The space rock, born at the birth of the Solar System, has long puzzled astronomers
For quite a while, an asteroid named Phaethon has presented astronomers with something of F a conundrum. When it passes close to the Sun during its orbit, a long tail of material can be seen leaving the rock. However, if Phaethon’s tail is the stuff of usual comets – ice and carbon dioxide – then it should be visible when the comet is as far away as Jupiter, too. But it’s not. Scientists have therefore had some theories about what Phaethon might be composed of, which could explain what trails behind when the asteroid passes by the Sun. In new research, astronomers have compared the infrared emissions of Phaethon analysed by NASA’s Spitzer Space Telescope to emissions of meteorites in laboratories, ultimately finding that Phaethon likely belongs to a rare class of meteorite of which only six specimens are known.
Phaethon’s emission spectrum corresponds to a type of meteorite called the ‘CY carbonaceous chondrite’. Conversely, other well-known asteroids such as Ryugu and Bennu, targets of recent Japan Aerospace Exploration Agency (JAXA) and NASA sample-return missions, are CI and CM meteorites respectively. All three classes are believed to have originated during the birth of the Solar System, as they all show signs of the chemical process in which water combines with other molecules to form phyllosilicate and carbonate materials. However, only the CY group seemed to show signs of drying and decomposition due to heating; it also exhibits a high iron sulphide content, which suggests a unique origin.
Analyses of Phaethon’s emission spectrum revealed olivine, carbonates, iron sulphides and oxide minerals – all of which supported the space rock’s connection to the CY class of asteroid. Carbonates in the asteroid indicate changes in water content, for instance, and the olivine is consistent with thermal decomposition of phyllosilicates at high temperatures. Researchers were able to show with thermal modelling how temperatures, such as those encountered when passing by the Sun, might affect minerals in the asteroid that release gases. As the asteroid gets nearer the searing ball of plasma at our Solar System’s centre, its surface temperatures can rise to 800 degrees Celsius (1,472 degrees Fahrenheit), which the team says is easily hot enough for the object’s carbonates to produce carbon dioxide and phyllosilicates to release water vapour and sulphides.
Data from other studies on asteroids, combined with the new thermal models of Phaethon, led the researchers to believe that pressure from the gas released by the asteroid heating up could cause the rock to break down, producing small dust particles that are lifted from its surface – a likely e
