The LISA mission will be comprised of three spacecraft orbiting the Earth in an equilateral triangle, detecting and measuring gravitational waves. In late 2015, the ESA launched an experimental spacecraft called the LISA Pathfinder to test out the technologies it plans to use on the actual mission.

Under the original partnership's terms, the two agencies were supposed to split the estimated $2 billion worth of expenses needed to run the project. Science says NASA might not be able to commit $1 billion even if it rejoins, but it will be significantly more than the $150 million it planned to contribute when it left the partnership.

Besides the confirmation of gravitational waves' existence, NASA might have also been compelled to get back into the thick of things when the ESA announced that the LISA Pathfinder has been performing well. In fact, the team will start accepting mission concepts for the Pathfinder next month instead of in 2018. Also, it plans to move up the actual LISA mission's launch from 2034 to "somewhere in the early 2030s."