Mars Rover “Curiosity” Launch: Saturday Landing: August 2012

Twice as long and five times as heavy as Spirit and Opportunity. Will examine whether Mars has ever been suitable for life and to find clues about past life forms that may have been preserved in rocks

Homework 8

Due: Monday, Nov. 28, 9:00 pm,

Exam 2: Weds., Nov. 30

Hertzsprung-Russell Diagram

Stars do not fall everywhere in this diagram

An HR diagram for about 15,000 stars within 100 parsecs (326 light years) of the Sun.

Most stars lie along the “Main Sequence”

Major Factors for life on the

Surface of a Planet:

Location, location, location:– must lie within a star’s habitable zone

Major Factors for life on the

Surface of a Planet:

Location, location, location:– must lie within a star’s habitable zone

Size is important: – Large enough to retain an atmosphere substantial

enough for liquid water– Large enough to retain internal heat and have plate

tectonics for climate stabilization

The Habitable Zone

An imaginary spherical shell surrounding a star throughout which the surface temperatures of any planets present might be conducive to the origin and development of life as we know it.

Essentially a zone in which conditions allow for liquid water

on the surface of a planet.

The Sun’s Habitable

Zone (today)

The Sun’s Habitable Zone

(thru time)

The Sun’s luminosity has changed with

time.

Habitable Zones for Different Stars

Lower mass (cooler) stars have smaller habitable zones

By contrast, the HZ of a highly luminous star would in principle be very wide, its inner margin beginning perhaps several hundred million km out and stretching to a distance of a billion km or more.

The size and location of the HZ depends on the nature of the star

Hot, luminous stars – spectral types "earlier" than that of the Sun (F, A, B, and O) – have wide HZs, the inner margins of which are located relatively far out:

To enjoy terrestrial temperatures:

Around Sirius (Spectral type A1: 26 times more luminous than the Sun), an Earth-sized planet would have to orbit at about the distance of Jupiter from the star.

Around Epsilon Indi (Spectral type K5: about one-tenth the Sun's luminosity), an Earth-sized planet would have to orbit at about the distance of Mercury from the star.

The size and location of the HZ depends on the nature of the star

The situation becomes even more extreme in the case of a red dwarf, such as Barnard's Star (M4: about 2,000 times less luminous than the Sun), the HZ of which would extend only between about 750,000 and 2 million km (0.02 to 0.06 AU).

However: if planets exist too close to its parent star, the development of life might be made problematic because the tidal friction would have led to synchronous rotation.

The same side of the planet will always face the star.

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There are 200 billion stars in our galaxy…

…one of them is our Sun.

The sun has eight planets…

…we know of one that has life.

WHERE TO SEARCH?

More massive, brighter stars have wider HZ.

However, massive, bright stars are much more short-lived than smaller, stars.

In the case of the massive O stars and B main sequence stars, these very objects race through their life-cycles in only a few tens of millions of years – too quickly to allow even primitive life-forms to emerge.

Less massive, cooler stars have narrower HZ.

But these stars live much longer than larger, more massive stars.

In the case of the low mass K and M main sequence stars, these very objects live many tens to hundreds of billions of years – considerable time to allow even advanced life-forms to emerge.

LIFE? Given the rate of evolution of life on Earth, it is possible that microorganisms might have time to develop on worlds around A stars.

INTELLIGENT LIFE? But in the search for extraterrestrial intelligence, the HZs around F stars and later must be considered the most likely places to look.

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Is there another Earth out there?

“There are infinite worlds both like and unlike this world of ours...We must believe that in all worlds there are living creatures and planets and other things we see in this world.”

Epicurius c. 300 B.C

Thousands of years ago, Greek philosophers speculated.

And so did medieval scholars.

The year 1584

"There are countless suns and countless earths all rotating around their suns in exactly the same way as the seven planets of our system . . . The countless worlds in the universe are no worse and no less inhabited than our Earth”

Giordano Brunoin De L'infinito Universo E Mondi 4

1995Discovery of the first planet around another star.

A Swiss team discovers a planet – 51 Pegasi –48 light years from Earth.

Artist's concept of an extrasolar planet (Greg Bacon, STScI)7

Didier Queloz and Michel Mayor

And then the discoveries started rolling in:

“First new solar system discovered”USA TODAY

April 16, 1999

“10 More Planets Discovered” Washington Post

August 6, 2000

“New Planet Seen Outside Solar System”New York TimesApril 19, 1996

http://planetquest.jpl.nasa.gov/A useful site to keep current on discoveries:

Some of the stars that have planets are bright enough to see in the night sky…

…if you know where to look

Just how far are these new planets?

from Mars…it would taketen minutes

from the nearest extrasolar planet…

it would takeover ten years!

from the Moon… it would takeone second

IF YOU WANTED TO RADIO HOME

FOR YOUR WORDS TO REACH EARTH

But not far on a cosmic scale.

would be the size of the United States.

Our Milky Way Galaxy

where we’ve found new planets would only be the size of Manhattan.

And the neighborhoodOur whole Solar System

would be this big

Imagine, if you shrunk our solar system to a little larger than a quarter:

Using a variety of methods involving powerful telescopes and computers

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How have we foundall these planets?

Planets and stars orbit their mutual center of mass.

Precise measurement of a star’s

velocity or

change of position

tells us the extent of the star's movement about this center of mass induced by a planet's gravitational tug.

From this information, the planet's mass and orbit can be deduced.

Doppler ShiftBecause of the Doppler shift, light waves from a star moving toward us are shifted toward the blue end of the spectrum. If the star is moving away, the light waves shift toward the red end of the spectrum.

The larger the planet and the closer it is to the host star, the faster the star moves about the center of mass, causing a larger Doppler shift in the spectrum of starlight. That's why many of the first planets discovered are Jupiter-class (300 times as massive as Earth), with orbits very close to their parent stars.

1 planet, e = 0.04

1 planet, e = 0.72

1 planet, e = 0.33

1 planet, e = 0.67

Astrometric MeasurementAs with the radial velocity technique, this methods depends on the slight motion of the star caused by the orbiting planet. In this case, however, astronomers are searching for the tiny displacements of the stars on the sky.

To measure the motion in the above example would require an observer in Bloomington to be able to read the date on a quarter in Denver!

Astrometric displacement of the Sun due to Jupiter as at it would be observed from 10 parsecs, or about 33 light-years.

Transit MethodIf a planet passes directly between a star and an observer's line of sight, it blocks out a tiny portion of the star's light, thus reducing its apparent brightness.

Sensitive instruments can detect this periodic dip in brightness. From the period and depth of the transits, the orbit and size of the planetary companions can be calculated. Smaller planets will produce a smaller effect, and vice-versa. A terrestrial planet in an Earth-like orbit, for example, would produce a minute dip in stellar brightness that would last just a few hours.

Since Kepler’s launch:

Zero to more than 80 Earth-sized planet candidates

Zero to 54 candidates in the habitable zone

At least five of the planetary candidates are both near Earth-size and orbit in the habitable zone of their parent stars."

Area searched: 105 square degrees, approx. 134 times the area of the Moon

Gravitational MicrolensingThis method derives from one of the insights of Einstein's theory of general relativity: gravity bends space. We normally think of light as traveling in a straight line, but light rays become bent when passing through space that is warped by the presence of a massive object such as a star.

When a planet happens to pass in front of a star along our line of sight, the planet's gravity will behave like a lens. This focuses the light rays and causes a temporary sharp increase in brightness and change of the apparent position of the star.

Astronomers can use the gravitational microlensing effect to find objects that emit

no light or are otherwise undetectable.

Direct ImagingSince planets do not give off their own light, observing them directly presents formidable challenges. While the parent star is the source of light that will make any planet visible, its glare is between a million and 10 billion times brighter than the faint little speck we are looking for. Therefore, any direct imaging of extrasolar planets requires methods to cover up or otherwise control the glare of the parent star. In addition, very high resolution is needed to separate the planet from its nearby host.

Three planets orbiting the sun-like star HR 8799. Each is thought to have several times the mass of Jupiter. The innermost planet, “d”, orbits at a distance approximately equal to Neptune’s orbit. The system is 130 light years

distant.

Stars are a billion times brighter…

…than the planet

…hidden in the glare.

Like this firefly.

Dusty debris disk and the 3 Jupiter mass planet Fomalhaut b. Its orbit is ~ 23 times the size of Jupiter’s orbit. The

system is 25 light years distant.

Dusty debris disk and planet orbiting the star Beta Pictoris. The orbit is approximately the size of Saturn’s orbit. The

system is 50 light years distant.