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SETI The search for extraterrestrial intelligence Dominated by quests for radio beacons, but with some searches for narrow-band laser transmissions
Fig. 20 -11, p. 423
Fig. 20 -17, p. 428
Why SETI will Fail
High-resolution imaging of young planets New infrared results from the VLT and the HST
Essentials of planet imaging • Young, preferably nearby, target stars • A high spatial resolution infrared camera system on a large ground-based telescope or on the Hubble Space Telescope
Adaptive Optics Imaging • At current state of the art, AO is sufficiently sensitive to detect only thermal emission from self-luminous, young planets. Reflected light is too feeble to be seen. • AO detectability is a function of a planet’s age, distance from Earth, and contrast with its primary star.
Planet imaging programs • Keck AO • VLT AO • HST/NICMOS To date, each telescope has been used to image ~100 stars
Fig. 20 -3 a, p. 418
Where do humans stand on the scale of cosmic intelligence? • Carl Sagan’s natural evolution of the Universe: Origin of the Universe => origin of galaxies, stars, elements, planets => origin of life => chemical and biological evolution => technological intelligence
From the SETI Institute webpage (10/15/05), on “The future of SETI research” • “Scientists who participate in this research are more optimistic than ever before that they could find signals from space that would indicate that we’re not alone. They are bolstered in this view by several recent developments. In the past 5 years astronomers have found that many stars have planets…”
Discoveries of extrasolar planets • Exoplanets => ETI is *less* likely for two reasons: Minor reason: planetary systems are unfavorable for life as we know it (but only for ~10%) Primary reason: people’s great interest in these discoveries
We live in a unique moment in history: SETI, but no “terrestrial planet finder” (TPF)
TPF/Darwin design concepts
These are first-generation instruments. Later generations could image Earth-size worlds revealing continent-ocean dichotomies, annual seasonal variations, the coming and going of ice ages, and long-term changes in vegetation patterns, both natural and human induced.
Suppose that TPF discovers a “living world” What happens next? SETI: For a decade? A century? A millennium?
If there is no answer, then our descendants can choose between two options: 1) do nothing (for a million years) 2) send a spaceship
• Everything we know about human nature and history indicates that intelligent creatures will follow the latter path - • Exploration of our solar system began with telescopic observations from Earth. But as soon as we developed the capability, we launched spaceships to explore planets and moons up close because observing from afar is limited and, ultimately, unsatisfying.
Biologist Penelope Boston, from the Discovery Channel’s program “Destination Mars”: “I am a biologist; I have a burning need to know about life in the Universe”
But dinosaurs, bugs, and flowers don’t do radio telescopes Passively pointing a radio telescope at a living world that lacks a technological civilization will never get Dr. Boston to where she wants to be -e. g. , knowledge of whether all life is carbon based or uses liquid water as a solvent, or is constructed from proteins and nucleic acids.
Robotic Interstellar Exploration in the 21 st Century • 1998 NASA/JPL 2 -day workshop • Engineers & Scientists • What “hook” might motivate humankind to provide the $$ needed to fund a mission to a nearby star?
Now let’s turn the situation around and look at things from the perspective of a technological extraterrestrial. Earth, thanks to life, has had an oxygenic atmosphere for about 2 billion years. Any extraterrestrials who possess the equivalent of our TPF and who passed near our Sun during those years, would have discovered our unusual atmosphere.
In summary, three simple postulates have major implications for SETI. 1) Soon after development of technology, all civilizations will build the equivalent of TPF. 2) Intelligent life is curious about other life forms, simple or technological. 3) 3) Having used TPF to discover a nearby “living world”, spaceships will be constructed to visit that world.
Extrasolar planets => ETI is now *less* likely than previously because of people’s great interest in such discoveries. (because of life)
If these simple postulates are true, then the absence of intelligent aliens in our solar system is strong evidence that they do not exist anywhere in our region of the Milky Way and SETI searches of nearby stars are destined to fail.
What is a planet? • The IAU Definition: • Mass < 13. 6 Jupiter masses • Orbits a star or stellar remnant • Don’t use formation mechanism to decide if yes or no
Light from science target Perfect Plane Wave Atmosphere corrugates the wavefront Telescope System Creates blurred images Seeing disk ~ 1 arcsecond Science Camera
Light from science target Light from reference star Creates partially sharpened images FWHM ~ 0. 040 arcsecond Deformable Mirror Science Camera Beam Splitter Computer Wavefront Sensor
Cooling Curves for Substellar Objects 0 Evolution of M Dwarf Stars, Brown Dwarfs and Giant Planets (from Adam Burrows) L/Lsum -2 2 M 1207 A BRO WN 2 M 1207 b -6 DWA PLA sun Log 0 1 -4 STARS (Hydrogen burning) RFS (Deu 80 M jup teriu NET S 200 M jup m bu rning ) NICMOS Companion Detection Limit (M type primary) 14 M jup -8 JUPITER -10 6 SATURN 7 8 Log 10 Age (years) 9 10
Epoch 5 astrometry - NICMOS Unequivocal common P. M.
Solar system time scales and ages of young nearby stars • Formation of Jupiter • Formation of Earth’s core • Era of heavy bombardment in inner solar system • • • Cha cluster TW Hydrae Assoc. Pictoris moving group Tucana/Horologium Assoc. AB Dor moving group < 10 Myr ~ 30 Myr ~ 600 Myr 8 Myr 12 Myr 30 Myr 70 Myr
HST/NICMOS CAMERA 1 2 nd FOLLOW-UP IMAGING 2 M 1207 A/b - 26 APR 05 NICMOS F 160 W (1. 6 mm) -2 to +2 ADU/second/pixel