Astronomy Lab- Exo-Planets

Big Idea: Planets orbiting other stars have orbital characteristics similar and different to our own solar system of planets orbiting our Sun.

Goal: Students will conduct a structured series of scaffolded scientific inquiries about the nature of observed exoplanets using the Internet sites prescribed, particularly the Exoplanet Data Explorer.

Computer Setup: Access URL http://exoplanets.org/

Needed Resources: Solar System Data Table (below), calculator, and these instructions

 

Phase I: Exploration Part A

This section concerns the planets in our own solar system; Phase II and beyond concerns exoplanets — planets orbiting OTHER STARS

 

 

A histogram is a bar-chart showing the number of objects in a particular category, so it is useful for showing how populations are distributed in a certain characteristic.

 

Consider the research question, “How are characteristics of exoplanets distributed?” Use the SOLAR SYSTEM DATA TABLE and sketch a histogram for each of the following three questions. REQUIRED: Include your actual sketches in your response. You will need to take pictures of your histograms using a camera phone or other digital camera, or else scan them in.

 

 

1.

 

 

 

 

Histogram 1: Distribution of Orbital Distance. Make a histogram showing the number of Planets Closer and Farther than Earth’s Orbital Distance, labeling your axes similar to the first example shown above.

Histogram 2: Distribution of Masses. Make a histogram showing the number of planets with Masses Less than Earth’s Mass and Greater than Earth’s Mass, labeling your axes similar to the second example shown above.

Histogram 3: Distribution of Orbital Periods. Make a histogram showing the number of Planets with orbital periods smaller than Earth’s period (P < PEarth), between Earth’s and Jupiter’s periods (PEarth ≤ PERIOD ≤ PJupiter), and longer than Jupiter’s period (P > PJupiter). (Note: Throughout this lab, “Period” and “Orbital Period” are synonymous.) Label your axes similar to the third example shown above.

 

 

You do not need any additional descriptive text beyond the image of your histograms. All three sketches can be on one page (one file) if you wish.

 

Phase I: Exploration Part B

This section concerns the planets in our own solar system; Phase II and beyond concerns exoplanets — planets orbiting OTHER STARS

 

Consider the research question, “What is the distribution of orbital distances for exoplanets?” A correlation-diagram (or “scatter plot”) is a graph of dots showing how two characteristics, or variables, are related. Use the SOLAR SYSTEM DATA TABLE and sketch a correlation-diagram (graph) for each of the following three descriptions. REQUIRED: Include your actual sketches in your response. You will need to take pictures of your graphs using a camera phone or other digital camera, or else scan them in.

 

 

2.

 

Title: Distance (AU) vs. Period (Years) for Planets Closer than Jupiter (not including Jupiter). (Vertical Y-axis Distance versus Horizontal X-axis Period). Your graph sketch should use the same labeled axes as those depicted in the example:

Title: Distance (AU) vs. Period (Years) for Planets With Orbits Jupiter-sized and larger. (Vertical Y-axis Distance versus Horizontal X-axis Period). Your graph sketch should use the same labeled axes as those depicted in the example:

Title: Distance (AU) vs. Mass (MEarth, which means in units of Earth’s mass) for ALL Solar System Planets. (Vertical Y-axis Distance versus Horizontal X-axis Mass). Your graph sketch should use the same labeled axes as those depicted in the example:

 

Upload all three sketches below (they can all be on the same page / file if you like):

 

Phase I: Exploration Part C

 

Consider the research question, “Which characteristics of exoplanets are most highly correlated with distance?” The notion of correlation is the idea that two characteristics are closely related to one another. IMPORTANT NOTE: CORRELATION IS NOT THE SAME AS CAUSE-AND-EFFECT.

 

3.

One of the two graphs below is Intelligence versus Height and the other is Weight versus Height. In the text box below them, precisely explain your reasoning about why which is which.

 

 

Explanation of why which graph is which:

 

4.

Based on your work above on analyzing the planets of our solar system, which variable, PERIOD or MASS, seems to be more highly correlated to DISTANCE? Explain your reasoning, using any needed labeled sketches, if you like, to illustrate your answer.

 

Phase II – Does the Evidence Match a Given Conclusion?

 

Very Brief Tutorial On Using The Exoplanets Data Explorer Table at http://exoplanets.org/

0) Hovering your mouse over a column header shows an explanation of what each term means. This is true later on, using the “Plot” feature as well.

1) Sorting: Clicking on a column header sorts the data table by that quantity. Clicking it again reverses the order of the sort.

2) Notice that the first column gives the exoplanet’s NAME. Try sorting the table by NAME.

3) The second column is the exoplanet MASS (times a factor called “sin(i)”, which we will ignore because it is small). The MASS of the planet is given in terms of how many times bigger (or smaller) than the mass of our planet Jupiter, mjupiter by default, but you can change the units by clicking on this label and selecting from a drop-down list of alternate units. Try changing the units of mass from ‘mjupiter’ (Jupiter Mass) to ‘mearth’ (Earth Mass), and then back to Jupiter Mass again.

4) The fourth column shows the exoplanet’s Orbital Period, a.k.a. PERIOD. The period is the length of time it takes the planet to go around its central host star once. By default the units are Earth days, but you can change the units by clicking on this label. Try sorting the table from largest to smallest period.

5) The third column shows the SEMI-MAJOR AXIS. This is another name for how far the planet orbits its star, on average. The default units of distance are AU, or Astronomical Unit. IMPORTANT DEFINITION: One AU is the average distance our Earth orbits our Sun.

6) Removing Columns: You can simplify the table by removing columns you don’t want to look at. If you hover your mouse over a column header, you should see a faint red “x” that allows you to remove that column. Try this with “Time of Periastron” as an example. You can always add a column back in after removing it.

7) Adding Columns: You can add columns to the table by clicking the large “+” (plus) sign at the top right of the page. There are many categories to choose from! Add in the column “Date”, as we will be needing it.

 

5.

PART A: Access the Exoplanet Data Explorer [http://exoplanets.org/], “Table” option, and sort and search the data to find a planet that was discovered (published) in 1995 and record data about it here. You will find it helpful to add a First Publication “Date” column to the table! (See the mini-tutorial above for instructions for adding columns.) The units are provided for Mass, but you must fill them in for Period and Semi-Major Axis.

Planet Name:

 

Property	number	units
Mass		Jupiter masses
Period
Semi-Major Axis Length

 

 

 

6.

Is this planet more massive than Earth?

yes

no

 

7.

If so, how many more times more massive? If not, what percentage of Earth’s mass does it have? Enter a number only:

 

PART B: Select “Plot” at the top left, then “Histogram Plot” at the right. Choose Semi-Major Axis as the “Data” to plot. (It’s in the third column, under “Orbit Parameters”.) All confirmed planets to date will be shown by default. Remember that Earth orbits our Sun at a distance of 1 AU and Jupiter orbits at about 5 AU.

 

8.

Click “Add Filter” to see the number of planets (#) under the Statistics After Cut section. How many exoplanets are initially shown in this data set? exoplanets. (Note: the answer you get will depend on the day you do it, as this number is continually updated to reflect the current total.)

 

9.

Clicking “Add Filter” lets you add a criterion to restrict the number of planets appearing on the plot. Under the “+” sign next to the “Filter” text box, choose “Semi-Major Axis”. A[au] should now appear in the box. (“A” is the abbreviation for semi-major axis, and AU are the units.) to the right of this, in the box, type “>10” to restrict the sample to planets whose orbits are larger than 10AU. Notice that the # of planets is now 0, since there are no currently known exoplanets with orbits that large. If you instead change this to “<10” (or erase it entirely), you will see the original number of planets back, because this is no restriction at all.

 

How many of the currently known exoplanets have orbits larger than Jupiter’s orbit about our Sun? exoplanets. (Note: the exact numbers you get may depend on the day you do it, as this database is continually updated to reflect the current known exoplanets.)

 

10.

What is the percentage of currently known exoplanets that have orbits larger than Jupiter’s orbit about our Sun? Your answer should be a number only between 0 and 100: %

 

11.

How many of the currently known exoplanets have orbits smaller than Earth’s orbit about our Sun? exoplanets (Note: the exact numbers you get will depend on the day you do it, as this database is continually updated to reflect the current known exoplanets.)

 

12.

What is the percentage of currently known exoplanets that have orbits smaller than Earth’s orbit about our Sun? Your answer should be a number only between 0 and 100: %

 

 

 

PART C: Click the red “X” next to your filter to remove it. Still using “Histogram Plot”, now choose Orbital Period as the “Data” to plot. All confirmed planets to date will be shown by default. Remember that Earth orbits our Sun once every 365 days and Jupiter orbits once about every 4,300 days.

 

13.

How many exoplanets in total are shown in this particular data set? exoplanets (Again, the exact numbers you get will depend on the day you do it, as this database is continually updated to reflect the current known exoplanets.)

 

14.

What percentage of the planets shown have orbital periods similar to our planet Mercury? Say, <100 days? Your answer should be a number between 0 and 100: %

 

15.

What percentage of the planets shown have orbital periods similar to our planet Venus? Say, <250 days? (Do not include the ones you counted above for Mercury!): %

 

16.

What percentage of the planets shown have orbital periods similar to our planet Earth? Say, <500 days? (Do not include the ones you counted above for Mercury OR Venus!): %

 

17.

What percentage of the planets shown have orbital periods similar to our planet Mars? Your answer should be a number between 0 and 100: %

 

18.

What percentage of the planets shown have orbital periods similar to our planet Jupiter? Your answer should be a number between 0 and 100: %

 

19.

Consider the research question, “How long do exoplanets take to orbit their star?” . If a fellow student proposed a generalization that “most exoplanets discovered take about the same length of time to orbit their star as Earth takes to orbit our Sun,” would you agree or disagree with the generalization based on the evidence you collected by looking at the range of possible orbital periods? Explain your reasoning and describe specific evidence, with sketches if necessary, either from the above tasks or from new evidence you yourself generate using the Exoplanets Data Explorer.

 

Phase III – What Conclusions Can You Draw from This Evidence?

 

What conclusions and generalizations can you make from the data organized using a correlation diagram (a.k.a. “scatter plot”) in terms of how does the size of an exoplanet’s orbit compare to its orbital period? Explain your reasoning and provide specific evidence, with sketches if necessary, to support your reasoning.

Remember, a picture is worth 103 words! Optional: Feel free to create and label sketches or graphs to illustrate your response.

 

EVIDENCE: Select “Scatter Plot” and choose the horizontal X-axis to be Semi-Major Axis (i.e. size of orbit) and the vertical Y-axis to be Orbital Period (i.e. time to complete an orbit). Expand the “Configure Axes” option at the top and try unchecking the “Log” boxes next to both X and Y, which makes the axes linear instead of logarithmic. (You should experiment with both types of axes in any plots that you make. Logarithmic scaling is often better at visually displaying data that are crowded or that cover a large range of values.) Once you have made a scatter plot, you can click and drag the graph around to center on different parts of it. You can zoom in or out on any portion of it by placing your mouse cursor over it and scrolling up or down. If your mouse doesn’t have a scroll wheel, you can always set a Min and Max by hand under Axes Configuration.

 

20.

Evidence-based conclusion:

 

Phase IV – What Evidence Do You Need?

 

Imagine your team has been assigned the task of predicting how far a newly discovered exoplanet would orbit from its central star. Describe precisely what evidence you would need to collect in order to answer the research question of, “If an exoplanet were discovered to have an orbital period of 21 days, what would you predict its semi-major axis orbital distance to be using a correlation diagram / scatter plot?” (This time the orbital period is the “independent”, or X-axis variable, and the semi-major axis of the planet’s orbit would be the “dependent”, or Y-axis variable.) You do not need to actually complete the steps in the procedure you are writing.

 

21.

Create a detailed, step-by-step description of evidence that needs to be collected and a complete explanation of how this could be done – not just “look and see what value it would have”, but exactly what would someone need to do, step-by-step, to accomplish this. You might include a table and sketches – the goal is to be precise and detailed enough that someone else could follow your procedure. Do NOT include generic nonspecific steps such as “analyze data” or “present conclusions” — these are meaningless filler. Be specific!

 

Remember, a picture is worth 103 words! Optional: Feel free to create and label sketches or graphs to illustrate your response. Please follow the instructions for uploading images link found under the “Lessons” tab.

 

Phase V – Formulate a Question, Pursue Evidence, and Justify Your Conclusion

 

Your task is to design an answerable research question, propose a plan to pursue evidence, collect data using the Exoplanets Data Explorer (or another suitable source pre-approved by your instructor), and create an evidence-based conclusion about about the characteristics of known exoplanets that you have not completed before.

 

REQUIRED this time: Create and label sketches, or include your graphs (or sketches of your graphs) to illustrate your response. The Exoplanets Data Explorer has an “Export” button at the top right that will allow you to download your graphs.

 

Research Report:

22.

Specific research question:

 

23.

Step-by-step procedure, with sketches if needed, to collect evidence. (Do NOT include generic nonspecific steps such as “analyze data” or “present conclusions” — these are meaningless filler. Be specific!)

 

24.

Data table and/or results: (include your graph(s) in this section)

 

25.

Evidence-based conclusion statement:

 

Phase VI – Summary

26.

Create a PITHY 50-word summary, in your own words, that describes the nature, frequency, or discovery of exoplanets and systems we have discovered so far. You should cite what you learned from doing each of the phases of this lab, not describe what you have learned in class or elsewhere.