This column was supposed to be about viewing Comet ISON, "the comet of the century." Starting a year ago, websites and some of the news media billed ISON as a glory that would "become dazzlingly bright, rivaling the brightness of a full moon" or even "100 times brighter than the moon." It would be enormous right now, lighting up the whole eastern sky before dawn.
We astronomers complained that ISON might be a nice comet but was being overhyped by people who were credentialed but uninformed and that some outlets were quoting only the newsiest declarations and using each other for confirmation.
We did hope for a nice comet that would be visible to the naked eye and beautiful in binoculars and telescopes. In fact, that was just 10 days ago. Now there is nothing to see at all.
The Hubble Space Telescope is about to take a look for Comet ISON's remains. Astronomers hope to detect a few surviving pinpoint specks at the limit of the Hubble's vision.
What happened?
Comet ISON was a drama queen from the outset. It tricked and misled comet specialists each step of the way since two Russian amateur astronomers discovered it 15 months ago. At first, its prospects seemed very good indeed. On its way into the solar system it started shining much earlier than comets usually do. Then it fizzled. Then it perked up somewhat as it headed closer to the warmth of the sun, and in the last month it grew into a gorgeous green ball with a long, blue-gray tail, for skilled astro-imagers using advanced cameras and processing techniques to pull it out of the background sky. From the Boston suburbs you could detect it in binoculars as a little tailed dot. It was fuzzy and pale greenish white.
The big test, everyone knew, would come on Thanksgiving Day when the comet would make an extremely close loop around the sun. The solar broiling might blow off a naked-eye tail for all to see in December. Or ISON might remain a target for binoculars and telescopes. Or it could vaporize to nothing.
By the day before, the comet was too close to the sun to see from Earth. But millions watched online through the eyes of sun-monitoring spacecraft. With hours to go, the comet finally blazed up to brilliance in the solar glare. Then it dwindled just as fast. Its head disappeared. The headless tail swung around the sun and seemed to vanish, too. Then a stream of rubble was seen coming out from the other side of the encounter. For a few hours the stream seemed to brighten, raising false hopes yet again. Then it began fading and dispersing for good: a thin, inactive cloud of dust and rock bits that has now vanished from sight.
Astronomers worldwide had mobilized to make this the most comprehensively observed comet drama in history. Lots of new science will yet come out of the data that was collected. But everyone was disappointed at being stood up by the star of the show just as the performance was nearing its peak.
A drama queen indeed — that is comets for you.
By contrast, I can bet my life that old reliable Jupiter will shine brightly for you in the eastern sky after dinnertime tonight, weather permitting, and that it will continue to shine brightly down from the constellation Gemini all winter.
Why the difference?
One answer is that planets are big and rugged, while comets are flimsy apparitions that arise from tiny snowballs, only a few miles wide at most, that are subject to extremes of deep-space cold and solar heat. Another answer is that the planets are in nice, nearly circular orbits where things never change much, while comets follow loopy orbits that are bad for their health.
A subtler answer is that the planets we see today have been doing their thing for 4.6 billion years since the solar system was born, so everything that can happen to them already has happened, and we see what is left.
Comets, on the other hand, are new arrivals to the main part of the solar system. They are either first-timers like ISON, or repeaters like Halley that have been at it for only thousands of years, not billions. Newbies tend to blunder into messes. We see them before the losers are weeded out.
There will be future comets that light the sky and awe the world, but astronomers will be especially cautious now about hyping them beforehand. Especially when they are sun-grazing drama queens whose grand performance depends on their coping when the heat is on.