a search for habitable planets j ohannes k epler a guy who thought a lot about planets ( by...

A Search for Habitable Planets

JOHANNES KEPLER

A guy who thought a lot about planets

( By permission Sternwarte Kremsmünster)


Kepler MissionA SEARCH FOR HABITABLE PLANETS

Nancy Schaff

Cornell University Dept. of Astronomy

Center for Radiophysics & Space Research

Adapted from a presentation by David Koch

NASA Ames Research Center


OVERVIEW

• What makes for a Habitable Planet

• Different Methods for Finding Planets

• Planets Discovered to Date

• Transit Photometry

• Kepler Mission


A Fundamental NASA Mission Goal:

•Does life in any form however simple or complex, carbon-based or other, exist elsewhere than on Earth?

•Are there Earth-like planets beyond our solar system?

– To place our Solar System in context with other planetary systems

– To provide data on possible platforms for astrobiology beyond our Solar System

These goals imply study of terrestrial planets in the habitable zones of solar-type (or smaller) stars…


WHAT DOES HABITABLE MEAN TO YOU?

• Right temperature

• Air

• Liquid water

• Light to keep you warm and to see

• Radiation shield

• Meteor (asteroid/comet) protection


THINGS THAT AFFECT TEMPERATURE

Looking for a temperature that makes liquid water on the surface of the planet possible…

1. Temperature of star

2. Distance from the star

3. Shape of planet’s orbit: how elliptical

4. Planet’s atmosphere: greenhouse gases

Factors that define the Habitable Zone (HZ) for a star:


aka “Goldilocks zone”

PLANET TEMPERATURE AFFECTS HABITABILITY


THE HABITABLE ZONE

FOR VARIOUS STELLAR TYPES

The Habitable Zone (HZ) in green is the distance from a star where liquid water is expected to exist on the planets surface.


WHAT IS IMPORTANT ABOUT AN ATMOSPHERE?

• Composition (Earth)free oxygen (about 21%)mostly inert (about 78% nitrogen)very little toxic gases

• Composition affects temperatureMinimize day-night extremes Greenhouse gases (water, CO2) hold in the heat

• Acts as an invisible protective shieldCosmic rays (high energy gamma-rays, protons, electrons)Solar wind and solar flares (charged particles)UV - ultravioletMicrometeoroids (e.g., puts holes in Space Shuttle window)

• Transports waterRain


PLANET SIZE AFFECTS HABITABILITY

• Planets form by accretion from a disk of gas and dust

• Too small (about <0.5 ME):

Can’t hold onto a life sustaining atmosphere (Mercury, Mars)

• Too big (about >10 ME):

Can hold onto the very abundant light gases (H2 and He) and turn into a gas giant (Jupiter, Saturn, Uranus, Neptune)

Copyright Lynnette Cook


KEY POINTS THAT GUIDE THE SEARCH

1. Stellar type => Which stars to search

2. HZ => Orbital periods and how long to look

3. Planet sizes => Sensitivity or precision needed


DETECTING EXTRA-SOLAR PLANETS(aka Exoplanets)

That is,Planets orbiting other stars


TECHNIQUES FOR FINDING EXTRASOLAR PLANETS

Method Mass Limit Status

Pulsar Timing Lunar Successful (4)

Radial Velocity super-Earth Successful (300+)

AstrometryGround sub-Jupiter In developmentSpace super-Earth Under study

Transit Photometry Successful (20+)Ground sub-Jupiter numerous groupsSpace sub-Jupiter HST, CoRoTSpace Earth Kepler

Reflection PhotometrySpace sub-Jupiter Kepler

MicrolensingGround super-Earth OGLE (4)

Direct ImagingSpace Earth Under study

(Source: J. Lissauer)t=period, a=semi-major axis, mp=planet mass, Ap=planet area, I=orbit inclination, e=eccentricity, Ds=distance to star


EXTRA-SOLAR PLANET DETECTIONS

Note: Masses are only lower limits except for transit cases and typically about 2x greater than shown

N.B. 430 exoplanets as of April 15, 2010


DISCOVERY OF EXTRASOLAR PLANETS

The “wobble” method gets the orbital period, semi-major axis, and a lower limit on the mass of the planet. This has detected down to 7 Earth-mass planets very close in, (but favors gas giant planets).


WE NEED A DIFFERENT APPROACH

• Earth-like planets are about 300 times less massive and about 100 times smaller in area than Jupiter

• Radial velocity (Doppler spectroscopy) method unable to detect Earth-size planets

• Need a different approach that can detect smaller planets

• No method exists for detecting habitable planets from ground-based observatories

• The Kepler Mission uses photometry to detect transits and can detect Earth-size planets from space

• The Kepler Mission is optimized to detect habitable planets in the habitable zone of solar-like stars

Exoplanet encyclopedia http://exoplanet.eu


Detecting Planets by Photometry

HD 209458


USING PHOTOMETRY TO DETECT EARTH-SIZE PLANETS

• The relative change in brightness (L/L) is equal to the relative areas (Aplanet/Astar)

• To measure 0.01% must get above the Earth’s atmosphere

• Method is robust but you must be patient:Require at least 3 transits preferably 4 with same brightness change, duration and temporal separation

Jupiter: 1% area of the Sun (1/100)

Earth or Venus0.01% area of the Sun (1/10,000)

MercuryTransit2006


Kepler MISSION CONCEPT

• Kepler Mission is optimized for finding

habitable planets ( 0.5 to 10 MÅ )

in the HZ ( near 1 AU ) of solar-like stars

• Continuously and simultaneously

monitor 100,000 main-sequence stars

• Use a one-meter Schmidt telescope:

FOV >100 deg2 with an array of 42 CCD

• Photometric precision:

Noise < 20 ppm in 6.5 hours V = 12 solar-like star

=> 4s detection for Earth-size transit

• Mission:

Heliocentric orbit for continuous viewing

> 3.5 year duration


Kepler PHOTOMETER

Photometer = CCD sensors+ TelescopeKepler will be 9th largest Schmidt ever built

and the largest telescope launched beyond earth-orbit

The Kepler photometer is a simple single purpose instrument• Schmidt telescope design with a 0.95-meter aperture and about 12 degree diameter field-of-view• Pointed at and records data from a single group of stars for the four year duration of the mission


Kepler Focal Plane

The photometer is composed of just one "instrument," which is, an array of 42 CCDs (charge coupled devices). Each 50x25 mm CCD has 2200x1024 pixels. The CCDs are not used to take pictures. The images are intentionally defocused to improve the photometric precision.


Kepler SPACECRAFT

Schmidt Corrector 0.95 m dia.

Spider with Focal Planeand Local Detector Electronics

Focal Plane95 Mega pixels, 42 CCDs

Primary Mirror1.4 m dia., 85% lt. wt.

Sunshade

Upper Telescope Housing

Lower Telescope Housing

Spacecraft bus integration

Fully assembled Kepler photometerMounted on the spacecraft


FIELD OF VIEW IN CYGNUS

The Kepler star field is a part of the extended solar neighborhood in the Cygnus-Lyra regions along the Orion arm.

It is located on one side of the summer triangle (Deneb-Vega-Altair)


SEARCHING THE EXTENDED SOLAR NEIGHBORHOOD

The stars sampled are similar to the immediate solar neighborhood. The stars actually come from all over the Galaxy near our radius, since they wander after being born. Young stellar clusters and their ionized nebular regions highlight the arms of the Galaxy.


Results announced January 4, 2010 from first six weeks of data collection after science operations commenced on May 12, 2009

• Known as "hot Jupiters" because of their high masses and extreme temperatures• Range in size from similar to Neptune to larger than Jupiter• Orbits ranging from 3.3 to 4.9 days• Estimated temperatures range from 2,200 to 3,000 degrees F, hotter than molten lava and much too hot for life as we know it • All five of the exoplanets orbit stars hotter and larger than Earth's sun.

EARLY RESULTS


SUMMARY

29

The Kepler Mission will:

Observe more than 100,000 dwarf stars

continuously for 3.5 to 6+ years

with a precision capable of detecting Earth’s in the HZ

The Kepler Mission can discover:

Planet sizes from that of Mars to greater than Jupiter

Orbital periods from days up to two years

About 600 terrestrial planetary systems if most have 1 AU orbits

About 1000 inner-orbit giant planets based on

already known frequency

A NULL result would also be very significant ! ! !

Results on giants expected 9 months after launch (March 2009)

and will continue for 3.5 to 6+ years

http://kepler.nasa.gov


Human Orrery


Introductory questions for

Detecting Extrasolar Planets

from Space Science Sequence Grades 6-8 Unit 4

Great Explorations in Math and Science (GEMS)

http://www.lhsgems.org


Do you think there are planets orbiting other stars?

... How many?


Are all stars the same size and temperature as the Sun?


How might the type of star affect whether it has habitable planets?


If there is a certain zone around a star where life might exist, what must be critical qualities of that

zone?


What things would you want to know about a newly discovered

planet?

Back to slide 14


Why would exoplanets be hard to detect?

What methods do astronomers use to find

planets?


WHAT’S THIS?


What happens when a planet transits a star?

Make a model that you can use to demonstrate a

planet transit.

A Search for Habitable PlanetsFor each team of 4–6 students:

• 1 snake book light

• 1 prepared Ping-Pong ball (see Getting Ready)

• several round, opaque plastic beads (ranging in size from 8 mm to 16 mm in diameter)

• 2 or more pipe cleaners

• 1 or 2 chopsticks or thin wooden dowels

• black thread

• 4" x 6” index cards

• tape

• paper or plastic bag to hold the materials

Create a model “star” by setting up a light bulb and socket in the middle of the classroom for teams to demonstrate their transits.

TRANSIT MODEL DESIGN ACTIVITY


What kind of orbit would allow us to see a transit?

Ball-on-stick demo


What’s wrong with this statement:

“If a star has an orbiting planet, astronomers can usually detect it by

transit observations”


Kepler is designed to monitor

brightness of 100,000 stars

simultaneously for over 3 years.


Scale of the model?

Return to questions about planets (slide 6)

• Are there more questions?• Do transit observations help us

answer the questions?


DEMO LEGO MODEL


Transit Tracks

trial investigation from Full Option Science System (FOSS)

Planetary Science course


Imagine you have a light sensor aimed at the star.

What would the transit of a book look like if you made a graph of

light intensity vs time?

TIME

BR

IGH

TN

ES

S


What would the transit of a planet look like if you made a graph of

light intensity vs time?

TIME

BR

IGH

TN

ES

S


It can lead to finding:

- The SIZE of the planet (based on brightness change and size of star)

- ORBITAL PERIOD of the planet – time between transits

- ORBITAL SIZE – distance from star(from mass of star and orbital period, using Kepler’s 3rd Law)

- TEMPERATURE of planet (from planet’s distance and temperature of star)

Why would those characteristics be important?

The graph is a “light curve”


How does a planet’s size and orbit affect the transit?


Is there a relationship between the planet’s period and how far it is

from the star?

Kepler’s Third Law:the square of the period (in years) equals the cube of the semi-major axis of orbit (in AUs)

P2 = a3

a search for habitable planets j ohannes k epler a guy who thought a lot about planets ( by...

Documents