The IAU has voted on a series of resolutions on what a planet is and what a planet isn't, and the verdict is... Pluto is not a planet. At least, not a major one. This is a big turnaround from the ...

Astronomers using the Hubble Space Telescope have observed a white dwarf – a highly compact stellar ember – that appears to have gobbled up an icy world akin to the dwarf planet Pluto, a finding with ...

Pluto was a planet in good standing for seventy-six years when in 2006, out of the blue, it was demoted and booted from our solar system’s family of planets. The stunning event – still hotly debated ...

Pluto — the celestial body, not the beloved Disney character — was demoted from its planetary status in 2006 by the International Astronomical Union (IAU). The argument had been over whether the ...

Although we now believe we understand how the Sun and our solar system formed, this early view is an illustration only. When it comes to what we see today, all we have left are the survivors. What was ...

If Pluto’s looking for someone — or something — to blame for being drummed out of the planetary corps back in 2006, it need look no further than Eris. The solar system’s ninth planet had long had its ...

Editor’s note: A version of this story originally appeared in Astronomy’s 2007 special issue 50 Greatest Mysteries of the Universe. For a more recent discussion of Pluto’s planethood, see “An ...

Normally when a medium-size star dies, it blasts away the bulk of material in its system. The Hubble discovery was surprising ...