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The Drake Equation

The star formation rate in our Galaxy(stars per year that form)

Term #1

How many stars per year form in the Milky Way?

1- 10 solar masses per year

1- 10 Msun per year

The Drake EquationTerm #2

Fraction of those stars that host exoplanetary systems.

CandidateTransiting

Exoplanetsfrom the KEPLERsatellite

(>2300 as of today)

Sun/Jupiter:

Known Exoplanetary Systems as of July 2015

The Drake Equation

~5%-15% of Sun-like stars are directlyobserved to have exoplanets.

Term #2

But is 0.05-0.15 a reasonable estimate?(No, because detection methods have known shortcomings).

A star and all the material that orbits it.Solar System

http://janus.astro.umd.edu/SolarSystems/

The Drake Equation

Number of exoplanets per planet-hosting star that could potentially support life.

(# of Earth-like exoplanets per planet-hosting star)

Term #3

Let’s look at our Solar System firstsince it’s the only place where life definitely exists.

sizes to scale, distances not to scale!

Asteroids can be dangerous...http://www.youtube.com/watch?v=gEDD-86BD-0

Some Basic Requirements for Life?• Stable source of energy (long−lived, low−mass stars best)

• Raw materials for complex chemistry

• Location for life to emerge (solid surfaces, atmosphere)

• Benign environmental conditions (low UV radiation, etc.)

• Water?

• Magnetic field?

The Solar System’s Habitable Zone

Habitable Zone:Region around a star in which it is possible for a

planet to have liquid water

Inside the zone, it’s too hot.

Outside the zone, it’s too cold.

The extent of the habitable zone depends on the star’s luminosity.It also changes as a star evolves.

Image is to scale

Habitable Zone Simulator

http://astro.unl.edu/naap/habitablezones/animations/stellarHabitableZone.html

Eccentric (non-circular) orbits can be a problem

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http://astro.unl.edu/classaction/animations/renaissance/kepler.html

Start animation on Kepler’s first law below. Increase eccentricity and think about why high e value might be bad.

Some of the exoplanets we’ve discovered are in the habitable zoneand very similar to Earth!

Corot 7B - The Hell Planet

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https://www.youtube.com/watch?v=phiJLBM5AQI

The Galactic Habitable Zone

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http://astro.unl.edu/naap/habitablezones/animations/milkyWayHabitability.html

The Drake Equation

3-5 exoplanets per planet-hosting star that could potentially support life!?

Term #3