A group of planetary scientists and former astronauts fighting to save the world from catastrophic asteroid impacts claim there's a huge hole in our defence strategy and "we will be hit".

Millions of asteroids on a potential collision course with Earth are going undetected and could wipe out humankind at any moment, according to experts.

The B612 Foundation is a US-based non-profit made up of former astronauts, scientists, mission planners and others who focus on protecting Earth from catastrophic asteroid impacts.

The organisation is run by former astronauts Ed Lu and Rusty Schweickart and collaborates with major international institutions on research, science and technological projects related to planetary defence. But it's a task so mammoth that Earth is currently wide open to being struck by an asteroid without us even knowing its coming.

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NASA was directed by Congress in 2005 to find 90 per cent of asteroids that were at least 140m in diameter and has since determined that, of those so far observed, none pose an immediate threat. But of the millions of asteroids in the 15-140m range estimated to be "near Earth", only about 18,000 of them are being tracked globally, with the majority not even located, monitored or catalogued.

So while humankind could deflect an incoming asteroid by nuking it, using lasers to vaporise it, sending a space "tractor" to drag it off course, or bumping it into a new direction, none of it will be of any use if we don't first spot the threat.

B612 president Danica Remy, who also heads the organisation's Asteroid Institute program, told news.com.au that while there are several operational telescopes worldwide that can detect asteroids on trajectories to Earth, they can only pick up a small number of them.

"The telescopes' field of view is very small and the sky is very big," Ms Remy said.

"We can currently determine in advance if one of the 18,000 asteroids we have observed is going to hit us, but we'd only know if one of the several million we haven't observed is on a trajectory for Earth if a land-based telescope observed it.

"It might be picked but it's more likely it wouldn't and that we'd first find out about it on impact."

The instruments and resources required to detect and track all near-Earth asteroids are so costly and extensive that it would take decades to achieve. But according to Ms Remy, it's a goal worth working towards. She said having systems in place for planetary defence was likely to determine the fate of humankind.

"It's 100 per cent certain we'll be hit, but we're not 100 per cent certain when," she said.

A meteor streaked across the sky in Russia's Chelyabinsk region, causing explosions and injuring hundreds of people in 2013. Photo / AP
A meteor streaked across the sky in Russia's Chelyabinsk region, causing explosions and injuring hundreds of people in 2013. Photo / AP

According to Ms Remy, the first step to being able to track all near-Earth asteroids and subsequently deflect the dangerous ones from impacting our planet is to "increase our rate of discovery".

"Right now we're going slow in our discoveries: the world detects about 1000 asteroids per year and we want to accelerate that rate of discovery to 100,000 per year but don't have the space instruments or telescopes to do that," she said.

"We need to find them before they find us."

'POTENTIALLY DEVASTATING CONSEQUENCES'

Throughout its 4.5-billion-year history, Earth has repeatedly been pummelled by space rocks that have caused anything from an innocuous splash in the ocean to species annihilation. When the next big impact will be, nobody knows. But the pressure is on to predict and intercept its coming because of "potentially devastating consequences".

"We only need to look back in history to see evidence of this," Ms Remy said.

In 2013, a 19m asteroid exploded near the Russian city of Chelyabinsk and released more than 30 times the kinetic energy of the Hiroshima bomb.

The resulting shockwave blew out the windows of nearly 5000 buildings and injured more than 1200 people.

"There was no warning time for that asteroid ... the world found out about it when it hit," Ms Remy said.

In 1908, an asteroid impacted Siberia, destroying an area the size of metropolitan London.

The blast flattened some 80 million trees over 2000 sparsely-populated square kilometres.

"And then there's the 10km asteroid that killed off dinosaurs and 70 per cent of existing species nearly 66 million years ago," Ms Remy said.

But near-Earth objects that whiz by or towards Earth are anything but rare.

The Minor Planet Centre, which operates under the International Astronomical Union as the official worldwide organisation in charge of collecting observational data for asteroids, has recorded 133 "near-Earth objects discovered" this month alone. But that's just the tip of the iceberg, according to Ms Remy.

"We just had one that passed between the Earth and the moon last week," she said.

"There are millions of them — we just can't see most of them going by.

"We get hit a couple of times a year by a significant impact."

A radar image of an asteroid hurtling through space in 2015. Photo / NASA
A radar image of an asteroid hurtling through space in 2015. Photo / NASA

The B612 Foundation is currently exploring various options to achieve its goals of mapping out all near-Earth objects and tracking them but it's not the only organisation on the case.

In 2013, the United Nation's General Assembly recommended tasks for a science technical subgroup of the Committee Of the Peaceful Uses of Outer Space (COPUOS) to co-ordinate the international response to a near-Earth objects impact threat. That included the establishment of an International Asteroid Warning Network (IAWN), and of a Space Mission Planning Advisory Group (SMPAG).

"The warning group works to understand closely a potentially hazardous asteroid coming to Earth," Ms Remy said.

"We're looking at how synthetic tracking technology on a space-based mission could complement other telescopes by finding and tracking the large component of asteroids which will be missed by land-based telescopes — including Large Synoptic Survey Telescopes (LSST) — and infra-red space telescopes such as NASA's proposed NEOCam."

The LSST, currently under construction, will survey the sky over 10 years for several science applications, including looking for hazardous asteroids. It's expected to start operations in 2023.

"It will deliver an unprecedented amount of new asteroid data when it opens up its roof and starts taking inventories of the sky," she said.

"It isn't going to deliver us millions of asteroids observations but it'll dwarf the current number we have of 18,000."

THE GRAVITY TRACTOR

Humanity has previously conducted successful missions where probes have met up with far away asteroids in deep space, including NASA's Dawn spacecraft which orbited the huge space rock Vesta. In 2005, the Japanese Hayabusa probe even plucked some pieces off the asteroid Itokawa, sending them back to Earth for analysis.

But it's the "gravity tractor" many researchers, including those associated with the B612 Foundation, that could be the best option for deflecting dangerous asteroids on a trajectory to Earth.

As long as there's a significant warning period, the robotic probe could be sent out to space, to rendezvous and ride along with the asteroid.

The spacecraft's modest gravity would exert a tug on the asteroid as the two cruise through space together. Over months or years, this "gravity tractor" method would pull the asteroid into a different, more benign orbit.

"With advanced warning you only need to move an asteroid a quarter of an inch to throw it onto a different orbit," Ms Remy said.

"The issue is the gravity tractor hasn't been tested.

"Everyone believes the physics will work. What the organisation has done over the years is advocate that the world on behalf of humanity needs to understand how to deflect asteroids.

"But more funding is needed to get it to the stage where it's launched."

According to Ms Remy, whether or not catastrophic asteroids impact Earth in the future "is in our power".

"Their orbits allow us to predict impending impact years ahead of time to put asteroids off course or tug them off course," she said.

"The thing that's really most important is we need a comprehensive map showing the location, features and routes to all of these asteroids so we can defend ourselves.

"Asteroids don't care where they hit. It could be Australia, Japan, or Columbus Ohio.

"It's really a global issue."

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