A2-MarkHowison
From CS294-10 Visualization Fa07
Contents |
[edit] Domain
Astronomy: Extrasolar Planets
[edit] Questions
1. Is there any correlation between different properties of recently discovered extrasolar planets?
2. Can they be clustered into groups that share similar characteristics (i.e. how the H-R diagram provides clusters/trend lines for stars)?
[edit] Data Sources
Through a Google search, I found a table of data on extrasolar planets [1], which I copy and pasted into OpenOffice Calc. Next, I cleaned up the data by removing rows that listed multiple or approximate values for any column. I also removed the Inclination column, since it had so many missing values. Finally, I exported the data to a .csv file.
I wasn't satisfied with the types of comparisons I could make with this data, so I hunted for more and found a website from the Paris Observatory [2] that allowed me to download a .csv file with more entries than the previous table, and with several additional columns, including properties of the planets' stars.
[edit] Visualization
Question 1. After loading my first data set into Spotfire, I created scatter plots for each pairwise combination of the data columns.
- Scatter Plots of Pairwise Combinations of Extrasolar Planet Data
- These six scatter plots compare each pairwise combination of the Minimum Mass, Period, Eccentricity, and Farthest Distance from Star columns. The only plot with a strong correlation is Period vs. Farthest Distance from Star, which is in fact a relationship given by Kepler's Third Law.
Question 2. Next, I loaded my second data set into Spotfire and filtered out rows with missing column entries. I began exploring combinations of planet and star properties, again using scatter plots, and found an interesting trend: most of the stars around which extrasolar planets have been discovered are within 0.8 to 3.0 solar masses (i.e., the mass of our sun) and 0.8 to 1.4 solar radii, and the outliers tend to have lower orbital periods. In the first two graphics below, the planet's semimajor axis is coded by color, such that the gradient displays Kepler's Third Law relationship (larger periods correspond to longer axes). Lastly, I noticed that the distribution of exoplanets around stars of different spectral classes is fairly uniform in terms of orbital eccentricity, but lower mass exoplanets have been found only around warmer stars.
- (a) Exoplanet's Period vs. Star's Radius
- (b) Exoplanet's Period vs. Star's Mass
- (c) Star Radius vs. Mass
- (a) Most known exoplanets orbit stars with radii clustering around 0.8 to 1.4 solar radii (the radius of our sun). Stars with radii outside this range tend to have exoplanets with smaller orbital periods. (b) Similarly, the stars' masses cluster around 0.8 to 3.0 solar masses, again with outliers of smaller period. (c) Finally, the reason these two plots in (a) and (b) have similar shapes is because star mass and radius appear to be correlated.
- Star's Spectral Class vs. Exoplanet's Mass
- Observed exoplanets with masses less than one Jupiter mass begin to appear as the spectral class of the orbited star decreases from hotter stars (F, ~6000K) down through cooler ones (M, ~3000K). Moreover, these smaller mass exoplanets all have highly eccentric orbits (indicated by color). However, orbital eccentricity appears to be uniformly distributed across spectral class. For reference, the sun is of spectral class G2V and Earth's mass is equivalent to 0.003 Jupiter masses.
