April 23, 2014
Sentinel Telescope May Help Save Us From Earth-Killing Asteroids
Lawrence LeBlond for redOrbit.com - Your Universe Online
Asteroid impacts on Earth – those on the scale of the one that wiped out the dinosaurs 65 million years ago – have been big hits in Hollywood. But in the modern world, are the impacts portrayed in movies like Deep Impact and Armageddon only the stuff of science fiction?The answer is likely no.
Scientists continue to warn us of the dangers that lurk in the skies above us and in the past dozen or so years, no less than 26 major impacts have occurred around the world. These impacts, while not comparable to the one that killed the dinosaurs, have ranged in energy from 1-600 kilotons. To put this into perspective, the atomic bomb that was dropped on Hiroshima in 1945 exploded with the energy of 15 kilotons.
The B612 Foundation released a video showing the locations and energy of these impacts, which occurred between August 25, 2000 and April 30, 2013. These impact sites were picked up using a network of sensors deployed to monitor the Earth for the infrasound signature of nuclear explosions. The data on these asteroid impacts was released by the Nuclear Test Ban Treaty Organization (CTBTO).
While most of the asteroid explosions occurred too high in the atmosphere to do any serious damage on the ground, the evidence is significant in estimating the frequency of impacts and the potential for a “city-killer-size” asteroid.
Of the 26 impacts felt by sensors around the world over the past 14 years, most were unheard of or went unseen and unfelt because they were either too small or occurred out in the middle of the ocean. However, one of the last impacts recorded by the CTBTO did make its presence known.
The February 15, 2013 meteor that exploded over the Russian city of Chelyabinsk was a warning that big impacts are out there and can strike anywhere, at any time. That day, the 500-kiloton meteor explosion caused serious damage to the city, shattering thousands of windows and injuring more than 1,200 people.
However, while the Chelyabinsk meteor was a terrifying event for those who were caught up in it, the event itself is quite small compared to some other historical impacts throughout Earth’s history.
The CTBTO data suggests that Earth is a bulls-eye for a multi-megaton asteroid impact – one large enough to destroy an entire city – about once every 100 years.
To be clear, it has been just over a hundred years since an asteroid exploded over Siberia, causing widespread damage. Fortunately, the Tunguska event of 1908 occurred in a very remote part of the world, minimizing the effects on human habitat.
"This is a bit like earthquakes," Ed Lu, former shuttle astronaut and CEO of the B612 Foundation, said to the BBC’s Jonathan Amos.
"In the cities that have a major danger - Tokyo, Los Angeles, San Francisco - they know the odds of big earthquakes by observing how many small earthquakes there are. Because there's a known distribution of earthquakes, meaning that earthquakes come in all sizes, small to large - if I can measure the small ones, I know how many big ones they're going to be. And you can do this with asteroids,” he explained.
"These asteroid impacts in the last decade have been ones that we haven't had much data on until recently, and they tell us that in fact asteroid impacts are more common than we thought," he told BBC News.
SENTINEL IN THE SKY
To help better quantify the risks of asteroid impacts and to also mitigate them, the B612 Foundation is pushing its Sentinel telescope concept into the light.
The $250m telescope is slated for a 2018 launch and is being funded through private donations. The telescope will be situated in a Venus-like orbit, looking out towards Earth for any signs of potential impacters that may go unseen by current telescopes on Earth, hidden by the glare of the sun.
Sentinel will operate in infrared as well, which will make it better suited for hunting down dark grey asteroids.
Surveys in the past have suggested that we have found in the vicinity of 90 percent of the most dangerous asteroids that are roaming our neck of the woods – the ones that could lead to an extinction level event if they were to strike Earth. The good news, however, is that it looks like none of these monsters will impact us anytime soon.
But data from NASA’s WISE observatory suggests that there could be close to 20,000 objects out there that range in size from 100-1,000 meters – the vast majority of which have yet to be identified.
When it comes to tracking potential earth-killers, time is precious. The sooner we find a dangerous rock, the easier it will be to deal with it.
SAVE OUR SHIP
Several plans have been discussed to save Earth from a potential global-killer.
Last year while Russia was dealing with the Chelyabinsk meteor impact, another rock – asteroid 2012 DA14 – was sailing high above Earth. At the same time, a pair of California scientists were proposing a new system that would help deal with such space rocks.
[ Watch the Video: Asteroid 2012 DA14 To safely pass Earth ]
Called DE-STAR, the system would be designed to shift the orbit of a large asteroid, deflecting it away from Earth and possibly into the sun. The system could also be used to assess the composition of asteroids to determine what kind of risks they pose.
According to BBC’s Jonathan Amos, another simple approach might be using a so-called “gravity tractor.” The technique involves positioning a spacecraft close to its target and using long-live ion thrusters to maintain the separation between the two. This technique would theoretically pull the rock off its trajectory.
"These types of mission are arguably less difficult than building Sentinel. The hard part is finding these things," said Lu. "Picture trying to spot something that's only the size of a small apartment building, that's tens of millions of miles from Earth, and that's black against a black background. That's incredibly hard. That's what requires the technological advances of Sentinel."
Speaking to Discovery News, Lu said that during the 5.5 years of operation of Sentinel, scientists should be able to spot 90 percent of near-Earth objects (NEOs) 460 feet in diameter or larger, and about 50 percent of NEOs 130 feet in diameter, which are the ones that have the potential to destroy us.
"Picture a large apartment building -- moving at Mach 50," he told Discovery News.
"Chelyabinsk taught us that asteroids of even 20-meter size can have substantial effect. The size range of what you would call a 'city-killer' is beginning to decrease," he said.
"The data we have is just on the edge of what's just large enough to destroy a city, but this is not the main point ... Whether or not these things happen once a century, once every 80 years or once every 150 years, we're going to find out once we launch Sentinel,” he explained. "What's important is that people need to understand that it's not once in million years, it's not once every 50 million years. It's not super-duper rare," Lu said.
After launching in 2018, B612 Foundation expects Sentinel to detect and track more than 200,000 asteroids within the first year of operation.
Image Below: The Sentinel Space Telescope in orbit around the sun. Credit: Image courtesy of Ball Aerospace.