Because the Centaurs cross the paths of the major planets, their orbits are unstable: some will eventually be ejected from the solar system, but others will be thrown onto trajectories bringing them inwards, therefore posing a danger to civilization and life on Earth. Credit: Duncan Steel

Because the Centaurs cross the paths of the major planets, their orbits are unstable: some will eventually be ejected from the solar system, but others will be thrown onto trajectories bringing them inwards, therefore posing a danger to civilization and life on Earth.
Credit: Duncan Steel

 

All the hoopla over that “should be there” Planet 9 has spurred speculation about its danger to Planet 3 – Earth.

So far, just mathematical modeling and computer simulations suggest this way out world could have a mass about 10 times that of Earth. Furthermore, this purported planet would make one full orbit around the Sun, a period of time that takes between 10,000 and 20,000 years.

This still to be seen planet orbits about 20 times farther from the Sun on average than does Neptune (which orbits the Sun at an average distance of 2.8 billion miles).

This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)

This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side.
Credit: Caltech/R. Hurt (IPAC)

Unnerving possibility

Is it reasonable to consider an unnerving possibility: whether the orbit of this still speculative globe might not arouse waves of objects to tumble inward into our solar system, placing our world in peril?

Inside Outer Space asked that question of Duncan Steel at the Center for Astrobiology, University of Buckingham, and Armagh Observatory in the UK.

Steel and his colleagues recently reported that the discovery of hundreds of giant comets in the outer planetary system over the last two decades means that these objects pose a much greater hazard to life than asteroids.

The giant comets — termed centaurs — move on unstable orbits crossing the paths of the massive outer planets Jupiter, Saturn, Uranus and Neptune. The planetary gravitational fields can occasionally deflect these objects in towards the Earth.

Planet 9 backers, Caltech professor Mike Brown and assistant professor Konstanin Batygin, have been working together to investigate distant objects in our solar system Credit: Lance Hayashida/Caltech

Planet 9 backers, Caltech professor Mike Brown and assistant professor Konstanin Batygin, have been working together to investigate distant objects in our solar system
Credit: Lance Hayashida/Caltech

Reassessment of extraterrestrial factors

More to the point, as Steel has written: “The discovery of many substantial objects in the outer solar system demands a reassessment of extraterrestrial factors putatively implicated in mass extinction events.”

Steel has calculated the terrestrial impact probability for all known asteroids and questions whether the old concept of single, random asteroid impacts causing mass extinctions is “deficient” given what is now known of the inventory of small bodies in the solar system.

Waves of objects

The “problem”, as such, Steel told Inside Outer Space, is stirring up trans-Neptunian objects (TNOs). “This Planet 9 would likely fit the bill. That is, we might expect waves of objects to come inwards whenever Planet 9 is near perihelion and thus enters a denser region of TNOs.”

Be clear that most of the objects out there will be far smaller than the TNOs detected to date, Steel adds, “big devils, they have to be, to be detectable.”

“If this Planet 9 exists, then it may show itself in other ways, such as a shower of comets entering the inner solar system whenever Planet 9 nears perihelion,” Steel says. “We might see the 20,000 year periodicity in cometary dust deposits on Earth, for example. A problem would be that we know that Earth’s climate cycle, due to terrestrial orbit variations, follows a similar periodicity.”

The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Also, when viewed in three dimensions, they tilt nearly identically away from the plane of the solar system. New work by Caltech’s Batygin and Brown show that a planet with 10 times the mass of the Earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. Credit: Caltech/R. Hurt (IPAC)/Diagram created using WorldWide Telescope.

The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Also, when viewed in three dimensions, they tilt nearly identically away from the plane of the solar system. New work by Caltech’s Batygin and Brown show that a planet with 10 times the mass of the Earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration.
Credit: Caltech/R. Hurt (IPAC)/Diagram created using WorldWide Telescope.

Jury still out

On the Planet 9 hypothesis, Steel points out: “The jury is out on this idea, and will be for some time. It’s a useful and interesting suggestion, not altogether unexpected. There are certain to be contrary ideas.”

But if the claims for a Planet 9 are correct, “then more TNOs with similar orbits to those identified should be discovered over the next decade, adding to the statistical weight of evidence,” Steel concludes.

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