dying, sun-like star produced a planetary nebula popularly known as the Helix. While exploring the Helix's gaseous envelope with the Hubble Space Telescope (HST), astronomers discovered indications of 1,000s of striking "cometary knots" like those shown above. So called because of their resemblence to comets, they are actually much larger - their heads are several billion miles across (roughly twice the size of the our solar system itself) while their tails, pointing radially away from the central star, stretch over 100 billion miles. Previously known from ground based observations, the sheer number of cometary knots found in this single nebula is astonishing. What caused them to form? Hot, fast moving shells of nebular gas overrunning cooler, denser, slower shells ejected by the star during an earlier expansion may produce these droplet-like condensations as the two shells intermix and fragment. An intriguing possibility is that instead of dissipating over time, these objects, could collapse and form pluto-like bodies. If so, these icy worlds created near the end of a star's life, would be numerous in our galaxy.
Scale of the Universe Debate in April 1996
NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.
Based on Astronomy Picture Of the Day
Publications with keywords: Helix Nebula - cometary globule
Publications with words: Helix Nebula - cometary globule