Clyde Tombaugh didn't set out to discover Pluto when he sent his sketches of the night sky to Lowell Observatory in Flagstaff ...

The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

Eight billion miles (14 billion kilometers) from Earth, at the solar system’s ragged edge, lies Eris — a planet-sized oddball of a world that emerged unexpectedly from the darkness 20 years ago.

Why is Pluto no longer a planet? Discover the real reason behind Pluto’s reclassification as a dwarf planet and the science that led to this change.

Saturn, Venus, Neptune, Uranus, Jupiter, Mars and Mercury will be visible in an uncommon planetary alignment this month.

“New Horizons shattered a major paradigm of planetary science,” says Alan Stern, the mission’s principal investigator. “Pluto ...

Today is about reflecting on your career, staying emotionally engaged, and preparing for upcoming changes in your ...

For decades, Pluto was celebrated as the ninth planet of our solar system. However, in 2006, the International Astronomical Union (IAU) redefined what constitutes a planet, leading to Pluto’s ...

Brown’s team discovered a dwarf planet, Eris, in January 2005. At the time, it appeared to be larger than Pluto. If Pluto hadn’t been demoted, Brown says, hundreds of celestial objects would ...

Trans-Neptunian objects (TNOs) are icy bodies that vary widely in size, from large dwarf planets like Pluto and Eris—each ...

According to a recent YouGov poll, 35% of Americans think Pluto is not a planet. But they are all wrong—kind of. To get to ...