Kepler Discovers 'Phantom' Exoplanet

astroengine writes "The Kepler space telescope has spotted an extra-solar planet with a very odd orbit. Sometimes Kepler-19b slows down by five minutes during its 9-day orbit. Other times it speeds up by five minutes. Johannes Kelper's laws of orbital dynamics never said a celestial body can arbitrarily speed up and slow down; another planetary body must therefore be gravitationally acting on Kepler-19b. Enter Kepler-19c, a world that hasn't been observed, but its gravitational effects have. This is an unprecedented discovery, one that could potentially be used in multi-planetary star systems to discover more 'phantom' worlds that would have otherwise gone unnoticed."

Comments

Unprecedented?

[Jaryn]

Unprecedented? Isn't this pretty well the way we discover all extra-solar planets? Through star wobble? Unless we're lucky enough to line up for a full on occlusion?

I mean, I guess in this case it's "planet wobble". But FTFA: "Interestingly, planets in our solar system have been detected through a similar method."

So uh... unprecedented?

Not 'unprecedented'

[bennetts2]

This is an unprecedented discovery

Er, no. Neptune and Pluto were both discovered because of the perturbations they caused of the orbit of Uranus.

Re:Not 'unprecedented'

[nedlohs]

They aren't exoplanets, and hence not a precedent.

Re:Yes

[tragedy]

FRY: This is a great, as long as you don't make me smell Uranus. Heh heh.
LEELA: I don't get it.
PROFESSOR FARNSWORTH: I'm sorry, Fry, but astronomers renamed Uranus in 2620 to end that stupid joke once and for all.
FRY: Oh. What's it called now?
PROFESSOR FARNSWORTH: Urectum.

Binary planet?

[gstrickler]

+/- 5 minutes in a 9 day orbit is a huge variation. This almost has to be a binary planet system, or planet with a massive moon, or something similar. Enough gravitational force to slow or speed up a planet large enough that we can detect it by transit dimming of it's star 650 LY from Earth, that's either a really light planet, or it's got a massive companion orbiting it. The other possibility is that there is a dark star (white/brown dwarf) orbiting the same star, but we should be able to detect that wobble via doppler shift, so the companion moon/planet seems more likely.

Re:Binary planet?

[DG]

That makes me wonder how much energy is being transferred to / from this planet every time its orbit speeds up / slows down.

I bet it's not the most geologically stable place in the universe - assuming it isn't a gas giant.

DG

Re:Binary planet?

[gstrickler]

Perhaps you missed the significance of a +/- 5 minute variance of a 9 day orbit. That's 5/(9*1440) = 5/12960 = 1/2592. That's nearly 0.04% variance in the orbital period of a planet. To achieve that much change in orbital period, the velocity change needs to be at least that great, and likely at least 2x that great (since speed changes won't be instantaneous, it will have to slow down 2x as much to average 0.04% slower orbital rate).

Given gravity is inversely proportional to the square of the distance between the centers of mass, how much more massive must the other body be to produce that much change in velocity? Even if the other body is in a 4:3 resonance, making it "relatively close", it would still need to be vastly more massive than the observed planet. If it's vastly more massive and in orbit around the same star in a 4:3 resonance, we would definitely be able to detect it by it's doppler shift of the star unless it's orbital plane is almost perfectly perpendicular to our line of sight, and then we would still likely observe an effect on the star.

The other possibility is that there is a third massive body in the system that playing tug-o-war with the planet, pulling it away from the star, then the star pulls it closer, constantly changing it's orbit. That way the velocity of the planet doesn't have to change as much, however, how such a system could produce such an oscillation in the planet's orbit, sometimes increasing it and sometimes decreasing it resulting in such large changes in orbital period without also causing measurable effects on the star is mystery.

We may eventually figure it out, but for now, that much variation in orbital rate is really bizarre.

Re:Binary planet?

[Mt._Honkey]

I did the calculation, after finding the details of the planet on the Kepler website. They don't have a mass value for 19b, just an upper limit at 14 earth masses. I just plugged in a value of 10 earth masses for my calculation, and I get 10^30 J, or about 200 zettatons of TNT equivalent, or enough energy to accelerate 3.6 billion pounds of bacon to the speed of the LHC beam.