Life at the SETI Institute: Laurance Doyle

Dr. Laurance Doyle is a true renaissance man who thrives on discovery. His passion is to immerse himself into scientific mysteries and go, as the oft-quoted Star Trek phrase states, "where no man has gone before." Long before the discovery of the first planet beyond our solar system, astronomer Dr. Laurance Doyle, who joined the SETI Institute in 1987, began theorizing about the habitability of planets around other stars and clarifying the conditions needed for a planet to bear life. Relying on his expertise in signal processing, he now looks for patterns in astronomical data while searching for extrasolar planets.

Laurance has begun using these same statistical tools to look for patterns in animal communication. Drawing on central concepts of information theory, he and colleagues from the University of California at Davis have precisely measured the complexity of the songs of humpback whales, comparing them with communication in other species--including humans. In the future, he plans to expand this innovative line of research, moving to the next level of understanding animal communication, and apply it to SETI (Search for Extraterrestrial Intelligence).

Tell us about your current research project.
I'm a Participating Scientist on NASA's Kepler science team. In layman's terms, my project involves searching for "Tatooine" planets, a nickname for a binary star system coined after Luke Skywalker's home planet in Star Wars. Ideally, the goal is to find a habitable planet that is going around two stars.

I'm in charge of detecting circumbinary planets that orbit eclipsing binary stars -- planets that orbit around both stars while the two stars orbit around each other. The stars that orbit each other across our line of sight eclipse each other regularly. This allows us to study the size of stars. Most of what we know about star size comes from eclipsing binaries.

The space-borne Kepler telescope is searching for the minute dips in brightness that occur when an orbiting planet crosses in front of its star, known as a "transit." When you plot the brightness with time, it's called a "light curve." The movement of the stars around each other while the planets move across the discs of the stars results in an unusual series of dips, which complicate the detection process.

How will you know if the planet is habitable?
For a planet to have the potential to be inhabited, it must be the right distance from the star so it will receive the right amount of light. The temperature of a habitable planet should allow liquid water to exist on the surface for long periods of time.

Based on the best available ground- and space-based data, I expected there would be about 350 eclipsing binaries in the Kepler data. Actually, there turned out to be more like 3,000 to 4,000 eclipsing binaries that Kepler sees. Just in our first year, we had to look at tens of thousands of light curves to pick out these eclipsing binaries.

Why should the public care about your research?
This work is important for two reasons. If we don't find a habitable planet, that means earths are rare. It puts the earth in perspective as a somewhat isolated spaceship. That knowledge may allow us to convey the concept that we need to take care of our own planet, and that would be a good thing. People think about moving to Mars, but Mars' land surface area is only equal to earth's (since three-fourths of earth is covered with water). With earth's population currently doubling every 54 years, moving to Mars would only buy us another half century. So earth is it for now.

If we do find another earth, whether it's around a circumbinary "earth" or a regular single sun-like star, I think people's thoughts are going to transition to becoming less self-centered. Finding another earth might also make us think more positively about finding other beings in the universe. We have a very real shot at finding other earths with the Kepler Mission. We could detect a potentially habitable extrasolar planet within the next three years. Kepler is hugely important for the question of life in the universe. This is a key time in history.

What created the connection for you to take your work in astronomy and apply it to animal communication?
SETI and the Drake Equation. I began with the question Are we Alone? and realized that we share a planet with many pretty intelligent species. There are many species that apply what might be considered an elementary form of tool use and have complex social and communicative behaviors. But then I began thinking about how whales, for example, communicate with other whales. This led me to the notion of detecting non-human intelligence in the oceans as a practice for the search for extraterrestrial intelligence in space.

We've found general rules for what makes an intelligent signal so my colleagues and I looked into what is required for a signal to carry intelligence complexity. Starting with dolphins, I began plotting the frequency of occurrence of dolphin whistles as if they were linguistic phonemes. The plot landed in such a way that indicated dolphin signals had the same distribution as human linguistics. I thought that was amazing! We then looked at babies' babbling before they learned language, and the baby dolphins plotted exactly the same. We could watch mathematically how they learned their whistle language as they grew up, and they mapped the same as humans' language development. After that, I was hooked!

How are animal communication and extraterrestrial intelligence linked?
The math we use, Information Theory, is how we're going to get a handle on what constitutes an intelligent signal. Our first paper on the dolphin research was published in 1999. We want to continue applying those studies to humpback whale communication. Taking these findings into our SETI research seems a natural transition. When SETI looks for a radio signal, it's more the search for extraterrestrial technology as we don't have an intelligence filter yet. With animal communications, we're deriving an intelligence filter we can apply to signals we receive from space to determine if they land on a linguistic type distribution.

Every communication system may lend itself to this area of study and we can compare which are more complex, such as orca whistles or the dance of bees. I'd like to see Information Theory used as a mathematical tool and applied to every critter. We can then start to study general species communication intelligence, which is what SETI will detect. What we are going to get over light years, if we detect anything, is communication intelligence, so that's what we should be quantifying. We're on the way to solving this problem, but it needs more support.

How do you detect the humpbacks' signals?

A few colleagues and I have special permission through the Alaska Whale Foundation to be among these amazing humpback whales, now an endangered species. Humpbacks react similarly to humans. We increase the volume or slow our speech when our environment gets noisy. If it's still noisy, we repeat. We can watch the humpbacks change the way they think about the environment and react by changing their data rate. Introducing this new tool will be invaluable for conservation as well.

What first sparked your interest in science and astronomy in particular?
When I was six, my dad gave me a map of the solar system. He told me, "The stars are other people's suns." That was it for me -- I was never on earth again. My love for space continued throughout my education. When asked to write an essay in second grade, mine was on the nine planets. When I was 10, I was teaching an astronomy class to the neighborhood kids every Tuesday night. I put up a map of the solar system, set up chairs, the kids would come in, and I'd teach them about the solar system. I was already a professor at age 10!

You believe your true calling is to teach. You still enjoy being a professor and are often inspiring Ph.D. students as well as giving lectures on astrophysics or using the Internet to teach quantum physics to the public. Do you have advice for students?
Science is really advanced nature appreciation. It isn't a scary weird thing. And if math isn't your strongest subject, Einstein once said, "Do not worry about your problems with mathematics, I assure you mine are far greater." I think I'm tied with Einstein on that one, but math is the language you have to learn. So one piece of advice I have for young people is to not get discouraged. Additionally, while going to school, it's important to learn as much as you can about the material given while simultaneously defending your individuality as best you can. Don't compromise your own unique contribution, because your thoughts will create something new that could have been rejected in the previous generation of science.

At the high school and undergraduate levels, it's important to think about your identity and figure out what you love. I believe what you love is the universe telling you what you should be doing. At the Ph.D. level, you start contributing to learning. You're at the point where the professor can no longer teach you about this subject. You have to ask the universe, and it's that step I really enjoy.

Can you offer some advice for educators?
I'd say the number one lesson for primary school teachers is to instill in their young and impressionable students that learning is fun. If you get that across, everything else is details. At an intermediate and high-school level, it's important to teach critical thinking -- how to learn, read, study, get things out of books and talk to people. This provides youth with the foundation they'll need to discover their true calling.

You're a fan of the Drake Equation and, like Frank Drake, enjoy being the first to discover or establish something new.

My career has evolved into a journey of exploration I thought I would get by walking on the Moon. What has kept me interested and engaged, however, has been the intellectual exploration. I've been able to study and discover things no one else knows. A little more than a hundred years ago, you could be the first to locate the source of the Nile. Now, the opportunities are more ones of intellectual discovery. I was one of the first to find out the age of the rings of Saturn when working on my dissertation, and I was the first to know dolphins have linguistic distribution. My colleagues and I may have been the first to apply Information Theory to animal communications. For example, we can now quantify the reaction of humpback whales to boat noise in Glacier Bay, Alaska. Knowing something for the first time is exciting. It's also very fulfilling when my work spins off to create new areas of science, research, and even conservation.

My research has always been up and down the Drake's Equation. I've tried to pick out elements that I thought could be answered, even if they were tough or nobody else was addressing them. One of the factors of the Drake Equation is detecting earth-like planets, so I advocated the transit method. Twenty years ago, there were three people working on the transit method. We couldn't get funding; it was all voluntary. I interested various people in that project, including the SETI Institute's Jon Jenkins, now on the project, and Dr. Hans Deeg, who leads the CoRoT (Convection, Rotation & planetary Transits) eclipsing binary planet search, a smaller scale French space mission. This is another example of a spin-off.

What is your philosophy of life?

Whoever has the most fun wins! Life is an adventure, and fun is a great way to navigate through life. This doesn't mean irresponsible indulgence; it means spending your time doing something that brings you deep joy. Joseph Campbell said, "Follow your bliss." So people make quilts and raise bees and do all sorts of things if they're following their bliss. I think that's the universe saying, "I want you to do this."

Source.

Beyond Earth: The Awe And Wonder Of The Extra Solars

By Adam Frank

It is not every day that a question haunting humanity for 2,500 years is answered once and for all. It is not every day that the gates of awe, possibility and potential are thrown open. It is not every day that for a brief moment we get to know -- truly know -- something wonderful for the first time.

That day came and went 15 years ago even if most of the planet wasn't paying much attention. It did not matter. A step had been taken and a line had been crossed. Now, deep into new terrain, it's getting more wonderful everyday.

A little less than 15 years ago, the first extra-solar planet was discovered. For astronomers "extra-solar" means a planet orbiting another star. The question of other worlds orbiting other stars is very, very old. For millennia humans have looked into the dark night sky and asked if those mysterious pinpricks of light might be other Suns and home to their own Earths. The "plurality of worlds" debate stretches at least as far back to the classical world of Hellenistic Greeks and their intellectual brethren. In the first century BC the Roman poet Titus Lucretius Carus, a dedicated atomist, surmised:

You must necessarily suppose that there are other orbs of earth in other regions of space and various races of men and generations of beasts.

Later, when the dark ages descended across Europe, classical inquiry and inquisitiveness fell victim to the Church's strangle hold on power. Discussion of the plurality of worlds became dangerous. Even as late as the 16th century, Giordano Bruno's advocacy of a sky rich with suns and planets and Life brought him the Inquisition's ire and was (at least) one factor that led to his burning at the stake.

Still the debate continued. In 1686 Bernard de Fontenelle would argue from the principle of plenitude that other worlds must exist. Our ignorance is nothing but lack of appropriate instruments for seeing these other planets:

"All philosophy...is based in two things only: curiosity and poor eyesight"

From Newton to Einstein, from Hubble to Sagan, our instruments (and eyesight) got better but were still too poor to (literally) resolve the arguments. Countless false claims of planet detection failed to clear the muddy waters. The ancient but simple question remained: "Do other planets exist outside our solar system"?

Then on October 6, 1995, Michel Mayor and Didier Queloz walked us over the threshold announcing the first definitive detection of an exoplanet orbiting an ordinary solar-type star (51 Pegasi). In the 15 years that followed a true census of exoplanets has begun. We now hold a list topping 400 other worlds including true exo-solar systems -- complete families of planets.

As often is the case in science, once there was actually something to study we found our ideas about solar systems were hopefully egotistical. Many of the newly discovered exo-systems look nothing like our own. Some stars have Jupiter-sized behemoths dancing around them in tighter orbits than even our scorched Mercury. Others stars have their giant planets locked in wild orbits that look more like a comet's path than the stately circles we expect from our own home system.

Most importantly we now know the magic number on which the cosmic plentitude life might depend. From our census of the new worlds it appears that somewhere between 10% and 15% of the Milky Way galaxy's solar-type stars harbor planets. When the dust settles and the math is done and that leaves (I hate to say this) at least billions and billions of worlds with orbiting planets.

How many of these (almost) countless worlds harbor life of any kind? We have no idea. How many of these worlds have watched life evolve to sentience and technological prowess? Anything we say would be pure speculation. The question of a plurality of life remains unanswered. Perhaps that question will fall next. Perhaps it will remain unanswered forever.

But for right now, let that larger question go. For right now, recognize what has happened. Stop what you are doing at some point today and look up. Recognize that after 2,500 years of questions, we now have answers. After 2,500 years of ignorance we are now enlightened. After 2,500 years of debate and discussion, hypothesis and heresy, we have crossed the Rubicon and no longer live in the bardo of the unknown. This is where the path and practice of science has taken us. We have taught ourselves to learn and learned our way into a vision as deep as space itself. We have answered at least one of our own oldest questions.

It does not happen every day and yet every day we need to remember that this is the miracle of being human in so rich a cosmos. Like our best attempts in art and poetry, like our most heartfelt longing of spirit to connect with each other and the wider world, this one vast question answered is an emblem of what is best in us and what we can achieve.

Source:- http://www.npr.org/blogs/13.7/2010/03/moving_heaven_other_worlds_and.html

Water On Jupiter-Like Corot-9b?

The newly discovered gas giant Corot-9b may have an interior that closely resembles those of Jupiter and Saturn in our own Solar System, according to a new paper published today in Nature.

Some evidence also suggest that the exoplanet, discovered last Spring, may also be temperate enough to allow the presence of liquid water.

Corot-9b orbits its star every 95.274 days, a little longer than Mercury takes to go round the Sun. It is the first transiting planet to have both a longer period and a near-circular orbit. Its orbit is slightly elliptical but at closest approach to its parent star it reaches a distance of 54 million kilometers.

Although that is only about the distance of Mercury in our Solar System, it is by far the largest orbit of any transiting planet found so far. Because it orbits a star cooler than our Sun, calculations estimate that Corot-9b's temperature could lie somewhere between -23°C and 157°C.



This is an artist's impression of an exoplanet around a star.

(Photo Credit: ESA (Illustration by AOES Medialab))

The new planet has a radius around 1.05 times that of Jupiter but only 84% of the mass. This leads to a density of 0.90 g/cc, or 68% that of Jupiter. "Corot-9b is the first exoplanet that is definitely similar to a planet in our Solar System," says Hans Deeg, a researcher at the Instituto de Astrofísica de Canarias.

The similarity is caused by the fact that Corot-9b is sufficiently far from its star to prevent tidal forces from heating its interior. Tidal forces are created by the strength of gravity weakening from the front to back of the celestial body. When the difference between the near side and the far side is great, the tidal force can prevent the planet from spinning quickly, forcing it to only show one face to the star. It can also provide heat to the interior of the planet, changing its physical condition.

Based on calculations, neither of these is possible in this case. "Although we don't know, because we can't see the planet directly, there is reason to believe that this planet has a normal day-night cycle," says Malcolm Fridlund, ESA Project Scientist for Corot. It means that lacking a tidal heat source, Corot-9b's interior is likely to have remained similar to the gas giants in our Solar System.

There is also one other tantalizing possibility about this world. Although the planet itself is a gas giant and hence has no solid surface to stand on, what if it possessed a moon like Saturn's Titan? If the temperature were towards the lower end of the estimated range, then any moon would be an ice ball. If it were towards the upper end, it would be rather too hot for liquid water. But what if it were somewhere in the middle?

Citation: Deeg et al., A transiting giant planet with a temperature between 250 K and 430 K', Nature, March 2010, 464, 384-387; doi:10.1038/nature08856

CoRoT-9b, a temperate exoplanet

The curve shows the change in the luminosity of the star as CoRoT-9b transits it. The Y-axis shows the intensity and the X-axis shows time. The dip in the curve shows a decrease of about 1.5 percent during transit.

Credit: Nature.

CoRoT-9b, a Jupiter-sized exoplanet thats orbits its star every 95 days, is the latest discovery of the CoRoT satellite, a project in which the German Aerospace Center (DLR) is a participant.

"This exoplanet stands out by virtue of its 'normality'. It is a very close approximation of the planets in our own solar system," says Professor Heike Rauer from the DLR Institute of Planetary Research in Berlin, who manages the German contribution to CoRoT.

CoRoT-9b lies far away from our Solar System, some 1500 light-years from Earth, and orbits a star in the constellation of the Serpent. From the duration of its orbit, it would appear that the distance between planet and star is roughly the same as the distance separating Mercury from our Sun. CoRoT-9b is therefore an entirely normal planet - presumably a gaseous planet with relatively moderate temperatures anywhere from -20° to 160° Celsius, depending on whether or not it is shrouded in a highly reflective cloud layer. The differences between its day and night sides are probably only slight. CoRoT-9b is therefore substantially different from the class of 'hot Jupiters', which orbit their central star about every three days. A planet with a short orbital period is located very close to its star and is therefore exposed to powerful stellar radiation. It isfrom this that the names of the planetary classes 'hot Jupiters' and 'hot Neptunes' are derived.

Waiting for the eclipse

With this discovery of a transiting exoplanet with a long orbital period (long-period planet), CoRoT has accomplished another mission objective. The mission's first such objective was accomplished with the discovery of a rocky exoplanet, CoRoT-7b, which was announced in February last year. CoRoT has now discovered a total of eight planets and has also tracked down a 'brown dwarf' star. With the planetary transit technique, the space telescope observes several thousand stars over a period of 150 days. Whenever the orbital path of a planet causes it to traverse the line of sight between the telescope and the central star, it darkens the image of that star slightly for several hours. CoRoT measures this reduction in brightness. For example, a planet like Earth darkens the Sun by a factor of one ten-thousandth during such a transit, and does so just once a year. Since each star is also subject to fluctuations in its luminosity, the search for 'transit events' of this kind is a long and laborious process.

The measurements that culminated in the discovery of this new planet were carried out in the summer of 2007, during a 150-day observation period. The task was made particularly difficult by the planet's wide orbit: The greater the orbital radius of a planet, the lesser the likelihood of the orbit to carry it across the line of sight from the telescope to the star. The discovery of CoRoT-9b has proved that the planetary transit technique is also useful for discovering exoplanets of this kind. "Once you have observed an exoplanet in transit, you can determine its radius. This is one of the fundamental parameters of a planet, one that can only be measured directly on transiting planets. Not only that, but transiting planets also provide an opportunity to learn something about their atmospheres. This is the key to the search for Earth-like planets on which life as we know it may be possible," says Professor Rauer. The discovery of CoRoT-9b has been published in an article in the journal Nature.

On the trail of extrasolar planets

To date, we are aware of the existence of more than 400 planets outside our Solar System. Transit events can be observed in about 70 of these. With a transit measurement, it is possible to derive the orbital period, the orbital inclination and the radius of a planet. If this method is supplemented with other observation techniques - for example, the radial speed method - the mass and therefore the density of the exoplanet can be determined. This enables scientists to distinguish between gaseous and rocky planets. Subsequent measurements of CoRoT-9b were carried out at the Teide Observatory on Tenerife, while radial velocity measurements were carried out using the high-resolution HARPS spectrometer on the European Southern Observatory (ESO) 3.6-metre telescope in Chile.

Exoplanet WASP-12 in Its Death Throes

Among the more than 400 exoplanets discovered thus far, the one known as WASP-12 is fairly important. Astronomers say that it is the only known planet orbiting a star outside our solar system that revolves around a yellow dwarf. The entire system, featuring the star WASP-12 and its planet, is located about 867 light-years away from Earth. Unlike our home world, which takes about 365 days to complete a full circle around the Sun, WASP-12b is so close to its parent star that it basically completes a single rotation in 26 hours – the length of its year.

This proximity between the two celestial bodies is causing massive devastation on the planet, which will most likely in the near future get disintegrated. It is a gas giant-class planets, about 1.4 times more massive than Jupiter, but with a diameter about 3.6 times larger than that of our neighboring planet. Because the surface of its star is so close to its own, the exoplanet is constantly experiencing temperatures that reach as high as 2,200 degrees Celsius, or roughly 4,000 degrees Fahrenheit. But the thing that amazes experts most is the fact that its body is so inflated. This is unnatural by cosmic laws, and a similar instance has not been encountered before.

At first, scientists thought that the massive heat levels the parent star produced were directly responsible for this phenomenon, but new data seems to indicate that other factors may be at play too. Chinese scientists from the Peking University in Beijing, led by astrophysicist Shu-lin Li, say that the gravity the star exerts apparently plays a very large part of how WASP-12b is deformed. The two bodies are tidally-locked, which means that the exoplanet always keeps the same face oriented towards its parent star. The same is true in the case of the Earth-Moon system, which is also tidally-locked.

“Whereas tidal force on the Earth leads to a few meter changes in the height of the ocean surface, that on WASP-12b is 10 million times larger,” the team leader says. He explains that the massive volume of inflation the planet experiences makes it lose a large portion of its atmosphere every year. Calculations place these quantities about 1/1000th of the Moon's mass. “We are witnessing the ongoing disruption and death march of a planet,” Li says. He also reveals that future observations of the exoplanet may reveal a jet of gas flowing from the planet into the star, which could become detectable by using a number of telescopes, Space reports.

The team also believes that the WASP-12 system may have not yet revealed all of its secrets. Li argues that another exoplanet orbits around this star, influencing the path that WASP-12b takes. This other planet is believed to be a super-Earth, a smaller planet between 5 and 10 times the mass of our own planet. Details of the study were published in the February 25 issue of the esteemed publication Nature.

Detecting an exoplanet

If a planet passes directly between a star and an observer's line of sight, it blocks out a tiny portion of the star's light, thus reducing its apparent brightness. Sensitive instruments can detect this periodic dip in brightness. From the period and depth of the transits, the orbit and size of the planetary companions can be calculated. Smaller planets will produce a smaller effect, and vice versa. A terrestrial planet in an Earth-like orbit, for example, would produce a very small dip in stellar brightness that would last just a few hours. This is one of several ways in which astronomers can find exoplanets.

Other-worldly pursuit

In the basement of the astronomy department at the University of California-Berkeley, a half-dozen researchers sit behind computers three or four nights each month and look for planets beyond our solar system. Using an internet interface and a video link, they remotely control one of the largest telescopes in the world—a 270-ton instrument at the W.M. Keck Observatory in Hawaii, where two round telescopes sit perched on the summit of Mauna Kea like eight-story snowballs.

As the astronomers analyze the starlight data collected by Keck, they look for repetitious shifts in the wavelengths of individual stars. Those shifts could mean a star is being orbited by its own planet.

"There's no sort of magic time—you know, a eureka moment—when suddenly, 'Ah-hah, it's there!'" says Andrew Howard, a member of the Berkeley team, explaining how a star suspected of hosting a planet must be measured over and over. "It's pretty exciting when you discover that there's a very good candidate: 'Wow! If this thing pans out it'll be the second smallest planet ever discovered!'"

The search for extrasolar planets—or exoplanets—is now one of the hottest pursuits in astronomy. Since the existence of exoplanets was confirmed in the 1990s, astronomers have tallied over 400 of them. It's a number that's growing quickly as planet-hunting technology expands and astronomers endeavor to find something out there comparable to Earth.

Howard's candidate did pan out: After magnifying a star inconveniently named HD156668 about 90 separate times over five years, the Berkeley team concluded it was being orbited by a planet about four times as heavy as the Earth—the second smallest exoplanet known to orbit a star similar to our sun. Howard's research team announced the discovery at the annual meeting of the American Astronomical Society (AAS) in January.

It was a significant discovery because of the technical difficulty of finding smaller exoplanets (it was "a nice sort of trophy" for the team, said Howard), and also because most exoplanets found so far have been comparable to the size of Jupiter, at 300 times the mass of the Earth, or even larger.

But finding an Earth-size planet is the gem many exoplanet hunters are looking for, and it's the chief goal of NASA's Kepler mission, which announced its own discovery of five new exoplanets at January's AAS meeting. Launched from Florida's Cape Canaveral in March of last year, the cylinder-shaped Kepler spacecraft orbits the sun rather than the Earth, and stares persistently into a single swath of space about the size of your hand at arm's length. It monitors the glow of 156,000 stars and beams information home to four clusters of computers, which take note of any star that suddenly dims by a small amount—perhaps 1 percent—then brightens again several hours later.

That light pattern may be the signature of an exoplanet dozens or hundreds of light-years away. It works like this: If the plane of an exoplanet's orbit lies edge-on toward us, the planet will pass in front of its star, blocking a portion of the light, like a moth near a lamp. The dimming will occur at regular intervals, each time the planet orbits the star, perhaps every few days—or every few years.

Technically, Kepler's method for detecting exoplanets is different from the Berkeley team's method, which measures fluctuations in wavelength rather than brightness. But astronomers combine the methods to confirm their data and get an accurate calculation of an exoplanet's diameter and mass, which reveals its density. Kepler's principal science investigator, William Borucki, said knowing the density helps theoreticians understand the structures of exoplanets: "High density? Gonna be something like the Earth. Low density? We're not quite sure what it means, but it's probably Jupiter-like. Something intermediate? Probably like Neptune."

The five exoplanets Kepler discovered last year are "hot Jupiters," so called because of their large size and intense temperatures (2,200°F to 2,900°F). The largest one of them turned out to be the least dense: Its average density was one-fifth that of water, or like "a piece of Styrofoam."

All five of Kepler's exoplanets are so close to their host stars that they complete their orbits every three to five days. Planets with longer orbital periods will take more of Kepler's time: Finding an exoplanet with an orbit similar to Earth's, for instance, requires three years of observation, since the planet must pass before its star three times before its discovery can be confirmed. Borucki said Kepler has identified hundreds of potential planets, but many will turn out to be false alarms, caused by other phenomena such as eclipsing binary stars.

The total number of exoplanets in space is a risky guess, but if each star in the Milky Way were orbited by just one planet, the galaxy would contain over 100 billion.

Popular interest in the question of life beyond our solar system is helping fuel the hunt for smaller and smaller exoplanets. Astronomers are looking for Earth-size planets that may lie within the "habitable zone" of their stars—an orbital distance where water can physically exist in its liquid form.

Jason Lisle, an astrophysicist who works as a research scientist for Answers in Genesis, a creationist organization, sounded upbeat about the hunt for exoplanets and said he expected improving technology to discover smaller planets. But, "I would not expect there to be another planet out there that's like Earth in the sense of having all the right ingredients for life, and having life on its surface. And so far, observations have borne out that prediction."

Lisle noted that some planetary systems—such as those with Jupiter-size planets orbiting close to their stars—or one discovered last year with a planet orbiting in the opposite direction of its star's rotation—throw a wrench in current theories about the formation of stars and planets.

Researchers have yet to find an exoplanet that can properly be called "Earth-like." Or hospitable. The smallest exoplanet discovered so far, CoRoT-7b, is 70 percent larger than Earth and has a density similar to Earth or Mercury, most likely making it a "rocky" planet. But with surface temperatures reaching perhaps 3,600°F, "lava" planet is a more realistic description.

Kepler has found even warmer and stranger worlds: "We've got a companion that is planet-sized, but is much hotter than the star it orbits," said Borucki. The star is about 16,500°F and the companion is 21,000°F, more than double the temperature of our sun. Borucki speculates the companion could be something like a white dwarf star, but he says, "We're a little bit puzzled about some of these things too."

But the Kepler mission itself is proof that perseverance precedes discovery. Borucki pioneered the idea of measuring star brightness to detect exoplanets in the '80s, and throughout the '90s tried to convince NASA to put a special telescope in space for that purpose. NASA rejected the idea as technologically impractical for several years. "And we were laughed at for a very long time," says Borucki. But by 2000 his team had overcome the technical challenges and sold the space agency on Kepler.

"What we're talking about is a major effort by humankind. You do it one step at a time," said Borucki of the extrasolar planet search. "The technology simply didn't exist 10, 15 years ago to do these things."

Source:- http://www.worldmag.com/articles/16409