Astro 101 Slide Set:

Kepler’s Exoplanet

Discoveries Exceed 1,000

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Topic: Exoplanets

Concepts: Transit Detection, ExoplanetStatistics

Mission: Kepler

Coordinated by:the NASA Astrophysics Forum

An Instructor’s Guide for using

the slide sets is available at the

ASP website https://www.astrosociety.org/e

ducation/resources-for-the-

higher-education-audience/

Developed by: the Kepler Team

The DiscoveriesIn January 2015, the Kepler team,

analyzing data gathered by the Kepler

spacecraft during its four-year primary

mission (2009-2013), announced its

1,000th verified extrasolar planet

(“exoplanet”) discovery—including three

more that are both less than two Earth

diameters in size, and orbit within the

“habitable zone” of their parent stars

(i.e., the regions where the temperature

range could allow for liquid water on

planetary surfaces)—bringing the

current total of these to eight.

The team also added 500+ candidates

to the roll of 3,000+ potential planets

yet to be verified, including six of near-

Earth size orbiting in the habitable

zones of Sun-like stars.

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Three of the eight verified near-Earth-size planets orbiting in

habitable zones are among the newly-validated. Two of these—

Kepler-438b and Kepler-442b--are less than 1.5 times the

diameter of Earth and are likely made of rock. They orbit stars

smaller and cooler than the sun, 475 and 1,100 light years away,

respectively. Credit: NASA Ames/Kepler Mission/W. Stenzel.

How Are the Discoveries Made?Kepler detects planets by taking a

photometric measurement of the

stars in its field of view every 30

minutes. A planet transit will show

as a small periodic dip in the “light

curve” of a star over time.

If the host star’s diameter and

temperature are known, then from

the simple dip in the the light curve

Kepler can determine the planet’s

diameter and orbital period; the

planet’s surface temperature can

also be estimated.

Kepler cannot independently

determine the planet’s mass or

composition, nor its atmospheric

composition.

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The animation shows how Kepler

detects planets. As the planet

passes between the host star and

the spacecraft, the observed star

brightness decreases slightly,

signaling the potential detection of a

planet. Kepler looked at over

150,000 stars continuously for four

years in the constellations Cygnus

and Lyra, seeking to record the slight

periodic brightness changes in stars

that could reveal the presence of

planets. Credit: NASA Ames/Kepler

Mission/SETI Institute/D. Berry.

Kepler field of view. Credit: NASA

Ames/Kepler Mission/C. Roberts

and W. Stenzel.

The Big Picture

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Prior to Kepler, the vast majority of known exoplanets were Neptune-size or larger.

This was a selection bias due to the difficulty of detecting smaller exoplanets. Kepler

can detect, and is detecting, smaller planets not possible by other methods, and is

increasing the odds of finding planets that resemble Earth.

An important goal in the search for exoplanets is to find that “other Earth”—one of

similar size, orbiting in the habitable zone of a sun-like star, possessing an Earth-like

atmosphere, possibly harboring life as we know it.

Artist’s conception of Kepler-186f. Credit: NASA

Ames/SETI Institute/Caltech.

Kepler’s 1,000 exoplanet discoveries—

and counting—have demonstrated that

planets are everywhere, and that small

planets are more common than large

ones.

What are the Implications?Kepler has shown that small planets

are more plentiful than larger, Jupiter-

sized worlds, and are abundant in our

galaxy.

Current models show that planets with

a diameter smaller than roughly 1.5

times that of Earth are more likely to

have rocky surfaces that could support

liquid water and appropriate conditions

to foster life as we know it.

Earth-size planets are therefore key to

discovering life beyond our solar

system. As Kepler finds more

exoplanets, that ultimate goal comes

closer!

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Credit: NASA Ames/Kepler Mission/W. Stenzel.

Resources

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The Kepler Misson Websiteso http://kepler.nasa.gov

o http://www.nasa.gov/Kepler

Scientific Papero Kepler Planet Catalog Paper, “Planetary

Candidates Observed by Kepler VI: Planet Sample from Q1-Q16 (47 Months)”http://arxiv.org/abs/1502.02038

Additional Resourceso Exoplanet Resource guide

http://www.astrosociety.org/education/astronomy-resource-guides/the-search-for-planets-around-other-stars/

o Online Exoplanet databasehttp://exoplanets.org

o The online Kepler data Repositoryhttps://archive.stsci.edu/kepler/

NASA Exoplanet Archive:o http://exoplanetarchive.ipac.caltech.edu/

Image Credit: NASA Ames/Kepler Mission/W.

Stenzel.

Kepler’s Exoplanet

Discoveries Exceed 1,000

BONUS CONTENT

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Exoplanet Discoveries

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Animation Credit: NASA

Ames/Kepler Mission/N.

Batalha

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Exoplanets Plotted

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This figure plots exoplanet

discoveries on a graph showing

the size (radius) versus the

orbital period.

Kepler transit discoveries are

shown as yellow dots. The pink

dots represent transit discoveries

by other means than Kepler.

The light blue dots represent

discoveries using the radial

velocity method (measuring the

toward-and-away wobbles of

stars induced by the gravitational

tugs of orbiting planets). The

other colors account for direct

imaging and other methods.

Image credit: NASA Ames/Kepler Mission/N. Batalha.

Planets in Habitable Zones

This figure shows both currently

confirmed and candidate

exoplanets orbiting in the habitable

zone of their respective stars.

Their positions on the graph are

determined according to the

surface temperature of their parent

star versus the energy received by

the planet. The green bands

represent the habitable zone—the

region in which water on a rocky

surface could exist in liquid form

under the right conditions.

The graph shows Venus, Earth and

Mars for reference. Recently

confirmed planets are labeled.

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Image credit: NASA Ames/Kepler Mission/N. Batalha/W. Stenzel.