The image captured March 11 by NASA’s Hubble Space Telescope shows Comet Siding Spring (C/2013 A1) at a distance of 353 million miles (568 million km) from Earth. Hubble can’t see Siding Spring’s icy nucleus because of its diminutive size. The nucleus is surrounded by a glowing dust cloud, or coma, that measures roughly 12,000 miles (19,000km) across.
But after applying image-processing techniques to remove the hazy glow of the coma, scientists revealed what appear to be two jets of dust coming off the location of the nucleus in opposite directions. This observation should allow astronomers to measure the direction of the nucleus’ pole and axis of rotation.
Hubble also observed Siding Spring on January 21 as Earth was crossing its orbital plane, which is the path the comet takes as it orbits the Sun. This positioning of the two bodies allowed astronomers to determine the speed of the dust coming off the nucleus.
“This is critical information that we need to determine whether, and to what degree, dust grains in the coma of the comet will impact Mars and spacecraft in the vicinity of Mars,” said Jian-Yang Li of the Planetary Science Institute in Tucson, Arizona.
Discovered in January 2013 by Robert H. McNaught at Siding Spring Observatory, the comet is falling toward the Sun along a roughly 1-million-year orbit and is now within the radius of Jupiter’s orbit. The comet will make its closest approach to our star October 25, at a distance of 130 million miles (210 million km) — well outside Earth’s orbit. The comet is not expected to become bright enough to be visible with the naked eye.