back and forth in the observer’s line of sight

Kepler Mission This space-based telescope points at a patch of the Milky Way and monitors the brightness of ~150,000 stars, looking for transits of Earth- sized (and other) planets 10  5 precision photometry  can find Earths Launched: March 7, 2009 Transit Method

Known extrasolar planets Few, if any, of these planets are very interesting, however, from an astrobiological standpoint –Gliese 581g (the “Goldilocks planet”) is probably not real Howard et al.(2010) 704 ~ 2300 more “candidate” planets from Kepler mission !!

December 2011 data release Candidate label Candidate size (R E ) Number of candidates Earth-sizeR p < Super-Earths1.25 < R p < Neptune-size2.0 < R p < Jupiter-size6.0 < R p < Very-large-size15 < R p < TOTAL of these planets are within their star’s habitable zone

Kepler-22b 600 l.y. distant 2.4 R E 290-day orbit, late G star Not sure whether this is a rocky planet or a Neptune (R Neptune = 3.9 R E ) kepler/news/kepscicon-briefing.html