Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2003 July 9 
Posted on 07/08/2003 9:29:04 PM PDT by petuniasevan
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2003 July 9
Explanation: Astronomers have discovered a planetary system more similar to our own Solar System than any known previously. The bright star HD70642, visible with binoculars toward the constellation of Puppis, was already known to be a star like our Sun. Now a planet with twice Jupiter's mass has been discovered in a nearly circular orbit at approximately half the orbital distance of Jupiter. Such an orbit allows the possibility of habitable Earth-type planets orbiting further in, a possibility not likely with all previously discovered planetary systems with massive planets occupying disruptive closer elliptical orbits. The above illustration indicates what the HD70642 planetary system might look like from a hypothetical moon orbiting the newly discovered planet. At only 90 light years distant, extremely faint early radio broadcasts from Earth are now passing this planetary system.
As yet no observatory has obtained a direct image of an extrasolar planet. The vast majority are detected through the effect of their gravitational force on their parent stars. As the unseen planet orbits, the star shifts back and forth in space. The light of the star changes slightly, increasing and decreasing in wavelength due to the 'Doppler shift’.
Earth-like planets exert a much smaller force on stars than giant planets like Jupiter. The resulting Doppler shift is much smaller, making it much more difficult to find terrestrial planets. But within the next decade both ESA and NASA plan to use orbiting observatories to look for them.
On a side note: the "HD" in this star's designation stands for the Henry Draper Catalogue.
You can read about this pioneering 19-century astrophotographer HERE.
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