Pictures: Green Comet Visible This Week

Comet or Power Pellet?

Photograph courtesy Rolando Ligustri

A backyard astronomer in Italy captured comet Hartley 2 sharing space with NGC 281, aka the Pacman nebula, on October 2 during the comet's journey toward the inner solar system.

The cosmic pair's proximity is an optical illusion—the starmaking nebula sits a whopping 9,500 light-years from Earth, while the comet was a mere 16 million miles (26 million kilometers) away when the picture was snapped.

Nearly a quarter century after its discovery, Hartley 2 is now poised to make its closest approach to Earth yet. On October 20 the comet will pass 11 million miles (17.7 million kilometers) from our planet—just 45 times the distance between Earth and the moon.

(Related: Find out why Pac-Man also lives on Saturn's moon Mimas.)

Published October 19, 2010

Hazy Hartley

Image courtesy ESA/NASA

The NASA/ESA Hubble Space Telescope snapped this false color picture of comet Hartley 2 on September 25 as part of planning efforts for the Extrasolar Planet Observation and Deep Impact Extended Investigation, or EPOXI, mission. The image was taken while the comet was still more than 20 million miles (32 million kilometers) from Earth.

On November 4, EPOXI's Deep Impact spacecraft—famous for firing a projectile into comet Temple 1 in 2005—will make a close flyby of Hartley 2. The craft will dive within 600 miles (965 kilometers) of the comet's surface, getting close-up images of its craters and the sources of its dust and gas plumes.

Already, the uniform appearance of the comet's head suggests to astronomers that Hartley 2 may be a relatively young comet with a fresh surface.

Published October 19, 2010

WISE Comet

Image courtesy NASA/JPL-Caltech/UCLA

Another NASA probe, the Wide-field Infrared Survey Explorer, or WISE, captured this picture of comet Hartley 2 on May 10.

In the infrared, the comet's crumb-like tail is clearly visible as a fuzzy streak to the right of Hartley 2. More than five months before the comet's closet approach to the sun, solar radiation had already begun to vaporize the icy surface of the nucleus, creating the dusty tail, which stretches for about 1.1 million miles (1.7 million kilometers).

Published October 19, 2010

Target Acquired

Image courtesy NASA/JPL/UM

En route to comet Hartley 2, NASA's Deep Impact spacecraft has also been taking pictures of the icy body, including this shot from September 5.

In the past, probes flying by comets such as Halley, Wild 2, Borrelly, and Temple 1 have found no standard appearance among the frigid dustballs. Now the EPOXI mission "may answer whether comet Hartley 2 has a family resemblance to one of these, or if it is also unique," Griffith Observatory's Cook said.

(Find out how a space probe measured one of the biggest comets known.)

Published October 19, 2010