Monthly Archives: October 2013

What’s In A Name?

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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’…

Cookie

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:]

relevantxkcd

1000 Exoplanets

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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

Related articles and blogs

Rogue Planet or Failed Star?

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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.

startoplanet

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.

starforming

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