Detecting Solar System Objects using Blocked Starlight: The Case of Planet 9

Summary

One of the greatest mysteries in astronomy today is that of Planet 9. Searching for Planet 9 with the current method has proven to be a challenge due to its low brightness. The alternative method proposed in this research is to use the light of the background stars that are blocked as Planet 9 moves across the sky. A review of the current research on Planet 9 shows that its angular size is large enough to occult stars completely. The data from exoplanet telescopes like the Kepler Space Telescope and TESS can be used for this method. Kepler has already observed the probable location of Planet 9 several times. The question being answered by this research is whether it is possible to develop a method to detect Solar System Objects (SSOs) such as Planet 9 using blocked starlight. The hypothesis is that the density of background stars is sufficient for Planet 9 to be detected using blocked starlight. This was tested by calculating the density of stars in the probable location of Planet 9. The concentration of stars was found to be sufficient for using blocked starlight as a method to detect SSOs. Current advances in Artificial Intelligence and pattern identification support the implementation of this method. The data recorded by telescopes can be mined to detect variations in the brightness of stars and probable paths of movement of the SSO can be identified. This method complements the existing method of SSO detection using movement as it identifies probable locations.

Question / Proposal

Calculations by astronomers have shown that the existence of a big planet in the outskirts of the solar system is necessary to explain the orbits of distant Kuiper Belt Objects. However, after almost three years of searching the skies by both professionals and amateurs, Planet 9 has yet to be found. The current method used to hunt for Planet 9 is the same used since ancient times: Observing the sky a few days apart to see if any object has moved. This method has proven to be very successful and enabled the discoveries of the planets Uranus, Neptune and the now demoted Pluto, and other SSOs like comets and asteroids. However, this method fails to detect objects with extremely low brightness as they cannot be observed by most telescopes. Planet 9's detection faces this challenge.

The method being proposed is to use the light of background stars being blocked by the passage of an object in front of them. As Planet 9 moves across the sky, it will block starlight along a predictable path. This is similar to the 'transit method' used to find exoplanets where the light of a star is blocked periodically by an orbiting exoplanet. 

Research Question

Can SSOs be detected by using the starlight that they block when passing in front of stars?

Planet 9 is used as an example of an SSO to examine this research question.

Hypothesis

The density of background stars is sufficiently high for Planet 9 to be detected using blocked starlight.

Research

For Planet 9 to be detected with blocked starlight it has to cover a significant portion of a star when passing in front of it. Planet 9's apparent diameter was found to be at least 1.5 x 10-2 arcseconds. This was calculated using the lowest estimate of its diameter (13,000 km) and assuming it is at aphelion (1200 AU). This is 10 to 100 times larger than the apparent diameter of most of the stars in the sky. Hence, Planet 9 can easily block the light of any star when passing over it.

To find Planet 9 using this method telescopes would have to observe a patch of sky for several hours or days to have a possibility of finding it.  The Kepler Space Telescope and Transiting Exoplanet Survey Satellite (TESS) were built to continuously monitor the brightness of thousands of stars and detect minute changes in brightness, which makes them the perfect instruments to look for Planet 9.

Experts believe that the most probable location of Planet 9 is where the constellations of Orion, Taurus, and Gemini meet. Kepler, since its launch, has studied several areas of the sky (fields). It studied each of them continuously for 80 days, which is sufficient time to see Planet 9's movement. Kepler's K2 Campaigns 0, 4 and 13 were located in the constellations of Gemini and Taurus, adjacent to Orion, close to the probable location of Planet 9. Hence, there is the possibility that Planet 9's existence is hiding in the data from one of these fields. Another place where Planet 9 could be hiding is at perihelion in the constellation of Scorpius. The traditional method used to find planets struggles in this part of the sky due to the immense number of background stars since this is an area near the galactic center. This condition works favorably for the proposed method as the huge number of background stars means that Planet 9 will occult stars very frequently making it hard to miss. The K2 Campaigns 2, 7, 9, 11 and 15 are all located in Scorpius and the surrounding area. Therefore, Planet 9 should be easily detected with this method if it is at perihelion even though the traditional method is blinded by the background stars.

TESS, the successor of Kepler, will observe 85% of the sky through 26 segments. Each segment will last for 27 days, which is sufficient time to detect Planet 9's movement. Hence, combining the data from Kepler and TESS implies that Planet 9 has almost nowhere to hide.

The pixel sizes on Kepler and TESS are 3.8 x 3.8 and 21 x 21 arcseconds respectively. This means that the pixels on Kepler are small enough to detect a drop in the brightness of an individual star though TESS may have some difficulty in the denser regions of the sky. Kepler and TESS can efficiently observe stars up to the 17th magnitude though they have the ability to observe stars up to the 20th magnitude.

Method / Testing and Redesign

Two tests (Test 1A and 1B) were conducted to calculate the density of stars in the probable location of Planet 9. This was used to check if the density is sufficient to detect Planet 9 using blocked starlight. Another test (Test 2) was performed to check if this method can be used to detect SSOs, using Jupiter as an example.

Test 1A

A density map was used to visualize the density of stars. Since Planet 9 is probably at aphelion in the constellation of Orion, 17 of the main stars in this constellation were used for this test: Betelgeuse, Rigel, Saiph, Bellatrix, Meissa, the belt stars (Alnitak, Alnilam and Mintaka), Mu Orionis, Nu Orionis, Xi Orionis, Chi1 Orionis, Chi2 Orionis, 1 Orionis, 2 Orionis, 3 Orionis and 8 Orionis. The Galactic Coordinates of the stars were used to mark their positions as accurately as possible on the density map. The stars were connected with lines to resemble the constellation of Orion. This shows that Orion, and hence Planet 9, is located in a dense part of the sky (25,000 to 200,000 stars/degree2).

Test 1B

The density of stars in Orion was calculated to confirm the visualization in Test 1A. Three stars in Orion, namely Betelgeuse, Meissa, and Mintaka, were chosen as reference points to calculate the density of stars in the surrounding area.

  1. The ICRS (International Celestial Reference System) coordinates of these stars were used to retrieve the total number of sources (stars) within a certain radius (in arcminutes) of the reference star. An optimal radius was chosen for each star since the density of stars varies from place to place. The limitation of the search engine used to retrieve the data was also considered (maximum of 2,000 results).
  2. This data was used to calculate the density of stars around each chosen star in sources/degree2.

Test 2

This test was performed to determine the viability of using the blocked starlight method for detecting SSOs. It was calculated whether Jupiter would cover sufficient stars to be detectable in the observational astronomical data. Jupiter was chosen as it is the largest superior planet and hence the easiest to detect.

  1. The angular area of Jupiter was calculated (in arcsecond2) using its monthly angular diameter. The angular diameter (in arcseconds) of Jupiter for 14 months was used.
  2. The density of background stars around Jupiter for each month was calculated (in stars/arcsecond2) using a nearby reference star (refer Test 1B).
  3. Using Jupiter's angular area and the density of stars the number of stars covered by Jupiter at a given time was calculated.
  4. A line graph was drawn to observe the correlation between the angular diameter of Jupiter, the density of background stars and the number of stars covered. It shows that Jupiter covers at least 1 star and up to 76 stars at a time.

The calculations show that theoretically Jupiter can be detected. Hence, the test proves that the blocked starlight method can be used to "rediscover" Jupiter by using observational data from telescopes.

Results

Test 1A&B

Identifying Orion on the density map showed that the constellation of Orion lies just under the galactic plane, where the density of stars varies between 25,000 and 200,000 stars/degree2.

The calculated densities around the selected three stars in Orion (shown in Table 1) further confirm that the density of the stars in this area is quite high.

Table 1: The density of stars around the chosen reference stars in Orion

STARS DENSITY OF SURROUNDING STARS (stars/degree2)
Betelgeuse 90,400
Meissa 68,800
Mintaka 44,700

 

Planet 9 is estimated to be in the northern part of Orion where the density of stars is 75,000 to 100,000 stars/degree2. (Link to the density map is provided in References.). This indicates that the average distance between stars in the location of Planet 9 is 11 to 13 arcseconds (calculated by converting the density of stars into arcseconds/star). The path of Planet 9 across the sky will be in loops due to retrograde motion caused by parallax. Assuming  Planet 9 is at aphelion at 1200 AU, it will move at a speed of 0.2 arcseconds/hour most of which comes from parallax. This implies that Planet 9 will occult a star once every few days in its probable location in Orion. The faster it moves, the more often it will occult stars which is favorable for this method.

Test 2

 

 

The table and graph with data from November 2018 to December 2019 show that the huge size of Jupiter causes it to occult sufficient stars at a time. The trend in Jupiter's angular area repeats in a 13-month cycle due to Jupiter's varying distance to Earth. The density of stars around Jupiter depends on Jupiter's location in the ecliptic, which changes in a 12-year cycle. In November 2018 Jupiter is at its furthest distance from Earth and the density of stars is not very high. As Jupiter moves closer to Earth (March 2019) it grows in size, and as it also moved closer to the galactic plane the density of stars increases. This causes it to occult more stars at a time. The number of occulted stars is at its peak (76) in April 2019 when the density of background stars is also at its peak and Jupiter's angular area is quite high. From the graph, it can be inferred that the number of occulted stars is a product of the angular area and the density of stars. The density of stars appears to have a comparatively larger influence on the number of occulted stars.

It was determined that Jupiter would cover sufficient stars even after considering the variations in both its angular area and the density of stars. Hence, Jupiter can be "rediscovered" using the blocked starlight method by identifying the change in the brightness of stars in the observational data. Planet 9 is also located in an area with a similar density of stars (the green area in the density map). Therefore, this method can be used to detect SSOs in a similar manner.

Conclusion

The proposed method of blocked starlight for detecting SSOs depends on the density of background stars for it to work. To test this method it was hypothesized that the density of stars was high enough to detect SSOs. Planet 9 was used as an example of the SSO to be detected. It was established that there were suitable telescopes, Kepler and TESS, which were recording data in the probable location of Planet 9. The Large Synoptic Survey Telescope (LSST), which is under construction has a very good angular resolution and should hence be a good instrument to use in the proposed method. The experiment tested the following: 1) the angular diameter of Planet 9 is sufficiently large to cover a star 2) the density of stars is high enough in the probable location of Planet 9. A second test was conducted to show that Jupiter can be "rediscovered" using the blocked starlight method. The tests that were performed proved the hypothesis by showing that the density of stars is high enough to detect SSOs like Planet 9. 

The method needs to be tested using astronomical data from telescopes. The astronomical data has to be analyzed to detect patterns of change in the brightness of the background stars. This indicates the presence of an SSO that is occulting the star. This can be initially used to detect known objects and refine the algorithm for detecting patterns before applying on harder targets. Several of the planets have passed through Kepler's observation fields, which makes them good candidates to test this method. This step was not conducted in this experiment due to constraints in the access to astronomical data from telescopes. 

The blocked starlight method is not a replacement for the current method of finding planets. The two methods complement each other as the current method works best where the density of stars is low, and the proposed method works best where the density of stars is high.

All calculations were done assuming that Planet 9 will be in its worst-case scenario i.e. it has the lowest estimated diameter, it is at aphelion and moving at its slowest speed across the sky. Even when all these factors are least favorable, this method appears to work quite satisfactorily. It was recently found that Planet 9 is probably much closer at 600 AU, which makes its detection easier with this method as it appears bigger and moves faster. The other probable location of Planet 9, at perihelion, is very favorable for this method as the density of stars is much higher and it will move much faster. This method can also be used for other undiscovered “wanderers” in the sky such as Kuiper Belt Objects (KBOs), asteroids or comets. Once the presence of an SSO is detected in the observational data with the proposed method telescopes can then try to directly image potential candidates. Using this method alongside the current method should make finding new objects like Planet 9 much easier.

About me

My name is Aniruddha Girish Aramanekoppa. I am 15 years old and study in class MYP4 at Blindern IB Diploma School, Oslo. I am a native of Bengaluru, India and have been living in Oslo, Norway since November 2015. I am deeply interested in Mathematics and Science. Astronomy has fascinated me since as long as I can remember. My favorite hobby is stargazing. I love observing the planets and the moon with my telescope which I received as a gift last year.

My ambition is to study astronomy at the university level and eventually become an astronaut. I a keen follower of space organizations like NASA, ESA, Virgin Galactic, SpaceX and Blue Origin. I am inspired by people like Neil deGrasse Tyson and Elon Musk who are extremely passionate about space exploration and the future of humanity. The work of Michael E. Brown was instrumental for me choosing this project.

Winning the Google Science Fair would be a huge motivation for me. It would reassure me to continue my studies on this topic, knowing that it is supported by others. I will continue to explore my project and would like to work on the observational data from telescopes to test the method. I hope my work on this topic contributes to our exploration of space and understanding of the universe.

Health & Safety

The experimenting phase of this project didn't require any special health and safety measures as all the testing done were calculations and research using a computer.

Bibliography, references, and acknowledgements

Bibliography

  1. Brown, M. E., Batygin, K., & Bailey, E. (2016, January 20). Where is Planet Nine? Retrieved September 02, 2018, from The Search for Planet Nine: http://www.findplanetnine.com/p/blog-page.html
  2. Desmars, J., Camargo, J., Braga-Ribas, F., Vieira-Martins, R., & Assafin, M. (2015, September 29). Orbit determination of Transneptunian objects and Centaurs for the prediction of stellar occultations. Retrieved November 2018, from arXive.org - Cornell University Library: https://arxiv.org/pdf/1509.08674.pdf
  3. Haworth, D. (2001, June). How Many Stars You Can Observe. Retrieved September 02, 2018, from Stargazing.net: http://www.stargazing.net/david/constel/howmanystars.html
  4. LSST Corporation. (2018). Welcome. Retrieved November 2018, from The Large Synoptic Survey Telescope: https://www.lsst.org/
  5. NASA. (2017, August 04). Spacecraft and Instrument. Retrieved from Kepler and K2: https://www.nasa.gov/mission_pages/kepler/spacecraft/index.html
  6. NASA. (2018). Characteristics of the TESS space telescope. Retrieved November 2018, from TESS Science Support Center: https://heasarc.gsfc.nasa.gov/docs/tess/the-tess-space-telescope.html
  7. NASA. (2018, November 07). Kepler & K2 Science Center. Retrieved December 07, 2018, from K2 Campaign Fields: https://keplerscience.arc.nasa.gov/k2-fields.html
  8. NASA. (2018). Observing technical details. Retrieved November 2018, from TESS Science Support Center: https://heasarc.gsfc.nasa.gov/docs/tess/observing-technical.html
  9. Plait, P. C. (1997, February 24). Phil Plait's Bad Astronomy. Retrieved September 02, 2018, from How Big is the Sky?: http://www.badastronomy.com/bitesize/bigsky.html
  10. Schwamb, M. E., Jones, R. L., Chesley, S. R., Fitzsimmons, A., & Fraser, W. C. (2018, February 06). Large Synoptic Survey Telescope Solar System Science Roadmap. Retrieved November 2018, from arXive.org - Cornell University Library: https://arxiv.org/pdf/1802.01783.pdf
  11. Wikipedia. (2018, August 02). Kepler (spacecraft). Retrieved September 02, 2018, from Wikipedia - The Free Encyclopedia: https://en.wikipedia.org/wiki/Kepler_(spacecraft)
  12. Wikipedia. (2018, November 01). Large Synoptic Survey Telescope. Retrieved November 2018, from Wikipedia - The Free Encyclopedia: https://en.wikipedia.org/wiki/Large_Synoptic_Survey_Telescope
  13. Wikipedia. (2018, May 17). Mira variable. Retrieved November 2018, from Wikipedia - The Free Encyclopedia: https://en.wikipedia.org/wiki/Mira_variable
  14. Wikipedia. (2018, September 02). Planet Nine. Retrieved September 02, 2018, from Wikipedia - The Free Encyclopedia: https://en.wikipedia.org/wiki/Planet_Nine
  15. Wikipedia. (2018, August 26). Transiting Exoplanet Survey Satellite. Retrieved September 02, 2018, from Wikipedia - The Free Encyclopedia: https://en.wikipedia.org/wiki/Transiting_Exoplanet_Survey_Satellite
  16. Wikipedia. (2018, October 31). Variable star. Retrieved November 2018, from Wikipedia - The Free Encyclopedia: https://en.wikipedia.org/wiki/Variable_star

Density map from Test 1A:  https://drive.google.com/file/d/1xZLaksfZ7HWK49fZiI1xwZKO3NkybDUL/view?usp=sharing

Tools used

  1. European Space Agency. (2018). Gaia Archive. Retrieved 2018, from https://gea.esac.esa.int/archive/ 
  2. Strasbourg Astronomical Data Center. (2018). SIMBAD Astronomical Database. Retrieved 2018, from http://simbad.u-strasbg.fr/simbad/
  3. Stellarium. (2018). Stellarium Astronomy Software. Retrieved 2018, from https://stellarium.org/
  4. Google Sheets and Microsoft Excel 2016 for spreadsheet and graph

Acknowledgments

I would like to acknowledge the role of several people who supported me during this project. Firstly, I thank my parents for their motivation and support in completing this submission. They were crucial in getting me started with this project and reviewing my submission. I would like to thank Ross Church, Senior Lecturer, Lund University, and Bo N. Andersen, Deputy Director General, Norwegian Space Center, for providing information and relevant sources. Their feedback and mentorship were vital in improving this project. I also thank my math teacher, Marius Ladegård Meyer for his support in developing this idea. Lastly, I thank the Google Science Fair 2018 and all its sponsors for arranging this competition. This is an amazing platform for students to exhibit their ideas and projects.