Science

discussion

RINGS & MOONS

Started by ggccg
Default_user
over 6 years ago

@ggccg

Just to clarify. The exomoon dip I was referring to above in APH23086770 is located near day 115. I think this is also the one punkymonkey suggested was an exomoon later on in the discussion thread. The one you have marked above, I think, classifies as a second exomoon candidate. The dip at 115 is perhaps 30 or 40 % of the main dip centred on day 113.7. I'm not sure if that would make the second dip too deep for an exomoon. Your second one looks quite good though.

Default_user
over 6 years ago
ggccg in response to AsAsAsBjornTh

AsAsAsGalaxyZoo:

@ggccg

Just to clarify. The exomoon dip I was referring to above in APH23086770 is located near day 115. I think this is also the one punkymonkey suggested was an exomoon later on in the discussion thread. The one you have marked above, I think, classifies as a second exomoon candidate. The dip at 115 is perhaps 30 or 40 % of the main dip centred on day 113.7. I'm not sure if that would make the second dip too deep for an exomoon. Your second one looks quite good though.

I see what you are talking about and you are right... I didn't understand you were referring to the d-115 event. I don't think it is too much of a dip at all, but it does concern me a little that it occurs exactly at the minima of the main eclipse. I'll post my markups of it a little later this evening.

Default_user
over 6 years ago

@ggccg

Sorry if I am being unclear. What I am proposing is simply that the entire dip from day 114.8 to 115.2 corresponds to an exomoon to the potential planet transiting from day 113.4 to day 114.2. The reason is simply that it seems an awfully big coincidence if we have two unrelated transits in just two days (without any other transit signs in other quarters). I am not exactly sure what an exomoon would look like in a light curve so it is great that we have this thread to discuss this matter. Thanks for your comments.

Default_user
over 6 years ago

The second possible exomoon transit on http://www.planethunters.org/sources/SPH10086770

Two possibilities here: 1) it's a possible exomoon and 2) it's just a transit-like formation occurring at the minima of the planet transit. I think an argument could be made for either, but let's just consider the exomoon possibility since that's what we're here for.

Here are my markups. The first one highlights the suspected transit. The second one shows the exomoon pixels moved up the maximum possible amount and was used to calculate the depth of the embedded transit.

Looking at the 2nd graphic, we see the main transit (without the exomoon) has a depth of ~.0007 (1.00025 minus .99955). The exomoon pixels moved up .00015 so the depth of the event is ~ .00015. This is ~21.4% of the main transit. This would mean that the exomoon obscured an additional 21.4% of the light from the star.

A Eureka Moment: while writing the above paragraph, it suddenly struck me that the only way that an exomoon could obscure light from a star is while it is NOT transiting it's planet, so calling these events transits is confusing and just doesn't make sense. Henceforth, I'll just call them EXOMOON EVENTS. In the diagram below, you can see how an exomoon NOT in transit of its planet will cause a drop in luminosity and that as soon as it moves either in front of or behind its planet, luminosity will increase. If the exomoon is already exposed as the planet transit begins, the extra drop from the exomoon will not be detectable as it will simply add to the obscuration of the star. What we have to be seeing is an exomoon just emerging from behind its planet or just exiting a transit of its planet, thus causing a drop in luminosity from the star.

Comments welcome.

Default_user
over 6 years ago
ggccg in response to AsAsAsBjornTh

AsAsAsGalaxyZoo:

@ggccg

Sorry if I am being unclear. What I am proposing is simply that the entire dip from day 114.8 to 115.2 corresponds to an exomoon to the potential planet transiting from day 113.4 to day 114.2. The reason is simply that it seems an awfully big coincidence if we have two unrelated transits in just two days (without any other transit signs in other quarters). I am not exactly sure what an exomoon would look like in a light curve so it is great that we have this thread to discuss this matter. Thanks for your comments.

I don't find it so incredible that two substantially different sized planets with orbits beyond 100 days would occasionally transit their star within a few of days of each other.

My current thinking is that the exomoon event necessarily has to be within a planet transit in order for a drop in luminosity to be seen. Seeing a moon alone, outside of a planet transit would be extraordinarily difficult, if not impossible. An event the size of 114.8-115.2 could only be a planet in order to create a drop in luminosity this large. An exomoon event, on the other hand just adds a small amount (proportional to the size of the exomoon compared to the size of the planet) to the luminosity drop as the exomoon either emerges from behind its planet or concludes a transit of its planet during the planet's transit of its star.

Default_user
over 6 years ago

@ggccg You might very well be right!

Is it not strange though that the moon would spend more time in front of the planet than it spends by it's side (contributing to the eclipse of the star)?

I have tried to do some simple calculations based on Jupiter and Ganymede. The Jovian system orbits the Sun with a velocity of roughly 13 km/s -> 47,000 km/h whilst Ganymede orbits Jupiter at a distance of about 1,000,000 km (this would be the maximum distance between the two objects for someone watching for transits). If the planet and moon line up properly Ganymede might not begin it's transit in front of the Sun until 1000/47 h = 21 h after Jupiter has started it's own. This would mean, I think, that Jupiter would be done with it's eclipse before Ganymede starts it's own. Please correct me if I am doing something wrong here (it is very possible). I agree though that the second (large) dip probably has too much delta flux compared to the first one in the example above. Source for numbers: Wikipedia.org

Saturn's rings, on the other hand, "only" extend 120,000 km out from that planet's equator.

Default_user
over 6 years ago
ggccg in response to AsAsAsBjornTh

AsAsAsGalaxyZoo:

@ggccg You might very well be right!

Is it not strange though that the moon would spend more time in front of the planet than it spends by it's side (contributing to the eclipse of the star)?

In order for there to be drop in luminosity, the moon CANNOT be in front of the planet. When the moon is on either side of the planet is when it will block light from the star. When it is in front of or behind the planet, it has no effect on the light curve.

This is why want to stop calling these events "moon transits"... the term is inaccurate and confusing. "Exomoon Events" is what I plan on calling them from now on.

Regarding your Jupiter calculations: I'm not suggesting that we will be able to detect every exomoon. I'm willing to concede that there are cases where it won't work out. I'm just trying to construct a theory based on unusual events that we have been able to observe. Currently, I am working on 5 variations of a theory visualizing what would happen in events like 1.) exomoon leads planet into transit 2.) exomoon trails planet into transit 3.) exomoon is transiting planet at start of planet transit, but emerges from that transit during the planet transit of the star, etc. It's a lot to think about, but I think it is coming together.

Default_user
over 6 years ago

@ggccg

I absolutely agree. "Exomoon event" sounds a lot cooler as well and it is much more accurate. It's also very interesting that the technique we are using for detecting planets is very suitable for finding exomoons. The other method, investigating the gravitational wobble of the star, does not work very well for detecting moons so maybe we have an advantage here (it makes it harder to confirm exomoons though).

You might be interested in this thread DPH100htuz (if you haven't seen it already) and also this page http://en.wikipedia.org/wiki/Extrasolar_moon .

Default_user
over 6 years ago
ggccg in response to AsAsAsBjornTh

AsAsAsGalaxyZoo:

@ggccg

It's also very interesting that the technique we are using for detecting planets is very suitable for finding exomoons.

Well... SOME exomoons, under certain rare circumstances, perhaps, I think.

Default_user
over 6 years ago

@Gerald

Yes, let me rephrase that. There is chance our method might not be completely worthless ;).

Please Log In to make comments.