ATMOSPHERIC CHEMISTRY/CARBON AND HYDROCARBON COMPOUNDS
Working Group for Planetary System Nomenclature

```r
library(tidyr)

nasa_keyword <- tibble(id = metadata$dataset$`_id`$`$oid`, 
                           keyword = metadata$dataset$keyword) %>%
  unnest(keyword)

nasa_keyword
```

```
## # A tibble: 126,814 x 2
##    id                       keyword      
##    <chr>                    <chr>        
##  1 55942a57c63a7fe59b495a77 EARTH SCIENCE
##  2 55942a57c63a7fe59b495a77 HYDROSPHERE  
##  3 55942a57c63a7fe59b495a77 SURFACE WATER
##  4 55942a57c63a7fe59b495a78 EARTH SCIENCE
##  5 55942a57c63a7fe59b495a78 HYDROSPHERE  
##  6 55942a57c63a7fe59b495a78 SURFACE WATER
##  7 55942a58c63a7fe59b495a79 EARTH SCIENCE
##  8 55942a58c63a7fe59b495a79 HYDROSPHERE  
##  9 55942a58c63a7fe59b495a79 SURFACE WATER
## 10 55942a58c63a7fe59b495a7a EARTH SCIENCE
## # ... with 126,804 more rows
```