A comet double take

Robert Bigelow

On October 20th Comet Hartley 2 will pass by Earth at a distance of about 11 million miles. Even though this is close in astronomical terms, the comet is small. So, it will appear very dim to Earth-bound observers. If you wish to spot this comet in the sky, you will need to be under a dark sky away from city lights. Binoculars will help. Star charts and observing tips can be found here.

If you don’t see the comet near closest approach, don’t fret. On November 4th, NASA’s Deep Impact spacecraft (under the mission name of EPOXI) will get a close look as it passes within several hundred miles of the comet’s nucleus. It will then send pictures and data back to Earth where anyone with access to the internet will be able to share its close up views.

This will be the second comet flyby for the Deep Impact spacecraft. In July 2005 the main spacecraft flew past Comet Tempel 1 while it sent a projectile slamming into the comet’s nucleus. It made detailed observations of the nucleus and the plume of debris that resulted from the collision.

This image of was taken 67 seconds after Deep Impact's impactor spacecraft collided with Comet Tempel 1. Scattered light from the collision saturated the camera's detector, creating the bright splash. CREDIT: NASA/JPL-Caltech/UMD

This image of was taken 67 seconds after Deep Impact's impactor spacecraft collided with Comet Tempel 1. Scattered light from the collision saturated the camera's detector, creating the bright splash. CREDIT: NASA/JPL-Caltech/UMD

After leaving the vicinity of the comet, the spacecraft was still healthy and had a supply of fuel. So, it was given a new mission under the name of EPOXI with two separate tasks. Its primary task was to investigate another comet. So, its orbit was altered to give it a close encounter with Comet Hartley 2. It completed its second task during its journey which was to have astronomers use Deep Impact’s onboard telescope to observe planets orbiting other stars. The spacecraft has now turned its attention to its second comet encounter. Stay tuned.

Orbital paths for the Deep Impact/EPOXI spacecraft from Comet Tempel 1 to Comet Hartley 2. Credit: NASA/JPL-Caltech/UMD/GSFC/Tony Farnham

Orbital paths for the Deep Impact/EPOXI spacecraft from Comet Tempel 1 to Comet Hartley 2. Credit: NASA/JPL-Caltech/UMD/GSFC/Tony Farnham

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