A strange thing that gets so close to the sun sometimes Saturnand other times it recedes as far as Uranusit has been found to have a transforming disk of dust around it that changes shape and can even mimic rings.
Minor planet 2060 Chiron called Centaur, captured comedy stuff which travels around the sun in a looping orbit between Jupiter and Neptune. Chiron is only 218 kilometers (135 miles) across and sometimes has outbursts like a comet. So far, however, no spacecraft has ever visited Centaur.
In 2011, Chiron went in front of a faint star from our point of view World. Such events are referred to as “stellar occultations,” and based on how an object such as Chiron blocks starlight, the shape and size of the occulting object can be determined by deduction. During the 2011 occultation, it was noted that the star’s light dimmed slightly – twice before Chiron itself occupied the star, and twice after Chiron moved over the star. This observation was interpreted as Chiron having a double ring system of dust.
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Then, Chiron engaged another star on November 28, 2018, in an event involving Amanda Sickafoose, who is a senior scientist at the Planetary Science Institute in Tucson, Arizona. Because Chiron’s shadow cast by the star is so small, it only crossed a narrow region of Earth, skirting southern Africa. So Sickafoose led a team that used the 1.9-meter (6.2-foot) telescope at the South African Astronomical Observatory in Cathay, South Africa, to observe the interrogation.
Their findings, published exactly five years later, tell a slightly different story from 2011.
“We felt dips in the starlight because it was blocked by the nucleus of Chiron as well as material located between 300 and 400 kilometers on either side,” Sickafoose said in his statement.
Specifically, as Chiron moved past the star, the Sickafoose team observed decreases in the starlight that produce dusty material at radii of 352, 344 and 316 kilometers (about 219, 214 and 196 miles) from Chiron’s center. In other words, that was between 100 and 130 kilometers (60 to 80 miles) above the Centaur’s surface. After Chiron moved away from the star, the scientists then observed two more drops at 357 and 364 kilometers (221 and 226 miles) from the center of Chiron.
If Chiron had only two stable rings, you would expect two pairs of symmetrical drops in light on either side of Chiron. The third anomalous fall on one side of the Centaur is evidence that the situation is not so clear. Furthermore, the diminutions that caused the mystery appear to have occurred thousands of kilometers away from the locations of the rings as measured in 2011 (although they fall within the margin of error of the 2011 observations). The IS size of the reductions in starlight caused by the matter, however, also different.
“The locations and amounts of material detected around Chiron are sufficiently different from previous observations to suggest that there is not a stable ring system but a surrounding material that is currently evolving,” said Sickafoose.
Another spectacular occultation of Chiron was seen on December 15, 2022 at the Kottamia Astronomical Observatory in Egypt by a team led by Jose Luis Ortiz from the Instituto de Astrofísica de Andalucía in Spain. They found the material around Chiron had changed again, relying on three symmetry structures on either side of Chiron. Two of the features are narrow and one is wide, and together they appear to form a wide disc 580 kilometers (360 miles) across.
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The origin and composition of this material around Chiron is still unknown, although it seems likely that it comes from Chiron itself, perhaps bursting in. space with comedic outbursts such as those seen in the summer of 2021 when Chiron dimmed by 0.6 magnitude. For context, a magnitude 0 object is 100 times brighter than a magnitude 5 object in this luminosity system. Another Centaur, the 250-kilometer (160 mile) wide Chariklo 10199, was also previously shown to have rings during a stellar occultation in 2013, and was confirmed during another stellar occultation observed by the James Webb Space Telescope on October 18, 2022. The JWST even water-ice sensor on Chariklo. However, the Chiron findings also cast doubt on the nature of the structures around Chariklo.
Faint occultations stars with Chiron it happens fairly regularly, and future observations now have a challenge on their hands to explain what is happening around the distant, apparently Centaur.
The results were published on 28 November The Planetary Science Journal.