2024-04-04

NASA Exoplanet Archive

https://exoplanetarchive.ipac.caltech.edu/index.html

The NASA Exoplanet Archive catalogs all known exoplanets and their properties. The first confirmed discovery of an exoplanet was in 1992. Today, new exoplanets are confirmed regularly every few weeks.

Many of the exoplanets were discovered by NASA’s Kelper and TESS space telescopes

The archive contains 5,602 confirmed exoplanets as of 3/26/2024

Transiting Exoplanet Survey Satellite

Image Credit: Orbital ATK / NASA (Public Domain)

Apart of NASA’s Explorer Program and was launched on 4/18/2024

TESS has discovered over 7,125 candidate-planets and 432 confirmed exoplanets to date

The planned mission duration was 2 years. TESS is still operational, and has been surveying the skies for over 5 years

Accessing the Archive

The table names and the Table Access Protocol (TAP) procedures are listed here

Star data are stored in the “stellarhosts” table and the column definitions can be found here

Our query will select the star system name, the number of stars in the system, the number of exoplanets in the system, and the position of the system in the ecliptic coordinate system.

Downloading the Star System data

query = "select+sy_name,sy_snum,sy_pnum,elat,elon,sy_dist+from+stellarhosts"
host = "https://exoplanetarchive.ipac.caltech.edu/TAP/sync"
rest_url = sprintf("%s?query=%s&format=csv", host, query)

# Be a good citizen and access server sparingly
#stars_df = read.csv(rest_url)

# Read/write cached response
#stars_df %>% write.csv("stars_data.csv")
stars_df <- read.csv("stars_data.csv")

Table contains one star per row, so select unique star system names. Also, filter out incomplete observations.

stars_df <- stars_df %>% 
  distinct(sy_name, .keep_all = TRUE) %>%
  filter(!is.na(sy_snum) & !is.na(sy_pnum) & !is.na(elat) 
         & !is.na(elon) & !is.na(sy_dist))

cat("Number of unique star systems:", nrow(stars_df))
Number of unique star systems: 4030

Converting Ecliptic Coordinates to Cartensian

Ecliptic Coordinates are essentially spherical coordinate where polar angle corresponds to the longitude and the azimuthal angle corresponds to the latitude. The xy-plane is the orbital plane of Earth.

\(x = \text{Distance}\;\cdot\;\cos(\text{Latitude})\;\cdot\;\cos(\text{Longitude})\)

\(y = \text{Distance}\;\cdot\;\cos(\text{Latitude})\;\cdot\;\sin(\text{Longitude})\)

\(z = \text{Distance}\;\cdot\;\sin(\text{Latitude})\) 

stars_df <- stars_df %>% 
  mutate(x = sy_dist * cos(elat) * cos(elon)) %>%
  mutate(y = sy_dist * cos(elat) * sin(elon)) %>%
  mutate(z = sy_dist * sin(elat))

Stellar Position Plot

Note: sy_pnum == Number of planets in the star system

Numbers of Exoplanets

Sample mean of the number of exoplanets contained in a star system

\(\bar x = \frac 1 N \sum x = 1.3508685\) exoplanets

Distance from Earth

Sample mean of exoplanet distance from Earth using a weighted average

\(\bar x = \frac{\sum w_i x_i}{\sum w_i}= 696.1447551\) parsecs

Sources