Comet ISON Has Moved Inside the Earth's Orbit on Journey toward the Sun

This article has been updated to note a change.

Comet ISON has moved inside Earth's orbit as it makes it way toward its rendezvous with the Sun scheduled for Nov. 28.

The so-called "comet of the century" hasn't disappointed: a sudden outburst on Nov. 13-14 increased the comet's brightness 10-fold, allowing even amateur astronomers to capture stunning images of the comet.

Whether or not the first-time visitor from the Oort cloud will survive its journey is uncertain, with possibilities ranging from vaporization at any time, to emerging from its solar flyby as a brilliant object visible to the naked eye.

"It is important to note that no matter what happens, now that ISON has made it inside Earth's orbit, any or all of these scenarios are scientifically exciting," Lowell Observatory astronomer Matthew Knight said in a statement. "We're going to learn a lot no matter what."

A member of NASA's Comet ISON Observing Campaign, Knight explained that in the first scenario, ISON spontaneously disintegrates -- an event that could take place at any time. If this happens, ISON would serve as the best-observed example of cometary disruption, offering scientists a more detailed look into how comets die.

A second scenario could be played out should ISON survive long enough to reach the Sun. The comet's closest approach to the star will raise the dirty snowball's equilibrium temperature to an estimated 5,000 degrees Fahrenheit, causing the majority of the dust and rock on its surface to vaporize.

Despite these extreme temperatures, the possibility of survival remains, according to NASA officials. To come out the other side, ISON needs to measure at least 200 meters wide. Current estimates place it between 500 meters and 2 kilometers.

However, even if ISON proves it can take the heat, it still faces the Sun's intense gravity, which could end up pulverizing the comet. Such was the fate of Comet Lovejoy, which passed within 100,000 miles of the Sun's surface December 2011, its debris creating a stunning streak in the sky.

In the case that ISON survives both the Sun's heat and gravity, scientists hope that it will break up "just a bit, say, into a few pieces." Should this happen, it would still give off enough debris to render the comet bright from the ground and leaving traces of the comet for researchers to examine.

"I'm clearly rooting for [number three]," Knight said.

Regardless of what happens, though, Knight said he and his colleagues will be "thrilled."

"Astronomers are getting the chance to study a unique comet traveling straight from 4.5 billion years of deep freeze into a near miss with the solar furnace using the largest array of telescopes in history," he said. "Hang on, because this ride is just getting started."