One of the planets completes its orbit in only ten hours, meaning that one solar year passes on the far-flung world in about the same time you spend between breakfast and dinner.
The planets, which are gas giants about the size of Jupiter, also orbit closer to their stars than any other known worlds.
They are only able to survive such close proximities because the stars they orbit are relatively light and dim, the scientists explained.
"These planets [are] extremely close to their stars—so close that they get heated by the stars' radiation to almost 3000 degrees Fahrenheit [1650 degrees Celsius]," said Kailash Sahu, principal investigator of the project.
If denser, brighter stars like our sun had similar planets orbiting so closely, "they would simply evaporate," he added.
Clues to New Planets
The astronomers were able to spot the planets using a pair of crucial clues.
One is a telltale "wobble" that a star often adopts in its path through space when a planet is orbiting it.
The other is a slight dimming that occurs when a planet passes in front of a star.
(See National Geographic magazine's "Search for Other Earths.")
But the would-be worlds' record-setting distance from Earth adds an element of uncertainty to the findings, the scientists said.
To confirm that an observed body is a planet, astronomers must be able to gauge its mass. The team was only able to do this with two of the planet candidates so far.
"These 16 candidates have passed every conceivable test that we could think of, in terms of [us] not being fooled by something else mimicking a planet," Livio said.
"However, without being able to tell the mass of [all of] these objects precisely … we came up with this very conservative estimate that at least seven surely should be planets. Two we know are planets. [But] it could be all 16 are planets."
While the remoteness of these objects poses certain challenges, Livio added, it also reinforces the significance of the discovery.
The more planets that are identified farther from our solar system, he explained, the greater the odds that a planet like Earth may one day be discovered.
"Ultimately, all of us are dreamers, and eventually we would like to find life elsewhere and perhaps even intelligent life," he said.
"What this study has shown is that there are many, many planets—that the galaxy is full of these planets—so chances are that somewhere out there you may find these other things."
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