What happened to the 'comet of the century'? Nasa begins search for fragments of ISON after close encounter with the sun

December 6, 2013 11:57 AM

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What happened to the 'comet of the century'? Nasa begins search for fragments of ISON after close encounter with the sun

When the ‘comet of the century’ ISON swung perilously close to the sun last month, scientists were left stumped as to whether it had survived.

Most astronomers now believe that the comet was destroyed by solar heat with Nasa stating a 90 per cent chance of this having happened.

What they believe now remains from its original 0.62 mile (1km) nucleus are 10 metre pieces of rubble.

There is, however, a 10 per cent chance of it having left behind some important fragments 100 metres in radius or larger which will be big enough to study.

The group’s STEREO spacecraft will be using their cameras to search for bright fragments throughout the week, along with the Nasa Infrared Telescope Facility (IRTF) in Honolulu.

Nasa's recently launched MAVEN spacecraft may try to observe ISON next week.

By mid-to-late December Nasa Hubble and Chandra observatories will be performing deep outer space searches for any remnants of the comet. Spitzer will also look for ISON in early 2014.

If there is nothing sizable and stable left, it will dissipate and disappear in this time, as already emitted dust leaves the vicinity.

If there is still a central source of emission, even if it is very much smaller, we will see a new, much fainter coma and tail form, which currently may be overwhelmed by the dust emitted from before the disruption event.

‘I believe that we will no longer see a brilliant display of ISON,’ Gerhard Schwehm, ESA’s Head of Solar System Science Operations Division told MailOnline.

Comet ISON headed towards the centre of our Solar System in Novermber passing within 1.2 million miles of the Sun’s surface.

At the time of discovery in September 2012, ISON was over 584 million miles from the Sun.

Its average speed in July was 55,405mph. It continued to accelerate steadily until November when it whipped around the Sun at an astonishing 425,000mph.

Early data analysis suggested Comet ISON’s size to be around three miles in diameter.

Most astronomers now believe that the comet was destroyed by solar heat with Nasa stating a 90 per cent probability of this having happened.

‘If one looks at the pre and post perihelion observations by ESA’s Solar and Heliospheric Observatory the comet must have disintegrated.

If previous sun grazing comets are any guides, there may be a sizeable piece of comet nucleus left.

At this point, though, scientists are waiting for a variety of telescopes to make observations before the status of Comet ISON can be confirmed.

What remains of Comet ISON appears to brighten and spread out, then fade. The disappearance of a strong central brightness condensation after perihelion is telling, the comet is clearly fainter and more diffuse going out than going in, but it continues to shine.

The spread out light is likely due to dust emitted in the few hours before perihelion going around the sun.

‘The fan-shape of the tail is a great example how the dust now moves on slightly different trajectories as compared to the nucleus,’ added Dr Schwehm.

‘Small dust grains experience radiation pressure and therefore see a reduced gravitational attraction by the Sun (both forces act radially) and depending upon the material and size the radiation pressure force varies.

‘For submicron highly absorbing grains and porous grains, this force can be even larger than the gravity and they are blown away from the sun.

The comet was believed to be straight from the Oort cloud on the fringes of the solar system, which is home to countless icy bodies - most notably the frozen balls of dust and gas in orbit around the sun known as comets.

For whatever reason, Ison was propelled out of this cloud and drawn toward the heart of the solar system by the sun's intense gravitational pull.

By the time ISON slingshot around the sun, it was be moving at 828,000 mph (1,332,000 kph).

ISON is named after the International Scientific Optical Network, used by a pair of Russian astronomers to detect the comet in September 2012, but it officially is known as C/2012 S1, which indicates when it was discovered.

Source: dailymail.co.uk

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