Installing Panoply requires Java 9 now, which requires a license from Oracle and is annoying. However, it’s not difficult to instead install the open source AdoptOpenJDK at https://adoptopenjdk.net/installation.html. Follow the installation instructions there, including changing paths to find the java executable.
Locate and run the panoply.jar file with:
java -jar panoply.jar
Create an alias for this command and you’re all set.