One of NASA's space telescopes has discovered what scientists believe may be the youngest planet ever spied -- a celestial body that at 1 million years old or less is a cosmic toddler.

In its first major findings, the Spitzer Space Telescope also has shown that protostars, or developing stars, are more common than was previously thought and that the planetary construction zones around infant stars have considerable ice, which could produce oceans.

"Oh my goodness, it knocked our socks off," University of Wisconsin astronomer Ed Churchwell said of the three discoveries, which were announced Thursday.

Spitzer is an infrared telescope that has been orbiting the sun and recording data since last summer. It did not actually "see" the toddler planet, but yielded evidence that enabled scientists to infer its existence.

The object is in the constellation Taurus, 420 light-years away. It is believed to be on the inner edge of a planet-forming dusty disk that encircles a million-year-old star.

University of Rochester astronomer Dan Watson said a sharply defined hole in the disk suggests that a planet created the opening. That gaseous planet would have formed after the star's formation.

The Earth and the rest of the solar system are 4.5 billion years old. Until now, the youngest planets observed around other stars were a few billion years old.

Astronomer Deborah Padgett at the Carnegie Institution of Washington said that the gap in the dusty disk could have been caused by asteroid formation or a smaller stellar companion rather than by a planet. She said it is also possible that the heat and light of the star formed the gap by blowing out dusty material. But she said that it was "very likely" a planet, and that additional research should settle the debate.

The Hubble Space Telescope previously observed the star -- named CoKu Tau 4 -- but could not make out details.

Watson said Spitzer has for the first time revealed without ambiguity the icy organic materials in the planet-forming disks surrounding young stars. He called these the building blocks of what might end up as a solar system like our own.

As for the proliferation of developing stars, Spitzer detected more than 300 star formations in one region in the constellation Centaurus, 13,700 light-years away.

"It's kind of blown our minds," Churchwell said.

Spitzer is the fourth spacecraft in NASA's "Great Observatories" series. It began with Hubble and continued with the Compton Gamma Ray Observatory and the Chandra X-ray Observatory.