From Nuclear Weapons to Death Stars

A low autumn sun illuminates white-tinted grasses and lichens, each covered in beads of ice from the first deep frosts of winter. A lone Arctic Fox treads lightly on freshly fallen snow, making its way south towards the treeline where the last minks might be grazing. This is the desolate Kola Peninsula in northern Russia which, on October 30th 1961, witnessed the single most destructive force humanity has ever released.

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It was named the Tsar Bomba: a 58 megaton nuclear bomb. When it exploded 4km above Siberia, it released more than 2000 times more energy than the weapons used at Hiroshima and Nagasaki in 1945, sent a mushroom cloud to the edge of space, broke windows 900km away and sent seismic waves around the earth more than three times. This was the single most energetic event in human history, releasing as much energy as the UK uses in more than 10 weeks in the blink of an eye.

While such a destructive event is not cause for celebration, it is remarkable to think about the rapid technological advancement that led led to it. It was only 50 years previously that the nucleus of atoms been discovered. 100 years earlier and electricity and magnetism were still mysterious, far-from-unified concepts that could capture public imaginations but certainly seemed to have little public applications.

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From this rapid development, it would seem to be that our species is likely in its infancy as a technologically capable civilisation. The vastness of space, and remarkable frequency of earth-like planets in the universe, also suggest that we are not the only ones. With trillions upon trillions of potential habitable worlds in the universe, it is almost impossible to conceive that other, remarkably advanced civilisations are not out there.

Given the track record of our own species, and our ability to turn technology into devastatingly destructive weapons, it only takes a short leap of the imagination to picture hyper-intelligent aliens doing the same. Except, rather than the desolate russian tundra, they might use interstellar space for their weapons testing grounds. While I would be the first to admit that this sounds like science fiction, there is certainly a case that such explosions might well be observable. In that one fateful second in 1961 the Tsar Bomba generated millions of times more energy than all of the power stations on Earth. Maybe, shining like a short-lived new star, there could be evidence of these interstellar ballistic missiles out there in the cosmos.

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The interesting thing is that we haven’t seen anything of the sort. Famously the Fermi Paradox asks why, if intelligent life is out there, hasn’t Earth been colonised yet? Maybe the non-detection of great alien weapons, or Death Star Paradox, has a simpler answer: either hyper-intelligent civilisations wipe themselves out in adolescence, or they don’t seem too intent on destruction. And, with the world becoming a more peaceful place over the last few decades, we can be hopeful the answer is the latter.

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What’s In A Name?

Hundreds of astronomers across the globe are currently searching nearby stars for a fleeting glimpse of astronomical gold dust: exoplanets. I am also part of the search, scanning through terabytes of data taken by the WASP and NGTS telescopes looking for the distinctive signal of a distant world crossing its star. Thanks to the mountains of data from NASA’s Kepler probe, it is now even possible for amateurs to go online and help out. And thousands of people have taken part, spurred on by the chance to become the first person in history to lay eyes on a new part of the universe.

It is a thrilling quest, but the question on everyone’s lips is this: do you get to name it? Surprisingly enough, the answer is a ‘No’. Or maybe a ‘Not yet’…

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Here on Earth it has long been custom that, for whatever it may be, the discoverer becomes the namer. Columbus, Cook and Magellan all took pleasure in naming new lands, doctors such as Alzheimer or Asperger gave their names to their respective disorders, even some recently named animal species include Attenborosaurus conybeari and Heteropoda davidbowie in honour of the researcher’s heros. Chemists discovering new elements are given a relative freedom over naming their discoveries. Even in astronomy, comets are named after their discoverer with names such as Lovejoy or McNaught often gracing comet codes. Exoplanets, on the other hand, are a very different kettle of fish.

The problem with naming planets comes from the stars they circle. As nice as it would be to name every object something eye-catching like ‘Permadeath’ or ‘Baallderaan’, to avoid confusion the name of the star must be listed first. This is much like the way biological names come with both genus (Homo) and species (sapiens). So how do we end up with names like HD80606b whereas biologists get Bushiella beatlesi? The first part comes down to how we name stars.

Too Many stars to Count

Unlike islands or animals, there exist a near infinite plethora of stars. Our galaxy alone has more than 100 billion. Attempt to name each in the Linnaean style and you would quickly run out of words (and sanity). Early sky-watchers soon realised this and, after giving a few hundred stars colloquial names such as Vega or Pollux, settled for simply numbering the stars by brightness in a certain area. This ‘Bayer’ designation, cooked up in 1603, ranked the stars from alpha down to omega and beyond. For example the brightest in the Centaurus constellation is Alpha Centauri, our Sun’s nearest neighbour. With limited telescopic power and Greek and Latin characters, Bayer gave up after about 1500 stars.

More recent surveys have used telescopes to attempt to sweep the rest of the sky into some sort of order. This has resolutely failed, with the majority of stars having numerous names under many different catalogues (HD, HR, Gliese, or HIP to name but a few). Each of these official catalogues simply orders the stars by number, giving rise to the cumbersome alphanumeric system we see today. {NB: Despite what some might insist, naming a star has never been done via gift subscription companies}. So, thanks to the sheer number of star systems, the sky is a mess and there would seem little hope of sorting it out. 

GJ581 Planets

But forgetting the star for a second, once a planet is found we do get to add a ‘species name’ to the stars, right? Dont get your hopes up: this is normally the lower-case letter b. The lower case shows it to be a planet (as opposed to ‘B’ which would designate another star) and the ‘b’ designates it as the second object in the system after the star itself. In multi-planet systems things get even more confusing, with the order of names increasing not outwards from the star but simply in order of which was discovered first. For example GJ581e circles within the orbit of ‘b’ and GJ 581g is sandwiched between ‘c’ and ‘d’. However, this fundamentally makes sense: planets in the same solar system are given names reflecting their sibling nature.

It may be a dysfunctional system that results in far-from eye-catching names, but it is one at least partly grounded in reason. The alternative, of letting discoverers name the planet whatever they want (my personal choice would be Hughtopia), would ultimately end in confusion and a lot more angry shouting matches at conferences.

Even worse, a whole host of recent crowd-sourced websites have sprung up attempting to get the general public to name the 100-strong list of current exoplanets (for money, of course).  The International Astronomical Union (IAU), who ultimately decide on the names of everything in space, have even given support to public-generated naming systems. The feeling among astronomers, though, is that such a move might not be such a good idea.

But is there a middle way? Could the ordered nomenclature remain intact while giving at least some naming rights to the discoverers? The Planetary Habitability Laboratory recently proposed a system that would retain the star name but allow free reign over the planetary name, for example allowing Alpha Centauri B b to become Alcen-B Rakhat. It is an intriguing idea, and one that could help improve the public perception of astronomy. I, for one, am still hopeful that ‘Betelgeuse Hughtopia’ can become a reality.

[Relevant XKCD:]

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1000 Exoplanets

At around midday on Tuesday this week, on a page buried deep in the internet, a small counter ticked over to an important new value. Despite it’s obscurity, the slow and infrequent beat of this clock feels the pulse of an entire scientific community. And it’s one that is gaining vitality and momentum with every year. 1000thExoplanet

This new number was, of course, exoplanet number 1000. It was also joined by numbers  1001 through 1010, which were announced simultaneously by the WASP team. These eleven new worlds were added to the swelling ranks of alien planets that, less than 20 years ago, seemed completely beyond the grasp of science.

While it may sound like a definitive tally, the politics over who keeps track of exoplanet numbers is a disputed area. The figure of 1000 was logged by the exoplanet.eu database which includes some unpublished and contentious planets. The NASA database and US-based exoplanets.org, on the other hand, lag behind with 919 and 755 entries respectively.

But despite the arguments, the real take-home message is that exoplanetary science is an incredibly dynamic young  field. This year alone has seen another 141 new worlds discovered, with more than a dozen expected by the end of the year (Our WASP team has another 30 confirmed planets to publish in the next few months). To put it into perspective; from the first discovery of such a planet in 1994, it took 11 more years to reach 150. Helped by new technology and a ground-swell of funding into the subject, we will reach this tally in one. ExoplanetProgress

A quick analysis of the numbers shows that the number really is expanding exponentially. If we continue to discover new worlds at this rate (as fitted by the x^4 red line above), that number will pass 10,000 worlds by 2029 and 100,000 in only 40 years. It was more than 2000 years ago that Epicurus wrote “there are infinite worlds both like and unlike this world of ours inhabited by living creatures and plants and other things we see in this world” and in the space of only 20 we have proved him right.

New WASP planets published here: http://arxiv.org/abs/1310.5654 , http://arxiv.org/abs/1310.5630 and http://arxiv.org/abs/1310.5607

Rogue Planet or Failed Star?

It sounds like an interstellar sob story: a lonely planet expelled from it’s Solar System at a young age and forced to wander the galaxy alone. But what makes us so sure such objects are even planets, and does their discovery change how we view the universe?

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More than 2 years ago, the PanSTARRS telescope on Hawaii captured a dim red blob on its sensitive cameras. However, the importance of this dot was overlooked and the image was added to a 4000TB database of images, where the evidence of this discovery sat in wait. More than 18 months later it was rediscovered by Michael Liu and colleagues at the University of Hawaii who decided to take a closer look.

They found the point of light, now named PSO J318.5-22, to be an extremely red object only 80 light years away and floating freely through space. By studying the colours of the object they were able to determine a surface temperature of only 1160K and a mass only 6.5 times more than Jupiter . To begin nuclear fusion in the centre of a star, it needs to be larger than 13 Jupiter masses, making this object far too cold and small to be a normal star.

It is not the first ‘Rogue planet’ to have been discovered, with a further 4 objects found by similar sky surveys. These all have sizes in the region between large Gas Giant Planets (5Mjup) and small Dwarf stars (15Mjup). In all cases, including with PSO J318.5-22, these size estimates are extremely unreliable with a margin for error of up to 5Mjup either way.

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Logic might suggest that, if a ball of gas is too small to be a star, it must be a planet. However the boundary between the smallest stars and the largest planets is a very blurred one. The astronomers involved were careful not to call their discovery a planet, instead giving it the label of “late-L dwarf”, similar to a Brown Dwarf (right). That being said, similar sized objects such as the gas giants around HR8799 have made it into the nearly 1000-strong catalogue of exoplanets. So what makes this a special case?

One reason is the loneliness of PSO J318.5-22. In 2006 the International Astronomical Union met for a now-infamous meeting to demote Pluto to the diminutive status of dwarf planet. This decision also came with a new set of definitions for what it takes for an object to be considered a planet. Not surprisingly, clause number one was: it must orbit a star.

While the recent discovery falls down on this particular point, many commentators have pointed out that PSO J318.5-22 may well have been formed around a star before being expelled. This is not as far-fetched as it might sound; many models of planet-star interactions in complicated two-star systems have shown that planets could be tossed around like billiard balls.

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However, there is another option: PSO J318.5-22 could have formed in a collapsing cloud of gas and dust just like every other star in the universe. Such a scenario would completely exclude it from the definition of planet, making it more ‘Failed Star’ than ‘super-Jupiter’. Without further investigations it is impossible to know the answer.

In many ways the question of formation is unimportant: without a star to orbit, these are not planets. It may be a case of  soul-searching but, while the slow cooling of PSO J318.5-22 from warm proto-star to a lifeless ball of gas might interest a handful of stellar physicists, it is conventional planets like our own that can really challenge the understanding of our place in the universe.

Read the paper here on ArXiv

MASCARA: Planet-Hunting on a Budget

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The European Southern Observatory, Chile

If you were told to picture a cutting-edge telescope capable of discovering new planets you would probably think of the $600million Kepler space telescope or the huge La Silla observatory high on a Chilean mountain top. A waist-high bin with a handful of digital cameras in would certainly not spring to mind. But that is exactly what Ignas Snellen and his team at Lieden University plans to use to potentially discover dozens of new exoplanets.

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NASA’s Kepler Telescope

Hidden away high on a hill at the La Palma observatory, the first MASCARA or Multi-site All-Sky CAmeRA is already being built, and will be joined by 4 other sites across the globe if all goes to plan. Five off-the-shelf digital cameras are the workhorses of the small observatories, and together are able to constantly take images of the entire night sky. By taking repeated measurements of thousands of stars over the course of more than a year, the team hopes to hunt for exoplanet transits, the dip in light when a planet crosses its host star.

Unlike other planet-hunting telescopes, the cameras remain stationary rather than tracking the stars as the Earth spins. They instead will rely on short exposures and software designed to calculate the change in light of the stars and spot an elusive transit. This approach also means only the brightest stars can be studied. While bright stars may seem like the lowest hanging fruit, previous transit surveys (eg SuperWasp) have focused on scanning thousands of dim stars in much smaller patches of the sky. These bright star planets may also be perfect for the new generations of telescopes able to probe the atmosphere of these alien worlds.

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Crude designs for MASCARA

Since the first transiting exoplanet to be discovered in 2002, ground-based surveys have discovered dozens of large Jupiter-sized worlds close to their star. MASCARA will hunt for the hottest worlds which orbit their stars every few hours, but the team also seem confident that the array of cameras will be able to pick up smaller planets too. They suggest up to 7 Neptune-sized planets and even a handful of rocky worlds could be found, however transit surveys with similar goals have struggled to overcome problems with noise and small planets have not been forthcoming.

La PalmaWhether it finds small worlds or not, Mascara is certainly a novel way of hunting for exoplanets. It’s innovative and relatively cheap design (only €50K per station) is proof that sometimes in astronomy big money isn’t the only way to get big results. 

Habitable Lifetimes: 50 Billion Years of Summer

For 4 billion years our planet has been a willing host to life; nurturing it as it evolved from the first primitive single celled organisms through to large, intelligent life forms such as ourselves. Over time our sun, too, has evolved; growing in brightness by perhaps as much as 30%. And someday in the distant future Earth’s long glorious summer will end; our fuel-hungry sun glowing ever brighter until the planet we call home is scorched beyond recognition.

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Media favourite: a dead, uninhabited Earth (in 4bn years)

That is certainly a disappointing conclusion for us Earth-dwellers, but not exactly the one myself and colleagues at the University of East Anglia came up with in a paper published in Astrobiology this morning (despite the mainstream news outlets you might have read).

The slow expansion of our sun has long been predicted by astrophysicists, who revealed the clockwork of stellar evolution as far back as the 1970s. Other developments in the 1990s confirmed this by estimating the range of distances from the sun (and hence temperatures) over which an Earth-like planet would retain liquid water at the surface. The idea of this Habitable Zone has since been the go-to tool for assessing whether a planet could support life, and for as long as it has existed it has been known that the Earth is edging closer and closer to the too-hot-for-life ‘inner edge’.

By using recent models of how stars expand and brighten over time, we were able to put a new (if somewhat uncertain) estimate on when such a transition might happen: between 1.75bn to 3.25bn years from now. But while that might be as far as the papers read, the real science goes much deeper…

By the time Earth is toast, our blue planet will have dwelled for between 5 and 7 billion years in this glorious goldilocks zone. This is the Habitable Lifetime, and by anyone’s standards it is astoundingly long. Without it, life on Earth would have never had time to evolve from inorganic soup into the wonderful range of complex and intelligent creatures we see today.

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Numerous habitable zone planets have now been discovered

But Earth is not the only potentially life-supporting planet out there, and instead our research was focused on how long these other planets might remain habitable. Before the sun had brightened, Venus may have enjoyed 1.3bn years of balmy temperatures, while Mars may spend a few billion years bathing in similar sunshine near the end of the sun’s 10bn year lifetime. Almost 1000 alien planets have also now been found including a handful near their star’s habitable zone, not to mention a further 3000 Kepler candidates waiting in the wings.HabLifetimes

Computing the habitable lifetimes of these exoplanets is a more difficult task, however, as every star evolves at a different rate. Luckily stars only change brightness based on one thing: their size, and this can be found for the majority of stars. The 34 planets produce a large range of habitable lifetimes from 0.1 to 20bn years. One particular case is Kepler-22b which will remain in the habitable zone for 4.3bn and 6.1bn years; almost the same as Earth.

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All stars <35% the size of the sun will give 50bn year habitable lifetimes

However, for the planet Gliese 581d things get a little interesting: it has a habitable zone lifetime of around 50 billion years! That is more than 10 times the age of the Earth and almost 4 times longer than the age of the universe. This unbelievable timescale is due to a simple quirk of nature. While the brightest stars live fast and die young, some of the smallest stars can survive for hundreds of billions of years; dozens of times older than our sun will ever manage. What’s more these small stars evolve extremely slowly, allowing a well-placed planet to be habitable for much longer than planets in our solar system. If Earth could allow such a plethora of unique and complex species in only 4 billion years, imagine what could happen on an earth-like planet similar to Gliese 581d with 50 billion years of summer?

What all this goes to show is that we already know of places in the universe where life may be able to take hold and survive for billions of years. Some of these planets may be lifeless until long after the Earth is toast, only to warm up and spend 50 billion years in the planetary sweet spot. And even in our solar system life-friendly temperatures may have existed on Venus and may yet occur on Mars, springing new possibilities of life. As I’m sure you’ll agree; that’s a much better message to spread than ‘The Earth is Doomed’.

PS: This was the first scientific paper ever to be published with my name on. To be able to write “myself and colleagues at the UEA came up with in a paper published in Astrobiology” and to say my handiwork is currently being studied by readers of dozens of news outlets makes me as giddy as a small child on christmas.

PPS: My contribution to the paper was to take complex models of how all stars evolve and produce a mathematical function allowing the luminosity for any time period and any stellar mass to be immediately calculated. This is the first step to working out how the habitable zone migrates and hence the habitable lifetime of any planet sat in it’s path. The majority of the work was performed by Andrew Rushby (who wrote a similar blog today) and Mark Claire, both of whom I am incredibly grateful to for the chance to be involved in this work.