There’s been a ton of justifiable excitement these days about the possible discovery of a ninth planet in our solar system — an object ten time the mass of Earth and 200 times further from the sun. Especially in the context of the recent demotion of Pluto from a planet to a dwarf planet, the announcement of a potential replacement seems almost karmic, stage managed, in its take-and-give. This is especially so since the astronomer probably most responsible for the diminished position of Pluto is also the one who now asserts the very far away presence of a different Planet 9 — planetary astronomer Michael Brown of the California Institute of Technology.
The validity of the possible detection of a Planet 9 has set off hot debates — with NASA officials, for instance, making clear that the agency sees the “discovery” as an exciting but early step towards establishing the existence of possible new planet. We are all drawn to discovery and controversy, so the presence, or non-presence, of the planet has been the focus of attention.
But another most intriguing aspect of the finding has been largely ignored — the way that such a Planet 9 would make our solar system surprisingly more similar to the many more eccentric exoplanet solar systems now known to be out there. Our solar system would also suddenly have a range of planets sized more like the galactic norm.
What’s more, there’s reason to consider that a Planet 9 could have been spun off another solar system rather than having been ejected from the inner solar system, as proposed by Brown and colleague Konstantin Batygin.
In other words, Planet 9 may be an “exoplanet” in origin. And if not, a finding that it was ejected long ago from our inner solar system would answer some questions about why our system seems to be so different from many of the other exoplanetary systems discovered so far.… Read more