Sunday, July 17, 2011

Solar system with Earth-size planet found

After six years of painstaking observations, astronomers have identified a distant solar system with at least five Neptune-class worlds orbiting within 130 million miles or so of the parent star--closer than Mars is to the sun. Two other planets are believed to be present, including one just 1.4 times as massive as Earth.

The presumed Earth-size planet orbits a scant 2 million miles from its star, completing a full orbit, or "year," every 1.18 days. If confirmed with additional observations, this hellish world would be the smallest yet discovered, additional proof that Earth-size planets are falling within the reach of current Earth-based instruments.

"We have probably found the system with the most planets known today, coming close to the solar system," Christophe Lovis of the University of Geneva, lead author of a paper reporting the discovery, told CNET in an e-mail exchange. "This means that we are now able to detect very complex systems of low-mass planets, which will help us a lot [in] understanding their diversity. This a step towards answering long-standing questions, such as, how common are habitable planets in the universe?"

As for the presumed Earth-size planet, Lovis said "it is probable that such a low-mass body cannot retain an atmosphere so close to its star. Most likely, this body is like a big melted-lava ball. Hard to imagine, since this is unknown in our solar system."

Over six years, Lovis and his colleagues used a sensitive spectrograph mounted on the European Southern Observatory's 3.6-meter (11.8-foot) telescope at La Silla, Chile, to measure subtle changes in the light from a sun-like star known as HD 10180 in the southern constellation Hydrus.

Located 127 light-years from Earth, HD 10180 wobbles ever so slightly, as it is tugged this way and that by the gravity of a retinue of unseen planets. Over the course of 190 observations, astronomers were able to confirm the presence of at least five Neptune-like planets between 13 and 25 times as massive as Earth.

All five worlds orbit HD 10180 at distances ranging from 0.06 and 1.4 times the distance between the Earth and the sun, out to about 130 million miles. The much smaller, yet-to-be-confirmed planet orbits inside the five Neptune-class worlds. A seventh Saturn-class planet is believed to be at a range of 3.4 times the Earth-sun distance, taking six Earth years to complete one orbit.

According to the Extrasolar Planets Encyclopaedia maintained by the Paris Observatory, 488 planets beyond Earth's solar system have been discovered to date. Some 15 solar systems feature at least three planets. A star known as 55 Cancri has five confirmed planets, including two Jupiter-class worlds.

The HD 10180 solar system is unique in that its planets circle the parent star in nearly circular orbits and seem to be positioned according to a relatively simple arithmetic rule that may be "a consequence of the various gravitational interactions that occur between the planets during their evolution," Lovis said.

"It is difficult to say at this point how significant this result is, but it will be very interesting to hear what our theoretician colleagues think of it," he added.

Surprisingly, perhaps, it appears the HD 10180 solar system is gravitationally stable over long time scales, despite the effects of five Neptune-class planets orbiting so close to their star.

"This was not an easy question, and answering it required in-depth dynamical analyses," Lovis said. "When modeling all major effects properly (including effects of general relativity), it turns out that the system is indeed stable over long time scales."

He said additional observations will be needed to pin down the orbit and mass of the innermost, Earth-class planet.

"We will dedicate some more telescope nights to observe the improve the coverage of the 1.18-day period," he said of the smaller planet. "At the moment, we are suffering from the fact that we take one single data point per night, which makes it difficult to be sure about a 1.18-day period. I expect that we will make progress on this system within a year or so."

The observations are extremely difficult. The gravitational tug of the low-mass planet amounts to a 1.8 mph wobble in a star 127 light-years away, "which is hard to measure and, if confirmed, would represent a new record in precision," Lovis said.

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Tuesday, July 12, 2011

Dawn Team Members Check out Spacecraft

Dawn Mission Status Update

Mission managers for NASA's Dawn spacecraft are studying the spacecraft's ion propulsion system after Dawn experienced a loss of thrust on June 27. Dawn team members were able to trace the episode to an electronic circuit in the spacecraft's digital control and interface unit, a subsystem that houses the circuit and a computer that provides the "brains" to Dawn's ion propulsion system. That circuit appeared to lose an electronic signal. As a result, the valves controlling the flow of xenon fuel did not open properly. Dawn automatically put itself into a more basic configuration known as "safe-communications" mode, where the spacecraft stopped some activities and turned its high-gain antenna to Earth.

Engineers were able to return the spacecraft to a normal configuration and restart the spacecraft's thrusting on June 30 by switching to a second digital control and interface unit with equivalent capabilities. One set of images for navigation purposes was not obtained on June 28 because the spacecraft was in safe-communications mode, and one other set, on July 6, was not obtained to allow the spacecraft to spend the time thrusting. Other sets of navigation images have been and will be acquired as expected. The ion propulsion system is now functioning normally.

"Dawn is still on track to get into orbit around Vesta, and thanks to the flexibility provided by our use of ion propulsion, the time of orbit capture actually will move earlier by a little less than a day," said Marc Rayman, Dawn's chief engineer and mission manager. "More importantly, the rest of Dawn's schedule is unaffected, and science collection is expected to begin as scheduled in early August."

In an unrelated event, the visible and infrared mapping spectrometer on Dawn reset itself on June 29. At the time of the reset, the instrument was gathering calibration data during the spacecraft's approach to the giant asteroid Vesta. Some of its planned observations were completed successfully before automatic sensors turned the instrument off.

On June 30, Dawn team members were able to trace the reset to an internal error in the instrument's central processing unit, though they don't yet know why the internal error occurred. By temporarily turning the instrument back on, the Dawn team confirmed that the instrument is otherwise in a normal configuration. They powered the instrument back off, as originally planned for this time. Team members are working to determine when they will turn it back on again.

After arriving at Vesta, Dawn will spend about one year orbiting the asteroid, which is also known as a protoplanet because it is a large body that almost became a planet. Data collected at Vesta will help scientists understand the earliest chapter of our solar system's history.

The Dawn mission to Vesta and Ceres is managed by the Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, for NASA's Science Mission Directorate, Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Ala. The University of California, Los Angeles, is responsible for overall Dawn mission science. Other scientific partners include Planetary Science Institute, Tucson, Ariz.; Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany; DLR Institute for Planetary Research, Berlin, Germany; Italian National Institute for Astrophysics, Rome; and the Italian Space Agency, Rome. Orbital Sciences Corporation of Dulles, Va., designed and built the Dawn spacecraft.

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Friday, July 01, 2011

NASA's Spitzer Finds Distant Galaxies Grazed on Gas

PASADENA, Calif. -- Galaxies once thought of as voracious tigers are more like grazing cows, according to a new study using NASA's Spitzer Space Telescope.

Astronomers have discovered that galaxies in the distant, early universe continuously ingested their star-making fuel over long periods of time. This goes against previous theories that the galaxies devoured their fuel in quick bursts after run-ins with other galaxies.

"Our study shows the merging of massive galaxies was not the dominant method of galaxy growth in the distant universe," said Ranga-Ram Chary of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena, Calif. "We're finding this type of galactic cannibalism was rare. Instead, we are seeing evidence for a mechanism of galaxy growth in which a typical galaxy fed itself through a steady stream of gas, making stars at a much faster rate than previously thought."

Chary is the principal investigator of the research, appearing in the Aug. 1 issue of the Astrophysical Journal. According to his findings, these grazing galaxies fed steadily over periods of hundreds of millions of years and created an unusual amount of plump stars, up to 100 times the mass of our sun.

"This is the first time that we have identified galaxies that supersized themselves by grazing," said Hyunjin Shim, also of the Spitzer Science Center and lead author of the paper. "They have many more massive stars than our Milky Way galaxy."

Galaxies like our Milky Way are giant collections of stars, gas and dust. They grow in size by feeding off gas and converting it to new stars. A long-standing question in astronomy is: Where did distant galaxies that formed billions of years ago acquire this stellar fuel? The most favored theory was that galaxies grew by merging with other galaxies, feeding off gas stirred up in the collisions.

Chary and his team addressed this question by using Spitzer to survey more than 70 remote galaxies that existed 1 to 2 billion years after the Big Bang (our universe is approximately 13.7 billion years old). To their surprise, these galaxies were blazing with what is called H alpha, which is radiation from hydrogen gas that has been hit with ultraviolet light from stars. High levels of H alpha indicate stars are forming vigorously. Seventy percent of the surveyed galaxies show strong signs of H alpha. By contrast, only 0.1 percent of galaxies in our local universe possess this signature.

Previous studies using ultraviolet-light telescopes found about six times less star formation than Spitzer, which sees infrared light. Scientists think this may be due to large amounts of obscuring dust, through which infrared light can sneak. Spitzer opened a new window onto the galaxies by taking very long-exposure infrared images of a patch of sky called the GOODS fields, for Great Observatories Origins Deep Survey.

Further analyses showed that these galaxies furiously formed stars up to 100 times faster than the current star-formation rate of our Milky Way. What's more, the star formation took place over a long period of time, hundreds of millions of years. This tells astronomers that the galaxies did not grow due to mergers, or collisions, which happen on shorter timescales. While such smash-ups are common in the universe -- for example, our Milky Way will merge with the Andromeda galaxy in about 5 billion years -- the new study shows that large mergers were not the main cause of galaxy growth. Instead, the results show that distant, giant galaxies bulked up by feeding off a steady supply of gas that probably streamed in from filaments of dark matter.

Chary said, "If you could visit a planet in one of these galaxies, the sky would be a crazy place, with tons of bright stars, and fairly frequent supernova explosions."

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the Spitzer Space Telescope mission for the agency's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at Caltech. Caltech manages JPL for NASA.