NGC 3242


In Hydra

From Jim Kaler's STARS; Return to Planetary Nebulae

NGC 3242 NGC 3242
For some odd reason, this planetary nebula reminded older observers of the planet Jupiter. The contrast between the two pictures, Curtis's century-old drawing and the Hubble, is a curious one. Hubble shows the usual extraordinary detail in the central ring and the shooting bipolar flow, which Curtis could not really see. Curtis, however, captured the outer halo or ring, which is only marginally present on the Hubble image, probably the result of short exposure time. Otherwise, we have an object that looks very much like NGC 7662 and a variety of others, in which the inner ring looks as if it has been snowplowed in the ejected gas by a hot fast wind from the central star.

There is a reasonable distance of 1600 light years found by comparing the angular expansion with the expansion velocity of just under 30 kilometers per second. The bright 12th magnitude (12.1) central star, with a temperature of 90,000 Kelvin, then shines with the total light of around 1000 Suns. Given that distance, the inner ring stretches to a maximum of around half a light year wide, the outer somewhat farther.

As a curious historical note, NGC 3242 was once thought to be the only planetary nebula radiating "non-thermal" radio radiation (radiation not produced by heat), perhaps from strong magnetic fields. It was just a coincidence, as the radiation from the nebula was confused with a distant background object that was indeed so radiating.

Left: Image by H. D. Curtis from Publications of the Lick Observatory, Volume 13, Part III, 1918. Right: Bruce Balick and Jason Alexander (U. of Washington), Arsen Hajian (U.S. Naval Observatory), Yervant Terzian (Cornell U.), Mario Perinotto (U. of Florence), Patrizio Patriarchi (Arcetri Obs), and NASA/ESA.