IF you missed the celestial drama on the 3rd, all may not be lost. It is possible that nature32 will stage yet another spectacular display, late November to early December.
Comet ISON is currently making its long-anticipated approach to the Sun, and will reach perihelion (its closest point) by the 28th. Depending on how tightly bound its components are, and the comets mass, the result could be a visual extravaganza that would rival the recent solar eclipse.
Astronomers caution though that something far less spectacular could occur—because ISON is a sungrazer. Hurtling inward, from the outer solar system, these icy bodies sideswipe the Sun. They plow through the crackling-hot corona (up to several million K at places) and then skim the Sun’s roiling and seething photosphere.
Some comets make it through, others don’t. The daredevil, Lovejoy, for instance, took the plunge and emerged intact, while Elenin turned out to be a kamikaze. Breaking up, it vanished into an ignominious void—to be remembered only as a disappointing dud.
Countless variables come into play, including the objects history, chemistry and physical structure, as well as the mechanical forces affecting it. As loosely bound aggregates of rock, dust ices and organic compounds, comets are prone to disintegration. So you never know, quite what to expect.
In a Science At NASA interview, Don Yeomans, of the California-based Jet Propulsion Laboratory, described cometic bodies to Dr. Tony Phillips as being “…fragile and loosely held together…So it doesn’t take much to get (them) to disintegrate”.
Two per cent of new comets break up, Yeomans says. Nor is it only sungrazers. C/2010X1, as Elenin is known, officially, arrived from the distant Oort cloud (50,000 times farther from the Sun than Earth) in 2011 and shattered during a perihelion passage of 72 million km.
By contrast, Lovejoy ploughed through the Sun’s superheated atmosphere (corona) for all of an hour, then passed just 120,000 km over its searing surface—and survived! The key, according to Karl Battams, a U.S. Naval Research Laboratory scientist (speaking to Phillips), was the size of its core.
Lovejoy’s survival is even more “astounding,” to use Battams’ expression, when one considers the other forces at work on sungrazers. In addition to steaming temperatures and the tug of powerful gravitational tides, an intruder is battered by plasma waves and bandied about in highly energetic magnetic fields.
Actually though, Lovejoy is part of a short-period comet (less than 200 years return time) that has already broken up. Astronomers believe this happened sometime in the 12th century (1300s). Australian amateur astronomer, Terry Lovejoy, discovered the fragment in December 2011.
Researchers quickly recognized the object as a “Kreutz Sunrazer”—a name derived, Science At NASA says, from German astronomer Heinrich Kreuetz, who first studied the normally 10-meter-wide and numerous cometary fragments. One falls into the Sun every few days.
Unlike Japan’s kamikaze pilots, who crashed their flying bombs into U.K. and U.S. ships during World War II, ISON (discovered through the Russian-based International Scientific Optical Network) may not be on a do-and-die mission.
At twice the size of Lovejoy, the one-time visitor from the Oort cloud could conceivably survive its close (1.1 million km) encounter with our Sun.
NASA points out too, that ISON’s “pristine surface” contains lots of volatile matter, which it can eject during perihelion—to produce a spectacular display late this month and in early December.
True to NASA prognosis, ISON has begun to do just that—reportedly exhibiting brilliant outbursts on the 13th thru 14th. Space Weather.Com offers to possible explanations: Either new veins of ice are opening up in ISON’s nucleus and “vaporizing furiously” as it approaches the Sun, or the comet is fragmenting.
It’s too early to tell, the newsletter advises, whether ISON’s sporadic eruptions are death throes or “just the first of many brightening events…as it plunges towards the Sun for a close encounter on…November 28th“.
Nevertheless, it reports naked-eye sightings of ISON from around the world. At the equator, where we are, monitoring the apparition means being outside around 5:30 a.m. and keeping a keen eye on the eastern sky until dawn.
As a side note, three other comets are also visible in that region of the sky: LinearX1 and its short-period consorts, Encke and (Yes!) Lovejoy *which is reportedly visible to the unaided eye from a dark location).
But ISON is still the comet of the hour—if not yet the “Comet of the Century”.
[The Guardian]
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