Exoplanets
Big Science: Big Telescopes
Jodrell Bank Discovery Centre
Contents
Part 1: Big Telescopes
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Why do we need so many
telescopes?
Why build big telescopes?
Part 2: Big Science
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Hunting for exoplanets
Are We Alone in the Universe?
Part 1: Big Telescopes
Why do we need so many telescopes?
Light is an electromagnetic wave that travels through space...
...but light is not the only EM wave travelling through space
Part 1: Big Telescopes
Why do we need so many telescopes?
An object can give off any of these EM waves...
Radio waves
km to metres
Microwaves
centimetres
Infrared
micrometres
Visible light
tenths of a
micrometre
Ultraviolet
nanometres
X-rays
tenths of
nanometres
Gamma rays
hundredths of
nanometres
Astronomers observe the universe in all of these waves
Part 1: Big Telescopes
Why do we need so many telescopes?
Part 1: Big Telescopes
Why build big telescopes?
The Lovell Telescope
Telescopes collect EM waves and
bring them to a focus
Part 1: Big Telescopes
Why build big telescopes?
Why build big telescopes?
• Larger telescopes collect more waves
• Fainter objects can be seen
• Like a pupil dilating in dim light!
Larger telescopes can also
create sharper images
Part 1: Big Telescopes
Why build big telescopes?
The Square Kilometre Array
• Planned for 2020, it will be the most powerful radio telescope ever
• It will be so sensitive it could detect an airport radar 50 light years away
• It will collect enough data every day to fill 15 million 64 GB iPods
1. How do you think it would it affect your vision, if your eyes
were half the size?
2. If your eyes could see radio
waves, what do you think a
mobile phone mast would
look like?
1. How do you think it would it affect your vision, if your eyes
were half the size?
Your eyes couldn’t collect as much light, so things would be darker.
Also, things would be more blurry.
2. If your eyes could see radio
waves, what do you think a
mobile phone mast would
look like?
It would look bright, like
a streetlamp!
Part 2: Big Science
The hunt for exoplanets
The hunt for exoplanets
Part 2: Big Science
The hunt for exoplanets
Before we continue…
1. Multiply your time by 100 days
(e.g. 2 seconds becomes 200 days)
This is to make your results more realistic!
2. How many Earth years does it take
for your planet to orbit its star?
Part 2: Big Science
The hunt for exoplanets
Analysing your results: How far out is your planet?
Kepler’s third law
For planets orbiting the Sun…
Orbit in Earthyears  DistancefromSun in A.U.
2
3
1 A.U. (or ‘Astronomical Unit’) is just the distance between the Earth and the Sun
T D
2
3
How far away would
your planet be from
its star?
Part 2: Big Science
The hunt for exoplanets
Analysing your results: How far out is your planet?
T D
2
3
3
T D
2
Compare your planet to our Solar System.
Distance from Sun to…
Mercury = 0.4 AU
Jupiter = 5 AU
Venus = 0.7 AU
Saturn = 9.5 AU
Earth = 1 AU
Uranus = 19 AU
Mars = 1.5 AU
Neptune = 30 AU
Part 2: Big Science
The hunt for exoplanets
Analysing your results: How big is your planet?
You have already calculated the percentage
starlight blocked by your planet (B)
Area of planet B  Area of star
Area of a circle?
r  B  R
2
Radius of Sun = 700,000 km
What’s the radius of your planet?
2
Part 2: Big Science
The hunt for exoplanets
Analysing your results: How big is your planet?
r  B  R
2
2
r  BR
2
Compare your planet to our Solar System.
Radius of Earth = 6,400 km
Radius of Jupiter = 70,000 km
Part 2: Big Science
Are we alone?
Are we alone in the universe?
August 2013: Scientists have detected a total of 929 exoplanets
Part 2: Big Science
Are we alone?
620 light years away
Star Kepler-22
Part 2: Big Science
Are we alone?
In 2011, astronomers found planet
‘Kepler-22B’ around this star…
Kepler-22B is…
• Approximately Earth sized.
• About the same distance away from its
star as the Earth is from the Sun.
AND, its star is very similar to the Sun!
Are we alone?
What do you think?
Part 2: Big Science
Extension activity
What type of exoplanets do you think are the easiest to find?
Why?
1. Larger exoplanets
2. Exoplanets that are closer to their stars
Both of these cause a larger dip in the star’s light, making them
easier to detect.
So far, most of the exoplanets found have been “hot Jupiters”.
These are large gas planets, but very close to their star.
Part 2: Big Science
Extension activity
What assumptions did we make when calculating the distance and
size of your exoplanet?
• That your star is like the Sun
In actual fact, the star may be a different mass. This will change how quickly a
planet orbits around it, which will affect the distance calculation.
Also, the star may be a different size. This will affect the planet size calculation.
In real life, astronomers take measurements of a star’s light to see if it is like
the Sun or not.
• That your planet passes next to your star
In actual fact the planet will likely be hundreds of millions of km closer to us
than the star, which will make it look slightly bigger. This will also affect the
planet size calculation.
In real life, astronomers estimate the distances to stars and planets, so they
can take this into account.
Part 2: Big Science
Extension activity
Consider the following questions...
1. Can you think of any situations where the method we have used to detect exoplanets
would not work? (hint: look at the animation below for one way)
2. We assumed that your stars were identical to the Sun. What effect would it have on
the size of your planet if the star were actually…
a) Larger than the Sun
b) Smaller than the Sun
3. What effect would it have on your planet’s
distance from the star if your star was…
a) More massive than the Sun (more gravity)
b) Less massive than the Sun (less gravity)
4. If your star is like the Sun, do you think there is
any chance of there being life on your planet?
Why?
5. Would there be more or less chance of life if
your star was…
a) Hotter than the Sun
b) Colder than the Sun
Part 2: Big Science
Extension activity
Answers…
1. This method only works if, from our point of view, the planet passes in front of the
star. If the planet orbits the star on a different plane, we will not see a dip in the light.
2. We calculated the size of your planet by comparing it to the size of your star, which
we said was the same as the Sun. If your star was…
a) Larger than the Sun; the planet would be larger than calculated.
b) Smaller than the Sun; the planet would be smaller than calculated
3. We calculated the distance of your planet from its star by looking at how fast your
planet was orbiting its star. We assumed the relationship was the same as the planets
of the Solar System going around the Sun. If your star was…
a) More massive than the Sun (more gravity), then the planet would orbit quicker
than expected. Therefore, the planet may be further out than calculated.
b) Less massive than the Sun (less gravity), then the planet would orbit slower than
expected. Therefore, the planet may be closer to its star than calculated.
Questions 4 and 5 depend on your results.