We, the pioneers.

As Voyager 1 cradles the edge of our Solar System, poised to enter the vacuous expanse of deep space, we are approaching a milestone that many on this planet are not aware of. As this magnificent example of human engineering leaves the confines of the warm embrace of our Sun, at ~120 AU a now faint and distant beacon in the enveloping darkness, we will become an interstellar species. The gravitas of this monumental achievement should not be overlooked.

Whilst it remains theoretically feasible that our universe may be teeming with life, intelligence of space-faring calibre may be exceedingly rare. We, the product of a knife-edge balancing-act between biological, geochemical and astronomical implausibility, are lucky to be  here at all.  The inordinate complexity, the innumerable coincidences and the eventual culmination of 3 billion years of evolution – we stand on the peak of the impossible, gazing out into the void, with Voyager as our first envoy to the stars.

It is unlikely, but not impossible, that any interstellar civilisation has come before us. We’ve been listening for our galactic neighbours, via the enormous ear of SETI, for over 50 years to no avail. No radio chatter, no xenoarchaeology nor ambassadorial spacecraft. Given the ubiquity of planet forming material, and what we consider the relative normality of our watery home, the emptiness – the silence, is paradoxical.

Voyager 1 is preparing to leave the heliosphere and enter the interstellar medium (IOP.com, 2011)

The galaxy is ~13.2 billion years old and our 4.5 billion year-old Solar System has orbited its centre ~25 times. This planet has been habitable for around 4 billion years, and based on our best estimates, we have another half a billion or so to go before the evolution of the Sun renders the planet uninhabitable. We’ve been hitching a ride through space for one hundredth of one percent (5 million years) of the age of our planet, and have had space technology for one thousandth of that  time (50 years).  Assuming this is the case for most habitable planets, and knowing as we do that exponential colonial growth is impossible, it seems likely that if intelligent civilisations had arisen at any point in the history of our galaxy, and at some coordinate closer to the galactic core, there has been little evidence to suggest that they ever made it out this far. Given that colonisation infers a survival value, the fact that nearby planets give no indication of being inhabited leads to the conclusion that there are likely to be no other colonisers out there.

What conclusions can we draw from the silence? Well, conjecture abounds. Perhaps the galaxy is teaming with civilisations who have consciously hidden themselves from us until we overcome some technological or societal hurdle that would usher our entry into the ‘galactic club’ – perhaps superluminal travel or the formation of a world government? Who knows. In the immediate future, and without too much speculation, we can possibly infer that we may be the only intelligent civilisation ever to have arisen, in this neighbourhood anyway. If so, that places quite a burden on us, whether we realise it or not, to protect our planet and each other until such time that we can make our own way through the stars. We, or most likely our distant descendants, may be the sole custodians of the true meaning of existence, nature and the universe; the formulators and keepers of the ‘theory of everything’. Their success, and ours in the meantime, depends on the decisions we make now.

We are the pioneers, but we are also most certainly endangered by our own machinations. Up to this point, some of those decisions have been rather poor and have possibly compromised the very habitability of the planet we draw life from. Others, like Voyager et al. have been great. This humble, unassuming vessel represents the first step of an infant civilisation adopting a truly universalist, extrospective outlook. With 10 – 15 years of power left, Voyager will continue to take measurements and beam information back to Earth on the transition through the heliopause and the composition of the interstellar medium. After its batteries have died and its instruments have gone silent Voyager will continue to obediently sail through the depths of space on a mission lasting an eternity; a mission with no end and no more formal objectives. The spacecraft will not decay in the vacuum of space and its form and technology will be preserved indefinitely as a timecapsule to the stars. Long after the Earth has ceased to exist, Voyager will remain.

What a truly magnificent thought! It is humbling to be part of the first generation of interstellar human beings and an honour to have Voyager as our flagship.

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My science friend Luke drew a comic about the Voyager probes, which can be found here.

New Planets for the New Year

2011 was an exciting year for exoplanets, mainly thanks to the Kepler mission and its abundance of results, and 2012 looks set to be even better. Even though we’re not quite half-way through January, a number of exoplanet discoveries have already been announced.

Yesterday the three smallest exoplanet candidates to date were unveiled at a NASA press conference. The three planets orbit an M-type star, denoted ‘Kepler Object of Interest’ (KOI) 961, which has about 60% the mass of the Sun but only one sixth its diameter. The three planets, KOI 961.01, KOI 961.02 and KOI 961.03 follow a diminutive orbit analogous to the moon system of a gas giant: the most proximate planet has a semi-major axis of roughly 1.5 million kilometres, or 0.010 AU, which is slightly more distant than the orbit of Titan around Saturn. All three planets’ orbits could be roughly contained within the orbit of Iapetus, Saturn’s third largest moon, which has a semi-major axis of 3.5 million kilometres.

The planetary system of the star 'KOI 961' consists of the three small planets in a very tight orbit. The size of the 'planet' is representative of it's radius (x-axis is on a logarithmic scale). Also included is the habitable zone (inner boundary in yellow, outer in blue), Gliese 581d (a larger planet that also orbits an M-type star) and Earth and Mars for scale.

The planets themselves are well within the ‘hot zone’ of the star, outside of the inner boundary of the habitable zone, with equilibrium temperatures (excluding greenhouse effects) of between 960 (KOI 961.01) and 1150 °K (KOI 961.02).  Their radii are reported as 0.57, 0.78 and 0.73 Earth radii respectively, the smallest of which is comparable to Mars. Kepler continues to surprise; these small planets in their miniature orbits are a testament to the sensitivity of the instrument, as well as an indication of the variety of  planetary systems and possible orbital configurations across the galaxy.

Circumbinary Planets

Artists rendition of the circumbinary planet Kepler 35b orbiting the binary Kepler 35(AB)

Also announced yesterday were the planets Kepler 34b and 35b, unique in the fact that they are both ‘circumbinary’ planets. This means that, along with Kepler 16b first announced in December 2011, they orbit two stars  in an orbital configuration now thought to be common throughout the galaxy. Weighing in at ~70 Earth masses Kepler 34b orbits two Sun-like (1.04 and 1.02 Solar masses) stars over the course of a 284 day orbit. The stars themselves orbit one another in 28 days and are separated by 0.22 AU, or ~32 million kilometres. At ~40 Earth masses, Kepler 35b is slightly smaller and orbits the binary pair Kepler 35A and B, with 0.80 and 0.88 solar masses respectively, at a distance of 0.60 AU. The stars are separated by 0.17 AU, or 25 million kilometres. Both planets appear to be within the HZ distance of their respective stars, but their complex orbits are likely to complicate this metric and any conclusions regarding their habitability will have to await further study. However, considering their masses and densities (0.61 and 0.41 g cm-3 respectively) they are likely to be low-density gas giants with little potential for habitability despite their residence within the habitable zone. Nevertheless, the possibility of orbiting habitable moons cannot be excluded.

Principal investigator Dr. William Welsh of San Diego State University says that the unique orbital configurations of  circumbinary planets would make for novel and interesting climate dynamics due to large multi-periodic variations in insolation over the course of a single orbit. Speaking at the American Astronomical Society meeting on behalf of the Kepler Science Team he said, “It would be like cycling through all four seasons many times per year, with huge temperature changes. The effects of these climate swings on the atmospheric dynamics, and ultimately on the evolution of life on habitable circumbinary planets, is a fascinating topic that we are just beginning to explore.”