Many, Perhaps Most, Nearby Sun-Like Stars May Form Rocky Planets

Sunday, February 17, 2008

Astronomers have discovered that terrestrial planets might form around many, if not most, of the nearby sun-like stars in our galaxy. These new results suggest that worlds with potential for life might be more common than we thought.

University of Arizona, Tucson, astronomer Michael Meyer and his colleagues used NASA's Spitzer Space Telescope to determine whether planetary systems like ours are common or rare in our Milky Way galaxy. They found that at least 20 percent, and possibly as many as 60 percent, of stars similar to the sun are candidates for forming rocky planets.

Meyer is presenting the findings at the annual meeting of the American Association for the Advancement of Science in Boston. The results appear in the Feb. 1 issue of Astrophysical Journal Letters.

The astronomers used Spitzer to survey six sets of stars, grouped depending on their age, with masses comparable to our sun. The sun is about 4.6 billion years old. "We wanted to study the evolution of the gas and dust around stars similar to the sun and compare the results with what we think the solar system looked like at earlier stages during its evolution," Meyer said.

The Spitzer telescope does not detect planets directly. Instead it detects dust -- the rubble left over from collisions as planets form -- at a range of infrared wavelengths. The hottest dust is detected at the shortest wavelengths, between 3.6 microns and 8 microns. Cool dust is detected at the longest wavelengths, between 70 microns and 160 microns. Warm dust can be traced at 24-micron wavelengths. Because dust closer to the star is hotter than dust farther from the star, the "warm" dust likely traces material orbiting the star at distances comparable to the distance between Earth and Jupiter.

"We found that about 10 to 20 percent of the stars in each of the four youngest age groups shows 24-micron emission due to dust," Meyer said. "But we don't often see warm dust around stars older than 300 million years. The frequency just drops off.

"That's comparable to the time scales thought to span the formation and dynamical evolution of our own solar system," he added. "Theoretical models and meteoritic data suggest that Earth formed over 10 to 50 million years from collisions between smaller bodies."

In a separate study, Thayne Currie and Scott Kenyon of the Smithsonian Astrophysical Observatory, Cambridge, Mass., and their colleagues also found evidence of dust from terrestrial planet formation around stars from 10 to 30 million years old. "These observations suggest that whatever led to the formation of Earth could be occurring around many stars between three million and 300 million years old," Meyer said.

Kenyon and Ben Bromley of the University of Utah, Salt Lake City, have developed planet formation models that provide a plausible scenario. Their models predict warm dust would be detected at 24-micron wavelengths as small rocky bodies collide and merge. "Our work suggests that the warm dust Meyer and colleagues detect is a natural outcome of rocky planet formation. We predict a higher frequency of dust emission for the younger stars, just as Spitzer observes," said Kenyon.

The numbers on how many stars form planets are ambiguous because there's more than one way to interpret the Spitzer data, Meyer said. The warm-dust emission that Spitzer observed around 20 percent of the youngest cohort of stars could persist as the stars age. That is, the warm dust generated by collisions around stars three to 10 million years old could carry over and show up as warm dust emission seen around stars in the 10- to 30- million-year-old range and so on. Interpreting the data this way, about one out of five sun-like stars is potentially planet-forming, Meyer said.

There's another way to interpret the data. "An optimistic scenario would suggest that the biggest, most massive disks would undergo the runaway collision process first and assemble their planets quickly. That's what we could be seeing in the youngest stars. Their disks live hard and die young, shining brightly early on, then fading," Meyer said. "However, smaller, less massive disks will light up later. Planet formation in this case is delayed because there are fewer particles to collide with each other."

If this is correct and the most massive disks form their planets first and the wimpiest disks take 10 to 100 times longer, then up to 62 percent of the surveyed stars have formed, or may be forming, planets. "The correct answer probably lies somewhere between the pessimistic case of less than 20 percent and optimistic case of more than 60 percent," Meyer said.

The next critical test of the assertion that terrestrial planets like Earth could be common around stars like the sun will come next year with the launch of NASA's Kepler mission.

Meyer's 13 co-authors include John Carpenter of the California Institute of Technology in Pasadena. NASA's Jet Propulsion Laboratory in Pasadena manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech. Caltech manages JPL for NASA.

Image Caption: Rocky, Terrestrial Worlds: This artist's concept illustrates the idea that rocky, terrestrial worlds like the inner planets in our solar system may be plentiful, and diverse, in the universe. (click image for Hi-Res version)

Image Credit: NASA/JPL-Caltech/R. Hurt (SSC-Caltech)

Source: NASA / JPL / Spitzer

Permalink: http://www.sflorg.com/comm_center/space/p259_05.html

Time Stamp: 2/17/2008 at 11:58:20 AM CST

The International Year of Astronomy 2009 welcomes the 100th participating state

Thursday, January 17, 2008

The organizers of the International Year of Astronomy 2009 (IYA2009), the International Astronomical Union and UNESCO, welcomed this week the 100th participating country to the growing ranks of participating states and organizations for this worldwide astronomy project. This milestone is reached only four weeks after the official Proclamation of IYA2009 by the United Nations.

The latest country to join the International Year of Astronomy 2009 initiative is the People's Republic of Bangladesh. This is a particularly welcome addition to the growing worldwide project since one of its aims is to promote astronomy and develop astronomical networks in developing countries.

Mr. F. R. Sarker the General Secretary of the Bangladesh Astronomical Society is the Chair of the Bangladesh IYA2009 National Node and explains why he and his country are participating in the International Year of Astronomy 2009:
"The IYA2009 is a historic event which will offer unique opportunities for the people of Bangladesh to learn more about the incredible developments in the field of astronomy."

The International Year of Astronomy 2009 projects and activities aim to help millions of people worldwide to rediscover their place in the Universe through the day and night time sky, and thereby engage a personal sense of wonder and discovery. The International Year of Astronomy 2009 represents the largest coordinated effort of professional and non-professional astronomers in history for popularizing astronomy. The President of the International Astronomical Union (IAU) Catherine Cesarsky says: "We are delighted that the International Year of Astronomy 2009 gives a chance to the astronomers from the IAU member countries to reach out to the rest of the world and share the new knowledge and excitement of today's astronomy"

Mr. F. R. Sarker adds: "Although being a developing country, Bangladesh has a large number of space enthusiasts, perhaps more than anywhere else in the world. The Bangladesh Astronomical Society aims to let 200,000 people observing the night sky through telescopes during 2009. On 22 July, 2009 a total solar eclipse will be visible on northern part of Bangladesh, this will be one of the most memorable celestial events in the history of the country. Our hope is that IYA2009 will enable Bangladesh to establish a large optical observatory in Chittagong to explore the mysteries of the Universe."

The International Year of Astronomy 2009 will be a global celebration of astronomy and its contributions to society and culture, highlighted by the 400th anniversary of the first use of an astronomical telescope by Galileo Galilei. In addition to the 100 states already involved in the IYA2009, 14 organizations are involved. Well over 140 states and many organizations are expected to participate in the initiative in 2009.

For more information about the International Year of Astronomy 2009 please visit the website at www.astronomy2009.org

Image Caption: The chair of the International Year of Astronomy 2009 (IYA2009) Bangladesh National Node, Mr. F. R. Sarker, giving a speech during the 2005 World Space Week. Bangladesh is the 100th participating country in the IYA2009 initiative.

Image Credit: Bangladesh Astronomical Society/IYA2009

Source: International Astronomical Union

Permalink: http://www.sflorg.com/comm_center/space/p205_04.html

Time Stamp: 1/17/2008 at 6:51:05 AM CST

Look Out For Comet Homes

Monday, October 29, 2007

Last week the normally very faint Comet Homes underwent a major outburst and is now around a million times brighter than expected, making it easily visible to the unaided eye.

Comet Homes is currently visible in front of the stars of the constellation of Perseus and looks set to stay bright for some days or even weeks.

The comet was discovered by amateur astronomer Edwin Homes in November 1892. It takes a little under 7 years to complete an orbit around the Sun. At its closest to the Sun (perihelion) it is still twice as far away as the Earth - around 300 million km from our local star - and is always located between the orbits of Mars and Jupiter.

Most of the time Comet Homes is extremely faint and only visible in large telescopes. This outburst is completely unexpected and the comet has also greatly increased in size. Through a pair of binoculars it now looks like a large fuzzy object with a sharper core.

The comet is seen at its best in dark skies, away from the light pollution of major cities.

This Image was taken by John Crilly from the Urban Observatory.

For a Hi-Res Version: SFL ORG. Gallery

To learn more about: John Crilly and the Urban Observatory

Source: RAS, John Crilly

Permalink: http://www.sflorg.com/comm_center/space/p144_03.html

Time Stamp: 10/29/2007 at 11:30:08 AM CST

Time to overhaul Newton's Theory of Gravitation?

Oct. 26, 2007

Galaxy Cluster Models cast doubt on Dark Matter

For almost 75 years, astronomers have believed that the Universe has a large amount of unseen or 'dark' matter, thought to make up about five-sixths of the matter in the cosmos. With the conventional theory of gravitation, based on Newton's ideas and refined by Einstein 92 years ago, dark matter helps to explain the motion of galaxies, and clusters of galaxies, on the largest scales.

Now two Canadian researchers at the Perimeter Institute for Theoretical Physics suggest that the motion of galaxies in a distant cluster is more easily explained by a Modified Gravity (MOG) theory than by the presence of dark matter. Graduate student Joel Brownstein and his supervisor Professor John Moffat of the University of Waterloo present their results in a paper in the 21 November edition of Monthly Notices of the Royal Astronomical Society.

The two scientists analysed images of the 'Bullet Cluster' of galaxies made using the Hubble Space Telescope, Chandra X-ray and Spitzer infrared observatories and the Magellan telescope in Chile. The Bullet Cluster consists of two merging clusters of galaxies and lies at a distance of over 3 billion light years in the direction of the southern constellation of Carina.

This arsenal of instrumentation gave them maps of the 150 million degree hot gas between the galaxies and show the effect of gravitational lensing, where the gravity of an intervening object -- here the Bullet Cluster - deflects the path of light emitted by a more distant galaxy.

Previous studies suggested that the Bullet Cluster clearly demonstrates the presence of dark matter. But when Brownstein and Moffat compared the observed gravitational lensing and distribution of gas with that predicted using MOG theory, they found no evidence for this. In other words, it is more natural to explain the appearance of this cluster using a revised theory of gravitation than by including dark matter.

MOG theory emerges from a generalization of relativity that eluded even Einstein. The theory has been developed by Moffat for nearly thirty years and is now yielding astronomical and cosmological results. It has been used to successfully explain the movement of stars in over 100 galaxies and the motion of galaxies in more than 100 clusters. MOG theory may also explain the apparent anomalous deceleration of the Pioneer 10 and 11 space probes, launched in the early 1970s and now more than 12000 million km from the Sun.

The two physicists are enthusiastic about their findings. Brownstein comments, "Using Modified Gravity (MOG) theory, the 'normal' matter in the Bullet Cluster is enough to account for the observed gravitational lensing effect. In time, better observations will lead to higher resolution pictures of the systems we are studying. Continuing the search for and then analyzing other merging clusters of galaxies will help us decide whether dark matter or MOG theory offers the best explanation for the large scale structure of the Universe."

Professor Moffat adds, "If the multi-billion dollar laboratory experiments now underway succeed in directly detecting dark matter, then I will be happy to see Einsteinian and Newtonian gravity retained. However, if dark matter is not detected and we have to conclude that it does not exist, then Einstein and Newtonian gravity must be modified to fit the extensive amount of astronomical and cosmological data, such as the bullet cluster, that cannot otherwise be explained.”

Image Caption 1: A contour plot of the purported dark matter in the Bullet Cluster. A significant amount of dark matter lies between the two components of the galaxy cluster. Image: J. R. Brownstein & J. W. Moffat, University of Waterloo, Perimeter Institute for Theoretical Physics.

Image Caption 2: A contour plot of the Bullet Cluster as predicted by MOG theory. There is a complete separation of the galaxy cluster components and no evidence for dark matter. Image: J. R. Brownstein & J. W. Moffat, University of Waterloo, Perimeter Institute for Theoretical Physics.

Source: RAS

Permalink: http://www.sflorg.com/comm_center/space/p139_02.html

Time Stamp: 10/26/2007 at 4:54:31 AM CST