Even with six months' notice, we can't stop an incoming asteroid.
- At an international space conference, attendees took part in an exercise that imagined an asteroid crashing into Earth.
- With the object first spotted six months before impact, attendees concluded that there was insufficient time for a meaningful response.
- There are an estimated 25,000 near-Earth objects potentially threatening our planet.
The asteroid 2021 PDC was first spotted on April 19, 2021 by the Pan-STARRS project at the University of Hawaii. By May 2, astronomers were 100% certain it was going to strike Earth somewhere in Europe or northern Africa. On October 20, 2021, the asteroid plowed into Europe, taking countless lives.
There was absolutely nothing anyone could do to deflect it from its deadly course. Experts could only warn a panicking population to get out of the way as soon as possible, if it was possible.
The above scenario is the result of a recently concluded NASA thought experiment.
The question the agency sought to answer was this: If we discovered a potentially deadly asteroid destined to hit Earth in six months, was there anything we could do to prevent a horrifying catastrophe? The disturbing answer is "no," not with currently available technology.
While Europe can breathe easy for now, the simulation conducted by NASA/JPL's Center for Near Earth Object Studies and presented at the 7th IAA Planetary Defense Conference is troubling. Space agencies spot "near-Earth objects" (NEOs) all the time. Many are larger than 140 meters in size, which means they're potentially deadly.
Credit: ImageBank4U / Adobe Stock
"The level [at] which we're finding the 140-meter and larger asteroids remains pretty stable, at about 500 a year. Our projection of the number of these objects out there is about 25,000, and we've only found a little over one-third of those so far, maybe 38% or so," NASA's Planetary Defense Office Lindley Johnson tells Space.com.
With our current technology, spotting an NEO comes down to whether we just happen to have a telescope pointing in its direction. To remove humanity's blind spot, the Planetary Society — the same organization that deployed Earth's first light sails — is developing the NEO Surveyor spacecraft, which they plan to deploy in 2025. According to the Planetary Society, it will be able to detect 90 percent of NEOs of 140 meters or larger, a vast improvement.
How to move an asteroid
The DART spacecraft will attempt to deflect an asteroid.Credit: NASA
The NASA/JPL exercise made clear that six months is just not enough time with our current technology to prepare and launch a mission in time to nudge an NEO off its course. (Small course adjustments become significant over great distances, which is why "nudging" an asteroid is a potential strategy.)
What would such a mission look like? Hollywood aside — remember Armageddon?— we know of no good way to redirect an NEO headed our way. Experts believe that shooting laser beams at an incoming rock, exciting as it might look, is not a realistic possibility. Targeted nuclear blasts might work, but forget about landing Bruce Willis, Ben Affleck, and Liv Tyler on an asteroid to set off a course-altering bomb, especially just a month after its discovery (as was the case in the movie).
Another thing that might work is crashing a spacecraft into an NEO hard enough to shift its course. That's the idea behind NASA's Double Asteroid Redirection Test (DART). This mission will shoot a spacecraft at the (non-threatening) asteroid Dimorphos in the fall of 2022 in the hope of changing its trajectory.
The deadly asteroid's journey
The asteroid "2021 PDC" hit Europe in NASA's simulation.Credit: NASA/JPL
The harrowing "tabletop exercise," as NASA/JPL called it, took place across four days at the conference:
- Day 1, "April 19" — The asteroid named "2021 PDC" is discovered 35 million miles away. Scientists calculate it has a 1-in-20 chance of striking Earth.
- Day 2, "May 2" — Now certain that 2021 PDC will hit Earth, space mission designers attempt to dream up a response. They conclude that with less than six months to impact, there's not enough time to realistically mount a mission to disrupt the NEO's course.
- Day 3, "June 30" — Images from the world's four largest telescopes reveal the area in Europe that will be hit. Space-based infrared measurements narrow the object's size to between 35 and 700 meters. This would pack a similar punch as a 1.2-megaton nuclear bomb.
- Day 4, "October 14" — Six days before impact, the asteroid is just 6.3 million km from Earth. Finally, the Goldstone Solar System Radar has been able to assess the size of 2021 PDC. Scientists calculate the blast from the asteroid will be primarily confined to the border region between Germany, Czechia, Austria, Slovenia, and Croatia. Disaster response experts develop plans for addressing the human toll.
"Each time we participate in an exercise of this nature," says Johnson, "we learn more about who the key players are in a disaster event, and who needs to know what information, and when."
Practically speaking, little can be done to hurry technological development along other than budgeting more money toward that goal. Maybe we should have Bruce Willis on call, just in case.
A study looks at how to use nuclear detonations to prevent asteroids from hitting Earth.
- Researchers studied strategies that could deflect a large asteroid from hitting Earth.
- They focused on the effect of detonating a nuclear device near an asteroid.
- Varying the amount and location of the energy released could affect the deflection.
Large asteroids don't tend to hit Earth very often. But when they do, major cataclysms result. Remember the dinosaurs?
Add to this the fact that since 1998, scientists have detected about 25,000 near-Earth asteroids, while in 2020 alone, a record 107 of them came closer to our planet than the distance to the moon. With so many asteroids floating by, protecting our planet from impacts by these giant space bodies is an existential priority.
To prepare for the day when an asteroid will be heading our way, a joint study published in Acta Astronautica from the Lawrence Livermore National Laboratory (LLNL) and the Air Force, looked at how to use neutron energy output from a nuclear blast to deflect such a threat.
The scientists devised sophisticated computer simulations to compare strategies that could divert an asteroid 300 meters in diameter. In particular, they aimed to identify the effects of neutron energies resulting from a nuclear "standoff" explosion on the space rock's path. (A standoff detonation involves detonating a nuclear device near a space object — not on its surface.) The goal would be to deflect the asteroid rather than blow it up.
Detonating a nuclear device near an asteroid deposits energy at and below the surface.Credit: Lawrence Livermore National Laboratory
The researchers understood that they could affect an asteroid's path by changing the distribution and strength of the released neutron energy. Directing the energy could influence how much melted and vaporized debris could be created and its speed, which in turn would alter the asteroid's velocity. As the authors write in the paper, "Changing the neutron energy was found to have up to a 70% impact on deflection performance."
The scientists see their work as a stepping stone in continuing research into how best to protect our planet. They plan to devise further simulations in order to comprehend more precisely the energy spread needed for the deflection strategy to work.
Lansing Horan IV led the research, while getting a nuclear engineering master's degree at the Air Force Institute of Technology (AFIT) in a program with LLNL's Planetary Defense and Weapon Output groups. Horan explained that their team decided to zero in on neutron radiation from a nuclear blast because neutrons are more penetrating than X-rays.
"This means that a neutron yield can potentially heat greater amounts of asteroid surface material, and therefore be more effective for deflecting asteroids than an X-ray yield," he shared.
Another possible strategy for getting rid of an asteroid threat would be through so-called disruption. It essentially involves blowing the asteroid up, breaking it into tiny fast-moving pieces. Most of these shards should miss the Earth but around 0.5% could make it to the surface. The strategy does seem to have some drawbacks, however, if a larger asteroid came close to Earth. Exploding something like that could create a significant amount of calamity for the planet even if the whole asteroid didn't graze us.
Horan thinks disruption may be more appropriate as a last-minute tactic "if the warning time before an asteroid impact is short and/or the asteroid is relatively small."
Deflection is ultimately safer and less likely to produce negative consequences as it involves a smaller amount of energy than it would take to explode it. Horan said that over time, especially if we detect and deflect asteroids years before impact, even small changes in velocity should make them miss Earth.
While some may be understandably worried about using nuclear blasts close to Earth, Hogan sees it as something that may have to be considered in situations when time is of the essence.
"It is important that we further research and understand all asteroid mitigation technologies in order to maximize the tools in our toolkit," Horan elaborated. "In certain scenarios, using a nuclear device to deflect an asteroid would come with several advantages over non-nuclear alternatives."
One such scenario would be if there's not enough warning and the approaching asteroid is large. In that case, a nuclear detonation might be "our only practical option for deflection and/or disruption," proposed the scientist.
The impact might have triggered the Ice Age.
- A new study examined data on lunar craters to gain a better understanding of ancient impact events on Earth.
- Although scientists know of some ancient impacts on Earth, weather and erosion makes it hard to study impacts that occurred beyond 600 million years ago.
- Studying craters on the moon can provide some clues.
Since Earth formed 4.5 billion years ago, it's been bombarded by countless asteroids, meteors and other space objects. We know of some of the major incidents. The Chicxulub impact crater in Mexico, for example, formed when a meteorite, between 7 and 50 miles in diameter, slammed into the planet 66 million years ago.
But if you rewind further back in history, 600 million years ago, all signs of impacts have been covered up by erosion, volcanoes and other natural resurfacing processes.
The moon is a different story. Without weather and erosion, the 59 large craters on the lunar surface have remained virtually unchanged over the ages. And scientists can study these ancient lunar craters to get a better understanding of the space objects that likely hit Earth in the distant past, before the sands of time concealed the evidence.
Chicxulub impact crater
In a new study published in Nature Communications, a team of researchers examined data collected by Japanese Space Agency's lunar orbiter Kaguya. The team determined that a massive asteroid shower hit the Earth-Moon system about 800 million years ago, when Earth's early multicellular animals were just undergoing their first splits.
This catastrophic event likely occurred after an asteroid 62 miles in diameter was disrupted and struck both the moon and Earth. The total mass of the shower was far greater than that which created the Chicxulub crater, and it might've triggered the ice age, according to the researchers.
Eight lunar craters that were likely formed simultaneously.
Terada et al.
"...it is not strange that an asteroid shower 800 million years ago might have triggered the Ice age, because a total mass flux 800 million years ago is 10 -100 times larger than those of Chicxulub impact and/or a meteoroid shower 470 million years ago," Kentaro Terada, lead study author and professor at Osaka University in Japan, told CNN.
By measuring the density of the smaller lunar craters that lie inside bigger ones, the team determined that eight of the moon's 59 craters likely formed at the same time. NASA data supports this hypothesis. In 1969, the Apollo 12 mission collected lunar samples ejected from the 58-mile-wide Copernicus crater. The samples were estimated to be 800 million years old.
Terada et al.
Although no complex animals would've been around to witness the impact on Earth, the asteroid shower could've brought elements to Earth that "influenced marine biogeochemical cycles" and caused "severe perturbations to Earth's climate system and the emergence of animals," the authors wrote.
Catastrophic impacts like these are extremely rare, occurring only once every 100 million years or so. In modern history, the most recent major impact was likely the Tunguska event, which occurred in Eastern Russia in 1908 when a meteor blitzed through the atmosphere and exploded, leveling some 80 million trees over 830 square miles, possibly killing several people.
Astrophysicist Michelle Thaller talks ISS and why NICER is so important.
- Being outside of Earth's atmosphere while also being able to look down on the planet is both a challenge and a unique benefit for astronauts conducting important and innovative experiments aboard the International Space Station.
- NASA astrophysicist Michelle Thaller explains why one such project, known as NICER (Neutron star Interior Composition Explorer), is "one of the most amazing discoveries of the last year."
- Researchers used x-ray light data from NICER to map the surface of neutrons (the spinning remnants of dead stars 10-50 times the mass of our sun). Thaller explains how this data can be used to create a clock more accurate than any on Earth, as well as a GPS device that can be used anywhere in the galaxy.
You think you've had a day where everything that went wrong could? T-Rex has you beat.
- A new study suggests that the object that brought about the end of the dinosaurs crashed into the Earth at a 60-degree angle.
- This is about the worst possible angle for such an impact.
- The findings also help explain the nature of the impact crater in Yucatan.
Talk about bad luck
The angle of an asteroid impact can have effects on the aftermath every bit as dramatic as increasing or decreasing the size of the asteroid itself.
According to the findings of this study, the asteroid struck Earth at around sixty degrees. At that angle, the amount of climate-changing gas released by the impact is up to three times higher than the amount released by an impact at a lower one. The result of this was a global impact winter that doomed the dinosaurs and took a fair amount of other plant and animal life down with them.
Had it struck at a lower angle, the force of the impact would have been dispersed more widely in more shallow layers of rock, sending fewer gasses into the air. A review of most craters suggests that impactors tend to come in at low angles. The odds of one coming in at sixty degrees or above is just one in four.
This was made worse by the location, just off the coast of what is now Yucatan. Gypsum deposits at the impact site would have released vast amounts of sulfur gas into the atmosphere, as described above. If the impact site had been somewhere else with a different geological makeup, fewer climate-altering gasses would have been released by the impact.
Sometimes, you just can't win.
The result of this perfect storm of high impact angle and sulfate laden location was apocalyptic. The impactor, assumed in this study to be a 12 kilometers (7 miles) wide asteroid made of granite, slammed into the Earth at terminal velocity. It blew a hole in the crust perhaps 30 kilometers (19 miles) deep, and sent up mountains of fluidized rocks to rival the Himalayas before they collapsed.
Endless supplies of vaporized sulfur were released into the atmosphere, severely reducing the amount of solar radiation reaching the Earth. Some estimates suggest this was severe enough to make photosynthesis impossible.
How do we know all this? I mean, it was 65 million years ago, and the dinosaurs didn't leave notes.
We do know what the impact crater looks like; you can see it for yourself in the Yucatan. The part that is on land is known for its sinkholes, which map out the impact site. If you know that you can model a variety of scenarios and compare them to the conditions we see. If they match, we have a winner. This is what the scientists did.
Professor Collins of the Imperial College of London and the lead author of this study explained the results: "If you run the model at different impact angles, at 30 degrees and at 45 degrees, say, you can't match the observations - you get centres of mantle uplift and of the peak ring on the downrange side of the crater centre. And for a straight overhead impact, at 90 degrees, the centres are all on top of each other. So, that's doesn't match the observations, either."
As a result, we know that if the angle of impact was flatter it would have produced different effects, and the people reading this might be advanced dinosaurs rather than intelligent apes. Likewise, Yucatan might not have its famous, beautiful sinkholes.
Now that would be a tragedy.