Although this scenario is realistic in many ways, it is completely fictional and does NOT describe an actual potential asteroid impact.
An asteroid is discovered on February 11, 2022 by a NASA-funded asteroid survey telescope. After the detection is confirmed by other observatories on the following night, the discovery is officially announced by the Minor Planet Center (MPC), and the asteroid is assigned the designation “2022 TTX”. (To reinforce the fact that this is not a real asteroid, we are using three letters in this designation, something that would never be done for a real asteroid.)
The discovery announcement triggers JPL’s Center for Near-Earth Object Studies (CNEOS) to download the available tracking observations for 2022 TTX (a dozen sky position measurements over two nights), and calculate its orbit. The asteroid is added to the JPL small-body database, and its orbit posted online. As can be seen from the CNEOS orbit viewer, the asteroid’s eccentric orbit extends from within the orbit of the Earth to just outside the orbit of Mars.
CNEOS invokes its Sentry impact monitoring system to check whether 2022 TTX has any chance of impacting Earth. Sentry identifies several future dates when an impact is possible, the most likely of which is August 16, 2022 – only six months away. When 2022 TTX is first announced, its probability of impact is quite low, about 1 chance in 2500. Asteroid observers are strongly encouraged to make more observations of this asteroid so that more accurate predictions of its future motion can be made.
At discovery, 2022 TTX is far from Earth (37 million miles or 60 million kilometers) and very faint (magnitude 21.5). It is tracked over the next few nights by several large observatories around the world, and these observations help make the asteroid’s orbit better determined.
Meanwhile, archival sky survey images taken from the week before discovery are analyzed, and pre-discovery detections (“precoveries”) are found. Although the asteroid was too faint for a definitive detection in those images, a marginal detection becomes possible once the asteroid’s approximate position was calculated.
As the tracking dataset for 2022 TTX grows, the accuracy of the orbit estimate improves, and its predicted position on the potential impact date becomes more certain. Since the Earth continues to remain within the narrowing envelope of possible trajectories on August 16, the impact probability increases. By 16 February 2022, the date of Module 0, the impact probability has risen to 5%.
The following diagram shows the orbits of 2022 TTX and Earth and their positions at the time the asteroid was discovered on February 11, 2022. Both bodies orbit the Sun in a counter-clockwise direction. The point at which the orbits intersect, and where an impact is possible on August 16, is indicated by the small red box. In three dimensions, the asteroid’s orbit is inclined by about 16 degrees: this diagram is a projection of the asteroid orbit into the plane of the Earth’s orbit. The asteroid moves above the plane of this diagram over the six months between discovery and the potential impact.
|Orbit of asteroid 2022 TTX|
|Current uncertainty in predicted position of asteroid 2022 TTX on August 16, 2022|
As the uncertainty region sweeps past Earth on August 16, only about 5% of it impacts our planet: that 5% fraction is the impact probability. The geographic locations of all the possible impacts forms the “impact region” on the Earth. Since the current uncertainty region in space is so large, the impact region on Earth covers an entire hemisphere, basically the hemisphere that faces the oncoming asteroid. The impact region even extends beyond the asteroid-facing hemisphere of Earth, because Earth’s gravity will cause some trajectories that might otherwise just miss Earth to curve towards impact.
The following images show the extent of the large region, here shaded in red/purple, where 2022 TTX could potentially impact on August 16, 2022. The region covers roughly 2/3 of Earth’s surface.
|Potential impact region for 2022 TTX|
|Potential impact region for 2022 TTX|
|Potential impact region for 2022 TTX|
Very little is known about the physical properties of 2022 TTX, parameters such as its size, shape, density and mass. This lack of knowledge does not affect the orbital calculations, since the trajectory of an asteroid is basically the same regardless of its size. But if the asteroid is headed for an impact, it will be very important to predict the extent of potential damage, and those predictions are highly dependent on the impactor’s physical parameters.
Measurements of an asteroid’s brightness can be used to provide a rough size estimate, but an assumption must be made on the asteroid’s reflectivity (referred to as “albedo”). For 2022 TTX, the brightness measurements indicate a size of about 100 meters (330 feet). But that estimate assumes an average asteroid reflectivity, and the reflectivity of this asteroid is not known. Since reflectivities vary widely from one asteroid to another, the size estimate for 2022 TTX is highly uncertain. If the asteroid’s surface is very dark, the size could be as large as ~400 meters (~1000 feet), while if it’s very bright it could be as small as ~40 meters (~100 feet).
The asteroid’s size is not the main parameter that needs to be known. Mass and strength are the key parameters for predicting the potential damage region and population risk for an impact, and for 2022 TTX, these are even more uncertain. The asteroid’s mass can estimated from its bulk density, but the density is also unknown. A wide range of possible densities would have to be accounted for. The bottom line for 2022 TTX is that its mass is extremely uncertain, by orders of magnitude, and predictions for the possible damage effects are similarly highly uncertain, again, by orders of magnitude.
Based on the full range of possible physical parameters for 2022 TTX, the possible energy released on impact would range from 1 Mt to 3 Gt (TNT equivalent), a 3-orders-of-magnitude range. The predominant hazard is an airburst causing blast overpressures possibly reaching unsurvivable levels. The size of the potential blast damage area could range from local (a few kilometers) at the small end of possible sizes, to regional (hundreds of kilometers) at the large end.
2022 TTX is approaching our planet at about 7.3 km/s (16,000 mph), and brightening somewhat, but it is heading “above” Earth’s orbital plane and will soon start receding from Earth and fading in brightness. Its closest approach to Earth on March 1 will be at a distance of 34 million miles (54 million kilometers), which is far too distant for a radar detection. Eventually 2022 TTX will approach much closer, but that doesn’t happen until July and August.
2022 TTX will be observable using large (at least 2-meter) ground-based optical telescopes on most nights up to its potentially hazardous encounter in August. The only foreseeable interruptions will be interference from the Moon for a few days every month. But the asteroid will generally be bright enough and far enough from the daytime sky to be observed using large optical telescopes.
Observations of 2022 TTX over the upcoming weeks and months will result in its orbit becoming better and better determined and the uncertainty region for the August 16 encounter increasingly smaller. Each time a new batch of observations becomes available, a new orbit is calculated and the impact probability is reassessed. It is not yet possible to predict whether future assessments will indicate the asteroid will miss the Earth or hit, but the chances that the impact will eventually be ruled out are high (95%).
Sky-image archives are now being searched for possible pre-discovery observations of the region of sky the asteroid may have traversed 7 years ago, when it made a distant pass by our planet. If the asteroid can be detected in those images, the observation timespan would extend to 7 years, and the orbit accuracy would improve dramatically. The predicted uncertainty region would then become some compact that the impact probability would jump to either 0% or 100%. In the latter case, the impact region would also become quite well defined.
The NEOWISE spaced-based infra-red satellite, still in operation, could be tasked to observe 2022 TTX, since it will pass through the satellite’s field of view in a month or so. An infra-red detection could provide a measure of the asteroid size. But 2022 TTX will be very distant, and likely too faint for NEOWISE to detect it, unless it is at the extreme large end of its possible size range.
A Google Earth kml file for the impact region shown above is available here.
The orbit for a “worst case” trajectory for 2022 TTX has been loaded into JPL’s online HORIZONS system, and can be accessed via the name “2022 TTX” or “TTX22”. This orbit is “worst-case” in the sense that it is the trajectory that impacts nearest the center of the “forward-facing” hemisphere on Aug. 16, 2022. HORIZONS can be accessed with this object preloaded via this web-interface here.
For those familiar with the SPICE Toolkit software, an SPK file for this orbit is available here:
This SPK file is consistent with and contains additional DE431 planetary ephemeris information over the time-span 1998-Jan-01 through impact on 2022-Aug-16, permitting retrieval of object state vectors at any arbitrary instant within that timespan.
The worst-case orbit for 2022 TTX has also been loaded into the JPL/Aerospace Corp. NEO Deflection App. This on-line tool allows users to study the velocity change (delta-v) required to deflect the 2022 TTX trajectory away from the Earth, as a function of deflection time. Specific amounts of impulsive velocity change can be applied at specific times before impact and the resulting deflection in the impact target plane is shown. The App can also be configured to calculate kinetic impactor spacecraft trajectories, using the maximum spacecraft masses that can be launched onto those trajectories by various launch vehicles. The App calculates the delta-v applied to the asteroid when the kinetic impactor hits it, and calculates the resulting new position in the target plane of the impact encounter. A complete description of the app is available here.
The 2019 PDC trajectory is also loaded into the App along with trajectories of many other simulated Earth impactors.