This is the 1st Graded Assignment at the University of Arizona course of Astrobiology: Exploring Other Worlds.
Writer: Menelaos Gkikas
We're actually searching for exoplanets and potentiality for habitability and it's essential to realize the singularity in scientific judgements. When you travel in space you may not have others "holding your hand"... For the purposes of the course and this assignment, even the knowledge, the inspiring instructor, the cloud environments as well as notes and calculations, plus the criteria of grading that focus mainly on the structure and the different parts and logic of this assignment concept, are not enough to make a "diagnosis", even if we are graded by an AI... When you make a diagnosis you need the exact calculations and the dozens of astronomical and comparative data not present in this course, not even in other courses, but accessible only to real time physicists and astronomers making observations or experimenting. Here, we become experimentalists beyond "right or wrong" bearing in mind that the viewing angle with which we choose to write is paramount.
Here, we mingle methods for the observations of exoplanets with Newton's law of gravity and global attraction, Kepler laws of planetary motions and then potentiality for habitability at a system that should not be confused with our solar system...
Science Prompt:
As a fledgling astrobiologist, you are given the following two sets of data, corresponding to two newly discovered exoplanets. There are two graphs for Star A, and one for Star B:
Your research advisor wants to do follow-up observations on the exoplanet that is most Earth-like. It is your job to analyze these data and determine which, if either, exoplanet has the potential for habitability. In 250-750 words:
Identify the method/s used to gather the data for each exoplanet (radial velocity, transit, gravitational lensing or direct imaging). Briefly explain how each method works.
Discuss what physical characteristics can be learned from the data for each exoplanet and explain your reasoning.
Identify which planet is more Earth-like, and the more likely habitable candidate. Use the information from the observational data to explain 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: 90%
Answer:
1.) The method used for gathering data about exoplanet A was the radial velocity method portrayed with its first graph and the transit method portrayed with its second graph.
The method used for gathering data about exoplanet B, was again the radial velocity method portrayed with its only graph for exoplanet B.
The radial velocity method – for both exoplanets - is founded so to measure the reflex motion of a star caused by an exoplanet as measured by an outside observer considering the approaching or receding body. This reflex motion that is caused by Newton’s universal law of attraction, a gravitational law indeed, affects the electromagnetic radiation emitted by the star, hence it also affects its wavelength and color of light if compared with the distance from the observer. It is therefore founded on the Doppler shift basis.
The transit method especially for the star – exoplanet system A, talks about a periodical dimming of the brightness of the star, displayed as an actual eclipse of the star caused by the periodical orbit of the exoplanet. This means that the exoplanet blocks a portion of the starlight of its host. The relative periodical decrease of the star’s brightness is portrayed in the graph.
2.) The physical characteristics that can be learned from the data for each exoplanet take place with the data portrayed by the radial velocity method and the transit method if combined with Kepler’s universal laws of planetary motions.
From the radial velocity diagrams of the host star for exoplanets A and B, we get to calculate the periods of the phenomena. We can then use Kepler’s 3rd law to calculate the orbital distances of exoplanet A and exoplanet B. By these, using the orbital distance and the implications of Kepler’s 1st law, we can calculate the velocities of the exoplanets A and B. Bear in mind that the orbital distance addresses elliptical orbits where if they are approximated as circles, we can simplify calculations. Once the velocities of the exoplanets are known we can calculate exoplanet mass using conservation of momentum.
We can then use the information provided from the transit method, especially for exoplanet A to calculate the physical size of the exoplanet, meaning, an approximate sense of how big it is, addressing its radius. Knowing the radius of the exoplanet A and assuming it a perfect sphere we can calculate the density of the exoplanet and argue of whether this density addresses more like gas giant planets or better rocky compositions suitable for habitability and life.
We can also visualize that the stronger reflex motion of exoplanet B caused to its star addresses a higher mass for exoplanet B, a longer orbital period for exoplanet A and by Kepler’s 3rd law calculations we can also deduct that exoplanet B is closer to the host than A. Knowing also that the transit depth of A is minimal and larger planets block more starlight, we derive a higher physical size for exoplanet B that can also be calculated by density equation.
3.) The period of exoplanet A is closer – even though not similar – to the period of Earth around the Sun. The orbital period of exoplanet A is a little above 150 days while the period of exoplanet B is a little bit higher of only 6 days…! Much faster. This means that exoplanet A has a little less that half the orbital period of Earth.
Knowing that the density of exoplanet B is higher than that of A, makes this exoplanet of more solid material which is more suitable for humans. Making the actual calculations of the Kepler’s 3 laws of planetary motions, we can also compare the physical characteristics and figures computed with those of Earth and other more habitable planets, to compare and contrast advantages and disadvantages of hosting life.
We can also determine the planet with more liquid or more solid composition. Nevertheless, knowing the mean density of the planet is not a full disclosure of its composition as there are many models that can match the single mean density measured. We just know that exoplanet B might be a more suitable candidate for habitability, a more Earth-like planet.
