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In the news this month... And Finally
IYA Galilean Nights and Moonwatch CREDIT:
IYA / Newbury AS / Megan
October was another busy month of International Year of Astronomy events. On the 22nd to the 24th of October, the IYA Cornerstone Project, Galilean Nights
, saw astronomers and enthusiasts taking to the streets all around the globe, pointing their telescopes at the same objects that Italian astronomer Galileo observed 400 years ago. Spread over three nights, the project saw hundreds of registered events take place with many people getting their first look through a telescope at Jupiter and the Moon.
Following on from Galilean Nights came the second MoonWatch
event of the year. This UK-based event ran from October 24th to November 1st, encouraging people to go out and observe the Moon. As part of the event, Moonwatch was also held on Twitter
on October 26th and 27th, turning it into a global event (see the trailer
). Unfortunately, many observers saw nothing but clouds on both nights, but this didn't stop many twitter users joining in, tweeting and re-tweeting images, information and live video from across the world. Astronomy FM
hosted a special Moonwatch show that went on for several hours including on the hour updates from Adrian West of Newbury Astronomical Society in the UK, and Elias Jordan
, Tavi Greiner
and Dr Ian O'Neill
in the US. Despite the clouds, this second Moonwatch event was again an astounding success with twitter users from around the world joining in with a virtual star party of epic proportions. The team behind Twitter Moonwatch are already planning their next event, a Meteorwatch
which will be held to coincide with the Geminid Meteor shower in December.
Posted by Megan on Saturday 31st Oct 2009 (10:38 UTC
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In the news this month... another impressive exoplanet haul from HARPS
Artists impression of the Earth-like planet Gliese 667 C discovered by HARPS CREDIT:
2009 has been a good year for exoplanets, and one team of astronomers have discovered most of them. Since the first planet was found orbiting a star other than the Sun, many more have been discovered using increasingly sensitive instruments and sophisticated techniques. Because they are so faint compared to their parent stars, most planets are discovered through indirect methods. One of the most successful has been the radial velocity method
which uses the principle of the Doppler effect to detect the tiny changes in velocity of a star caused by an orbiting planet.
This is the technique used by the High Accuracy Radial Velocity Planet Searcher, or HARPS
, instrument, mounted on the European Southern Observatory's 3.6-m telescope at La Silla in Chile which repeatedly measures the radial velocities of stars that might host planetary systems. On the 19th of October, members of the HARPS team presented their latest results: the discovery of another 32 new planets
, bringing the total number of known exoplanets to more than 400. The radial velocity technique is most sensitive to large planets orbiting close to their parent star, but due to its high precision HARPS is capable of detecting smaller planets known as super-Earths. The new batch of exoplanets range in size from just five times the mass of the Earth to up to 10 times the mass of Jupiter.
HARPS has been largely responsible for the detection of 24 of the 28 known planets with masses below 20 times that of Earth and has now discovered more than 75 of the 400 known exoplanets
, making it the most productive current planet finder. However, HARPS will soon have competition in the form of Kepler
, a NASA satellite launched in March with the aim of detecting Earth-sized planets in the habitable zone, the region around a star where water can exist as a liquid. Rather than measuring the wobble of stars, Kepler will monitor their brightness looking for the tiny dips in intensity caused by planetary transits.
Mayor, M.; Pepe, F.; Queloz, D.; Bouchy, F.; Rupprecht, G.; Lo Curto, G.; Avila, G.; Benz, W.; Bertaux, J.-L.; Bonfils, X.; dall, Th.; Dekker, H.; Delabre, B.; Eckert, W.; Fleury, M.; Gilliotte, A.; Gojak, D.; Guzman, J. C.; Kohler, D.; Lizon, J.-L.; Long (2003). Setting New Standards with HARPS Messenger (114), 20-24 Other: 2003Msngr.114...20M
Posted by Megan on Saturday 31st Oct 2009 (10:13 UTC
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In the news this month... a record-breaking distant cluster
X-ray and optical composite of JKCS041 CREDIT:
X-ray: NASA/CXC/INAF/S.Andreon et al Optical: DSS; ESO/VLT
Look deep enough with a sensitive telescope and a seemingly empty patch of sky is full of galaxies. Look closely and you'll see that they are often gathered together in clusters. These massive collections of galaxies are the largest gravitationally bound objects in the universe, but it is uncertain how long ago these clusters formed. Now, using a variety of instruments, a team led by Stefano Andreon of the National Institute for Astrophysics
in Milan, Italy, has discovered
the most distant galaxy cluster ever found.
The cluster, known as JKCS041, is located in the constellation of Cetus and lies about 10.2 billion light years away, beating the previous record holder by almost one billion light years. It is so far away that the light now arriving at Earth was produced by the cluster when the universe was only about a quarter of its current age.
The astronomers first discovered the galaxy in infra-red observations made with the UK Infra Red Telescope, UKIRT
, in 2006. The optical light from galaxies this far away is shifted into the infra-red part of the spectrum due to the expansion of the universe, so old galaxies like these are often detected by infra-red telescopes. Further observations with both optical and infra-red telescopes confirmed the distance to the object, but could not rule out the possibility that, rather than being a genuine gravitationally bound cluster, the object could just be a chance alignment of galaxies along our line of sight. To test this, the team examined X-ray observations from the Chandra
Nearby galaxy clusters have extended X-ray emission, caused by hot gas in the space between the galaxies. This gas, known as the hot intra-cluster medium
, is only observed in genuine gravitationally bound clusters of galaxies and so is a good test of whether a group of galaxies just lie along the same line of sight by chance, or are physically associated. When the astronomers examined the Chandra observations of JKCS041, they found a significant amount of extended X-ray emission within the cluster coming from hot gas of the intra-cluster medium, showing that it is a physically connected group of galaxies.
This is an important discovery because this is close to the distance limit expected for a galaxy cluster based on how long it should take for them to assemble following the big bang, and studying its characteristics can reveal more about how the universe evolved.
Andreon, S., Maughan, B., Trinchieri, G., & Kurk, J. (2009). JKCS041: a colour-detected galaxy cluster at zphot~1.9 with deep potential well as confirmed by X-ray data Astronomy and Astrophysics DOI: 10.1051/0004-6361/200912299
Posted by Megan on Saturday 31st Oct 2009 (09:31 UTC
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In the news this month... shaping the heliosphere
IBEXs view of the heliosphere CREDIT:
Adler Planetarium/Southwest Research Institute
Solar physicists thought they knew the shape of the Sun's heliosphere, but new results from the Interstellar Boundary Explorer
have revealed a huge ribbon of intense emission that was completely unexpected. The space between stars is not empty, but filled with a very tenuous gas known as the interstellar medium. As the Sun moves through this gas it emits a fast moving plasma know as the solar wind. These charged particles spread out spherically creating the heliosphere
, a cavity in the interstellar medium swept out by the solar wind.
Launched in October 2008, the Interstellar Boundary Explorer, IBEX, was designed to investigate the nature of the interactions between this solar wind and the interstellar medium at the edge of the solar system where the wind hits the ISM and slows down in a termination shock
at what is known as the interstellar boundary. This boundary region emits no light so it cannot be detected by conventional telescopes. Models predicted that the shape of the heliosphere resembled a comet, a sphere that was swept back by the Sun's movement through the ISM, but what IBEX found was something different.
IBEX was designed to detect particles known as energetic neutral atoms
. These start off as ionised atoms in the boundary region where they can pick up electrons and become neutral. Ionsed atoms have electrical charge and are affected by the charged plasma of the solar wind and the magnetic fields that are carried with it. Once they become neutral they are no longer affected by these magnetic fields and travel along straight trajectories. The detectors on IBEX were designed to pick up these energetic neutral atoms coming from the boundary region and over six months of observations, they mapped the whole sky.
What the results show is an unexpectedly bright ribbon of emission running almost 360 degrees around the sky, a feature that was not predicted by models of the heliosphere. This ribbon is thought to be where charged particles are becoming bunched at the boundary. The reason for this is not certain, although David McComas, IBEX's principle investigator, suggests that it could be caused by the magnetic fields of the Milky Way's own galactic wind interacting with the heliosphere.
, published in the journal Science during October, put the observations of the Voyager spacecraft in context. The two Voyager probes were launched in 1977 and are currently traveling through the interstellar boundary region where the energetic neutral atoms originate. While the results from IBEX match what the Voyager probes are encountering, the bright strip discovered by IBEX runs right between the positions of the two spacecraft. Eric Christian, IBEX deputy mission scientist at NASA's Goddard Spaceflight Centre likens this effect to having two weather stations which miss a big storm passing directly between them. The ribbon has also been detected in data from the Cassini spacecraft, although at different energies to the particles detected by IBEX. While it seems clear that the true shape of the heliosphere is somewhere between a comet and a perfect sphere, much more modeling is needed.
McComas, D., Allegrini, F., Bochsler, P., Bzowski, M., Christian, E., Crew, G., DeMajistre, R., Fahr, H., Fichtner, H., Frisch, P., Funsten, H., Fuselier, S., Gloeckler, G., Gruntman, M., Heerikhuisen, J., Izmodenov, V., Janzen, P., Knappenberger, P., Krimigis, S., Kucharek, H., Lee, M., Livadiotis, G., Livi, S., MacDowall, R., Mitchell, D., Mobius, E., Moore, T., Pogorelov, N., Reisenfeld, D., Roelof, E., Saul, L., Schwadron, N., Valek, P., Vanderspek, R., Wurz, P., & Zank, G. (2009). Global Observations of the Interstellar Interaction from the Interstellar Boundary Explorer (IBEX) Science DOI: 10.1126/science.1180906Funsten, H., Allegrini, F., Crew, G., DeMajistre, R., Frisch, P., Fuselier, S., Gruntman, M., Janzen, P., McComas, D., Mobius, E., Randol, B., Reisenfeld, D., Roelof, E., & Schwadron, N. (2009). Structures and Spectral Variations of the Outer Heliosphere in IBEX Energetic Neutral Atom Maps Science DOI: 10.1126/science.1180927Mobius, E., Bochsler, P., Bzowski, M., Crew, G., Funsten, H., Fuselier, S., Ghielmetti, A., Heirtzler, D., Izmodenov, V., Kubiak, M., Kucharek, H., Lee, M., Leonard, T., McComas, D., Petersen, L., Saul, L., Scheer, J., Schwadron, N., Witte, M., & Wurz, P. (2009). Direct Observations of Interstellar H, He, and O by the Interstellar Boundary Explorer Science DOI: 10.1126/science.1180971Fuselier, S., Allegrini, F., Funsten, H., Ghielmetti, A., Heirtzler, D., Kucharek, H., Lennartsson, O., McComas, D., Mobius, E., Moore, T., Petrinec, S., Saul, L., Scheer, J., Schwadron, N., & Wurz, P. (2009). Width and Variation of the ENA Flux Ribbon Observed by the Interstellar Boundary Explorer Science DOI: 10.1126/science.1180981Schwadron, N., Bzowski, M., Crew, G., Gruntman, M., Fahr, H., Fichtner, H., Frisch, P., Funsten, H., Fuselier, S., Heerikhuisen, J., Izmodenov, V., Kucharek, H., Lee, M., Livadiotis, G., McComas, D., Moebius, E., Moore, T., Mukherjee, J., Pogorelov, N., Prested, C., Reisenfeld, D., Roelof, E., & Zank, G. (2009). Comparison of Interstellar Boundary Explorer Observations with 3-D Global Heliospheric Models Science DOI: 10.1126/science.1180986Krimigis, S., Mitchell, D., Roelof, E., Hsieh, K., & McComas, D. (2009). Imaging the Interaction of the Heliosphere with the Interstellar Medium from Saturn with Cassini Science DOI: 10.1126/science.1181079
Posted by Megan on Saturday 31st Oct 2009 (08:51 UTC
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Ethics of Big Science
The stereotypical view of the research scientist is often a solitary figure in a lab coat and glasses, pouring over a bench experiment in a cluttered lab (smoking test tubes optional). In this picture, the experimentalist is a solitary creature who devotes their life to studying some esoteric piece of knowledge that has no bearing whatsoever on the "real world" around them. This does happen, of course, but these days it is rarely the case. As we try to probe smaller, further, deeper in search of an understanding of the universe around us, we need bigger, sharper, more powerful instruments to make progress, and this requires cooperation. All you have to do is take a look at the new papers on the astro-ph preprints server to see how many results are actually the result of collaborations, some of them very large. There was one paper recently that had more than 200 co-authors. This is common in particle physics, less so in astronomy.
This is Big Science: experiments that require so much equipment, funding and manpower that no one country, let alone a single research group at one university, can afford it on their own. The Large Hadron Collider at CERN is one current well-known Big Science project, ESO and ESA are organisations set up to enable Big Science projects within Europe, and the Square Kilometre Array is a global example, a project to build a radio interferometer on such a large scale that not one but nineteen countries are currently involved.
The ATLAS experiment at CERN, an example of Big Science CREDIT: Frank Hommes
Science is often about challenges, usually intellectual, sometimes personal, but all too often financial and political, especially where Big Science is concerned. The current financial situation of the STFC
is rather worrying for the whole community (there's a discussion about this by some well-known figures in the astronomy community going on in the comments over on Andy Lawrence's blog
), not just Big Science, and the British government's apparent push
for research that will provide short-term economic return for the country is seen by many as short-sighted. The problem has been around for a while of course, but the recent wider global problems have just made an already bad situation worse.
Big Science is a topic that comes up regularly when talking to the public, especially somewhere like Western Australia where most of the population have heard of the SKA and are aware that it is a big project, even if they are fuzzy on the details. Live "Ask an Astronomer" sessions are a lot of fun; the challenge of having to quickly think on your feet really gets the adrenalin going, but sometimes you do get a tough audience. One recent group I had were particularly vocal on the ethics of Big Science projects.
Astronomy is not usually thought of as a science that involves ethics: unlike biotech, genetics, drug testing, etc. we don't have to run our plans for experiments past ethics committees. But that's not to say that we can live in our own little world, away from the problems around us. A recent school group I talked to asked a lot of questions about how we can justify spending ∀3b on a telescope when there are people starving in the world. Getting one question on the point or usefulness of astronomy in a talk is fairly common, but it was obviously something this group felt very strongly about. I really felt like I was defending astronomy, and science in general, trying to justify why we carry out pure research to a room full of students who might never have had the chance to carry out an experiment where they didn't already know the answer before they started.
I tried in several ways to convince them that there are benefits to these projects, beyond just keeping a few astronomers off the streets. Things that are being discovered or investigated for the first time now in pure science experiments may develop into highly useful technological applications in the future, for example some image processing techniques developed by astronomers have led to important improvements in medical imaging, helping to spot the early signs of cancer. The discussion also ranged over engineering spin offs, development (and installation in remote communities) of high-speed networks, computing, the training of future scientists and engineers, jobs (it's going to take a lot of people to build the SKA!), as well as less tangible reasons for doing it like satisfying our curiosity and the sheer excitement of science (I think one of my comments was along the lines of "being a scientist is like being a kid forever, it's great!"). Another very cynical defense would be that even if you said "OK, we wont build the SKA, we'll give the money back to governments so they can build shelters for the homeless", would those governments actually use the money to help them, or would they just build another aircraft carrier? I don't know.
The fact that we get these questions from the public is not really that surprising, they are paying our wages after all. We have to justify ourselves to the funding agencies and the government anyway, why shouldn't the tax payer ask us to justify ourselves? That young people are asking these questions gives me some hope for the future. I hope that they grow up questioning things around them, not just accepting everything because it's always been that way. Curiosity drives science, and we're going to need plenty of good scientists and engineers to solve the practical problems that lie in our future.
Posted by Megan on Monday 05th Oct 2009 (14:58 UTC
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And finally: Planck's first light survey
A map of the sky at optical wavelengths shows a prominent horizontal band which is the light shining from our own Milky Way. The superimposed strip shows the area of the sky mapped by Planck during the First Light Survey CREDIT:
ESA, LFI & HFI Consortia. Background optical image: Axel Mellinger
Launched on the 14th of May this year, the Planck spacecraft released the results of it's "first light" survey during September. Since its launch along with the Herschel telescope, Planck has been undergoing testing, commissioning and calibration of its instruments, making its first observations on the 13th of August. Designed to detect the cosmic microwave background, the relic radiation left over from the Big Bang, Planck has several survey instruments on board. In order to maximise their chances of detecting the tiny fluctuations in the temperature of the CMB, the sensitive detectors must be cooled down almost to absolute zero, a temperature of minus 273
Celcius. Starting on August 13th, the satellite began a first light survey to verify the stability and calibration of the instruments. The survey lasted two weeks during which Planck continuously surveyed the sky, scanning a strip 15 degrees wide. Following the completion of this test observation, routine operations began on August the 27th. Full-time operations will continue for the next 15 months, with the first all-sky map expected to be assembled after approximately six months.
Planck first light yields promising results
, ESA press release, 17th September 2009
Posted by Megan on Monday 05th Oct 2009 (11:19 UTC
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In the News this month: first results from a panoramic survey of the Andromeda galaxy
The Andromeda galaxy, M31 CREDIT:
Edwin Hubble's original classification of galaxies into various types based on their visible shapes and structures has been a feature of extra-galactic astronomy since the 1920s. The scheme, originally thought to depict an evolutionary sequence, has two major groups: spiral galaxies with a small central bulge, spiral arms and possibly a central bar, and elliptical galaxies that are more spherical in structure with no spiral arms or disk. There are however, many galaxies which do not fit into this scheme, being neither spherical or disk-like, and these are usually lumped together into a class called the irregulars. These disturbed galaxies are surprisingly common, and many are the result of collisions or close encounters between galaxies. Such interactions happened frequently throughout the history of the universe, but it is also going on right now in our own galactic neighbourhood.
The nearest major galaxy to our own is the Andromeda Galaxy, otherwise known as M31, slightly larger than the Milky Way and located 2.5 million light years away. It is heading towards the Milky Way at some 300 km/s and, in a few billion years, the two galaxies will eventually collide. In some cosmological models, galaxies grow over time by disrupting and absorbing smaller galaxies in such collisions. In such violent processes, a significant number of stars should be tossed out of the galaxies involved, forming a diffuse halo which can provide clues to the merger history of a galaxy, if they are bright enough to be detected. In research reported in the journal Nature on the 3rd of September, a team of astronomers led by Alan McConnachie at the Herzberg Institute of Astrophysics in Canada, report a panoramic survey of Andromeda and its nearby neighbour, the Triangulum galaxy, M33, which shows clear evidence of the remnants of galactic mergers.
Detecting this evidence is difficult as these stellar populations are extremely faint and distributed over a huge area, so the astronomers are using the MegaCam camera on the 3.6-metre Canada-France-Hawaii telescope to build up a sensitive wide-field survey of the Andromeda galaxy and it's companions. The so-called Pan-Andromeda Archaeological Survey will cover more than 300 square degrees when completed in 2011, but has already produced results showing the vast extent of M31's stellar halo, covering an area of nearly 100 times the classical optical disk of the galaxy.
These early results from the survey lend support to the idea that large galaxies build up through the accretion of smaller galaxies. The halo stars discovered away from the disk of M31 are unlikely to have been formed at their present positions because there is not enough gas there for star formation to occur. The most likely explanation is that they have been thrown out in a tidal interaction. Another piece of evidence that they are relics from previous galactic mergers is that the stars in this faint population are often located in huge arcs, loops and other diffuse structures which are characteristic of the gravitational disruption of dwarf galaxies undergoing a merger with a larger galaxy.
As well as lending support to the hierarchical model of galaxy formation, the team's results also show a new diffuse stellar structure around M33, M31's largest companion galaxy. This newly discovered feature matches up with a distortion in the disk of M33, as well as a mild warp seen in the outer disk of M31, adding to the evidence of a past tidal interaction between the two galaxies.
McConnachie, A., Irwin, M., Ibata, R., Dubinski, J., Widrow, L., Martin, N., Côté, P., Dotter, A., Navarro, J., Ferguson, A., Puzia, T., Lewis, G., Babul, A., Barmby, P., Bienaymé, O., Chapman, S., Cockcroft, R., Collins, M., Fardal, M., Harris, W., Huxor, A., Mackey, A., Peñarrubia, J., Rich, R., Richer, H., Siebert, A., Tanvir, N., Valls-Gabaud, D., & Venn, K. (2009). The remnants of galaxy formation from a panoramic survey of the region around M31 Nature, 461 (7260), 66-69 DOI: 10.1038/nature08327
Posted by Megan on Monday 05th Oct 2009 (11:06 UTC
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In the News this month: discovery of water on the Moon
A very young lunar crater on the side of the moon that faces away from Earth, as viewed by NASAs Moon Mineralogy Mapper on the Indian Space Research Organizations Chandrayaan-1 spacecraft CREDIT:
It is thought that the Moon was formed about four and a half billion years ago by the collision of a Mars-sized object with the Earth. The heat from the impact and subsequent accretion of material created a magma ocean which would have caused the loss of most of the volatile materials from the surface, so-called because they have low boiling points and evaporate easily. In a press conference at NASA on Thursday 24th September, results were announced from three separate spacecraft showing evidence of water on the lunar surface in far greater quantities than has previously been seen. Two of these spacecraft, Cassini and Deep Impact, observed the Moon as they passed by on their way to other parts of the solar system while the third, India Space Research Organisation's Chandrayaan-1, observed the lunar surface from orbit around the Moon.
What each of these probes detected was an absorption feature in the infra-red part of the spectrum at a wavelength of about 3 microns, a wavelength characteristic of absorption by hydroxyl - a hydrogen atom joined together with an oxygen atom. Add another hydrogen to hydroxyl and you produce H20, water, which also absorbs infra-red light near 3-microns. It has been known since the observations of the Lunar Prospector spacecraft in the late 1990s that there is an estimated 10 to 300 million metric tones of water ice buried in permanently shadowed craters at the lunar poles. These new results however, show that the hydroxyl and water signature is in fact present over large parts of the lunar surface, not just at the poles.
Launched on October 22nd 2008, India's Chandrayaan-1 carried several scientific instruments on board. One of these was the Moon Mineralogy Mapper, or M3, built by NASA, a spectrograph operating in the infra-red part of the spectrum. Although Chandrayaan-1 sadly ceased operations last month, it had already returned many months of usable data from the instruments on board. When the data from the M3 experiment was analysed, researchers found absorption features consistent with patterns expected for water and hydroxyl over most of the lunar surface. Although M3 only probed the top few millimetres of the lunar regolith, they found a strong hydroxyl signature across the surface, stronger towards the lunar poles at higher latitudes, and varying throughout the lunar cycle, suggesting that the Sun has some effect on the distribution.
According to the scientists, the most likely origin for this water is a reaction between protons in the solar wind and oxygen atoms already present in the lunar dirt. The M3 results were subsequently confirmed by observations by the Deep Impact spacecraft which also has instruments that observe in the infra-red and regularly uses observations of the Moon for calibration purposes, and also in old data from the Cassini spacecraft which observed the Moon during a flyby in 1999. The data show that there may be as much as 0.1 to 1 per cent water by weight in the regolith, in contrast to the rocks brought back by the Apollo missions which were incredibly dry. This is roughly equivalent to a litre of water per cubic metre of regolith but, since it is only present in the top few millimetres of soil, extracting usable amounts of water would require processing a very large surface area.
The results from the three spacecraft were announced together to coincide with the publication of three papers in the journal Science on September 24th, and come just two weeks before another spacecraft, NASA's LCROSS, the Lunar Crater Observation and Sensing Satellite, is due to crash into the Moon's surface near the south pole in an attempt to kick up water ice buried in the regolith in craters which rarely see sunlight.
Sunshine, J., Farnham, T., Feaga, L., Groussin, O., Merlin, F., Milliken, R., & A'Hearn, M. (2009). Temporal and Spatial Variability of Lunar Hydration as Observed by the Deep Impact Spacecraft Science DOI: 10.1126/science.1179788Pieters, C., Goswami, J., Clark, R., Annadurai, M., Boardman, J., Buratti, B., Combe, J., Dyar, M., Green, R., Head, J., Hibbitts, C., Hicks, M., Isaacson, P., Klima, R., Kramer, G., Kumar, S., Livo, E., Lundeen, S., Malaret, E., McCord, T., Mustard, J., Nettles, J., Petro, N., Runyon, C., Staid, M., Sunshine, J., Taylor, L., Tompkins, S., & Varanasi, P. (2009). Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M3 on Chandrayaan-1 Science DOI: 10.1126/science.1178658Clark, R. (2009). Detection of Adsorbed Water and Hydroxyl on the Moon Science DOI: 10.1126/science.1178105
Posted by Megan on Monday 05th Oct 2009 (10:50 UTC
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In the News this month: first evidence of a solid exoplanet
Artists impression of the exoplanet Corot-7b CREDIT:
Using various techniques, astronomers have, over the last decade, discovered many hundreds of planets outside our own solar system. Most of these techniques are indirect because planets are much fainter than the stars they orbit, and so are very hard to detect directly. Because their effects are easier to spot, larger planets are easier to find, but smaller and smaller planets are being discovered as techniques and technology improve. One of the smallest exoplanets known to date is CoRoT-7b, a planet discovered by the CoRoT satellite in February 2009, orbiting an otherwise unremarkable 11th magnitude star catalogued as TYC 4799-1733-1, located almost 500 light years away in the constellation of Monoceros. Most of the known exoplanets are thought to be larger versions of Jupiter, likely to be large gas giants, but new observations of CoRoT-7b suggest that it is far more like our own Earth.
A team of astronomers, led by Didier Queloz at the Geneva Observatory in Switzerland, used the HARPS instrument on ESO's 3.6-metre telescope at the La Silla observatory in Chile, to observe the CoRoT-7 system and try and determine the mass of CoRoT-7b. HARPS, or the High Accuracy Radial velocity Planet Searcher, is a high resolution spectrograph which enables astronomers to measure the tiny changes in velocity of a star as it is gently tugged by the gravitational pull of it's orbiting planets. These velocity shifts are extremely small, so very accurate spectrographs are needed to see the effects.
In the case of CoRoT-7b, the planet is so close to its parent star that it completes one orbit every 20.4 hours, blocking out a tiny fraction of the stars' light for just one hour during each orbit. Because the planet is so small, the team had to obtain more than 70 hours of observations to see the tiny changes in the stars' spectrum that would tell them about the planet. What the team found was that CoRoT-7b is one of the lightest exoplanets known, with a mass of just 4.8 times that of the Earth, putting it in the category of so-called "super-Earths". Since the planet directly transits the star, passing directly between the star and us, astronomers have already been able to determine that the planet's radius is less than twice that of Earth. If you know both the mass and the radius of a planet, you can calculate its density. The team did this and found that CoRoT-7b has a density of 5.5 grams per cubic centimetre, very similar to the density of the Earth. This suggests that CoRoT-7b is a rocky planet, not a gas giant like Jupiter, and is likely to be composed mainly of silicates with a small iron core, the first time such a determination has been made for such a small exoplanet.
As well as determining the mass and density of CoRoT-7b, the team also discovered a new planet, CoRoT-7c, which is slightly larger with a mass of 8.4 times that of Earth. Unfortunately, this planet does not directly transit the star, so its radius, and hence density, cannot be determined. The research will be published in the journal Astronomy and Astrophysics on October 22nd.
Queloz, D., Bouchy, F., Moutou, C., Hatzes, A., Hebrard, G., Alonso, R., Auvergne, M., Baglin, A., Barbieri, M., Barge, P., Benz, W., Bordé, P., Deeg, H., Deleuil, M., Dvorak, R., Erikson, A., Ferraz Mello, S., & M. Fridlund et al., . (2009). The CoRoT-7 planetary system: two orbiting super-Earths Astronomy and Astrophysics DOI: 10.1051/0004-6361/200913096
Posted by Megan on Monday 05th Oct 2009 (10:21 UTC
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Eyes Up - October 2009
Brief round up of what to look out for in the southern skies this month (times correct for Perth, WA).
Spring is well under way and the days are getting longer once again. The Sun rises at 5.55am on October 1st and 5.20am by the end of the month, setting at 6.41pm by October 31st. The Moon is full on October 4th and new on the 18th.
Jupiter continues to be prominent during the evening and is just three degrees south of the Moon on October 27th (for comparison, the Moon is just half a degree in diameter). Both Mercury and Venus will be visible during the first half of the month, low in the east before sunrise (as always, NEVER look at the Sun through any optical device!). Venus will be the easiest to spot at magnitude -3.5, with Mercury much fainter and lower down in the sky. Mars and Saturn are also morning objects this month, Mars will be fairly high in the eastern sky before dawn and obvious by its orange colour, Saturn will be low in the eastern sky before sunrise during the second half of the month.
At this time of year the familiar Southern Cross is fairly low in the sky to the south, but the bright constellation of Orion is visible in the east in the evening, rising by 8.30pm by the end of the month. During most of October, the Orionid meteor shower is active in this part of the sky. The maximum rate of this meteor shower will be on October 21st and is predicted to be about 30 per hour, although from the city you will see less than this due to light pollution. If you're camping this month, try and find a spot with a clear horizon to the east (no trees!) and sit back to watch the show. You probably wont see hundreds of shooting stars, but you might be lucky and spot a few really bright ones!
And finally, a quick plug for an exciting event coming up in November. The biggest event in WA for the International Year of Astronomy will be taking place on the campus of Curtin University on Saturday November 28th between 2pm and 10pm. "Astrofest" will be a huge FREE event for families where you can look through telescopes, watch a show in an Scitech's portable planetarium, see exciting science demos and exhibitions, find out about the Square Kilometre Array and talk to real astronomers. Coordinated by AstronomyWA and hosted in the new Curtin Stadium, this is an event not to be missed. Keep an eye on the AstronomyWA website for details.
Posted by Megan on Friday 02nd Oct 2009 (07:21 UTC
) | 2 Comments
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Last updated: Sunday, 22-Jun-2014 23:32:13 BST