Habitable Zones Cara Bryan
docx
keyboard_arrow_up
School
Florida State College at Jacksonville *
*We aren’t endorsed by this school
Course
2010C
Subject
Astronomy
Date
Dec 6, 2023
Type
docx
Pages
9
Uploaded by okcfan200015
Habitable Zones
Big Idea:
Earth is the only planet known to harbor life of any kind, past or present. As part of the
search for evidence of life on other planets, both in our Solar System and in other planetary
systems, we are looking not just for evidence of living organisms themselves, but for evidence
of the conditions that might even be hospitable to life as we know it. One feature that
astronomers consider to determine whether a planet MIGHT have the conditions necessary for
life as we know it is whether the planet falls within a 'habitable zone' of its host star.
If you have already learned about habitable zones in another astronomy class or from your own
general knowledge, great. If not, or if you'd like to get a stronger background before proceeding,
please read more about habitable zones at one or more of the following websites:
astro.unl.edu:
http://astro.unl.edu/naap/habitablezones/chz.html
universetoday.com:
http://www.universetoday.com/32622/habitable-zone/
astronomynotes.com:
http://www.astronomynotes.com/lifezone/s2.htm
space.com:
http://www.space.com/2021-growing-habitable-zone-locations-life-abound.html
Goal:
Students will conduct a series of inquiries about the nature of circumstellar habitable
zones and the factors they depend on, and the timescale for the evolution of life on Earth.
Computer Setup:
To access the University of Nebraska’s Habitable Zone Simulator, you will
need to download and install the Native App at the URL:
https://astro.unl.edu/nativeapps/
Phase I. Exploration
A habitable zone is a region around a star where the amount of light received from the star by
objects in that region (namely planets) leads to temperatures in which any water on the surface
could exist in liquid form. The amount of light received by a planet from a star depends on its
distance from the star (farther away means less light), and therefore so does the planet’s
surface temperature.
In this definition of habitable zone...
1.
What is meant by "habitable"?
It is meant that in that zone the average temperature on a planet allows for liquid water with
which to make porridge. Not just water we would hunt for but water that would show signs of
alien life.
2.
Why is it a "zone" and not one specific location?
It is a zone because the temperature at a certain distance will not change so around the star
as long as you stay at the certain distance of the star's habitable zone you will be in it. The
zone is mainly based on the distance from the star not in what direction.
3.
What type of astronomical object is it surrounding?
A Star
4.
What object(s) may be located within it?
Earth-like planets or any other objects that would be orbiting the star.
5.
What is the possible temperature range for a planet in the habitable zone of its star
(quantitatively)?
0 degrees celsius to 100 degrees celsius
Load the Habitable Zone Simulator. The flash simulator will show you a visual diagram of the
solar system in the top panel, a set of simulation settings in the middle panel, and a timeline of
the habitability of the Earth in the bottom panel. The timeline units will either be Megayears
(Myr), which means millions of years, or Gigayears (Gyr), which means billions of years. To run
the simulation, click run in the bottom panel. This button immediately becomes a pause button,
which will allow you to pause the simulation at any time.
The simulation runs pretty quickly by default. To adjust the speed, use the rate slider bar to the
right of the run button. You can also manually advance the simulation forward or backward by
clicking and dragging the upside-down dark grey triangle above the timeline. To restore the
simulation to the original default settings, press the reset button at the very top of the simulation.
6.
The simulation is currently set to zero-age - this is the Solar System as it was when it first
formed, about 4.5 billion years ago. Which planet(s) were in the Habitable Zone at this time,
if any?
Earth
7.
The blue region marked on the diagram is the Habitable Zone around our Sun. Notice how
there is both an inner edge and an outer edge - the planet’s interior to the habitable zone is
too hot to support liquid water, while the planet’s exterior to it is too cold. Why?
The planets on the interior of the habitable zone are close to the sun making it too hot
meanwhile the planets on the exterior are so far that the sun does not provide enough heat
and the water and other liquids on the planet freeze.
8.
Below are two stars and their habitable zones, with distances drawn to the same scale
(stars not drawn to scale). Which star is brighter/hotter? How do you know?
Star B is brighter and hotter because we know from the astronomy notes source that the hot
luminous star has a larger and wider habitable zone compared to the smaller habitable zone
in star A which would be the cooler and dimmer star.
9.
Press the
start
button and watch the Habitable Zone change with time. Pause the
simulation when it reaches an age of 4.5 billion years (age=time since star system
formation; you can keep track of the time by looking at the timeline marker in the bottom
panel). This is the Solar System as it is today - which planet(s) are in the Habitable Zone
now, if any?
Earth is still the only planet in the habitable zone.
10. Allow the simulation to run until the Earth is no longer in the Habitable Zone. At what age
does this happen? How long from now until this happens? (You can use the timeline bar in
the bottom panel to determine your answers. Be sure to include units with your numbers
above.)
The Earth leaves the habitable zone at the 5.5 Gy mark or, five and a half billion years. If four
and a half is where we are now this leaves another billion years before Earth leaves the
habitable zone.
11. After the Earth is no longer within the Habitable Zone, what do you think the conditions on
Earth will be like, and why?
The world would start to flood and all of the ice would melt at an alarming rate even faster
than they do now with global warming. This is because we would be on the interior of the
habitable zone making us too hot of a planet to sustain liquid water and life.
12. Resume the simulation and let it run until the end. Which planets other than the Earth will fall
within the Habitable Zone at any point during the Sun's life, if any?
Mars, Jupiter, and Saturn all fall within the habitable zone before the Sun’s life ends.
13. Why does the habitable zone change during the Sun's lifetime? Pay attention to how the
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
properties of the Sun change, and explain how this can affect the habitability of planets.
The habitable zone will increase and stretch further away as the luminosity of the Sun grows.
The effects on planets can be severe as the Sun can and will become so bright in the future
that Earth will no longer be in the habitable zone and that Mars, Jupiter, and Saturn will be
there eventually possibly making them a habitable planet for us.
14. Around 12 billion years, the Earth's distance from the Sun suddenly changes. Why?
Due to the Tidal effects that take place we slowly move away from the Sun as it is and the
Sun growing in energy as the life cycle goes on the more energy will push us away faster than
it does now.
Phase II. The History of Life on Earth
As you saw in the simulations above, the Earth has been
within the Habitable Zone of our Sun nearly since its
formation 4.5 billion years ago. Complex life, however, did
not develop immediately. And humans did not appear until
later still. The timeline at right delineates several milestones
in the history of life on Earth.
15. For each of the events on the timeline, determine how
long after the formation of Earth this event occurred (in
Gigayears -- "Giga" means billion) Then, calculate what
fraction of its current age (4.5 billion years) the Earth
was at that time. Fill in your answers on the table below.
For example, in the 2nd row: the first primitive life arose
3.8 Gyr ago, which was 0.7 Gyr after Earth formed (4.5
Gyr - 3.8 Gyr = 0.7 Gyr). At that time, when Earth was
0.7 Gyr old, that was 0.7/4.5 = 0.155 = 15.5% of Earth's
current age.
Significant Event
Age of Earth at the time (Gyr)
% of Earth’s current age
Earth forms
0.0
0
First life emerges
0.7
15.5%
First photosynthesis
1.7
37.7%
Multicellular organisms
3.0
66.6%
Land animals
4.05
90%
First humans
4.4995
99.9%
16. Think about your answers to the previous timeline question. What do you think was the
purpose of that exercise? What is the take-home message? (Think about whether primitive
life arose early or late. What about humans?)
I believe the purpose was to know the amount of time it took for the first life to emerge all the
way to when the first humans were on Earth. The take home message for me is that it took
the Earth almost all of its age right now just to have us be here, and it may be possible that
making another planet habitable may not be a possibility due to the amount of time it takes for
it to start photosynthesis.
Phase III. The Habitable Zones of Different Kinds of Stars
Now that you've simulated the Habitable Zone (HZ) around our Sun, we'll run the same
simulation for other stars. For seven different star types, your job will be to find the
planet orbit that remains in the HZ the longest. This will take some time! This is the main
part of this lab.
Astronomers classify stars with letters: O, B, A, F, G, K, and M. The O stars are the
hottest and most luminous, while M stars are the coolest and dimmest. Every types of
star has its own HZ, with brighter stars having more-distant HZs. Imagine putting an
extra log on a campfire; the campers all have to back off a few feet to maintain the
same comfortable temperature.
Below is a table of the different types of stars in the classification scheme above. Notice
how they each have a different mass - in fact, the
mass
of a star is the underlying
determining factor for all other stellar properties (luminosity, temperature, etc.), and
therefore dictates how it will be classified. The highest-mass stars are hottest.
Reset the HZ simulator with the reset button at top, and then adjust the star mass with
the initial star mass slider bar in the middle panel. The units of star mass are Solar
Masses (M); our Sun's mass is exactly one Solar Mass (1.0 M) by definition. Notice how
the HZ immediately changes in size. Notice also that you can adjust the orbit of “Earth”
(i.e., the planet under consideration) by adjusting the initial planet distance slider bar in
the middle panel. You can also adjust it by clicking on the planet itself and dragging it
closer or farther from the star. The units of distance from the star are AU - astronomical
units, which is defined as the real-life distance of the Earth from the Sun. The Earth is 1
AU from the Sun by definition.
17.
For each type of star in the table below, run the simulator with the closest mass you
can find to that listed as "typical" for that type. Indicate what mass you chose in the
third column, even if it was identical to the typical mass listed in the second column.
Adjust the initial planet distance (we suggest dragging the planet back and forth
slowly through the HZ while keeping an eye on the total length of the blue bar,
indicating time of habitability, on the bottom) until you find the one that gives the
longest amount of time continuously in the HZ; record both the initial planet distance
used and the corresponding total time in the HZ. Note: you are recording the total
time continuously in the HZ for the longest stretch, not necessarily just the time
when the planet leaves the HZ, which may be different. Finally, in the last column,
record the most advanced life (if any) that could develop in this amount of time,
using your answers from the table in the previous part.
For some of the lower-mass stars, you should find that the planet becomes tidally
locked even while it is still in the habitable zone. Ignore tidal locking, and just pay
attention to when the planet is in the HZ.
Star
Type
Typical
Star
Mass
(M
Sun
)
Simulated
Star Mass
(M
Sun
)
Orbit Size of the
longest
habitable orbit
(AU)
Habitable
Lifetime (Gyr*)
Most advanced life that
could develop
O
16
15
189
0.115
None
B
5
4.0
21.2
1.74
Photosynthesis
A
2
2.0
5.55
1.15
Photosynthesis
F
1.3
1.2
1.81
5.25
Humans
G
1.0
1.0
1.17
8.18
Humans
K
0.7
0.70
0.50
7.18
Humans
M
0.4
0.40
No habitable
orbit
0
None
* WARNING: Sometimes the numbers on the timeline are shown in Myr (Megayears, where "Mega" = million) instead
of Gyr (Gigayears, where "Giga" = billion) in cases where the star lives are short enough to warrant these units. Be
sure to convert times in Myr to Gyr as necessary before you enter your answer!
18. Given your answers in the table above, and keeping in mind that the Universe is only 13.7
billion years old, what type of star do you think would be the best place to look for planets
harboring life, and why?
A G star because they have a lifespan of about 8.18 billion years. That would give us the most
time possible for us to habit the planet and make it liveable and get back to our lives. Although
since the universe is already 13.7 billion years old I do not know how long we will be able to
survive.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
19. What do you notice about the TOTAL lifetimes of the different types of stars? (That is, the
lifetimes of the stars themselves, ignoring any planets and the HZ.) Which live the longest,
and which the shortest?
The lower mass stars I noticed have longer life spans as the scale of which the gyr were
measured were larger due to the timeline needing more years. The larger mass stars
happened to live the shorter lives and became dwarfs faster.
16. Which type of star is most luminous? Which is least? So which is easiest to detect and
monitor?
The higher mass stars were more luminous and the lower stars were the least luminous. This
means that the higher mass stars would be easier to detect and monitor as they stand out
more and give off more energy as they are brighter, hotter, and about to explode and become
dwarfs.
17. What type of star is our Sun? Compared to our Sun's type, what do you think the
development of life on planets orbiting hotter types of stars would be like? What about cooler
types of stars? (Note: Do you think that life in such conditions is even possible? Either way,
justify your above answers in one or two sentences each.)
Our Sun is a G type star. This makes sense to me as the G type star in the table had the best
chance of having life that can be sustained on a planet for the longest amount of time. I
believe that there is a way for planets hotter and colder than Earth to habituate humans, of
course not ones like mercury or neptune which are way too cold to do so but Mars can have a
strong possibility. This is because of the habitable zone and the length left on the star's life
that we would need to use to make the planet safe for humans to live on.
19. If you were the director of a NASA program to search for life beyond Earth, toward which
type of star would you direct your attention, and why? Justify your answer, including evidence
from previous questions. You may also use any additional lines of reasoning you like.
I would direct my attention towards the G type stars. This is because of all the research I
conducted and the information gathered and put into the most recent table above. The G type
stars will have the longest span of which a planet will be in its habitable zone. Therefore for
the sake of the humans on Earth I would go after stars that will give them the longest amount
of time possible to live on that planet before needing to relocate to another.
Phase IV. The Habitability of Different Kinds of Stars
20. Jupiter's moon Europa is currently covered with water ice (H2O), and possibly liquid water
beneath. How is this possible, given that Jupiter is well outside our Sun's current HZ? Be
sure to consider on which side of our Sun's HZ Jupiter and Europa are located, and include
in your answer what assumptions go into the standard definition of "habitable zone" as used
by this simulator.
This is possible because Jupiter and Europa are on the exterior of the habitable zone making
water and liquids possible, they would just be frozen over. From the simulator this would not
be habitable because the habitable zone would not be in Jupiter for a very long time and then
when it is in the habitable zone the amount of time it would probably take too long for the ice
to melt before the planet leaves the habitable zone.
21. If a planet or moon IS inside the habitable zone, does that necessarily mean it is habitable?
Why or why not? (Hint: Earth's Moon is inside our Sun's habitable zone. Is it habitable?)
No it does not, this is shown with the moon because the moon is in out habitable zone but is
inhabitable. This is due to the lack of atmosphere and oxygen on it. With other planets the
conditions on the planet may not be suitable for life. For example Mars may be suitable,
however on Jupiter the big red spot which is twice the size of Earth may very well easily make
that planet inhabitable as we would not be able to survive such a violent storm constantly
raging.
Phase V. Formulate a Question, Pursue Evidence, and Justify Your Conclusion
Your task is now to design an answerable research question, propose a plan to pursue
evidence, collect data using Solar System Simulator, and create an evidence-based conclusion
about some motion or changing position of a moon of the solar system that was not previously
addressed.
Specific research question:
Which option from the planet drop down menu would be the best option to consider as
another planet for life?
Step-by-step procedure, with sketches if needed, to collect evidence:
To start off you would go into the drop down and select the first planet, now run the simulation
and observe and take note of how long it takes for the planet to leave the habitable zone.
Repeat this process until you have taken note of the time each planet in the list spends in the
habitable zone.
Data table and/or results:
Gliese 581 - inhabitable
55 Cancri A - 8.20 Gy
51 Pegasi - inhabitable
HD 40307 - 4.90 Gy
HD 189733 - inhabitable
HD 93083 - 2.09 Gy
Evidence-based conclusion statement:
From the evidence collected from the simulation, the best option star to look at as a new
home would be 55 Cancri A as it has a habitable period of 8.20 billion years. Giving a planet in
its habitable zone enough time to develop and be ready for humans to live on said planet.
Phase VI. Summary
Create a 50-word summary, in your own words, that describes the motions, orbits, or rotations
of Jupiter’s moons and how this changes over time. You should cite specific evidence you have
collected in your description, not describe what you have learned in this course or elsewhere.
Feel free to reference things learned in specific phases (I-V), or to create label sketches to
illustrate your response.
In this project I learned that there are other stars out there which can provide us a habitable
zone that may contain a planet where we will have the time to develop life and find a new
home. I also learned in phase two just how long it actually took for the Earth to develop into
having humans.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help