by Scientists may have learned the history of the bee contact-binary moon orbiting an asteroid 152830 Dinkinswhich was the first space stop for NASA Lucy spaceship. Maybe that moon took her parent more away an asteroid when Dinkinesh was sent spinning through space after absorbing and re-emitting sunlight.
After its launch in 2021, the Lucy mission is on its way to investigate the Trojan asteroids, which share the orbit of Jupiter – but, to reach them, Lucy must travel through the asteroid belt between Mars and Jupiter. In a silver lining, however, this gave Lucy the opportunity to test her abilities on a mini-world in the asteroid belt before reaching Troy, located at Jupiter L4 and L5 Lagrange points.
Related: The Lucy mission: NASA’s trip to the Trojan asteroids
On November 1, 2023, Lucy flew within 268 miles (431 kilometers) of Dinkinesh, nicknamed ‘Dinky.’ That may not seem like a significant distance until you consider that Dinkinesh is only 787 yards (720 meters) in diameter. However, the spacecraft’s autonomous detection and tracking system was able to lock onto Dinkinesh, allowing the Lucy Long-Range Reconnaissance Imager (L’LORRI) to image the asteroid.
What he found was surprising: Dinkinesh is not alone!
L’LORRI he discovered a natural satellite orbiting Dinky every 52.7 hours for a distance of 1.9 miles (3.1 kilometers). It is not surprising that an asteroid would have a moon; astronomers are finding that about 15% of small asteroids have companions, such as Dimorphos, which is the small body orbiting the asteroid Didimos and was subject to NASA DART planetary defense mission in 2022. What is particularly interesting about Dinky, however, is that its small moon, called Helloit is itself a contact binary — two things stuck together as one.
Again, they are not so rare in and of themselves; the comet 67P/Churyumov-Gerasimenkofor example, visited by the European Space Agency Rosetta mission for two years between 2014 and 2016, there was binary contact. Arrokothwhich is the Kuiper belt object to New Vision fly down on New Year’s Day 2019, it is also a contact binary.
However, Selam is the first contact-binary-asteroid-moon situation.
Specifically, Selam appears to have two objects, or lobes, connecting end to end. They are the same size: one lobe is about 230 yards (210 meters) across and the other is 250 yards (230 meters) across. Selam is tidally locked to Dinkinesh, meaning that one lobe that is closest to the larger asteroid remains permanently. Frustratingly, the point of contact between the two lobes is hidden in shadow in L’LORRI’s images.
Of course, the astrologers wanted to know how Selam created like this. The clues, according to a team led by the mission’s principal investigator, Hal Levison of the Southwest Research Institute in Boulder, Colorado, can be found on Dinkinesh’s surface.
The largest asteroid is distinguished by a large trough that runs longitudinally around it, as well as an equatorial ridge superimposed on top of that trough and moving around its axis of rotation. Levison’s team argues that these features are the result of a massive structural shock that occurred when the asteroid’s rotation was spun by a phenomenon known as the YORP effect.
Short for Yarkovsky–O’Keefe–Radzievskii–Paddack, after the scientists who first modeled it, the YORP effect describes how a relatively small object such as Dinkinesh can be swept away by the effects of sunlight. absorption and then re-emission. The momentum of solar photons hitting the surface, and then thermal photons emitted from the surface as the surface is exposed to sunlight, creates small amounts of thrust that can push around an asteroid smaller than about 3.1 miles (5 kilometers) in width. Although such a thrust would be extremely smooth, above all, it would be capable of building enough power to significantly disrupt the rotation of an asteroid. In Dinkinesh’s terms, the YORP effect increased the rotation of the space rock – today, it rotates once every 3.7 hours.
But that was not all.
The centrifugal force as a result of Dinkinesh, scientists now learned, then caused some material to rise from the surface of the spinning, loose held together, asteroid. That material then settled into a debris ring around the asteroid’s equator. Structurally destabilized, a crack was literally visible on the surface of Dinkinesh – the large tank we see today.
Some of the material ejected from Dinkinesh fell back onto the asteroid, forming the equatorial ridge, while the rest combined to form two satellites. This, by the way, is the mechanism it is believed to have Didymos’ moon Dimorphos was formedtoo.
Dimorphos, however, is just one ordinary satellite – so to create a contact binary like Selam there must be more to the story.
Related Stories:
— NASA’s Lucy spacecraft successfully completes first ‘Dinky’ asteroid flyby
– Surprise! Asteroid ‘Dinky’ is a double space rock, revealed by NASA’s Lucy probe (photo)
— A strange double moon discovered in the orbit of asteroid ‘Dinky’ now has a name
Levison is intrigued by the fact that the two lobes are almost equal in size, and wonders whether this is telling us something about the process of satellite formation. Regardless, once the two halves of Selam met, they must have edged closer and closer together, moving at a very low relative velocity, until they were close enough to kiss. From there, gravity was able to hold them together.
It seems that nature has done a very delicate operation in creating Selam.
If these lobes had been associated with a higher relative velocity, they would have joined together to form a single lobe, or, more likely, they would have broken apart. Instead they connected, and now are literally stuck with each other.
The analysis of Lucy’s comments on Dinkinesh and Selam is published in Nature.
