Glenbrook South Year-End Projects

Search For ET

Basic Research Questions

Your role as researcher for this project involves acquiring a wealth of technical information about the physics of a variety of new ares, particularly Universal Gravitation and Center of Mass. The process of conducting a literature search for the physics of discovering planets should yield some basic information about the universe such as what holds planets in orbit? Is momentum 0 for a planet/sun system? How do scientists discover a planet which they do not actually see? And how do you calculate the center of mass of a two body system. When finished, you should be able to conceptually and mathematically describe the motion of a planet around a sun. Some basic topics for research and ultimate discussion have been listed below to assist you in the initial stages of your literature search. The role of this listing is to provide an initial framework for your literature search and not a conclusive list of topics to be discussed. Your group will be required to answer a majority of the following questions. Fell free to skip the questions you feel VERY comfortable with, but for the most part finish each question. Your group is expected to go beyond these topics, exploring diverse areas of individual interest about the physics of discovering extrasolar planets.

Basic Data Table

Use the Basic Data Table above for challenges 1-3.

1. Determine the gravitational force that attracts the Earth to the Sun.

2. Determine the gravitational force that attracts the Sun to the Earth. Explain its relationship to your answer in question 1.

3. Determine the gravitational force that attracts Jupiter to the Sun.

4. Determine the speed needed for the space shuttle to orbit the Earth 400,000 meters above its surface.

Use the Basic Data Table above for challenges 5 & 6.

5. Calculate the following ratios of the planet's mean radius of orbit(R) to the planet's period of revolution (T).

6. Which ratio remains relatively constant?

7. State Kepler's 3 Laws.

8. With which of Kepler's 3 laws is your answer to challenge 6 consistent?

9. Derive Kepler's 3rd law using universal gravitation and the centripetal force equation.

10. Physicists say that the total momentum of the Earth-Sun system is zero as viewed from a point at rest with respect to our solar system. Explain how this is possible.

11. Using the Basic Data Table above, determine the velocity with which the Earth is hurling around the Sun.

12. Again using the Basic Data Table above, determine the velocity with which the Sun would need to move to provide the total system with zero momentum.

13. Determine the velocity with which the Sun would have to move to provide the Sun-Jupiter system with zero momentum.

14. Determine the position of the center of mass of the Sun-Jupiter system with respect to the center of the Sun.

15. Does this point lie within the Sun's Radius? Explain what your answer means.

16. Does your answer to challenge 15 agree with your answer to challenge 13? Explain.

17. Determine the observed frequency of a 400 Hz horn if the source of the horn's sound moved

(a) toward you with a velocity of 45 m/s.
(b) away from you with a velocity of 45 m/s.

18. Does light also experience a Doppler Shift? Explain including the terms "Blue Shift" and "Red Shift".

The following graphs and data (below star pictures) represent data collected for what scientists claim to be evidence of a planet existing around a star entitled Rho in the constellation Corona Borealis as shown below. Use this data to determine the answers to challenges 19 - 27.

Harvard University The Constellation Corona Borealis page, [online] Available page, [online] Available

The following represents data set up by Sylvain G. Korzenn ( Use the data and graph shown below to answer challenges 19 - 27.

Harvard University A Planet Orbiting the Star rho Coronae Borealis page, [online] Available

Precise Doppler measurements of the star Rho Coronae Borealis have been made during the past year by Robert W. Noyes, Saurabh Jha, Sylvain G. Korzennik, Martin Krockenberger, Peter Nisenson, Timothy Brown, Edward Kennelly, and Scott Horner using the "Advanced Fiber Optic Echelle" spectrometer. Rho Coronae Borealis (link to picture) is a Solar-Type star (G0V), and is probably at least as old as the Sun, judging from its weak chromospheric activity. The Doppler periodicity for Rho Cor Bor is very convincing, having an amplitude of 67 meters/sec.

The research team concluded that the period is 39.6 days, the minimum mass is 1.1 Jupiter masses, the orbit has small eccentricity, and the orbital radius is 0.23 AU. You will be comparing your results below to these.

The physical parameters of the star rhoCrB are: (from the scientific literature)

R.A.: 16:01:03.39
Dec.: +33:18:51.5 (2000.0)
Vis Mag.: 5.40
aka: HD 143761, HR 5968
Spectral Type: G0V or G2V
T(eff): 5760, 5783, 5868 K
Parallax: 60 +/- 6 mas
Distance: 16.7 +/- 1.7 pc, or 54.5 +/- 5.5 ly
Luminosity: 1.61 L(Sun)
Age: 10 Gyr
Mass: 1.0 M(Sun)
P(rotation): 20 d
log(g): 4.11, 4.19, 4.23

More on the Planetary Companion to rhoCrB

The orbital parameters are: (based on the AFOE's observations)

Period: 39.645 +/- 0.088 days
K1: 67.4 +/- 2.2 m/s
e: 0.028 +/- 0.040
omega: 210 +/- 74 degrees (longitude of periastron)
T: 2,450,413.7 +/- 8.2 (time of periastron, HJD)
a1 sin(i): (36.75 +/- 0.92) x 1E+6 m
f1(m): (1.258 +/- 0.093) x 1E-9 M(Sun)
m2 sin(i): 1.13 M(Jup)
T(transit): 2,450,559.37 +/- 0.54 (HJD)


19. Determine CorBr period of rotation.

20. Determine the planet's period of rotation.

21. Determine the radius of the planet's orbit.

22. Determine the velocity of the planet in its orbit.

23. Determine the velocity of the sun it its orbit.

24. Using the fact that the planet and sun have a total momentum of zero, determine the mass of the planet.

25. Using the radius of the planet, the mass of the sun and the mass of the planet, determine the center of mass of the sun-planet system.

26. Use the radius of the sun's orbit and its period to determine the velocity of the sun as it orbits. Does this value agree with your answer in challenge 21.

27. Are any of your answers significantly different than the answers found by the research group? Explain any significant differences.

Return to:

The Physics of ET Project

Project Home Page

ET Project

Coasters Links

Basic Research Qs

Collabor'n Ideas

The Lab Report

Project Pitfalls

Scoring Rubrics

Project Timeline

Other GBS Resources

GBS Physics Page

Physics 163 Page

Physics Projects Home Page

The Refrigerator

The Physics Classroom

Multimedia Physics Studios

The GBS Physics staff invite you to send electronic mail:

Tom Henderson

Howard Jenewein

John Lewis

Neil Schmidgall

Dave Smith

Suzanne Webb

Brian Wegley

Questions and comments can be sent to Brian Wegley.

This page last updated on 3/9/98.