23. September 2022
Planetary defence

Im­pact 11 mil­lion kilo­me­tres away

A few seconds before impact
A few sec­onds be­fore im­pact
Image 1/7, Credit: NASA/Johns Hopkins AP

A few seconds before impact

In the ear­ly hours of Tues­day at 01:14 CEST, NASA's 610-kilo­gram DART space­craft will pur­pose­ful­ly smash in­to the 160-me­tre as­ter­oid Di­mor­phos (left) at a speed of al­most 22,000 kilo­me­tres per hour. The aim of the mis­sion is to al­ter the or­bit of Di­mor­phos around its bi­na­ry com­pan­ion Didy­mos. Cal­cu­la­tions pre­dict that the cur­rent 12-hour or­bital pe­ri­od will change by a few min­utes (artist's im­pres­sion).
Binary asteroid system
Bi­na­ry as­ter­oid sys­tem
Image 2/7, Credit: NASA/Johns Hopkins APL

Binary asteroid system

Didy­mos and Di­mor­phos are a bi­na­ry as­ter­oid sys­tem that came with­in six mil­lion kilo­me­tres of Earth in 2003 dur­ing their 25-month or­bit around the Sun. Di­mor­phos, the small­er of the two bod­ies with a di­am­e­ter of just un­der 170 me­tres, will be im­pact­ed by NASA's DART space­craft at al­most 22,000 kilo­me­tres per hour on Tues­day, 27 Septem­ber at 01:14 CEST. This is ex­pect­ed to change the ap­prox­i­mate­ly 12-hour or­bital pe­ri­od of Di­mor­phos around Didy­mos by a few min­utes. The im­pact of the 360-kilo­gram space probe will be ob­served by two pre­vi­ous­ly de­ployed small satel­lites called LI­CI­ACube. Tele­scopes from Earth will al­so be used to track the event, which will take place 11.1 mil­lion kilo­me­tres away.
Dimorphos (front) and Didymos
Di­mor­phos (front) and Didy­mos
Image 3/7, Credit: NASA/Johns Hopkins APL

Dimorphos (front) and Didymos

Artis­tic rep­re­sen­ta­tion of the bi­na­ry as­ter­oid sys­tem Didy­mos (Greek for twin) and Di­mor­phos (front, Greek for 'two-shaped' in ref­er­ence to the im­pend­ing change in the shape of the as­ter­oid due to the im­pact of the DART space­craft). Di­mor­phos has a max­i­mum di­am­e­ter of 165 me­tres, Didy­mos of 780 me­tres. Di­mor­phos or­bits Didy­mos at a dis­tance of ap­prox­i­mate­ly 1100 me­tres. Didy­mos was dis­cov­ered in 1996, Di­mor­phos in 2002.
The target is already in sight
The tar­get is al­ready in sight
Image 4/7, Credit: NASA/JPL DART Navigation Team

The target is already in sight

On 27 Ju­ly 2022, the Didy­mos Re­con­nais­sance and As­ter­oid Cam­era for Op­ti­cal nav­i­ga­tion (DRA­CO) on board the DART space­craft pho­tographed the mis­sion's tar­get, the Didy­mos/Di­mor­phos bi­na­ry as­ter­oid sys­tem, from a dis­tance of ap­prox­i­mate­ly 20 mil­lion kilo­me­tres. The space­craft is steered in­to its tar­get, the small­er of the two as­ter­oids, Di­mor­phos, four hours be­fore im­pact by an au­tonomous op­ti­cal nav­i­ga­tion sys­tem called the Small-body Ma­neu­ver­ing Au­tonomous Re­al Time Nav­i­ga­tion sys­tem (SMART Nav).
Size comparisons
Size com­par­isons
Image 5/7, Credit: NASA/Johns Hopkins APL

Size comparisons

Didy­mos and Di­mor­phos are small as­ter­oids. To­day, over one mil­lion as­ter­oids of more than 100 me­tres in di­am­e­ter are known to or­bit the Sun be­tween Mars and Jupiter in the Main As­ter­oid Belt. Of these, ap­prox­i­mate­ly 25,000 to 30,000 of these bod­ies move along or­bits that could cross Earth's path and bring them close to the plan­et. The col­li­sion of an as­ter­oid the size of Didy­mos or Di­mor­phos would cause con­sid­er­able dam­age on Earth – even if it hit the ocean, where it would trig­ger a tsuna­mi. As­ter­oid im­pacts have oc­curred fre­quent­ly in Earth's his­to­ry, but none of the Earth ‘or­bital cruis­ers’ known to­day has an or­bit that is on a col­li­sion course with our plan­et.
Launch of DART on 24 November 2021
Launch of DART on 24 Novem­ber 2021
Image 6/7, Credit: NASA/Johns Hopkins APL/Ed Whitman

Launch of DART on 24 November 2021

Ear­ly on the morn­ing of 24 Novem­ber 2021, the jets of fire from a SpaceX Fal­con 9 rock­et lit up the Cal­i­for­nia coast­line at Van­den­berg Air Force Base, launch­ing NASA's Dou­ble As­ter­oid Redi­rec­tion Test (DART) space­craft in­to space. DART was de­vel­oped and man­aged by the Ap­plied Physics Lab­o­ra­to­ry (APL) at Johns Hop­kins Uni­ver­si­ty in Lau­rel, Mary­land (USA), for NASA's Plan­e­tary De­fense Co­or­di­na­tion Of­fice. It is the world's first mis­sion to test tech­nol­o­gy to de­fend the plan­et from po­ten­tial as­ter­oid or comet threats.
The last photo transmitted by DART
The last pho­to trans­mit­ted by DART
Image 7/7, Credit: NASA/Johns Hopkins APL

The last photo transmitted by DART

The last ful­ly trans­mit­ted pho­to from the DRA­CO cam­era aboard DART be­fore the im­pact on Di­mor­phos shows the as­ter­oid sur­face cov­ered in rock de­bris. The pho­to was tak­en two sec­onds be­fore the im­pact from a dis­tance of 12 kilo­me­tres. The im­age is 31 by 31 me­tres. Di­mor­phos' north is at the top of the im­age.
  • NASA's DART spacecraft will reach the Didymos-Dimorphos binary asteroid system on 27 September 2022 at 01:14 CEST and impact the asteroid Dimorphos during a targeted approach.
  • The spacecraft will crash on the 170-metre-diameter companion at almost 22,000 kilometres per hour, nudging it into a slightly tighter orbit around the 800-metre-diameter asteroid Didymos.
  • It is the first time in the history of spaceflight that an attempt is made to change the orbit of a celestial body.
  • Focus: Spaceflight, exploration, planetary defence, asteroids

+++Update: NASA's DART spacecraft impacted the asteroid Dimorphos 11 million kilometres from Earthas planned at 01:14 CEST on 27 September 2022. This marks the first successful attempt to deflect a celestial body. Travelling at 22,000 kilometres per hour DART transmitted image and navigation data to the ground station at the Applied Physics Laboratory of Johns Hopkins University in Maryland (USA). "The navigation team did a fantastic job," says a delighted Jean-Baptiste Vincent of the German Aerospace Center (DLR). "DART seems to have hit Dimorphos right in the middle." The scientist from DLR's Institute of Planetary Research in Berlin is a member of the DART Science Team. He will now analyse the data from DART and the observations from the Italian small satellite LICIACube, which was launched by DART 15 days ago and flies behind it at a short distance, as well as many Earth-based telescope observations. "We are currently checking how much the orbital period around the larger Didymos has actually changed," says Stephan Ulamec from the DLR Microgravity User Support Center (MUSC) in Cologne. The model calculations assume one percent or a few minutes. "If that were the case, DART would be an important first step in protecting Earth from asteroid impacts. "+++

In the early hours of Tuesday morning, NASA's Double Asteroid Redirection Test (DART) mission, which was launched in November last year, will test whether it is possible to change the course of an asteroid. DART will then reach the Didymos-Dimorphos asteroid binary system and impact the 170-metre wide 'moonlet' Dimorphos during a targeted approach. The 'kinetic momentum' transferred in the process is expected to alter the orbit of Dimorphos around its larger companion, Didymos. This is the first time in the history of spaceflight that an attempt is being made to influence the orbit of a celestial body by a human-made body. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) is involved in the analysis of the impact. In 2026, the ESA mission Hera, in which Germany is significantly involved through the German Space Agency at DLR, is to explore the asteroid system and its shifted orbit.

Earth has always been threatened by asteroid collisions. Although almost all of the approximately one million 'known' celestial bodies over 100 metres in size move in stable orbits between Mars and Jupiter, about 30,000 of these have orbits that intersect with Earth's orbit around the Sun. It is these bodies that could potentially collide with our planet. A collision of a body even a few hundred metres in size with Earth would cause quite considerable damage. Such danger may be averted by using space probes to alter the course of a potential Earth-colliding asteroid very early on so that it simply flies past our planet.

"We live in the age of space travel. This gives us the opportunity to use space probes to deflect an asteroid that may potentially collide with Earth," says Jean-Baptiste Vincent from the DLR Institute of Planetary Research. DLR has been observing and characterising Earth-crossing asteroids for decades. "On the one hand, we try to characterise these small, but sometimes dangerous, celestial bodies to understand their physical properties, and on the other hand we observe them to be able to draw conclusions on how we could ward them off should our calculations show that they could collide with Earth in the future," explains Stephan Ulamec from the DLR Microgravity User Support Center (MUSC) in Cologne.

Change in orbital period by a few minutes

The two DLR scientists are involved in NASA's DART mission. DART is a cube-shaped satellite with an edge length of just under two metres and a mass of 610 kilograms. The mission was launched on 24 November 2021 and steered on an elliptical orbit to its target, the asteroid pair Didymos and Dimorphos. Didymos, the larger of the two bodies, has an irregular diameter of nearly 800 metres, Dimorphos of about 170 metres. Dimorphos orbits Didymos – Greek for twin – in 12 hours at a distance of 1200 metres. Together, the two asteroids orbit the Sun in 25 months on an orbit that crosses Earth's orbit, making them potentially dangerous Near-Earth Objects (NEOs). In 2003, the two asteroids came within six million kilometres of Earth.

"We assume that Dimorphos' orbital period around Didymos will change by a few minutes due to DART's momentum," predicts DLR researcher Stephan Ulamec. "However, we do not know what Dimorphos is like," adds Jean-Baptiste Vincent. "Is it a compact body or are its components only very loosely assembled? In other words, is Dimorphos maybe just a pile of rock fragments, a 'rubble pile' as we say in asteroid research?" The task of the two DLR scientists in the DART team is to determine the exact shape of the small asteroid, its precise mass and to analyse the crater and the transmission of the momentum and ejecta produced by the impact.

The spacecraft will, of course, be completely destroyed in the process, but the impact of DART on Dimorphos will be observed by two small cubesats which were deployed on 11 September. The two LICIACubes were developed by the Italian Space Agency (ASI) to make flyby observations of the Didymos binary asteroid system following DART’s impact. The small satellites will communicate directly with Earth before, during and after the impact. Two cameras (LUKE and LEIA) will confirm the impact and capture images of the ejecta cloud and possibly a crater. Three minutes after DART's impact, they will have flown past Dimorphos, turning and still taking pictures of the far side of Dimorphos, which of course DART will not get to see up close. LICIACube is the first all-Italian autonomous space probe in space. NASA's Lucy mission, launched last year to the 'Trojan' asteroids in Jupiter's orbit, will also observe the impact from a distance of 19 million kilometres.

Will we be able to deflect asteroids in the future?

The targeted collision of the DART spacecraft with Dimorphos will occur on 27 September 2022 at 01:14 CEST at a distance of just over 11 million kilometres from Earth, the closest the binary asteroid system will be to Earth in the near future (the asteroid pair will not pass Earth at a similarly close distance again until 2062). Being this 'close' to Earth also provides good observing opportunities for telescopes on the planet's night side, especially from Europe; observations that will be used for complementary analyses during and after the collision. These and other telescopes will also record light curves of the binary asteroid system in the nights after the event to contribute data on Dimorphos’ orbital alteration to the overall analysis.

Nearly 11 million kilojoules of energy are converted during DART's impact with Dimorphos. The researchers assume that the impact will create a crater several tens of metres in diameter and that the asteroid’s orbital period will change measurably, by a few minutes. This corresponds roughly to a change in velocity of half a millimetre per second. "How efficiently an asteroid is deflected by colliding with a space probe is decisively influenced by the physical properties of the body, in other words, it depends on how porous and solid the rock is," explains Kai Wünnemann from the Museum für Naturkunde Berlin, whose team has been developing computer simulations of the impact process in order to make predictions that are as precise as possible. At the Museum für Naturkunde Berlin, various scenarios of the nature of Dimorphos are run and simulated in order to predict the size of the crater, among other things.

In October 2024, the European Space Agency (ESA) will launch Hera, a mission coordinated with NASA, which will be developed and built largely in Germany, to study the impact and its consequences in detail. The German Space Agency at DLR, based in Bonn, manages the German ESA contributions for Hera. Hera will reach the binary asteroid system in December 2026, approximately four years after the impact of DART. Hera's detailed investigations will then significantly expand knowledge about the possibilities afforded by asteroid deflection. DART and Hera are missions of the international research project AIDA (Asteroid Impact and Deflection Assessment).

Repeated asteroid impacts in Earth's history

In the foreseeable future, there is currently no reason to worry about an asteroid hitting Earth. But asteroid collisions have happened again and again in Earth's four-and-a-half billion years of history. Traces of these can be found in the craters left behind when asteroids hit, such as the Nördlinger Ries in southern Germany or the Barringer Crater in Arizona. The Moon, littered with impact craters, makes it clear that asteroid collisions used to be much more frequent. However, on the dynamically ever-changing Earth, almost all traces of impacts have been erased. The extinction of the dinosaurs was caused by an asteroid collision 65 million years ago. That the danger of an asteroid hitting Earth remains real today, albeit on a much smaller scale, became clear on 15 February 2013. At that time, an unknown asteroid entered Earth's atmosphere and exploded over the Russian city of Chelyabinsk. The shockwave of compressed air from Earth's atmosphere caused considerable damage in the city. Thousands of window panes were shattered, injuring more than 1600 people. The total damage was estimated at 30 million euros. Yet the asteroid in Chelyabinsk was only about 18 metres in diameter.

  • Falk Dambowsky
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 2203 601-3959
    Linder Höhe
    51147 Cologne
  • Stephan Ulamec
    Phi­lae Lan­der Project Man­ag­er
    Ger­man Aerospace Cen­ter (DLR)
    Space Op­er­a­tions and As­tro­naut Train­ing
    Mi­cro­grav­i­ty Us­er Sup­port Cen­ter (MUSC)
    Münchener Straße 20
    82234 Weßling
  • Jean-Baptiste Vincent
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Ex­tra­so­lar Plan­ets and At­mo­spheres
    Rutherfordstraße 2
    12489 Berlin
  • Prof. Dr. Kai Wünnemann
    Mu­se­um für Naturkunde
    Leib­niz In­sti­tute for Evo­lu­tion and Bio­di­ver­si­ty Sci­ence
    Telephone: +49 30 2093-8857
    Invalidenstraße 43
    10115 Berlin


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