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NASA's MESSENGER spacecraft on Tuesday and Wednesday captured and delivered to Earth the first photographs of Mercury ever taken from within the planet's orbit. Taken at 5:20 am EDT Tuesday, the historic first photo was soon joined by 364 more of the solar system's innermost planet, and several of them were released on Wednesday. Photos were taken by MESSENGER's Mercury Dual Imaging System as the spacecraft sailed high above the planet's south pole, providing a glimpse of portions of Mercury's surface that had not previously been seen by humans. "The entire MESSENGER team is thrilled," said Principal Investigator Sean Solomon.
I believe there is a factual error in this article:
Earth is the densest planet in the solar system, not Mercury. Earth has a mean density of 5.515g/cm3. Mercury is the second densest at 5.427 g/cm3.
There is no nuclear reactor there.