Unrecognised risk: Earth may lie in the path of many thousands of unseen 'dark' comets.
Credit: NASA
SYDNEY: Comets could be the most significant impact hazard to Earth, with sky surveys underestimating the number that are potentially devastating by a factor of between 10 and 100, British astrophysicists say.
Astronomers may be missing these so-called 'dark comets' because their icy and reflective surfaces have become hidden under an obscuring layer of dust.
Near Earth objects (NEOs) are comets or asteroids that have been nudged into a possible collision path with the Earth. The international program to discover NEOs; Spaceguard, which includes NASA's NEO program, has identified around 6,000 NEOs so far, most of which are asteroids.
History of violence
But dark comets with unpredictable orbits may pose a greater threat than asteroids, which are easier to spot, according to astrophysicists Bill Napier, from the Cardiff Centre for Astrobiology in Wales, and David Asher, from Armagh Observatory in Northern Ireland.
"We may be dealing with a population of dark objects, carrying a lot of kinetic energy, which are not being properly picked up in the Spaceguard surveys," the researchers write in the February issue of the journal Astronomy & Geophysics.
Some comets scoot into the range of Earth from near Jupiter or further out, but appear regularly, like Halley's Comet. Others originate in the distant Oort cloud, a spherical comet nursery predicted to exist around one light-year from the Sun. These have orbits in the range of a million years, and are harder to predict or to spot, especially if they are too far away from the Sun to develop a characteristic comet tail as their icy surface melts.
When the Solar System passes through the galactic plane – the flattened disc of the Milky Way galaxy – molecular clouds may send Oort cloud objects hurtling into the inner Solar System, said the researchers.
Galactic mix-up
They say the timing of the Solar System's passage through the galactic plane – around 20 to 30 million years – closely matches spikes in the distribution of large impact craters on Earth for the past 250 million years. They conclude that comets have been responsible for most of Earth's impact craters and may pose an unrecognised risk to our civilisation.
Current NEO programs might be "monitoring a swarm of bees while standing on a railway line with an express train due," says the study.
Earth under threat from dark comets
Sure, I have no doubt. A comet will inevitably hit the earth wreaking devastation and species extinction. I also think that we ought to as a species get together for a change and set up a system in orbit that can send such objects into a safer deflection so that we have a kind of permanent insurance policy. Perhaps on the moon or in a partcularly useful near earth orbit. Laser systems that can be aimed at such objects as they enter into the inner solar system so that oblation of the surface acts as a method of slowing down or speeding up the comet from a distance. Slow but steady in other words. What is needed is very accurate imaging and locating of such objects, careful and dedicated analysis of such objects for proper targeting. Seems that the US, Canada, China, Russia, Japan and the EU would be well off considering a shared proposal and shared costs in this. Of course, judging from the news today, the Brits and the French who are ostensibly allied do not even bother to inform each other about submarines in the Atlantic carrying nukes. Getting together for a comet seems rather far fetched but logical nonetheless.
How can it be a comet without a tail?
"Dark" comets don't heat up as they approach the inner solar system, start spewing ice and gas behind them? Then it's not a comet, is it now? It's an asteroid.
Why
I'd like to know _why_ "dark" commets are harder to spot than asteroids. I don't understand why a layer of dust which would probably be similar in composition to that of an asteroid would be harder to spot than an asteroid.
Secondly, dark surfaces absorb more heat. As the "dark" commet moves into the inner solar system, greater heating would no doubt cause high levels of outgassing. And the resultant tail would no doubt be visible against the background of space.
Perhaps the writer meant that exhausted commet cores would be harder to spot (no more outgassing) than regular commets. I would agree with that assertion, but I doubt the assertion that such a commet would be harder to spot than, say, a carbonaceous chondrite asteroid. Think "Mathilde."
Great...
Well that's just perfect, now we have to face planet killing ninja comets, we're doomed.
Earth under threat from dark comets.
Christ sake!!! purveyors of doom and gloom. Do you people sit there all day just to think up any or all pessimistic reasons to the destruction of the planet?? In the sixties all these morons walked around the cities touting "the end is near" - and we are all still here.
Sure we live on a little ball with significant perils in space (and elsewhere) that could wipe us out at any moment, but surely we can organise the "STAR WARS" technology to track the heavens to perhaps deal with such a catastrophic "hit" instead of trying to blow the shit out of each other on earth. Perhaps we deserve to be "hit".
Get a life - how about some optimistic views. I happen to think the human race in general will rise to these challenges as they happen, They always seemed to have done!!!
Re: Earth under threat from dark comets.
Rise to these challenges as they happen? What?, like the bang-up job we are doing with Global Warming? Perhaps you need to re think your opening phrase as well, not really fitting in well with a Science site.
re: Earth under threat from dark comets...
"In the beginning GOD made the heavens and the earth..." Perhaps as we try to understand our observations, we should consider the Creator has a pretty good plan, that has worked out fairly well, in spite of us!
Earth under threat from dark comets
United Nations may take up the issue of earth's vulnerability before all member countries to pool up funds to protect mother earth from such hazards.
Comets? How about the solar max?
With the increased gravitational and EM forces affecting the Sun when passing through the plane, coupled with the Suns recent inactivity and a buildup of plasma. I'm more concerned about coronal ejections with an extremely active cycle when we begin to really intersect with the plane. That regular solar cycles are a result of our changing position with the core of our galaxy. It's too quiet IOW's
The fact that we may see objects change orbits and pose a threat is secondary at this point. We will lose our satellites and quite possibly see complete disabling of our semi conductor technology... power grids automobiles cells anything that has chips.
A nice comet would just be icing on the cake.
CMEs vs comets interactions...
Any thoughts concerning the coming alignment of the sun, earth and the black hole at the center of Milky Way in 2012?