[meteorite-list] Two Giant Planets May Cruise Unseen Beyond Pluto

[Ron Baalke]

http://www.newscientist.com/article/dn25711-two-giant-planets-may-cruise-unseen-beyond-pluto.html 

Two giant planets may cruise unseen beyond Pluto
by Nicola Jenner
New Scientist
11 June 2014

The monsters are multiplying. Just months after astronomers announced 
hints of a giant "Planet X" lurking beyond Pluto, a team in Spain says 
there may actually be two supersized planets hiding in the outer reaches 
of our solar system.

When potential dwarf planet 2012 VP113 was discovered in March, it joined 
a handful of unusual rocky objects known to reside beyond the orbit of 
Pluto. These small objects have  curiously aligned orbits, which hints 
that an unseen planet even further out is influencing their behaviour. 
Scientists calculated that this world would be about 10 times the mass 
of Earth and would orbit at roughly 250 times Earth's distance from the 
sun.

Now Carlos and Raul de la Fuente Marcos at the Complutense University 
of Madrid in Spain have taken another look at these distant bodies. As 
well as confirming their bizarre orbital alignment, the pair found additional 
puzzling patterns. Small groups of the objects have very similar orbital 
paths. Because they are not massive enough to be tugging on each other, 
the researchers think the objects are being "shepherded" by a larger object 
in a pattern known as orbital resonance.

Planet shepherd

For instance, we know that Neptune and Pluto are in orbital resonance 
- for every two orbits Pluto makes around the sun, Neptune makes three. 
Similarly, one group of small objects seems to be in lockstep with a much 
more distant, unseen planet. That world would have a mass between that 
of Mars and Saturn and would sit about 200 times Earth's distance from 
the sun.

Some of the smaller objects have very elongated orbits that would take 
them out to this distance. It is unusual for a large planet to orbit so 
close to other bodies unless it is dynamically tied to something else, 
so the researchers suggest that the large planet is itself in resonance 
with a more massive world at about 250 times the Earth-sun distance - 
just like the one predicted in the previous work.

Observing these putative planets will be tricky. The smaller bodies are 
on very elliptical orbits and were only spotted when they ventured closest 
to the sun. But the big planets would have roughly circular orbits and 
would be slow moving and dim, making them tough for current telescopes 
to see. "It's not at all surprising that they haven't been found yet," 
says Carlos.

"As there are only a few of these extremely distant objects known, it's 
hard to say anything definitive about the number or location of any distant 
planets," says Scott Sheppard at the Carnegie Institution for Science 
in Washington DC, one of the discoverers of 2012 VP113. "However, in the 
near future we should have more objects to work with to help us determine 
the structure of the outer solar system."

Reference: arxiv.org/abs/1406.0715