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This text explores the possibility of life on moons within our solar system, focusing on Titan and Enceladus. It discusses their unique characteristics, such as subsurface oceans and ice plumes, and compares them to other moons in the solar system. The text also delves into the factors important for life on the surface of a planet, including location and size.
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Young, crater-free surface regions with like those on Europa • Orbit resonancewith Dione • South polar hot spot and ice plumes • Thin “atmosphere” of water vapor • Subsurface ocean!?
Ice Plumes from Enceladus Area of plumes is much warmer than surroundings - evidence of subsurface reservoir of liquid water
Most likely, there is subsurface liquid water, simple organics, and water vapor welling up from below. Over billions of years, heating of this cocktail of simple organic molecules, water, and nitrogen could have led to some of the most basic building blocks of life.
Moons of Uranus No large moons, nothing of particular interest as far as the search for life
Named moons of Uranus Cordelia Ophelia Bianca Cressida Desdemona Juliet Portia Rosalind Belinda Puck Miranda Ariel Umbriel Titania Oberon Caliban Sycorax Prospero Setebos Stephano Trinculo What do these names have in common? They are all characters from the works of Shakespeare & Alexander Pope
Moons of Neptune One location of interest
Neptune’s Triton • Extremely cold (< 40K) objects made from volatile materials produce icy volcanism. • Huge geysers of nitrogen! • Pluto and the Kuiper Belt Objects may look and act similarly.
Solar system beyond Saturn • Decline of probability of life • Main factor is temperature • Europa Ganymede Callisto Titan Enceladus ? • Triton • Retrograde rotation capture • Uneven surface: • Cantaloupe terrain, Smooth parts, Frost deposits?, Wind streaks • Few impact craters recent geological activity (10100 Myr) • Pluto and remaining moons • Too cold and too small • But, amino acids seen in meteorites
Star A mass of gas held together by gravity in which the central temperatures and densities are sufficient for steady nuclear fusion reactions to occur.
Color Spectral type Temperature Stars are often described by their “spectral type”, which is a function of its temperature
The required mass to have fusion reactions in the core is at least a few percent of the mass of the sun.
Nuclear fusion occurs in the core of a star. Fusion of hydrogen to helium is the nuclear process functioning over most of a star’s lifetime. We refer to this time as the Main Sequence lifetime
A convenient way to gain insight into the life and death of stars is through the “Hertzsprung-Russell Diagram”
Hertzsprung-Russell Diagram A plot of the temperature of stars against their brightness (luminosity)
Hertzsprung-Russell Diagram Stars do not fall everywhere in this diagram An HR diagram for about 15,000 stars within 100 parsecs (326 light years) of the Sun. Most stars lie along the “Main Sequence”
Hot stars (bluer) are found at the upper left hand end of the Main Sequence while cooler (redder) stars are found to the lower right. Stars are all classified according to temperature and spectral type, with the hotter stars called ‘O’ type stars and the coolest called ‘M’ type stars. The order of classification is: O-B-A-F-G-K-M
Stars live most of their lives on the “Main Sequence”. These stars generate energy by nuclear fusion of hydrogen into helium in their core.
Very rare Hotter “Main Sequence” stars are much less common than cooler Main Sequence stars Very common
107 yrs Hotter stars have shorter Main Sequence lifetimes than cooler stars 108 yrs 109 yrs 1010 yrs 1011 yrs
Major Factors for life on the Surface of a Planet: • Location, location, location: • must lie within a star’s habitable zone
Major Factors for life on the Surface of a Planet: • Location, location, location: • must lie within a star’s habitable zone • Size is important: • Large enough to retain an atmosphere substantial enough for liquid water • Large enough to retain internal heat and have plate tectonics for climate stabilization
The Habitable Zone An imaginary spherical shell surrounding a star throughout which the surface temperatures of any planets present might be conducive to the origin and development of life as we know it. Essentially a zone in which conditions allow for liquid water on the surface of a planet.
The Sun’s Habitable Zone (thru time)The Sun’s brightness (luminosity) has changed with time.
By contrast, the HZ of a highly luminous star would in principle be very wide, its inner margin beginning perhaps several hundred million km out and stretching to a distance of a billion km or more.
The size and location of the HZ depends on the nature of the star • Hot, luminous stars – spectral types "earlier" than that of the Sun (G3-G9, F, A, B, and O) – have wide HZs, the inner margins of which are located relatively far out: • To enjoy terrestrial temperatures: • Around Sirius (Spectral type A1: 26 times more luminous than the Sun), an Earth-sized planet would have to orbit at about the distance of Jupiter from the star. • Around Epsilon Indi (Spectral type K5: about one-tenth the Sun's luminosity), an Earth-sized planet would have to orbit at about the distance of Mercury from the star.