The Search For Life in the Universe Lecture 27
Our basic search technique: 1: Find the planets 2: Isolate the planets light from the stars light 3: Get a spectrum of the planet Its atmosphere, maybe is reflected surface light
4 basic techniques to find planets: 1: Transits 2: Radial Velocity 3: Microlensing 4: Direct imaging
Brown Dwarf + exo planet
One dip in the stars brightness is not sufficient to say that you have found a planet. Requires at least three dips, at a regular period. (Any two dips could still be random) So you need to stare at a star for a long time, and you need to be able to measure its brightness with great accuracy. Why does this mean that we need to do such a mission from space?
What does the transit method tell you about a planet? 1: Planets diameter compared to stellar diameter. Only gives the size of the planet if we know the size of the star. 2: Orbital period of the planet This tells us the size of the orbit if we know the mass of the star 3: Does not tell us the mass of the planet or the density of the planet But it does seem that big planets are gas giants and smaller planets are rocky
Kepler detector array: note the attempt to match the field curvature
Kepler Mirror
Kepler focal plane
Mission Operations at the University of Colorado (research park) http://www.colorado.edu/news/releases/20 15/03/04/cu-boulder-students-help-controlinstruments-nasa-spacecraft-probemagnetic
105 square degrees Moon is about 3/16 square degrees
Radial velocity
2010 Transits: green M Earth Radial velocity: blue 1AU
October, 2013 Blue = Radial Velocity Green = Transits
What s next for radial velocity techniques? Need high precision. Want 10 cm/s accuracy (1 part in 3 Billion accuracy) Very difficult Would allow detection of Earths
Aspen Center for Physics Approaching the Stellar Astrophysical Limits of Exoplanet Detection: Getting to 10 cm/s
Direct Imaging of exoplanets
Sign of Life: BioMarkers or BioSignatures
BioMarkers are features in the spectrum of exo-planet that will indicate the presence of biological activity. The spectrum will tell us about atoms and molecules in the atmosphere, as well as the reflectance of the surface (whatever the starlight is reflecting off of).
Three fundamental BioMarkers 1: Reflected light from living organisms 2:Gases in atmosphere that we attribute to life 3: Inferred biology due to incompatible gasses in atmospheres
Detecting Life Remotely Pale Blue Dot Visible or IR radiation contain spectral fingerprint of planet s surface or atmosphere: look for BIOSIGNATURES Some slides from Nigel J Mason Physics & Astronomy, The Open University, UK.
Oxygen (either as O 2 or Ozone (O 3 ) Is considered a good bio-marker Oxygen is highly reactive it wants to bond with other materials (burn). The only known process to produce atmospheric oxygen on earth is photosynthesis
Methane (CH4) will react with oxygen The presence of both gasses indicates a continuing supply of both On earth, this is biology
Neptune has plenty of methane, but no oxygen: NO LIFE
Terrestrial exoplanets Magma Snowball Jurassic Early Mars Early Venus Jungleworld Desertworld Waterworld Superearth
Earth-in-Time Atmospheres Magma Hadean Archaean Proterozoic Snowball Atmospheric Composition Silicate CO 2 CO 2 N 2 N 2 Steam H 2 O N 2 O 2 CO 2 O 2
Factors affecting terrestrial atmospheres Size, Mass (gravity, pressure) Orbit (mean distance, eccentricity) Central star (spectral type) Atmospheric composition (greenhouse gases, photochemistry) Atmospheric mass (pressure) Ocean (hydrological cycle) Tectonics (volcanism, magnetism) Age (Photon flux, evolution) Biology (Emissions, CO 2 cycle...)
Archaean atmosphere 2.5 billion years ago CO 2 (x10,x100) CH 4 (x10) O 2 (x0.1, 0.01) UV (x100) T surface (30-80 o C) Photon flux = 83% modern Biomarker abundances?
Proterozoic atmosphere 2.2 billion years ago CO 2 (x5) CH 4 (x2, x5) O 2 (x0.1, 0.01) UV (x100) T surface (30-80 o C) Photon flux = ~90% modern Biomarker abundances? (O 3, N 2 O)
Snowball Earth atmosphere CO 2 (x10) CH 4 (x2) O 2 (x0.1, 0.01) UV (x100) Biomarker abundances? (O 3, N 2 O)
Jungleworld atmosphere High vegetation emissions High O 2 (21-35%) Biomarker abundances? (O 3, N 2 O)
Superearth atmosphere Earth composition P surface e.g. 1bar, 2bar Biomarker abundances? (O 3, N 2 O)
What do you conclude about this synthetic planet spectrum?
This is the real spectrum of Mars
It is proposed that these type of observations be made in the 2030 s
HDST
What would it take to convince you that we had found a planet bearing life?
What would it take to convince you that we had found a planet bearing life? What would it mean for you?