Light spectography. Take the spectogram of liquid water or water vapour and see if you can find it out there. Absolutely not foolproof but a nice start. Next step could look for stuff like chlorophyl and complex carbohydrates. But that requires finding rocks first.
Only because current detection methods only detect those types.
We can't see the small ones yet. Nor can we see those that take 20 years for one orbit.
BTW, having habitable planets much bigger than Earth isn't impossible. Most of the Earths mass is made up of Iron, which is a relatively heavy element. Half of the table of elements is lighter than Iron.
Since the mass of a planet creates it's gravity, you could have a ball of mostly aluminium and other stuff that's 4 times the size of Earth but still has the same gravity as Earth.
One thing we have learned from the discovered exoplanets is that they keep surprising us.
So are corporate tax-breaks. How much do those cost this year alone again...?
That's funny. Old estimates 'hoped' for roughly one in ten stars having one planet. They calculated that just in this galaxy alone several million intelligent civilizations would exist over the course of the age of the galaxy.
Now we have probably several planets per star to add to that calculation. My guess is: Life is everywhere. In incredible abundance and diversity.
Just imagine a supergiant planet with 5 G gravity, liquid metal and a silicon-based evolutionary process....Life goes where it has time and energy.
We'll probably try selling them stuff.
well similar in size is not required, similar in gravity is more important. This is also the main reason why Mars is a 'failed' Earth. Being only 1/3 as big as Earth, it lacked the gravity to contain an atmosphere. Even Earth vents about 5000 tons of atmosphere daily into space.
Mars used to have running water, in large amounts. For that you need temperature or air pressure. We know the Sun wasn't as hot as it is now, so that leaves only one thing to have created running water on Mars: an atmosphere.
Results will come in very slowly over many years, so don't hold your breath.
I think up to 1.5 G would be reasonable. And we have absolutely no idea what the minimum amount of gravity needs to be.
If we want to terraform Mars we need to weigh it down a bit to sustain an atmosphere. Smash some asteroids into it.
That's an important issue. But the galaxy is very diverse. For instance, the distance between us and Aplha Centauri is 4.6 lightyears. But for a lot of stars in our galaxy that distance is much smaller, sometimes less than a lightyear. So cross-pollination is quite possible for stars that are very close to each other.
And at the same time, life on Earth is over 3.5 Billion years old, but that also means we can safely assume life in our galaxy is 3.5 Billion years old. Probably a lot older. I think it's quite likely that life is now much more present in absolute terms than it was 3.5 Billion years ago, accros the entire galaxy. This would make not only cross-polination much more likely, but also the dispersal of life-precursors, stuff like proteins, carbohydrates etc. Once you've got those complex chemicals in place, the creation of life would very likely go a lot quicker.
Do notice that I use a lot of probably's and likely's, because in truth, nobody knows. But I think that life is simply a form of complexity, a form of entropy that just tends to get everywhere. We see that happen al the time on Earth, irrespective of habitat. So why should the galaxy be any different, besides being amazingly bigger and more diverse?