After only six months in orbit around Mercury, NASA’s MESSENGER spacecraft is sending back information that has revolutionized the way scientists think about the innermost planet. Analyses of new data from the spacecraft show, among other things, new evidence that flood volcanism has been widespread on Mercury, the first close-up views of Mercury’s “hollows,” the first direct measurements of the chemical composition of Mercury’s surface, and the first global inventory of plasma ions within Mercury’s space environment.
The results are reported in a set of seven papers published in a special section of Science magazine on September 30, 2011.
“MESSENGER’s instruments are capturing data that can be obtained only from orbit,” says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. “We have imaged many areas of the surface at unprecedented resolution, we have viewed the polar regions clearly for the first time, we have built up global coverage with our images and other data sets, we are mapping the elemental composition of Mercury’s surface, we are conducting a continuous inventory of the planet’s neutral and ionized exosphere, and we are sorting out the geometry of Mercury’s magnetic field and magnetosphere. And we’ve only just begun. Mercury has many more surprises in store for us as our mission progresses.”
New observations by NASA’s Wide-field Infrared Survey Explorer, or WISE, show there are significantly fewer near-Earth asteroids in the mid-size range than previously thought. The findings also indicate NASA has found more than 90 percent of the largest near-Earth asteroids, meeting a goal agreed to with Congress in 1998.
Astronomers now estimate there are roughly 19,500 — not 35,000 — mid-size near-Earth asteroids. Scientists say this improved understanding of the population may indicate the hazard to Earth could be somewhat less than previously thought. However, the majority of these mid-size asteroids remain to be discovered. More research also is needed to determine if fewer mid-size objects (between 330 and 3,300-feet wide) also mean fewer potentially hazardous asteroids, those that come closest to Earth.
The results come from the most accurate census to date of near-Earth asteroids, the space rocks that orbit within 120 million miles (195 million kilometers) of the sun into Earth’s orbital vicinity. WISE observed infrared light from those in the middle to large-size category. The survey project, called NEOWISE, is the asteroid-hunting portion of the WISE mission. Study results appear in the Astrophysical Journal.
The most recent spacecraft telemetry was acquired on September 27 from the Deep Space Network tracking complex at Madrid, Spain. The Cassini spacecraft is in an excellent state of health and with the exception of one science instrument being powered off, all subsystems are operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the “Present Position” page at: http://saturn.jpl.nasa.gov/mission/presentposition/.
High-mass stars are important because they are responsible for much of the energy pumped into our galaxy over its lifetime. Unfortunately, these stars are poorly understood because they are often found relatively far away and can be obscured by gas and dust. The star cluster NGC 281 is an exception to this rule. It is located about 9,200 light years from Earth and, remarkably, almost 1,000 light years above the plane of the Galaxy, giving astronomers a nearly unfettered view of the star formation within it.
NGC 281 is known informally as the “Pacman Nebula” because of its appearance in optical images. In optical images the “mouth” of the Pacman character appears dark because of obscuration by dust and gas, but in the infrared Spitzer image the dust in this region glows brightly.
Hubble’s famous images of galaxies typically show elegant spirals or soft-edged ellipses. But these neat forms are only representative of large galaxies. Smaller galaxies like the dwarf irregular galaxy Holmberg II come in many shapes and types that are harder to classify. This galaxy’s indistinct shape is punctuated by huge glowing bubbles of gas, captured in this image from the NASA/ESA Hubble Space Telescope.
The intricate glowing shells of gas in Holmberg II were created by the energetic life cycles of many generations of stars. High-mass stars form in dense regions of gas, and later in life expel strong stellar winds that blow away the surrounding material. At the very end of their lives, they explode in as a supernova. Shock waves rip through these less dense regions blowing out and heating the gas, forming the delicate shells we see today.
Holmberg II is a patchwork of dense star-forming regions and extensive barren areas with less material, which can stretch across thousands of light-years. As a dwarf galaxy, it has neither the spiral arms typical of galaxies like the Milky Way nor the dense nucleus of an elliptical galaxy. This makes Holmberg II, gravitationally speaking, a gentle haven where fragile structures such as these bubbles can hold their shape.
Full Story: http://www.spacetelescope.org/news/heic1114/
NASA will host a two-day launch Tweetup for 150 of its Twitter followers on Nov. 23 and 25 at the agency’s Kennedy Space Center in Florida. The Tweetup is expected to culminate in the launch of the Mars Science Laboratory Curiosity rover aboard a United Launch Alliance Atlas V 541 from Cape Canaveral Air Force Station. The launch window open is scheduled to open at 10:21 a.m. EDT on Nov. 25.
The Tweetup will provide NASA’s social media followers with the opportunity to tour Kennedy Space Center; speak with scientists and engineers; and, if all goes as scheduled, view the spacecraft launch. The event also will provide participants the opportunity to meet fellow tweeps and members of NASA’s social media team.
An international team led by Leen Decin, a K.U.Leuven astronomer, has discovered a series of dust shells in the vicinity of CW Leonis, a dying giant star. The star expelled the shells in the course of its long life: the most distant shell was expelled 16,000 years ago and, in that time, has drifted more than 7,000 billion kilometres from the star.
CW Leonis is an evolved star in the Leo constellation, 500 light-years from Earth. The dying star has become a carbon-rich red giant star: “Until recently, it was thought that giant star’s surroundings were homogenous: evenly distributed matter without any exceptionally large clumps, but there are more and more indicators suggesting that this is not a reliable picture,” says Leen Decin. “New images from the Herschel satellite confirm this in a spectacular way: We discovered more than a dozen shells expelled throughout the star’s life as a giant. The weakest shell we found is 7,000 billion kilometres from the star.”
Full Story: http://www.astronews.us/2011-09-28-0230.html