THE SOUTHWORTH PLANETARIUM 207-780-4249 www.usm.maine.edu/planet 70 Falmouth Street Portland, Maine 04103 43.6667° N, 70.2667° W Founded January 1970 "A proud part of Portland's underground." THE DAILY ASTRONOMER Thursday, January 21, 2016 New World Oh, no, not again! So despaired the descending bowl of Petunias in Douglas Adams' "The Hitchhiker's Guide to the Galaxy." We can relate to the petunia's lament as we are confronted, yet again, with the possibility that the solar system's planet census number might need to change. For the benefit of those few afflicted with rich lives devoid of pointless diversions, we should offer some background. In August 2006, that coterie of sinister intelligences, the International Astronomical Union, convened its triennial meeting in Prague. During the last part of this conference, the remaining members (approximately 450) voted a motion to reclassify the term "planet." They specified three different criteria. One, a planet has to revolve around the Sun. Two, its has to be massive enough so that its internal gravity will mold it into a spherical shape. Third, it has to also be gravitationally powerful enough to have incorporated all nearby material into it. Pluto doesn't fulfill this third requirement, as it travels close to the Kuiper Belt, a region from which short period comets originate. Pluto, being only 0.2% as massive as Earth, is unable to attract many of these proximate Kuiper Belt Objects and thus hasn't cleared its debris field. Consequently, the IAU has officially declared that our solar system contains only eight planets. They have remained steadfast in this contention despite the widespread condemnations that followed Pluto's demotion. Many people insist that the solar system harbors nine planets, not eight. Now, astronomers at Cal Tech have found evidence of what they believe is a highly massive planet well beyond Neptune. If their estimates are accurate, this large body could be ten times more massive than Earth and 20 times farther from the Sun than Pluto. At such a distance, its orbital period would be between 10,000 - 20,000 years! Compare this time period with Pluto's comparatively brief 248 year period. The researchers haven't yet observed this planet. Instead, they have inferred its existence through observations of some Kuiper Belt Objects. Many of these bodies describe orbits directed toward one particular direction. The orientation of so many KBO's toward one direction suggests the presence of a gravitationally powerful body in the general vicinity. Were there no such body, the Kuiper Belt objects should follow various orbits without any disproportionate favoritism toward any specific direction. Computer models based on these observations have yielded an estimation of the unseen planet's mass and distance. What is not yet know is its present location. The announcement of the planet's existence will undoubtedly prompt many astronomers to find it. Such a search will prove quite challenging. First, such a distant planet will be quite faint, as it would only shine through reflected light. Secondly, the search field is vast. This planet's orbit is not only hundreds of billions of miles long, but it could, like Pluto, be highly inclined relative to Earth's orbit, called the ecliptic. The greater the inclination angle, the wider the area the planet could occupy. The "Ninth" planet, as people are now calling it, hasn't yet been found. If and when astronomers do locate it, the International Astronomical Union might be compelled to designate it as a major solar system planets. Then, of course, we'll have nine planets again. Unless, of course, astronomers happen to find yet another planet, in which case we'll have ten, and, well, let's not discuss it now. Written by Edward Gleason