Exoplanet Discoveries, discussion of the latest finds Options

[Guest_PhilCo126_*]

Well-known exoplanet researcher Dr Michel Mayor ( discoverer of Peg 51b with Dr Didier Queloz in 1995 ) today announced the discovery of the lightest exoplanet found so far. The planet, “e”, in the famous system Gliese 581, is only about twice the mass of our Earth. The team also refined the orbit of the planet Gliese 581 d, first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist:
http://www.eso.org/public/outreach/press-r...9/pr-15-09.html

[Explorer1]

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)?

[JRehling]

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.

[TheAnt]

.....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.

[JRehling]

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.

[Julius]

[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?