- Could a cloud of hundreds of tiny probes find the elusive Planet 9 in outer space?
- Scientists have said Planet 9 could be a planet or an “exotic compact object.”
- Sending hundreds of probes at once ensures wider coverage with more likelihood of success, physicist Edward Witten says.
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.
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.
“If further study of the Kuiper belt strengthens the case for existence of Planet 9, but discovery via telescopic searches or a dark matter annihilation signal does not follow, then a direct search by a fleet of miniature spacecraft may become compelling,” Witten writes.
Voyager 1 launched in 1977, and it took until the end of 2004 for the unmanned spacecraft to cross the termination shock: the place where our sun’s influence meets and gives over to forces of interstellar space, at the very edge of our solar system. Planet 9, which NASA calls Planet X, “orbits our Sun in a highly elongated orbit far beyond Pluto.” For a fleet of tiny probes to reach it in just a decade would indeed be revolutionary.
Witten cites the Breakthrough Starshot project, which is a collaboration between billionaires and geniuses who want to put a similar exploratory craft in Alpha Centauri within 20 to 30 years of launch. To do that would mean the fastest space travel ever attempted, and Witten wonders if the same technology could fling his fleet of Planet 9 probes just as fast.
Each probe would beep a signal back to Earth. By combining a pinpoint-accurate, on-board time measure with the relatively simple math of the transmission time lag, scientists can make an interactive map of where each of the hundreds of probes is, Witten says.
That sounds easy, but it’s not. Precise clocks on Earth rely on services like global time synchronization. “Sufficiently accurate timekeeping in a miniature spacecraft may be the biggest obstacle to this project, though there are numerous other challenges,” Witten writes.
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