Published on January 9, 2025 7:59 PM GMT
This is a post I originally wrote for the effective altruism forum, which you can read here. But I recently re-examined my probability estimates and updated the post with some additional cosmic threats, so I decided to also adapt it for lesswrong too.
Asteroid impacts receive much more focus than any other risk arising from space - we have sent two missions to test and evaluate asteroid deflection, and asteroid impacts are common in popular culture (e.g. Dont Look Up and anything related to dinosaurs). Even in The Precipice, Toby Ord only covered 'Asteroids and Comets' and 'Stellar Explosions'. This focus may cause most cosmic threats like supernova explosions, solar flares, and pulsar beams to be grouped together as a set of extremely low probability events. This is true, but they are also independent of each other and require separate analyses of their probability and impact. These other cosmic threats may also be overlooked by researchers, potentially causing us to miss signs that they may occur in the future. Research on the severity and probability of many cosmic threats on this list is missing, outdated, or scarce.
So I thought it would be useful to provide an up-to-date and exhaustive list of all cosmic threats. I'm defining cosmic threat here as any global catastrophic risk potentially arising from space.
I will list each cosmic threat, provide a brief explanation, and find the best evidence I can to provide severity and probability estimates for each. Enjoy :)
I'll use this format:
Cosmic Threat [Severity of worst case scenario /10] [Probability of a scenario as bad as that occurring in the next 100 years] Explanation of threat
Explanation of rationale and approach
Severity estimates
Severity estimates are from 0-10, where 10 is the extinction of all intelligent life on Earth, and 5 is destruction at a similar scale to the destruction of multiple cities. It was difficult to pin down one number for threats with multiple outcomes (e.g. asteroids have different sizes). So the severity estimates are for the worst-case scenarios for each cosmic threat, and the probability estimate corresponds to an event occurring that is as severe as that scenario. Note that there are much more informative ways of doing this, but I focused on providing an intelligible overview that people can dive further into if they want to.
Probability estimates
Probabilities are presented as % chance of a worst case scenario-type event occurring in the next 100 years. I have taken probabilities from the literature and converted values to normalise them as a probability of their occurrence within the next 100 years (as a %). This isn't a perfect way to do it, but I prioritised getting a general understanding of their probability, rather than numbers that are hard to imagine. When the severity or likelihood is unclear or not researched well enough, I've written 'unknown'.
I'm trying my best to ignore reasoning along the lines of "if it hasn't happened before, then it very likely won't happen ever or is extremely rare" because of the anthropic principle. Our view of past events on Earth is biased towards a world that has allowed humanity to evolve, which likely required a few billion years of stable-ish conditions. So it is likely that we have just been lucky in the past, where no cosmic threats have disturbed Earth's habitability so extremely as to set back life's evolution by billions of years (not even the worst mass extinction ever at the Permian-Triassic boundary did this, as reptiles survived).
An Exhaustive List of Cosmic Threats
Format:
Cosmic Threat [Severity of worst case scenario /10] [Probability of a scenario as bad as that occurring in the next 100 years] Explanation of threat
Solar flares [1/10] [10-20%(1,2)]. Electromagnetic radiation erupts from the surface of the sun. Solar flares occur fairly regularly and cause minor impacts, mainly on communications. A large solar flare has the potential to cause electrical grids to fail, damage satellites, disrupt radio signals, cause increased radiation influx, destroy data storage devices, cause navigation errors, and permanently damage scientific equipment. The largest solar flare in history was in 1859, the "Carrington Event". Solar flares have also caused local black outs like the 1989 Quebec blackout. This threat is mainly managed by the World Meteorological Organisation (WMO) and COSPAR.
Super flares [9/10] [0.1%-0.16%] Super flares are like solar flares but they could lead to changes to Earth's surface temperature and the destruction of our ozone layer, though the predicted effects are still unknown. Some predict that space weather events like these have the potential to cause the extinction of many species and severe destruction to technology and global infrastructure. Resulting failures in nuclear threat detection or global panic could trigger other x-risks. This threat is mainly managed by the World Meteorological Organisation (WMO) and COSPAR.
Supernova explosions [8/10] [~0.001%]. According to this study, the closest stars that could pose a threat to humanity if they went supernova are IK Pegasi and Betelgeuse, but they are not expected to go supernova until 1.9 billion years and several million years, respectively. However, no systematic survey of all white dwarf stars (e.g. using GAIA data) has been conducted, and there may be others. The impact of a supernova explosion would be quite devastating to life on Earth, primarily due to damage to our ozone layer. This threat is mainly managed by ESAC in theory.
Kilonovas [8/10] [<0.001%]. Binary neutron star systems (or binary systems of a neutron star and a black hole) pose a potential threat. If the neutron stars merge, they can generate a gamma ray burst followed by a kilonova. Gamma-ray bursts could destroy our ozone layer and radioactivate our environment, and the resulting kilonova will have similar effects to a supernova explosion. There have been very few detections of binary neutron star systems (see intro of this paper), but they are much rarer than supernovae. So the probability can be constrained to 'lower than supernovae explosions'. This threat is mainly managed by ESAC in theory.
Large Asteroid Impacts [10/10] [0.02%]. This has happened many times in Earth's past. Space missions such as DART, Hera, and NEOWISE have prepared us well to detect and deflect asteroids. We have evidence that asteroids have the potential to cause extinction events through direct impact destruction, tsunamis, and giant ash clouds that block out the sun. This threat is mainly managed by SMPAG and IAWN.
Other Impacts [6/10] [a: 0.003% b: 0.06%]. Other near-Earth objects (not necessarily asteroids - there are many smaller objects in the Solar System) smashing into Earth are common. Probability 'a' is the probability that an object impacts and kills more than 1 million people. Probability 'b' is the probability that an object impacts and forms a crater larger than 1km in diameter. This threat is mainly managed by SMPAG and IAWN.
Conflict with intelligent alien life [10/10] [unknown]. Pretty self-explanatory. Hopefully no aliens exist that want to invade and kill us all. No one manages this threat seriously, the closest thing is SETI.
Alien Technology [10/10] [unknown]. Conflict with alien technology is slightly more likely than direct conflict with intelligent alien life. Self-replicating robots may have been sent out throughout the galaxy, consuming the resources of a planet, replicating themselves, and moving on. This is theoretically possible, and the universe is a very large place. SETT is an off-shoot of SETI, in recognition of the fact that we're more likely to find signs of alien technology than of life itself.
Rogue Celestial Bodies [10/10] [0.002%]. Rogue celestial bodies include black holes, planets, and stars that are not gravitationally bound but wander around the galaxy. One of these celestial bodies could potentially enter our Solar System. There are many exciting possibilities from this point.. Earth could be knocked out of its orbit, sending us hurtling through open space. Another planet (or planetoid) could impact us, or if the rogue celestial body is exotic, we could be swallowed by a black hole or boiled by a second sun. Managing this threat is futile.
Vacuum decay [10/10] [unknown]. Vacuum decay is a hypothetical scenario in which a more stable vacuum state exists than our current "false vacuum". A bubble of this true vacuum could form somewhere in the universe or in a high-energy particle accelerator. To quote Nick Bostrom, "This would result in an expanding bubble of total destruction that would sweep through the galaxy and beyond at the speed of light, tearing all matter apart as it proceeds.". The standard model of physics is not yet developed enough to pin down whether this is actually possible. No one manages this from a cosmic threats perspective, but research on vacuum decay is quite active in cosmology and quantum field theory research.
Magnetar flares [9/10] [unknown]. Similar to solar flares, except with less research into the probability of their occurrence. A magnetar is a neutron star with an extremely powerful magnetic field. It sends out high-energy electromagnetic radiation like X-rays and gamma rays. This threat is mainly managed by ESAC in theory.
Alien Microbes [7/10] [<0.0001%]. Some have considered cancelling NASA and ESA's Mars Sample Return mission due to concerns about biosecurity. Termed back contamination in astrobiology (as opposed to forward contamination where we contaminate Mars samples with life from Earth), the idea is that bringing back extremely hardy life that may have evolved on Mars could either cause a pandemic or introduce a species capable of outcompeting microbes on Earth, undercutting ecosystems. This threat is managed extremely seriously by NASA, ESA, COSPAR and CETEX.
Pulsar beams [9/10] [unknown]. "A pulsar (from pulsating radio source) is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles." Pulsar beams hit Earth frequently and don't cause much harm, but if a pulsar were to be very close to us, it could wipe out our ozone layer and expose us to the radiation of space - not good. This threat is mainly managed by ESAC in theory.
Cosmic Rays from Galactic Core Explosions [10/10] [unknown]. Hundreds of thousands of times more damaging than supernova explosions, these cosmic rays originate from the cores of galaxies. Some theorise that cosmic rays from other galaxies have already caused mass extinctions on Earth. Explosions from the core of the Milky Way likely make the inner galaxy uninhabitable, so large explosions may have catastrophic impacts on Earth. This threat is mainly managed by ESAC in theory.
Quasar ignition [10/10] [unknown]. Quasars form around black holes. "The inflow of gas into the black hole releases a tremendous amount of energy, and a quasar is born. The power output of the quasar dwarfs that of the surrounding galaxy and expels gas from the galaxy in what has been termed a galactic superwind" This "superwind" drives all gas away from the inner galaxy, and would certainly rip off our atmosphere, leaving us rather exposed. This threat is mainly managed by ESAC in theory.
and finally, some honourable mentions...
The heat death of the universe [10/10] [0%]. It's worth the inclusion as the heat death of the universe will eventually destroy everything. It's an inevitable outcome of the application of the first two laws of thermodynamics - entropy increases in an isolated system. So eventually the universe will reach a point where all energy is evenly distributed and not a lot will happen - certainly not life.
The increasing luminosity of the sun [10/10] [0%]. The sun's luminosity is increasing over time. In ~1 billion years the luminosity will be so high that the oceans will boil away and the Earth will no longer be habitable. Hopefully we'll be intergalactic by then!
Artificial cosmic threats [10/10]. In the event that humanity colonises the solar system, the cosmic threat may arise from our descendants. For example, an asteroid orbit may accidentally be placed on a collision path with Earth by messing up stable gravitational interactions, by accidental collisions of resource extraction equipment and asteroids, or re-directed intentionally as a weapon. Other future technologies like stellar engineering projects gone wrong, or by the creation of out of control von-neumann probes could destroy us in the future. Interplanetary war involving interplanetary missiles or lasers is also not an unlikely future scenario given humanity's history.
Other unknown risks [unknown] [unknown]. The space (& physics) community is essentially discovering a new existential threat every few years, and we are likely to discover more. For example, we know very little about dark energy or how common life is in our universe. Most threats are extremely low probability, but maybe the next one won't be.
If you have any feedback, edits, or additions to the list, please comment.
Acknowledgements: I extend my gratitude to Matt Allcock and Darryl Wright for their invaluable discussions and insights on these topics, which significantly contributed to the accuracy and direction of my research. All inaccuracies are my own.
Discuss
