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. 20-3a, 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)

AIRS spectrum

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

telescopesPassively 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 21st 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) 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

ScienceCamera

Light from science target

Telescope System

Perfect Plane Wave

Atmosphere corrugates the wavefront

Creates blurred images

Seeing disk ~ 1 arcsecond

ScienceCamera

Light from science target

Light from reference star

Deformable Mirror

Beam Splitter

ComputerWavefront

Sensor

Creates partially sharpened images

FWHM ~ 0.040 arcsecond

0

6 7 8 9 10Log10 Age (years)

80Mjup

14Mjup

JUPITER

SATURN

STARS (Hydrogen burning)

BROWN DWARFS (Deuterium burning)PLANETS

200Mjup

Evolution of M Dwarf Stars, Brown Dwarfsand Giant Planets (from Adam Burrows)

-10

-8

-6

-4

-2

Log 1

0 L

/Lsu

m

sun

Cooling Curves for Substellar Objects

NICMOS Companion Detection Limit (M type primary)NICMOS Companion Detection Limit (M type primary)

2M1207A

2M1207b

Epoch 5 astrometry - NICMOSUnequivocal common P.M.

Solar system time scales and ages of young nearby stars

• Formation of Jupiter < 10 Myr• Formation of Earth’s core ~ 30 Myr• Era of heavy bombardment

in inner solar system ~ 600 Myr

Cha cluster 8 Myr• TW Hydrae Assoc. 8 Myr Pictoris moving group 12 Myr• Tucana/Horologium Assoc. 30 Myr• AB Dor moving group 70 Myr

2M1207A/b - 26 APR 05 NICMOS F160W (1.6m)

-2 to +2 ADU/second/pixel

HST/NICMOS CAMERA 1 2nd FOLLOW-UP IMAGING