The Asteroid: Final Impact
The Double Asteroid Redirection Test (DART) mission was designed to test a kinetic impact, a technique that humans might use to adjust a threatening asteroid's orbit and keep Earth out of harm's way. Kinetic impact is just a more scientific way to describe slamming something heavy and fast-moving into an asteroid. So that's precisely what the DART spacecraft did tonight (Sept. 26) at 7:14 p.m. EDT (2314 GMT), crashing into a small asteroid called Dimorphos. And the result is a truly spectacular series of images.
Until DART's fleeting visit, scientists knew very little about Dimorphos, which orbits a larger asteroid called Didymos; the system appears as just a point of light to telescopes on Earth. But the spacecraft captured images all the way in, sending home one image every second, with our final view of the asteroid taken about two and a half seconds before the crash, according to a timeline NASA provided before impact.
Over the coming days, scientists will be receiving more images of Dimorphos, ones snapped by the Light Italian Cubesat for Imaging Asteroids (LICIACube), a tiny spacecraft that rode along with DART until earlier this month. LICIACube flew past the impact site just three minutes after the collision, photographing the cloud of debris that DART's abrupt arrival flung into space. However, the cubesat also turned its two cameras to the unscarred side of Dimorphos, giving scientists additional data about the space rock.
And scientists have another opportunity to see Dimorphos in detail, this time for much longer. The European Space Agency will launch Hera, a follow-up mission, in 2024. Hera will arrive in 2026 and, unlike DART, will stay in the neighborhood, exploring both Dimorphos and Didymos. The mission will give scientists a better look at the impact crater itself after the dust has settled, as well as at the asteroids' natural states.
The next day, she informs Jack and Adam of the possibility of an impact and calls them in. She tells them of two asteroids: Helios and Eros, whose orbits have been disrupted by the comet and may hit the Earth. Helios would hit with the force of 1,000 Hiroshima bombs and generate temperatures five times hotter than the Sun in the area of impact. Everything within a 150-mile radius would be destroyed and the impact would also spray molten rock another 70 miles.
Eros is four miles across and would cause a global ecological disaster if it did indeed hit. Then, Max Jenson (Brian Hill), one of Lily's assistants, informs Lily, Jack and Adam that Helios is getting closer to the Earth and that the observatory in Mauna Kea, Hawaii had picked up some smaller asteroids that the National Observatory cannot see and they believe that a small one hit Montana. Jack and Adam realize that the fire was indeed caused by an asteroid impact. Lily and Max check Helios' trajectory and realize that it will indeed hit the Earth.
Their numbers show that Helios will hit the Kansas City area within 48 hours. They inform the President and he orders that the city be evacuated. Ultimately, a fragment of Helios strikes a dam in the Kansas City area, causing flooding in the city. Wallach, who drives into the city to rescue two stranded firefighters and a drunk driver who struck their vehicle, gets caught in the flood. He and the firefighters survive, but the drunk driver dies. Wallach is then informed by McKee that Eros is, in fact, going to impact Earth.
The largest piece and several smaller fragments of Eros hit Dallas, Texas, where Lily's son and father are. The city is devastated by the impacts. Lily desperately searches the city for her father and son, who survive the blast and aftershocks. Her father ends up trapped and hurt in the ruins of the hospital where he worked, while her son Elliot wanders off trying to find help. Meanwhile, Adam is shot and killed by a refugee while addressing an evacuation camp. After a search, Lily locates her father and with the help of nearby firemen, rescues him, but goes on to try to rescue Elliot. After searching the ruined city, she finally locates Elliot in a large impact crater. Jack arrives to help in a helicopter and rescues Elliot. The four return to base where they watch the comet pass by Earth, and are relieved it won't return to cause trouble for another 4,000 years.
Josep Maria Trigo-Rodríguez, a researcher at the Institute of Space Sciences in Barcelona, Spain, led the international team of scientists who analyzed the meteorite's orbit. They calculated the fireball's size and path through Earth's atmosphere by examining its flight and the meteorite's final impact site. A computer model based on these figures was used to estimate the space rock's orbital path. [Crash! 10 Biggest Impact Craters on Earth]
The 1,100-pound (500 kilogram) meteorite is an ordinary H5 chondrite, a type of stony meteorite responsible for 31 percent of Earth's impacts. The fragments are called the "Annama meteorite" because the meteorite fell near the Annama River in Russia.
ATLAS is an asteroid impact early warning system developed by the University of Hawaii and funded by NASA. It consists of four telescopes (Hawaii ×2, Chile, South Africa), which automatically scan the whole sky several times every night looking for moving objects.
DART recorded and beamed back its final moments with its onboard Didymos Reconnaissance and Asteroid Camera for Optical Navigation (DRACO), which was also responsible for automatically navigating the spacecraft onto its collision course. As DART came ever closer to the space rock, its camera feed showed the asteroid's landscape bloom from a single pale gray pixel to a rough and craggy terrain strewn with sharp, shadowy rocks.
"We saw that we were going to impact. This asteroid was coming into the field of view for the first time. We really had no idea what to expect," Elena Adams, a mission systems and the spacecraft systems engineer for the DART mission, said at a news conference (opens in new tab) after the event. "All of us were kind of holding our breaths."
These won't be the only telescopes put to use to study the impact. NASA's James Webb Space Telescope and Hubble Space Telescope, and the agency's Lucy spacecraft will also train their lenses on the asteroid to study the impact's aftermath. Their observations will help scientists understand how much force is needed to successfully divert an asteroid from our planet.
Ralph Semmel, the director of the Johns Hopkins University APL, said that the impact represented an "historic accomplishment" and was a "game-changing" first demonstration of humanity's ability to protect itself from future asteroid threats.
With DART, NASA is testing the efficacy of a planetary defense strategy known as the kinetic impactor technique. In this method, a spacecraft must travel fast enough to not only hit, but move, an asteroid off its typical course so its path is no longer a threat to Earth. By measuring how far Dimorphos budged, scientists will better understand how viable the kinetic impactor technique is in real-life.
Impact time and location predictions for asteroid 2018 LA. The long blue bar shows the predictions prior to ATLAS data being obtained. The much shorter red bar in the image shows the prediction including ATLAS data, while the yellow star marks the actual location. ATLAS clearly made it possible to associate the impact with the observed asteroid. MC: Aren Heinze (IfA/ATLAS), Brooks Bays (SOEST), Bill Gray (Project Pluto)
By measuring the asteroid more than two hours after it was last seen from Arizona, and less than five hours before it exploded, ATLAS greatly improved the accuracy with which the pre-impact orbit could be calculated, helping to prove the bright meteor subsequently seen over Botswana was indeed the fiery demise of 2018 LA.
ATLAS currently discovers about 100 asteroids bigger than 30m every year. Were it to hit Earth, an asteroid that size would impact with enough energy to destroy a city like Honolulu. For the first time in history, astronomers can provide sufficient warning to move people away from the impact site.
The final four images show the spacecraft passing by Didymos with Dimorphos growing larger and larger in the frame until we see only its surface. And then, KABOOM, the last frame is almost completely red due to the transmission cutting. According to NASA, that image was taken just four miles from the surface of the asteroid and one second before impact.
In 1980, Nobel Prize-winning physicist Luis Walter Alvarez and his geologist son Walter published a theory that a historic layer of iridium-rich clay was caused by a large asteroid colliding with Earth. The instantaneous devastation in the immediate vicinity and the widespread secondary effects of an asteroid impact were considered to be why the dinosaurs died out so suddenly.
Paul says, 'An asteroid impact is supported by really good evidence because we've identified the crater. It's now largely buried on the seafloor off the coast of Mexico. It is exactly the same age as the extinction of the non-bird dinosaurs, which can be tracked in the rock record all around the world.'
The impact site, known as the Chicxulub crater, is centred on the Yucatán Peninsula in Mexico. The asteroid is thought to have been between 10 and 15 kilometres wide, but the velocity of its collision caused the creation of a much larger crater, 150 kilometres in diameter - the second-largest crater on the planet.
Iridium is one of the rarest metals found on Earth. It is usually associated with extraterrestrial impacts, as the element occurs more abundantly in meteorites. © Hi-Res Images of Chemical Elements/ Wikimedia Commons (CC BY 3.0)
Like dominos, this trailed up the food chain, causing the ecosystem to collapse. The reduction in plant life had a huge impact on herbivores' ability to survive, which in turn meant that carnivores would also have suffered from having less food available.
In what is now central India, there was substantial volcanic activity that, although unrelated to the asteroid impact, was causing problems of its own. The resulting lava outcrop is now known as the Deccan Traps. 2b1af7f3a8