DART changed Dimorphos’ circuit

On September 26 at 23.14 in Universal Time (2 hours more on the French mainland) DART probe weighing around 500 kg, hit Dimorphos at a speed of 23,760 km/h. The stated goal of this NASA mission was to change the orbit of this small moon.

A significantly shorter course

160 m wide, Dimorphos orbiting Didymos, a 780 m asteroid discovered in 1996. The duo follows a circle around the Sun and does not threaten our planet. The impact on September 26th took place 11 million kilometers from Earth.

The DART impact on Dimorphos on September 26 caused a dust plume to be captured by the small Italian satellite LICIACube, which was dropped by the NASA probe a few days before. In the center of the image, the asteroid Didymos and below Dimorphos.
Credit: ASI/NASA

Working on the LICIACube images, the researchers were able to extract data describing the impressive jet generated by the DART impact (image below).

The rectangles are explained with different contrast settings to better show the plumes coming from Dimorphos after the DART crash on this small moon.  Credit: ASI/NASA

The rectangles are explained with different contrast settings to better show the plumes coming from Dimorphos after the DART crash on this small moon.
Credit: ASI/NASA

In the days that followed, several observatories investigated the consequences of this collision, especially to determine with precision Dimorphos’ orbit around Didymos.

This radar image of the duo Didymos and Dimorphos was obtained by combining observations from radio telescopes at Goldstone in California and Green Bank in West Virginia.  The light blue circle shows the expected position of Dimorphos if its orbit had not been altered.  The green circle indicates the observed position of the moon.  DART has therefore changed Dimorphos' circuit.  Credit: NASA/Johns Hopkins APL/JPL/NASA JPL Goldstone Planetary Radar/National Science Foundation's Green Bank Observatory

This radar image of the duo Didymos and Dimorphos was obtained by combining observations from radio telescopes at Goldstone in California and Green Bank in West Virginia. The light blue circle shows the expected position of Dimorphos if its orbit had not been altered. The green circle indicates the observed position of the moon. DART has therefore changed Dimorphos’ circuit.
Credit: NASA/Johns Hopkins APL/JPL/NASA JPL Goldstone Planetary Radar/National Science Foundation’s Green Bank Observatory

The radar sighting shown above isn’t the only one DART mission officials relied on. However, the conclusions are the same: Dimorphos’ 11 hour 55 minute orbit around Didymos is now 11 hours 23 minutes, or a reduction of 32 minutes !

Deflect a threatening object

When presenting the mission, NASA most often referred to 10 minutes about reducing Dimorphos’ turnaround time. The 10 minute figure was actually a value within a range derived from complex calculations. The result of 32 minutes is also in it. However, this is a change of circuit, which is at the top of the possibilities, minimum 72 seconds. NASA therefore assesses that DART exceeded the lowest expected result by 25 times (below a video recording of the October 11 press conference announcing these numbers).

DART thus validates a deviation method which could be implemented if an object one day threatens our planet. If the modification achieved with DART on Dimorphos seems modest, it should be understood that the principle is to apply it to an asteroid that would be discovered decades or even centuries before the impact. Over time, the small change in trajectory would lead to a few thousand kilometers necessary for the Earth to be spared.

This logic is explained in the IMAX film Chasseurs d’asteroïds 3D presented at the Cité de l’Espace in Toulouse. Below is the trailer in English (the film is in French in Cité de l’Espace).

In October 2024, the European Space Agency (ESA) will send the Hera probe to the Didymos-Dimorphos binary system (expected to arrive in September 2026), which will investigate in detail the consequences of the DART impact and provide additional data for this logical protection. of the Earth.

This image made with the Hubble Space Telescope on October 8 shows the tail of debris caused by the DART collision on Dimorphos.  Other observations will be carried out to scrutinize the behavior of this cloud of debris (which poses no danger to Earth).  Credit: NASA/ESA/STScI/Hubble

This image made with the Hubble Space Telescope on October 8 shows the tail of debris caused by the DART collision on Dimorphos. Other observations will be carried out to scrutinize the behavior of this cloud of debris (which poses no danger to Earth).
Credit: NASA/ESA/STScI/Hubble

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