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Peering more than 26,000 light years away, UCLA and NASA scientists using the Hubble Space Telescope have discovered 16 new planet candidates, leading them to conclude there are probably billions of planets spread throughout the galaxy.

The discovery also marks the opening of a new category of planets, “Ultra-Short-Period Planets.” Five of these candidates complete an orbit in less than one Earth day, according to a NASA press release.

The small piece of the sky examined by Hubble was only about a 10th of the size of the moon as seen from Earth, yet the telescope saw over 180,000 stars as it looked toward the central bulge of the galaxy, said Dr. Michael Rich, a UCLA professor of astronomy and member of the Sagittarius Window Eclipsing Extrasolar Planet Search team.

“We monitored stars near the galactic center continuously for seven days,” said team leader Dr. Kailash Sahu of the Space Telescope Science Institute, Baltimore. “If (a planet) orbits around the star, and happens to come in front of the star, then it blocks a small amount of light. ... We detected 16 such planet candidates that pass in front of a star.”

To confirm that the dimming was caused by an object orbiting a star rather than something simply passing by it, the team used Hubble to detect between two and 15 consecutive transits, or instances of the planet passing in front of the star, for each of the 16 planet candidates, NASA said.

Examining the center of the Milky Way, the scientists found that planets are spread out uniformly throughout the galaxy.

In the solar neighborhood, 6 percent of the stars have planets around them, and the new information from Hubble confirmed that roughly 5 percent to 6 percent of stars in the galactic center have planets as well.

“The frequency of planets in the solar neighborhood is similar even at such a large distance as the galactic bulge,” Sahu said.

“That gives us some confidence in extrapolating our solar neighborhood results to the entire galaxy ... so now we can say, yes, indeed, there are billions of planets in the galaxy,” he said.

Rich said some planets scientists have recently discovered are called “hot Jupiters,” gas giants that orbit very close to their stars. Since these planets bear some similarity to planets in our own solar system, Rich said it is reasonable to infer that we might someday find Earth-like planets orbiting other stars as well.

But he added that it would be difficult to detect Earth-like planets using the methods scientists employed for this study, which currently detects objects roughly the same size as Jupiter.

“While (Earth-like planets) do block out some of the light, it would be too small for Hubble to measure,” Rich said.

NASA’s future Kepler Mission will continuously monitor about 100,000 stars in the Milky Way for four or five years to detect transiting planets, Sahu said. Kepler will be sensitive enough to detect possibly hundreds of Earth-size planet candidates in or near the habitable zone, the distance from a star where liquid water could feasibly exist on a planet’s surface, NASA said.