Scenario

We've got a terrestial exoplanet three times the size of Earth, 1800 light years away and with an atmosphere similar in composition to Earth's. It is determined via studies that atmosphere would be able to support terrestial life without needing any life support. More studies and in greater detail are made en route to the system which would prove that the assumptions made back on Earth weren't fully right.

Questions

• How much and what kind of information would humans be able to get about it right now and in a near future (no more than 4 decades)?
• Would scientists be able to even detect the atmosphere?
  • If yes, then what margin of error would the estimates have?
• How clearer the data would as scientists would approach the planet? Let's take numbers of 900 light years, 100 light years and 1 light year away. The scientists on the ship approaching the planet would have near-future equipment.