The solar system beyond Neptune is a dark and mysterious place. It is also crowded. Besides Pluto and its moon Charon, there are planetesque chunks of rock and ice like Sedna and the recently discovered 2003UB313 as well as a host of asteroids and comets in the Kuiper belt and beyond. Determining which of these objects constitute new planets and which do not remains controversial work currently under review by the International Astronomical Union (IAU). Some astronomers have even argued that Charon deserves to share the planet title since it is roughly half the ninth planet’s size and might have a similar atmosphere. But new observations, reported today in Nature by Amanda Gulbis of the Massachusetts Institute of Technology and her colleagues prove that Charon lacks an atmosphere and therefore lacks one potential criterion for planet status. “I think having an atmosphere is a key component,” Gulbis says. “Our findings show that it doesn’t have an atmosphere. I would say that Charon is definitely not a planet.” The astronomers took advantage of a rare moment when Charon crossed in front of a distant star and blocked its light to determine whether it has an atmosphere. If it had one, the star’s light would be gradually blocked as opposed to the more precise cutoff that would be expected for a nearly gas-less moon. On July 11, 2005, Charon passed in front of UCAC2 26257135, revealing less of an atmosphere than either Pluto or even Earth’s own moon has. “It’s astounding that our group could be in the right place at the right time to line up a tiny body three billion miles away,” says team member Jay Pasachoff of Williams College.
This occultation, the first to be observed since 1980, also allowed the scientists to come up with a measurement of Charon’s radius, roughly 605 kilometers or “about twice the size of Massachusetts,” Gulbis notes. Using this radius and mass measurements from the Hubble Telescope, the astronomers calculate that Charon is only roughly 63 percent rock. This means it may have formed in the same way as our own natural satellite: when a large object hit the parent planet and ejected a plume of lighter materials that coalesced into a moon. Similar occultations could provide data on Sedna and 2003UB313. That, in turn, could decide whether they are planets, because the IAU is working on a definition based on minimum size. If Pluto continues to qualify as a planet, then 2003UB313 may indeed become the 10th planet because it appears to be roughly the same size, meaning that Charon–the ferryman of the Kuiper belt–may help a new member of the solar system cross a river of doubt.

Are we alone?

Are we alone?

Paul Davies
Paul Davies
The only evidence of life that we are aware of occurs in our planet, but man continues to search outer space for signs of other life forms. From the time of the Viking Mission to Mars until the recent research into Jupiter’s satellites, science tries to find answers. A new field of science, astrobiology, is redefining and analysing life on Earth and by doing so is creating the basis on which scientists of the future will work. If the life is implicit in the mechanisms of the universe the response waits for us out there. Professor Paul Davies gives this public lecture entitled: The eerie silence: Are we alone in the Universe? on Friday, 18 May 2012 at The Australian National University. Paul Davies is a theoretical physicist, cosmologist, astrobiologist and best-selling author. He is Regents’ Professor at Arizona State University, where he directs the Beyond Center for Fundamental Concepts in Science — a cosmic think tank that tackles the “big questions” of existence, from the origin of the universe to the origin of life and the nature of time. Davies also directs a National Cancer Institute research program that tackles cancer from a physics perspective. Among his research accomplishments, Davies helped explain how black holes radiate energy, what caused the ripples in the cosmic afterglow of the big bang, and why life on Earth may have come from Mars. Davies has written about 30 books, most recently The Eerie Silence: Are We Alone in the Universe? His preoccupation with deep conceptual problems and his fearless championing of bold new ideas earned Davies the epithet of ‘The Disruptor’ in a recent profile in Nature magazine. His many media projects include presenting two six-part series on The Big Questions for Australian television. He has awards from The Royal Society and the UK Institute of Physics, and also received the 1995 Templeton Prize. In 2007 he was named a Member of the Order of Australia in the Queen’s birthday honours list Paul Charles William Davies, AM is an English physicist, writer and broadcaster, a professor at Arizona State University as well as the Director of BEYOND: Center for Fundamental Concepts in Science..

Radio telescopes scan the skies, and computers crunch the results looking for the patterns that might indicate an artificial signal coming from deep space. Alien hunters stand watch out in the desert, looking for lights in the sky flying over military bases. Both are looking for answers to the same question: Is our little civilization on our little blue planet alone in the galaxy; or are there others, like us, who want to meet us as much as we want to meet them?