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Exoplanet Discoveries, discussion of the latest finds
fredk
post Feb 23 2017, 09:33 PM
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Looks good, Hendric. (But that's 23' from the sun's limb.)

Taking into account the RA proper motion only helps, since it's eastward, ie towards the ecliptic. So it might only take a couple of thousand years...
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ngunn
post Feb 23 2017, 11:33 PM
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Brilliant stuff guys, thanks for taking an interest in a casual question. It has set me off thnking though about the invariable plane of the solar system. All the planetary orbits must eventually relate to that as they evolve over time but I can't find it plotted on a star map as the ecliptic and galactic equator commonly are. Can anybody help?
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Explorer1
post Feb 24 2017, 12:33 AM
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QUOTE
It's possible to resolve this, eventually, by measuring the orbital inclinations between pairs, which can be done by measuring the duration of transits, but this requires a lot of data, because in any particular instance, two planets could both transit their star even if their orbits are highly inclined because the line where their planes cross could happen to go right through the star.


Wouldn't direct imaging also work (i.e. a starshade)?
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JRehling
post Feb 24 2017, 02:38 AM
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QUOTE (Explorer1 @ Feb 23 2017, 05:33 PM) *
Wouldn't direct imaging also work (i.e. a starshade)?


Yes, I got to that at the end of the post… "visually resolve…"

One should note, though, that when we will be able to resolve certain cases, many others will remain unresolved, and something like the orbits around Trappist 1 are a tall order – these are on the order of 0.02 AU and are located 39 light years away. This is about 1/400th the angular size of a 1-AU orbit around Alpha Centauri! It seems quite likely that a whole generation (or several) of technological advances will be needed to go from the one to the other… and we're nowhere near able to achieve the easier of those two cases yet or in the foreseeable future.
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TheAnt
post Feb 24 2017, 08:17 AM
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QUOTE (JRehling @ Feb 24 2017, 03:38 AM) *
.....something like the orbits around Trappist 1 are a tall order – these are on the order of 0.02 AU and are located 39 light years away. This is about 1/400th the angular size of a 1-AU orbit around Alpha Centauri!


Yes I thought so too, yet thank you for giving it in straight numbers JRehling.
With all orbits closer than Mercury and almost as tight as the moons around Jupiter, I had the gut feeling that taking direct images would be near impossible.
The good thing about these transiting planets is that we should be able to get a good idea of the makeup of the atmospheres of these planets - or lack thereof.
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hendric
post Feb 24 2017, 05:33 PM
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In a related Nova episode on the Origami Revolution, they demonstrate how a starshade could deploy for a future exoplanet telescope mission. http://www.pbs.org/wgbh/nova/physics/origami-revolution.html


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scalbers
post Feb 25 2017, 12:47 AM
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For visually resolving I remain a fan of the old Planet Imager (PI) mission concept, a network of space interferometers spread over thousands of kilometers. Each interferometer in the network is a Terrestrial Planet Finder (TPF) with several telescopes on the order of meters or a few kilometers from each other. The TPF link below is simply to the smaller nested interferometer element.

https://science.nasa.gov/missions/tpf


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JRehling
post Feb 25 2017, 10:45 PM
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QUOTE (TheAnt @ Feb 24 2017, 01:17 AM) *
Yes I thought so too, yet thank you for giving it in straight numbers JRehling.


To clarify further:

The JWST, 39-meter E-ELT and other future telescopes will be able to resolve exoplanet systems well enough that a planet at 1 AU and its star will be in different pixels. It is an open question, however, whether the point spread function will be adequate to allow spectroscopy that can identify the presence of atmospheric components, and this is a function of many unknowns, both in the instrument and in the universe itself. The best hope is for solar-like stars (or even bigger/hotter ones) that are particularly nearby (e.g., less than 30 light years). The problem is that there aren't that many solar-like stars within 30 light years – about 20 class G stars. If 10% of them have an earth-sized planet in the habitable zone, we're talking about very few cases – plausibly zero!

Red dwarfs will have their habitable zones in closer, which makes it absolutely impossible to get the planet and star in different pixels with planned instruments. However, there are a lot more of them and a much higher probability of planets that transit. So what we count on here is to examine the spectra of planets when they transit and/or are eclipsed. Moreover, the star is much less bright than the planet.

So, there are factors that favor the solar-like case and factors that favor the red dwarf case and these will be, to some extent, two complementary branches of exploration. The red dwarf case is probably going to be more productive over the next few decades because studies based on sheer light gathering do not require good resolution and we could conceivably build huge light-bucket telescopes for these studies. But, one final problem with the red dwarf case – we don't even know if the kinds of planets that we hope to find are capable of existing in red dwarf systems. Suppose that tidal locking means no magnetic field – then the planets may lose their H2O and go the path of Venus or something equally dead.

I suppose that mass light gathering is going to work better than superior resolving power – it involves fewer unknowns, and scales better to systems that are further away, whereas increased distance is inherently problematic for efforts to resolve planets. Given enough light gathering, we could – in principle – generate light curves that show the presence of different surface units, oceans and continents, etc.

For any and all of the above, nature has to cooperate. I think one of the terrible problems that we'll encounter will be clouds. For some fraction of the interesting worlds we find, clouds will block our view of the surface and lower atmosphere, and we'll be in the same situation that we were in with Venus in 1950, but with no way for probes or radar to solve the problem for us.
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ZLD
post Feb 26 2017, 03:00 PM
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QUOTE (scalbers @ Feb 24 2017, 06:47 PM) *
For visually resolving I remain a fan of the old Planet Imager (PI) ...


Same here. Interferometers offer the best ROI for visual observations. One change to their proposal I always wished for was the capability to add more telescopes to the constellation in the future. And also a pre-planned robotic servicing craft that could be sent to refuel them. One can only dream I suppose. rolleyes.gif


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Julius
post Feb 26 2017, 08:10 PM
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[quote name='JRehling' date='Feb 25 2017, 11:45
Suppose that tidal locking means no magnetic field – then the planets may lose their H2O and go the path of Venus or something equally dead.

[/quote]
Could you explain more why tidal locking means no magnetic field?
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Hungry4info
post Feb 26 2017, 08:44 PM
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The default assumption is the slower rotation periods will make it harder for planets to generate magnetic fields, but this is still a topic of ongoing research.
http://nexsci.caltech.edu/conferences/Flag...opezMorales.pdf


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fredk
post Feb 26 2017, 09:30 PM
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Well, for these new planets their orbital periods are as short as a couple of days, so if tidally locked their "rotation" periods relative to the distant stars would be not much slower than that of the earth. I don't see that the magnetic fields would care if it's orbital or spin angular momentum.
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ngunn
post Feb 26 2017, 10:13 PM
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I also wondered the same thing, and noted that all these worlds probably rotate a lot faster than Mercury and Venus. If it's about tidal locking per se then there is the counterexample of Ganymede which manages to have a magnetic field despite being tidally locked to Jupiter. Ganymede is a lot smaller than the Trappist-1 planets so if it can do it maybe they can.
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JRehling
post Feb 26 2017, 10:23 PM
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I can only say "Suppose that tidal locking means no magnetic field…"

We really have very few examples and what conditions allow for a magnetic field are unknown at present. Particularly if we put that in terms of the properties that can be observed from light years away.

The fact that neither Venus nor Mars have appreciable magnetic fields is troubling. The fact that Mercury has one is intriguing. It remains a possibility that a lot of otherwise potentially hospitable exoplanets will have lost their H2O to stellar winds, but we can't say if that will be 5% or 95%, or what factors will determine it.

We may be able to resolve this question remotely – conceivably, we can see aurora around exoplanets, and atmospheric composition may give us other clues. This isn't something we can do at present, but we may know a lot about this in the decades to come.
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Explorer1
post Feb 27 2017, 05:17 AM
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If 59 day rotation is fast enough to get a magnetic field (albeit a weak one that certainly couldn't protect Mercury's primordial atmosphere), all of these Trappist-1 planets would easily spin fast enough to retain one. They are all much more massive than Mars too. Just so many variables, and so far out of reach of our magnetometers.
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