Asteroids are usually found hundreds of millions of kilometers from our planet, so telescopic images only show points of light moving between the stars. The images of the asteroid DonaldjoHanson obtained by Lucy are a good example of the scientific value of the space missions: they reveal the size, the intricate structure and the characteristics of these rocky bodies, witnesses of exception of the great collisions that occur in the solar system.
How it acquired its intriguing form
The asteroid now visited by the Lucy probe has carbonaceous nature, being representative of the meteoritic group known as carbonaceous chondritas for containing a small percentage of carbon in its composition. It is located in the inner region of the main asteroid belt, between the orbits of Jupiter and Mars.
Our knowledge of 52246 DonaldjoHanson before Lucy’s arrival was quite scarce. The photometric models suggested an average size of 5 km, but the images of the probe reveal that it is a bilobular asteroid with two main axes: one of 8 km and another 3.5 km.
Surveuel of the asteroid DonaldjoHanson for the Lucy probe. NASA/GODDARD/SWRI/APL OF JOHNS HOPKINS, CC BY
A gigantic collision survivor
The characteristics of DonaldjoHanson indicate that it is a survivor of gigantic collisions, such as most large objects stored in the main asteroid belt.
In fact, the bilobular structure reveals that its current stadium is a consequence of the meeting of two asteroids that, after an impact at low relative speed, were united by a rocky neck. This area shows several folds that had to arise from the compression induced by the shock wave generated after the impact that the two blocks joined, conferring its peculiar shape.
The family of 163 Erígone
More than a decade ago, various researchers pointed out the recent origin of the asteroid family to which DonaldjoHanson belongs. Apparently, this group was born after a catastrophic collision that fragmented the progenitor body in thousands of large blocks about 170 million years ago. Asteroid 163 Erigone ended up being the greatest of them and has given the family.
The 163 Erígone family is exceptionally young in astronomical terms. Hence its scientific interest, as an example of colossal impacts that occurred recently.
The structure of the asteroid Donaldjohanson suggests that it is formed by the aggregation of several solid blocks of what would have been the aforementioned parent asteroid.
Kilometric craters
Unlike other objects of less than a kilometer in diameter, studied by other space probes, DonaldjoHanson has a sufficient gravitational field to accumulate large rocks produced in impacts, which have been stacking on their surface.
In addition, the large size of the asteroid indicates that under that regolite coverage (loose rock and sprayed minerals) must have large monolithic blocks, hidden under the pile of rubble created by successive impacts that produced innumerable impact craters.
As we pointed out in a recent work, the presence of kilometer size craters on the surface of an asteroid reveals that it is covered with regolito. In fact, this stacked rock cover will have a depth similar to that of the size of the largest craters on its surface.
The images obtained by the Lucy probe show several of those kilometer craters, from which it follows that DonaldjoHanson must effectively possess a deep coverage of stacked rocks, a consequence of the innumerable impacts experienced since their formation.
On the other hand, the stability of the family of 163 Erígone also concludes the interest of the scholars of celestial mechanics. We could say that they are “balanced” asteroids because their orbits oscillate due to gravitational disturbances generated by various planets.
Next destination: The Trojan asteroid region
After the fleeting meeting with the asteroid DonaldjoHanson at a relative speed of 13.4 km/s, the Lucy spacecraft will continue to travel for a year and a half through the main asteroid belt. He plans to meet one of his greatest scientific objectives, the fascinating asteroid Trojan Eurybates, in August 2027.
The Trojan asteroids coorbitate the solar system around the gigantic planet Jupiter, and there we hope that Lucy will meet asteroid elderly capable of revealing stories never told about the very origin of our planetary system.
This article was originally published in The Conversation.
