This is the 2nd Graded Assignment from the University of Arizona in Astrobiology: Exploring Other Worlds. Taking into account the Visual Storytelling Image in this article as well as having detected 3 exoplanets, here we analyze, we prioritize and we explore habitable worlds in exoplanetary systems that can be much different than our solar system.
Writer: Menelaos Gkikas
For the purposes of this assignment, I discuss key concerns in the search for habitable worlds, ranging from the host star and its type, the orbital distance from the star that can affect the "Goldilocks Zone", meaning the range from the host star in Astronomical Units where water can exist on the surface of the exoplanet as liquid hence referring to a surface temperature as well, plus the atmosphere indicated by whether the exoplanet is massive enough to possess geologic activity that affects the retaining of a thick atmosphere.
Furthermore, to define of whether exoplanetary systems resemble our solar system or not, we take into account that host stars are classified by their spectral type which indicates the mass of the star (computed as a figure of solar masses). The existence of liquid water or not is the major criterion in this assignment.
Science Prompt:
Three Earth-like exoplanets are detected. Exoplanet-1 orbits an A star, exoplanet-2 orbits a G star, and exoplanet-3 orbits an M star. Each exoplanet orbits at the same orbital distance of 1 AU.
Yousef says that all three Earth-like planets likely have liquid surface water because they all orbit at 1 AU. Since the Earth orbits at 1 AU from the sun, and we know Earth has liquid surface water, then these exoplanets should as well.
Lora says that both exoplanets 2 & 3 will have liquid water, but not exoplanet-1. The star for exoplanet-1 is spectral type A, which is too big and hot and would evaporate water on exoplanets. But exoplanet-2 and exoplanet-3 orbit around favorable spectral types G and M, therefore they likely have liquid surface water.
Consider both Yousef and Lora’s statements. In 250-750 words, write a response to Yousef and Lora about whether you agree or disagree with their assessment of the surface conditions on each exoplanet. The table below has information that may be helpful for supporting your reasoning.
BEFORE YOU BEGIN!
Plan ahead: Create a rough-outline so that you may better express your thoughts in a clear and ordered fashion. Be sure to use facts and relevant examples to reinforce your response.
BEFORE YOU SUBMIT!
Before you submit your writing, be sure to self-assess based on the rubric.
Instructions:
You are limited to a 750 word response.
There is no set writing format we ask you to follow, but we do recommend that you carefully read the writing prompt and address exactly what is asked. A good way to ensure this is to restate the question(s). For example, should the writing prompt ask:
"What is the Scientific Method?"
You might begin by stating:
"The Scientific Method is..."
And then order your paragraphs/sections accordingly.
You might consider composing your response in a word processor (e.g., Microsoft Word) in order to better facilitate your writing. Once complete, simply copy and paste your text.
Do not attach external documents or images or cite outside sources. There is no need to do so. The information provided by Dr. Impey in his video lectures and slides is sufficient to answer all questions.
Grade: 100%
Answer:
To state my agreement or disagreement with Yousef and Lora, my argumentation begins with the order and the hierarchy of the spectral types of stars, beginning from the least massive, coolest and least luminous towards the most massive, hottest and most luminous from left to right and indicated by the letters MKGFABO.
Exoplanets detected, beginning from exoplanet 3, continuing with exoplanet 2 and then exoplanet 1, orbit around an M, G and A star respectively. To search for habitable exoplanets means to define criteria related with the host star, the orbital distance from the star, the surface temperature of the exoplanet as well as the atmosphere of the exoplanet.
Since all exoplanets orbit their host star at a distance of 1 AU, which is the identical orbital distance of our Earth hosted by the Sun, we use this figure as our measure of a possible orbital distance where water can exist in the surface of the exoplanet as liquid, the “Goldilocks Zone” in other words.
Based on the previous discussion we judge the M, G and A hosts.
In general, the F, G, K, M stars in the order are the best habitable candidates with lifetimes spanning from 3 billion years and above, whereas O, B and A stars possess shorter lifetimes where complex life would be annihilated by a supernova at the end of the star’s lifetime.
Additionally, since the M host is the coolest, least massive and least luminous but a more probable candidate, I make a first distinction between the M, G hosts from one side and the A host from the other side. Planets that are more massive in general can possess significant geologic activity that could affect the existence of a thick atmosphere. Sufficient atmospheric pressure which is necessary for liquid water is another criterion but these last arguments are merely the comparison evidence.
A smaller planet but with sufficient mass to retain an atmosphere but limited heating from geological activity could potentially maintain liquid water near the star.
Host star M is the least massive but has much lesser range of a Goldilocks zone if compared with the 1 AU, it’s only 0.3-0.4 AUs. The previous mean that the criterion for liquid water is not satisfied.
Host star G, a very much Sun-like host – including mass and lifetime - is almost equalized with the orbital distance of 1 AU to be inside the range of 0.9–1.8 that defines the limits of habitability, so this can be the only exoplanetary system that resembles our solar system.
Host star A is the most massive, hottest and most luminous of the 3 but since the exoplanet orbits at 1 AU and here the Goldilocks Zone addresses 3.5 to 7.1 AUs, then this exoplanet is not habitable in terms of maintaining liquid water on surface, since it orbits around the hottest star with this concrete habitable zone, water will probably be evaporated.
Neither Yousef nor Lora are completely right or completely wrong. Yousef is right about G but wrong about M and A. Lora Is right about G and A but wrong about M. The exoplanet orbiting M probably reaches or even surpasses the cryogenic biosphere.
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