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.
Differences in the way that the Hubble constant—which measures the rate of cosmic expansion—are measured have profound implications for the future of cosmology.
- The Hubble constant is used to estimate the rate of expansion of the universe.
- There are two different ways to calculate its value, but they give different results.
- The difference may give physicists an opening to find new cosmic laws, but there is huge uncertainty about which path to take in finding them.
There's something wrong with the universe. Okay, it's not the universe that's the problem; it's our understanding of the universe. The problem lies with cosmology—the branch of science that studies cosmic evolution—and it's only getting worse. But that may, or may not, turn out to be a good thing.
Talk to an astronomer or a physicist about the state of the art in understanding the universe and they'll tell you we've entered the "Precision Age" of cosmology. The data relevant to cosmic evolution have gotten so good we know all the relevant parameters – things like the universe's age and average density – down to a few decimal places. That's a pretty impressive achievement.
One of the most important of these cosmic parameters is what's known as the Hubble constant (cosmologists write it as Ho). Modern cosmology tells us the universe has been expanding since its beginning in the Big Bang. The Hubble constant specifies the rate of that expansion. It's also related to the age of the universe. Larger values of Ho mean a younger universe. Smaller values of Ho mean an older universe.
A conflict between different ways of measuring [the Hubble constant] is now making big news in cosmology, and no one is sure what's the right next step.
Back when Edwin Hubble first discovered that the universe was expanding, his crude data gave Ho = 500 (we'll ignore the units). This value was so large it gave an age of the universe that was shorter than the age of the sun or the earth. Better measurements soon gave much lower values of Ho, resolving this conflict. But the idea of conflicts with measured values of Ho didn't go away. A conflict between different ways of measuring Ho is now making big news in cosmology, and no one is sure what's the right next step.
More constants, more problems
There are basically two modern ways to measure the Hubble constant. The first is based on looking at what cosmologists call the "late" universe. Astronomers try to make direct measurements of how fast distant objects are moving away from us (i.e., their redshift). There are two parts to these kinds of observations. First, astronomers need an accurate measurement of an object's distance. Then they need to obtain an accurate measurement of its redshift. Using supernovae as "standard candles" for getting distances to far away galaxies, this late universe method gives a value of the Hubble constant of Ho = 74.03.
The other method relies on data from the "early" universe, i.e., right after the Big Bang. Microwave radiation emitted by matter about 300,000 years after the cosmic beginning provides astronomers with a rich source of early universe measurements. The best data from this cosmic microwave background comes from the Planck satellite launched back in 2009. And the best analysis of the Planck data yields Ho = 67.40, which is clearly not the same value as supernova data. Hence the two methods produce conflicting results. Not knowing which value is right, we can't pin down other properties like, for example, the exact age of the universe.
The conflict between the two approaches is itself not news. People have been playing this game for a while, and during all that time, there was always some difference between the early and late universe approaches. But everyone thought it was just a matter of time until new and better data resolved the conflict. Eventually, it was believed, the final value would lie somewhere between Ho = 74.03 and Ho = 67.40. But things haven't worked out that way and that is news.
Over the last few years, measurements of the late universe approach have been getting better and better. This means the inherent "errors" or "uncertainty" in this value of Ho are getting so small there's no chance for a reconciliation with the early universe methods. The gold standard for a measurement is when it achieves the "5 sigma" level, which basically means the confidence in the measured value reaches astronomical (no pun intended) levels. With measurements announced in 2019, the late universe value of Ho was close, or had crossed, the 5 sigma threshold.
So, if the late universe measurement is solid, then what's going on? What are cosmologists missing? The most exciting possibility is that the conflict is not about errors in measurement or analysis but instead point us towards the holy grail of new physics.
To make their early universe measurements of Ho, cosmologists must heavily rely on their dominant cosmological model. This is something called the "Lambda Cold Dark Matter" model or Lambda-CDM. It is based on the universe being made mainly of dark energy (lambda) and a slow moving form of dark matter. This model (or theory) makes predictions that have been very, very well tested. In other words, it works. But the tension between the two methods of determining Ho has some cosmological theorists ready to make changes to Lambda-CDM that could have big consequences for our understanding of the universe. These changes range from just fiddling with the nature of dark energy all the way up to changing Einstein's theory of relativity.
The problem is Lambda-CDM works so well, in so many ways, that it's not something one throws out lightly. Any change to any of its components will have consequences that can mess up the places that it already does work in explaining what we see in the cosmos. What all this means is that the tension in Hubble's constant offers us a lesson in how science progresses. Cosmologists have a paradigm they love and it mostly works. But along comes this problem and, as philosopher of science Thomas Kuhn pointed out, there are typical ways scientists will respond to the problem. At first everyone thinks the problem will go away. But then it doesn't. So what should they do? They could tinker with the old theory in a way that looks jury-rigged. They could abandon the old theory entirely at enormous cost. They could also keep poking around and hope things work themselves out. So what should they do? What would you do?
We're cautiously optimistic about our new findings.
Dark matter, microscopic black holes and hidden dimensions were just some of the possibilities. But aside from the spectacular discovery of the Higgs boson, the project has failed to yield any clues as to what might lie beyond the standard model of particle physics, our current best theory of the micro-cosmos.
So our new paper from LHCb, one of the four giant LHC experiments, is likely to set physicists' hearts beating just a little faster. After analysing trillions of collisions produced over the last decade, we may be seeing evidence of something altogether new – potentially the carrier of a brand new force of nature.
But the excitement is tempered by extreme caution. The standard model has withstood every experimental test thrown at it since it was assembled in the 1970s, so to claim that we're finally seeing something it can't explain requires extraordinary evidence.
The standard model describes nature on the smallest of scales, comprising fundamental particles known as leptons (such as electrons) and quarks (which can come together to form heavier particles such as protons and neutrons) and the forces they interact with.
There are many different kinds of quarks, some of which are unstable and can decay into other particles. The new result relates to an experimental anomaly that was first hinted at in 2014, when LHCb physicists spotted "beauty" quarks decaying in unexpected ways.
Specifically, beauty quarks appeared to be decaying into leptons called "muons" less often than they decayed into electrons. This is strange because the muon is in essence a carbon-copy of the electron, identical in every way except that it's around 200 times heavier.
You would expect beauty quarks to decay into muons just as often as they do to electrons. The only way these decays could happen at different rates is if some never-before-seen particles were getting involved in the decay and tipping the scales against muons.
While the 2014 result was intriguing, it wasn't precise enough to draw a firm conclusion. Since then, a number of other anomalies have appeared in related processes. They have all individually been too subtle for researchers to be confident that they were genuine signs of new physics, but tantalisingly, they all seemed to be pointing in a similar direction.
The big question was whether these anomalies would get stronger as more data was analysed or melt away into nothing. In 2019, LHCb performed the same measurement of beauty quark decay again but with extra data taken in 2015 and 2016. But things weren't much clearer than they'd been five years earlier.
Today's result doubles the existing dataset by adding the sample recorded in 2017 and 2018. To avoid accidentally introducing biases, the data was analysed "blind" – the scientists couldn't see the result until all the procedures used in the measurement had been tested and reviewed.
Mitesh Patel, a particle physicist at Imperial College London and one of the leaders of the experiment, described the excitement he felt when the moment came to look at the result. "I was actually shaking", he said, "I realised this was probably the most exciting thing I've done in my 20 years in particle physics."
When the result came up on the screen, the anomaly was still there – around 85 muon decays for every 100 electron decays, but with a smaller uncertainty than before.
What will excite many physicists is that the uncertainty of the result is now over "three sigma" – scientists' way of saying that there is only around a one in a thousand chance that the result is a random fluke of the data. Conventionally, particle physicists call anything over three sigma "evidence". However, we are still a long way from a confirmed "discovery" or "observation" – that would require five sigma.
Theorists have shown it is possible to explain this anomaly (and others) by recognising the existence of brand new particles that are influencing the ways in which the quarks decays. One possibility is a fundamental particle called a "Z prime" – in essence a carrier of a brand new force of nature. This force would be extremely weak, which is why we haven't seen any signs of it until now, and would interact with electrons and muons differently.
Another option is the hypothetical "leptoquark" – a particle that has the unique ability to decay to quarks and leptons simultaneously and could be part of a larger puzzle that explains why we see the particles that we do in nature.
Interpreting the findings
So have we finally seen evidence of new physics? Well, maybe, maybe not. We do a lot of measurements at the LHC, so you might expect at least some of them to fall this far from the standard model. And we can never totally discount the possibility that there's some bias in our experiment that we haven't properly accounted for, even though this result has been checked extraordinarily thoroughly. Ultimately, the picture will only become clearer with more data. LHCb is currently undergoing a major upgrade to dramatically increase the rate it can record collisions.
Even if the anomaly persists, it will probably only be fully accepted once an independent experiment confirms the results. One exciting possibility is that we might be able to detect the new particles responsible for the effect being created directly in the collisions at the LHC. Meanwhile, the Belle II experiment in Japan should be able to make similar measurements.
What then, could this mean for the future of fundamental physics? If what we are seeing is really the harbinger of some new fundamental particles then it will finally be the breakthrough that physicists have been yearning for for decades.
We will have finally seen a part of the larger picture that lies beyond the standard model, which ultimately could allow us to unravel any number of established mysteries. These include the nature of the invisible dark matter that fills the universe, or the nature of the Higgs boson. It could even help theorists unify the fundamental particles and forces. Or, perhaps best of all, it could be pointing at something we have never even considered.
So, should we be excited? Yes, results like this don't come around very often, the hunt is definitely on. But we should be cautious and humble too; extraordinary claims require extraordinary evidence. Only time and hard work will tell if we have finally seen the first glimmer of what lies beyond our current understanding of particle physics.
Harry Cliff, Particle physicist, University of Cambridge; Konstantinos Alexandros Petridis, Senior lecturer in Particle Physics, University of Bristol, and Paula Alvarez Cartelle, Lecturer of Particle Physics, University of Cambridge
Researchers propose a new method that could definitively prove the existence of dark matter.
- Scientists identified a data signature for dark matter that can potentially be detected by experiments.
- The effect they found is a daily "diurnal modulation" in the scattering of particles.
- Dark matter has not yet been detected experimentally.
Dark matter, a type of matter that is predicted to make up around 27 percent of the known universe, has never been detected experimentally. Now a team of astrophysicists and cosmologists think they found a clue that may lead them to finally detect the elusive material, so hard to find because it does not absorb, reflect, or emit light.
The existence of dark matter has so far been predicted by inference from its gravitational effects on the motion of the stars and galaxies rather than direct observation. No existing technologies can pick it out. This has led researchers at the Shanghai Jiao Tong University and the Purple Mountain Observatory of the Chinese Academy of Sciences to identify characteristic dark matter signatures that would be easier to detect.
Their new paper proposes a new type of effect that relates to the so-called "sub-GeV dark matter" which is boosted by cosmic rays. Looking for this effect can potentially allow direct detection of dark matter using nuclear recoil techniques.
The diurnal effect of accelerated dark matter rays. Credit: Ge et al.
The research team included Shao-Feng Ge and Qiang Yuan, who explained that their approach is to look for a prominent signature of accelerated dark matter particles that come from the galaxy's center, where dark matter and cosmic rays are at high density. They found that these particles have a "diurnal modulation" – a scattering pattern that is linked to the time of day. At periods when the Galaxy Center faces the side of the planet that's opposite the location of the detector, the Earth shadows a large amount of these particles. At other times, they come in as a signal with "higher recoil energy."
"The conventional diurnal effect is only for slow moving (nonrelativistic) DM particles in our galaxy (so-called standard DM halo)," Ge and Yuan said to Phys.org. "The effect is negligibly small either from direct experimental constraints, or due to the detection threshold. For light DM particles, on the other hand, the DM-nucleus interaction is much less constrained, which leaves room for strong diurnal modulation."
Researchers Ning Zhou and Jianglai Liu, who were also involved in the study, said in an interview that the signature they are proposing could be "a smoking gun of cosmic ray boosted dark matter detection".
The researchers plan next to look for the signature in previously gathered data, as well as in underground dark matter experiments.
They are also encouraging scientists around the world to look for this signature in their data.
Check out the new paper "Diurnal Effect of Sub-GeV Dark Matter Boosted by Cosmic Rays" published in Physical Review Letters.