EXOPLANET INFORMATION VISUALIZATION SYSTEM
UI Design, Interaction Design, Front-end programming (CSS/JS)
To create a novel and useful interactive visualization for understanding “Earth-like” exoplanets
Until nearly a decade ago, our understanding of how planets form around a star and how life forms on the planet was based only on one sample set – Earth and its solar-system. But with the persistent curiosity to search for “life outside earth”, astronomers as of today have discovered 1763 exoplanets (planets outside our solar-system). Of those, 273 are accounted to be “habitable zone” planets, meaning the temperature on these planet is in a range similar where earth-like life can exist (a temperature range between 180K and 310K). The data-set containing information about the physical and detection parameters of all the discovered exoplanets and “potential candidate” exoplanet is kept up-to-date by NASA and CALTECH.http://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html.
But one of the main problems is that this data-set is presented through a large spreadsheet, containing thousands of details. Non-astronomy experts would have trouble understanding what are the distinct features of this data-set in comparison to our solar-system. Planetary astronomers and astrophysicists might have trouble understanding how to easily compare different exoplanet systems and physical parameters to say, test and build their theoretical models.
In this data rich era of exoplanet astronomy, where new planets are discovered almost every week and scientists are constantly testing and redefining the fundamental ideas about solar-system formation and what it means to have “planets that can sustain life,” it would be extremely useful to represent the data-set such that experts and non-experts a like can ask more informed question. The primary goal of our infovis is provide a visual and interactive arena where one can find patterns to connect “habitable zone” planets, with other complex attributes representing of its parent star and the solar-system it resides in.
KEPLER’S TALLY OF PLANETS
This information visualization is from the NY Times. In this system, animations represent the stars and exoplanets in each of the 950 solar systems. The stars represent two attributes: size relative to our sun and temperature, while the planets show their relative orbital timing, the size, and distance to their star. It is cool and flashy because of the animations, but the list is very large and does not let you compare two systems with each other (you would need to open two separate copies of the viz to do this).
EXOPLANET VIZ CONTEST
While this visualization presents some interesting information, it is too focused on specifics of a few systems at a time. It does not let the user see a big picture, with in-depth context that is shared between all of the stars and planets, but only shows a few exoplanet systems at a time. One advantage this info vis has is that it give the user some form of interactive control, which none of the others had.
Our users are astronomers, particularly those working in exoplanet research. Many of the current visualizations show all of the exoplanets together, but none of them really focus on the habitable planets. This means that the users of the visualization could range from astronomers looking for patterns exoplanet systems to anyone with a curiosity about habitable exoplanets.
Some of the typical questions that an astronomer might explore with this visualization would be:
– How do solar systems with habitable exoplanets form?
– Is there a typical set-up that exists, or do habitable planets exist in similar system types?
– Where are these exoplanet systems in the night sky? (for follow-up research)
– Is there a pattern between the types of habitable planets and their distance from their star?
– What are the types of stars that have habitable planets?
– How likely are habitable planets to exist out of all of the exoplanets?
– What does a habitable planet system look like compared to our solar system?
The first idea was to create a skymap from Earth with all the star systems that have been found mapped out in the sky. This will allow users to see where the systems are in the night sky, as something astronomers have issues with is knowing the spatial relativity of the systems from earth. The users would be able to input a location on earth and see which systems one can see from that location. They could pan around the night sky and the map would show the longitude and latitude locations of these systems in the sky. They would then be able to explore these systems by clicking on them, which would indicate with a circle which system is currently being looked at. Since there are 454 star systems that have been found, it would be hard to distinguish them in the night sky. We would label the systems on the map, as this would likely be more useful for those who are already familiar with the data.
We decided to avoid this visualization as it is a more presentation of the data, rather than an abstract representation that could provide a different insight. This visualization could still prove beneficial for more experienced astronomers, as they are interested in seeing how the data relates to each other in a more spatial sense, which the skymap would do by showing the systems from our typical view. It would also spark interest for casual users who are looking to learn more about the universe by making the data more relatable.
The second design idea was to display the star systems with all confirmed exoplanets in the context of the galaxy, oriented at our solar system. The design would be a zoomable 2D planar view looking “down” on the galactic plane or a 3D cylindrical view, all depending on the user’s desired context. Choosing one of the stars with exoplanets, a path from our sun to that star would appear, prompting the user to select it. Once selected, the view would update to show the details of that current system (a moving model of the star system chosen, mass, distance from the sun, theoretical travel time from earth, temperature, and number of planets). Many of these attributes would be filters, as well.
Some of the main feedback we got about this design was that it was still a very one-to-one mapping of data to a display. It contains a great deal of black, unused space and in that respect there is a lot of ink for not much data. While we were trying to keep the information in a best context as possible, it could be seen as too much “chart junk” as Tufte called it. As mentioned earlier, one of the strengths is that is is within context, and could help orient a user who does not have much background knowledge in astronomy orient themselves easier.
This design was in part a reaction to initial feedback from Part 1, that included criticism of our idea as being too much of a one-to-one mapping. We began discussing other ways of representing the data that were more abstract and came up with a radial chart concept.
All exoplanets exist in elliptical orbits around their parent star at varying distances. By representing that relationship in a circular orbit diagram, and placing all discovered exoplanets in it, it opens up the possibility of seeing interesting patterns in the relationship between distance from parent star (orbital period), and planet mass, planet radius, composition, etc for all the exoplanets. The information would be mapped in a similar way to previously mentioned designs where the size of the circles could represent planet size, the color could represent the type of planet or composition.
There are a number of different interactions the user can perform to analyze the data. They can filter ranges of variables and see how that affects the collection of planets in the main visualization. They can also sort the planets by certain variables, and the planets are laid out in a pack layout sorted by either semi-major axis, planet radius, or orbital period.
Additionally, they can hover over a planet to see specific data, and they can select the planet to see the local system which that planet is part of. This brings up the secondary visualization and additional data which can help with further analysis.
The planets are circles sized according to their actual radii, but with logarithmic scaling. This is due to the very large range of planet sizes (ranging from as little as 0.24x Earth’s radius to 164.03x Earth’s radius for all planets, and 0.77x to 54x Earth’s radius for the habitable planets).
They are colored according to Equilibrium Temperature. Although all of the planets shown in the visualization are in the habitable zone, some are on the colder end (blue) and some on the hotter end (red). A future version of the system may include more color encodings to choose from.
The secondary visualization uses a generic “parent star” that is colored based on it’s surface temperature, which is a direct mapping to how it looks in real life. It also animates the planets rotating around their star, based on their orbital period. In this model, it would take Earth 22.5 minutes to complete one revolution around the sun.
This visualization system utilizes variables that we know for ALL habitable exoplanets. Certain variables like planet mass are either impossible or very difficult to find with current detection methods, and are therefore only available for certain planets. For this reason, we decided to omit those variables from the system. The non-trivial parameters we have in our toolkit:
Stellar Flux At Planet (in SI units): The amount of radiated power from the parent star that reaches the planet (eg: Stellar flux for Earth = 1370 W/m2)
Planets in System: The number of parents orbiting the parent star (eg: for Solar System = 8)
Planet-to-Star-Radius: The ratio between radius of the parent star (in Earth radius) to the radius of the planet (in Sun radius) (eg: for sun-to-earth = 1)
Semi Major Axis (in AU): Distance from parent star to the planet (eg: semi-major axis of Earth = 1 AU = 1.5E11 m)
Orbital Period (in Days): Time taken by planet to complete one orbit around parent star (eg: orbital period of Earth = 365 Days)
Equilibrium Temperature (in K): Average temperature on the planet assuming albedo of 0.3 (eg: Equilibrium Temp of Earth = 255 K = -18o C)
RA, DEC: Location of the parent star in sky, where Right Ascension (RA) being like longitude and Declination (DEC) being equivalent of latitude.
My team developed a fully interactive prototype based on our design using D3. My role was in UI design, visual design and front-end programming (HTML, CSS, JS), while my team members covered the back-end programming (D3). The prototype can be viewed by clicking on the image below.
I wasn’t completely happy with the design, and new I could do better, plus the prototype was lacking some features and data that I knew would eventually be available, so I later rethought the interface. I used a much better grid system. Below are wires and a visual design in Illustrator