Kepler’s Theory in Duplicate


We recently discussed the three laws stated by Johannes Kepler, written from 1609-1619, and now it is time to relate this to a recent astronomical discovery. First and foremost these three laws are as follows:

  1. The orbit of each planet about the Sun is an ellipse with the Sun at one focus.
  2. As a planet moves around it’s elliptical orbit, it moves faster when it is nearer to the Sun and slower when it is farther from the Sun, with its speed varying in such a way that the planet’s path sweeps out equal areas in equal times.
  3. Planets obey the relationship p^2 =a^3, where p is the planet’s orbital period in years and a is its average distance from the Sun in astronomical units.

**The information above was gathered from the text “The Essential Cosmic Perspective” 7th ed. by Bennett, Donahue, Schneider, and Voit.

The article linked at the top discusses how astronomers at the Gemini Observatory  South telescope and the European Observatory Very Large Telescope have discovered a white dwarf star, orbited by a brown dwarf star, with evidence of rocky planets orbiting both. The scientists have not officially found a planet yet, instead they have viewed a ring of dust that most likely used to be a planet orbiting the two stars, with some dust clumps being large enough to be considered asteroids. This was still a major discovery for the astronomers because till this date the only circumbianary planets  (planets that orbit two stars) were gas giants. Finding evidence of non-gas giant circumbianary planets is exciting for then “Star Wars nerd” within these astronomers because of the fictional planet of Tatooine, which was a sandy desert planet which orbited two stars. Scientists in England look forward to the James Webb Telescope launch, which will allow them to view the dust and see what chemicals/elements it contains. Until then they plan on viewing the stars through an infrared lens so to calculate what gasses are being burnt off.

Because Kepler’s laws of planetary motion are universal, they can be applied to how a planet would circumvent these two stars, if one is to be discovered. The first law is not as distorted as I previously assumed. The two stars orbited each other in a small circle, about 300,000 miles apart from on another. The planet then would orbit around both of the stars as if they were one. Both stars would then be at one focus of the ellipse as the planet made its orbit. The second law would remain the same as it would with any other normal system. The planet will make its orbit and as it got closer to both the stars it would gain speed. Now, in this case it would gain more speed than planets in our solar system, not because it orbits two stars bit instead, because one of the two stars it orbits is a white dwarf star, which has a much, much greater mass than that of our sun. This great mass is why, astronomers believe, there is only evidence of a planet, and not a planet itself. They believe that the planet was sucked into the white dwarf. Kepler’s third law is the difficult one to relate because a planet has not actually seen so the orbital period in years cannot even be predicted. But, because this is not some backward dementional solar system, this same principles would apply, the planet would make its orbit around the stars at varying distances and speeds while still respecting the relationship of  p^2 =a^3.

I always enjoy reading articles about new discoveries in space. Especially when scientists get excited about it, because if the experts get all flustered, you know it’s something for us amateurs to get worked up about. In relating this to something we did in class, I would say that in the lecture-tutorial, pg 24 question 12, the orbital patern that would best match this planets would be C, due to the major pull from the white dwarf.


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