Two Nearby Rocky Worlds Could Show Aliens Planets Reversing Course

But a planet that can host life doesn't automatically produce a civilization capable of doing science. Conditions for existing and conditions for understanding the universe are separate questions. For the search for extraterrestrial intelligence (SETI) to succeed in detecting technological traces, Zee argues, researchers must look beyond survival and ask whether science and technology could plausibly develop.

To capture that idea, the paper proposes a new concept: "developmentability." It asks how an exoplanet's astronomical environment might shape the way intelligent beings there come to understand the universe.

Zee gave the concept a concrete test. Using orbital and physical data from the NASA Exoplanet Archive, and drawing on two decades of exoplanet discoveries — including many multi-planet systems — he placed a hypothetical observer on each planet and calculated how neighboring worlds would move across its sky.

The analysis didn't stop at whether retrograde motion happens at all. It checked four conditions:

• Does the reversal last long enough, and span a large enough angle, to be noticeable?
• Is the neighboring planet bright enough to see with the naked eye?
• Does it appear far enough from its host star to stand apart from the star's glare?

The takeaway: seeing a planet reverse course requires a specific combination of geometry, brightness and timing, not just any neighboring world will do.

Which two worlds made the cut?

The study identified two potentially habitable rocky planets where a neighbor's retrograde motion should be clearly visible to the naked eye.

The first case: an observer on GJ 1002 b, watching the neighboring planet GJ 1002 c. The system orbits the star GJ 1002, roughly 16 light-years from Earth.

The second: an observer on Teegarden's Star c, watching Teegarden's Star d, in a system about 12.5 light-years away.

Both systems sit relatively close to Earth, and both observing platforms are planets that may have conditions suitable for life. That combination — possible habitability plus a good view of the sky — is exactly what makes them stand out.

Does this mean aliens live there?

No. The study does not establish that life or civilizations exist on either planet. And even a clear view of retrograde motion doesn't guarantee that a scientific civilization would follow.

What the paper does offer is a reframed question. Just as planetary motion helped humanity realize Earth wasn't the center of everything, could similar phenomena in alien skies steer the scientific progress of any civilizations that arise there? Zee raises the possibility that hypothetical astronomers on GJ 1002 b or Teegarden's Star c might one day watch a neighbor backtrack, conclude their world isn't the cosmic center, and produce their own "alien Copernicus" and "alien Galileo."

The broader shift is from "Where can life exist?" to "What environments could support civilizations capable of understanding the universe through science?" That's a new lens for SETI, and one that can be tested against real catalogued planetary systems.

The results are preliminary in the sense that they rest on modeled skies and hypothetical observers, not on any detection of life. Still, they show how archived exoplanet data can probe questions that once belonged purely to science fiction.