What kind of planet would qualify as a “major discovery”?
Hmm. Anybody know where they’ve had it turned recently? That might give us a clue as to what it could be. I doubt if they could spot an Earth-like world very far away from us, but they might be able to get a good idea that one’s around one of the closer stars. If they show us something that looks like this, I think we might ought to get worried. 
Perhaps it has buildings on it.
These things are obnoxious. I don’t want to hear about it until they actually make the announcement. The last time one of these went around, it was a disappointment. People were speculating all sorts of wondrous things, but it turned out to be another supernova, just a younger one than we’d seen before.
There ws a 4-page thread here about it:NASA set to announce discovery... any guesses as to what it is? - Factual Questions - Straight Dope Message Board
Maybe it’s shaped like Mickey Mouse’s head.
Count me in the “NASA has cried wolf too many times” crowd. I just ignore this stuff.
My guess? A planet that is in some significant way “earthlike”.
Whether that way is significant to the layperson as well as to the planetary astronomer is a good question.
Extrasolar, Earthsized, warm, & with water.
The Planet of the Apes
A planet just like earth, except the water is made with two parts hydrogen, one part oxygen and a pinch of oregano
The last two are not possible to know with the current state of technology.
And elephants!!
Supernova hate press release! Supernova angry!
An all-water world with a single continent that looks just like Mohamed-peace be upon him.
NASA isn’t ‘crying wolf’. That supernova, for instance, was a big damned deal to astronomers and cosmologists.
The problem is that the things that are big, press-release worthy items to NASA’s fellow scientists aren’t the same things that the public finds exciting.
Reading the press release, it doesn’t say there’s a major discovery about a planet, it says “NASA will hold a Science Update to report on a significant discovery about planets orbiting other stars”. That suggests to me more of a general principles kind of thing, not necessarily the discovery of a new planet. Or maybe it’s a new planet, but the planet itself is less important than the information it gives us about how they form, or how likely we are to find them, or what kind of orbit they can have, or something like that.
Pretty sure you’re wrong on that one.
We can tell where the sweet spots are on most stars, that “habitable zone” that would allow for surface water. So if there is a planet, and it’s in that zone, if it’s the right size there is a better than even chance it’ll have liquid water.
Venus is in that zone for our Sun, and it’s the same size as Earth. Additionally, we cannot yet determine the orbital distance of a given extrasolar Earth-sized with sufficient precision to place it the so-called Life Zone. It’s also like that Earth only has an atmosphere due to its magnetic field, another thing we can’t detect on an extrasolar world. So, we can certainly guess whether a given planet is warm and has liquid water, but we cannot know for certain.
That’s not the same thing he was talking about.
Its not exact, but its pretty close.
And was given a great thread title as I remember 
Maybe NASA were looking through the wrong end of Hubble and wondered why the aliens looked like excited humans in white coats running around screaming.
