# Can the explanation of Tabby's star KIC 8462852 be an intervening planet in orbit around another star?

Can an intervening planet in orbit around a nearby star cause periodic occultation?

Please excuse the crude text graphics:

Tabby ...... PlanetP ......................................... Earth
|
StarX

• StarX and Tabby's star are close to each other (maybe part of some local cluster, like the Centauri brothers) so the line of sight with our Sun/Earth has maintained over the recent handful of years.
• PlanetP orbits StarX with a period of around 750 Earth days. Its ecliptic is at an angle (somewhat perpendicular) to the line of sight with Earth.
• PlanetP's orbit rotates (precession?) a bit around StarX, so the amount of occultation of Tabby's star by PlanetP varies from 15% to 22% to whatever.
• It could be a reason but honestly I dont think so, if the planetP is in the local cluster of tabby, the planet coudln't be big enough to block ALL tabby's luminosity – Alberto Martínez Jun 5 '17 at 10:40
• I heard that Jupiter blocks 1% of the Sun's luminosity at 43 light minutes distance. Even if PlanetX only had 1% occultation compared to Jupiter (combination of smaller planet size, partial eclipse, etc,), then it could still block 20% of Tabby at 2000x the distance (about 10 light weeks). This is about the distance between Proxima Centauri and Alpha Centauri. – Jabir Amirali Jun 5 '17 at 12:08
• Welcome to Astronomy Stack Exchange! I would assume we would have been able to see this second star, right? – HDE 226868 Jun 5 '17 at 14:09
• Something line-of-sight but not near the star would explain the lack of infrared, but it would need to be much bigger than a planet; something like an interstellar dust cloud. – antlersoft Jun 5 '17 at 17:57

The answer is no, because the light curves simply do not match up.

Astronomers have detected planets before using the transit method. Large planets cause dips in a star's light curve when they move between their parents star and Earth; if these dips are regular and strong enough, we can conclude that there is a planet-like body orbiting the star. It's not perfect (best used on conjunction with other methods), but if there is a planet orbiting a star that is detectable like this, we should see a couple key features:

• Periodicity, corresponding to the planet's orbital period.
• Relative regularity in the depths of the transits.

Transits aren't always easy to see, but sometimes you can rule them out as the cause of light curves. The light curves of KIC 8462852 are one of these cases. Boyaijan et al. (2015) provided some of their light curves from the observations of the star. Here's one from Figure 1(b), showing a number of "dips":

There is neither regularity nor periodicity in the data, meaning that your proposed explanation is not possible. Looking at the dips in more detail (see the rest of the paper) confirms the conclusion.

• Could we not propose that dips 8,9,10 are caused by three different planets around StarX? Depending on the line of sight, only one planet (dip 5), or three different planets (dips 8,9,10) of StarX happen to obstruct the light of Tabby's star? If StarX has some small motion relative to Tabby's star, perhaps in the plane out of the page, then it's ecliptic might intersect the line of sight just so. – Jabir Amirali Jun 5 '17 at 22:13
• @JabirAmirali You could, yes, but the planets would all have to have extremely similar semi-major axes, and such a system would likely be unstable. – HDE 226868 Jun 5 '17 at 22:14

No.

First your scale is all wrong. If the scale of the diagram is such that the planet orbits Star X of a centimetre (on the diagram) then the distance between the stars would be 50 km or so. In other words, it would be an unimaginable coincidence for a planet to line up exactly. And since the stars are moving relative to each other (even if they are in a cluster) by the time the planet has orbited once, the planet would no longer be lined up.

The hypothesis doesn't explain much of the observed strangeness, the very large variation in brightness, the odd shape of the brightness graph.

And finally, if the planet can orbit of star X, where is the star. We can't see a star in the right location.

So this hypothesis doesn't explain the observations, so would have to be rejected.

• The diagram is not to scale. The distance between Tabby and StarX might be 10 light weeks, but the distance to Earth is 1500 light years. And, of course, the orbital distance of PlanetX around StarX would only be a few light minutes. Also, the two stars need not have motion relative to each other, at least not in the last few years. Finally, StarX might just happen to be behind a dust cloud. Far fetched scenario, I agree, but less so than a Dyson sphere or alien megastructure. – Jabir Amirali Jun 5 '17 at 22:03