# lab 6 29 14

Exoplanets

Big Idea: Planets orbiting other stars have 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

Resources:  Solar System Data Table, calculator, and these pages

SOLAR SYSTEM DATA TABLE

NAME

MASS

(MEarth)

MASS

(MJupiter)

PERIOD

(Earth-Years)

[Earth-Days]

SEMI-MAJOR AXIS DISTANCE (AU)

Object Name

How many times larger than (or fraction of) planet Earth’s mass

How many times larger than (or fraction of) planet Jupiter’s mass

How many Earth-years the planet takes to orbit our Sun

How many Earth-Sun distances away the planet orbits our Sun

Mercury

0.06

0.0002

0.24        [88]

0.39

Venus

0.82

0.003

0.62      [226]

0.72

Earth

1.00

0.003

1.00      [365]

1.00

Mars

0.11

0.0003

1.88      [687]

1.52

Jupiter

318

1.00

11.86   [4332]

5.20

Saturn

95.2

0.299

29.5 [10,775]

9.54

Uranus

14.5

0.046

84.0 [30,681]

19.2

Neptune

17.1

0.054

165  [60,266]

30.1

Pluto *

0.002

0.00001

249  [90,947]

39.5

Note:  Pluto* is not currently be defined as a planet by the International Astronomical Union. Numerical data obtained from http://www.nasm.si.edu/research/ceps/etp/ss/ss_planetdata.html

Phase I:  Exploration Part A

A histogram is a bar-chart showing the number of objects in a particular category.  Use the SOLAR SYSTEM DATA TABLE above and sketch histograms for each of the following.

1) Title:  Distribution of Orbital Distance:  Number of Planets Closer and Farther than Earth’s Orbital Distance

Less than 1 Earth orbit

Equal to or greater than 1 Earth orbit

7654321

2) Title:  Distribution of Masses: Number of Planets with Masses Less than Earth’s Mass and Greater than Earth’s Mass

Less than 1 Earth mass

Equal to or greater than 1 Earth mass

7654321

3) Title:  Distribution of Orbital Periods:  P < PEarth; PEarth ≤ PERIOD ≤ PJupiter; P > PJupiter

Less than 1 Earth orbit

PEarth ≤ PERIOD ≤ PJupiter

More than 1 Jupiter orbit

7654321

Phase I:  Exploration Part B

A correlation-diagram is a graph of dots showing how two characteristics, or variables, are related.  Use the SOLAR SYSTEM DATA TABLE above and sketch a correlation-diagram for each of the following.

4) Title: Distance (AU) vs. Period (Years) for Planets Closer than Jupiter (not including Jupiter)

(Vertical Y-axis Distance versus Horizontal X-axis Period)

|          |          |          |           |

1          2          3         4           5

PERIOD (years)

3.53.02.52.01.51.00.5

Distance (AU)

5) Title: Distance (AU) vs. Period (Years) for Planets With Orbits Jupiter-sized and larger

(Vertical Y-axis Distance versus Horizontal X-axis Period)

|          |          |          |          |

50       100     150     200     250

PERIOD (years)

4035302520151005

Distance (AU)

6) Title: Distance (AU) vs. Mass (MEarth) for all Solar System Planets

(Vertical Y-axis Distance versus Horizontal X-axis Mass)

|          |          |          |          |         |

50     100     150     200     250    300

Mass (MEarth)

4035302520151005

Distance (AU)

Phase I:  Exploration Part C

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.

7) One of the two graphs below is Intelligence versus Height and the other is Weight versus Height.  In the space below, precisely explain your reasoning about why which is which. Which one shows a correlation?

Height

Height

A

B

Explanation of why which graph is which:

8) Now, go back and look at the correlation diagrams you created in questions 4, 5, and 6. Compare them to graphs A and B above, and explain which variable of planets, PERIOD or MASS, seems to be more highly correlated to DISTANCE? Explain your reasoning. What is it about your correlation diagrams that tells you which is correlated and which is not?

Phase II – Does the Evidence Match a Given Conclusion?

User Notes On Using The Exoplanets Data Explorer Table

1) Notice that the first column gives the exoplanet’s NAME.

2) The second column is the exoplanet’s MASS.  The MASS is given in terms of how many times bigger (or smaller) it is than the mass of our planet Jupiter, MJup.

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

4) The fourth column shows the exoplanet’s ORBITAL PERIOD.  The period is the length of time in Earth-days it takes the extra-solar planet to go around its central host star once.

5) Clicking on a column heading will sort the data by that property. Clicking again will sort it in the opposite order.

9) PART A:  Access the Exoplanet Data Explorer [http://exoplanets.org], and click on “Table” to see a table of confirmed extrasolar planets and their associated data.  Click on the large “+” button in the upper right-hand corner, and select “Date.” You may not be able to see the Date column that was just added, so mouse over column headers and click the red X to remove columns you don’t need (for example, you don’t need the others after “Orbital Period.” Then click on the new “Date” column heading to sort the extrasolar planets with the most recent at the top.  Choose the most recent exoplanet planet listed in the table to the answer the following questions, and record data about it here using the units seen below. Note that sometimes the “Name” column may be slightly cut off, but you can click on the name to see the full name. If the most recent exoplanet has an unknown mass, chose the most recent one that has a mass listed, so that you can answer all of the questions below.

NAME: ___________________________

MASS:  ____________________ MJupiter

PERIOD: ____________________ years

SEMI-MAJOR AXIS

LENGTH:  _____________________ AU

10) Is this planet more massive than Earth?  Highlight or underline one:    Yes      No

If so, how many times more massive? ___________________________

11) Is this planet more massive than Jupiter?Highlight or underline one:    Yes      No

If so, how many times more massive?  ___________________________

PART B:  Select “Plots” at the top of the screen, then choose Histogram Plot on the right-hand side, and select “Advanced” mode (“Visual Style > Bars” should already be selected).  Choose the “Data” to be “Semi-Major Axis” by clicking on the +. Under bins, enter minimum distance = 0 AU and maximum distance = 10 AU.  Then adjust the “# Bins” = 10.  You should be able to read the number of planets in each bar by placing the cursor over the top of the bar.  (Earth orbits the sun at a distance of 1 AU, and Jupiter orbits at about 5 AU.)

Remember that Earth orbits our Sun at a distance of 1 AU and Jupiter orbits at about 5 AU.

12) How many extra-solar planets are shown in this data set?

13) How many of the currently known extra-solar planets have orbits larger than Jupiter’s orbit about our Sun?

14) What is the percentage of currently known extra-solar planets that have orbits larger than Jupiter’s orbit about our Sun?

15) How many of the currently known extra-solar planets have orbits smaller than Earth’s orbit about our Sun?

16) What is the percentage of currently known extra-solar planets that have orbits smaller than Earth’s orbit about our Sun?

PART C:  Next, choose the “Data” to be “Orbital Period” with minimum period = 0 days and maximum period = 900 days.  Then adjust the “# Bins” = 18.  You should be able to read the number of planets in each bar by placing the cursor over the top of the bar. Answer the following questions about the data, using the SOLAR SYSTEM DATA TABLE above for comparison.

17) How many extra-solar planets in total are shown in this particular data set?

18) What percentage of the planets shown have orbital periods similar to our planet Mercury?

19) What percentage of the planets shown have orbital periods similar to our planet Venus?

20) What percentage of the planets shown have orbital periods similar to our planet Earth?

21) What percentage of the planets shown have orbital periods similar to our planet Mars?

22) What percentage of the planets shown have orbital periods similar to our planet Jupiter?  (you will likely need to change the min/max setting)

23) If a student proposed a generalization that “most extra-solar planets 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?  Explain your reasoning and describe specific evidence either from the above questions or from evidence you yourself generate using the Exoplanets Data Explorer.

Phase III – What Conclusions Can You Draw From the Evidence?

What conclusions and generalizations can you make from the data organized using a scatter plot in terms of “What range of planet masses and range of star masses are observed? How are planet masses and star masses correlated (if at all)?” For your evidence, select “Scatter Plot” on the right-hand side of the Plots window, and select “Advanced” mode.  Choose the “Data > X” to be “Mass of Star,” and the “Data > Y” to be “Msin(i).” (Msin(i) is the minimum estimated mass of a planet in Jupiter masses. Current detection methods really only tell us this minimum mass, and different data is required to tell us the maximum.)  If the data points seem to be too concentrated in a certain region of the scatter plot, then select the “Log” checkbox for both axes in order to rescale the axes and “uncrowd” the data points.  (Utilize this feature whenever necessary for other scatter plots.)

Explain your reasoning and provide specific evidence, with sketches if necessary, to support your reasoning.

24) 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 extra-solar planet would orbit from its Sun-like central star.  Describe precisely what evidence you would need to collect in order to answer the research question of, “If an extra-solar planet was 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? (This time the orbital period is the “independent” or x-axis variable, and the semi-major axis of the planet’s orbit is the “dependent” or y-axis variable.)  You do not need to actually carry out the procedure you’ve written (but it would be instructive to actually display this scatter plot).

25) 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 how many are merging,” 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.

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

Your task is design an answerable research question, propose a plan to pursue evidence, collect data using the assigned Internet data set (or another suitable source pre-approved by your lab instructor), and create an evidence-based conclusion about the characteristics of known exoplanets.

Research Report:

26) Specific Research Question:

27) Step-by-Step Procedure, with Sketches if Needed, to Collect Evidence:

28) Data Table and/or Results:

29) Evidence-based Conclusion Statement:

Phase VI – SummaryPRINT YOUR NAME

30) Create a 50-word summary, in your own words, that describes the nature and frequency of exoplanets we have discovered so far.  You should cite specific evidence YOU have collected in your description, not describe what you have learned in class or elsewhere. Feel free to create and label sketches to illustrate your response.