Astrônomos começam a caça de exoluas orbitando exoplanetas
http://eternosaprendizes.wordpress.com/2009/02/01/astronomos-comecam-a-caca-de-exoluas-orbitando-exoplanetas/
So, let’s find the exomoons!
Tks
ROCA (Brazil)

'"exocreatures" .. I like it ! That other word has become sort of … xenophobic ?'

Yes, but I wonder about when the first manned spaceship will be designed to also carry weapons onboard. Will there once be a need to defend against or dominate over other "earthlings" during missions in space? Or will weapon systems once be integrated into space exploration vehicles or armament be foreseen in view of some "strange" (alien) events?

I have noticed some confusion about how the method works so I thought I would briefly summarise the idea. I'm very happy to see so many interesting discussions on the topic!

The key point to bear in mind is that we are looking at the wobble of the planet, not the the wobble of the star. Every time a planet transits the star, it affords us information about the position and velocity of the planet. Even if the moon is too small to show up in the transit lightcurve, its effects on the host planet are not.

Both the position and velocity of the planet will be perturbed by the presence of a moon. The spatial perturbation causes the planetary transit to occur slightly earlier or slightly later than expected. The velocity perturbation causes the transit duration to be slightly greater or slightly smaller. Remarkably, these effects can be minutes in magnitude.

The two effects, called transit time variation (TTV) and transit duration variation (TDV) always exhibit a 90 degrees phase difference. In other words, we have a quite unique signature. In addition, the ratio of the two amplitudes allows for a determination of both the moon's mass and its orbital distance from the host planet.

It's really fantastic to see so many people interested in exomoons. Who knows how common these exomoons may be and what potential for habitability they possess! Ultimately, the only way for us to answer these questions is to start looking!

All the best and continue to ask questions!
David

If they watch things long enough, they'll see patterns and cycles, just as humans did. Perhaps more importantly, such beings might not waste time on the kind of Ptolemaic, planet-centered Universe that western civilization on Earth did…

Beings living on a body directly or indirectly circling one component of a double star might likewise be less inclined to believe the Universe literally revolves around them (unless the companion star was so distant and slow orbiting that it could be mistaken for a background star…)

I'm scrambling to keep up. Did we get over some kind of "hump" here ? Even if those exoplanets and now exomoons don't harbour life, the techniques being developed will be invaluable.

D. Clayton:

If the moon is far enough away, and had an inclination relative to the planet, then it would only pass into the planet's shadow on occasion. Even if it does regularly pass into the shadow, it be cyclic, and any life forms would have no trouble adapting.

the reason we are so susceptible to it is because we are shielded from it, but what if you were always exposed to it, wouldnt life have found ways to mitigate the problems that arise from it. After all, there are bacteria that are very radiation resistant on earth, so i dont think that idea is very strange at all.

In short, I have no answer to Jorge's question

Oh. Too bad. I was really looking forward to learning something new here.

So, either the experiment doesn't make sense or there's something here that's eluding us. Ian, can't you squeeze something else about this out of your sources?

I mean OUR month of course. They probably would never have developed a time intervall like a month, which is caused by the observation of our moon.

*#-)*

How could they establish a celestial coordinate system so easily? And the seasons on Earth are caused by the change of the inclination during one revolution around the sun. But their seasons would change with every circle around their planet, maybe every month. Thus, what concept of time would they have developed?

Consider the Moon of the Earth. One could see the Moon in the shadow of the Earth just about hundered times throughout the whole 21st century.

Since its orbit would constantly take it within its parent planet's shadow, wouldn't this affect life for the worse?

Also, as far as radiation belts go, both Ganymede and Europa orbit within its radiation belts, although the former is known to host a very strong magnetic field (unfortunately it does not block out all of Jupiter's radiation).

I think Titan would be a better example, of a large moon that orbits just within its parent worlds magnetic field (despite the fact that it lacks one itself).

Perhaps something like a global winter and summer. Titan might be a good model.

I think this would be very possible, and a worthy effort!

Yes, but that center of mass will not move in complete accordance with Kepler's Laws. It will periodically speed up and slow down. Which is Kipping's whole point.

Hm… still trying to wrap my head around this. So. I can think of only one way for this to happen: if the motion is such that we have to throw in relativity. Right?

If so, surely the variations would be minute?…

Yea, I would guess that the much shorter frequency of wobble induced by an earth sized moon would be easier to detect than that of a earth sized planet.

The concept of a Titan or Europa like moon in the habitable zone of a star is exciting.

Sorry, but your intuition is wrong. An earth sized planet going around a star can not be detected (yet) because the wobble it induces is too small. If a gas giant planet induces a readily detectable wobble, the speed with which it rises and falls is much easier to measure. I have no links handy, but in several known multi-planet systems, planets' gravitational influence on each other has already been found.