From: baalke@zagami.jpl.nasa.gov   
      
   Penn State Erie   
      
   Contact:   
   A'ndrea Elyse Messer, (814) 865-9481, aem1@psu.edu   
      
   August 25, 2003   
      
   Planetary Tilt Not A Spoiler For Habitation   
      
   Erie, Pa. -- In B science fiction movies, a terrible force often pushes the   
   Earth off its axis and spells disaster for all life on Earth. In reality, life   
   would still be possible on Earth and any Earth-like planets if the axis tilt   
   were greater than it is now, according to Penn State researchers.   
      
   "We do not currently have observations of extrasolar planets, but I imagine   
   that   
   in the near future, we will uncover some of these small planets," says Dr.   
   Darren M. Williams, assistant professor of physics and astronomy, Penn State   
   Erie, the Behrend College. "The issue before us is what will they be like? Will   
   they have moons? What will their climates be like? Will they be teaming with   
   life or will life be rare?   
      
   "I suspect, based on simulations and our own solar system, that many Earth-like   
   planets will have spin axes that are tipped more severely than Earth's axis."   
      
   Williams, working with David Pollard, research associate in geoscience at Penn   
   State, used general circulation climate models to simulate a variety of tilts,   
   carbon dioxide levels and planets. They reported on their findings in the   
   International Journal of Astrobiology.   
      
   The researchers first looked at present-day Earth with tilts of 23, 54, 70 and   
   85 degrees. Earth's tilt today is about 23 degrees. The simulation that   
   mimicked   
   today's Earth and tilt closely matched today's climate, including regional   
   precipitation patterns, snow and ice cover and drought.   
      
   "Tilts greater than the present produce global annual-mean temperatures higher   
   than Earth's present mean temperature of about 57 degrees Fahrenheit," says   
   Williams. "Above 54 degrees of tilt, the trend is for the global annual-mean   
   temperature to decrease as tilt increases."   
      
   The Penn State scientist explains that this decrease occurs because more land   
   exists north of the equator in present-day Earth. Annual-mean temperatures,   
   however, are not the best way to determine if a planet might be habitable, as   
   seasonal temperature variations could be extreme.   
      
   The researchers also looked at these tilted Earths with ten times the carbon   
   dioxide in the atmosphere. Carbon dioxide as a greenhouse gas increases the   
   temperatures on a planet. These models produced Earths with 11 to 18 degrees   
   Fahrenheit higher annual-mean temperatures.   
      
   Because all planets will not have Earth's geography, the researchers took a   
   page   
   from Earth's history and modeled a 750-million-year-old Earth representing the   
   Sturtian glaciation and a 540-million-year-old Earth, the closest approximation   
   available for the Varanger glaciation.   
      
   "During the Sturtian, land masses were mainly equatorial and clumped mostly   
   within 30 degrees of the equator," says the Penn State Erie researcher. "In the   
   Varanger model, everything is close to the south pole."   
      
   While current day Earth is about 30 percent land to 70 percent water, these   
   ancient geographies are about 22 percent land and 78 percent water.   
      
   "The highest temperatures and seasonal variations happen with the largest land   
   areas at the mid to high latitudes," says Williams.   
      
   The researchers also ran some of the model Earths with zero tilt.   
      
   "Present Earth is one of the most uninhabitable planets that we have   
   simulated,"   
   says Williams. "Approximately 8.7 percent of the Earth's surface is colder than   
   14 degrees Fahrenheit on average, and this percentage peaks at 13.2 percent in   
   February owing to the large landmasses at high latitude covered by snow."   
      
   The only planets colder than today's Earth are those planets simulated with no   
   tilt.   
      
   The Varanger simulation, with most land in the southern hemisphere, is the most   
   extreme with 15.6 percent of the surface below 14 degrees Fahrenheit in July   
   and   
   9.3 percent of the surface above 122 degrees Fahrenheit in January. On average,   
   nearly 28 percent of this planet's land mass is uninhabitable by Earth   
   standards.   
      
   "This simulation suggests that planets with either large polar supercontinents   
   or small inventories of water will be the most problematic for life at high   
   obliquity," says Williams.   
      
   None of the planets with increased tilt had permanent ice sheets near the   
   equator. This, however, does not guarantee that a world is suitable for life,   
   the researchers note. The extremes of temperature on most of the simulated   
   earths would make it difficult for all but the simplest Earth life forms to   
   survive. Extremes caused because the tilt puts large portions of the planet in   
   24-hour darkness or 24-hour sunlight for long periods would also inhibit   
   photosynthetic organisms.   
      
   The researchers suggest that even with high tilt, life can exist on the planets   
   they modeled.   
      
   "Provided the life does not occupy continental surfaces plagued seasonally by   
   the highest temperature, these planets could support more advanced life," the   
   researchers say. "While such worlds exhibit climates that are very different   
   from Earth's, many will still be suitable for both simple and advanced forms of   
   water-dependent life."   
      
   So there is no reason to eliminate Earth-like planets with more tilt than Earth   
   from future searches for life beyond the solar system.   
      
   "We have one planet and we have a lot of species on this planet, but it is only   
   one data point," says Williams. "Maybe one day we will figure out everything   
   about life on our own planet, but no where near what is possible elsewhere."   
      
   The National Science Foundation supported this work.   
      
   The International Journal of Astrobiology, founded in 2002, is published by   
   Cambridge University Press. The editors are Dr. Simonj Mitton (Cambridge),   
   smitton@cambridge.org and Dr. Lynn Rothschild (NASA-Ames),   
   Irothschild@mail.arc.nasa.gov .   
      
   **aem**   
      
   EDITORS: Dr. Williams may be reached at 814-898-6008 or at dmw145@psu.edu by   
   email. Dr. Pollard may be reached at 814-865-2022 or at pollard@essc.psu.edu by   
   email.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)