7 Earth-size worlds found orbiting star; could hold lifePosted: Updated:
By MARCIA DUNN, AP Aerospace Writer
CAPE CANAVERAL, Fla. (AP) -- For the first time, astronomers have discovered seven Earth-size planets orbiting a single nearby star - and these new worlds could hold life.
This cluster of planets is less than 40 light-years away in the constellation Aquarius, according to NASA and the Belgian-led research team who announced the discovery Wednesday.
The planets circle tightly around a dim dwarf star called Trappist-1, barely the size of Jupiter. Three are in the so-called habitable zone, the area around a star where water and, possibly life, might exist. The others are right on the doorstep.
Scientists said they need to study the atmospheres before determining whether these rocky, terrestrial planets could support some sort of life. But it already shows just how many Earth-size planets could be out there - especially in a star's sweet spot, ripe for extraterrestrial life. The more planets like this, the greater the potential of finding one that's truly habitable. Until now, only two or three Earth-size planets had been spotted around a star.
[Raw video: NASA briefing on newly discovered planets]
"We've made a crucial step toward finding if there is life out there," said the University of Cambridge's Amaury Triaud, one of the researchers.
The potential for more Earth-size planets in our Milky Way galaxy is mind-boggling. The history of planet-searching shows "when there's one, there's more," said Massachusetts Institute of Technology astrophysicist Sara Seager.
"With this amazing system, we know that there must be many more potentially life-bearing worlds out there just waiting to be found," she said.
NASA's Thomas Zurbuchen, associate administrator for the science mission, said the discovery "gives us a hint that finding a second Earth is not just a matter of if, but when," and addresses the age-old question of "Are we alone out there?"
"We're making a step forward with this, a leap forward in fact, toward answering that question," Zurbuchen said at a news conference.
Last spring, the University of Liege's Michael Gillon and his team reported finding three planets around Trappist-1. Now the count is up to seven, and Gillon said there could be more. Their latest findings appear in the journal Nature.
This crowded yet compact solar system - 235 trillion miles away - is reminiscent of Jupiter and its Galilean moons, according to the researchers.
Picture this: If Trappist-1 were our sun, all seven planets would be inside Mercury's orbit. Mercury is the innermost planet of our own solar system.
The ultracool star at the heart of this system would shine 200 times dimmer than our sun, a perpetual twilight as we know it. And the star would glow red - maybe salmon-colored, the researchers speculate.
"The spectacle would be beautiful because every now and then, you would see another planet, maybe about as big as twice the moon in the sky, depending on which planet you're on and which planet you look at," Triaud said Tuesday in a teleconference with reporters.
Years are exceedingly short in this star system - the planets take just 1 1/2 to 20 days to orbit Trappist-1.
The Leiden Observatory's Ignas Snellen, who was not involved in the study, is excited by the prospect of learning more about what he calls "the seven sisters of planet Earth." In a companion article in Nature, he said Gillon's team could have been lucky in nabbing so many terrestrial planets in one stellar swoop.
"But finding seven transiting Earth-sized planets in such a small sample suggests that the solar system with its four (sub-) Earth-sized planets might be nothing out of the ordinary," Snellen wrote.
Altogether, astronomers have confirmed close to 3,600 planets outside our solar system since the 1990s, but barely four dozen are in the potential habitable zone of their stars, and of those, just 18 are approximately the size of Earth.
Gillon and his team used both ground and space telescopes to identify and track the seven Trappist-1 planets, which they label simply by lowercase letters, "b'' through "h." As is typical in these cases, the letter "A'' - in upper case - is reserved for the star. Planets cast shadows on their star as they pass in front of it; that's how the scientists spotted them.
Tiny, cold stars like Trappist-1 were long shunned by exoplanet-hunters (exoplanets are those outside our solar system). But the Belgian astronomers decided to seek them out, building a telescope in Chile to observe 60 of the closest ultracool dwarf stars. Their Trappist telescope lent its name to this star.
While faint, the Trappist-1 star is close by cosmic standards, allowing astronomers to study the atmospheres of its seven temperate planets. All seven look to be solid like Earth - mostly rocky and possibly icy, too.
They all appear to be tidally locked, which means the same side continually faces the star, just like the same side of our moon always faces us. Life could still exist at these places, the researchers explained.
"Here, if life managed to thrive and releases gases similar to that that we have on Earth, then we will know," Triaud said.
Chemical analyses should indicate life with perhaps 99 percent confidence, Gillon noted. But he added: "We will never be completely sure" without going there.
Cool facts about 7 Earth-size planets circling single star
AGE OF AQUARIUS
This star system is less than 40 light-years from Earth, or 235 trillion miles away, in the constellation Aquarius. At the hub is a small, faint star known as Trappist-1. Seven planets circle Trappist-1, with orbits ranging from 1 1/2 to 20 days. If Trappist-1 were our sun, all these planets would fit inside the orbit of Mercury. That's how close they are to their star and why their orbits are so short. The planets have no real names. They're only known by letters, "b'' through "h." The letter "A" refers to the star itself.
Three of the planets are smack dab in the so-called habitable zone, also known as the Goldilocks zone, where conditions are just right for water and life to flourish - not too much and not too little stellar energy. The four other planets are tantalizingly close to the Goldilocks zone- so close that they, too, could harbor water and potentially life. But just because a planet is in this sweet spot, doesn't mean life exists or ever did. If aliens were observing our solar system from the Trappist-1 network, they might be saying, "Hey, there are three habitable planets there, Venus, Earth and Mars," said Sara Seager, a Massachusetts Institute of Technology astrophysicist who did not take part in the study. The point is, "let's wait and see what's out there," she cautioned.
HOW'S THE VIEW?
Trappist-1, one of numerous ultracool dwarf stars out there in the galaxy, glows red. If you were to stand on one of the planets, the star might appear to be salmon-colored. Its planets are clumped so closely together, they would appear twice as big as our moon in the sky. The temperature could be pretty similar to Earth as well, at least on one of these planets.
Scientists need to study the atmospheres of these almost assuredly rocky planets before jumping to any conclusions about water and life. The Hubble Space Telescope already is on the case. The still-under-construction James Webb Space Telescope will join in once it's launched next year. The Webb will search for gases that might be a byproduct of life: oxygen, ozone and methane. Scientists say it should take five years to get a handle on all these atmospheres, and figure out whether water - and maybe life - are present. Altogether, astronomers have confirmed close to 3,600 planets outside our solar system since the 1990s, but barely four dozen are in the potential habitable zone of their stars, and of those, just 18 are approximately the size of Earth.
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