If Planet 9 really exists, here’s the wild way we could hunt it

Trying to find such an item with a “conventional search” using telescopes is something like a needle in a haystack

Scientists have long suspected a so-called Planet 9 in the outer reaches of our solar system. Could we finally discover it using hundreds of tiny probes, equipped with only clocks and radio transmitters?

Legendary string theorist Edward Witten suggests this in a new paper, which hasn’t yet undergone peer review:

“A possible alternative is to probe the gravitational field of this object using small, laser-launched spacecraft, like the ones envisioned in the Breakthrough Starshot project. With a velocity of order .001 c, such spacecraft can reach Planet 9 roughly a decade after launch and can discover it if they can report timing measurements accurate to 10⁻⁵ seconds back to Earth.”

How would these tiny probes search for the missing celestial body? Since scientists don’t actually understand what Planet 9 really is, they’ve extrapolated based on what they observe around it: slightly changed orbits and other signatures that a massive body with gravity of its own is influencing the very outer reaches of our solar system.

Trying to find such an item with a “conventional search” using telescopes is something like a needle in a haystack, simply because of the huge size of the asymmetrical, far-away orbit.

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Instead, Witten suggests that advancing spacecraft technology now allows the idea of a cloud of hundreds of probes. These will spread out in order to cover much more of the area where Planet 9 might be, and if indeed the “planet” is something else—a primordial black hole (PBH) or other “exotic compact object,” Witten says—the probes will observe it in a way a conventional search never could.

Read more: Popular Mechanics