In decades of searching, NASA has visually confirmed 5,044 planets beyond our own solar system. Finding all these exoplanets has reshaped our understanding of the Milky Way galaxy. The more planets there are, the less unusual our own planet is—and the less likely it is that we are unique. More planets means more places where alien life might thrive now, or might have thrived in the past.
Those 5,000 “exoplanets” within a radius of 28,000 light-years from Earth—the farthest our telescopes can see planets with meaningful fidelity—might be just the tip of the cosmological iceberg. There are undoubtedly countless planets, potentially a hundred billion just in our galaxy, that are too far away for us to see with even our best telescopes.
But it’s possible there are also hundreds of planets hiding unseen in star systems that are close enough for us to directly observe. A team led by UCLA astronomer Thea Faridani has proposed one way of determining where these “hidden companion” exoplanets might be—without actually laying eyes on them. The technique involves calculating the possible effect of their gravity on the visible planets in their system.
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