Since when have we been able to detect exomoons...?
If it is large enough and passes between its host star and us then Kepler can detect it, regardless of whether it orbits the star directly or not, though confirming an moon would be more challenging than confirming a planet.
Also: omgomgomgomgomgomgomgomg!!!!!! *squeeeeeeeeeeeeeeeeeeeellllll* I did not know about this!
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I hope it's not a "Well, there's a gas giant in the habitable zone, IF it has a moon then we can surmise it MAY be habitable" situation...
I just did a little poking around and it does seem likely that that's what's going on in this case :/ Oh well, I still wouldn't be surprised if Kepler found some moons.
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Yeah, a potential exomoon detection is total news to me... I checked the journal databases and only found one paper with any reference to KOI 433, and it has no mention of exomoons. Doesn't mean there isn't a candidate signal, but if so I sure as heck can't find a reference for it.
People are looking really hard for exomoons though, I can assure you of that, and the first detection will be met with a great deal of excitement and publicity.
the first detection will be met with a great deal of excitement and publicity.
You've got that right. I'll probably race around the yard squealing and jumping around until I shortly realize just how out of shape I am, then I'll come back inside and script that purdy little world for SE
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They just select most massive giant planets in the habitable zone, multiplied their mass by 0.0001 and used it as mass of exomoon, then derived its radius from known mass-radius relations for rocky planets. This is predicted exomoons, using prediction that gas giant's satellite system have a mass of 0.0001 planet's mass (emperical fact of our Solar system), and that almost all this mass is concentrated in a single large satellite (Titan and Triton is example).
This is KOI-1422, with updated stellar parameters it have a 0.92 Earth mass planet in the habitable zone! I would like to include it in v0.97, together with unconfirmed planets of HD 10180. Anyway, here the code (for 0.97, but it may work in 0.96):
Code
StarBarycenter "KOI-1422" { RA 286.540009 Dec +49.437328 Dist 384.8 //AppMagn 15.921 Class "M1V" //Mass 0.94 Radius 0.2255 //0.5 Teff 3712 //3862 FeH 0.168 Age 13.0 }
Code
Star "KOI-1422 star" { ParentBody "KOI-1422" Class "M1V" Radius 156941 // 384000 Teff 3712 //3862 Age 13.0 Orbit { Type "Static" } }
If it is large enough and passes between its host star and us then Kepler can detect it, regardless of whether it orbits the star directly or not, though confirming an moon would be more challenging than confirming a planet.
Would it be very difficult to distinguish its transits from its host planet's? I know detecting moons at all is impossible with radial velocity, but it seems like it'd be quite a big challenge with the transit method too.
I'm suddenly struck by how awesome it is that whole new worlds are being discovered countless light-years away, and here we are rendering likenesses of them and exploring them from the comforts of home!
I've been asked "if you could live at any period in history, when would it be?" and I always answer with "right now".
Would it be very difficult to distinguish its transits from its host planet's? I know detecting moons at all is impossible with radial velocity, but it seems like it'd be quite a big challenge with the transit method too.
Difficult, yeah, but just because they are smaller. The main requirement is that the moon is large enough such that it blocks out enough of the star light for its transit to be detectable. Given that, then the moon's signal will show up as a smaller extra dip in the light curve, before, during, or after the main planetary transit. On repeated transits the timing of this extra dip would be expected to change as the moon won't be in the same position in its orbit, and given enough transits we could characterize its orbit.
Just as with planets, the moon's transit depth will tell us its physical size, and if we know the planet's mass via radial velocity measurements, and the period of the moon's orbit, then we can figure out the moon's mass as well, which would allow us to figure out what it's made of.
I've been asked "if you could live at any period in history, when would it be?" and I always answer with "right now".
I think I would answer "all of them".
Quote (Watsisname)
On repeated transits the timing of this extra dip would be expected to change as the moon won't be in the same position in its orbit, and given enough transits we could characterize its orbit.
Yes, but intuitively this sounds very complex if there are several moons, and perhaps a ring.
Does Kepler also detect sunspots, and what has been learned about such "exospots"?
90% of Kepler planets are too close to its parent star to have stable orbits. But distant ones have too long orbital period and have only few transits detected. We need more Kepler-like telescopes and decades of observation time to collect more transit events.
I don't think a planetary ring would do much to the transit depth, or if it did it would be symmetric with the planet signal and there would be no time variation across repeated transits. The existence of multiple moons shouldn't be a problem either; the same methodology as for a single moon will still apply. You'd have multiple ingress/egress events in addition to the main planetary one, assuming the moons are large enough to be detectable.
Good question on the exospots. I know they are detectable and introduce unwanted variation that has to be accounted for, and there has been research that uses this starspot data, but I'm not familiar with what has been learned from it. If you're interested, this paper looks like it's relevant.
Given that Triton is almost certainly a captured object I'm not sure if it is the best example.
Quote (apenpaap)
Would it be very difficult to distinguish its transits from its host planet's?
No, it would be pretty easy. The only thing that matters is whether the moon is large enough to create a detectable transit event, and that it is not transiting its parent planet at the time of stellar transit.
Quote (Watsisname)
I've been asked "if you could live at any period in history, when would it be?" and I always answer with "right now".
I've thought about this many times and decided that pretty much all of them would probably be bad. There are enough problems with the world right now that I can't really call this a good time to live in, and it seems that many of the things that I love might be less relevant in the future by the time those major problems are solved, so it would still not be ideal (though it could be better). The past of course would be pretty awful at just about any point in history.
Quote (Watsisname)
I don't think a planetary ring would do much to the transit depth, or if it did it would be symmetric with the planet signal and there would be no time variation across repeated transits.
Correct.
Quote (Watsisname)
he existence of multiple moons shouldn't be a problem either; the same methodology as for a single moon will still apply.
Indeed. It is somewhat analogous to detecting multiple planets from radial velocity data. The RV curve looks all kinds of funky with all the different weird sine waves in there from all the planets, but you can still figure out what's going on. Different methods would apply for exomoon systems with transits, but you could still figure it out.
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