Over the coming days, the pre-dawn sky over Abu Dhabi may be graced by one of the most awe-inspiring of natural spectacles – a bright comet, seemingly suspending over the south-eastern horizon.
Since its discovery more than a year ago, Comet ISON, named after the Russian observatory that found it, has been racing through our solar system for a close encounter with the sun later this month.
A very close encounter, in fact. Astronomers calculate that Comet ISON will shoot past the sun barely 700,000 kilometres above its surface, a hair’s breadth by astronomical standards.
This may well prove disastrous for the comet, which is likely to be torn apart by the combined forces of the sun’s heat and gravity field.
Its death-throes could prove to be the comet’s saving grace, however. As it plunges in towards it closest approach to the sun – “perihelion” – at the end of this month, Comet ISON will shed huge amounts of icy debris, and these may create one or more spectacular “tails” fanning out into space.
Such sights filled our forebears with dread, the appearance of comets having been long linked to earthly disaster. Quite how this linkage came to be made is unclear. What is clear is that it has some basis in fact.
Over its 4.5-billion-year existence, the Earth has been struck by comets on countless occasions.
Travelling in from beyond the solar system and reaching speeds over 100,000kph, these kilometre-sized snowballs pack a punch far more violent than even the simultaneous detonation of all the world’s nuclear weapons.
The result is so devastating that comets have been invoked as the cause of several mass extinction of life on Earth over the past 500 million years.
A comet impact is often cited as the cause of the demise of the dinosaurs (and consequent rise of mammals like us) 65 million years ago.
Chunks of comet may even have struck the Earth during recorded history. Over the years, researchers have blamed them for everything from the Ice Ages to the start of the Dark Ages – whose name may reflect conditions back then, the result of the smoke from huge fires triggered by the impact.
Yet despite all the theories, hard evidence for impacts between the Earth and comets – as opposed to more local cosmic debris, such as chunks of asteroids – has only just emerged. The current issue of Earth and Planetary Science Letters reports the discovery of a strange glassy mineral found in the Sahara in south-western Egypt, which appears to be some kind of melted sand.
According to team member Dr David Block, of Wits University, Johannesburg, chemical analysis has shown it has an isotope “signature” unique to comets.
Until now, only tiny specks of cometary dust has been available to scientists, lurking in the Earth’s atmosphere and the ice of Antarctica.
Now the glassy material strewn over a huge area in Egypt is being hailed as the first sizeable chunk of comet debris ever found.
As such, it could give astronomers new insights into the origin of these strange denizens of deep space. Most are thought to come from the so-called Oort Cloud, a colossal cloud that surrounds the sun far beyond the orbit of Neptune.
Left over from the formation of the solar system, these chunks of debris are stirred up by the gravity of passing stars, occasionally ending up on trajectories ending with a collision with the Earth.
Astronomers believe our planet came in for an especially violent pounding in the earliest days after its formation (and our battered moon still bears the scars).Yet there is now mounting evidence that comets may have delivered more than just mayhem.
Analysis of cometary material suggests these icy objects gave our planet much of its water – something to ponder next time you’re taking a shower.
Now there is mounting evidence that comet impacts may have been crucial in the creation of life itself.
Earlier this year, this newspaper reported on computer simulations of the impact process that suggested they could convert simple molecules found on comets into biologically important chemicals.
Now a team led by Dr Mark Price at the University of Kent in the UK, has gone one better, and recreated the impact process in the laboratory, by firing steel projectiles at speeds up to 25,000kph into comet-like material. According to the online site Space.com, the team has found that the impacts converted the frozen mix of molecules like ammonia and methanol into several amino acids – the building-blocks of proteins used by living organisms.
Dr Price and his colleagues stress that they haven’t created life. That would require the formation of self-replicating molecules like DNA or prion proteins.
But the experiments are at a very early stage, and the smart money is on further surprises.
These latest discoveries confirm the importance of comets in our understanding of the cosmos and our place within it.
The successful prediction of the return of Halley’s comet in 1758 by the eponymous astronomer confirmed the cosmic power of Newton’s laws of motion and gravity.
Some historians even claim that Newton was inspired to his law of gravity not by the fall of an apple but by the appearance of a spectacular comet in the winter of 1680.
As it happens, Comet ISON was initially thought to be the very same comet that Newton saw.
But as more observations came in, astronomers realised it is on a so-called hyperbolic trajectory. That means that even if it survives its impending close encounter with the sun, it will hurtle round the sun so fast it will be ejected from the Solar System, never to return.
So this is definitely a one-off performance – but one potentially well worth getting out of bed early to see.
Robert Matthews is visiting reader in science at Aston University, Birmingham, England