Title: The Double Asteroid Redirection Test (DART) is NASA’s probe to redirect asteroids.Successful contact with the target asteroid took place on 26 September 2022. NASA, 2022.
The Double Asteroid Redirection Test (DART) is the first mission aimed at demonstrating a method of asteroid deflection through kinetic impact. In 2021, NASA launched a spacecraft to travel and collide with an asteroid system. Contact with the target took place on 26 September 2022.
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Updates
26sep2023: DART's success. A year leter.08aug2023: Dimorphos' boulder swarm.
01mar2023: Hubble photos' details.
11oct2022: Asteroid effect confirmed.
29sep2022: Hubble captures impact.
Background
About the DART mission.DART's payload.
LICIACube companion.
DART's journey.
Missions related to DART.
ESA's Hera mission 2024.
Live broadcast of impact 26 Sep 2022.
DART's success.
Asteroids, a potential threat.
UPDATES
First anniversary of DART’s impact on Dimorphos – 26sep2023
A year ago, on 26 September 2023, the Double Asteroid Redirection Test (DART) mission culminated in a precise intentional impact of the spacecraft onto its target, the moonlet Dimprphos, of the binary asteroid system Didymos, located 11 million kilometres away.
On the first NASA interplanetary defence test mission, DART travelled almost a year through space to demonstrate the capability of a kinetic impactor in changing the trajectory of an asteroid.
Although the Dymorphos system orbit around the sun does not intercept that of the earth, on that date, it was the closest to our planet to perform a test.
Now we know that a kinetic impactor is a viable option should an asteroid be discovered in the future that appears to be a threat to our planet.
Boulders ejected by DART’s impact on Dimorphos – 08aug2023
Particle Swarm ejecta resulting from the impact of DART on Dimorphos was a predicted event when the mission was planned as the small moon has a small gravitational power that loosely attaches rocks to its surface.
Attention-seeking media exaggerated the report with alarming headlines like “Nasa asteroid blunder unleashes boulder storm as deadly as Hiroshima” (Yahoo! News, 08 Aug 2023), and “NASA’s voyager-2 alien invasion, a human error” (Telegraph, 03 Aug 2023), but thy were bound to include factual information: “although the impact succeeded in knocking Dimorphos slightly off course, it also dislodged 37 boulders, which are currently zipping through space at 20,900 km/h.
Prof David Jewitt, UCLA.About boulders ejected by DART’s impact on Dimorphos (2023, ApJL, 952 L12).
In the original study published on 20 July 2023, David Jewitt, a professor of Earth and planetary sciences at UCLA, and his co-authors, examined images of the Near-Earth asteroid 65803 Didymos and its small companion Dimorphos taken by the Hubble Space Telescope in 2022 (26 Sep “impact”, and 19 Dec), and 2023 (04 Feb and 10 Apr). “Impact” on the first date refers to the deliberate crash of the DART spacecraft on the surface of the asteroid Dimorphos of the Didymos–Dimorphos binary system, with the purpose of changing its course as an experiment for the planetary defence programme.
The Hubble Space Telescope captured images of the Didymos asteroid before, during and after DART’s impact on 26 September 2022. NASA, 2010.The authors analysed images taken by the 2.4m Hubble Space Telescope, which uses a camera (WFC3) with two 2015x4096 px Charged Couple Device (CCD) sensors.
The impact of DART on 26 Sep. 2022, resulted in the ejection of debris that formed a long, comet-like tail, directed away from the sun as it was swept by solar radiation pressure. This cloud of debris provides the opportunity to learn more about the mission and its effects.
Images were enhanced to separate them from the cosmic background, re-oriented to bring the celestial north to the top and composited from a series of similar images taken on that date (24 images taken in 5hr on 19 Dec). The team identified 37 boulders circled in the image below. The spikes emanating from the Didymos system resulted from telescope diffraction and rotation of superimposed images.
Identified boulders surrounding the Didymos-Dimorphos binary system after the impact of DART in Sep. 2022.Enhanced image from Hubble Space Telescope. Jewitt D (2023) ApJL, 952 L12).
The comparison of Hubble’s images from December 2022 and February 2023 provided more detail about positional changes and acceleration of visible boulders.
Theoretical calculations suggested that boulders that were launched at less than 0.09m/s were not able to surpass the binary system’s escape speed of 0.24 m/s and fell back onto the surface of Dimorphos within hours, while those that gained faster speeds were able to escape the system but remained close.
Comparison of position of the boulders ejected by DART between 19 Dec 2022 and 04 Feb 2023.
Images by Hubble Space Telescope. Jewitt D (2023) ApJL, 952 L12).
Some of the boulders not included in the count, were embedded in the particle trail (marked with T in the enlarged image), which left 37 identifiable boulders circled around the binary system.
Close up of boulders embedded in the tail.
Images by Hubble Space Telescope. Jewitt D (2023) ApJL, 952 L12).
The analysis of DART’s penultimate photo of the surface of Dimorphos before impact provided with vast information on the features of the surface. Taken from 12 m from the surface and covering 30x30m or 1% or the surface of Dimorphos. The impact site is marked on the photo with a yellow dot, located next to the largest boulder named Atabaque (5m wide). Measuring the boulders and building a simulation of an impact provided an estimation of the size of the crater resulting from the impact of DART (40-60m).
Image of the surface of Dimorphos taken by DART before impact.The crash point marked by a yellow spot. DART 26 Sep. 2022. NASA, Jewitt D (2023) ApJL, 952 L12).
The main mechanism of ejection was cratering, by which particles are displaced in a hollow cone configuration and seismic shaking resulting from the propagation of the impact shock that launched boulders that were sitting on the surface with sufficient speed to overcome the escape speed.
The team of researchers reported the following:
- They identified approximately 40 boulders that are now moving with the asteroid within a region spreading 10,000 km. The largest has a diameter of 7m and the smallest 4m.
- They calculated that the combined mass of the boulders is 5,000 tonnes, which corresponds to 0.1% of the total mass of Dimorphos (4 million tonnes).
- The projected speed of the boulders relative to Dimorphos is comparable to the gravitational scape speed from the system. The boulders carry 0.00003 parts of the kinetic energy delivered by the DART impactor.
- The number, sizes and shapes of those objects appear to be those of objects dislodged from 2% of the surface of the asteroid that correspond to a circular patch of at least 50m in diameter (Jewitt D (2023) ApJL, 952 L12).
Prof Jewitt said: “The boulder swarm is like a cloud of shrapnel expanding from a hand grenade. Because those big boulders basically share the speed of the targeted asteroid, they’re capable of doing their own damage.” Because DART was an experimental mission to learn the effects of redirecting an asteroid, this new evaluation suggests that in a real scenario of an asteroid redirected after approaching our planet, the dislodged particles would still be able to cause damage if they were to impact our planet. According to the Professor, given the high speed of a typical impact, a 4.5m boulder hitting Earth would deliver as much energy as the atomic bomb that was dropped on Hiroshima, Japan, during the Second World War (Kanapton S (2023) Yahoo! News).
Hubble’s photos of DART’s impact analysed - 01mar2023
The NASA/ESA Hubble Space Telescope captured a series of photos of rapid changes to the asteroid Dimorphos when it was deliberately hit by a 545-kilogram spacecraft on 26 September 2022. The primary objective of the NASA mission, called DART (Double Asteroid Redirection Test), was to test our ability to alter the asteroid’s trajectory as it orbits its larger companion asteroid, Didymos. Though Dimorphos poses no threat to Earth, data from the mission could help inform researchers how to potentially change an asteroid’s path away from Earth, if ever necessary.
Debris were flung into space as the DART impactor spacecraft crashed into Dimorphos at 21,000 Km/h. It is estimated that the blast ejected over 900,000 kg of dust off the asteroid.
The images show an Ejecta Cone with spiral swirls of debris caught up along the Dimorpho's orbit around Didymos.
Superimposed yellow lines show the direction of the ejecta cone, the curved ejecta stream and the double tail formation on photos after the impact of DART on Dimorphos. Images between 27 Sep. and 08 Oct 2022. Hubble ST/ESA, 01 March 2023.
The movie starts 1.3 hours before impact when the binary asteroid system is at the centre, although they look like one spot as they are close together. Hubble's optics produce artefacts that appear as straight spikes coming from the centre.
The next image, 2 hours after the crash, shows debris flying away faster than 6.5km/h and forming a hollow cone with long stringy filaments.
By 17 hours post-collision the interaction of the binary system affects the ejecta pattern producing a pinwheel shape caused by the gravitational pull of the larger Didymos. Later, the pressure of sunlight on the dust gave the ejecta a comet-tail-like shape, which split into 2 for a few days.
Note development of ejecta patterns over time. Hubble Space Telescope. NASA/ESA, 26 September to 08 October 2022.
NASA confirmed change in Asteroid’s orbit – 11 Oct 2022
The DART mission was a success!
Scientists confirmed a significant change in the orbit of the moonlet Dimorphos following the purposeful impact of a spacecraft on 26 September 2022.
The goal of the mission was to crash the spacecraft in the opposite direction of the orbital movement of the asteroid so that it would lose some of its kinetic energy and deflect to a lower orbit, closer to Didymos than the original one. Success was defined at NASA by a change in orbital period of 73 seconds or a shorter time to complete its new orbit.
Graphic of DART planned impact with Dimorphos changing its orbit to a lower one around Didymos.Note the accompanying imaging spacecraft LICIACube. NASA, 2022.
Before the impact, Dimorphos completed its orbit around the parent asteroid Didymos in 11 hours and 55 minutes. Using the same methods of measurement via Earth telescopes, astronomers measured an orbit of 11hr, 23 minutes after the impact, which confirms that the crash of the spacecraft altered the speed of rotation of the asteroid by 32 minutes (margin of uncertainty of 2 minutes).
The full effect of the impact is still being studied as the focus shifts towards measuring the efficiency of momentum transfer, calculated as 22,530 km per hour collision with its target. Analysis includes the tons of asteroidal rock displaced by the impact. This material, known as “ejecta” exits the asteroid at high speed creating a blast that further pushes the asteroid in the opposite direction, enhancing the effect of DART’s push against Dimorphos.
Hubble observed debris around Dimorphos, known as ejecta, still present on 08 October 2022. NASA, 2022.
Telescopic facilities contributing to the observations used by the DART team to determine this result include: Goldstone, Green Bank Observatory, Swope Telescope at the Las Campanas Observatory in Chile, the Danish Telescope at the La Silla Observatory in Chile, and the Las Cumbres Observatory global telescope network facilities in Chile and in South Africa.
Hubble captures DART’s impact – 29 Sep 2022
Hubble captures DART’s impact.NASA/ESA/JWST, 29 September 2022.
The impact of DART on Dimorphos was observed and recorded by two space telescopes.
This is the first time both telescopes, the Hubble Space Telescope and the James Webb Space Telescope observe the same object simultaneously.
Coordinating Hubble and Webb was an operational milestone. The combination of both observatories demonstrated the capability of the technical and scientific teams, opening more opportunities for research.
Webb captures DART’s impact.NASA/ESA/CSA/JWST, 29 September 2022.
The analysis of images by Webb and Hubble together will provide information about the characteristics of the surface of Dimorphos as the collision produced an ejection of material that can be studied using the various wavelengths.
Hubble’s image is in the visible spectrum of light, while Webb’s image is in the infrared range. Webb took one observation of the impact location before the collision took place, then several observations over the next few hours. Images from Webb’s Near-Infrared Camera (NIRCam) show a tight, compact core, with plumes of material appearing as wisps streaming away from the center of where the impact took place (NASA/ESA/CSA/DART/JWST, 2022).
Planning and developing methods to track asteroids moving very fast took several years and intensified in the weeks leading to the impact. Webb obtained 10 images during an observation of five hours, while Hubble took 45 images from before to hours after the impact.
Hubble’s Wide Field Camera 3 showed material ejected as rays stretching out from the body of the asteroid. In the following series of images in visible light, the border on the left that fans out more prominently corresponds to the side that Dart hit the asteroid (left side of the asteroid on the image below). Brightness of the asteroid system increased threefold, lasting more than eight hours after impact.
Hubble’s images taken 22 minutes, 5 and 8 hours after the impact show material ejected into space, more evident on the left, where DART impacted. NSA/ESA, 2022.
Hubble will monitor the Didymos asteroid system 10 more times in the weeks following the impact, to observe how the cloud of particles expand and fade away.
“This is an unprecedented view of an unprecedented event,” summarized Andy Rivkin, DART investigation team lead of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland (NASA/ESA/CSA/DART/JWST, 2022).
About the DART mission
The asteroid Didymos as a target.
The target of this mission was carefully selected from known asteroids that are visible but do not come close the Earth in their paths.
While there are no known asteroids larger than 140 metres in size that shows a significant chance of hitting Earth in the next 100 years, only around 40% of those asteroids have been found as of August 2023.
One of the early candidates visible to most astronomic instruments was the Didymos binary asteroid system imaged by the Arecibo Radio Telescope in 2003.
Didymos binary asteroid: 14 sequential radio-telescope original images on the left; enhanced on the right. NASA/Arecibo Radio-Telescope. 2003.The radio-telescope images above show the smaller Dimorphos at different stages of its orbit around the larger asteroid Didymos.
The target was the Asteroid Dimorphos, photographed here by DART’s camera shortly before the spacecraft impacted on its surface. NASA/DART, 26 September 2022.
This binary celestial object coded “Asteroid 65803”, was composed of a 780 metre-diameter large asteroid called Didymos and its moonlet, a 160 m-diameter small asteroid named Dimorphos
Dimorphos orbits Didymos at 1.18 km from its centre at an orbital period of 11.9 hr. The latter rotates rapidly with a rotation period of 2.26 hr, while Dimorphos seems to have a rotation synchronous with the orbit, therefore always showing the same face to the larger asteroid.
The name of the asteroid derives from the Greek word Didymos meaning Twin.
Greek twins Artemis and Apolloand their mother Leto.
The DART mission.
The Double Asteroid Redirection Test (DART) is the first NASA interplanetary defence test mission. This successful test opens the possibility of saving the planet from a strike by an asteroid in the future, provided it is discovered early giving time to deploy a reaction.
The DART mission had two goals:
- Strike the moonlet Dimorphos at a speed of 6.4 km per second.
- Slow down its orbit by 10 minutes from its known regular orbit of 11hr 55min.
The initial goal was achieved successfully, and it was an unprecedented achievement, considering the size of the target and that the asteroid system is 11 million kilometres away.
The second goal was determined weeks after the impact. Teams of astronomers from all over the world analysed the orbit of Dimorphos to find differences compared with the data obtained before the impact.
DART, impactor spacecraft
The main structure of DART is a box of width/height/length (depth): 1.2 x 1.3 x 1.3 metres. Considering the extensions, it reaches the size w/h/l: 1.3 x 2.6 x 1.9 m. In addition, the spacecraft has 2 solar arrays that extend 8.5 m each.
DART’s weight was 610 kg at launch, including 50 kg of Hydrazine propellant for manoeuvres, and 60 kg of Xenon for the Ion Propulsion Engine. After using some of the fuel, the spacecraft was approximately 580 kg at impact.
The interaction between the spacecraft and the asteroid in space followed the universal laws of physics and therefore, in theory, it could be predicted mathematically.
One of the physical concepts involved in this transaction of energy is momentum. When DART crashed into Dimorphos, the spacecraft transferred its Momentum to the asteroid’s, resulting in a change of velocity, orbital rotation and possibly altitude around Didymos.
Momentum
Momentum of a pool cue ball is transferredto the racked balls after collision. Wikipedia, 2023.
Momentum is a property of physical objects that results from the product of the object’s mass and velocity. Momentum is also a Vector and has a Magnitude and a Direction.
Still objects have a mass but because they are not in motion, they have no velocity, therefore no momentum. The physical symbol for Momentum is “p” (from the Latin “pellere”, meaning "push” or “drive"). Consequently, a standing object has “0” momentum, or p = 0.
To calculate the momentum of an object, follow the equation:
momentum = mass x velocity. p = m v
By convention, the units are:
- Momentum (p) is measured in kilograms metres per second (kg m/s), equivalent to newton-second.
- Mass (m) is measured in kilograms (kg).
- Velocity (v) is measured in metres per second (m/s).
For example, if a skater has a mass of 60 kg and travels at a speed of 15 m/s, the formula would be:
p = 60 x 15 or p = 900 kg m/s.
Vector analysis in the collision of 2 objects on a flat plane.Wikipedia, 2023.
Considering the multiple variables involved in a collision of two objects in space the complexity of these calculation rapidly increases.
Some of the experts conducting research in this area work at the Impact Simulation Working Group at Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland. The NASA article “Predicting the unpredictable” (Rehm J, 2020), explains the essential thinking that took place during the planning of the DART mission.
Simulation of a projectile colliding with the surface of a rubble-pile asteroid. Resulting ejecta in opposite direction of the impact. JHUAPL/ Angela Stickle, 2020.
Researchers at APL calculated the change of direction after the collision and also theorised about the dispersion of particles following the impact of a small object onto a loose conglomerate of rocks, which is the case of the surface of Dimorphos.
It was predicted that the crater created by DART would displace between 9 tons (the mass of 2 elephants) and 100 tons (the mass of a whale) of surface rocks into space, creating what is know as “Ejecta” in all directions, some of it visible through telescopes.
Images that followed the impact of DART (see updates above) demonstrated multiple size particles that continue in relative proximity to the asteroid from which they originated as their resulting momentum dictates their direction of travel.
Another factor the plays a role is the gravitational force of the large objects, which was the reason that kept the smaller rocks on their surface to begin with.
DART’s Payload
DRACO camera
The DRACO camera, a high magnification imager onboard DART.DART, 2023.
DART carries a single instrument, the Didymos Reconnaissance and Asteroid Camera for Optical Navigation (DRACO), which consists of a high-resolution camera of the Long Range Reconnaissance Imager (LORRI) type, originally developed by the Johns Hopkins University Applied Physics Laboratory (JHUAPL) for the New Horizons mission that went past Pluto in 2015.
This is a panchromatic high-magnification imager with a 20.8 cm aperture telescope that focuses visible light onto a Complementary Metal-Oxide Semiconductor (CMOS) light detector, a cheaper version of the original and expensive Charged-Coupled Device (CCD) used in New Horizons. This camera helped locate Dimorphos to support the SMART Nav Autonomous Navigation system (see below). DRACO captured the closest images of the asteroid’s surface just before impact.
Autonomous navigation system
DART featured a Guidance, Navigation and Control (GNC) system based on mathematical algorithms known as Small-body Manoeuvring Autonomous Real Time Navigation (SMART Nav), which allowed for autonomous navigation to solve the problem of aiming for a 160-metre target located at 11 million kilometres from Earth. Once the two objects were identified, about one hour before impact, the GNC elements guided the spacecraft towards the smaller one. The system was the result of decades of research on missile guidance.
The RLSA planar high-gain antenna onboard DARTprovided outstanding communications. DART, 2023.
In addition, DART demonstrated the use of a single-board computer and an interface module to control the advance avionics system. The CORE Small Avionics suiTe (CORESAT) also provided imaging processing, communications, and propulsion system management.
An improved communications system was provided by the Radial Line Slot Array (RLSA) low-cost high-gain antenna, which has a planar configuration and the shape or a disk with slots and able to send and receive data accurately and efficiently.
Advanced Ion propulsion.
The NEXT-C advanced Ion propulsion took DART to its destination.DART, 2023.
DART demonstrated the NASA’s Evolutionary Xenon Thruster-Commercial (NEXT-C) engine, developed at NASA Glenn Research Center and Aerojet Rocktdyne. This electric engine is solar-powered and uses a Gridded Ion propulsion that produces thrust by electrostatic acceleration of ions (electronically charged atoms) formed from the Xenon propellent. An improved and more efficient version of the system used in the Dawn mission (2007-2018) and the Deep Space 1 mission (1998-2001).
Roll-out solar arrays
Electrical power for DART was provided by the Roll-Out Solar Array (ROSA) that consisted of two large arrays launched as compacted rolls at both sides of the main body. Each system rolled out to reach 8.5 m in length. This technology was tested at the International Space Station (ISS) in 2017. An improved version developed by Redwire’s Deployable Space systems in California, USA, was installed on the spacecraft.
The NEXT-C advanced Ion propulsion took DARTto its destination. DART, 2023.
A new technology, Transformational Solar Array was demonstrated on the panels, which contains reflective concentrators that provide 3 times more power than regular arrays. An important advancement that will reduce the need of heavy fuels in future missions.
DART’s companion, LICIACube.
The Light Italian CubeSat for Imaging of Asteroids (LICIACube) is a CubeSat constructed by the Italian Space Agency (ASI). Its mission was to observe and analyse the Didymos asteroid binary system during and after DART’s impact. The satellite bypassed the asteroids at 56.7km and took pictures of its target.
The small satellite, measuring 20x30x10cm travelled attached to the DART spacecraft and was ejected from its spring-loaded box 15 days before DART’s impact, on 11 September 2022. After release, as part of the testing process to calibrate the miniature spacecraft and its cameras, LICIACube captured images of a crescent Earth and the Pleiades star cluster, also known as the Seven Sisters.
Insert: LICIACube attached to DART in the lab.Background: Artist impression of DART and LUCIACube as they approach the moonlet Dimorphos of the Didymos asteroid binary system. NASA/ASI, 2022.
LICIACube’s image of DART impacting Dimorphos shows the “ejecta” or particles emitted by the collision.
Image taken by LICIACube as DART crashed onto the moonlet Dimorphos, ejecting particles into space.The large object at the bottom is the main asteroid Didymos. NASA/ASI, 26 September 2022.
DART’s journey
DART launched onboard the SpaceX Falcon 9 rocketon 24 November 2021. NASA, 2021.
DART was launched on 24 November 2021 onboard a Falcon 9 rocket from Space Launch Complex 4E at Vandenberg Space Force Base in Santa Barbara County, California, USA. The rocket carried a 624kg payload and after launch, the primary booster successfully landed autonomously on a drone ship stationed on the Pacific Ocean and was re-used in subsequent flights.
Falcon 9 is a partially reusable medium lift launch vehicle that can carry cargo and crew into Earth orbit, produced by American aerospace company Space Exploration Technologies Corporation (SpaceX), funded by Elon Musk in 2002.
Since June 2010, rockets from the Falcon 9 family have been launched 191 times, with 189 full mission successes, one partial failure and one total loss of the spacecraft. In addition, one rocket and its payload were destroyed on the launch pad during the fuelling process before a static fire test was set to occur.
After 10 months, 2 days and 17 hours of travel through space at a speed of approximately 6.1 km per second, the mission concluded with the spacecraft crashing onto the asteroid Dimorphos on 26 September 2022.
Missions related to DART
ESA’s Hera mission 2024.
Hera is a Space Safety programme mission led by the European Space Agency (ESA) to study the impact of DART on the Didymos binary asteroid system on 27 Sep. 2022. It will measure the size and characteristics of the crater allowing to measure the efficiency of deflection produced by a calculated impact on an asteroid.
Planned to launch in October 2024, Hera will carry cameras, an altimeter, a spectrometer, and will deploy two CubeSats or nano-satellites called Milani and Juventas. In addition to studying physical properties, it will record measurements of the sub-surface and internal structures of the asteroid.
Scientific exploration will depend on gathering data using Hera’s advanced instruments:
Surface features of the asteroids and the crater will be captured by two Asteroid Framing Cameras (AFC) developed by JenaOptronik, each with a 1020x1020 pixel sensor (FaintStar panchromatic) and a telephoto lens. They can resolve 1 metre at 10 km.
Images in visible and infrared light will be captured by the Hyperspectral imager Hyperscout-H, an instrument that detects that type of light in 25 bands between 665 and 975 nanometres (visible to near infrared light).
Distance to the asteroids will be measured with a Planetary Altimeter (PALT) that uses and infrared laser to track the ground with an accuracy of 50cm of altitude.
Temperatures will be tested with a Thermal Infrared Imager (TIRI) developed by the Japanese Space Agency, capable to resolve 2.3 metres at 10 km.
The asteroids’ gravity field, rotational speed and orbits will be measured by detecting radio wave disturbances using the X-Band Radio Science (X-DST) instrument based on the Doppler effect that measures the change in wave frequency resulting from movement of an object in relation to the observer.
Image of DART taken by LICIACube as the spacecraft crashed on the moonlet Dimorphos. Notice the emitted particles known as ejecta.The large object at the bottom is the main asteroid Didymos. NASA/ASI, 26 September 2022.
NASA's DART and ESA's Hera missions are the result of an international collaboration called "The Asteroid Impact and Deflection Assessment (AIDA)", in a similar fashion to Hubble and James Webb space telescope missions.
The asteroid monitoring system was developed by NASA and ESA in early 2000s and despite a temporary dip in funding the project revived in 2017 with a new name, Hera, inspired by the ancient Greek goddess of marriage, women and family, and the protector of women during birth.
According to Homeric Greek, Hera is the queen of the 12 Olympians and Mount Olympus, sister and jealous wife of Zeus, daughter of the Titans Cronus and Rhea. Her vengeful nature was fuelled by Zeus’ infidelities that included a mortal woman Alcmene, who became pregnant with his child. Zeus announced that this child would become the new ruler, therefore Hera did her best to prevent Alcmene from delivering, but eventually she gave birth to Heracles.
The new-born was hated by his stepmother Hera, who sent two serpents to kill him in his cot, but he played with them instead. Zeus then decided to trick Hera into nursing infant Heracles, but when she discovered who he was, she pulled the infant from her breast and a spurt of her milk formed a smear across the sky, called since then “The Milky Way”. Her milk also created a white flower, the Lily.
“The origin of the Milky Way” from Hera’s breast milk spilt after she pulled away infant stepson Heracles, the illegitimate son of Zeus.Oil artwork by Venetian painter Jacopo Tintoretto from 1575.
Live broadcast of the impact – 26 Sep 2022
On Monday 26th September 2022, millions of people around the world tuned to NASA’s live broadcast of DART’s impact onto the asteroid Dimorphos. The spacecraft followed a series of programmed events autonomously all the way to its destination. The last minutes of DART’s journey were followed closely from the Mission Control Centre at Johns Hopkins Applied Physics Laboratory in Maryland, USA. This research laboratory serves as a technical resource for the Department of Defence, NASA, and other government agencies.
The last moments of the mission were tense but full of jubilation as consecutive milestones confirmed the precision of the plans and calculations conducted by countless teams involved in constructing, flying and processing data sent by the spacecraft as it travelled through space. The last step called “Precision lock” was confirmed 17 minutes before the expected impact, indicating that DART had a lock on Dimorphos from 100 km away, and was invariably aiming at her target.
As the spacecraft approached her destination, she flew past Didymos heading for Dimorphos at 6.6 km/sec. The onboard camera sent progressively more detailed images of the small asteroid’s surface, showing an untidy conglomerate of rocks before transmission was lost. The last image was mostly a red screen that signalled the end of the mission as the spacecraft crashed successfully on the surface of the asteroid.
DART mission's success – 26 Sep 2022
Confirmation of success
Following DART’s impact, astronomers from all over the world focused on measuring the orbiting speed of the moonlet Dimorphos around the asteroid Didymos. As both asteroids are cold and do not emit light, the largest is only visible by the light it reflects from nearby objects. The moonlet can be detectable when it eclipses the larger one as it crosses in front during its orbit. From Earth, it looks like a decrease in brightness the duration and frequency of which, allows astronomers determine the orbital speed.
Asteroids, a potential threat
Redirection of potential threats to Earth
DART is a demonstration of the potential redirection of a celestial body should an Earth-threatening asteroid be discovered in the future. To date, there is no known asteroid larger than 140 metres that threatens our planet for the next 100 years, but it is thought that only 40% of those asteroids have been detected. This means that there are tens of thousands near-Earth asteroids, big enough to cause damage to Earth that we do not know about and maybe detected at any point in the future.
In an interview with the BBC in 2014, Jonathan R. Tate, Director of the National Near Earth Objects Information Centre (NNEOIC), also known as the Spaceguard Centre in Knighton, Powys, UK, showed a fragment of the meteorite that fell over Chelyabinsk in 2013.
Video evidence of the undetected asteroid that exploded over Chelyabinsk, Russia on 15 February 2013, causing a shockwave that struck six cities across the country. It was estimated that the asteroid had a diameter of 18 metres and broke down in smaller particles as it travelled at high speed, causing shockwaves that caused extensive damage to nearby towns.
REFERENCES
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» DART (2023) Impactor Spacecraft. [Online article]. Available at DART’s website. Accessed: 04 September 2023.
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» DART (2022) Webb, Hubble Capture Detailed Views of DART Impact. DART. [Online article]. Available at DART’s website. Accessed: 30 September 2022.
» ESA (2023) Hubble captures movie of DART asteroid impact debris. [Online article]. Available at European Space Agency (ESA) website. Accessed: 03 March 2023.
» Jewitt D, et al (2023) The Dimorphos Boulder Swarm. The Astrophysical Journal Letters, Volume 952, Number 1. DOI: 10.3847/2041-8213/ace1ec. Available at The Astrophysical Journal Letters website. Accessed: 08 August 2023.
» JHUAPL (2022) DART Impact. Johns Hopkins Applied Physics Laboratory, 27 Sep 2022. [Online video]. Available at JHUAPL’s YouTube channel. Accessed: 28 September 2022.
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