Ariel Xie

Exoplanet Sunsets

April 13, 2021   /  

Name: Ariel Xie
Majors: Physics, Mathematics
Minor: Computer Science
Advisors: Dr. Lindner, Dr. Kelvey

How does sunset look like on exoplanets? For some eccentric planetary orbits, the host star appears to move backwards in the sky as the orbital speed momentarily exceeds the rotation speed near the periapsis, when the planet is nearest to its star. This necessitates a new definition of a day. Thus, a new definition “apoday” is defined as the time between two consecutive noons in the dominant direction of motion of the host star, excluding the noons caused by its reversal and recovery. This thesis begins with an exploration of conditions necessary for apoday to happen.

Over the past decade, NASA’s Kepler and K2 missions have discovered thousands of planetary candidates for human settlement, of which 2000 have been confirmed. This thesis examines the apparent motion of the host star as viewed from exoplanets. Mathematica simulations model the motion of the host star. The simulations involve numerical integration of orbital equations of motion and analytic computation of the altitude of the sun observed from the planet. For the special case of zero obliquity(tilt), an exact nonlinear equations delimiting apodays in the space of orbital eccentricity and spin-orbit (day-year) ratio is derived, confirmed by numerical simulations.

Future work includes developing model for observers at different longitude. We can also consider applying the analysis to more specific exoplanets. However, spin-orbit ratio is hard to measure for exoplanets and beta Pictoris b is the first (and so far only) exoplanet with known spin-orbit ratio, obliquity, and eccentricity. Exoplanets that have chaotically rotating stars or in multiple star systems is another possibility.

Click to view Ariel’s poster presentation.

Ariel will be online to field comments on April 16:
8-10am EDT (PST: 1-3pm, Africa/Europe: late evening)

15 thoughts on “Exoplanet Sunsets”

  1. Bounding the apoday region in {spin, eccentricity} with simple but nonlinear functions is wonderful! Is that possible in {spin, eccentricity, obliquity} or will that need numerics?

  2. Ariel, I have missed seeing you this year! What a cool I.S. I love the poster. Congratulations on a wonderful four years at Wooster. Please stay in touch.


  3. Ariel, this is a great poster! I have missed seeing you. around this year. What do the colors represent in your boundary plot? Do the numbers have units? Also, what is obliquity? I’m assuming it has to do with planet tilt?

  4. This is very cool work, Ariel! Congratulations, and we wish you all the best in your plans beyond Wooster!

  5. Stellar poster, Ariel! Congratulations. Can you speculate what is the length of an apoday, in Earth-days? For example, an apoday on beta Pictoris b?

  6. Fun work. Someday we will be standing on one of those planets and can say, “This is how professor Xie said it would look.”

  7. Congratulations on this I.S. work! Ariel, your work made me curious about how planets in other solar system move and how long is their “day” and “night”. Are there direct measurements available to scientist about, let’s say, the closest exoplanet? Do scientists know how the closest exoplanet orbits around its own sun?

    It was a pleasure to cross paths with you at Wooster. You will do great in whatever you decide pursuing!

  8. Hi Ms. Xie, I scrolled down through the list of presenters and then started with yours – so glad I did! Very interesting and well presented…this old COW physics major (’73) learned something! Congrats – well done.

  9. Congratulations, Ariel! This is really interesting work … I wonder whether it would be possible to take your simulations and create a video model where one could “watch” what a sunset might look like for an exoplanet with particular parameters. Wishing you all the very best for your future!!

  10. William Rogers, Scientist at Texas A&M University in College Station, Texas. wjrogers

    Thank you, Ariel Xie, for your outstanding work to help us continue to look up and be inspired to explore our universe and in doing so, learn more about our planet so we can help to build a better world to reduce or eliminate starvation, and where everyone will benefit from science, technology, and the humanities.

    Many people do not believe that the earth revolves around the sun once a year. Also, people can be shown why we refer to “Sunrise” and “Sunset”, given that, because of the earth’s rotation, the sun only appears to rise and fall. You can help other people to understand other events in nature, such as why clouds are usually white and snow is white to our ROYGBIV eyes. Knowing the science behind events increases the enjoyment of nature and everything in nature, which should be part of student education at all levels so we are more likely to support and benefit from nature and science.

    Best wishes, Ariel Xie and other students, for your opportunities and career after Wooster.

    Thank you, students, Sarah Bolton, faculty, and staff, for your informative and inspiring Symposium!

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