On Thursday, Toyota announced on Twitter that a second Prius model will be revealed in January at the 2011 Detroit Auto Show. The tweet revealed little about the vehicle other than saying that it will be an "all-new model w/more comfort, style and versatility."

The message followed a Facebook post from October 10th - which marked the tenth anniversary of the launch of the Prius in the United States in 2000 - that links to a video of the construction of billboard in Malibu, Calif. depicting a white Prius obscuring a larger, blue vehicle above the tag line "The Prius Family is Getting a Whole Lot Bigger."

It has been long anticipated that Toyota was planning to expand its lineup of Prius-branded hybrid vehicles in order to further leverage the marketability of the successful nameplate. Now in its third generation, the five-door hatchback is by far the best-selling hybrid in the world, with over 139,000 sold in the U.S. in 2009, alone.

Based on the billboard image, speculation is that the vehicle will be a small minivan, similar to the Mazda5 or Kia Rondo, with three rows of seating for six or seven passengers. The on sale date is unknown at this time, but The Wall Street Journal reported earlier this week that Toyota is planning to have a three model Prius lineup in place in the U.S. by 2013, with one larger and one smaller than the current vehicle. The 2010 Toyota Prius was officially introduced at the 2009 Detroit Auto Show and went on sale later that year.