![In Memoriam: Pierre Morel [1933–2024]](https://assets.science.nasa.gov/dynamicimage/assets/science/esd/earth-observer/2025/2025-in-memoriam/InMemoriam-Morel.jpg)
Cassiopeia A Supernova Remnant
December 27, 2017
| Credit | NASA/CXC/SAO |
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Cassiopeia A (Cas A) is the remnant of a massive star that exploded about 300 years ago. The X-ray image shows an expanding shell of hot gas produced by the explosion.
