Earth-like Planet Forming In Nearby Star System, Astronomers Believe

Source:

http://www.sciencedaily.com/releases/2007/10/071003130744.htm

Science Daily — An Earth-like planet is likely forming 424 light-years away in a star system called HD 113766, say astronomers using NASA's Spitzer Space Telescope.

Scientists have discovered a huge belt of warm dust – enough to build a Mars-size planet or larger – swirling around a distant star that is just slightly more massive than our sun.
The dust belt, which they suspect is clumping together into planets, is located in the middle of the system's terrestrial habitable zone. This is the region around a star where liquid water could exist on any rocky planets that might form. Earth is located in the middle of our sun's terrestrial habitable zone.
At approximately 10 million years old, the star is also at just the right age for forming rocky planets.
"The timing for this system to be building an Earth is very good," says Dr. Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. "If the system was too young, its planet-forming disk would be full of gas, and it would be making gas-giant planets like Jupiter instead. If the system was too old, then dust aggregation or clumping would have already occurred and all the system's rocky planets would have already formed."
According to Lisse, the conditions for forming an Earth-like planet are more than just being in the right place at the right time and around the right star – it's also about the right mix of dusty materials.
Using Spitzer's infrared spectrometer instrument, he determined that the material in HD 113766 is more processed than the snowball-like stuff that makes up infant solar systems and comets, which are considered cosmic "refrigerators" because they contain pristine ingredients from the early solar system. However, it is also not as processed as the stuff found in mature planets and the largest asteroids. This means the dust belt must be in a transitional phase, when rocky planets are just beginning to form.
How do scientists know the material is more processed than that of comets? From missions like NASA's Deep Impact – in which an 820-pound impactor spacecraft collided with comet Tempel 1 – scientists know that early star systems contain a lot of fragile organic material. That material includes polycyclic aromatic hydrocarbons (carbon-based molecules found on charred barbeque grills and automobile exhaust on Earth), water ice, and carbonates (chalk). Lisse says that HD 113766 does not contain any water ice, carbonates or fragile organic materials.
From meteorite studies on Earth, scientists also have a good idea of what makes up asteroids – the more processed rocky leftovers of planet formation. These studies tell us that metals began separating from rocks in Earth's early days, when the planet's body was completely molten. During this time, almost all the heavy metals fell to Earth's center in a process called "differentiation." Lisse says that, unlike planets and asteroids, the metals in HD 113766 have not totally separated from the rocky material, suggesting that rocky planets have not yet formed.
"The material mix in this belt is most reminiscent of the stuff found in lava flows on Earth. I thought of Mauna Kea material when I first saw the dust composition in this system – it contains raw rock and is abundant in iron sulfides, which are similar to fool's gold," says Lisse, referring to a well-known Hawaiian volcano.
"It is fantastic to think we are able to detect the process of terrestrial planet formation. Stay tuned — I expect lots more fireworks as the planet in HD113766 grows," he adds.
Lisse's article, Circumstellar Dust Created by Terrestrial Planet Formation in HD 113766, will be published in an upcoming issue of Astrophysical Journal. He will also present his findings at the upcoming meeting of the American Astronomical Society Division for Planetary Sciences in Orlando, Fla. Lisse's research was funded through a Johns Hopkins Applied Physics Laboratory Stuart S. Janney Fellowship and a Spitzer Space Telescope guest observer grant.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.
The University of Maryland is responsible for overall Deep Impact mission science, and project management is handled by JPL.
Note: This story has been adapted from material provided by Johns Hopkins University.

Fausto Intilla

www.oloscience.com

Cornucopia Of Earth-sized Planets Modeled By NASA

Source:

http://www.sciencedaily.com/releases/2007/09/070924132510.htm

Science Daily — In the Star Wars movies fictional planets are covered with forests, oceans, deserts, and volcanoes. But new models from a team of MIT, NASA, and Carnegie scientists begin to describe an even wider range of Earth-size planets that astronomers might actually be able to find in the near future.

Sara Seager, Massachusetts Institute of Technology, Cambridge, Mass.; Marc Kuchner, NASA Goddard Space Flight Center, Greenbelt, Md.; Catherine Hier-Majumder, Carnegie Institution of Washington, (deceased); and Burkhard Militzer, Carnegie, have created models for 14 different types of solid planets that might exist in our galaxy.
The 14 types have various compositions, and the team calculated how large each planet would be for a given mass. Some are pure water ice, carbon, iron, silicate, carbon monoxide, and silicon carbide; others are mixtures of these various compounds.
"We’re thinking seriously about the different kinds of roughly Earth-size planets that might be out there, like George Lucas, but for real," says Kuchner.
The team took a different approach from previous studies. Rather than assume that planets around other stars are scaled-up or scaled-down versions of the planets in our solar system, they considered all types of planets that might be possible, given what astronomers know about the composition of protoplanetary disks around young stars.
"We have learned that extrasolar giant planets often differ tremendously from the worlds in our solar system, so we let our imaginations run wild and tried to cover all the bases with our models of smaller planets," says Kuchner. "We can make educated guesses about where these different kinds of planets might be found. For example, carbon planets and carbon-monoxide planets might favor evolved stars such as white dwarfs and pulsars, or they might form in carbon-rich disks like the one around the star Beta Pictoris. But ultimately, we need observations to give us the answers."
The team calculated how gravity would compress planets of varying compositions. The resulting computer models predict a planet’s diameter for a given composition and mass. For example, a 1-Earth-mass planet made of pure water will be about 9,500 miles across, whereas an iron planet with the same mass will be only about 3,000 miles in diameter. For comparison, Earth, which is made mostly of silicates, is 7,926 miles across at its equator.
Some of the results were expected, such as the fact that pure water planets (similar to the moons of the outer planets in our solar system, which consist mostly of water ice) were the least dense of the solid planets, and pure iron planets are the most dense. But there were some surprises. The team discovered that no matter what material a planet is made of, the mass/diameter relationship follows a similar pattern.
"All materials compress in a similar way because of the structure of solids," explains Seager. "If you squeeze a rock, nothing much happens until you reach some critical pressure, then it crushes. Planets behave the same way, but they react at different pressures depending on the composition. This is a big step forward in our fundamental understanding of planets."
The team hopes that these models will yield insights into planet compositions when astronomers start finding Earth-sized planets around other stars. Missions such as the French Corot satellite, which launched on December 27, 2006, and NASA’s Kepler spacecraft, scheduled to launch in 2009, can find planets not much larger than Earth by watching them pass in front of their host stars, events known as transits. The transits yield the planet’s size, and follow-up studies can measure the mass. By comparing a planet's size and mass, astronomers might be able to determine whether it is mostly water ice or mostly iron, for example.
But astronomers using the transit method will find it difficult at best to distinguish a silicate planet from a carbon planet, because they’re about the same size for a given mass. "To make this finer distinction, we will need some help from NASA’s James Webb Space Telescope or Terrestrial Planet Finder," says Kuchner. "With these instruments, we could take spectra of Earth-mass planets, which will tell us about their chemistries."
The team’s paper is currently scheduled to appear in the October 20 issue of the Astrophysical Journal.
Note: This story has been adapted from a news release issued by NASA Goddard Space Flight Center.

Fausto Intilla

www.oloscience.com

Exoplanet Offers Clues To Earth's Future

Source:

http://www.sciencedaily.com/releases/2007/09/070912130828.htm

Science Daily — An international team of astronomers that includes Steve Kawaler of Iowa State University has announced the first discovery of a planet orbiting a star near the end of its life.

The news provides a preliminary picture of what could be the Earth's destiny in four to five billion years. That's when the sun will exhaust its hydrogen fuel, expand enormously as a red giant and expel its outer layers in an explosive helium flash.
The planet discovered by the researchers, "V 391 Pegasi b," has survived all those changes to its sun.
The international research team was led by Roberto Silvotti from the INAF-Osservatorio Astronomico di Capodimonte in Naples, Italy. They discovered the planet orbiting "V 391 Pegasi," a faint star in the constellation of Pegasus.
"The exciting thing about finding a planet around this star is that it indicates that planetary systems can survive the giant phase and the helium flash of their parent star," said Kawaler, an Iowa State professor of physics and astronomy. "It bodes well for the survival of our own Earth in the distant future. Before V 391 Pegasi lost its outer regions at the helium flash, the planet orbited the star at about the same distance that the Earth orbits our sun."
But, Kawaler said, "We shouldn't take too much heart in this -- this planet is larger than Jupiter, so a smaller planet like the Earth could still be vulnerable."
Kawaler helped the 23-member research team make its discovery by coordinating observations during a 2003 run of the Whole Earth Telescope. Iowa State is a lead institution in the Whole Earth Telescope, a worldwide network of cooperating observatories that allow astronomers to take uninterrupted measurements of variable stars that change in brightness. The discovery of V 391 Pegasi b was made by detailed measurements of the clocklike variation of the star caused by the planet tugging on it.
Kawaler also advanced the project by doing theoretical calculations to make sure irregularities of the star's orbital motion were caused by the orbiting planet.
The astronomers found that at the present time, V 391 Pegasi b has an orbital distance 1.7 times the medium distance between the Earth and the sun. As stars age and reach their red giant phase, they undergo an enormous expansion (with their volume increasing by a factor of millions) that can easily reach and engulf their inner planets.
"The same will happen to the sun," Silvotti said. "As far as our planets are concerned, we expect Mercury and Venus to disappear in the sun's envelope, whereas Mars should survive. The fate of the Earth is less clear because its position is really at the limit: it appears more likely that the Earth will not survive the red giant expansion of the sun either, but it is not for sure."
As is the case for almost all planets beyond our solar system, V 391 Pegasi b cannot be seen directly. Silvotti said it took seven years of observations and calculations to confirm the existence of the planet.
The announcement, culminating seven years of research, will be published in the Sept. 13 issue of the journal Nature.
Note: This story has been adapted from a news release issued by Iowa State University.

Fausto Intilla

www.oloscience.com

Astronomers Baffled By Basalt In The Outer Asteroid Belt

Source:

http://www.sciencedaily.com/releases/2007/08/070824130652.htm

Science Daily — Analysis of the chemical make up of two asteroids in the outer asteroid belt has thrown the classification system for these small bodies, which orbit between Mars and Jupiter, into disorder.

Dr Rene Duffard, who is presenting results at the European Planetary Science Congress in Potsdam on Wednesday 22nd August, said, "We appear to have detected basalt on the surface of these asteroids, which is very unusual for this part of the asteroid belt. We do not know whether we have discovered two basaltic asteroids with a very particular and previously unseen mineralogical composition or two objects of non basaltic nature that have to be included in a totally new taxonomic class."
The presence of basalt means that the asteroid must have melted partially at some time in the past, which implies that it was once part of a larger body which had internal heating processes. However, there do not appear to be other basaltic fragments in the region and, from spectral analysis, it is not clear whether the two are fragments of the same parent body or not.
Until recently, most of the known basaltic asteroids, which are classified as V-type, were thought to be fragments of Vesta, the second largest object in the asteroid belt. Since 2001, several V-type asteroids have been identified as not belonging to this Vesta family, including (1459) Magnya, the first basaltic object to be detected in the outer asteroid belt.
Dr Duffard, of the Instituto de Astrofisica de Andalucia in Spain, and his colleague, Dr Fernando Roig, from the Observatorio Nacional in Rio de Janeiro, Brazil, selected the two asteroids, (7472) Kumakiri and (10537) 1991 RY16, for investigation by from a group of six candidate V-type asteroids identified using photometric data from the Sloan Digital Sky Survey (SDSS).
The reflectance spectra of the two bodies seem to show the characteristics of a V-type asteroid. However, there is a shallow absorption band around the wavelength of red visible light, which has never been observed before in other V-type spectra. This means that these objects have a slightly different chemical composition and do not fit into any existing category of asteroid. The unexpected dip in the spectra could have two sources: it could be due to impacts with other asteroids or comets "shocking" iron-rich compounds into a oxidized state, or it could indicate the presence of olivine, a green mineral that is also known as the semi-precious gemstone.
Dr Duffard said, "We need now to observe both objects in the near-infrared range to confirm whether they have a basaltic surface. If they do, we will need to try and work out where they came from and the fate of their parent objects. If they do not, we will have to come up with a new class of asteroid."
Note: This story has been adapted from a news release issued by European Planetology Network.

Fausto intilla

www.oloscience.com

Largest Transiting Extrasolar Planet Found Around A Distant

Source:

http://www.sciencedaily.com/releases/2007/08/070806121128.htm

Science Daily — An international team of astronomers with the Trans-atlantic Exoplanet Survey just announced the discovery of TrES-4, a new extrasolar planet in the constellation of Hercules. The new planet was identified by astronomers looking for transiting planets -- that is, planets that pass in front of their home star -- using a network of small automated telescopes in Arizona, California, and the Canary Islands.

TrES-4 was discovered less than half a degree (about the size of the full Moon) from the team's third planet, TrES-3."TrES-4 is the largest known exoplanet," said Georgi Mandushev, Lowell Observatory astronomer and the lead author of the paper announcing the discovery. "It is about 70 percent bigger than Jupiter, the Solar System's largest planet, but less massive, making it a planet of extremely low density. Its mean density is only about 0.2 grams per cubic centimeter, or about the density of balsa wood! And because of the planet's relatively weak pull on its upper atmosphere, some of the atmosphere probably escapes in a comet-like tail." The new planet TrES-4 was first noticed by Lowell Observatory's Planet Search Survey Telescope (PSST), set up and operated by Edward Dunham and Georgi Mandushev. The Sleuth telescope, maintained by David Charbonneau (CfA) and Francis O'Donovan (Caltech), at Caltech's Palomar Observatory also observed transits of TrES-4, confirming the initial detections. TrES-4 is about 1400 light years away and orbits its host star in three and a half days. Being only about 4.5 million miles from its home star, the planet is also very hot, about 1,600 Kelvin or 2,300 degrees Fahrenheit."TrES-4 appears to be something of a theoretical problem," said Edward Dunham, Lowell Observatory Instrument Scientist. "It is larger relative to its mass than current models of superheated giant planets can presently explain. Problems are good, though, since we learn new things by solving them." "We continue to be surprised by how relatively large these giant planets can be," adds Francis O'Donovan, a graduate student in astronomy at the California Institute of Technology who operates one of the TrES telescopes. "But if we can explain the sizes of these bloated planets in their harsh environments, it may help us understand better our own Solar System planets and their formation."By definition, a transiting planet passes directly between the Earth and the star, blocking some of the star's light and causing a slight drop in its brightness. To look for transits, the small telescopes are automated to take wide-field timed exposures of the clear skies on as many nights as possible. When observations are completed for a particular field -- usually over an approximate two-month period -- astronomers measure very precisely the light from every star in the field in order to detect the possible signature of a transiting planet. "TrES-4 blocks off about one percent of the light of the star as it passes in front of it," said Mandushev. "With our telescopes and observing techniques, we can measure this tiny drop in the star's brightness and deduce the presence of a planet there." Not only is the planet TrES-4 mysterious and intriguing, but so is its host star cataloged as GSC 02620-00648. Georgi Mandushev explains: "The host star of TrES-4 appears to be about the same age as our Sun, but because it is more massive, it has evolved much faster. It has become what astronomers call a 'subgiant', or a star that has exhausted all of its hydrogen fuel in the core and is on its way of becoming a 'red giant', a huge, cool red star like Arcturus or Aldebaran."In order to help confirm they had found a planet, Gáspár Bakos of the Hungarian Automated Telescope Network (HATNet) and Harvard's Guillermo Torres switched from the 10-centimeter TrES telescopes to one of the 10-meter telescopes at the W. M. Keck Observatory on the summit of Mauna Kea, Hawaii. Using this giant telescope, they confirmed that the TrES team had indeed found a new planet. In order to measure accurately the size and other properties of TrES-4, astronomers also made follow up observations with bigger telescopes at Lowell Observatory and Fred L. Whipple Observatory in Arizona. The authors of the paper "TrES-4: A Transiting Hot Jupiter of Very Low Density", accepted for publication in the Astrophysical Journal, are: Georgi Mandushev and Edward Dunham of Lowell Observatory; Francis T. O'Donovan and Lynne Hillenbrand of the California Institute of Technology; David Charbonneau, Guillermo Torres, David Latham, Gáspár Bakos, Alessandro Sozzetti, and José Fernández of the Harvard-Smithsonian Center for Astrophysics; Mark Everett and Gilbert Esquerdo of the Planetary Science Institute; Markus Rabus and Juan Belmonte of Instituto de Astrofísica de Canarias in Tenerife, Spain; and Timothy Brown of the Las Cumbres Observatory Global Telescope.This research is funded by NASA through the Origins of Solar Systems Program.

Note: This story has been adapted from a news release issued by Lowell Observatory.

Fausto Intilla

www.oloscience.com