Earth-size planets among the final tally of NASA’s Kepler
MOUNTAIN VIEW, Calif.—Arewestillalone?
Setting the stage for the next chapter in the quest to end cosmic loneliness, astronomers released a list Monday of 4,034 objects they are 90 percent sure are planets or biting other stars.
The new list is the final and most reliable result of a four-year cosmic census of a tiny region of the Mil ky Way by NASA’ s Kepler spacecraft.
“The search for planets is the search for life ,” said al ha, a Kepler mission scientist from NASA’s Ames Research Center .“These results will form the basis for future searches for life .”
Extrapolated from one small patch to the entire sky, the data will help NASA design a space telescope for the 2030s or thereabouts, big and powerful enough to discern the images of planets around o ther stars.
The catalog—the eighth in the endeavor—was release data meeting of ex op la net astronomers here at the Ames Research Center that represents alas th ur rah for the survey mission, which will end Sept .30. The space telescope itself is doing fine, and it has embarked on a new program of short-term searches called K2.
Among other things, Bat al has aid, for the first time there is at least one planet, known as KO I 7711( forof Interest ), that almost matches the Earth, at only 30 percent wider and with an orbit of almost exactly one year.
In all, there are 219 new planet candidates in the of them, moreover, are in the habit able zones of their stars, the so-called Goldilocks realm, where the heat from their stars is neither too cold nor too hot for liquid water.
They are fascinating, but Kepler’ s mission is not to pinpoint the next tourist destination—it is to find out on average how far away such places are. Or, as Bat al has aid ,“We’ re not stamp collecting, we’ re doing statistics.”
Another result reported Monday deepened a mystery about how nature goes about making planets. Over the years, Kepler has discovered that nature likes to make small planets, but it makes them in two ways: rocky, like Earth, and gaseous, like Neptune.
A new study, led by BenjaminFulton of the California Institute of Technology, of 1,305 stars and 2,025 planets that orbit them has found a curious gap in the planet population that seems to mark the boundary between rocky planets, which can be up to 11/2 times the size of the Earth ,( sometimes called super-Earths) and gaseous planets, so-called m in i-Neptunes, which aremore than about twice the size of Earth. (Neptune itself is four times the diameter and 17 times the mass of Earth.)
Andrew Howard, a Cal tech professor who worked with Fulton, compared this splitting of small planets into two discovering a major branch point in the tree of life.
All planets seem to start out with about the same amount of rock in their co res, he said. How much gas—mostly hydrogen and helium from the primordial cloud that birthedthem makes all the difference. While the Earth, which has hardly any all by weight, is a pleasant place, the pressure on a world with just a little more gas would be toxic.
Presumably, Fulton said, the planets that are rocky now, like Earth, had their gassy envelopes stripped away or evaporated by radiation from their stars. But nobody really knows how it works. Adding to the mystery is that our own solar system has no example of a mini-Neptune, and yet they are prevalent in alien planet systems.
In 1984, William Boruc ki, a NASA physicist and expert on photometry,light intensity, and a colleague, the late David Koch, had a pretty simple idea: If a distant star blinked or dim med periodically, it might mean there was a planet going around it.
At the time, nobody knew if any other stars besides the sun harbored planets. NASA turned down Bo ru ck ia nd Koch five times before the experiment was finally approved in 2001.
Kepler was launched into an orbit around the sun on March 6,2009, with a simple mission: to star eat some 160,000 stars in a patch of sky in the constellation Cygnus. If any of those stars dim med periodically, the size of the di pin light could tell you how big the planet passing in front of it was. The length of time between bl inks would tell you how many days long its year was.
In the case of the Earth as seen from space, the amount of dim med light would be about 0.008 percent of the sun’s light—about as much asa few fleas crossing a car head light—once a year. Kepler can detect the equivalent of one flea in the head light. Since the rules of engagement required three transits to verify a planet, that meant it would take that many years on average to discover an exact analog of our own home: Earth 2.0, it was sometimes called.
At the time Kepler was launched, more than 300 ex op lane ts, planets outside our solar system, had been found, mostly by one by one to see if they showed signs of being perturbed—“wobbled”— by the gravitational pull of a planet or planets.
Those on the Kepler team did not know what they were going to find. Bat al ha recalled that they had argued about how to construct their catalog of interesting objects — whether it would only be able to goto 1,000 or 10,000. In the end, they almost ran out of room on the list, Bat al hare called, which wound up running to 9,000.
In its first few months of observations, Kepler almost immediately doubled the number of known orop lane ts. The tally kept climbing, to 1,200 by February 2011 and to more than 4,700 a year ago.
Unfortunately, Kepler also discovered that stars are more jittery than astronomers had expected, complicating the problem of discerning planet trans its from random fluctuations in the stars. This volatility made it especially hard for Kepler’ s crew members to see what they most wanted to see— small rocky planets with years as long as the Earth’ s.