Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-26
Course Announcements
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How is the sunset/sunrise observing going?
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SW-chapter 7 posted: due Fri. Oct. 30
SW-chapter 8 posted: due Wed. Nov. 4
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Exam-3 Wed. Nov. 4: Ch. 6,7, 8
Take more astronomy!
Registration for the Spring semester starts soon so think
about taking more astronomy.
ASTR-1010/1011: Planetary Astro & lab (Tell your friends)
ASTR-1020/1021: Stellar Astronomy & lab (Reg. + Honors)
ASTR-2020: Problems in Stellar Astronomy
ASTR-3010: History of Astronomy
ASTR-3040: Intro. To AstroBiology
PHYS-2468: Intro. To Physics Research
ASTR-3030/3031: Instrumentation & Techniques
 Planets can gather gasses from the disk
by core accretion-gas capture.
 This creates the primary atmosphere.
 Low-mass planets cannot hold on to their
primary atmospheres.
 Some low-mass planets later emit gasses
from their interiors (e.g., from volcanoes),
producing a secondary atmosphere.
 Each of the four terrestrial planets lost its
primary atmosphere.
 Low-mass planets lose their primary
atmospheres.
 Recall that temperature measures the
average speed of motion of gas atoms.
 If the gas moves quickly enough, it will
escape the planet.
 Low-mass planets have low escape
velocities.
 Also, hot planets will have fast-moving gas
particles.
 The four inner planets are rocky.
 The four outer planets are gaseous giants.
 Asteroids and comets are leftover
planetesimals, while moons formed from the
giant planets’ accretion disks.
Lecture Tutorial: Temp. & Formation
of Our Solar System: pg. 111
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with
one another. Take time to understand it
now!!!!
• Come to a consensus answer you both agree
on.
• If you get stuck or are not sure of your answer,
ask another group.
 The physical processes that led to the Solar
System should be commonplace.
 We can see young stars with disks.
 Extrasolar planet: a body that orbits a star
and has a mass less than 13 Jupiters.
 We have found more than 1000 confirmed
extrasolar planets, or “exoplanets.”
 Four main techniques to find these
planets:
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Spectroscopic radial velocity method
Transit method
Microlensing method
Direct imaging
Spectroscopic radial velocity method:
 Gravity is a mutual force, so both stars
and planets orbit one another.
 Motion can be detected by Doppler shifts.
 Some stars have periodic velocity
changes; therefore, they are orbited by
planets.
MATH TOOLS 7.2
 In the spectroscopic
radial velocity
method, the Doppler
shift of the star’s
wobble can be used
to estimate the mass
and orbit of the
planet.
 M is the combined
mass, and the star’s
mass is much bigger
than the planet’s.
 A planet passing in front of a star
(transiting) can decrease the total
brightness of the star.
 Microlensing makes a star temporarily
brighter, through a planet’s gravity focusing
its light.
MATH TOOLS 7.3
 By measuring the amount by which a star’s
light is dimmed during a planet’s transit as
well as the length of time the planet is in front
of the star, you can estimate the size of the
planet.
Direct imaging:
 It is very difficult to directly see a faint planet
in the bright glow of its star.
 A few dozen planets have been identified this
way so far.
 Many known planets
have 1 to ten times
the mass of Jupiter.
 Some of these orbit
close to their stars
and are called hot
Jupiters.
 It is easier to find
these very large
planets due to the
greater “wobble” they
cause for their stars.
 Most planetary
systems found to date
do not resemble ours.
 Researhers have also
found mini-Neptunes
and super-Earths.
 Planet locations,
orbital inclination
angles, and orbital
directions are different
than our Solar
System.
 Kepler
Mission seeks
to find rocky
planets using
transits in the
habitable
zone of their
stars.
 Potential
conditions for
liquid water.
Concept Quiz Hot Protostars
We know that stars have different temperatures. Consider a
newly forming star that was much hotter than the protoSun. What would we expect about its planets?
A. The planets orbit at random angles around the star.
B. Rocky planets might be formed over a wider range of
distances than in our Solar System.
C. The star would be “naked,” without a surrounding disk.
Concept Quiz Other Planets
Which of these is not a reason why we can find planets
around other stars?
A.
B.
C.
D.
The planet’s gravity causes the star to orbit.
We can take images and directly see the planets.
We can detect radio signals from life on the planets.
A star’s light could be affected by its planet.
Concept Quiz Protoplanets
Which of the following statements is false?
A. Planetary systems begin as a disk of material around a
protostar.
B. Planetesimals accrete material to become planets.
C. All the planetesimals in our Solar System have become
planets.
PROCESS OF SCIENCE
 Different scientists
can reach the same
conclusions.
 Beginning from
fundamental
observations,
theorists, planetary
scientists, and
stellar astronomers
converge to the
collapsing nebula
hypothesis.