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.
Sitting Ducks
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.
You might not have heard of them if you aren't an astronomer, but the largest known objects in the universe aren't galaxies or the super-clusters they form together. They're actually ghostly webs of dark matter that form the boundary between the voids of deep space and the clusters of galaxies where stars shine, planets form, and most of the astronomical phenomena you know reside.
This filament, which spreads throughout the cosmos forming a foam-like structure, attracts dust along its main stretches while galaxies seem to cluster at its nodes. Despite the massive size of these filaments—a typical length would be in the 200-500 million light-year range—it isn't easy to actually see these things directly.
This is why a new study, published in Astronomy and Astrophysics, is so exciting. It provides the first direct look at the cosmic spider web holding the universe together and reveals hidden galaxies to astronomy.
The universe is held together by cosmic spider webs?
"The image shows the light emitted by hydrogen atoms in the cosmic web in a region roughly 15 million light years across. In addition to the very weak emission from intergalactic gas, a number of point sources can be seen: these are galaxies in the process of forming their first stars."
© Jeremy Blaizot / projet SPHINX
Lots of things in space are hard to look at directly, but it is possible to observe their effects on things near them. Ever since the filament was first noticed in the 1980s, astronomers have been looking at the effect it has on light, such as how it can refract the light from objects behind it when it sits between that object and Earth, and how it interacts with extremely bright quasars. While this provided some data, it left much to be desired.
Luckily, science marches forward, and it was probably inevitable that somebody would figure out how to get a better look at the stuff.
Using the aptly named Very Large Telescope in Chile and a device called the Multi-Unit Spectroscopic Explorer, an international team of researchers aimed at Hubble Ultra-Deep Field. This region, known for being where some of the most revealing images of the cosmos are taken from, was observed for 155 hours, 140 of which produced useful images. After a year of processing, the team produced these images:
The blue is the hydrogen collecting near the filament. The background is the Hubble Ultra-Deep Field Image.
Credit: Roland Bacon/David Mary/ESO/NAS
The long exposure time allows for the dim light from hydrogen emissions to be collected and formed into an image.
The images you see also include a large number of galaxies that previously escaped detection. A follow-up analysis of the data also suggested that the hydrogen detected by the spectroscopic explorer could be accounted for by assuming the presence of a large number of previously unknown dwarf galaxies. While these galaxies are currently too small to see individually, follow-up studies will know where to start looking for them.
As lead author Roland Bacon explained to CNN:
"We cannot see these galaxies, because they are intrinsically faint and too far: we are observing them 2 billion years after the Big Bang -- at a distance of 11 billion light-years. But there are so many that we can see the integrated light produced by them."
While fascinating in its own right, this discovery will lay the foundations for further study of the filament and may lead to a new understanding of dwarf galaxy formation.
