I really like what they have done to the planets and stars on TNG so far. Sometimes the original footage was kept (and it looks excellent in HD), in other cases, the planets had to be redone. Let’s see what we have so far:
Deneb IV („Encounter at Farpoint“) remains unchanged, as the original matte painting created by ILM looks great in HD.
Qo’Nos („Sins of the father“) had to be redone because the planet was created in SD.
Red giant („The naked now“): It seems the original footage was used, maybe slightly enhanced.
Three more planets have been seen so far, two in the startrek.com article
http://www.startrek.com/article/tng-the-first-season-blu-ray-arrives-on-july-24
and one in the Entertainment Weekly article:
http://insidetv.ew.com/2012/04/30/star-trek-tng-blu-ray-season-1/2/
Here are screenshots of the planets as they appear on the DVDs. No large screenshots of the HD planets from the new transfers are available at the moment.
Haven („Haven“) is unchanged and looks great in HD. The same footage of the planet was re-used in „11001001“ to depict Bynaus, it will be interesting to see if the footage was re-used unchanged as well.
Earth („Conspiracy“): The planet on the viewscreen is Earth. As it didn’t look too good in the original, it was changed. Knowing the Okudas, this is probably real footage of Earth.
Red planet: This planet is seen on the TV screen in the picture of the Okudas and the CBS producers. This shot of the Enterprise is only seen in front of a reddish planet in two season 1 episodes, „When the bough breaks“ and „Skin of evil“, so it’s either Aldea or Vagra II. As footage of Aldea was re-used for Vagra II, it doesn’t really matter, anyhow. This planet was redone as well and looks great!