The Hubble Space Telescope has captured the image of an outburst of dust from the volatile and icy nucleus of comet Temple 1, giving a preview of what it might be seen on July 4 when a NASA probe is set to strike the comet, scientists said Monday.

One of the images snapped on June 14 by the orbiting observatory from 120 million km away reveals the dust jet extended about 2,200 km pointing in the direction of sun. Scientists said Hubble's views complement close-up images being taken by cameras carried by Deep Impact, which is speeding toward the comet.

NASA's Deep Impact space probe is set to collide with the comet. Scientists said the collision could create a similar dust plume.

Comets frequently show outbursts in activity, but astronomers do not know why. Temple 1 is moving closer to the sun, it might be because the increased heat opened up a crack in the comet's crustysurface, enabling trapped dust and gas to spew out.

It is also possible that part of the comet's crust was lifted off the nucleus by the pressure of heated gases beneath the surface, and the crust might then crumble into small dust particles, producing a fan-shaped coma.

Astronomers hope the July 4 collision will unleash more primordial material trapped inside the comet, which formed billions of years ago.

Comets are thought to be "dirty snowballs", porous agglomerates of ice and rock that dwell in the frigid outer boundaries of our solar system.

Source: Xinhua