DR EMILY BALDWIN
ASTRONOMY NOW
Posted: October 27, 2009

On 31 December 2007 NASA's MESSENGER spacecraft made the first detection of solar neutrons at less than one astronomical unit from the Sun.

MESSENGER was just 0.5 AU from the Sun when it was bathed in high energy neutrons ejected in a solar flare, giving scientists a first close up look at neutron production from a solar flare. Previously, only the neutron bursts from the most powerful solar flares have been recorded on neutron spectrometers on Earth or in near-Earth orbit, which typically last for up to a minute at the Sun.

"But we recorded neutrons from this flare over a period of six to ten hours, and what that´s telling us is that at least some moderate-sized flares continuously produce high-energy neutrons in the solar corona," says William Feldman, Co-Investigator for MESSENGER's Neutron Spectrometer, one of two sensors on the Gamma-Ray and Neutron Spectrometer instrument. "From this fact, we inferred the continuous production of protons in the 30-100 million electron volt (MeV) range due to the flare."

Around 90 percent of all ions produced in a solar flare remain locked to the Sun on closed magnetic field lines, but a second population results from the decay of neutrons near the Sun which can be accelerated through interplanetary space by the shock waves produced by flares.

"So the important results are that perhaps after many flare events two things may occur: continuous production of neutrons over an extended period of time and creation of seed populations of neutrons near the Sun that have decayed into protons," explains Feldman. "When coronal mass ejections (nuclear explosions in the corona) send shock waves into space, these feedstock protons are accelerated into interplanetary space."

There has always been some debate as to why some coronal mass ejections produce almost no energetic protons that reach the Earth, while others produce huge amounts, and now it seems that the answer lies within the seed populations of energetic protons residing near the Sun. "It´s easier to accelerate a proton that already has an energy of 1 MeV than a proton that is at 1 keV (the solar wind)," adds Feldman.

The seed populations are not evenly distributed, however, and it is pot luck as to whether they are in the right place for shock waves to send them careering towards the Earth or in a different direction entirely.

Studying the effects of solar flare radiation is of high level interest to spaceflight programs since flares can damage satellites and of course endanger astronauts working on the International Space Station, the Moon or Mars. Fortunately MESSENGER is in an ideal location - between 0.3 and 0.6 AU - to build up a picture of this type of activity over the coming years.

"What we saw and published is what we hope will be the first of many flares we´ll be able to follow through 2012," says Feldman. "The beauty of MESSENGER is that it´s going to be active from the minimum to the maximum solar activity during Solar Cycle 24, allowing us to observe the rise of a solar cycle much closer to the Sun than ever before."

MESSENGER will reach orbit around Mercury in March 2011 where it will be within 0.45 AU of the Sun for one year. The results from the December 2007 flare are discussed in a forthcoming paper to be published in the Journal of Geophysical Research.

Peering far beyond our solar system, NASA researchers have detected the basic chemistry for life in a second hot gas planet, advancing astronomers toward the goal of being able to characterize planets where life could exist. The planet is not habitable but it has the same chemistry that, if found around a rocky planet in the future, could indicate the presence of life.

"It's the second planet outside our solar system in which water, methane and carbon dioxide have been found, which are potentially important for biological processes in habitable planets," said researcher Mark Swain of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Detecting organic compounds in two exoplanets now raises the possibility that it will become commonplace to find planets with molecules that may be tied to life."

Swain and his co-investigators used data from two of NASA's orbiting Great Observatories, the Hubble Space Telescope and Spitzer Space Telescope, to study HD 209458b, a hot, gaseous giant planet bigger than Jupiter that orbits a sun-like star about 150 light years away in the constellation Pegasus. The new finding follows their breakthrough discovery in December 2008 of carbon dioxide around another hot, Jupiter-size planet, HD 189733b. Earlier Hubble and Spitzer observations of that planet had also revealed water vapor and methane.

The detections were made through spectroscopy, which splits light into its components to reveal the distinctive spectral signatures of different chemicals. Data from Hubble's near-infrared camera and multi-object spectrometer revealed the presence of the molecules, and data from Spitzer's photometer and infrared spectrometer measured their amounts.

"This demonstrates that we can detect the molecules that matter for life processes," said Swain. Astronomers can now begin comparing the two planetary atmospheres for differences and similarities. For example, the relative amounts of water and carbon dioxide in the two planets is similar, but HD 209458b shows a greater abundance of methane than HD 189733b.. "The high methane abundance is telling us something," said Swain. "It could mean there was something special about the formation of this planet."

Other large, hot Jupiter-type planets can be characterized and compared using existing instruments, Swain said. This work will lay the groundwork for the type of analysis astronomers eventually will need to perform in shortlisting any promising rocky Earth-like planets where the signatures of organic chemicals might indicate the presence of life.

Rocky worlds are expected to be found by NASA's Kepler mission, which launched earlier this year, but astronomers believe we are a decade or so away from being able to detect any chemical signs of life on such a body.

If and when such Earth-like planets are found in the future, "the detection of organic compounds will not necessarily mean there's life on a planet, because there are other ways to generate such molecules," Swain said. "If we detect organic chemicals on a rocky, Earth-like planet, we will want to understand enough about the planet to rule out non-life processes that could have led to those chemicals being there."

"These objects are too far away to send probes to, so the only way we're ever going to learn anything about them is to point telescopes at them. Spectroscopy provides a powerful tool to determine their chemistry and dynamics."

This interactive web feature, developed by JPL, conveys the story of exoplanet exploration through a rich tapestry of words and images spanning thousands of years, beginning with the musings of ancient philosophers and continuing through the current era of space-based observations by NASA's Spitzer and Kepler missions. The timeline highlights milestones in culture, technology and science, and includes a planet counter that tracks the pace of exoplanet discoveries over time.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency and is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. The Space Telescope Science Institute, Baltimore, Md., conducts Hubble science operations. The institute is operated for NASA by the Association of Universities for research in Astronomy, Inc.., Washington, D.C.

JPL manages the Spitzer Space Telescope mission for NASA. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA. 
 

DR EMILY BALDWIN
ASTRONOMY NOW
Posted: October 19, 2009

At an international exoplanet conference held in Porto today, HARPS (High Accuracy Radial Velocity Planet Searcher) scientists announce a hand of 32 new exoplanets, boosting the count to over 400.

The new additions cover the complete spectrum of exoplanets uncovered by previous searches, from "typical" hot jupiters, super-Neptunes and super-Earths, to planets found around low mass and low metallicity stars and in multiple planet systems.

"HARPS is a unique, extremely high precision instrument that is ideal for discovering alien worlds," says Stéphane Udry, who made the announcement. "We have now completed our initial five-year programme, which has succeeded well beyond our expectations."

The HARPS instrument is the spectrograph for ESO's 3.6 metre telecope at the La Silla observatory in Chile and detects exoplanets by monitoring small changes in the star's radial velocity as it wobbles from the tug of an orbiting planet. During the first five years of operations the team utilised 530 nights for observing, and to date have discovered the first super-Earth, a trio of Neptune-type planets, the first super-Earth in the habitable zone of a small star, and the lightest exoplanet.

One aspect of the HARPS planet-hunting program focused on the search for planets around low mass dwarf stars, or stars with a lower metal content than our Sun, so-called M-dwarfs. These stars are thought to be less favourable for the formation of planets, which form in the metal-rich disc around the young star. However, the team found three candidate exoplanets of up to four Jupiter masses around stars that are metal-deficient, demonstrating that planets can indeed form around low metal stars.

"By targeting M dwarfs and harnessing the precision of HARPS we have been able to search for exoplanets in the mass and temperature regime of super-Earths, some even close to or inside the habitable zone around the star," says team member Xavier Bonfils.

The new findings also include two six-Earth mass planet candidates orbiting their low mass M-dwarf hosts in seven day periods, a 0.47 Jupiter mass planet orbiting with a fifty seven day period and a four Jupiter mass planet orbiting in one thousand days. The results also suggest that some 40-60 percent of Sun-like stars could host low mass planets.

Although the first phase of the observing programme is now officially complete, HARPS has secured its place as one of the world's top exoplanet hunters and will push on towards the detection of more Earth-type planets in the coming years.

This discovery was announced today during the ESO/CAUP conference "Towards Other Earths: perspectives and limitations in the Extremely Large Telescope era", taking place in Porto, Portugal all this week.