Asteroid Didymos is sending rocks flying into outer space

The recent observations prove that not all asteroids are boring objects simply hanging out in space.
Loukia Papadopoulos
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Asteroid Didymos.


Gone are the days when we believed asteroids to be just large rocks hanging out in space. As space exploration has progressed, we have come to note that they are much more complex than that.

A great example of this is the asteroid Didymos, which according to a new study published on Monday, is literally spitting rocks into outer space due to the excessive speeds at which it is spinning.

Didymos has been studied for quite some time now in preparation for NASA’s DART (Double Asteroid Redirection Test) and the European Space Agency’s Hera mission. DART has now had first-hand experience with the asteroid up close (before crashing into its moon Dimorphos), giving researchers troves of data about its shape, mass, and rotation.

Spinning fast

The experts have discovered the asteroid is spinning very quickly, completing one full rotation every 2 hours and 16 minutes. That’s super fast.

The researchers described Didymos in their work as an asteroid “on the edge of stability” due to its impressive rotational speeds. The effects of the spin are felt the strongest at the celestial object’s equator.

In this region, rocks and dust are able to lift off the surface and even move into orbit. This makes Didymos a spinning asteroid that is spewing out constant materials in its vicinity and beyond.

“Massive particles potentially levitate for some time, land on the surface and lift off again, repeating such cycles over and over, or just land at latitudes from which further lift off is not possible,” the authors wrote in their study.

The elements ejected by Didymos either reach orbit or are deposited onto the moon Dimorphos. Some may even escape the system, guided by the power of the solar wind.

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It should be noted that the bigger objects tend to stay afloat longer than the smaller ones. This phenomenon is caused by the solar radiation pressure found on the day side of the celestial object that constantly pushes the smaller grains back down to the surface.

Last year, NASA purposefully slammed its DART spacecraft into Dimorphos to test a planetary defense method. The mission successfully reduced the orbital period of the moon around Didymos by roughly 32 minutes, although it seems to have had little impact on the asteroid itself.

The study is published in the journal ArXiv.

Study abstract:

An increasing number of Near Earth Asteroids (NEAs) in the range of a few hundred meters to a few kilometres in size have relatively high spin rates, from less than 4 h, down to 2.2 h, depending on spectral type. For some of these bodies, local acceleration near the equator may be directed outwards so that lift off of near-equatorial material is possible. In particular, this may be the case for asteroid Didymos, the primary of the (65803) Didymos binary system, which is the target of the DART (NASA) and Hera (ESA) space missions. The study of the dynamics of particles in such an environment has been carried out -- in the frame of the Hera mission and the EC-H2020 NEO-MAPP project -- according to the available shape model, known physical parameters and orbital information available before the DART impact. The presence of orbiting particles in the system is likely for most of the estimated range of values for mass and volume. The spatial mass density of ejected material is calculated for different particle sizes and at different heliocentric orbit epochs, revealing that large particles dominate the density distribution and that small particle abundance depends on observation epoch. Estimates of take off and landing areas on Didymos are also reported. Available estimates of the system mass and primary extents, after the DART mission, confirm that the main conclusions of this study are valid in the context of current knowledge.

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