Transcript ES 5F Extra Solar Planet Detectionx

5) Earth in space and time. The student
understands the solar nebular accretionary
disk model. The student is expected to:
(f) compare extra-solar planets with planets in our solar system
and describe how such planets are detected.
• Observation with telescopes of other star systems based on the
star’s radial velocity caused by the gravitational force between
the planets and the star (Wiggle-Wobble Effect)
• Transit Method; Photometric method; Gravitational Microlensing
Any planet is an extremely faint
light source compared to its
parent star.
In addition to the incredible
difficulty of detecting such a
faint light source, the light from
the parent star causes a glare
that washes it out. For those
reasons, only a very few
extrasolar planets have been
directly observed.
Instead, astronomers have generally had to resort to indirect
methods to detect extrasolar planets. At the present time, several
different indirect methods have yielded success.
A star with a planet revolving around it will move in its own small orbit in
response to the planet's gravity. This leads to variations in the speed with
which the star moves in relation to the Earth. I.e. the variations are in the
radial velocity of the star with respect to Earth.
This has been by far the most productive
technique used by planet hunters. It is also
known as Doppler spectroscopy. It is generally
only used for relatively nearby stars out to
about 160 light-years from Earth.
Disadvantages:
While DS easily finds massive planets that are
close to stars, detection of those orbiting at
great distances requires many years of
observation.
The objects that emit light make up only a tiny portion of the
mass of a galaxy. Microlensing allows the study of objects that
emit little or no light, like brown dwarfs, black holes, and
planets.
https://youtu.be/FHh0Qx7LPJY
A pulsar is produced by a neutron star: the small,
ultra-dense remnant of a gigantic star that has
exploded as a supernova. Pulsars emit radio waves
extremely regularly as they rotate.
These regular rotations can be used to track the pulsar's
motion.
Like an ordinary star, a pulsar will move in its own small orbit
if it has a planet. Calculations based on pulse-timing
observations can then reveal the size and shape of that orbit,
and the probable planet.
Drawbacks:
The main drawback of the pulsar-timing method is that pulsars
are fairly rare, so it is unlikely that a large number of
planets will be found this way.
Also, and perhaps more importantly, life as we know it could not
survive on planets orbiting pulsars since high-energy radiation
there is extremely intense.
1. Why must scientists resort to “indirect” methods to detect
extrasolar, or exoplanets?
2. Doppler Spectroscopy, also known as ____________ ___________
method, measures the star’s “Wiggle-Wobble” as influenced by an
orbiting planet.
3. The most productive method of extrasolar planet detection is…?
4. Describe ONE disadvantage of using DS method.
5. What method helps scientists view extrasolar objects that don’t
emit light, like brown dwarfs, black holes and planets?
6. What are the two drawbacks of using the pulsar timing technique?
When a planet crosses in front of a
star, then the star’s brightness dims
by a small amount.
This is measurable, and the method
used by space telescopes that were
launched in the last decade.
Disadvantage:
One limitation of this method is
that it is only possible to detect
these crossings, also known as
transits, when the planet and the
star are perfectly aligned with the
line of sight of the detection
instrument on Earth or in space.
This method, also called the
photometric method can
determine the radius of a
planet.
The amount the star dims
depends on the relative
sizes of the star and the
planet.
About 10% of planets with
small orbits have such
alignment, and the fraction
decreases for planets with
larger orbits.
Stellar
Spectroscope
The transit method also makes
it possible to study the
So…there MUST be methane in Saturn’s
atmosphere!
atmosphere of the transiting
planet.
When the planet transits the
star, light from the star
passes through the upper
atmosphere of the planet.
By studying the stellar
spectrum carefully, as it
filters through
that
planet’s
Missing frequencies through the spectroscope are clues, indicating
elements or
compounds
that
atmosphere, one can detect
absorb light at those frequencies are present in the atmosphere.
For example, if the light frequencies corresponding to methane
and carbon
monoxide
are
elements
present
in that
missing from an analysis of the starlight, the atmosphereatmosphere.
contains methane and carbon
monoxide, which absorbed the missing light.
https://youtu.be/t2xTlv_I6ac
We use similar methods to determine atmospheric components around
planets in our own solar
system.
Being able to identify the gases in an orbiting planet’s atmosphere
is most important to a branch of science known as astrobiology.
These scientists are interested in finding Earth-like planets, and
in doing so, finding the signatures of life.
Neil deGrasse Tyson
What types of
elements and
molecules would
you expect to
find in the
atmospheres of
Carl Sagan
these
planets?
Oxygen?
Water Vapor?
Ozone?
Carbon Dioxide?
Nitrogen?
Michio
Kaku
Michio Kaku
So far, the extrasolar planets that have
been easiest to detect are large, and in
small, close orbits of their star.
Many of these are gas giants like the
planet Jupiter but orbiting as close to
their sun as planet Mercury.
This type of planet has been called a
“hot Jupiter”.
Why couldn’t planets like hot Jupiters
have formed close to the sun in our solar
system?
At this stage, it appears to be fairly common for Sun-like stars to have
planets. This would mean there is an enormous number of planets in our galaxy,
given there are at least 200 billion stars. AND REMEMBER…that is only our galaxy!
7. _______________, or photometric method relies on a star’s dimming as a
planet moves in a direct path between the observer and the star.
8. Describe ONE limitation of using the transit method to detect exoplanets.
9. Describe how spectroscopy used during the transit method can help determine
what a planet’s atmosphere is like.
10. Why would an astrobiologist be interested in spectral analysis of a
planet’s atmosphere?
11. If you were an astrobiologist looking for evidence of life on exoplanets,
what signatures would you be looking for in your spectral analysis of the
planet?
12. What is a “Hot Jupiter” and what is the currently accepted theory for
their formation?