keywords: planets astronomers mars twin nasa
text: NASA to Announce New Class of Planets Astronomers have discovered four new planets in a week's time, an exciting end-of-summer flurry that signals a sharper era in the hunt for new worlds.    While none of these new bodies would be mistaken as Earth's twin, some appear to be noticeably smaller and more solid - more like Earth and Mars - than the gargantuan, gaseous giants identified before...