Download The Discovery of Planets beyond the Solar System

The Discovery of Planets
beyond the Solar System
Luis A. Aguilar
Instituto de Astronomía, UNAM.
México
First of all,
What is a planet?
.
Contrary to what you may have thought,
this is something difficult to
answer
Have you ever wondered, what exactly is a planet?
.
When we think about planets, what
comes to mind are the planets of the
Solar System:
.
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,
Neptune and Pluto.
You may think that a planet is a heavenly body
that doesn’t shine with its own light and goes
around a star ......
. but
asteroids are not luminous and go around the
Sun!
What is then a planet?
.
What is then a planet?
You may be surprised to know that not even astronomers
.
are sure
Let’s see if we can define what is a planet
First of all, a planet is not a star
.
Let’s see if we can define what is a planet
First of all, a planet is not a star
.
The fundamental difference between a star and a planet is its size, or more
precisely, its mass. The more massive a heavenly body, the greater the pressure
and temperature at its center. In a star it gets so hot, that thermonuclear
explosions get started, and these produce so much energy, that a star shines
with its own light.
The minimum stellar mass is 0.08 of the Sun’s mass
Let’s see if we can define what is a planet
This makes a star shine with its own light, while a
planet can only reflect the light it receives from a
star.
.
Let’s see if we can define what is a planet
However, there are so called “brown dwarfs”, which are “failed
stars” that couldn’t get thermonuclear reactions started.
A brown dwarf is less massive than a star, but more massive than a planet.
A brown dwarf shines but not as much as a star.
To.be a brown dwarf an object must have a mass at least 10 times Jupiter’s mass.
Let’s see if we can define what is a planet
So, the largest mass that a planet can have is about
10 times Jupiter’s mass!
.
and what is the smallest mass?
Let’s see if we can define what is a planet
Here the mass is important to determine the shape
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Let’s see if we can define what is a planet
Here the mass is important to determine the shape
In a planet, the force of
gravity is strong enough to
squeeze it into a round
shape.
.
Let’s see if we can define what is a planet
Here the mass is important to determine the shape
In a planet, the force of
gravity is strong enough to
squeeze it into a round
shape.
.
In a smaller object, like an
asteroid, the force of gravity
can’t overcome the stiffness of
rocks, and so it remains
irregularly shaped.
Let’s see if we can define what is a planet
Here the mass is important to determine the shape
In a planet, the force of
gravity is strong enough to
squeeze it into a round
shape.
.
In a smaller object, like an
asteroid, the force of gravity
can’t overcome the stiffness of
rocks, and so it remains
irregularly shaped.
Let’s see if we can define what is a planet
But there are spherical objects in the Solar System
that we don’t call planets......
Some, like the moon, don’t go around
the Sun, but around a planet.
But others, like the recently discovered,
Sedna and Quaoar, go around the Sun.
The
. smallest mass of a planet is not well defined, for some
astronomers it is Pluto’s mass, which is a hundred thousand times
smaller than Jupiter’s.
A planet is then:
A heavenly body with a mass between a hundred-thousandth
and ten times that of Jupiter
It does not shine with its own light, but with reflected light
It travels around a star
It is spherical
.
To
call it a planet, an object must satisfy all these conditions.
How is a planet?
.
How is a planet?
Mercury
Mars
Venus
Earth
Pluto
In the Solar System there are two different types of planets:
.
On one side, we have the terrestrial planets: these are small,
made of rock and with a metallic core. Except for Pluto,
which is the smallest and most distant, they move close to
the Sun.
How is a planet?
Uranus
Neptune
Saturn
Jupiter
In the Solar System there are two different types of planets:
We also have the gaseous giants: these are big, made of
gas and light elements. All are far from the Sun and spin very
. fast.
How is a planet?
Orbits
.Except for Pluto, all planets follow almost circular paths around
the Sun and lie on the same plane.
How is a planet?
Sizes
Orbits
Compared
to Earth, their diameters span from a fifth for Pluto, to
.
eleven times for Jupiter.
How is a planet?
Sizes
Distances
Orbits
Mercury
goes around the Sun 3 times closer than Earth, while Pluto is 40
.
times farther away.
Are there planets going around
other stars?
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For a long time, philosophers, writers and
scientists, have speculated about the
existence of worlds beyond the Solar
System
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For a long time, philosophers, writers and
scientists, have speculated about the
existence of worlds beyond the Solar
System
And populated them with a zoo of fantastic creatures
.
However, astronomers studying the formation of
the Solar System, had many reasons to believe
that there ought to be many other planets
We think that when a star is born, a gaseous disk surrounds it. Dust condenses
in the disk, and through sticky collisions, it forms gravel, pebbles, rocks and so
on, all the way to planetesimals and planets,
.At the end, planet formation shuts down when the bright light from the infant star
dissipates the gaseous disk.
However, astronomers studying the formation of
the Solar System, had many reasons to believe
that there ought to be many other planets
. process of planet formation can be studied using computer simulations
This
However, astronomers studying the formation of
the Solar System, had many reasons to believe
that there ought to be many other planets
In fact, astronomers have recently seen disks of gas and dust surrounding
.
young stars. It is thought that planets are being formed in them
But finding a planet beyond out planetary system is an
extremely hard task.
.
Why is so difficult to find extrasolar planets?
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Why is so difficult to find extrasolar planets?
One reason is the vast distances involved. Earth is only 8 light.minutes away from the Sun, but the closest star is 4 light-years
away.
At this distance, it is very, very hard to see a planet.
Why is so difficult to find extrasolar planets?
Another reason is because planets don’t shine with their own light,
this makes them very faint compared to their stars.
.
Have
you noticed how the same flashlight looks bright at night and
dim during the day?.
How to find then an extrasolar planet?
.
How to find then an extrasolar planet?
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When two stars move around each other, they move equally
How to find then an extrasolar planet?
But when a planet moves around a star, the star moves very little,
.
because
the planet is a lot less massive.
How to find then an extrasolar planet?
The tiny stellar motion can be measured ...
.
How to find then an extrasolar planet?
The tiny stellar motion can be measured ...
Using what is called the Doppler effect.
When a car approaches, we hear a high pitch sound, and when it recedes,
the sound turns to a lower pitch.
Sound is a wave, when the car is approaching us, the wave is “compressed”,
when the car recedes, it is “stretched”.
A .short wave is a high pitch tone, a long wave is a low pitch tone.
How to find then an extrasolar planet?
The tiny stellar motion can be measured ...
Using what is called the Doppler effect.
The same happens with light, here short waves correspond to blue light,
.
while long waves are red light.
This can be used to detect the motion of a star.
How to find then an extrasolar planet?
The tiny stellar motion can be measured ...
Using what is called the Doppler effect.
The variation in color is very, very small. It is equivalent to a highway patrol
officer detecting a difference between a car moving at 60 mph and another
.
moving
at 60.05 mph, a difference of about 80 yards per hour!
How to find then an extrasolar planet?
Another way to discover planets is by occultation
.
How to find then an extrasolar planet?
Another way to discover planets is by occultation
.
When going around a star, a planet may pass in front of its star,
as seen from Earth. When this occurs, the brightness of the star
will appear to diminish a little bit.
How to find then an extrasolar planet?
Another way to discover planets is by occultation
The size of the effect depends on the relative sizes of the planets and
the star. Since planets are very small compared to their stars, the
effect will be very little.
.
How to find then an extrasolar planet?
Another way to discover planets is by occultation
The size of the effect depends on the relative sizes of the planets and
the star. Since planets are very small compared to their stars, the
effect will be very little.
For
. Jupiter passing in front of the Sun, the dimming is only 3%. This is like
distinguishing between a 97 watt and a 100 watt light bulbs.
For the Earth the effect is much smaller.
Discovering extrasolar planets
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Discovering extrasolar planets
Despite all these difficulties, on October 5, 1995, two
French astronomers: Michel Mayor and Didier Queloz,
From the Observatoire de Haute Provence, announced
to the world the discovery of the first extrasolar planet.
.
Discovering extrasolar planets
Despite all these difficulties, on October 5, 1995, two
French astronomers: Michel Mayor and Didier Queloz,
From the Observatoire de Haute Provence, announced to
the world the discovery of the first extrasolar planet.
.
It was a planet with half the mass of Jupiter, going around the star
51-Pegasi, a star like the Sun 50 light-years away.
The change in the star’s velocity was only 55 yards/s.
Discovering extrasolar planets
Despite all these difficulties, on October 5, 1995, two
French astronomers: Michel Mayor and Didier Queloz,
From the Observatoire de Haute Provence, announced to
the world the discovery of the first extrasolar planet.
Just a week later, the American astronomer Geoff Marcy confirmed this discovery from
Lick observatory. After centuries of search, the race to find the first extrasolar planet had
a photo finish!
. the new planet took everybody by surprise: it went around its star in only
But
4 days, moving at one twentieth of the Earth-Sun distance.
Discovering extrasolar planets
And then the avalanche of discoveries began ....
.
Discovering extrasolar planets
And then the avalanche of discoveries began ....
In January of 1996, Marcy discovered the second extrasolar planet.
It went around the star 70-Virginis, 57 light-years away.
.The new planet was a giant 7 times more massive than Jupiter, moving
around its star in 116 days at half the Earth-Sun distance.
Discovering extrasolar planets
And then the avalanche of discoveries began ....
The following month, a third planet was discovered. It went around
the star 47-Ursa Majoris, 45 light-years away.
.The new planet had a mass in between the previous two: 2.5 times the
mass of Jupiter. The size of its orbit was larger: 2 time the Earth-Sun
distance, going around its star in 3 years.
Discovering extrasolar planets
And then the avalanche of discoveries began ....
In August of the same year, additional planets are discovered
around 55-Canceri, Tau-Bootis and Upsilon-Andromedae.
In 1996 a total of 6 planets are discovered.
One in 1997.
Eight in 1998.
Thirteen in 1999.
.And 28 in 2000!
Up to April 16th, 2005, 154 extrasolar planets have been discovered.
What have we learnt about extrasolar planets?
.
What have we learnt about extrasolar planets?
All discoveries have been in stars near the Sun.
. But this is just because the closer the star, the easier to detect a planet.
What have we learnt about extrasolar planets?
With a pair of exceptions, all discovered planets move very close to their
stars.
. This is due to the Doppler effect used in most discoveries: the star
motion is larger when the planet going around is closer
What have we learnt about extrasolar planets?
.
The masses span a range from one half to ten times Jupiter’s mass,
right at the limit were brown dwarfs begin.
What have we learnt about extrasolar planets?
.
The Doppler effect technique can not discover planets like those in the Solar System, at least
not yet, because these are either too small or move to far away from the Sun.
What have we learnt about extrasolar planets?
However, in 1999 the discovery of a planet around the star HD-209458 was
announced. The importance of this discovery lies in that it was the first planet
discovered using the occultation technique. This opens up new possibilities
for discovery
.
What have we learnt about extrasolar planets?
What have we learnt about their orbits?
Contrary to expectations, many planets follow orbits that are quite
. elongated. This is still a big mystery.
What have we learnt about extrasolar planets?
Something important to us is the
extent of the “habitable zone”, this is
the region around a star were water
can exist in liquid form on a planet’s
surface.
This is the region to look for life.
Unfortunately, most of planets found
to date lie outside this zone.
.
The diversity of discovered planets was a big
surprise to Astronomers
There is a planet so small, that its mass is only 0.2 times that of Jupiter.
There is one so big, that is 11 times more massive than Jupiter.
There is a planet going around its star in only 3 days, there is another
that takes 4.5 years.
The planet closest to its star moves at only 0.04 of the Earth-Sun
distance. The planet moving the farthest away is at 2.8 times the EarthSun distance from its star.
In the Solar System, all planets move in near-circular orbits (except
Pluto); among the discovered extrasolar planets, almost a third move in
very elongated orbits.
Planets have been found even around pulsars, which are the remains of
massive stars that exploded as Supernovae.
.
There may be enough planets in our Galaxy to give one to each person on
Earth!
What to expect next?
The direct exploration of
planets in the Solar System
will continue
Landing of the probe Huygens in Titan, one of Saturn’s
satellites. The Cassini spacecraft is at upper right (December
2005).
.
What to expect next?
The direct exploration of
planets in the Solar System
will continue
Around 2007, NASA will
launch Kepler, a satellite that
will detect minute variations in
the brightness of nearby
stars. It will search for planets
passing in front of their stars.
Kepler will search for extrasolar planets using the
occultation technique
.
What to expect next?
The direct exploration of
planets in the Solar System
will continue
Around 2007, NASA will
launch Kepler, a satellite that
will detect minute variations in
the brightness of nearby
stars. It will search for planets
passing in front of their stars.
SIM will use sophisticated interferometric techniques to
try to get direct images of extrasolar planets.
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Even more ambitious is the
SIM mission planed for 2009.
Its goal is to get direct images
of extrasolar planets.
What to expect next?
Pioneer and Voyager, the first emissaries of mankind, are leaving
the Solar System .
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We live in extraordinary times.
I hope you have enjoyed this talk and
learnt something new
The End
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