Two planets orbiting a distant star represent the first Earth-sized planets to be discovered at a distance from the host sun that allows them to be warm enough to sustain liquid water, an essential element to support life.
The NASA-led project, involving a Beaver Falls native and 2003 graduate of Penn State Erie, discovered five planets orbiting the star Kepler-62 that lies 1,000 light-years from Earth. One of those planets is 1.6 times the size of Earth and another is 1.4 times Earth's size.
Planets as large as three times the size of Earth are terrestrial, or made of rock. Larger planets typically comprise gases or a combination of gases and rock, which would not support life, said Justin R. Crepp, now an assistant professor of physics the University of Notre Dame.
While Earth-like planets within the habitable zone represent the holy grail of astronomy, technology in development will be necessary to determine whether the two planets contain oxygen, carbon dioxide, methane or water -- all elements necessary for life.
"When they are in the habitable zone, they are the right temperature to have water, which is the Goldilocks region -- not too hot and not too cold," according to NASA's Kepler mission study published today in Science magazine.
The Kepler mission -- a space telescope launched in 2009 -- has been searching the Milky Way galaxy for Earth-like planets. It has focused on 150,000 stars within 1,000 light-years of Earth. The spacecraft identifies planets orbiting stars by measuring stellar brightness, which dims ever so slightly when a planet crosses the face of the star as seen from the vicinity of Earth.
The dimming of starlight in a predictable pattern can indicate that a planet is orbiting the star. Mr. Crepp's role was to study candidate planets to determine if other cosmological factors, including a binary star, could account for the dimming of starlight.
The discovery of the Earth-like planets in habitable zones represents a historical first and raises the hope of evidence of life elsewhere in the galaxy. But the Kepler mission also has shown that the galaxy likely has billions of Earth-sized planets that could harbor life.
To date, Kepler has identified 3,000 objects of interest, Mr. Crepp said, each of which must be analyzed thoroughly to determine planet size and distance from the host star.
But Kepler, he said, already has shown that the most common stars in the galaxy are smaller than the sun, with 100 billion of such stars estimated have planets orbiting them. Further calculations reveal that 15 percent of such stars have terrestrial worlds orbiting in habitable zones, which means 15 billion stars could have planets supporting life.
"That's why Kepler is revolutionizing our field," Mr. Crepp said. "This is the most exciting thing going on. The holy grail is the spectrum of Earth-sized or -massed planets in the habitable zone. Kepler tells us that the galaxy is teeming with planets. Numbers exist that have conditions preferable for life."
David Templeton: firstname.lastname@example.org or 412-263-1578.