Friday, November 29, 2013

"Isons" hell of a ride in the blazing sun - Spiegel Online

Thursday night racing comet “Ison” by the sun closest point of its orbit. Just removed a solar diameter, he passed the seething ball of gas around our Sun. In places, his comet nucleus was extremely hot in the small distance, astronomers estimate the temperatures between 2000 and 3000 degrees Celsius. Can a comet, composed mainly of ice, survive such a thing?

NASA had its sun SDO satellite (“Solar Dynamics Observatory”) separately pivoted from its normal direction of observation in order to have a better look at “Isons” Sun Passage. Apparently, in vain, had as SDO researchers Dean Pesnell grant: “The comet seems to have disappeared and vanished in the last few hours.” Because SDO images showed only yawning empty space, where there is actually a comet or at least if his relics should be.

SDOs enigmatic None led to perhaps hasty farewell to the comet. For other satellites have recorded the hot ride through the sun’s atmosphere, the corona, as successful. Above all, through the instruments of the European-American Scout SOHO sun, the researchers were virtually live.

Unlike Pesnell they come to more positive assessments: “‘Ison’ has the rail industry survived with the least distance from the Sun,” says Hermann Böhnhardt from the Max Planck Institute for Solar System Research (MPS) in Göttingen. The comet expert recognizes current SOHO photos even two dust tails. “One comes from the days before the sun encounter, the other was born in the hours of greatest close to the sun – something we had expected.”

opinion changed

Karl Battams has revised his initial pessimism. “Isons” fateful encounter sun could astrophysicist from the Naval Research Laboratory, according to be expired: Already on the way the comet began to fall apart, but its fragments were not too large. As evidence Battams alluded to the great quantities of dust, which grew in this phase to a long, thin tail – this can be seen clearly on the SOHO images


Then flew “Ison” in the corona, which further advanced the resolution process: The comet completely lost its gaseous envelope and its tail – like the Lovejoy comet in 2011, which is also set to lose its tail in its solar passage. But when “Ison” then back away from the sun, seems to be at least somewhat left of his comet nucleus. Because “Ison” took its activity again and again pushed gas and dust out! Battams: “Just like then, at the Lovejoy’s tail grows back.”

The researchers stressed that this scenario is preliminary and at crucial points still incomplete. “We have no idea how big the remaining comet nucleus is, if it exists at all.” Therefore, it is too early to forecast whether it will create “Ison” in early December at the evening sky.

secrets of Urstoffs

But it is clear already that “Isons” sun ride is a treasure trove for researchers. For a long time they had to prepare for the unique opportunity as well as at Göttingen MPS. Scientists led by Werner Curdt yesterday for the first time the spectrograph SUMER (“Solar Ultraviolet Measurements of Emitted Radiation”) of the SOHO satellite used to decipher the chemical composition of a comet.

This is possible because “Ison” has left its spectral fingerprints in the interaction with the hot corona. With the measurements, the researchers break new ground: “From such a fresh comet, which is also approached so close to the sun, never before spectra have been recorded.”

The observations took place at a critical moment, as “Ison” was invisible to all other telescopes. Because the sunlight is usually shielded by a shutter in the optical path. Curdt: “Exactly the largest perihelion, when the comet disappeared in other telescopes behind the diaphragm, SUMER went into action.”

hundreds of spectra, the MPS researchers were able to record before was fired after 50 minutes, “Ison” out of sight. The evaluation will take some time. The data will probably reveal some secrets about the primary matter of the birth of the solar system.


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