Looking For Earth-Like Exoplanets 73
Discover Magazine is running a story detailing the search for planets like Earth orbiting other stars. While we've been able to locate a few "super earths" so far, none of them really compare in size or the potential for habitability with our own world. Fortunately, advances in data analysis and new space-based telescopes — such as Kepler, the James Webb Space Telescope, and the already-launched CoRoT (PDF) — have some astronomers predicting we'll find such an exoplanet by 2010, and a habitable one by 2012. Earth-based telescopes are also in the hunt, though the article notes, "even if a habitable Earth-like world is found first from the ground, it will most likely take a space observatory to search for the chemical signals that tell us what we really want to know: Is anything living out there? If the planet is one that can be observed transiting, it just might be possible to provide a hint of an answer in the next few years."
Re:Wow... An article about planets that isn't... (Score:3, Interesting)
There definitely needs to be some refinement of what qualifies as "earth like". I would consider Mars to be a the extreme outer edge of "earth like". Some of the more extreme bacteria and lichen from earth might be able to survive, maybe. I wonder what the parameters for "earth like" should be. Maybe: 0.4G to 1.4G gravity range, a temperature range between 180K and 335K, atmospheric pressure of 1kPa to 110kPa. What else would need to be included for a meaningful "earth like" definition?
Re:High resolution images possible in near future? (Score:5, Interesting)
It's harder than that. I assume by "see" you mean two-dimensional visible or near-visible light images. To produce images like that you have to be able to move each telescope in your interferometer (or have lots of them), in two dimensions. The big radio interferometers put the radio telescopes on train tracks. Some proposals for space interferometers put one on each end of a tether, spin them, then winch them closer and farther apart to trace out a spiral.
The other problem with crazy long baseline interferometry is that you need to transmit the received signal (including phase) between the individual elements. For radio that's not too bad because you can actually detect and record the phase, for low enough frequencies. For optical it's much harder.
Plus you have the problem that interferometers have great resolution but poor light gathering capability. They can't see things that aren't bright.
A back of the envelope calculation (which might be wrong) shows that a 50 km city at 50 light years would be about 2 x 10^-5 miliarcseconds. To get that kind of resolving power in the middle of the visible spectrum you'd need a telescope about 6000 kilometres across. That's not too insane. You might be able to pull it off with an array of a hundred or so reasonably sized space telescopes all orbiting around a L point somewhere. If you could collect enough light, and distinguish between the city light, the non-city planetary light and the star, of course.
Re:Wow... An article about planets that isn't... (Score:4, Interesting)
... I wonder what the parameters for "earth like" should be....
Do you mean by that the conditions necessary to develop intelligent life, such as the SETI project is looking for? Assuming that the laws of physics are the same everywhere in the universe, the molecular binding energies for living things would dictate the temperature range. For practical purposes this would mean the temperature range in which water remains liquid at least some of the time. This would require a stable orbit around a star the output of which does not fluctuate too much. Orbital mechanics show that such a star must not have a neighbor closer than about 3.8 ly. By that specification alone, about one half of all stars in the universe are disqualified from having such a planet because they are too close to each other.
Really big stars are also disqualified because their output varies too much in order for intelligent life to develop or exist. If a star is too small, a potential planet must be placed too close in order to get enough heat. Any such close in planets all are unlikely to freely rotate, thereby having one side always facing the star. That would mean the dark side would get extremely cold. Assuming there was a viable atmosphere, it would circulate violently between the day and night side.
Living processes involve large complex molecular structures which only the element carbon allows. Therefore, any physical life must be based on the chemistry involving carbon. Of course, there may be nonphysical life, but that is not what we are talking about here.
Re:Wow... An article about planets that isn't... (Score:3, Interesting)
Re:High resolution images possible in near future? (Score:3, Interesting)
A telescope at the Sun's gravity focus.
http://www.centauri-dreams.org/?p=785 [centauri-dreams.org]
(the comments contain some interesting information as well.
The resolving power is a bit of slippery subject, because gravity microlensing doesn't work quite like a regular refractive lens. According the the comments, you can basically see anything, no matter how far away (subject to caveats when you start getting insanely far away) as if it were in close orbit around the sun. So the resolution you can obtain really depends on what kind of telescope you put out at the gravity focus. One of the commenters calculated that if we put Hubble out there we could see things about the size of Mercury, at ANY distance. The light collecting ability is also enormous.
There are some problems though. First, you have to get out there. Farther than anything we've ever sent. Also, 550 AU (about 20 Pluto distances) probably won't work, because then the light you're collecting has to skim the surface of the sun. Better would be to go out to about 1000 AU (about 1/200th of the way to Alpha Centauri) so that you're not trying to see through the thick parts of the sun's atmosphere.
Once you get there, you have to be able to accurately record smeared out images while staring into the sun.
Finally, you can really only look at one thing. If you want to look in a different direction, you have to move the probe a LONG way. These would probably be single purpose missions, which means you'd basically have to know exactly what you wanted to look at before you sent out the probe.
We use microlensing caused by other objects all the time though. There's even a project to look for extrasolar planets that happen to be revealed by microlensing events.