The observed cloud-level atmospheric circulation on the outer planets of the Solar System is dominated by strong east–west jet streams. The depth of these winds is a crucial unknown in constraining their overall dynamics, energetics and internal structures. There are two approaches to explaining the existence of these strong winds. The first suggests that the jets are driven by shallow atmospheric processes near the surface, whereas the second suggests that the atmospheric dynamics extend deeply into the planetary interiors. Here we report that on Uranus and Neptune the depth of the atmospheric dynamics can be revealed by the planets’ respective gravity fields. We show that the measured fourth-order gravity harmonic, J4, constrains the dynamics to the outermost 0.15 per cent of the total mass of Uranus and the outermost 0.2 per cent of the total mass of Neptune. This provides a stronger limit to the depth of the dynamical atmosphere than previously suggested, and shows that the dynamics are confined to a thin weather layer no more than about 1,000 kilometres deep on both planets.
Read more at: http://phys.org/news/2013-05-uranus-neptune-confined-thin-atmosphere.html#jCp
A corona mass ejection (CME), associated with a solar flare, blew out from just around the edge of the Sun today in a glorious roiling wave (May 1, 2013).
The video, taken in extreme ultraviolet light by NASA’s Solar Dynamics Observatory spacecraft, covers about 2.5 hours. SOHO’s C2 and C3 coronagraphs shows a large, bright, circular cloud of particles heading out into space.
STEREO spacecraft, from their different perspectives in space, observed the flare. CME’s carry over a billion tons of particles at over a million miles per hour.
One of our Sun’s unusual features is its orbit around the center of the galaxy, which is significantly less elliptical (“eccentric”) than those of other stars similar in age (and therefore metallicity, or proportion of an object’s chemical composition other than hydrogen and helium) and type and is barely inclined relative to the Galactic plane. This circularity in the Sun’s orbit prevents it from plunging into the inner Galaxy where life-threatening supernovae are more common. Moreover, the small inclination to the galactic plane avoids abrupt crossings of the plane that would stir up the Sun’s Oort Cloud and bombard the Earth with life-threatening comets.
In fact, the Sun is orbiting very close to the “co-rotation radius” of the galaxy, where the angular speed of the galaxy’s spiral arms matches that of the stars within. As a result, the Sun avoids crossing the spiral arms very often, which would expose Earth to supernovae that are more common there. These exceptional circumstances may have made it more likely for complex life and human intelligence to emerge on Earth. According to Guillermo Gonzalez (an astronomer at Iowa State University), fewer than five percent of all stars in the galaxy enjoy such a life-enhancing galactic orbit. Other astronomers point out, however, that many nearby stars move with the Sun in a similar galactic orbit.
The Sun resides in a pancake region of the Galaxy called the “disk” with a strong concentration of stars (and gas and dust) within 3,000 light-years (ly) of the galactic plane, which includes the so-called “thin disk” that has more relatively younger stars within 1,500 ly of the plane (more on stellar population groups in our Milky Way Galaxy). This region contains relatively young to intermediate-aged stars that within around five billion years old with relatively higher average metallicity than other galactic regions located outside of the galactic core, in a circular band that broadens with time. Generated by the deaths of older stars, the greater availability of elements higher than hydrogen and helium in this galactic region favor the formation of rocky inner planets as large as Earth, or bigger (Gonzalez et al, 2001). Moreover, the galactic orbits of stars in this region tend to be relatively circular — with low to moderate eccentricity. According to one recent definition of the galactic habitable zone, as much as 10 percent of all stars in the Milky Way may have experienced chemical and environmental conditions suitable for the development of complex Earth-type life over the past eight to four billion years for evolutionary development (press release; and Lineweaver et al, 2004, in pdf). (Further discussion of the different galactic regions and their distinctive stellar populations is available from ChView’s “The Stars of the Milky Way.”)
In recent millenia, the Sun has been passing through a Local Interstellar Cloud (LIC) that is flowing away from the Scorpius-Centaurus Association of young stars dominated by extremely hot and bright O and B spectral types, many of which will end their brief lives violently as supernovae. The LIC is itself surrounded by a larger, lower density cavity in the interstellar medium (ISM) called the Local Bubble, that was probably formed by one or more relatively recent supernova explosions. As shown in a 2002 Astronomy Picture of the Day, located just outside the Local Bubble are: high-density molecular clouds such as the Aquila Rift which surrounds some star forming regions; the Gum Nebula, a region of hot ionized hydrogen gas which includes the Vela Supernova Remnant, which is expanding to create fragmented shells of material like the LIC; and the Orion Shell and Orion Association, which includes the Great Orion Nebula, the Trapezium of hot B- and O-type stars, the three belt stars of Orion, and local blue supergiant star Rigel.
The Hubble Space Telescope was launched on April 24, 1990. Since then, it has provided us with some amazing images of stars, nebulae, galaxies and other objects. It is expected to function until 2014, when it will be replaced by the James Webb Telescope.
To celebrate the launch date of the HST, here are some Hubble facts, via space.com:
The Hubble Space Telescope is a joint project between NASA and the European Space Agency. Here are some basic facts about the telescope and the mission, courtesy the Space Telescope Science Institute (STScI), which operates Hubble for NASA:
- Length: 43.5 ft (13.2 m)
- Weight: 24,500 lb (11,110 kg)
- Maximum Diameter: 14 ft (4.2 m)
- Launch: April 24, 1990 from space shuttle Discovery (STS-31)
- Deployment: April 25, 1990
- Servicing Mission 1: December 1993
- Servicing Mission 2: February 1997
- Servicing Mission 3A: December 1999
- Servicing Mission 3B: February 2002
- Servicing Mission 4: May 2009
- Orbit: Average altitude of 307 nautical miles (569 km, or 353 miles), inclined 28.5 degrees to the equator.
- Time to Complete one orbit: 97 minutes
- Speed: 17,500 mph (28,000 kph)
Hubble transmits about 120 gigabytes of science data every week. That would be roughly 3,600 feet (1,097 meters) of books on a shelf. The collection of pictures and data is stored on magneto-optical disks.
- Energy Source: The Sun
- Mechanism: Two 25-foot solar panels
- Power usage: 2,800 watts
- Batteries: 6 nickel-hydrogen (NiH), with a storage capacity equal to 20 car batteries
- Primary Mirror Diameter: 94.5 in (2.4 m)
- Primary Mirror Weight: 1,825 lb (828 kg)
- Secondary Mirror Diameter: 12 in (0.3 m)
- Secondary Mirror Weight: 27.4 lb (12.3 kg)
NASA’s Hubble Space Telescope has snapped a spectacular new image of an iconic nebula to celebrate its 23 years of peering deep into the heavens.
Image: This new Hubble image, captured and released to celebrate the telescope’s 23rd year in orbit, shows part of the sky in the constellation of Orion (The Hunter). Rising like a giant seahorse from turbulent waves of dust and gas is the Horsehead Nebula, otherwise known as Barnard 33. Image released April 19, 2013. Credit: NASA, ESA, and the Hubble Heritage Team (AURA/STScI)
The Hubble observatory, which launched on April 24, 1990, captured the Horsehead Nebula in infrared light, peering through obscuring veils of dust to reveal the object’s hidden features.
“The result is a rather ethereal and fragile-looking structure, made of delicate folds of gas — very different to the nebula’s appearance in visible light,” mission officials wrote in an image description today (April 19). The new observations allowed astronomers to create a dazzling video of the Horsehead Nebula based on Hubble’s photos.
There are two elements in our universe which are both overwhelmingly abundant, and can be used to make an awful lot of different things: carbon and oxygen. Earth and the rest of the solar system happened to form from an oxygen-rich part of space. Earth’s crust contains a huge amount of oxygen, in rock. All Earth rocks are made of silicate, a chemical compound of silicon and oxygen. So are there any planets which are rich in carbon instead of oxygen? Actually, yes there are, and we’ve already found two! One is PSR J1719-1438, a planet orbiting a neutron star, bathed in x ray sunlight. The other is 55 Cancri e, a super-Earth orbiting a Sun-like star. Carbon planets are likely to be chemically very different from Earth. Their cores would be made from naturally alloyed steel, and they would likely have entire mountain ranges made of diamond.
Eagle Nebula by Piotr Wachowicz
This image of reflection nebula vdB 141 was obtained with the wide-field view of the Kitt Peak National Observatory’s Mosaic Camera on the 4-meter Mayall telescope. Located in the constellation Cepheus, the nebula is sometimes referred to as the “ghost nebula.” Its awkward name derives from Sidney van den Bergh’s catalog numbers of reflection nebulae, published in 1966.
Image credit: T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF
The Horsehead and the Flame Nebulas in the constellation Orion
It is a large group of old stars that are closely packed in a symmetrical, somewhat spherical form. Globular clusters, so called because of their roughly spherical appearance, are the largest and most massive star clusters.
The globular clusters in the Milky Way are all estimated to be at least 10 billion years old and therefore contain some of the oldest stars in the galaxy.
Nuclei accretion disk visible with galaxy brightness stripped away. — Steven Marx
[The graphic shows habitable zone distances around various types of stars. Some of the known extrasolar planets that are considered to be in the habitable zone of their stars are also shown. On this scale, Earth-Sun distance is one astronomical unit, which is roughly 150 million kilometers. Click on the image for a higher resolution version. Credit: Chester Herman]
“Researchers searching the galaxy for planets that could pass the litmus test of sustaining water-based life must find whether those planets fall in a habitable zone, where they could be capable of having liquid water and sustaining life. New work, led by a team of Penn State researchers, will help scientists in that search.
Using the latest data, the Penn State Department of Geosciences team has developed an updated model for determining whether discovered planets fall within a habitable zone. The work builds on a prior model by James Kasting, Evan Pugh Professor of Geosciences at Penn State, to offer a more precise calculation of where habitable zones around a star can be found.
Comparing the new estimates with the previous model, the team found that habitable zones are actually farther away from the stars than previously thought.
“This has implications for finding other planets with life on them,” said post-doctoral researcher Ravi kumar Kopparapu, a lead investigator on the study, which will be published described in Astrophysical Journal.
For the paper, Kopparapu and graduate student Ramses Ramirez used updated absorption databases of greenhouse gases (HITRAN and HITEMP). The databases have more accurate information on water and carbon dioxide than previously was available and allowed the research team to build new estimates from the groundbreaking model Kasting created 20 years ago for other stars.”
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