What Happened to ISON?

ISON Survives, from SOHO (NASA)

Comet ISON made its closest approach to the Sun yesterday, and it’s not quite clear yet in just what form the comet has emerged from its close encounter. Comets are composed of conglomerations of ice and rock, and exposure to the Sun’s intense heat and gravity during close passes can tear them apart. The comet’s nucleus orbits the Sun like any other solid solar system body, while the gas and dust of the coma and tail make up the dramatic, visible portion of the comet as they are blasted off the nucleus by solar heat and pressure. During live observations with NASA’s SDO satellite yesterday, observers did not see ISON come back into view as expected—in fact, it was surprisingly not seen by SDO at all. The suspicion began to grow that the comet hadn’t survived in any meaningful state. Later, however, SOHO images (above) revealed that something had survived, as an obvious cloud emerged from near the Sun, following ISON’s orbital path. But there is still not enough evidence to make any confident judgments about what this post-encounter ISON is. Clearly, ISON in some form is now headed away from the Sun, but whether it is ISON’s nucleus, substantially intact, or scattered fragments, like the famous Shoemaker-Levy 9, remains to be seen.

Updates are available from NASA and from the Bad Astronomer Phil Plait.

Image: NASA

Comments are closed.