NASA has begun searching for what remains of Comet ISON, which was expected to make a close approach to the sun on November 28. The comet was first discovered in 2012, and was initially thought to be a potential "Great Comet." However, as the comet approached the sun, it began to break apart and fade. By the time it reached its closest approach to the sun, ISON was only a faint smudge in the sky.

NASA is now using the Solar and Heliospheric Observatory (SOHO) to search for any debris that may have been left behind by ISON. SOHO is a joint project between NASA and the European Space Agency, and it has been observing the sun since 1995. SOHO is equipped with a coronagraph, which is a special instrument that blocks out the bright light of the sun, allowing astronomers to see objects that are close to the sun.

NASA is also using the Hubble Space Telescope (HST) to search for ISON debris. HST is a powerful space telescope that has been orbiting Earth since 1990. HST is capable of taking images of objects that are much fainter than what can be seen with ground-based telescopes.

NASA is hopeful that either SOHO or HST will be able to spot any debris that may have been left behind by ISON. If debris is found, it could provide valuable information about the composition of the comet and its history.

The search for ISON debris is a challenging task, but it is also an important one. By studying the debris left behind by ISON, scientists can learn more about the nature of comets and their interactions with the sun. This information could help scientists better understand the early history of the solar system and the formation of planets and moons.