The Interplanetary Travel Guide

The last couple of weeks have seen exciting developments in exoplanet astronomy. After 3 years of observations, astronomers at the European Southern Observatory discovered a planet orbiting the closest star system to our own Sun. Detecting this Earth-mass planet required measuring the velocity changes of Alpha Centauri B to a remarkable accuracy of 51cm/s (or 1.1mph). Not only was this the closest exoplanet yet found, it was also one of the smallest, with a minimum mass only 1.3 times that of Earth. However, this rocky world orbits so close to its star that day-side surface temperatures are likely to be around 1500K. Not exactly a habitable world, but it shows that exoplanet astronomy is progressing towards finding Earth-like worlds.

Another planetary discovery, announced on Thursday, appears to be a much better candidate for life. This planetary system, around 32 light years away, contains six planets orbiting the dim star HD40307. One of these planets, a super-Earth orbiting at 0.6AU, has a surface temperature of between -17° and 52°C. Although more than 7 times the mass of Earth, such a planet may have the potential to support life.

These discoveries have generated lots of talk about interplanetary exploration, especially along the lines of 'Lets drop everything and send humans and spaceships to these planetary systems!'. However, the gulf of space is unimaginably huge. Even with the fastest spacecraft ever built by humans, Voyager 1, it would take 70,000 years to get to Alpha Centauri B. If the distance between Earth and the Sun were scaled to fit in the palm of your hand, the nearest star would be 13 kilometres away! So what would humanity need to actually get there? Here is, entirely in my own view as a student of exoplanets, what we need to do to send a space-probe to another planet.

1. Find them all. With space missions like Gaia and ground-based scans like HARVPS & MEarth we could probably find all the earth-like planets around local stars by 2030.
2. Get a closer look. If the planet passes between us and its star (transits) we can get a glimpse at its atmosphere using something like JWST or EChO. Non-transiting exoplanets like this one are a little tougher, but projects such as TPF and Darwin will be able to image them and check their atmospheres for oxygen & water. Timeframe: by 2040.
3. Explore the solar system. Sending humans to an asteroid, and eventually Mars is just as important in the interplanetary space race. There's not going to be any appetite for space travel if we don't keep exploring our own solar system. Timeframe: by 2050


Sending a probe 10 light years in a human lifetime is going to take some big technological developments including:


4. Laser-powered Nuclear Fusion. This looks, according to an old UK study called Daedalus, to be the best bet for fuel on an interplanetary spacecraft, achieving speeds up to 12% of the speed of light (0.12c). Timeframe: 2030
5. Cheap launches to Earth-orbit. To assemble such a large craft in orbit will require cheap delivery to ever be feasible. Timeframe: 2040+
6. Earth-orbit refuelling and asteroid mining. Timeframe (if Planetary Resources are to be believed): 2020
7. Global Cooperation. Unless one country wants to be shackled with the most expensive mission ever, we're gonna need everyone involved. Timeframe: never?.
8. Mining the materials, building the parts, organising thousands of rocket launches and finally assembling more than 50,000 metric tonnes of metal and fuel into a spacecraft that might take a lifetime to reach the nearest stars and cant even stop or slow down at the other end. Timeframe: 2100+

So there's lots to do, and everyone can get involved! I'm going to concentrate on 1 & 2 for now by writing some code for my project on the Exoplanet Characterisation Observatory (EChO), but probably the best way to help our species get to another planet is to support science! Only if scientific agencies like NASA and ESA are widely supported by the public and adequately funded will such a project ever get off the ground.

Finding Life in Other Solar Systems

After a busy day at work, you emerge from the office into a fading March evening of 2029. Taking the usual route home, you check your phone for the first time in hours and discover 12 new messages. The first one simply says “Have you heard?!”. Your heart rate quickens. What could this exciting news be? Fumbling for the next message you quickly skim the text… In a state of shock, the phone drops from your hand. This is the moment you, like the rest of humanity, learn of the most important scientific discovery in centuries: that life exists elsewhere in the universe.

Although this vision of the future may seem speculative, the technology to detect life on planets around other stars already exists. All that is lacking is the enthusiasm of the general public and the financial backing of the world’s governments.

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The 20^th century was a truly optimistic time for those looking for life elsewhere in the universe. The early part of the century saw huge public intrigue over possible canals on Mars. However, by the time the Viking probes arrived in the 1960s, Mars was known to be a cold and desolate place. More recent rovers have confirmed that if Mars was ever habitable, it has not been so for billions of years. Missions to Jupiter and Saturn have also captivated public attention, with moons such as Europa and Titan being hyped to as possible havens for life. While the presence or lack of alien life in the solar system has not been settled, no environment has been found as comfortable for life as Earth’s surface.

However, in 1995 astronomers discovered the first solar system outside of our own. While this first ‘extra-solar’ planet was far from supportive to life, it marked the beginning of a new age of discovery for science. To date more than 750 exoplanets have been confirmed, and NASA spacecraft Kepler has found more than 2321 candidates including numerous Earth-sized planets. The Gaia mission, launching next year, could also potentially discover tens of thousands more. This revolution is space sciences mean there are now thousands more places to look for life in the universe, and missions have already been proposed to do just that.

The Darwin mission, with 6 space telescopes.

Since the early 00s both NASA in America and ESA in Europe hatched similar plans to fly an array of planet-hunting space telescopes high above the Earth. NASA’s Terrestrial Planet Finder, or TPF-I, and ESA’s Darwin mission comprised of between three and six 1.5m telescopes collecting infra-red light from a target star system. The telescopes would fly in a precise formation, allowing the light detected from each dish to be digitally combined. Not only does this processing give an effective telescope diameter of 100m, it also enables the light from the parent star in this system to be removed. This is called interferometry and is frequently used on ground-based telescopes including the Very Large Telescope array in Chile. Unlike in Chile, however, the distorting effects of Earth’s atmosphere are removed, and this array of space telescopes would be able to directly observe and characterise Earth-like planets.

The spectra of  Mars, Earth and Venus.
Only Earth, with H2O, CO2 and O3 is habitable

By measuring the light coming from such a planet across a variety of wavelengths, the TPF-I or Darwin missions could take spectra of any Earth-like planet discovered. These infra-red spectra could probe their atmosphere, and can tell if such a planet is inhabited. Life as we know it produces a distinctively imbalanced atmosphere. On Earth large amounts of oxygen coexist with methane, ozone, carbon dioxide and water; a mix that without life’s unique processes could not exist for long. “I would be 99% sure that life was present if I saw this combination of planetary characteristics” says Professor James Kasting, writer of the book How to Find a Habitable Planet.

These missions were capable of putting to rest one of the biggest questions ever asked by a conscious mind: ‘Are we alone in the universe?’ Geoffrey Marcy, exoplanet pioneer, said “I think TPF is our Human Genome Project”. What happened to TPF and Darwin, I hear you ask. In 2007 Darwin were indefinitely shelved, and  in 2011 Terrestrial Planet Finder was cancelled completely. In total both projects wasted more than 10 years planning and many millions of dollars of funding with no end result.

One of the main factors blocking the development of such an Earth-finding mission is cost. Such a project could plausibly run to tens of billions of pounds. While this figure dwarves the biggest science experiment ever made, the Large Hadron Collider at CERN (a mere $9bn), it pales in comparison to other projects, such as war in Afghanistan ($120bn a year) and global tax evasion ($3100bn!). Just like the LHC, this cost could be spread between European states and the US, and even new space-faring nations such as India and China. For a project that might answer fundamental questions about our universe and captivate people across the planet, a few billion pounds really doesn’t seem that much to ask.

James Kasting believes that, without the interference of politics, such a concept could be designed, built and flown into space within 15 years. And the only way to get such plans onto the table is to tell the politicians and policy-makers of the world that this matters to us. This groundswell of public interest in exoplanets & astrobiology could mean that on one evening in 2029 you discover that our Earthly biology has done the unthinkable; discovered life on another world.

Another Earth?

A few years ago, during the course of a pre-university preparation week, I took part in an Arts vs Sciences debate. (I say 'took part', I was one of the 90% that, never having debated before, stood at the back trying to avoid participation of any sort). But during the course of this petty intellectual squabble one argument stands out in my mind:.
"Art simply poses questions. It is up to science to answer them."
     I think the reason this stuck in my memory like gum to a shoe was because I was so opposed to it. When, I thought, has art ever given science a helpful push in the right direction? Was it only with John Milton's Paradise Lost that Newton could invent his law of gravitation? Did Picasso's 'Blue period' inspire Einstein to create the special theory of relativity. Could Stanley Kubrick's 2001: A Space Odyssey have led to our knowledge of black holes. The answer, to me, seemed to be a resounding No. Art kept to its corner of society, science kept to ours.

But today a piece of art set my mind rolling along avenues usually reserved for scientific thinking. The inceptive art piece was a trailer for an independent movie released in October called 'Another Earth'. The plot is set around the fantastical premise that a second planet Earth has appeared in the solar system, and on it is contained a carbon copy of all human life, including ourselves. Ok, so at first the idea of a planet cloning itself seems a little wacky, and I would completely agree. But it led me to think -how impossible would it be for two habitable planets, orbiting each other to circle a star such as our sun? Could there be a planetary system, somewhere, with two Earths?

Many bodies in the universe orbit each other in binary partnerships. Most stars are thought to have stellar companions formed when gas collapsed under their own gravity. Some of these binary systems such as Mizar and Acrux can be seen on clear nights. A handful of asteroids have been found that orbit each other as they slowly move about the sun. The dwarf planet Pluto and its large moon Charon are also often called a double planet system. This is because Charon, weighing in at one ninth of the mass of Pluto, orbits a combined centre of mass that lies between it and Pluto. But how about Earth-sized bodies?

Just like in art, original ideas are hard to come by in science - often it seems like everything interesting has been done. However, despite many discovered binary systems, a quick journal search for binary planet formation shows almost no results! Exploring whether these equal-mass double-planet systems are possible would not only be incredibly interesting, but also could become testable as more and more exoplanets are discovered. In fact, the detection of a binary exoplanet might even put to rest one of the longest standing arguments in planetary science - whether large, Jupiter-like planets formed by gravitational instabilities (which, being similar to star formation, might create binary systems) or by accretion (which wouldn't). They might also help explain why planets have been found wandering freely through the galaxy, as it might be easier for binary planets to destabilise and be thrown from the solar systems.  'Three-body problems' are extremely complex, however, and the interaction of the sun and with other large planets may make such systems impossible.

Despite my previous opposition, bouncing scientific ideas off art can generate interesting and unproven results. So maybe, just maybe, art has a use after all...