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Asteroids are the rocky crumbs left over after the formation of the planets in our Solar System. Most are found in a huge ring of space known as the asteroid belt- somewhere between the planets Mars and Jupiter. However, some are found outside the main asteroid belt. Three groups called Atens, Amors, and Apollos are the ones we worry about here on Earth. These are known as near-Earth asteroids and they spiral around in the inner parts of the Solar System and can sometimes cross the path of Earth and Mars.
Of the near-Earth objects (NEOs) so far discovered, there are more than 1700 asteroids currently considered hazardous. NASA’s Near-Earth Object Wide-field Infrared Survey Explorer, or NEOWISE, spacecraft, in orbit around Earth, uses asteroid-hunting thermal sensors that allow an infrared view of asteroids without the obscuring effects of Earth’s atmosphere. The space agency said they have fond 788 NEOs and 136 comets. Ten of the newly discovered objects have been classified as potentially hazardous asteroids, based on their size and their objects. “NEOWISE continues to expand our catalog and knowledge of these elusive and important objects,” said Amy Mainzer, NEOWISE principal investigator from NASA’s Jet Propulsion Laboratory in Pasadena, California.
When meteor exploded over Chelyabinsk, Russia, in February 2013, injuring more than 1,600 people, reminded that world is still vulnerable to a potentially catastrophic asteroid strike. The Chelyabinsk strike, was caused by an object that is thought to be about 65 feet (20 meters) wide. The Tunguska event was much more powerful; a space rock perhaps 130 feet wide (40 m) exploded over a mostly unpopulated region of Siberia, flattening 800 square miles (2,070 square kilometers) of forest.
Threat of Asteroid Strike
NASA’s planetary defense officer, Lindley Johnson, said scientists have found 95 percent of all these near-Earth objects measuring one kilometer (two-thirds of a mile) or bigger. But the hunt is still on for the remaining 5 percent and smaller rocks that could still inflict big damage. Altogether, NASA has cataloged 18,310 objects of all sizes. Slightly more than 800 are 460 feet (140 meters) or bigger.
NASA has made substantial progress in finding the asteroids that pose the biggest threat to Earth, but there’s still a lot of work to do, said John Holdren, director of the White House’s Office of Science and Technology Policy. “We are not fully prepared, but we are on a trajectory to get much more so,” Holdren said at NASA’s Goddard Space Flight Center, during a discussion of the agency’s planned Asteroid Redirect Mission (ARM). Since it formed over 4.5 billion years ago, Earth has been hit many times by asteroids and comets, collectively known as Near Earth Objects or NEOs, and they still pose a danger to Earth today.
Minor Planet Centre that maintains a Danger List of objects, whose orbits pass within about 7.5 million kilometres of Earth’s and that boast a diameter of 110 metres or more found 93 newly-spotted objects during 2014 out of 1,534 such objects known so far. While the chances of a major collision are not great in the near term, there is a high probability that one will happen eventually unless defensive actions are taken.
NASA’s spacecraft Near-Earth Object Wide-field Survey Explorer (NEOWISE) which is on its three year mission since December 2013, has been tasked with discovering and characterizing space rocks orbiting within 28 million miles (45 million km) from Earth’s orbit of the Sun. Scanning the skies with its infrared telescope, in the twelve months the project has discovered three new comets and 40 previously-unknown near-earth objects, eight of which have Earth-bonking potential.
Strikes such as the Chelyabinsk impact are thought to happen once every hundred years, he added, while Tunguska is regarded as a once-in-1,000-years event. But, Holdren said, “if we are going to be as capable a civilization as our technology allows, we need to be prepared for even those rare events, because they could do a lot of damage to the Earth.” “This is a hazard that, 65 million years ago, the dinosaurs succumbed to,” he added. “We have to be smarter than the dinosaurs.”
Bridenstine pointed to the meteorite that exploded over the Russian city of Chelyabinsk in 2013, which had “30 times the energy of the atomic bomb at Hiroshima” and injured around 1,500 people. Just 16 hours after the crash, NASA detected an even larger object that approached the earth but did not land on it, he revealed.
“I wish I could tell you that these events are exceptionally unique, but they are not,” Bridenstine said. “These events are not rare – they happen. It’s up to us to make sure that we are characterizing, detecting, tracking all of the near-earth objects that could be a threat to the world.” According to scientific modelling systems, such events are expected to happen once every 60 years – but Bridenstine pointed out that destructive meteorites had crashed on the earth three times in the last century.
According to its Near-Earth Object Observations Program, which scans the skies for potential threats, there are no asteroids or comets that could impact the Earth anytime in the ‘foreseeable future.In fact, of all known potentially hazardous asteroids, there is a 0.01 per cent chance one of them will impact Earth in the next 100 years. However though NASA has a pretty good map of many of the killer asteroids out there, there are still about 10 percent that the space agency doesn’t know about.
In Oct 2019, The European Space Agency (ESA) added a new asteroid into its risk list due to the space rock’s chances of hitting Earth in the future. The risk list is a catalogue of all space objects for which the probability of them impacting Earth is considered high enough to keep track of. Based on the data collected by the ESA, the dangerous asteroid could collide with the planet in “less than 70 years from now”. According to the ESA, the asteroid has been identified as 2019 SU3. It is currently listed as the fourth most dangerous asteroid in the agency’s risk list. According to the agency, the asteroid’s chances of hitting Earth are “one out of 152”.
Astronomers have revealed that an asteroid named ‘Apophis’ is expected to pass extremely close or may hit the Earth in 2068 due to a phenomenon called Yarkovsky effect. Interestingly, the asteroid is named after The Egyptian god of Chaos and Evil.
Researchers at the University of Hawaii Institute for Astronomy (IfA) have announced the detection of Yarkovsky acceleration on the near-Earth asteroid Apophis. This acceleration arises from an extremely weak force on an object due to non-uniform thermal radiation. Discovered in 2004, asteroid Apophis is a 1,120-foot-wide (340-meter-wide) asteroid, about the size of three-and-a-half football fields, NASA said. Earlier, it was believed that the asteroid would pass by leaving the earth unscathed, but astronomers are no longer certain now.
The detection of the Yarkovsky effect acting on Apophis means that the 2068 impact scenario is still a possibility. This force is particularly important for the asteroid Apophis, as it affects the probability of an Earth impact in 2068, the astronomers said. “All asteroids need to reradiate as heat the energy they absorb from sunlight in order to maintain thermal equilibrium, a process that slightly changes the orbit of the asteroid,” they wrote.
Apophis is noteworthy because of its extremely close approach to the Earth on April 13, 2029, when the 300 metre-sized asteroid will become visible to the unaided eye as it passes within the belt of communications satellites orbiting the Earth. Earlier, SpaceX CEO Elon Musk had also predicted that huge asteroid Apophis will eventually hit humanity and there will be no way out.
Devastating Impact
According to Jan 2020 report by Yale-led team of researchers, Asteroids played a direct role in the mass extinction event that killed the dinosaurs. Most scientists acknowledge that the mass extinction event, also known as K-Pg, occurred after an asteroid slammed into Earth. Some researchers also have focused on the role of volcanoes in K-Pg due to indications that volcanic activity happened around the same time. To pinpoint the timing of volcanic gas emission, Hull and her colleagues compared global temperature change and the carbon isotopes (an isotope is an atom with a higher or lower number of neutrons than normal) from marine fossils with models of the climatic effect of CO2 release. They concluded that most of the gas release happened well before the asteroid impact—and that the asteroid was the sole driver of extinction.
NASA, the Federal Emergency Management Agency and other government agencies engaged in a planetary protection exercise considered the potentially devastating consequences of a 330 foot asteroid hitting the Earth. The simulation projected a worst case blast wave by an asteroid strike in 2020 that could level structures across 30 miles, require a mass evacuation of the Los Angeles area and cause tens of thousands of casualties.
The strike of asteroid on the Earth at a speed between 15 and 30 Km/s has a devastating effect due to the release of an enormous kinetic energy: blast waves, tsunamis, atmospheric and electromagnetic changes. In addition an impact winter is caused by the sunlight blocking effect of placing large quantities of pulverized rock dust into the stratosphere.
The amount of energy released can be significantly higher than generated by the most powerful nuclear bombs, and will depend on the size of the asteroid colliding with the Earth; causing massive damage on local to global scales. The Chelyabinsk meteor which caused a 500 kiloton explosion over Russia in 2013 was estimated to be around 20 metres in diameter.
”(At 140 meters) it’s big enough to destroy a state in the United States of America,” Bridenstine said. “It’s big enough to destroy an entire European country.” The impact of an object much larger than 1 km diameter could well result in worldwide damage up to, and potentially including, extinction of the human species. There is also the threat from comets coming into the inner Solar System. The impact speed of a long-period comet would likely be several times greater than that of a near-Earth asteroid, making its impact much more destructive; in addition, the warning time is unlikely to be more than a few months.
Asteroid Threat Mitigation
A mission to defend planet Earth could involve hitting the asteroid or comet with big, fast-moving robotic spacecraft in hopes of changing its path; or worst case, launching a nuclear device not to blow up the asteroid but rather to superheat its surface and blow off enough material to divert it.
Countries are developing new Asteroid destruction and deflection technologies to counter the threat. There are two basic strategies for changing the course of an asteroid/comet, destruction and delay. The National Science and Technology Council released a report calling for improved asteroid detection, tracking and deflection. NASA is participating, along with federal emergency, military, White House and other officials.European Space Agency (ESA) and NASA with their Asteroid Impact and Deflection Assessment (AIDA) mission, proposed to launch in 2020 want to investigate the possibility that a robotic spacecraft might be able to push a deadly asteroid off its collision course.
In April 2019, NASA announced that it had selected Elon Musk’s SpaceX to provide launch services for its $69 million Double Asteroid Redirection Test (DART) mission — adding to the ever-growing list of collaborations between the two entities. NASA’s DART mission will launch aboard a Falcon 9 rocket in California in June 2021. The goal is to smash a satellite into the Didymos asteroid’s small moon in October 2022. If all goes according to plan, the collision will change the asteroid’s motion, and NASA will be able to use what it learns from the mission to redirect a future asteroid on track to impact Earth, saving humanity from potential extinction.
Russian researchers have determined, among other things, that it would probably take a 3-megaton nuclear bomb to obliterate a 650-foot-wide (200 meters) stony asteroid. And any nuke’s destructive power would be increased by exploding it inside a crater or cavity within the space rock, the researchers found.
https://www.youtube.com/watch?v=Vj9_qeph3kI
Threat Detection and Warning of Near Earth Objects
It is estimated that of the million or so asteroids that could cause major damage on Earth, we are aware of only about 10,000 – or one per cent. More than 100 leading scientists and astronauts from Dr Brian May to Chris Hadfield have signed a declaration asking for increased action to tackle objects that could end life on Earth. The experts are calling for a 100-fold increase in the detection and monitoring of so-called near Earth objects (NEOs).
ASE group’s International Panel on Asteroid Threat Mitigation in a report back in 2008 entitled “Asteroid Threats: A Call for Global Response,” wrote “Because NEO impacts represent a global, long-term threat to the collective welfare of humanity, an international program and set of preparatory measures for action should be established.”
Ground telescopes are good at picking up asteroids zooming into the inner solar system and approaching from the night side of Earth, Johnson said. What’s difficult to detect are rocks that have already zipped past the sun and are heading out of the solar system, approaching from the day side. That’s apparently what happened in 2013 when an asteroid about 66 feet (20 meters) in size suddenly appeared and exploded over Chelyabinsk, Russia, damaging thousands of buildings and causing widespread injuries.
NASA’s Near Earth Object office at the Jet Propulsion Laboratory detects and tracks NEO objects under their “Spaceguard” programme. It determines their nature such as what is their mass or weather they could do harm to our planet. Nasa tracks around 12,992 near-Earth objects which have been discovered orbiting within our solar system close to our own orbit. It estimates around 1,607 are classified as Potentially Hazardous Asteroids.
Scientists hope to learn a lot more about asteroids from a pair of missions currently underway. NASA’s Osiris-Rex spacecraft will reach the asteroid Bennu and return samples in 2023, and Japan’s Hyabusa 2 is closing in on the asteroid Ryugu, with samples to be returned in 2020. Scientists hope to learn a lot more about asteroids from a pair of missions currently underway.
In June 19, NASA’s OSIRIS-REx spacecraft performed another significant navigation maneuver—breaking its own world record for the closest orbit of a planetary body by a spacecraft. The maneuver began the mission’s new phase, known as Orbital B, and placed the spacecraft in an orbit 680 meters (2,231 feet) above the surface of asteroid Bennu. The previous record—also set by the OSIRIS-REx spacecraft—was approximately 1.3 kilometers (0.8 miles) above the surface.
Upon arrival at Bennu, the team observed particles ejecting into space from the asteroid’s surface. The spacecraft will map the entire asteroid using most of its onboard science instruments: the OSIRIS-REx Laser Altimeter (OLA) will produce a full terrain map; PolyCam will form a high-resolution, global image mosaic; and the OSIRIS-REx Thermal Emission Spectrometer (OTES) and the REgolith X-ray Imaging Spectrometer (REXIS) will produce global maps in the infrared and X-ray bands. All of these measurements are essential for selecting the best sample collection site on Bennu’s surface.
In 2018, the White House published an action plan that required NASA to detect, track and characterize 90% of near-earth objects measuring 140 meters (460 feet) in diameter – but NASA Administrator Jim Bridenstine admitted that the space agency had a long way to go to meet that goal. “We’re only about a third of the way there,” he said. “We want more international partners that can join us in this effort. We want more systems on the face of the earth that can detect and track these objects, and we want to be able to feed all of that data into one single operating system so that ultimately, we have the best, most accurate data that we can possibly get.” Bridenstine warned that failing to invest in such a network could have catastrophic consequences.
The new decadal survey by the U.S. National Academies of Sciences, Engineering and Medicine found that ground-based radar could be one of humanity’s best tools for protecting Earth against the threat of asteroids.
Using Micro satellites to track Asteroids
Paulo Lozano, director of the Space Propulsion Lab at the Massachusetts Institute of Technology, say sending the tiny satellites to asteroids could help improve space research (or even save the planet from an asteroid attack, he said). “Instead of going to an asteroid every five, 10 years the traditional way, release a fleet of these tiny little CubeSats and visit 100 asteroids because it’s so cheap,” he said. “Because some of these asteroids, especially the very small ones, have the potential to collide with the Earth. Detecting them in time is important [for stopping them], but also knowing their composition.”
Lozano has developed electrospray thrusters that can carry less propellant — Lozano’s fuel tanks are the size of sugar cubes — but move more efficiently. Lozano hopes his tiny thrusters can help CubeSats reach Mars or send them on asteroid scouting voyages. “Since they are so small, you can actually land on the asteroid with these rockets and take off again,” Lozano said. By launching a fleet of CubeSats, scientists could learn the chemical compositions of asteroids, which could be the key to destroying or redirecting them. An asteroid made of silicon, for instance, would be much tougher to stop than one made of iron. Lemmer said CubeSats with propulsion could also provide a cheaper way to test new space technologies.
Chinese project will bounce signals off asteroids to see how dangerous they are to Earth
A leading Chinese university has begun constructing an array of more than 20 large radar antennas to track asteroids that have the potential to be hazardous to Earth. The project, named China Fuyan (or “compound eye”), is led by the Beijing Institute of Technology. The array aims to bounce signals off asteroids within 93 million miles (150 million kilometers) of Earth (about as distant as the sun) to image and track objects and determine the possibility that they could impact our planet.
So far, two antennas have been constructed at a site in Chongqing, in southern China. The pair is expected to be tested and become operational by September 2022, according to the Chinese-language outlet Science and Technology Daily(opens in new tab), which first reported the development.
The finished system will include more than 20 radar antennas, each with a diameter of 82 to 98 feet (25 to 30 meters). Chinese news reports claim that the system will be the world’s farthest-reaching radar system, but few details about the project, such as the wavelengths at which it will operate, are available.
Long Teng, president of the Beijing Institute of Technology, told Beijing news outlet Global Times(opens in new tab) that the project will meet the country’s requirements for near-Earth defense and space sensing capability, as well as frontier studies on the formation of asteroids. The system could also have applicability for tracking satellites and debris in Earth orbit.
The new decadal survey by the U.S. National Academies of Sciences, Engineering and Medicine found that ground-based radar could be one of humanity’s best tools for protecting Earth against the threat of asteroids.
In April 2022, the China National Space Administration announced that it is working on a planetary defense plan that includes tracking near-Earth objects and launching an asteroid-deflection test mission in the next few years, Space.com previously reported.
Mitigation Strategies
There are two basic strategies for changing the course of an asteroid/comet, destruction and delay.
Destruction concentrates on rendering the impactor harmless by fragmenting it and scattering the fragments so that they miss the Earth or burn up in the atmosphere. Destruction of Asteroid by “nuking it”, carries the risk that shattered asteroid could merely become a swarm of slightly smaller and still very destructive space rocks heading towards our planet, hence it is only considered at a very, very last resort.
Changing the course of an asteroid/comet destruction and delay
Delay exploits the fact that both the Earth and the impactor are in orbit. Delaying, or advancing the impactor’s arrival by or slightly over seven minutes can, depending on the exact geometry of the impact, cause it to miss the Earth. Edward T. Lu and Stanley G. Love have proposed using a large heavy unmanned spacecraft hovering over an asteroid to gravitationally pull the latter into a non-threatening orbit.
C.Bombardelli and J.Peláez from the Technical University of Madrid have recently proposed the use of a low divergence ion thruster pointed at the asteroid from a nearby hovering spacecraft. The momentum transmitted by the ions reaching the asteroid surface produces a slow but continuous force that can deflect the asteroid in a similar way as done by the gravity tractor but with a lighter spacecraft.
H. Jay Melosh proposed to deflect an asteroid or comet by focusing solar energy onto its surface to create thrust from the resulting vaporization of material, or to amplify the Yarkovsky effect. Over a span of months or years enough solar radiation can be directed onto the object to deflect it. The impact of a massive object, such as a spacecraft or even another near-Earth object, is another possible solution to a pending NEO impact. An object with a high mass close to the Earth could be sent out into a collision course with the asteroid, knocking it off course.
Initiating a nuclear explosive device above, on, or slightly beneath, the surface of a threatening celestial body, is a potential deflection option, with the optimal detonation height dependent upon the composition and size of the object.
The Asteroid Impact and Deflection Assessment (AIDA) study examines ways to potentially deflect asteroids from trajectories that could lead to them impacting Earth. The Johns Hopkins University Applied Physics Laboratory would work with NASA and ESA on the mission, which includes two independent spacecraft: an impactor (to be built by APL for NASA) and an impact monitor (to be built by ESA).The target of this mission is the binary asteroid system Didymos. The impactor would strike the smaller secondary of Didymos, while the monitor would observe and measure any change in the relative orbit.
Astronomers have revealed that an asteroid named ‘Apophis’ is expected to pass extremely close or may hit the Earth in 2068 due to a phenomenon called Yarkovsky effect. Interestingly, the asteroid is named after The Egyptian god of Chaos and Evil.
Russia to develop nuclear weapon to deflect asteroids
Researchers in Russia have modeled the destruction of dangerous space rocks in the lab, using tiny asteroid replicas and laser blasts to mimic the effect of nuclear warheads. The team determined, among other things, that it would probably take a 3-megaton nuclear bomb to obliterate a 650-foot-wide (200 meters) stony asteroid. And any nuke’s destructive power would be increased by exploding it inside a crater or cavity within the space rock, the researchers found.
For the new study, the researchers manufactured tiny artificial asteroids, basing their structure and composition on a piece of the space rock that exploded over the Russian city of Chelyabinsk in February 2013. The meteorite the team used was recovered from the bottom of Russia’s Lake Chebarkul, the researchers said.
“Under the EU seventh framework programme on development of scientific research and technologies between 2012 and 2015, was carried out the NEOShield project on research of all means to influence hazardous objects,” the institute’s press service said. “The work was distributed among different participants from various countries, and the task on deflecting hazardous space objects by nuclear explosions was placed with Russia, represented by the Central Machine Building Research Institute.”
Russian scientists say a nuclear explosion near a hazardous asteroid is a most effective way to prevent its collision with the Earth, though presently nuclear explosions in space are banned. “However, if due to an asteroid threat will rise the issue of enormous damage or even the very existence of life on the Earth, those bans, of course, will be dropped,” the press service said.
The institute’s experts say, it is most safe to make a nuclear explosion in the far space where it is sufficient time before an asteroid approaches the Earth. “In this case, a nuclear explosion is made so that an asteroid is not falling into parts, but ejects the substance, thus causing the jet thrust, which changes its orbit. This change will be evident most as the asteroid approaches the Earth next time – it will be deflected to a security distance from the planet.”.
China plans to test asteroid monitoring and defence system by 2025, reported in April 2022
China has plans to build an asteroid monitoring and defence system, according to Global Times. The country also plans to carry out a technical experiment of the same by closely tracking and attacking an asteroid in 2025, according to the publication.
As part of the project, China will set up a ground-based and space-based monitoring and warning system that will catalogue and analyse asteroids that pose a threat to human space activities. After that, it will develop relevant technology and engineering to dispel the threats.
The China National Space Administration (CNSA) will reportedly develop software that simulates possible impacts from asteroids that pass by Earth and will use it to rehearse defence processes to address the threat.
Chinese researchers want to send more than 20 of China’s largest rockets to practice turning away a sizable asteroid — a technique that may eventually be crucial if a killer rock is on a collision course with Earth.
At China’s National Space Science Center, researchers found in simulations that 23 Long March 5 rockets hitting simultaneously could deflect a large asteroid from its original path by a distance 1.4 times the Earth’s radius. Their calculations are based on an asteroid dubbed Bennu, orbiting the sun, which is as wide as the Empire State Building is tall. It belongs to a class of rocks with the potential to cause regional or continental damage. Asteroids spanning more than 1 km would have global consequences. The science center cited a recently published study in Icarus, a journal on planetary science.
“The proposal of keeping the upper stage of the launch rocket to a guiding spacecraft, making one large ‘kinetic impactor’ to deflect an asteroid, is a rather nice concept,” said Professor Alan Fitzsimmons from the Astrophysics Research Centre at Queen’s University Belfast. “By increasing the mass hitting the asteroid, simple physics should ensure a much greater effect,” Fitzsimmons told Reuters, although, he added, the actual operation of such a mission needs to be studied in greater detail.
Evaluation of Strategies
In 2011, Bong Wie, director of the Asteroid Deflection Research Center at Iowa State University, studied strategies to respond to a threatening asteroid on short notice of a year or so, and determined that to provide the required energy, a nuclear explosion is likely the only thing that would work against a very large asteroid in this short time frame. Other systems designed to divert an asteroid such as tugboats, gravity tractors, solar sails and mass drivers require 10 or 20 years of advance notice.
Jason C. Reinhardt, Matthew Daniels, and M. Elisabeth Paté-Cornell from Stanford University, Stanford in their paper “Probabilistic Analysis of Asteroid Impact Risk Mitigation Programs” compared three types of possible space missions to alter the orbits of hazardous asteroids namely kinetic impactors, standoff nuclear explosions, and gravity tractors.
They found Standoff nuclear detonations outperform kinetic impactors and gravity tractors at every considered NEA diameter. Gravity tractors are superior to kinetic impactors for diameters larger than approximately 400 meters. For NEAs with diameters less than 400 meters, kinetic impactors are fairly effective. “The results of this analysis suggest that we most likely have the technology to successfully mitigate most of the risk from asteroid impacts, given sufficient time between NEA discovery and a potential Earth impact”, according to authors.
References and Resources also include:
http://www.space.com/34070-earth-vulnerable-to-major-asteroid-strike.html
https://isupportaim.com/letter/
https://www.pahomepage.com/news/us-stepping-up-earths-protection-from-asteroids-comets/1251719220
http://idstch.com/wp-admin/post.php?post=1852&action=edit
https://indianexpress.com/article/technology/science/deflecting-asteroids-with-rockets-7392997/
https://www.space.com/china-asteroids-planetary-radar-project
