How Much of ISON Survived Its Closest Approach To the Sun? 84
A reader writes "This Ars Technica article examines what may be left of ISON and contains a detailed animated GIF from the NASA STEREO Ahead spacecraft. '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 kms from that fiery surface. This distance may seem large, but it is close enough to have subjected the comet to temperatures of around 2,700C. 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 afterwards. 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.'"
Re:So... (Score:5, Informative)
The reason for why the comet appears to be so huge is the massive coma around the core as well as the tail originating from the core and scattering like a bowwave from a ship it extends and expands the further away it is from the source. The sudden seemingly increase in size of the tail when ISON re-appears above the sun comes from the sudden change of direction and the new direction how the ejected material is forced away from the core by the solar wind.
Most comets have a nucleus (the center of a comet) that is less than about 6 miles (10 km) wide. The size of a comet changes depending on how close it is to the sun. As a comet gets closer to the sun, the ices on the surface of its nucleus vaporize and form a cloud called a coma around the nucleus that can expand out to 50,000 miles (80,000 km). A tail also forms on a comet as it approaches the sun. Comet tails can be over 600,000 miles (1 million km) long.
An awesome gif indeed. A little closer to home is ....
http://www.dailygalaxy.com/my_weblog/2013/12/image-of-the-day-a-spectacular-meteor-streaking-through-the-aurora-borealis.html [dailygalaxy.com]
No, and no (Score:4, Informative)
The ejected material could come off at a significant velocity, so it wouldn't have quite the same orbit.
Solar wind (and light pressure) have more effect on small particles than large ones, since they act based on surface area (r^2) against mass (r^3). This is why the solar wind can sweep dust out of the solar system, but not planets.
There is also drag from the corona to consider. The comet effectively did an air dip.
TL;DR Any lost material was either blown out into space, or fell into the sun. Either way, this comet will not 'pull itself back together'
Really, really hot (Score:4, Informative)
What emerged from the other side was almost, but not quite, entirely unlike tea.
Re:2700 degC? (Score:5, Informative)
Look, you asked how to define the temperature in vacuum and I answered
Put in a good number of assumptions and, based on them, one (with enough skill in the craft) will be able to estimate [wikipedia.org] the internal temperature.
Of course it will still be an estimate and nothing more (one doesn't need to ask, it's only natural that precise data could be obtained only if you have unambigous direct observation of the phenomenon - and not even then)
Other than that, yes, the black-body radiation is correct for all macroscopic bodies (be them in one piece or crumbling) - the only requirements are: that body to expose a surface, be made of enough particles [wikipedia.org] to display a statistical behavior and be at thermal equilibrium.
There was this guy, Plank [wikipedia.org], that put his name at stake on the correctness of it: to date, nobody ashamed him (his initial estimation of the constant was within 1.2% of the more precise value we accept today, which is quite remarcable IMHO)