Chinese scientists have their eyes and ears fixed on the heavens, waiting for a sign that may come soon - or a lot later 

An artist's depiction of select planetary discoveries made by the Kepler mission. In May the mission announced that it had verified 1,284 new planets, the single largest finding of planets. (Photo:Nasa/W. Stenzel) 

When the NASA spacecraft Juno arrived at Jupiter this week after a journey of nearly 3 billion kilometers, the scientists who had toiled in relative obscurity over many years to make it happen finally got the chance to fete their great success before the world.

But for space scientists like Mao Shunde, those kinds of public accolades may never come. Instead he must have the patience to devote his all to a task that may well prove fruitless in his own lifetime.

If Mao is pessimistic on that score he barely shows it, instead exuding a quiet confidence that the tools at his disposal are increasing his chances of realizing his dream - to find life elsewhere in the universe.

"We are lucky to be in a special era, with the next generation of giant telescopes on the way," says Mao, director of the Center for Astrophysics at Tsinghua University in Beijing. "There may be some exciting discoveries in the next 10 to 20 years."

Our galaxy has hundreds of billions of stars, many with solar-like planetary systems, and there are hundreds of billions of galaxies in the universe. So in the scientific world it is generally regarded as reasonable to infer that Earth-like planets may be common, and that the universe may teem with life.

"I think primitive life is likely to be abundant, but intelligent life may be rarer," says Mao, also director of the Galaxy and Cosmology Division of the National Astronomical Observatories of China at the Chinese Academy of Sciences.

The next generation of giant telescopes may help astronomers resolve some long-standing issues, such as analyzing the spectrum of distant planets, making it possible to detect biomarkers of life.

Biomarkers are certain elements that suggest the existence of life. An important biomarker, oxygen molecules, without supporting life, can only last for a short time compared with the 13.7 billion-year history of the universe. Oxygen easily reacts with other elements, and Mars appears red as a result of oxidation.

"If we find a lot of oxygen molecules in the atmosphere of an extraterrestrial planet, they are probably produced by life activities," Mao says.

The most common method of searching for extraterrestrial life is to search first for planets similar to Earth, with plenty of sunshine, liquid water and a protective atmosphere.

However, that method is constantly questioned as some speculate that life elsewhere in the universe may be markedly different to that on Earth.

"We don't know how to start if we don't know what kind of life we are looking for," Mao says. "At least we know what conditions are needed for life on Earth, so scientists tend to search for planets around sun-like stars and put forward the concept of the 'habitable zone'."

The "habitable zone" is the distance from a star where a planet could have liquid water.

"However, nature has a much more wild imagination than we do," Mao says. "For example, whether life can exist in ice at extremely low temperatures is unknown to us. It's easy for scientists to start with familiar conditions and then gradually expand the search to an unknown territory."

Over the past 10 years astronomers worldwide have identified more than 3,000 extra-solar planets. However, most are giant planets, probably composed of gas, because they are more easily detectable.

A few dozen are Earth-like planets, which are probably composed of silicate rocks or metals and may have water on them.

"Astronomers first pick sample planets suitable for life, and then think about further study and analysis, or even communication with them," Mao says.

To further analyze the atmospheric composition of a planet, the telescope must be very sensitive to the sharp contrast of the light intensity between the star and the planet. The Earth is about one billionth of the sun in optical brightness, a contrast still far beyond the range of current telescopes.

The 500 meter aperture spherical telescope in Pingtang county, Guizhou, to be completed in September, is expected to be the world's largest, overtaking Puerto Rico's Arecibo Observatory, which is 300 meters in diameter. (Photo/Xinhua)

For more effective observation, astronomers are also striving for breakthroughs in another critical technology: adaptive optics.

When light from a star or any other astronomical object enters the Earth's atmosphere, it can be distorted by atmospheric turbulence, which can blur images produced by any telescope larger than tens of centimeters.

This annoyed Isaac Newton more than 300 years ago when he discovered that larger telescopes could not form clearer images due to atmospheric distortions.

But today, after years of development, many observatories around the world, including those with telescopes of 8 to 10 meters in diameter, are equipped with adaptive optics systems.

Adaptive optics is a technology that aims to correct the distortions induced by atmospheric turbulence. There are three main components in the system: a wavefront sensor, a deformable mirror and a real time controller.

The wavefront sensor is like an eye and it measures the light distortions a few hundreds or even thousands of times in one second, so that the turbulence distortion almost looks like a cartoon played frame by frame to the system; the real-time controller acts like a super fast brain, and it calculates how correction should be applied and sends commands to the deformable mirror; and finally, like the hand of the system, the deformable mirror, carries out those commands, and changes its surface shape to correct the distortions before the next command arrives.

The next generation of ground-based telescopes, including the Thirty-Meter Telescope, the Giant Magellan Telescope and the European Extremely Large Telescope, will have better adaptive optics systems, so they will be central to future observations, says Feng Lu, an associate researcher with the National Astronomical Observatories of China.

Ground-based telescopes can be larger than space telescopes and are connected to more instruments, and can work longer and look deeper into space. The adaptive optics technology will improve their resolution so that is as good as or even better than that of space telescopes, making them capable of observation tasks previously impossible on the ground, such as tracking extra-solar planet candidates, Feng says.

For example, with the help of adaptive optics, the Thirty-Meter Telescope will have a resolving power and sensitivity much greater than the Hubble Space Telescope when it goes into use about the mid-2020s. One of its major tasks will be to analyze the spectrum of extra-solar planets.

Setiathome. Berkeley. Edu.(Photo provided to China Daily)

Better eyes 

But the next generation of space telescopes will also revolutionize astronomy. The Transiting Exoplanet Survey Satellite (TESS), to be launched by NASA next year, is one of them.

Kepler, TESS' predecessor, which NASA launched in 2009, is the world's first space observatory dedicated to searching for planets outside our solar system. So far Kepler has confirmed 2,325 extra-solar planets, more than 70 percent of the total. Twenty-one of them are Earth-like, staying in habitable zone and within twice the size of Earth.

While both can monitor planetary transits, TESS can carry out all-sky surveys, but Kepler can observe only a small part of our region of the Milky Way.

"More importantly, TESS will look for extra-solar planets in orbit around the brightest stars, which will help analyze the physical nature of these planets," Mao says. "Kepler's planets are often around dim stars, which makes it difficult to carry out follow-up studies.

"The number of planets that TESS will detect is not necessarily much more (than Kepler), but the quality will be more advanced."

As well as searching for Earth-like planets, scientists also scan the skies for extraterrestrial signals via radio telescopes, as some believe other civilizations will inevitably produce and release radio waves, as we do, during their evolution.

Frank Drake, a US astronomer and astrophysicist, was the first to test the method. In 1960 he started Project Ozma, a pioneering SETI (search for extraterrestrial intelligence) experiment, at the US National Radio Astronomy Observatory at Green Bank, West Virginia. The aim was to examine nearby sun-like stars for signs of life through interstellar radio waves.

Although the project ended without success, it triggered dozens of SETI programs later.

However, the work of selecting possible meaningful signals from massive background noise eats up a lot of time and resources. The Space Sciences Laboratory at the University of California, Berkeley, launched the SETI@home project in 1999 to search for possible radio transmissions from extraterrestrial intelligence via public volunteer computing.

As part of the worldwide SETI effort, the project uses observational data from the Arecibo Observatory in Puerto Rico, the world's largest telescope, and the Green Bank observatory. The data, taken piggyback, or passively, while the telescopes are used for other scientific projects, are divided into small chunks and sent to millions of home computers for analysis. The software searches for signals with variations that cannot be ascribed to noise, hence possibly contain information.

So far, about 9 million volunteers in 226 countries have analyzed a total of 15 years of data from the Arecibo telescope, says Dan Werthimer, co-founder and chief scientist of the SETI@home project.

"We have identified about 100 very short radio bursts, about one millionth of a second long, that we don't fully understand," Werthimer says. Radio communications from Earth have not been ruled out as the source of these signals.

No signals have been confirmed as from extraterrestrial civilizations. "We've only had radio for 100 years and lasers for 60 years," Werthimer says. "We are just getting in the game and just beginning to explore the potential different frequencies and signal types that another civilization might use. There's a long way to go before we can do a thorough search.

"The good news is that the capabilities of earthlings are growing. The computing power is developing quickly and the FAST telescope will be very powerful."

TMT.ORG; SETI@home on a home computer.(Photo provided to China Daily)

East-West cooperation 

The Five-Hundred-Meter Aperture Spherical Telescope, now being built deep in the mountains of Guizhou province in Southwest China, will become the world's largest radio telescope once completed in September.

With a dish the size of 30 football fields, FAST is 500 meters in diameter and made of 4,450 panels. Scientists have depicted it as a super-sensitive ear that will be able to detect very weak messages - if there are any - from any relatives we may have out there.

It will be 10 times more sensitive than the telescopes in the Breakthrough Listen project, a $100 million initiative by Russian tycoon Yuri Milner to search for extraterrestrial civilizations, says Li Di, chief scientist with the radio astronomy department of the National Astronomical Observatories of China.

Werthimer is seeking cooperation with Chinese astronomers to develop a SETI@home project for FAST. "We hope to work with China to do SETI at the same time while the telescope carries out sky surveys to search for pulsars, fast radio bursts and to map the galaxy as planned."

Though unsure of how such collaboration would work, Li Di is interested in working with the SETI@home project. "With their experience and advanced technologies, they will help us improve the telescope's scientific capabilities and operating conditions. It's like standing on the shoulders of a giant."

Active participation 

Chinese scientists have also actively participated in the preparations for the Square Kilometer Array, a large multi-radio telescope project to be built in Australia and South Africa.

It will eventually use thousands of dishes and up to a million antennas, which will enable astronomers to monitor the sky in unprecedented detail and survey the entire sky much faster than any system now operating. The search for extraterrestrial life is one of its key science programs.

Scientists have surveyed the entire sky with radio telescopes for a half-century now, and they have found interesting signals occasionally.

On August 15, 1977, a strong narrow-band radio signal, bearing the expected hallmarks of extraterrestrial origin, was detected by Jerry Ehman, an astronomer working on a SETI project at the Big Ear radio telescope of Ohio State University. The signal appeared to come from the constellation Sagittarius and lasted 72 seconds.

Ehman circled the signal on the computer printout and wrote the comment "Wow!" beside it, which that event is now commonly called. But it has never been detected again.

"Some strange signals have been found, but it's hard to confirm their origins, because these signals do not repeat," Li Di says.

"We look for not only television signals, but also atomic-bomb signals. We shall give full play to our imaginations when processing the signals. It's a complete exploration, as we don't know what an alien is like."

Radio telescopes sometimes misread signals from astronomical objects. For example, astronomers once mistook signals from a pulsar for extraterrestrial signs, because a pulsar can also give out very stable periodical signals.

"We don't know when earthlings will discover ET," Werthimer says. "It could be 1,000 years from now, or in our lifetimes. It could be next year, when FAST gets going on the sky surveys."

However, with no clues of extraterrestrial life over the past 50 years, questions are constantly asked as to whether the search methods are appropriate.

Even on Earth, land and sea host completely different forms of life. "It is highly possible that life on other planets is entirely different from that on Earth, and it might not be carbon-based," says Jin Hairong, deputy curator of Beijing Planetarium.

Liu Cixin, a Chinese science-fiction writer and winner of the Hugo Award for his novel The Three Body Problem, says the current method assumes that aliens also communicate in radio waves. "But if it's a truly advanced civilization, it is possible to use other more advanced forms of communication, such as gravitational waves."

Mao believes many methods deserve a try.

"Who knows what they are and how they think?"

When we study the origin of life, he says, we risk going down a blind alley if we stick rigidly to life on Earth as the model to look for.

He cites astronomy to illustrate how earthbound thinking can hobble scientific inquiry.

When scientists started looking for planets around sunlike stars, he says, they worked on the supposition that these planets' orbits would give them a much longer year than ours. In fact, the first such planet discovered outside our solar system takes just four days to orbit its host star, an observation that many were skeptical of because it runs counter to their experience.

"If we really discover extraterrestrial life, I'd like to know how life spreads in the universe. Is it distributed uniformly in space, or clustered?

The more samples of life we find in the universe, "the more comprehensively we can look at the puzzle and solve it more easily", he says. But then again, should Mao, get his wish to satisfy his curiosity, not all are convinced that mankind would be the better for the experience.

Biological instinct 

The British astrophysicist Stephen Hawking has warned that communicating with aliens could be a threat to Earth. "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans."

Liu's The Three Body Problem depicted the universe as a jungle with every civilization as a hidden hunter. Those who are exposed will be eliminated.

But Han Song, another Chinese science fiction writer, believes humans naturally want to connect, and he cites the internet as proof.

"I think aliens may think similarly. It is a biological instinct to connect with each other. Everyone wants to prove that they are not alone in the universe. Loneliness is intolerable to humans."

He also points out that the contact will be driven by curiosity and real requirements. "Humans will ultimately go to space to find resources and expand their living area, so it will be hard to avoid aliens. Contact with them, especially those with more advanced intelligence, may help us leap forward in civilization."

Regardless of the theoretical debate, scientists have never wavered in the search.

"I think we shall call out," Mao says. "In fact we have been yelling for years, and our radios and televisions are broadcasting in space all the time. Aren't you curious about what our counterparts would look like?

"If they are inferior or equal to us in terms of civilization, we won't be easily destroyed. If they are much more intelligent than us, they wouldn't be so narrow-minded as to compete with us. Some worry they will come to rob us of our natural resources, but they probably have the power to transform the entire globe already. What's the point of eliminating a much lower civilization?"

Mao believes the result will be significant however it turns out. "If we find other life it will undoubtedly be the most important scientific discovery in our history. If not, it shows that life on Earth is unique and we should respect life and cherish each other.

"No matter the outcome, we shall never stop searching, and I hope to hear more voices and contributions from Chinese scientists." (China Daily)