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In the news this month... And Finally, NASA's SDO returns spectacular images
Soon after the instruments opened their doors, the Sun began performing for SDO with this beautiful prominence eruption. This AIA data is from March 30, 2010, showing a wavelength band that is centered around 304 Å. This extreme ultraviolet emission line is from singly ionized Helium, or He II, and corresponds to a temperature of approx. 50,000 degrees Celsius.
CREDIT: NASA SDO
NASA's
Solar Dynamics Observatory made its first light observations during April. Launched aboard an Atlas V rocket on February 11th, the spacecraft is on a five year mission to observe our nearest star in detail. The observations will help solar physicists understand solar activity and how it impacts us here on the Earth. The first light observations were released on April 21st and show a turbulent and dynamic surface. As well as taking images at a variety of wavelengths in order to probe different levels of the solar atmosphere, the instruments on board SDO can pick out features as small as 350 km across and take images every few seconds so events can be studied in detail. One of the main goals of SDO is to try and understand how the Sun's magnetic field is generated and how the energy stored in the magnetic field is released into the heliosphere. Data from SDO's instruments should help predict solar variations that affect life here on Earth. Images and movies from the first light observations are available on the
SDO website.
Posted by Megan on Monday 31st May 2010 (
14:24 UTC) |
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In the news this month... volcanoes on Venus
Pancake domes - volcanic features on the surface of Venus
CREDIT: NASA
Closer to home,
the planet Venus shows large amounts of evidence of
volcanic activity. Despite being shrouded under a thick layer of cloud, spacecraft have been able to map the surface of our nearest neighbour using radar, leading to the realisation that much of the planet's surface is comparatively young, suggesting that at some point in the recent past the planet underwent a complete resurfacing. However the question remains whether Venus is currently a geologically active planet.
Most of the planet's surface is known to be covered by features caused by volcanic activity:
shield volcanoes,
coronae,
pancake domes and other features caused by lava flows or crustal uplifts. The relative lack of craters, compared to known ancient surfaces like the Lunar and Martian highlands, implies that the surface is comparatively young. While the thick atmosphere of Venus prevents observers from seeing directly signs of current volcanic activity, a team using data from the Visible and Infrared Thermal Imaging Spectrometer on board the
European Space Agency's Venus Express orbiter have
discovered evidence of recent resurfacing.
The team used data from the VIRTIS instrument to examine closely several known hot spots on Venus. These hot spots are analogous to their terrestrial counterparts such as the Hawaiian chain of islands in that they have distinctive rises compared to the surrounding terrain, major volcanic centres and gravitational anomalies, suggestive of active plumes of material flowing up through the planet's mantle.
By studying the thermal emissivity of these regions, the researchers have identified compositional differences in lava flows at these hot spots compared to the surrounding surfaces, which they interpret as being due to a lack of surface weathering. Since weathering is a gradual process which occurs over long time scales, this all implies that the features are younger than 2.5 million years, and possibly much younger, showing that Venus has been actively resurfacing, at least partially, in the recent past. The results were published in Science Express on April 8th.
This blog post is a news story from the
Jodcast, aired in the
May 2010 edition.
Smrekar, S., Stofan, E., Mueller, N., Treiman, A., Elkins-Tanton, L., Helbert, J., Piccioni, G., & Drossart, P. (2010). Recent Hotspot Volcanism on Venus from VIRTIS Emissivity Data Science, 328 (5978), 605-608 DOI: 10.1126/science.1186785 Posted by Megan on Monday 31st May 2010 (
14:09 UTC) |
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In the news this month... the strange atmosphere of GJ 436b
Light from the distant planet, GJ 436b, and its star, as measured at infrared wavelengths
CREDIT: NASA/JPL-Caltech/UCF
Most known extrasolar planets are massive gas giants orbiting close to their parent stars. If one of these planets happens to pass directly between us and its parent star during its orbit, then sensitive spectroscopy can be used to determine the chemical make-up of its atmosphere. Models of such atmospheres predict which gases should be present and in what relative abundances, based on physical conditions such as the temperature. Recent infra red observations carried out with the
Spitzer Space Telescope have provided the first details of the atmospheric composition of a so-called hot Neptune.
The planet, known as
GJ 436b, orbits an M-type dwarf star in the constellation of Leo. It is similar to Neptune in size, but orbits its parent star in just 2.6 days. Previous observations of the planet showed that its surface temperature was estimated to be 712 K, higher than predicted due to stellar heating alone, and the new observations (
reported in the April 22nd issue of Nature) suggest that its atmosphere may not be in equilibrium. The team, led by Kevin Stevenson at the University of Central Florida, observed the planet's day side as it passed around the far side of the star and examined the infra red spectrum for various chemical signatures. What they found was a high abundance of carbon monoxide and a deficiency of methane compared to predictions from atmospheric models at this temperature for an atmosphere thought to be dominated by hydrogen. In an atmosphere such as this, methane (one carbon atom and four hydrogen atoms) should be the main carbon-bearing molecule, but the observations show the actual abundance is less than that predicted by a factor of seven thousand. The large amount of absorption due to carbon monoxide is also unexpected, the results suggesting that the atmosphere may not be in thermochemical equilibrium.
One alternative explanation considered by the authors is that the atmosphere may not be dominated by hydrogen, but this is unlikely given the dominance of hydrogen in planet forming disks. Another possibility is that vertical mixing within the atmosphere may dredge up carbon monoxide from lower, hotter parts of the atmosphere, although the authors point out that, in order to explain the observed abundances, the amount of mixing would have to be large. These new data will provide useful information for future atmospheric modeling.
This blog post is a news story from the
Jodcast, aired in the
May 2010 edition.
Stevenson, K., Harrington, J., Nymeyer, S., Madhusudhan, N., Seager, S., Bowman, W., Hardy, R., Deming, D., Rauscher, E., & Lust, N. (2010). Possible thermochemical disequilibrium in the atmosphere of the exoplanet GJ 436b Nature, 464 (7292), 1161-1164 DOI: 10.1038/nature09013 Posted by Megan on Monday 31st May 2010 (
13:49 UTC) |
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In the news this month... the nature of the eclipsing binary system epsilon Aurigae
The eclipsing binary epsilon Aurigae
CREDIT: NASA/JPL-Caltech/R. Hurt (SSC/Caltech)
Many stars vary in brightness, sometimes due to changes within the star itself such as novae or Cepheid variables, others because of external factors. One
well-known variable star is
epsilon Aurigae, an F-type supergiant in the constellation of Auriga, located at an estimated distance of 625 parsecs (2,100 light years). Since its variable nature was discovered in the 1820s, the star has been seen to fade in brightness every 27.1 years. During these eighteen-month-long eclipses, the brightness of the star fades to around 50 per cent of its normal magnitude. While the variability of the system has been well-studied, the exact physical nature of the eclipsing companion is less certain as it has remained undetected, and many models have been put forward to explain the unusual nature of the system. Observations of epsion Aurigae show that the star and its darker companion have a similar mass which, until recently, was thought to be around 15 times the mass of the Sun.
More recent observations have shown that the supergiant star has a much lower mass of between two and three solar masses, and that the companion may be a single B5V-type star embedded within a disk of opaque material.
Now, using the CHARA interferometer, an array of infrared telescopes located on Mount Wilson in California, a team led by Brian Kloppenborg from the University of Denver have
for the first time imaged the eclipsing object as it transits the disk of the star. This is the first time a spatially resolved observation of an eclipsing binary has been made. Their observations show that the eclipsing object is an opaque disk of dust, tilted to our line of sight by an estimated 84 degrees. From the motion of the disk between two observations carried out in November and December 2009, the team infer that the companion object is more massive than the visible F-type supergiant. Assuming the B-type star within the disk has a typical mass of 5.9 solar masses, the researchers calculate a mass of 3.6 solar masses for the F-type supergiant. They also calculate that if the disk is composed entirely of dust, then its mass is less than 10 per cent of the Earth's.
While the nature of the disk is now clearer, there are still several unanswered questions which remain. The model that best fits the data is of a geometrically thin disk tilted to our line of sight, rather than a thick disk seen edge on. However, the fact that it is opaque suggests that its nature is more like a debris disk than a dusty accretion disk around a young stellar object. The tilted disk model also predicts a central hole which should cause a mid-eclipse brightening of the F-type star. Observers the world-over will continue to monitor the system during the eclipse, and the data should help build up a profile of the disk and constrain the evolutionary history of the system.
This blog post is a news story from the
Jodcast, aired in the
May 2010 edition.
Kloppenborg, B., Stencel, R., Monnier, J., Schaefer, G., Zhao, M., Baron, F., McAlister, H., ten Brummelaar, T., Che, X., Farrington, C., Pedretti, E., Sallave-Goldfinger, P., Sturmann, J., Sturmann, L., Thureau, N., Turner, N., & Carroll, S. (2010). Infrared images of the transiting disk in the ε Aurigae system Nature, 464 (7290), 870-872 DOI: 10.1038/nature08968 Posted by Megan on Monday 31st May 2010 (
12:19 UTC) |
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Seeing things
The other day I was browsing through the pictures on APOD (Astronomy Picture of the Day) and I came across one in particular that caught my eye. It's a stunning photograph of the Milky Way spanning the sky over a 7000-year old piece of rock art in a canyon in Utah. Rock art is found all over the place and there's a lot of it here in Australia. It is often thought to depict animals or people and sometimes astronomical patterns or events, but often it 's meaning is unclear. This particular one reminded me of a certain blue box....
Posted by Megan on Saturday 22nd May 2010 (
07:22 UTC) |
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