[This post interweaves two separate and distinct writings by Seth Shostak. Normal font is from the SETI web article, “Planet Nine: Are We Not That Special?” . The italic is from the SETI email,”Planet Nine: What Would It Mean?”. I have included all of the internet article and most of the email article. Links to both are below.]
Seth Shostak, Senior Astronomer
Is there a planet ten times the mass of Earth hanging out in the dismal and distant fringes of our solar system?
It could be the first new planet discovered in the last 170 years — or at least the last 85, if you’re one of those stubborn folk who still insist on calling Pluto a planet.
Two researchers at Caltech, Mike Brown and Konstantin Batygin, have reported phenomena that they interpret as smoking gun evidence for a world roughly 500 times farther from the Sun than our own.
The evidence consists of a strange alignment of some so-called Kuiper Belt objects – ice-ball worlds similar to Pluto that populate the farthest realms of the solar system.
About a dozen of these KBO’s seem to have orbits that are similarly aligned – an unlikely situation, akin to throwing a handful of pencils onto a table and finding that they pretty much all point in the same direction.
A predicted consequence of Planet Nine is that a second set of confined objects should also exist. These objects are forced into positions at right angles to Planet Nine and into orbits that are perpendicular to the plane of the solar system. Five known objects (blue) fit this prediction precisely.Credit: Caltech/R. Hurt (IPAC) [Diagram was created using WorldWide Telescope.]
What could account for this bizarre orientation? On the basis of computer simulations, the Caltech astronomers conclude that the most likely explanation is that the KBOs are being nudged into these orbits by the gravitational interactions with a planet roughly twice the diameter of Earth. This object would be located on the side of the solar system opposite to the lined-up Kuiper Belt objects.
No one has actually seen this putative planet with a telescope, but you can bet that many are looking. It will take a large instrument to bring the object into view, as sunlight so far out in the solar system would be 300 thousand times weaker than on Earth. In addition, the exact position of this hefty planet is unknown – so the search has to cover a relatively large amount of sky. It’s a bit like finding a floating volleyball in the ocean from 40,000 feet, when you don’t have a good fix on the volleyball’s location. Still, Batygin estimates that the planet might be discovered within eight years or so.
And what is the significance of “Planet 9,” as it’s being called? For those who look for biology beyond Earth, such a world would make our solar system more in keeping with those we find around other stars. Many of the so-called exoplanets discovered by the Kepler mission and other telescopes are what are called “Super Earths” – worlds that are up to ten times the mass of our home planet. Until now, we didn’t think that our solar system had a Super Earth.
For those in the know about science history, this is all reminiscent of work done by two mathematically adept young astronomers in 1845 — one French and the other British. Each had independently reckoned that irregularities in the orbit of Uranus might be caused by a planet still farther from the Sun. It took almost a year before that planet was seen and recognized in a telescope. We call it Neptune. It’s fair to say that Neptune was discovered with pencil and paper, and it now seems that history might repeat itself with Planet 9.
Some folks, seduced by apocalyptic visions, will say that this work supports claims that have been made for decades that a malevolent planet named Nibiru is prowling the solar system and will (soon) sail by Earth, causing tsunamis, earthquakes, and scenes of destruction hitherto envisioned only by Industrial Light and Magic.
Well, forget that. Planet 9, if it’s really out there, will never come closer to Earth than about 20 billion miles, a distance 40 times farther than Jupiter. And, as you may readily note, Jupiter — although heavier and closer — is not messing with your gusto-grabbing lifestyle.
Then there’s this: Planet 9 is far enough away that if you landed a telescope on it, you could use the Sun as a gravitational lens, producing the mother of all telescopes. It would be an instrument whose capabilities would dwarf anything on Earth or in orbit. Sure, no one’s about to rocket telescope hardware to Planet 9 anytime soon, but that’s not the same as never.
And finally, for those who look for biology beyond Earth, Planet 9 would offer some encouraging news. In the past five years, we’ve found thousands of so-called exoplanets — worlds around other stars. Many of these are “Super Earths” — worlds larger than our own, and up to about ten times more massive. Until now, we didn’t think our solar system had a Super Earth. That made it seem special.
But if the predictions are correct – if Planet 9 actually exists – then our solar system will better comport with many of those we find elsewhere. And if our solar system is not so special, then there’s added reason to suspect that the biology it has spawned may not be so unusual either.
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