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.
Scientists have long puzzled over how Mars, a cold and dry planet, was once warm enough to support liquid water.
- In a recent study, researchers created a computer model to explore how varying levels of surface ice would have affected clouds above the Martian surface.
- The results showed that icy, high-altitude clouds would have formed if Mars was covered in relatively small amounts of ice. These clouds would have helped warm the planet.
- NASA's Perseverance rover may soon confirm this hypothesis by taking geological samples of the Martian surface.
In 2008, NASA's Phoenix lander directly confirmed the presence of water ice on Mars. It wasn't exactly a surprise. Satellite imagery had previously suggested that, approximately 4 billion years ago, the red planet was flush with lakes and rivers.
But what's long puzzled scientists is how water developed on what's now a cold, dry planet. To support those ancient lakes and rivers, Mars would have needed an atmosphere that produced sufficient warming through the greenhouse effect. The planet's atmosphere is too thin today to produce such warming.
One hypothesis for how Mars once supported water posits that an asteroid collided with the planet, and the resulting heat enabled liquid water to exist. But some researchers have noted that this heating effect would have only lasted a couple years. That wouldn't have been long enough for water to leave the visible geological evidence of lakes and rivers we see today.
A new hypothesis for water on Mars
New research published in PNAS explores another hypothesis: Mars once had icy, high-altitude clouds, similar to cirrus clouds on Earth, that created a greenhouse effect capable of supporting a lake-forming climate.
First proposed in 2013, this explanation has been criticized because it would have required Mars to have had clouds with unusual properties. Specifically, water would have had to stay trapped within clouds for much longer periods of time compared to Earth's water cycle. The recent study sheds new light on how these unusual clouds might have formed and warmed the planet.
Credit: NASA / JPL-Caltech / USGS
In previous versions of the cloud-greenhouse hypothesis, researchers had assumed that large swaths of the Martian surface were covered with ice. Such conditions would have prevented high-altitude clouds from forming. But if the surface had less ice, a layer of high-altitude, icy clouds could have formed.
Lead study author Edwin Kite explained this process to Big Think:
"The distribution of surface water affects the height of the clouds. If there is surface water everywhere on the planet, then the relative humidity will be ~1 in updrafts, and clouds will form at low level in those updrafts. However, if surface water is only found in cold places, most of the surface is warmer than the cold traps, and so low-level clouds can't form over most of the surface (higher temperatures --> lower relative humidity --> no condensation --> no clouds). High up in the atmosphere, temperatures are lower and so clouds can form."
Clouds are complicated
To explore how different amounts of surface water and clouds would have affected the planet, the researchers created a computer model of early Mars. The model represented a planet that was mostly dry but with patches of ice at some locations, like on mountaintops and at the planet's poles. Above these "cold traps," clouds would have formed at low altitudes.
But above the rest of the planet's warmer and drier areas, the researchers noted that "clouds are found only at high altitudes" because the lifting condensation level (LCL) is high. (LCL refers to the height at which an air parcel has cooled enough to become saturated and form clouds. Compared to air near cold traps, air near warm surfaces needs to rise higher to cool enough to form clouds, so it has a higher LCL.)
So, why does cloud height matter in terms of warming?
Kite et al.
"Clouds absorb infrared emitted from the ground and then re-emit it to space (purple arrows; greenhouse effect)," Kite told Big Think. "Planetary energy balance requires that energy in (absorbed sunlight) equals energy out (infrared emitted to space). If the clouds have the right particle size and thickness to effectively absorb infrared, this means that the cloud-top temperature is constant for a given amount of absorbed sunlight."
"If the cloud-top temperature is constant with cloud height, then why does the surface temperature depend on cloud height? This is because below the clouds, the temperature always falls with height within the atmosphere. So if the clouds are higher, then the temperature difference between the cloud tops and the surface must be greater — implying a warmer surface."
Although the model fits with scientists' current understanding of ancient Mars, the researchers said the results don't definitively rule out the collision hypothesis. But NASA's Perseverance rover could soon settle the debate by analyzing samples of Martian rocks, giving scientists insight into the atmosphere of early Mars, and, more broadly, what makes planets habitable.
"Mars is important because it's the only planet we know of that had the ability to support life — and then lost it," Kite said in a press release. "Earth's long-term climate stability is remarkable. We want to understand all the ways in which a planet's long-term climate stability can break down — and all of the ways (not just Earth's way) that it can be maintained. This quest defines the new field of comparative planetary habitability."
The research suggests that roughly 1 percent of galaxy clusters look atypical and can be easily misidentified.
Their results, published in March, suggest that roughly 1 percent of galaxy clusters look atypical and can be easily misidentified as a single bright galaxy. As researchers launch new cluster-hunting telescopes, they must heed these findings or risk having an incomplete picture of the universe.
Galaxy clusters contain hundreds to thousands of galaxies bound together by gravity. They move through a hot soup of gas called the intracluster medium, which contains more mass than all the stars in all the galaxies within it. This hot gas fuels star formation as it cools and emits X-ray radiation that we can observe with space-based telescopes.
This bright gas cloud creates a fuzzy halo of X-rays around galaxy clusters, making them stand out from more discrete point sources of X-rays produced by, for example, a star or quasar. However, some galactic neighborhoods break this mold, as MIT Associate Professor Michael McDonald learned nine years ago.
In 2012, McDonald discovered a cluster unlike any other, which shone bright like a point source in the X-ray. Its central galaxy hosts a ravenous black hole that consumes matter and spews X-rays so bright as to drown out the diffuse radiation of the intracluster medium. In its core, the cluster forms stars at a rate roughly 500 times higher than most other clusters, giving it the blue glow of a young star population instead of the typical red hue of aging stars.
"We'd been looking for a system like this for decades," McDonald says of the Phoenix cluster. And yet, it had been observed and passed over years prior, assumed to be a single galaxy instead of a cluster. "It'd been in the archive for decades and no one saw it. They were looking past it because it didn't look right."
And so, McDonald wondered, what other unusual clusters might be lurking in the archive, waiting to be found? Thus, the Clusters Hiding in Plain Sight (CHiPS) survey was born.
Taweewat Somboonpanyakul, a graduate student in McDonald's lab, devoted his entire PhD to the CHiPS survey. He began by selecting potential cluster candidates from decades of X-ray observations. He used existing data from ground-based telescopes in Hawaii and New Mexico, and visited the Magellan telescopes in Chile to take new images of the remaining sources, hunting for neighboring galaxies that would reveal a cluster. In the most promising cases, he zoomed in with higher-resolution telescopes such as the space-based Chandra X-Ray Observatory and Hubble Space Telescope.
After six years, the CHiPS survey has now come to a close. Today in The Astrophysical Journal, Somboonpanyakul published the survey's cumulative results, which include the discovery of three new galaxy clusters. One of these clusters, CHIPS1911+4455, is similar to the rapidly-star-forming Phoenix cluster and was described in a paper in January in The Astrophysical Journal Letters. It's an exciting finding since astronomers know of just a few other Phoenix-like clusters. This cluster invites further study, however, as it has a twisted shape with two extended arms, whereas all other rapidly-cooling clusters are circular. The researchers believe it may have collided with a smaller galaxy cluster. "It's super unique compared to all the galaxy clusters that we now know," says Somboonpanyakul.
In all, the CHiPS survey revealed that older X-ray surveys missed roughly 1 percent of galactic neighborhoods because they look different than the typical cluster. This can have significant implications, since astronomers study galaxy clusters to learn about how the universe expands and evolves. "We need to find all the clusters to get those things right," McDonald explains. "Ninety-nine percent completion isn't enough if you want to push the frontier."
As scientists discover and study more of these unusual galaxy clusters, they may better understand how they fit into the broader cosmic picture. At this point, they don't know whether a small number of clusters are always in this strange, Phoenix-like state, or if this is perhaps a typical phase that all clusters undergo for a short period of time — roughly 20 million years, a fleeting moment by spacetime standards. It's difficult for astronomers to tell the difference, as they only get a single snapshot of each cluster nearly frozen in time. But with more data, they can make better models of the physics governing these galactic neighborhoods.
The conclusion of the CHiPS survey coincides with the launch of a new X-ray telescope, eROSITA, which aims to grow our catalogue of clusters from a few hundred to tens of thousands. But unless they change the way they look for those clusters, they will miss hundreds that deviate from the norm. "The people that are building out the cluster searches for this new X-ray telescope need to be aware of this work," says McDonald. "If you miss 1 percent of the clusters, there's a fundamental limit to how well you can understand the universe."
This research was supported, in part, by the Kavli Research Investment Fund at MIT, and by NASA through the Guest Observer programs for the Chandra X-ray Observatory and Hubble Space Telescope.
Oxygen is thought to be a biomarker for extraterrestrial life, but there are at least three different ways that a lifeless planet can produce it.
- If an exoplanet houses life, it almost certainly will have gaseous oxygen.
- But a new study modeling the development of rocky planets identifies three scenarios in which oxygen can form abiotically.
- The notion that oxygenated exoplanets are all candidates to host life should be treated with skepticism.
Research that aims to identify exoplanets that might contain life usually use oxygen as a biomarker. But a new study published in AGU Advances explains that this can be very misleading: Oxygen can easily accumulate in an exoplanet's atmosphere without any biological origin.
Oxygen is considered a biomarker because photosynthesis — the process by which plants use sunlight to fix carbon dioxide into sugar — produces oxygen as a waste product. Thus, a planet with oxygen in its atmosphere is considered a strong candidate to host some kind of lifeform.
The team, led by Joshua Krissansen‐Totton of UC Santa Cruz, developed a model of planetary formation that allowed them to tinker with variables that could affect how an Earth-like planet develops. Using their model, the researchers were consistently able to produce three scenarios in which an Earth-like planet has levels of oxygen in its atmosphere similar to ours, but life was not part of the formula.
Three oxygenated worlds with no life
The planetary evolution model. Arrows show the flow of certain substances and heat energy between different layers of the Earth and its atmosphere.Krissansen-Totton et al./ AGU Advances
In the first scenario, an exoplanet has very high levels of carbon dioxide and water in the atmosphere. Under these conditions, a strong greenhouse gas effect means there will be no water on the exoplanet's surface. When hit by ultraviolet (UV) light, water vapor in the upper atmosphere can occasionally split into hydrogen and oxygen. The lighter hydrogen gas escapes into space, leaving the heavier oxygen gas behind.
In the second scenario, an exoplanet "waterworld" contains anywhere from 10 to 230 times as much water as the Earth has today. Under these conditions, the oxygen cycle — which involves the circulation of oxygen through the atmosphere, lifeforms, and rocks — essentially doesn't exist. Pressure from the massive oceans on the crust would shut down the geological activity necessary to recycle oxygen, leaving it in the atmosphere.
In the third scenario, an exoplanet "desertworld" has conditions exactly the opposite of those in the "waterworld." This type of exoplanet has very little water, no more than a third of what Earth has in its oceans. Under these conditions, the molten surface of a young exoplanet can freeze while the limited water supply is still found only as steam (vapor) in the atmosphere. This prevents oxygen from being absorbed by the crust. Then, as with the first scenario, UV light breaks up water into hydrogen and oxygen.
Implications for the hunt for E.T.
An infographic illustratingthe three planets described above and how they might form.Illustration by J. Krissansen-Totton
None of the three scenarios assures an oxygen-rich atmosphere; they simply allow for oxygen to occur abiotically. Professor Krissansen‐Totton described the utility of the model in a press release:
"This is useful because it shows there are ways to get oxygen in the atmosphere without life, but there are other observations you can make to help distinguish these false positives from the real deal. For each scenario, we try to say what your telescope would need to be able to do to distinguish this from biological oxygen."
Such telescopes should be in orbit by 2030. Now the scientists using them know what to look for.
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.