If there is one thing we know about comets, it is that their behavior is really hard to predict. Comets will always surprise us—sometimes to our disappointment.
It looks like comet ISON, or most of it, did not survive its encounter with the Sun yesterday, when it made a close approach at just 1.2 million km from that fiery surface. This distance may seem large, but it is close enough to have subjected the comet to temperatures of around 2,700 degrees Celsius. To survive such a close shave with the Sun may sound unlikely, but a few other sungrazing comets have managed the feat during even closer passes. So some people hoped ISON would perform a death-defying stunt and emerge intact.
ISON did not leave us without a final serving of mystery though. Soon after reaching its nearest point to the Sun (known as perihelion), there was no sign of it emerging afterward. Twitter and news agencies were alight, lamenting its loss and assuming it disintegrated—RIP ISON.
But then, moments later, new images emerged showing a hint of something appearing on the other side of the Sun. Was this still a diminished comet ISON or a ghostly version of its former self? Well, even comet experts are not sure.
The image below shows that whatever appeared after perihelion had enough matter in it to produce a tail, which started fading as it got farther from the Sun. (Note: This animated gif will take some time to load, but it is worth the wait.)
In order to say anything more, scientists need more data—which they don't have. ISON is still too close to the Sun and remains too faint for equipment to record anything that can provide definitive answers. What can be said for certain is that, whatever the size of the nucleus of the remnant (if it even has one), it will be much smaller than it was a few weeks ago when it was visible to the naked eye from Earth.
Comet of the century
Comet ISON had been dubbed the Comet of the Century. When it was first spotted in September 2012, some scientists believed it had the potential to shine brighter than the Moon. Although ISON didn't quite live up to these predictions, it has certainly put on a good show on its journey in from the Oort cloud, a region of icy bodies lying nearly a light year from the Sun. ISON had orbited there for 4.6 billion years.
In recent weeks, ISON has sent varying levels of dust and ice streaming from its nucleus. As it got closer to the Sun, the dust production of ISON had, at times, seemed to completely shut down. This led some scientists to suspect the comet died very early, its potential extinguished. But then ISON surprised us by turning on again—the last sightings before perihelion suggested that it had not yet run out of juice.
Bright comets from the Oort cloud that pass the Earth are extremely rare. Astronomers study these icy objects to learn more about the outer solar system. ISON holds secrets 4.6 billion years old, including potential information about the earliest gases and dust in our solar system. But despite what has become of comet ISON, scientists have acquired lots of new data about the comet during its journey to the Sun. This will help them understand, and hopefully better predict, the behavior of future cometary visitors.
The rarity of this event explains why scientists have been unsure as to what the comet was going to do—they simply do not have much to compare it to. Passing so close to the Sun is certainly not easy on the comet: the extremes of gravity and heat act to rip apart its nucleus and could vaporize it in a split second.
We have probably been denied the opportunity to observe a beautiful comet blazing through our night skies in December, but it is not all bad news. ISON’s curtailed life allowed us to learn more about the behavior of these ancient icy dust balls. And while scientists pore over new comet data, we can all anticipate the next one to be spotted hurtling toward the Sun. It could be a good few years, but there’s one thing we can be assured—comets will always take us on a thrilling ride.
Natalie Starkey is a research associate at the Open University. This article was originally published at The Conversation.
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