Jetty has existed in Maven Central almost since its inception, however under a couple of different coordinates over the years. When Jetty was being developed at SourceForge and then The Codehaus it was located under the groupId of org.mortbay.jetty. With Jetty 7 the project moved to the Eclipse foundation and moved to a new groupId at that time to reflect its new home.

The top level pom for the jetty project is located under the following coordinates.

<dependency>
  <groupId>org.eclipse.jetty</groupId>
  <artifactId>jetty-project</artifactId>
  <version>${VERSION}</version>
</dependency>

The changes between versions of jetty are tracked in a file called VERSIONS.txt under source control and is generated on release. Those generated files are also uploaded into Maven Central during the release of the top level pom and can be found as a classifer marked artifact.

http://repo2.maven.org/maven2/org/eclipse/jetty/jetty-project/9.0.0.RC0/jetty-project-9.0.0.RC0-version.txt

<dependency>
  <groupId>org.eclipse.jetty</groupId>
  <artifactId>jetty-project</artifactId>
  <version>${VERSION}</version>
  <classifier>version</classifier>
  <type>txt</type>
</dependency>