habitable-zones-report
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Florida International University *
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1002L
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Astronomy
Date
Jan 9, 2024
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
Habitable Zones
Exercises
Please read through the background pages entitled Life, Circumstellar Habitable Zones, and The Galactic Habitable Zone before working on the exercises using simulations below.
Circumstellar Zones
Open the Circumstellar Zone Simulator. There are four main panels:
The top panel simulation displays a visualization of a star and its planets looking down onto the plane of the solar system. The habitable zone is displayed for the particular star being simulated. One can click and drag either toward the star or away from it to change the scale being displayed.
The General Settings panel provides two options for creating standards of reference in the
top panel.
The Star and Planets Setting and Properties panel allows one to display our own star system, several known star systems, or create your own star-planet combinations in the none-selected mode.
The Timeline and Simulation Controls allows one to demonstrate the time evolution of the star system being displayed.
The simulation begins with our Sun being displayed as it was when it formed and a terrestrial planet at the position of Earth. One can change the planet’s distance from the Sun either by dragging it or using the planet distance slider.
Note that the appearance of the planet changes depending upon its location. It appears quite earth-like when inside the circumstellar habitable zone (hereafter CHZ). However, when it is dragged inside of the CHZ it becomes “desert-like” while outside it appears “frozen”.
1.
Drag the planet to the inner boundary of the CHZ and note this distance from the Sun. Then drag it to the outer boundary and note this value. Lastly, take the difference of these two figures to calculate the “width” of the sun’s primordial CHZ.
Credit ~ NAAP
CHZ Inner Boundary
CHZ Outer Boundary
Width of CHZ
.816 AU
1.17 AU
.354
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
2.
Let’s explore the width of the CHZ for other stars. Complete the table below for stars with a variety of masses.
Solar Mass
(
M
⨀
)
Star
Luminosity
(
L
⨀
)
CHZ Inner
Boundary
(AU)
CHZ Outer
Boundary
(AU)
Width of CHZ
(AU)
0.
3 0.
0
1
3
2 0.
1
0
9 0.0132
0.109
0.157
0.04
8
0.7
0.04
8
0.7
0.04
8
0.7
0.04
8
Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
0.
1
5
7 0.
0
4
8
0.
7 0.
0
3
4 0.7
0.048
Credit ~ NAAP
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
0.
3
5
3 0.
5
0
1 0.
2
1
9
1.
0 Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
0.
7
3
9 0.
8
2
2 1.
1
7 0.
3
Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
4
8
2.
0 1
6.
5 3.
8
7 5.
5
5 1.
Credit ~ NAAP
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
6
8
4.
0 2
4
1 1
4.
8 2
1.
2 6.
Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
4
0
8.
0 2
6
9
0 4
9.
5 7
0.
8 Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
2
1.
3
1
5.
0 1
9
0
0
0 1
3
1 Credit ~ NAAP
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
1
8
8 5
7
0.
3 0.
0
1
3
2 0.
1
Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
0
9 0.
1
5
7 0.
0
4
8
0.
7 0.
0
Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
3
4 0.
3
5
3 0.
5
0
1 0.
2
1
Credit ~ NAAP
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
9
1.
0 0.
7
3
9 0.
8
2
2 1.
1
7 Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
0.
3
4
8
2.
0 1
6.
5 3.
8
7 5.
5
Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
5 1.
6
8
4.
0 2
4
1 1
4.
8 2
1.
Credit ~ NAAP
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
2 6.
4
0
8.
0 2
6
9
0 4
9.
5 7
Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
0.
8 2
1.
3
1
5.
0 1
9
0
0
0 1
Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
3
1 1
8
8 5
7
0.3
0.7
0.034
0.353
0.501
0.219
1.0
0.739
0.822
1.17
0.348
2.0
16.5
3.87
5.55
1.68
4.0
241
14.8
21.2
6.40
8.0
6.40
8.0
6.40
8.0
6.40
Credit ~ NAAP
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
8.0
2690
49.5
70.8
21.3
15.0
19000
131
188
57
3.
Using the table above, what general conclusion can be made regarding the location of the CHZ for different types of stars?
The mass of a star influences the position of the CHZ. When the star's mass decreases, the habitable zone shifts closer to the Sun, whereas an increase in the star's mass results in the zone moving farther away.
4.
Using the table above, what general conclusion can be made regarding the width of the CHZ for different types of stars?
5.
The
width is less when the star mass is lower and a Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
higher
star mass means
the width 6.
incr
eases
The width is less when the star mass is lower and a higher star mass means the width increases
Exploring Other Systems
Begin by selecting the system 51 Pegasi. This was the first planet discovered around a star using the radial velocity technique. This technique detects systematic shifts in the wavelengths of absorption lines in the star’s spectra over time due to the motion of the star around the star-planet center of mass. The planet orbiting 51 Pegasi has a mass of at least half Jupiter’s mass.
7.
Zoom out so that you can compare this planet to those in our solar system (you can click-hold-drag to change the scale). Is this extrasolar planet like any in our solar system? In what ways is it similar or different?
he extrasolar planet is similar to Mercury since Credit ~ NAAP
Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
both are extremely hot on the outside and extremely cold on the opposite side of the planet, the difference is that the extrasolar planet
is closer to the Sun than Mercury
The extrasolar planet bears similarities to Mercury in that both exhibit extreme heat on one side and extreme cold on the opposite side. However, the key distinction is that the extrasolar planet is situated closer to its host star than Mercury is to the Sun.
8.
Select the system HD 93083. Note that planet b is in this star’s CHZ. Now in fact this planet has a mass of at least 0.37 Jupiter masses. Is this planet a likely candidate to have life like that on Earth? Why or why not?
Yes, it’s in a habitable zone
9.
Note that Jupiter’s moon Europa is covered in water ice. What would Europa be like if it orbited HD 93083b?
It would be water because it is in the CHZ.
Credit ~ NAAP
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
Select the system Gliese 581. This system is notable for having
some of the smallest and presumably earth-like planets yet discovered.
Look especially at planets c and d which bracket the CHZ. In fact, there
are researchers who believe that the CHZ of this star may include one
or both of these planets. (Since there are several assumptions involved
in the determination of the boundary of the CHZ, not all researchers
agree where those limits should be drawn.) This system is the best
candidate yet discovered for an earth-like planet near or in a CHZ.
The Time Evolution of Circumstellar Habitable Zones
We will now look at the evolution of star systems over time and investigate how that affects the circumstellar zone. We will focus exclusively on stellar evolution which is well understood and assume that planets remain in their orbits indefinitely. Many researchers believe that planets migrate due to gravitational interactions with each other and with smaller debris, but that is not shown in our simulator.
We will make use of the Time and Simulation Controls panel. This panel consists of a button and slider to control the passing of time and 3 horizontal strips:
The first strip is a timeline encompassing the complete lifetime of the star with time values labeled
The second strip represents the temperature range of the CHZ – the orange bar at the top indicates the inner boundary and the blue bar at the bottom the outer boundary. A black line is shown in between for times when the planet is within the CHZ.
The bottom strip also shows the length of time the planet is in the CHZ in dark blue as well as labeling important events during the lifetime of a star such as when it leaves the main sequence.
Stars gradually brighten as they get older. They are building up a core of helium ash and the fusion region becomes slightly larger over time, generating more energy.
10.
Return to the none selected mode and configure the simulator for Earth (a 1
M
⨀
star at a distance of 1 AU). Note that immediately after our Sun formed Earth was in the middle of the CHZ. Drag the timeline cursor forward and note how the CHZ moves outward as the Sun gets brighter. Stop the time cursor at 4.6 billion years to represent the present age of our solar system. Based on this simulation, how much longer will Earth be in the CHZ?
5.6 billion years
11.
What is the total lifetime of the Sun (up to the point when it becomes a white dwarf and no longer supports fusion)?
Credit ~ NAAP
Planet
Earth Mass
e
> 1.9
M
⨁
b
> 15.6
M
⨁
c
> 5.4
M
⨁
d
> 7.1
M
⨁
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
12 billion years
12.
What happens to Earth at this time in the simulator?
You may have noticed the planet moving outwards towards the end of the star’s life. This is due to the star losing mass in its final stages.
We know that life appeared on Earth early
on, but complex life did not appear until several
billion years later. If life on other planets takes a
similar amount of time to evolve, we would like
to know how long a planet is in its CHZ to
evaluate the likelihood of complex life being
present.
To make this determination, first set the
timeline cursor to time zero, then drag the planet
in the diagram so that it is just on the outer edge
of CHZ. Then run the simulator until the planet is
no longer in the CHZ. Record the time when this
occurs – this is the total amount of time the planet
spends in the CHZ. Complete the table for the range of stellar masses.
13.
It took approximately 4 billion years for complex life to appear on Earth. In which
of the systems above would that be possible? What can you conclude about a star’s mass and the likelihood of it harboring complex life?
The first 4
Credit ~ NAAP
Solar
Mass (
M
⨀
)
Initial Planet Distance (AU
)
Time in CHZ
0.3
0.157
380 Gy
0.7
0.5
30
1.0
1.15
8.32
2.0
5.44
2.10
4.0
20.8
0.176
8.0
69.5
0.0324
15.0
187
0.0114
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Name: Sachintha Peiris AST1002L RVC RVF RVD RVE 1238
Tidal Locking
We have learned that large stars are not good candidates for life because they evolve so quickly. Now let’s take a look at low-mass stars. Reset the simulator and set the initial star mass to 0.3 M
⨀
. Drag the planet in to the CHZ.
Notice that the planet is shown with a dashed line through its middle. What has happened is that the planet is so close to its star that is has become tidally locked due to gravitational interactions. This is analogous to Earth’s moon which always presents the same side towards Earth. For a planet orbiting a star, this means one side would get very hot and the other side would get very cold. (
However, a thick atmosphere could theoretically spread the heat around the planet as happens on Venus. In answering the following questions, please put aside this possibility.
)
14.
What would happen to Earth’s water if it were suddenly to become tidally locked to the Sun? What would this mean for life on Earth?
Tidal locking of Earth to the Sun would lead to extreme water redistribution, causing one side to become arid and the other frozen. Life on the Sun-facing side would struggle in extreme heat, while the dark side would face bitter cold. Biodiversity and ecosystems would be severely disrupted, with some extremophiles possibly surviving in the twilight region. Overall, it would pose significant challenges for life on Earth.
15.
Complete the table below by resetting the
simulator, setting the initial star mass to the value in the table, and
positioning the planet in the middle of the CHZ at time zero. Record whether or not the planet is tidally locked at this time. If
tidal locking reduces the likelihood of life evolving on a planet,
which system in the table is least conducive towards life?
CHZ Summation
We have seen that low-mass stars have very small CHZs very close to the star and that planets become tidally locked at these small distances. We have seen that high-mass stars have very short lives – too short for life as we know it to appear.
The combination of these two trains of thought is often referred to as the Goldilocks hypothesis – that medium-mass stars give the optimal opportunity for complex life to appear.
Credit ~ NAAP
Solar
Mass
(
M
⨀
)
Tidally Locked?
0.3
yes
0.5
yes
0.8
no
1.0
No
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