A SOHO image released by Nasa shows comet Ison coming from the bottom right and moving towards the upper right. Image Credit: ESA/NASA/SOHO/SDO/GFSC
Dec. 3: A body of ice, frozen gases and dust that astronomers had last year named comet Ison has perished near the Sun, swiftly disintegrating after a three-million-year journey from a region far beyond the orbit of Pluto, scientists say.
Astronomers tracking the comet’s closest approach to the Sun on November 28 watched it go behind the Sun in an explosive flash and emerge much fainter, indicating that the solar head had vaporised a vast amount of its material.
“We see a dust tail, but it’s getting fainter and fainter,” said a scientist at the Max Planck Institute for Solar System Research (MPISSR) in Germany. “It appears the comet has fragmented — it will not be visible to the naked eye.”
Comet Ison, first spotted by Russian astronomers last year, was subjected to an unprecedented observation campaign with professional and amateur astronomers worldwide tracking its hurtle towards the Sun in recent months.
Scientists believe the comet was a member of the Oort Cloud, a nursery of comets beyond the orbit of Pluto.
“The final disintegration of the comet occurred in two steps,” Hermann Boehnhardt, an astronomer at MPISSR, told The Telegraph.
About a day before its closest approach, a rapid rise in its brightness marked the first step, most likely an explosion caused by increasing gas pressures owing to ice in the comet’s nucleus directly turning into gas. The explosion would have shattered the nucleus into fragments, large and small.
In the second step, the fragments would continue to disintegrate, said Boehnhardt, who used an instrument aboard a US-European space observatory called SOHO to observe Ison’s encounter with the Sun.
He said that during the hour after the comet’s closest approach — about 1.8 million kilometres from the Sun — the ice and the glueing material in the fragments would have been exhausted and there would be nothing to keep the solid dust together.
Nasa said yesterday that astronomers were still trying to determine whether the residual fragment was dust debris or a small nucleus of the original ball of ice.
“There is no doubt (that) the comet shrank in size as it rounded the Sun, and there is no doubt something made it out on the other side to shoot back into space,” the agency said in a statement. “It seems likely that on December 1, there was no nucleus left.”
Astronomers say a cometary nucleus breaks up near the Sun typically once in 100 years. The residual dust cloud is expected to disperse in interplanetary space and become part of the interplanetary dust environment.
“Depending on the size of the dust grains,” Boehnhardt said, “they will end up evaporating in the Sun or will be expelled from the inner solar system in hyperbolic orbits which may allow them to leave the solar system if they survive long enough.”