The biggest story in the universe

The discoveries are coming so fast—1,235 new planets—that the universe as we knew it is history

Tracking down other Earths

Tim Pyle/NASA

Just one generation ago, the thought of finding a planet that might support life was the stuff of science fiction. Last week, NASA scientists announced they’d discovered a whopping 1,235 potential planets orbiting faraway stars, using the Kepler space telescope. If confirmed, this would almost triple the number of known planets outside of our solar system (called “exoplanets”), which currently stands at just over 500. “What we’re anxious to learn is whether there’s other life in our galaxy,” says Kepler co-investigator Natalie Batalha. She and other members of the team are trying to learn whether planets like our own are abundant or rare. “The answer will drive all future missions,” she says.

Among Kepler’s haul were 54 possible planets in the habitable zone, where temperatures could allow for liquid water at the surface, which is necessary to support all life as we know it. Five are close in size to Earth, and orbit in the habitable zone of stars that are smaller and cooler than our sun. The rest range in size from so-called “super-Earths” (up to twice the size of our planet) to ones bigger than our solar system’s kingpin, Jupiter. Most of Kepler’s findings still need to be confirmed as actual planets, but it’s almost certain the vast majority of them will be.

The mission’s goal is to find other planets like Earth, but along the way, we’re finding all sorts of things we didn’t expect: like a system of six confirmed planets orbiting a sun-like star called Kepler-11, packed so tightly together that, according to Jack Lissauer of NASA Ames Research Center, who led the work on Kepler-11, “we didn’t know such systems could even exist.” It’s becoming clear that the universe is much more diverse, and more prolific, than we ever imagined.

Launched in March 2009, the Kepler space telescope orbits our sun and stares unblinkingly at some 156,000 stars—which range from a few hundred to a few thousand light years away—searching for the telltale winking of light that might signal a planet passing in front, like a moth flying by a porch light. It’s taking a sample from one neck of the Milky Way galaxy, from which planet hunters hope to discover whether Earth twins are statistically common or not. “We ultimately want to look for life,” says Kepler co-investigator Dimitar Sasselov, who leads Harvard University’s Origins of Life Initiative. “This is how we get to that point.”

Kepler is only looking at one-400th of the sky, a small sliver of the Milky Way—which, in turn, is one of countless galaxies in the universe. All these possible planets were found in that one area within just the first six months of its mission (from May to September 2009), which is slated to last 3½ years at least. With so many planets being found so fast, and with 54 of these possibilities in the habitable zone, it looks almost certain that there are more planets like our own out there. And we’ve only just begun to look. One can’t help but feel that our view of the universe—and whether or not we’re alone—is different today than it was just one week ago, before NASA announced Kepler’s findings.

“It’s a golden age for astronomers,” says Jaymie Matthews, a professor of astronomy and astrophysics at the University of British Columbia. “I’m personally convinced that 400 years from now, people will look back at this era—even this past decade—in the same way we look back at the times of Copernicus, Kepler and Galileo. We’re the first generation in the history of our species capable of searching for another Earth. And we’ve only had that capability for a few years.”

Imagine looking out at the Empire State building at night, with all its window shades open and the windows lit up from the inside. Now, imagine the dip in brightness that would occur if one person stood at one of those windows, and pulled down one window shade by just seven centimetres. “Kepler was designed to measure light variations to that level in a bright star,” Matthews says, “and even smaller.”

Tracking down other Earths

Ball Aerospace;

Matthews is mission scientist on MOST, Canada’s first space telescope, which was designed to take such precise measurements, too. Both MOST and Kepler use a photometer (light meter) to measure the brightness of stars. Originally intended as a one-year mission, MOST launched in 2003 and is still collecting data today. Unlike Kepler, which is a planet hunter, MOST was built specifically to study stars. With a budget just a fraction of Kepler’s, “we’re the Zellers of space telescopes,” Matthews jokes. “But we showed you can achieve this precision and that Kepler, if launched, would work.”

MOST can study about 40 stars at once, but Kepler can observe many, many more. “Kepler is the exoplanet equivalent of a long-form census,” he says. “It’s doing the demographics of 150,000 citizens of our galactic city.” Kepler continuously monitors an entire field of stars around the constellations Cygnus and Lyra. Every 30 minutes, it photographs them. (Kepler is equipped with the largest digital camera NASA has ever flown in space.) If a planet happens to be passing in front of one of these stars, Kepler might catch a wink in brightness, which can last from about an hour to half a day.

The Kepler space telescope represents a huge leap forward for planet hunters. Of the 500 exoplanets we’ve known about until now, most were discovered using what’s called the Doppler technique, which was pioneered by Canadian astronomers Gordon Walker and Bruce Campbell back in the 1970s. This method involves measuring tiny changes in a star’s spectrum of light (called Doppler shifts) to show that gravity from an orbiting planet is tugging away on it, causing the star to sway, according to the University of Toronto’s Ray Jayawardhana, author of Strange New Worlds: The Search for Alien Planets and Life Beyond our Solar System.

Using the Doppler technique, planet hunters have found plenty of massive planets orbiting extremely close to their host stars, because they’re easier to see. But they haven’t found many smaller, cooler, rocky planets like Earth. The first exoplanet ever discovered around a sun-like star, 51 Pegasi b, was announced in 1995; it’s about the same mass and size as Jupiter. This became the model for a bizarre new type of planet, “hot Jupiters,” which look like our Jupiter but orbit extremely close to their suns. It’s hard to imagine life existing in a place like that—but, until Kepler, our ability to find planets more like our own has been quite limited.

Kepler scientists shy away from talking about the search for “Earth-like planets,” since this conjures up visions of oceans, a breathable atmosphere, maybe even some kind of native life. Our current technology isn’t good enough to detect those things from so far away. Instead, their mission is very specific: to search for Earth-size planets in an Earth-like orbit around a sun-like star, so these planets sit the right distance from their host star for liquid water on the surface.

With each month that goes by, that goal gets closer. In January 2010, Kepler announced its first five new exoplanets, all of them “hot Jupiters.” This January, it revealed its first rocky planet, named Kepler-10b. About 1.4 times the size of Earth, it’s the smallest planet ever found outside our solar system, but it’s nowhere we could possibly live. One side of the planet constantly faces its star, which it whips around in less than one Earth day. (Kepler-10b is more than 20 times closer to its star than Mercury is to our sun.) Its starlit side, scientists say, must be a lava sea.

On the hunt for other Earths, Kepler’s finding places so strange we never could have imagined them. “We started out finding planets Jupiter’s mass and size, and now we’re down to super-Earths,” Matthews says. “There’s no analog for that in our solar system—we never even thought about these things before.” Of the 1,235 potential planets Kepler has found so far, 662 are the size of Neptune, a gas giant with no solid surface. “That’s crazy, because no one really understands how Neptune formed,” says Kepler team member Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology. But maybe Neptune-like planets are far more common than we realized.

Tracking down other Earths

Dana Berry/Kepler Mission/NASA;

The Kepler-11 system, which was announced last week, sounds like something out of a science fiction paperback. All six of these planets are huddled quite close to their star. Five of the six even have orbits smaller than Mercury’s, the closest planet to our sun—making it the most densely packed solar system ever discovered. Unlike the eight major planets in our solar system, which circle the sun along slightly tilted paths, the Kepler-11 planets’ orbits are surprisingly flat and circular: “flatter than a CD case,” according to Lissauer.

These six small planets are packed so snugly together that they actually drag each other back and forth, causing their orbits (which range from 10 to 47 days for the five inner planets) to vary by as much as 20 minutes, Seager says. Earth’s year, by comparison, “doesn’t even vary by a nanosecond.” That strange dance was a boon to scientists, who—by measuring each planet’s gravitational tug on its neighbours—could calculate their masses. Once they had each planet’s radius (which the Kepler telescope finds by checking how much light it blocks as it passes a star), they could then figure out density, which hints at whether the planet is made up of gas, rock, ice, or some exotic combination.

That’s how we know the planets that orbit Kepler-11 are formed mostly of gases, with rock and maybe some iron, too. These planets might even have some water in their makeup, but it’s hard to imagine life thriving there (or life as we know it, anyway). If there is rock at the centre of one of these planets, it’s “below a massive atmosphere,” says Daniel Fabrycky, a Hubble fellow at the University of California, Santa Cruz. “If you lived on the surface, there would be crushing pressure, like living at the bottom of the ocean. And you’d not see the sun.”

The fact that scientists could confirm there were planets orbiting the Kepler-11 star, using Kepler data alone, is a huge leap forward. Confirming planets with ground-based observations can be a long and difficult task: in September, U.S. astronomers announced they’d found the first potentially habitable planet outside our solar system, Gliese-581g. Astronomers believe there could be six planets orbiting that same red dwarf star, and they’ve been observing it for 11 years. But even then, it seems, something was off. Excitement about Gliese-581g was quickly dampened after other scientists looked over the data and said they doubted the planet even existed. A distant star’s winks and wobbles might suggest it’s hosting a planet, but confirming it is “very time consuming,” says Batalha, a professor of physics and astronomy at San Jose State University, “and telescope time is hard to come by.”

Confirming all 1,235 of the possible planets Kepler has found will be a monumental job, but experts estimate that over 80 per cent of these candidates will turn out to be real planets. For William Borucki, Kepler team leader, one of the most exciting tasks will be checking out the five potential planets that are close in size to Earth, and orbit in the habitable zone of stars that are smaller and cooler than our sun. “In the coming year, we expect to go through them, and determine which we can confirm,” he says.

Some of the 54 candidates in the habitable zone might even have moons with liquid water, he suggests. As the Kepler mission progresses, “we’ll start discovering planets with longer orbital periods,” he says: planets that travel around their suns in 100 days, then 200 days. And, eventually, maybe some that take about 365 days to orbit their own sun—just like Earth. “Very importantly,” Sasselov adds, “Kepler is not finished yet.” To find an Earth-size planet orbiting a star like our sun in a one-year orbit would take three years, since three different sightings are needed to confirm it isn’t a fluke. Their signals are incredibly faint. But Kepler, these scientists believe, can find them.

It might seem myopic to hunt for other forms of life by seeking out planets that look exactly like our own. After all, we still don’t understand how life sprung up here on Earth, and we’re just beginning to learn all the surprising forms it can take on our own home planet. “We don’t have a good definition for life,” Sasselov says. “How do we search for something we cannot properly define?”

And how can we hope to understand what life might look like on planets so far away? “We can’t even begin to imagine what the possibilities are out there in the universe. But we have earthling eyes,” Batalha says. “We look around here on Earth and ask ourselves the question, ‘Where does life exist?’ It exists in every nook and cranny, but they all require liquid water.” So we’ll continue hunting for planets that could support water, like Earth, and maybe even life.

As the Kepler mission is showing us, it’s impossible to predict what we could find. This space telescope is just watching 156,000 stars “out of a couple hundred billion in the Milky Way galaxy,” Jayawardhana says. How many galaxies are out there? “Many billions and billions.”




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The biggest story in the universe

  1. How can noone have commented on this?
    This is HUGE!!!
    Never mind that we have managed to put a telescope in orbit around THE SUN … How cool is that?!?
    We’ve discovered 1235 potential homes for sentient life somewhere other than earth!!!
    Maybe it’s just the Trekkie in me, but THAT’S AWESOME!!!

  2. Yup, our governments will spend a trillion $ saving some banksters, but find it difficult to fund a paltry couple billion to uncover the secrets of the universe around us.

    • And how do you know that? Just your wish to bash the government?

  3. I just hope they are closer than 100000,00000000,0000000 light years away…..unless they are bad aliens then that is too close.

  4. Our Galaxy must be at least 200 light years across, so I think it would be quite possible that “life” might exist. It would take a superior ego or religious nut not to think that life might exist…..and of the millions of other galaxies, we may never know.

    • “It would take a superior ego or religious nut not to think that life might exist”

      Or an atheist who understands probability.

      Running around saying “golly there’s a lot of planets in the sky, must mean life evolved all over the place”, is equivalent to saying “Gee the universe is complex, must mean there’s a god”. It’s also a logical fallacy because it does not take into account other possibilities, and is referred to as “affirming the consequent”.

      For a planet to have life a lot of factors have to come into
      play:
      1. You need the right location in the right kind of galaxy. Most of the known universe, including large parts of our galaxy, can’t support life. The parts of a galaxy where complex life is possible make up the galactic habitable zone. This zone is primarily a function of distance from the galactic center. As that distance increases:
      a) Star metallicity declines. Metals are necessary to the formation of terrestrial planets. This rules out the outer reaches of a galaxy.
      b) The X-ray and gamma ray radiation from the black hole at the galactic center, and from nearby neutron stars, becomes less intense. Radiation of this nature is considered dangerous to complex life, hence the early universe, and galactic regions where stellar density is high and supernovae are common, will be unfit for the development of complex life. This also rules out galactic inner regions.
      c) Gravitational perturbation of planets and planetesimals by nearby stars becomes less likely as the density of stars decreases. So the further a planet lies from the galactic center or a spiral arm, the less likely it is to be struck by a large object. So this rules out globular clusters and the spiral arms of spiral galaxies. As one moves from the center of a galaxy to its furthest extremity, the ability to support life rises then falls. Hence the galactic habitable zone may be ring-shaped, sandwiched between its uninhabitable center and outer reaches.

      2. The planet needs to be orbiting at the right distance from the right type of star. The Goldilocks Zone is far less common than breathy news reports would have you believe. The most common star, small red dwarfs have small habitable zones wherein planets are in tidal lock–one side always faces the star and becomes very hot and the other always faces away and becomes very cold–and are also at increased risk of solar flares. Life possible “G type” stars like our Sun comprise only 9% of the stars in the Milky Way.

      3. The right arrangement of planets. A planetary system capable of sustaining complex life must be structured more or less like the Solar System, with small and rocky inner planets and outer gas giants. The large mass and gravitational attraction of the gas giants provides protection for the inner rocky planets from impacts.

      4. A continuously stable orbit. Most planets discovered so far have chaotic orbits.

      5. A terrestrial planet of the right size. A planet that is too small cannot hold much of an atmosphere. Hence the surface temperature becomes more variable and the average temperature drops. Substantial and long-lasting oceans become impossible. A small planet will also tend to have a rough surface, with large mountains and deep canyons. The core will cool faster, and plate tectonics will either not last as long as they would on a larger planet or may not occur at all.

      6. Plate tectonics that assist in global temperature regulation, a carbon cycle and most importantly, a protective magnetic field.

      7. A large moon to enable the plate tectonics.

      8. Chance. The chances of amino acids forming naturally even under ideal conditions are greater than 10 to the 24 power. Roughly the same chance as there are estimated stars in the universe.

      I would love a universe full of Gulliverian Star Trek characters to explore. But you’d have to be some kind of “religious nut” to ignore the fact that the chances are pretty slim.

      • Please wear a pointy hat at every party you attend from this day forward so that I can make a tire-squealing U-turn whenever we are on a collision course. U R 2 brain 4 eye.

        • Lol, whut?

      • For an atheist, you still portray us as pretty special in the universe. Some of the conditions you state are probably necessary (elements up to iron, liquid water), but they’re not uncorrelated with one another. The rocky planets that meet them are probably common on run-of-the-mill suns like ours, but they’re hard to see. The processes of detection we’ve used so far are firmly biased against them. It is true that binary star systems are more common than loners like our sun – that’s where your chaotic orbits come in. For one star with one planet-forming disc you’re going to get something like the worlds we have.

        It’s probably nice to have a magnetic field, but that comes with the hot iron. The tectonics come with the planet size and age. The tides are probably a nice-to-have that speed things up, but even lacking a large impact moon like ours you’ll probably still get a couple of smaller ones. And amino acids occur literally everywhere there’s carbon and energy – on comets, on Europa. The only thing that really needs explaining is their chirality (which is probably due to weak-interaction non-conservation of parity, ie. something universal).

        That’s all assuming that life even needs to look like something that can blink back at you and be recognised. There could be thinking gas clouds talking about that storm on Jupiter for all we know.

        Life isn’t a different pattern from the universe that creates it; it’s an inevitability that entropy-exporting systems will emerge from the physical degrees of freedom and interaction we see. It probably does occur “as we know it” only at certain scales, but that doesn’t mean it’s not part of a larger scale-free pattern.

        I wonder if part of the problem is that extraterrestrial life is always presented in fiction as a kind of allegorical human – eyes, hands, mouth. Writers like Robert L. Forward have produced some much more interesting (and just barely plausible) ideas about weirder life.

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