IT'S 2060. Your grandchildren are sitting in their classroom. On the wall hangs a photograph of a blue planet. But it isn’t Earth. It’s a planet in a distant star system. And we know that this planet harbours life. Humanity is not alone. Now imagine a different scenario. Suppose our search for planets with alien life finds nothing. What if Earth is the only fertile oasis in the galaxy and there is nowhere else to go? Wouldn’t that make preserving our planet’s environment even more important.
Dan Goldin, NASA’s ninth and longest-serving administrator, set science on a quest to get some answers. Possibly the most influential administrator in recent history, he made astronomers dream. While his ambition outstripped the technology of the 1990s, Goldin pushed astronomers to think about an incredible idea: Could we take a picture of another planet that orbits a distant star? Imagine having an image of a distant cousin of the Earth in your hands, and knowing life flourished there. What effect would it have? Would it divide or unite our global village? Would the realization that there are other habitable planets spur people on to seriously consider a voyage to the stars? Right now, these are just questions. But answers to them could realistically be found within the next 50 years.
Stephen Hawking is one of a number of big thinkers who believes we should take these questions seriously. Hawking, who promotes research into interstellar travel, suggests that we need a “Planet B.” Why? Because in his opinion, we are destined to make this planet uninhabitable for humankind. Whether this happens through the slow asphyxiation of climate change or the instant disaster of nuclear war doesn’t really matter.
But right now, we have no Planet B. None of the known planets around other stars can support life as we know it. Even our solar-system neighbours are too hot or too cold. Thus, fixing climate and other problems we’ve created seems morally correct, and eminently practical too. We’re all on spaceship Earth together. Discovering what’s up there only helps put into perspective the value of what we have down here and our need to protect it.
In the last 80 years, scientists have learned a lot about stars. Astronomers know how they form and die, and that almost all the atoms except hydrogen and helium were formed in their unimaginably hot cores. Think about that for a second. It means that the atoms in your body were created by a star. You and every piece of the Earth are made of stardust. And where did the hydrogen and helium come from? The start of it all – the Big Bang.
Our solar system, it turns out, is made of the ashes of long-dead stars. In this sense, the universe is the ultimate recycler. Generations of stars reuse material at each stage of their life. It will happen to us too. In five billion years, the sun will destroy the Earth. Billions of years after that, a new star will form from our ashes.
Each time a star is born, planets are likely formed too. So, if scientists want to find new planets, they need to look for new stars. And in about three years’ time, an amazing new radio telescope called ALMA will help scientists do precisely that. Sharper and more sensitive than other radio telescopes, ALMA will capture images of the dusty disks that surround forming stars and their planets.
But it’s the presence or creation of life that really captures everyone’s attention. That means researchers need to look for older, more mature systems, since the violent early stages of star and planet formation are not conducive to life.
Before scientists can hope to find life-bearing planets, they need to know where to look. Kepler, a space telescope launched in 2009, is the current best hope for finding Earth-sized planets. Why Earth-sized? Because almost all of the ones they’ve found so far resemble Jupiter. Big and made largely of gas, these giants have inhospitable environments. Although Carl Sagan wondered about the possibility of life evolving in Jupiter’s gas clouds, modern research indicates that this is very unlikely.
Another problem with the planets that have been found so far is that they are too close to their stars – closer even than Mercury is to our sun. But this has led to some unique discoveries. In one planetary system, the planet is so close to its star that the atmosphere is literally boiling away under the intense heat. Some truly ingenious measurements have allowed scientists to determine the make-up of this atmosphere as it disappears. As a result, humankind has already measured the atmosphere of a planet around another star.
But Kepler will revolutionize our knowledge. Simultaneously monitoring the light from 145,000 stars, this feat of engineering is searching for a tiny blink caused when a star’s planet moves in front of it. This isn’t as easy as it sounds. If the distant solar system is tilted relative to us then, from our viewpoint, a planet will never be in front of its star, and Kepler won’t detect any blockage of light.
Everything has to be just right, and the odds of that are really low. The solution is to follow hundreds of thousands of stars. But if optimistic estimates are correct, Kepler could identify as many as 500 Earth-sized planets. That may not sound like a lot, but it is 500 more than we currently know about. At present, the smallest known extra-solar planet is almost twice as big as Earth and hundreds of degrees warmer. It seems unlikely that life will be found there.
The goal for Kepler is to find planets that might harbour life and then to determine if they actually do. That requires a different space telescope – the Terrestrial Planet Finder (TPF).
With TPF, we’ve entered the realm of unfunded projects. While NASA has spent millions on initial design work, TPF exists only on the drawing board. It is perhaps the most ambitious space telescope ever proposed. One design involves linking a number of spacecraft together over a vast area to form a single giant telescope. This was Dan Goldin’s dream, and he hoped it would fly in 2008 – but there is some doubt about whether TPF will ever fly.
As challenging as it may be, building the telescope isn’t the biggest problem. The main challenge is that no one knows if it’s possible to formation fly with the accuracy needed. The positions of the spacecraft have to line up to within a fraction of the wavelength of light. That’s an incredible degree of precision over hundreds of metres.
Conservative plans don’t include TPF taking the nice pictures that Goldin envisioned. They do, however, indicate that it would be able to measure the atmospheric composition of extra-solar planets. The key is to find something that signals the presence of life – a biomarker such as oxygen. Many forms of life release this gas, others consume it. Without life, it doesn’t stay in the atmosphere for long. So oxygen is what TPF will look for.
Some scientists believe that the TPF concept could be extended to take that amazing picture of a blue orb. Such a “hypertelescope” would need a fleet of spacecraft separated not by hundreds of metres, but by 150 kilometres. That’s a tall order even for dreamers, yet laser technologies being developed in Canada right now might make this possible. If TPF were to find Planet B, could we get there? NASA and others, it turns out, have been doing their homework on this question. Remarkably, there have been a number of design studies on ships capable of interstellar travel. The technology, money and even the motivation to build them may be missing, but plausible concepts definitely exist.
It’s estimated that building an interstellar vehicle, NASA’s Longshot spaceship for example, would cost about one trillion dollars. To put this into perspective, the estimated cost of carbon taxation amortized over 20 years is 20 trillion dollars – a sobering thought that makes interstellar travel sound reasonably affordable, if not exactly cheap.
The time it would take to reach Planet B is also a consideration. Astoundingly, as Albert Einstein discovered, travelling at close to the speed of light slows time down for occupants of the spacecraft due to a phenomenon called time dilation. But making a ship go this fast is really difficult, so we’re fortunate a few stars are close enough that we wouldn’t need to worry about it. Nonetheless, the harsh realities of physics mean that interstellar travel will take hundreds or even thousands of years. Generations would live and die on the journey.
If Planet B could be reached, what might we find? The burgeoning field of astrobiology tackles this question. Far from something out of Star Trek, astrobiology is a serious academic research area. Its goal is to understand how life is formed. Given that Earth is the only known planet with life, it should be no surprise that this is where astrobiologists focus their attention. From the creatures living in the dense, hot crust of the Earth, to those that survive in the deepest oceans, all of them tell us about life’s capacity for survival.
Sunlight, either directly or indirectly, sustains many life forms. But some micro-organisms, called extremophiles, can survive on the heat and nutrients they obtain from hydrothermal vents at the bottom of oceans. Tremendously robust, extremophiles are also found in hot springs, and very acidic and alkaline lakes – places inhospitable to most biological cells. If life is capable of evolving in such strange environments, where else might we find it?
No one knows for sure whether these bizarre creatures adapted to these environments or if they originated in them. But one thing is clear: On our own planet, simple life appeared very quickly. Just a half a billion years after the Earth came into being, fossil records indicate that colonies of cyanobacteria existed. Their descendants continue to thrive today.
But this grand start ground down into a three-billion-year-long rut. The buildup to complex multicellular life seems to have taken a very, very long time. As a result, many astrobiologists expect that Earth-like planets will support only bacteria-like micro-organisms. The possibility of finding sentient beings on Planet B seems remote.
If the Earth is the only planet in the galaxy with intelligent life, then our blue orb is precious in a way few of us ever anticipated. It would mean humankind is not just the keeper of our planet, but the guardian of the cradle of intelligent life. That’s a heady responsibility. Only time will tell if we are up to the task.
So the next time you see a sky full of twinkling stars, stop and look up. Allow yourself to wonder: Are we truly alone? And remember, we might call Earth home, but our birthplace, and perhaps our future, is the stars.
Sidebar: What Space Travel Taught Us in 1968
What was most significant about the lunar voyage was not that men set foot on the Moon, but that they set eye on the Earth.
– Norman Cousins, Congressional Hearings 1975
Using some of the most influential photographs ever taken, Murvai looks at the impact of the Apollo missions on the modern ecology movement. Framing her ideas around the theme for World Environment Day on June 5 – Many species. One Planet. One Future – she explores how our first views of the Earth from space shaped our concept of our planet.
View "Our Window into Home" by Michelle Murval (pdf)
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