Carnival of Space: 203

It’s Carnival time in the Gutter again! We’re hosting this week’s round-up of space and astronomy blogging news. If you’d like to find out more or get involved yourself check out the Carnival’s homepage over at Universe Today.

We’re kicking off this week with the massive Solar flare that exploded from the Sun on 7th June. The Chandra blog explains what they had to do to protect the satellite from the incoming radiation. If you didn’t see any of the movies of the flare, or if you’re unsure just how big this eruption was I strongly recommend the following, courtesy of Matt Parker:

Next up is the Pan-STARRS1 project which has discovered a new comet in the outer Solar System which could reach naked eye visibility in March 2013. One of the astronomers who discovered the comet Richard Wainscoat outlines how it was found and what we know about its orbit.

Virtual telescopes such as Google Sky, World Wide Telescope and Wiki Sky have allowed people to explore the sky in great detail at many different wavelengths, and look for their own mysterious sky objects. However, if you don’t have some understanding of what you’re looking at you can end up with misidentifications, such as the ones discsussed by the Astroblog for comet Elenin and the mythical planet Nibiru.

If you want to know more about why astronomers use many different wavelengths for their observations check out the first of Cheap Astronomy’s two part podcast series on astronomy across the electromagnetic spectrum.

Over to Mars now. Vintage Space looks at the challenges in designing and testing the parachutes that slow the descent of the landers that are sent there. Once they reach the surface the pictures they send back can seem very familiar – head over to The Meridiani Journal to see an excellent example of “mud polygons” or mud cracks on Earth, and their striking similarity to the bedrock terrain seen by Opportunity in Meridiani on Mars.

Could Saturn’s moon Enceladus have a salt-water ocean? NASA’s Cassini spacecraft has already confirmed that there’s liquid water below the surface, but now it may also have detected salt grains in the plumes of icy spray shooting up from its surface. Both Discovery News and Weirdwarp have the full story.

Next Big Future brings news of a new supersonic business jet concept, the SonicStar, which was unveiled at the Paris airshow. It promises flight times from Paris to New York of under 2 hours thanks to its revolutionary engine design. If you want to travel a little further though, they also have an interview with writer Keith Henson about his ideas for cheaper space launches using a combination of Skylon rocket planes and concentrated lasers.

There’s two slightly more offbeat offerings to end on. First, shhh, don’t tell anyone but Universe Today has been spying on spy satellites, thanks to the skill of astrophotographer extraordinaire Thierry Legault. Check out the post if you want to know how he does it.

Finally, could the forthcoming movie Iron Sky have any basis in fact? Everyone knows that WW2 Germany developed rockets far in advance of the Allies, but some argue that in 1945 the Third Reich was on the verge of developing a space program. Armagh Planetarium’s Astronotes finds out more.

Well, that’s it for this week. Hope you’ve enjoyed this somewhat surprising journey from solar flares to spies and Nazis!

When a comet’s not a comet after all

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Back in January the Lincoln Near Earth Asteroid Research (LINEAR) survey saw something a bit odd amongst the asteroids in the main asteroid belt (found between Mars and Jupiter). Initially the mystery object, P/2010 A2, was designated as a main-belt comet (a rare object found within this region of the Solar System, unlike the majority of comets which orbit a lot further away) because of its elongated fuzzy appearance. However, two sets of results published in Nature today suggest that this thing is actually the aftermath of a collision between two asteroids that occurred some time in February or March 2009.

A comet generally has a fan shaped tail, topped with a dust-enshrouded nucleus; when the first team looked at P/2010 A2 with the Hubble Space Telescope though they saw that it has a more rectangular shaped tail, beginning in an X-shape:

The second team also saw a distinctly un-comet like structure (shown left) when they imaged the object with the OSIRIS camera onboard the Rosetta spacecraft. This had a really good view as it was approaching the asteroid belt at the time, in preparation for its flyby of the asteroid Lutetia.

Modelling the structures seen in both images by the two teams independently revealed that the main body of P/2010 A2 is about 120 metres across, that it was formed from a collision with a much smaller body, and that all this occurred about a year before we first saw it. Discovering all this isn’t possible from Earth though, as ground based telescopes, such as the one used by LINEAR, can’t see it from the right angle.

This sort of collision between asteroids of this approximate size are only predicted to occur roughly once every 12 years, so its likely that P/2010 A2 will remain unique for a few years yet.

Images credit NASA & ESA

ResearchBlogging.orgJewitt, D., Weaver, H., Agarwal, J., Mutchler, M., & Drahus, M. (2010). A recent disruption of the main-belt asteroid P/2010 A2 Nature, 467 (7317), 817-819 DOI: 10.1038/nature09456

ResearchBlogging.orgSnodgrass, C., Tubiana, C., Vincent, J., Sierks, H., Hviid, S., Moissl, R., Boehnhardt, H., Barbieri, C., Koschny, D., Lamy, P., Rickman, H., Rodrigo, R., Carry, B., Lowry, S., Laird, R., Weissman, P., Fitzsimmons, A., Marchi, S., A’Hearn, M., Angrilli, F., Barucci, A., Bertaux, J., Cremonese, G., Da Deppo, V., Davidsson, B., Debei, S., De Cecco, M., Fornasier, S., Gutiérrez, P., Ip, W., Keller, H., Knollenberg, J., Kramm, J., Kuehrt, E., Kueppers, M., Lara, L., Lazzarin, M., López-Moreno, J., Marzari, F., Michalik, H., Naletto, G., Sabau, L., Thomas, N., & Wenzel, K. (2010). A collision in 2009 as the origin of the debris trail of asteroid P/2010 A2 Nature, 467 (7317), 814-816 DOI: 10.1038/nature09453

Could Kepler find something closer to home?

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You might have heard about Kepler and NASA space mission to find planets around other stars. But recently this paper came out recently showing how it could be used to probe unknown distant reaches of our own solar system.

One of the successful methods in the rapidly developing field of discovering worlds around other stars over the last decade has been the transit method. Put simply, the planet that orbits the star gets in the way, blocking out a bit of the light from the the star’s surface. Hence for a brief period the star appears slightly dimmer. Detecting this requires staring at a star on and off for a long period and making very precise brightness measurements, what Kepler is designed to do, stare at lots of stars and look for these dips in brightness. But couldn’t something else get in the way too? Yup.

Comets are collections of ices (frozen water, carbon dioxide etc.) that occasionally pass through the inner solar system on their orbits around the Sun. These appear to be made of two separate populations, one of comets with short orbital periods that seem to orbit in the same plane as the other planets in the solar system and one of longer period comets which have orbits with random inclinations. It’s thought that these two populations have two separate places of origin. The short period comets are thought to come from a disk of objects extending from 30AU (1AU is the distance from the Earth to the Sun) to maybe 100AU. Longer period comets seem to come from much further away. The idea of a distant spherical cloud of icy bodies as an origin for long period comets was first thought up by my second favourite Estonian astonomer Ernst Opik (Brits who recognise the surname may know his grandson, cheeky boy MP Lembit) and later resurrected by the Dutchman Jan Oort. This is now known as the Oort Cloud, icy bodies in a spherical shell extending from a few thousand AU to tens of thousands of AU. To put that upper bound into context, the nearest star to the Sun is only 260,000AU away.

Unfortunately there are no definite Oort Cloud members known. Their distance and small size make direct detection difficult. However a paper out this week by astronomers in the US and in Israel has suggested that the Kepler mission could detect them by chance. The principle is
the same as the detection of planets by transits. An icy body in the Oort Cloud passes in-front of a background star and thus blocks out some of its light thus dimming it. The rate at which these events happen will depend on the number of objects in the Oort cloud and how close to the Sun it’s inner boundary is. The study finds that Kepler could detect occultations (when a solar system body passes in-front of a background star) of up to one hundred 10km+ in size Oort Cloud objects. The precise detection rate could allow astronomers to constrain the dimensions and density of the Oort Cloud by observations for the first time.

Eran O. Ofek, & Ehud Nakar (2009). Detectability of Oort cloud objects using Kepler Submitted to ApJL arXiv: 0912.0948v1

Was there a comet impact in AD 536? Maybe.

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In the year AD 536 something catastrophic happened which caused a drop in the global temperature lasting several years and led to widespread famine, and possibly plague outbreaks too. This is right in the middle of the Dark Ages – a time about which by definition we know very little – so how can we be so sure about this? Well, it turns out that when human records are sparse, tree records step in to fill the gap. The series of concentric rings in the trunk of a tree provide a history of its growth and, seeing as a new ring is made every year, its age. If a summer is a lot colder than normal then a tree has to conserve its energy and so forms a narrower ring than it would have if the weather had been better. This is exactly what’s seen in the tree ring record for nearly ten years, beginning in AD 536.

The historical record of this period isn’t completely Dark, and the surviving accounts provide a clue as to what could have caused the prolonged cold snap. The interestingly named Michael the Syrian wrote that “…the Sun was dark and its darkness lasted for eighteen months; each day it shone for about four hours, and still this light was only a feeble shadow” while someone called Lydus in Constantinople observed that “…the Sun became dim…for nearly a whole year…so that the fruits were killed”. There are also numerous Chinese references to obscured skies and summer frosts.

All of this points towards something in the atmosphere – a ‘dust veil’ – which blocked sunlight and cooled the planet. But what could have put a load of dust into the atmosphere? Here, things get more intriguing. The obvious culprit is the ash and sulphuric acid produced by an enormous volcanic eruption – a phenomenon known as a ‘volcanic winter’. 1816, the ‘Year Without a Summer’, is a more recent example of this, caused by the eruption of Mount Tambora in Indonesia. However, volcanic debris is easy to spot as it leaves a very recognisable acid layer trapped in an ice sheet in somewhere like Greenland. Therefore all we have to do is extract an ice core, figure out which bit of it corresponds to the sixth century and look for the layer. Simple. Unfortunately for this theory though, by the late 90s no convincing volcanic signature had been found……

The alternative, astronomical, scenario for the AD 536 dust veil is an asteroid or comet impact. No impact crater has ever been linked to this time period which points towards a mid-air explosion called an airburst. These release large amounts of energy in the form of a tree-flattening shockwave (as happened in Tunguska in 1908) and can also potentially trigger forest fires, which could in turn inject large quantities of soot into the atmosphere. This is where I get involved. Several years ago I was part of a group that tried to calculate how big a comet-triggered-fire would have to be to cause the observed cooling. It turned out that the answer to this is an area the size of Northern Europe which seems rather unlikely! Surely there would have been some record if this had happened? Clearly fires could have added to the cooling but they couldn’t have been the sole contributor. Comet impact plumes may provide the solution. When the comet airbursts, some energy from the explosion, along with the debris, is funneled back along the impact path causing a plume of material, which then falls back onto the top of the atmosphere and causes the dust veil. Case closed, right? As with most things in astronomy, it’s not that simple.

The comet impact theory looked to be the most likely explanation until early last year when Larsen et al. published a paper presenting new and improved ice core measurements. These finally showed a clear volcanic related acid signal for AD 536, larger than the one found for the Tambora eruption mentioned earlier.

This should be the end of the story. Indeed, until several hours ago when I started putting this together and happened to come across this abstract, I thought it was. Their tantalising, but still unpublished, detection of impact debris in the AD 536 layer of another ice core points back to the cometary culprit again. Without reading the full paper nothing’s certain, which means that the Larsen et al detected volcano is the best option for now!


Comet vs. volcano!

Larsen, L., Vinther, B., Briffa, K., Melvin, T., Clausen, H., Jones, P., Siggaard-Andersen, M., Hammer, C., Eronen, M., Grudd, H., Gunnarson, B., Hantemirov, R., Naurzbaev, M., & Nicolussi, K. (2008). New ice core evidence for a volcanic cause of the A.D. 536 dust veil Geophysical Research Letters, 35 (4) DOI: 10.1029/2007GL032450