Free Astronomy Magazine November-December 2017

18 NOVEMBER-DECEMBER 2017 SPACE CHRONICLES In September 2016, just be- fore the asteroid 288P made its closest approach to the Sun, it was close enough to Earth to allow astronomers a detailed look at it us- ing the NASA/ESA Hubble Space Telescope. The images of 288P revealed that it was actually not a single object, but two asteroids of almost the same mass and size, orbiting each other at a dis- tance of about 100 kilome- tres. That discovery was in itself an important find; be- cause they orbit each other, the masses of the objects in such systems can be mea- sured. But the observations also revealed ongoing activ- by NASA/ESA Hubble discovers a unique type of object in the Solar System W ith the help of the NASA/ESA Hubble Space Telescope, a German-led group of astronomers have observed the intriguing characteristics of an un- usual type of object in the asteroid belt between Mars and Jupiter: two asteroids orbiting each other and ex- hibiting comet-like fea- tures, including a bright coma and a long tail. This is the first known binary as- teroid also classified as a comet. The research has been re- cently presented in a paper published in the journal Nature . T his artist’s animation shows the binary main-belt comet 288P. From a distance the comet-like features of the system can clearly be seen: among them, the bright coma surrounding both components of the system and the long tail of dust and water pointing away from the Sun. Only a closer look reveals the two components of the system: two asteroids circling each other on an eccentric orbit. [ESA/Hubble, L. Calçada, M. Kornmesser]