Artist’s impression of Gliese 667 Cb with the Gliese 667 A/B binary in the background, from Wikimedia Commons. Reproduced under the Creative Commons Attribution 3.0 Licence.
Earth is a tenant in a strange neighbourhood. Next door, rusty dust scatters red light across the Martian sky. A sunset viewed from Mars isn’t like a sunset on Earth: a Martian sunset is blue. Venus lives on our other side. A day on Venus lasts 243 Earth days, while its yearly calendar is completed after 225 Earth days. This is because Venus orbits the Sun quicker than it rotates on its own axis, and thus a day on Venus is longer than its year. Around the corner on Jupiter, a hellish storm the size of two Earths hasn’t stopped raging since it was first observed 300 years ago. Seasons on Uranus last for about twenty Earth years. If you were to stand on, say, the north pole of Uranus, you would see the Sun rise, crawl along the sky for eighty-four Earth years, and upon its setting, you’d be in total darkness for the next eighty-four years. Neptune resides in a dangerous section of the neighbourhood, where winds reach speeds of over 2,100 kilometres an hour. Boasting exquisite rings and sublime auroras, Saturn is undoubtedly the mansion of our planetary community.
There is much oddity across the eight planets orbiting the Sun. We’ve become familiar with the alien-ness of each. But it’s a small community: if the Solar System is our neighbourhood, then the Milky Way Galaxy is our city, scattered with 200 billion stars like our Sun. Most of these, scientists estimate, have at least one planet, so there are perhaps 100-400 billion planets in the Milky Way. And the eight planets in our area are so wild and different. How unusual could the planets orbiting these other stars be? In the words of British scientist J.B.S. Haldane, “The Universe is not only queerer than we suppose, but queerer than we can suppose.”
Of course, these worlds seem banal compared with Earth – a world that has given birth to life, a world that has nurtured its own children with such indifference only to find itself a casualty of that same indifference, a victim of matricide. As human beings continue to wreak havoc, the search for exoplanets—worlds that orbit stars outside of our Solar System—is looming as more important than ever. The hunt is especially skewed towards planets able to not only harbour life, but to host human life. We human beings may one day find ourselves evicted from Earth. This is the story of our search for a new home.
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In 1992, Polish astronomer Aleksander Wolszczan, along with his colleague Dale Frail (who probably had a rough time at high school), announced that they had detected two planets orbiting a distant star. These were to become the first exoplanets ever discovered. However, excitement amongst scientists was restrained. The history of exoplanet discovery is poisoned with error and regret. Only a few months before Wolszczan and Frail’s announcement of their historic discovery—or, perhaps, ‘unearthing’—astronomer Andrew Lyne of the University of Manchester appeared before a crowd eager to hear his miraculous tale of exoplanet discovery only for Lyne to open his presentation with, “The planet just evaporated.” (It was never there to begin with.) While disappointed astronomers in the audience shook their heads, the failure was a reminder of just how difficult it is to find exoplanets. After all, if observing distant suns is a problematic task, how on Earth can we find distant planets?
Two complementary methods are generally employed by planet hunters to detect faraway worlds. The first is known as the “radial velocity method”, which sounds difficult, but the concept is relatively simple. A planet orbits a star because the star has more mass and therefore the star is attracting the planet towards it. However, the planet itself also has a gravitational tug on the star. This causes the star to wobble. Thus, not only does detecting a star’s wobble indicate the presence of an exoplanet, but depending on how much the star moves, the size and shape of the exoplanet’s orbit can be calculated, along with its mass. This technique is responsible for more than half the discoveries of exoplanets so far.
The other method: imagine you’re reading a book under a lamp. You hear a fly buzzing around the globe and notice that the light seems to flicker. The fly begins to encircle the light bulb, causing a repetitive, flickering dimness. This is analogous to how astronomers find exoplanets: telescopes, both on Earth and those we have launched into space, are pointed towards a star deep in our Milky Way, and as a planet passes between its star and our Earth, a drop in starlight is detected. The larger the drop in sunlight, therefore, the larger the planet.
Once these exoplanets are confirmed, researchers can determine whether or not the planet orbits within the habitable zone—where temperatures are suitable for water—and general profiles of the planets can be calculated.
So far, we have located and confirmed the existence of roughly 1,000 exoplanets, with a further 3,000 awaiting data analysis. Many of these discoveries are courtesy of the Kepler space observatory—a $US600 million telescope launched into orbit in March 2009—for the sole mission to discover Earth-like planets orbiting other suns. As the search for a twin Earth continues, and hundreds of new, weird planets are found each year, we’ve learned that even our finest creative minds in science fiction are mocked by the wild imagination of our universe.
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It’s the 14th of November 2013 and a mystery bidder has placed their final offer – £51.7 million, equivalent to $AU95.5 million. The offer is accepted, and the unidentified buyer walks away with a 59.6 carat (11.92 grams) pink diamond. A sparkling photograph of the majestic gemstone, named ‘Pink Star’, adorns many newspapers the following day, escorted with headlines hailing the diamond as the world’s most expensive. This, however, isn’t entirely accurate, as Queen Elizabeth II owns a series of extravagant diamonds known as the Cullivan diamonds. Cullivan I, aka The Star of Africa, is a pear shaped diamond weighing an astonishing 530.20 carats – 106.04 grams. Unsurprisingly, it’s not for sale. The Cullivan is one of the largest diamonds in the world. But all these diamonds, even the Cullivan, are tiny compared to 55 Cancri e – a planet made, at least partly, of diamond.
Discovered in 2004 in the constellation of Cancer, NASA’s Spitzer Space Telescope determined 55 Cancri e’s mass and radius, subsequently allowing researchers to calculate its density. The result was unfathomable. 55 Cancri e, it seems, features a subsurface layer made of kilometres-thick diamond. And it’s twice the size of Earth. And it shares a solar system with four more planets just like it.
If you’ve seen Lars von Trier’s 2011 apocalyptic film Melancholia, you’ll be familiar with the concept of rogue planets. These nomadic worlds are endless travellers with no star to call home. Losers of a gravitational tug of war, rogue planets are orphans that have been kicked out of their solar system families and left wandering the galaxy. The thought is frightening – if a ‘mere’ asteroid can wipe out dinosaurs, what would happen if a rogue planet smashed into Earth? Well, Earth has likely collided with planets before. The current hypothesis states that 4.5 billion years ago another planet smashed into Earth—explaining why Earth is tilted on an angle—and debris from the collision was caught by Earth’s gravity, eventually forming the Moon. While researchers approximate rogue planets in the billions, their existence has yet to be confirmed anywhere near our neighbourhood. The nearest rogue planet discovered is CFBDSIR2149, approximately seventy-five light years away – hundreds of trillions of kilometres.
In 2013, for the first time ever, astronomers identified an exoplanet’s colour. The planet affectionately known as HD 189733b has a deep, cobalt blue hue, similar to Earth. That is basically where the similarities between the two sapphire planets end. HD 189733b is a 1,000 degree Celsius gas giant where it rains glass—sideways—in scorching winds of up to 7,000 kilometres per hour.
The above are just a few peculiar examples of the strange planets in our galaxy. There are hundreds more. Like WASP-12b – an exoplanet slowly being devoured by its sun. Or in the faraway NGC 4845 galaxy, where astrophysicists witnessed a dormant black hole awakening to feast upon a wandering planet. These extraordinary cataclysmic events, thankfully, do not threaten our planet. We instead face our own deadly hazards – asteroids, nuclear war, global warming, Creationists. So, if something were to happen, where would we go (assuming we had the time and wherewithal)? And how would we get there?
Essentially, we’re looking for water; it’s necessary for life, as far as we know. The holy grail of exoplanet hunting is finding a planet within a star’s habitable zone, where the sun is close enough that the planet has surface temperatures conducive to liquid water but not too far where the atmosphere will be too cold. (An astronomy inside joke: Which is the real uninhabitable planet? Venus = no human deaths. Mars = no human deaths. Jupiter = no human deaths. Earth = 100,000,000,000 deaths. Even the Sun is safer! Know the facts.)
This has been the true goal of exoplanet discovery since the first discovery in 1992 – to find planets within a star’s ‘Goldilocks Zone’. In 2007, the announcement of a super-Earth called Gliese 581c, which orbited within a star’s Goldilocks Zone, ignited the public’s imagination. Soon after, the scientific community determined that the planet’s surface temperature more closely resembled Venus rather than Earth. Just as astronomers began resigning themselves to searching once more, a neighbour of Gliese 581c was discovered – Gliese 581d. Although Gliese 581d receives significantly less solar energy than our Earth does from the Sun, researchers suggest that the planet’s greenhouse effect could allow it to retain water on its surface. This would create a water cycle. And, possibly, life.
In June 2013, scientists not only located another planet orbiting inside of a different Goldilocks Zone, they found three planets circling the same star. Furthermore, the Gliese 667C system is ‘only’ twenty-two light years away. The fascinating part is that Gliese 667C is a red dwarf star. This type of star is the most populous throughout our galaxy, so the discovery of three habitable planets orbiting a red dwarf inspires much hope in the likelihood of life outside of Earth.
What does this all mean? Once we confirm all these potential twin Earths, then what? Do we yet possess the technology to travel outside of our Solar System? No, we do not. Current propulsion technology is insufficient for any worthwhile voyage. The speed of light, at just under 300,000,000 metres per second, is the speed limit of the cosmos. Gliese 667C is twenty-two light years away, which means light from our Sun takes twenty-two years to reach Gliese 667C. The fastest manned spacecraft ever flown was NASA’s Apollo 10 moon mission, which reached roughly 11,000 metres per second – barely 0.004% of the speed of light. The consensus is that it would take, with current technology, tens of thousands of years to arrive to our closest stellar neighbour. Furthermore, the cost would be astronomical.
At NASA’s Marshall Center, extensive work is underway on propulsion systems for effective space travel. One of their strongest developments is a colossal solar sail: just like a sail on a ship catches wind to thrust a vessel forward, a solar sail reflects sunlight from the Sun and uses that reflection to propel itself forward. But if this spaceship requires the Sun in order to move, what happens once we leave our Solar System? Simple, apparently: attach a massive laser behind it, and use that to propel it forward. The difficulty is in finding a material that is both extremely light yet can stretch across 966 kilometres, an astonishing size that NASA engineers calculate is just large enough to carry a hypothetical spaceship at an optimal speed. The material that NASA are currently testing is forty times thinner than hair, and yet, according to their mathematics and modelling, they must develop a material ten times lighter than this.
From nuclear-powered spaceships firing mini helium bombs in order to reach 16% the speed of light, to theoretical propulsion systems involving the contraction and expansion of space, interstellar space travel awaits a technological breakthrough. With each passing decade providing exponential technological growth, the impossible dream may only be a few sleeps away.
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Tonight, if it’s clear and you’re in the southern hemisphere, you can step outside and search for an exoplanet on your own. Scan the sky for the iconic Southern Cross, easily found if you follow the direction of two bright stars—The Pointers—accompanying the celebrity constellation. But there is in fact something incredibly special about one of these two shining stars. Glance towards the brightest star of the pair, Alpha Centauri. You are actually looking at two stars – Alpha Centauri A and Alpha Centauri B. If you have a telescope, you can observe the gap between them and admire their celestial dance up close. But you are not just looking at two separate stars. You are witnessing the closest exoplanet to Earth detected so far, Alpha Centauri Bb, orbiting the slightly dimmer star. It is just four light years away. Most scientists believe that with current technology, it could take 40,000-70,000 years to arrive there. Some contend we are on the brink of propulsion breakthroughs that could get us there in a few hundred years. Let’s just hope when we finally visit Alpha Centauri that our spaceship is occupied by astronauts driven by the human desire to explore, rather than overloaded with praying survivors, desperately searching for a new home, graduates of extinction.
When writing for The Age, Beat Magazine and more, every time Nick Taras finishes a paragraph, he takes a bath and listens to Montell Jordan’s This Is How We Do It.
This is the first in Nick Taras’ continuing series of columns on astronomy for The Lifted Brow. It originally appeared in The Lifted Brow #22, which you should go and buy now.