The sky seems to be full of interesting objects that are breaking apart. They’re always worth studying, as we learned through the impacts of the famous ‘string of pearls’ comet — Shoemaker-Levy 9 — on Jupiter in 1994. For one thing, the celestial display they afford is uncommonly interesting; for another, they are a reminder of the kinds of debris that we need to track just in case any of it turns out to be on an Earth-crossing trajectory.
No apparent chance of that with 60558 Echeclus, a 50-kilometer ‘centaur’ out beyond the orbit of Saturn. Centaurs are icy planetoids that, in the case of both 60558 Echeclus and Chiron (the first centaur to be discovered), seem to display cometary properties. 60558 Echeclus is now even more interesting with the news that a large chunk of the object seems to have broken away. The resultant dust cloud is 100,000 kilometers across as both centaur and breakaway fragment blow off dust and gas, with more coming from the fragment than the main body (and that, too, remains a mystery).
Watch the theories fly as astronomers try to figure out what caused the breakup, there being no gravitational disturbances to account for it. And watch, too, the dying comet 73P/Schwassmann-Wachmann 3. For reasons unknown, the comet’s nucleus broke into three parts in 1995. The resulting mini-comets, of which there are now at least eight, are going to pass Earth in May, closer than any comet has come in twenty years, providing an unusual visual display for the Hubble instrument, not to mention legions of amateur astronomers. The fragments will give us our first close-up look of a comet’s end and may provide an accompanying shower of meteors.
As to what made this one break up, Paul Wiegert (University of Western Ontario) has this to say:
“The most likely explanation is thermal stress, with the icy nucleus cracking like an ice cube dropped into hot soup: the comet broke apart as it approached the Sun after a long sojourn in the frigid outer solar system. If this is truly what happened, then the debris cloud should be expanding slowly, and there will be no strong meteor shower.”
No Earth-crossing danger here, either, with the closest fragment still six million miles away. But perhaps the very instability shown by these two breakups should remind us that the Solar System is still an evolving place, one where large planetary impacts can’t be ruled out. Shoemaker-Levy 9’s collision with Jupiter was spectacular indeed; such impacts on Earth would be catastrophic. Groups like the B612 Foundation, which argues the need for anticipating potential collisions and building the technologies to prevent them, continue to merit your support.