Is Anyone Out There? The Search for Extra Terrestrial Life By Ulrike Lahaise Georgia Perimeter College November 2012.

Is Anyone Out There?The Search for Extra Terrestrial

Life

By Ulrike LahaiseGeorgia Perimeter College

November 2012

OverviewNecessities for Life as We Know It Search For Extra Terrestrial Life In Our

Solar SystemExtreme Life On EarthSearch For Extra-solar

Planets, aka ExoplanetsSearch For Life on

ExoplanetsHow You Can Get

Involved With Exoplanets

What’s essential for life?

Deprived of ___________, you would die in a 1. few weeks.

2. few days.3. few minutes.

A. Food B. Air C. Water

Planet Atmospheres

Which “Planets” have 5. no significant atmosphere? 6. a very thick outer gas layer? 7. a relatively thin but significant

atmosphere?

A. Earth, Venus, MarsB. Mercury, Pluto, the MoonC. Jupiter, Saturn, Neptune

Planet SizesWhich “planets” below are

7. medium-sized (1/2 to 2x Earth’s diameter)?8. large-sized (over 3 times Earth’s diameter)?9. small-sized (less than 1/3 Earth’s diameter)?

A. Jupiter, Saturn, NeptuneB. Mercury, Pluto, the MoonC. Earth, Venus, Mars

Water Based Lifeforms

10. Which choice below is the percentage of liquid water in the bodies of most animals (there are exceptions)?

A. 464 to 470 D. -163 to 427B. -133 to 27 E. 0 to 100C. 50 to 70

Surface Temperatures

Which choice below is the temperature range

12. on Venus in Celsius?13. on Mercury in Celsius?14. on Mars in Celsius?

A. 464 to 470 D. -163 to 427

B. -133 to 27 E. 0 to 100C. 50 to 70

Question: Is There Extra Terrestrial Life Similar To Us?

Need to look for planets/moons that have Medium size Temperature range allowing liquid water at surface Atmosphere, not too thick or thin Surface conditions that don’t vary too much

Most obvious place to look: Our Solar System

Water-Based Life In Solar System? (1)

Look at Classical Earthlike PlanetsMercury? NO

No atmosphere, no water, day too hot, night too cold

Venus? NOFairly thick atmosphere, no liquid water, day- and

night way too hot (would melt lead!)Earth? YES

Perfect! Let’s not mess it up!Mars? NOT TODAY BUT MAYBE IN PAST!

Thin atmosphere, too cold for liquid water to persist but temperatures can get above freezing

BUT: Mars’ landscape shows dried up rivers!!!

Water-Based Life In Solar System? (2)

Look at Classical Jupiter-like PlanetsJupiter and Saturn? NO

Very large planet with large gravityVery thick hydrogen/helium atmosphere that

becomes denser and denser, eventually liquid, large pressures

Uranus and Neptune? NOStill pretty large planet with larger gravityThick hydrogen/helium atmosphere that

becomes denser, eventually high pressure watery slush

Some Jupiter-like Planets have pretty large moons… need to look at those!

Life in Our Solar System? Best Candidates (1)

Follow the liquid water !!! Jupiter’s moon Europa Saturn’s moon Enceladus Mars (maybe not

today but in the past)

Life in Our Solar System? Best Candidates (2)

MarsToday: frozen, dry, no life!Past: Thicker, warmer air, evidence of long

periods with liquid water!

Nirgal Vallis, MarsAres Vallis, Mars

Ancient flood plainsDried up river beds

Craters with muddy splashes

Best Candidates For Life (3)Curiosity searches for a habitable environment (but cannot search for actual life)Landed in Mars’ Gale Crater on August

5, 2012Can verify three conditions needed for

life Necessary chemical ingredients (organics)Liquid waterEnergy source

Best Candidates For Life? (4)

Jupiter’s icy moon Europa

Far from SunSurface covered by

very cold ice sheets possibly over 100 miles thick

But: heated by Jupiter’s and other moons’ tidal forcesAnalogy: like heat

stress on racquet ball being hit repeatedly

NASA

Fracturing is evidence ofMotion below due to heat

Best Candidates For Life? (5)

Current model of Europa Convecting ice layer beneath ice sheets! Cause variety of surface features Liquid watery ocean below ice, then rocky

interior and metallic core

NASA

lpi.usra.edu

Best Candidates For Life? (6) Enceladus (as tiny as Scotland) experiences

tidal heating due to Saturn and its other major moons Space probe Cassini saw icy geyser-like plumes:

Evidence for sub-surface liquid water in south polar region

Possibly salty (NaCl found in Saturn’s E-ring)

Univ. of Idaho

Best Candidates For Life? (7)

Europa’s and Enceladus’ sub-ice liquid/slushy oceans are extremely cold

What, if any, life could there be?Example from Earth: cold loving bacteria

like archaea or “methane worms”?

http://archives.microbeworld.org

http://faculty.cascadia.edu/

Extreme Life On Earth (1)Life similar to Earth’s

“extremophiles” might thrive on other worlds

Microbes that thrive in extreme conditions Bone dry, freezing cold,

super hot, very acidic or basic

Two miles deep in rock, live on radioactivity (left) or metal (right)!

Check out PlanetQuest’s Alien Safari: http://planetquest.jpl.nasa.gov/system/interactable/3/index.htm

l

Extreme Life on Earth (2)What other worlds might extremophiles exist on? Mars: cold/dry, Europa and Enceladus: cold/icy-

watery There could be many planets and moons orbiting

other stars that are like them (called “exoplanets”/”exomoons”)

Hot super-earths that are hot and possibly dry or rocky or acidic/basic, or ocean covered super-earths that are like our ocean floors?

Let’s see what’s OUT THERE!!!

Search for Exoplanets (1)“Exoplanet” A planet that orbits a star

other than the Sun Wikipedia: http://en.wikipedia.org/wiki/Extrasolar_planet

“Exomoon” A moon that orbits an exoplanet

Why are they so hard to find? Planets don’t have own light They are far, far, far away (tens or more light years)

The closest neighbor star, Alpha Centauri, is 4.3 ly away!

Blinding glare of their parent stars Analogy: Looking for a planet orbiting Alpha

Centauri is like observing a moth near a spotlight in San Diego from Boston!

Search For Exoplanets (2)Direct Imaging Coronography:

blocks light of star with masking device See orbiting planets

better Interferometry:

combines light from several telescopes to cancel star’s light Planet’s light stays

Ground based telescope and image processing technology started being sensitive enough around 2003 Adaptive optics to counteract atmospheric

distortions

Hubble Space Telescope

Search For Exoplanets (3)Gravitational Microlensing: Measure

relativistic light bending effect of exoplanet on light from much more distant starPlanet’s gravity acts like lens: focuses star

lightDistant star will appear brighter and at a

slightly different place

Search For Exoplanets (4) Motion of Exoplanet around its star:

Gravitational tug of planet makes star “wobble” System’s center of mass: not exactly in star’s

center All objects, including star, orbit center of mass Star “wobbles” around a point not exactly in its

center Analogy: balancing a mobile with items of different

masses

Search For Exoplanets (5)Radial Velocity Method - uses Doppler Shift of

star light to measure its wobble Analogy: sound of ambulance

Toward us: higher pitch

Away from us: lower pitch

Change in level of sound Not change in loudness

When star moves toward us: higher pitch in

light makes wavelengths shorter

Away from us: lower pitch in light makes wavelengths longer

The larger and closer the planet, the faster the wobble and the greater the shift: earliest discoveries were of Jupiter-sized planets

Search For Exoplanets (6)Astrometry:

measure tiny change in star’s position due to planet’s tug The smaller and

further the planet the smaller the effect

Transit Method: measure change in brightness of star’s light when planet passes in front of star The smaller the

planet the smaller the dip

NASA

Search For Exoplanets (7) Kepler Space Telescope First instrument to detect

Earth sized exoplanets Started operating May 12,

2009 Uses transit method Images from

NASA/JPL

Search For Exoplanets (8)NASA Exoplanet Archive (current tally) http://exoplanetarchive.ipac.caltech.edu/index.html

809 confirmed, 2,320 exoplanet candidates

Closest Exoplanet:Alpha Centauri Bb

Orbits host star Alpha Centauri B (discovered Oct. 16, 2012) Wikipedia Entry:

http://en.wikipedia.org/wiki/Alpha_Centauri_Bb

At 4.37 light years Solar-type star Part of triple star

system Discovered by

European Southern Observatory (ESO) By Doppler Shift method

Only 1.13 Earth masses BUT orbits star in 3 days!

ESO

Life On Exoplanets? (1)What makes a planet or natural satellite (moon) habitable?NASA’s criteria

Extended regions of liquid waterFavorable conditions to form organic

moleculesEnergy sources to sustain a metabolism

Need the right type of starNeed to be at the right distance from

the starIn Habitable Zone (HZ) or “Goldilocks

Zone”Need the right type of planet

Life On Exoplanets: Right Distance

If we look for life similar Earth

Then look in “Habitable Zone” – distance from a star where liquid water can existToo close: water

will be a gasToo far: water will

be frozen

Life On Exoplanets: Right Star (1)

Habitable Zones (HZs) around different stars Cool red dwarfs:

close and narrow Sunlike stars:

medium distance and width

Hot blue giants: far and wideWould this

planet be instar’s habitablezone?

Life On Exoplanets: Right Star (2)

Which type of stars are best?Cool red dwarf: planet so close that same

side always faces star (tidally locked like the Moon around Earth)

Very slow spin, extreme day and night temperatures

Atmosphere not protected by a magnetic field

Life On Exoplanets: Right Star (3)

Hot blue giant: star doesn’t last very long, burns out after less than 1 billion years

Not enough time for complex, intelligent life to evolve

Medium yellow or even slightly cooler orange star

Just right! Life needs enough time to develop and enough protection from harsh radiation and solar wind

Life On Exoplanets: Right Planet (1)

Look for Earthlike (terrestrial) planets Made of silicate rocks without

hydrogen/helium outer gas layers Should have about Earth’s mass up

to a few times more Jupiterlike (jovian) planets may not

be habitable but their terrestrial moons can be Could be much smaller than Earth, tidal heating

from their planet and fellow moons keeps them geologically active

NASA’s habitability conditions are basic necessities for single cell life such as bacteria, archaea More complex necessities (more stringent

conditions) for multicellular life, such as animals and plants

Life On Exoplanets: Right Planet (2)

Need the right orbit and rotation: stable, no variations Earth has almost

circular orbit Almost always the same

distance from the Sun Earth has the right axis

tilt for moderate seasons Quick enough rotation

Moderate day/night temperature differences Maintain magnetic dynamo

Presence of Earth’s large Moon stabilizes tilt of axis Still controversial among astronomers

Jatakacs.edublog.org

Life On Exoplanets: Right Planet (3)

Need the right chemical elements Four elements most vital for life: carbon,

hydrogen, oxygen, and nitrogen React and form molecules most easily (e.g. amino

acids) Amino acids have even been found in meteorites They are the building blocks of proteins

Add common elements sulfur and phosphorus Now you can build proteins,

DNA, RNA, and molecules for our metabolism

Gasses from volcanoes when crust first formed plus energy can lead to amino acids BUT: cannot account for huge amounts of water!

Popsci.com

Life On Exoplanets: Right Planet (4)

Need the right solar system companions Icy comets from outer solar system with

other compounds like amino acids impacted on Earth right after it formedComet reservoir

is far enough away from Sun that water/other compounds could remain solid

Lynette Cook, Science Photo Library

Life On Exoplanets: Best Candidates (1)

Gliese 581 (in Libra) – red dwarf star, 22 ly away 3 confirmed planets (radial velocity): e, b, c; one

probable: d 2 disputed: f, g c: more like Venus d: more like Mars g: disc. Sept. 2010

middle of HZ, most likely for liquid water, 37 day orbit, ~ 1.7 Rearth, tidally locked, nearside always lit , farside always dark! Dense enough atmosphere moderates.

Henrykus, European Southern Observatory

Life On Exoplanets: Best Candidates (2)

Kepler-22b: Wikipedia http://en.wikipedia.org/wiki/Kepler_22b

Discovered by NASA’s Kepler Space Telescope using transition method On May 12, 2009 Confirmed Dec. 5, 2011

Host star: Kepler-22 Sunlike, tad smaller

289 day orbit 2.4 times Earth size 6.36 times Earth mass About 600 light years away from Earth! No info yet on orbit shape and atmosphere

NASA

Life On Exoplanets: Best Candidates (3)

HD 40307g in constellation of Pictor, at 43 ly, orange host star 0.75 Sun’s mass

200 day orbit at 0.6AU, ~ 7 Earth masses, e ~ 0.2, gets 62% of Earth’s solar radiation

Far enough from star to not be tidally locked

5 other Super-Earths (a – f) orbit much closer

No atmospheric info yet!

Discovered by European SouthernObservatory Team with radial velocitymethod, Nov. 2012

Wikipedia: http://en.wikipedia.org/wiki/HD_40307_g

Life On Exoplanets: ESI (1)Earth Similarity Index (ESI) (Developed by Schulz-Makuch et. al., Planetary Habitability Laboratory, Arecibo, http://phl.upr.edu/projects/earth-similarity-index-esi)

Multiparameter statistical assessment of Earth-likeness for solar - and exoplanets 0 (no similarity) <= ESI <= 1 (identical to Earth)

A product with weighted factors xi can be any planetary property (i.e. Tsurface in

Kelvin) xio is the corresponding Earth value (i.e. 288K) n is the number of properties wi is the weighting exponent (sensitivity of

property)

Life On Exoplanets: ESI (2)

Definition of Earth-like planet Properties: mean radius, bulk density, escape

velocity, Tsurface

Interior ESI: Rmean, Dbulk

Surface ESI: vescape, Tsurface

ESI > 0.8: similar terrestrial composition and an atmosphere suitable for most terrestrial vegetation

0.6 < ESI < 0.8: barely habitable, too hot or too cold, suitable only for terrestrial extremophiles (i.e. Mars)

Life On Exoplanets: ESI (3)ESI plot Orange: Sol. Sys.

objects > 100 km Blue: 258 known

exoplanets Red shading:

rocky interior Blue shading:

temperate surface

GREEN SHADING: Earth-like

Dashed lines: constant ESI

HD 40307g, Kepler 22b not included yet

Life On Exoplanets: ESI (4)

ESI plot with 1235 Kepler candidates ESI was

estimated with mass-radius relationships for gas, ocean, and rocky planets

Potential abundance of rocky planets

Two candidates in Earth-like zone!

Life On Exoplanets: ESI (5)

Life On Exoplanets: Atmospheric Analysis (1)

Spitzer Space Telescope (observes in infra red) Looks at light from planet

by subtracting out light of star

Can detect gases in atmosphere

For transit method only If there is water,

oxygen, carbon dioxide could indicate lifeAs simple as algae or a complex

civilizationNeed to eliminate non living causes of

these gases

Spitzer Space Telescope

Life On Exoplanets: Atmospheric Analysis (2)

Diffraction spectra of star and planet by ESO’s VLT• Spectra were obtained by an infrared instrument mounted on the VLT (Very Large Telescope) (independent of planet

orientation)

• Planet • Star

• HR 8799 is a young, 1.5 solar mass star, 130 ly away

• 3 giant companion planets, the middle one was measured• 10 Jupiter masses, 800 C hot

Get Involved With Real Exoplanets

Jet Propulsion Laboratory’s PlanetQuest, The Search For Another Earth: http://planetquest.jpl.nasa.gov/ Science/technology info, images/video and

interactives With Planet Hunters you can help discover

real exoplanets: http://www.planethunters.org/ Volunteers discovered

exoplanet Oct. 15, 2012! With Agent Exoplanet

you can help study properties of known exoplanets: http://portal.lcogt.net/agentexoplanet/

Planet Hunters

Resources Habitable Planet Questions, GEMS (Great Explorations in Math and Science)

Activity developed with NASA’s Kepler Mission Michelle Thaller, Spitzer Space Center, “Probing Extrasolar Planets with the

Spitzer Space Telescope”, Astronomical Society of the Pacific, No. 75, Spring 2009 http://www.astrosociety.org/education/publications/tnl/75/75.html

Nancy Neal-Jones, Cynthia O’Carroll, “Earthlike Planets May Be Common in Known Planetary Systems”, Goddard Space Flight Center, 2006: http://www.nasa.gov/centers/goddard/news/topstory/2006/hot_jupiter.html

NASA, JPL Planetquest: http://planetquest.jpl.nasa.gov/ Alien Earths, traveling exhibition: http://www.alienearths.org/ Cool Cosmos from Caltech (IPAC, NASA): http://coolcosmos.ipac.caltech.edu/ Kepler Mission: http://kepler.nasa.gov/ Wikipedia: http://en.wikipedia.org/wiki/Habitable_zone ,

http://en.wikipedia.org/wiki/Goldilocks_planet Neil DeGrasse Tyson, Goldilocks and the Three Planets,

http://www.haydenplanetarium.org/tyson/category/subjects/habitablezone Jason Major, Universetoday.com, http

://www.universetoday.com/98379/astronomers-find-tantalizing-hints-of-a-potentially-habitable-exoplanet/

Joshua Rodriguez/PlanetQuest “Earth on Steroids? Unraveling the Mystery of Super-Earths”: http://www.nasa.gov/topics/universe/features/super_earths.html

Discovery Channel News web site: http://dsc.discovery.com/news/briefs/20050228/europa_zoom0.html

National Science Foundation “Special Report: Extreme Microbes”: http://www.nsf.gov/news/special_reports/microbes/

Space.com’s articles on Curiosity and its capability to search for traces of life: http://www.space.com/16801-mars-rover-curiosity-science-instruments-infographic.html, http://www.space.com/17306-mars-rover-curiosity-red-planet-life-search.html