Wednesday, 29 September 2010

Asteroid 2002 AA29: Half-way a moon, entirely enigmatic.


As ever, all links are numbered, and the addresses listed at the end.

A little place and a big tease:
This is only a short post, as its about a place that is firstly extremely tiny, and secondly mostly interesting for what we don't know about it : The near Earth asteroid 2002 AA29[1]. This is a tiny little chunk of space stuff, as modest in its brightness as its size (magnitude 20.4 at its closest to earth). What could set apart this airless island rock that is at most 100 meters across and perhaps a little as 50?

Image above: The dot in the cross hairs is 2002 AA29, part of Earths co-orbital family. Image courtesy of P.Birtwhistle.


The first unusual thing is; its orbit is of a rare type. It has a 1:1 orbital resonance[2] with Earth, making it a co-orbital asteroid[3], one of only hand full following Earth. It has a year the same as ours, orbiting just inside Earths orbit (just slightly faster), then at its closest approach the gravity of the sun and the Earth move it to an orbit just outside ours (just slightly slower) and it recedes again, until Earth catches it, and it goes back to orbiting inside Earths orbit. It's orbit is angled with respect to ours, almost the only thing setting the two tracks apart.
From our frame of reference these things combine so it looks like it is following a weird U shaped spiral around us, coming close but never quite passing us. Close approaches are every 95 years; in its own very slow way the little rock is teasing us.



Video above: 2002 AA29's odd orbital path, seen from our frame of reference. Courtesy of the University of Western Ontario.

The orbit is very very circular, more so than Earths in fact. Orbital dynamics studies tell us that this means it may have been co-orbital with Earth for a very very long time- since the time the Earth formed perhaps.

We are almost totally ignorant about its surface, as it is much to small to ever appear as more than a dot. However we can infer that it cannot be made of volatile material, as that would evaporate giving off a detectable tail of gas. In that regard this seems a very well behaved little speck of presence in the vastness.

We do know some things, although they don't add up very well: The gigantic Arecibo radio telescope[4] bounced signals off it, and what it found[5] was a bit confusing:
2002 AA29 has an unusually weak radar echo, meaning either its actually even smaller than we think and extremely reflective to light, or it absorbs radio waves much better than it should. Either way, its not made of the normal shopping list of asteroid materials.
Arecibo also found it to be spinning roughly every 33 minutes or less, which is fast enough that if it were anything other than a solid chunk of material it would fly apart. Yet its surface density seems low, which would usually suggest it was a rubble pile filled with voids.

So it's small, it follows the Earth and may have done for a long time, its made of rock, or at least not ices, and its not made of the usual asteroid material. It's one single lump of stuff, not a pile of bits, although its not as dense as it should be. It seems that this cheeky little speck is laughing at us- teasing us with more than just a peek-a-boo orbit. What does the evidence suggest?

We really might have a cheeky relative on our hands: One of the most plausible explanations is that 2002 AA29 is related to Earth [6] or our Moon. It could be an exceptionally large fragment sent screaming into space by a monstrous asteroid impact. That would make it an interesting little curiosity, one that could educate us some more on giant impacts, and even the state of our Earth or Moon in a long lost epoch. But there is a similar, even more violent, possibility. One that goes back to before the Earth and Moon as we know them even existed:

To J.Gott[7] and E. Belbruno[8] the anomalies surrounding this little rock suggest that it just might be a fragment from a collision [9] between the primordial Earth, and a long lost world called Theia. Theia was, so goes the theory, a Mars sized protoplanet that smacked into Earth 4.5 billion years back. The unimaginable heat this event caused not only turned the whole surface of the Earth to magma, it blew enough material into orbit to form a whole giddy new world [10]: Earths Moon.

This tiny, tantalisingly enigmatic, little rock is definitely unusual- and worth investigating- but perhaps it goes further than that; perhaps modest little 2002 AA29 is a window directly onto the last really huge event in the construction of our Earth. And that makes it well worth a blog post.

How do we know about 2002 AA29?

2002 AA29 was discovered in 2002 by the LINEAR project[11]. Once it's unusual orbit was established some follow up observations were done by Arecibo, and that's it really. LIINEAR employs the specially built GEODSS[12] telescope as part of an automated survey to track  near Earth objects. However we do know of some other co-orbital asteroids, like 3753 Cruinthne[13], and can infer and guess things about 2002 AA29 by looking at them as a group.


Image above: The LINEAR projects GEODSS ( Ground Based Electro Optical Deep Space Surveillience) telescope under construction. Image courtesy of NASA.


Image above: The GEODSS telescope in its observatory on Kwejalein atoll Image Courtesy of ESA.


List of links:
[1]www.space.com/scienceastronomy/earth_asteroid_021021.html
[2]http://space.wikia.com/wiki/Orbital_resonance
[3]http://science.nasa.gov/science-news/science-at-nasa/2006/09jun_moonlets/
[4]http://www.naic.edu/
[5]http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-49V1DPH-6&_user=10&_coverDate=12%2F31%2F2003&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1477638702&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=8d6888fa09c240c71548eb27d5f2f7c5&searchtype=a
[6]http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1565.pdf
[7]http://www.princeton.edu/astro/people/faculty/jrg/
[8]http://www.edbelbruno.com/home.html
[9]http://iopscience.iop.org/1538-3881/129/3/1724/204215.text.html
[10]http://www.es.ucl.ac.uk/research/planetary/undergraduate/bugiolacchi/moonf.htm
[11]http://www.ll.mit.edu/mission/space/linear/
[12]http://space.au.af.mil/factsheets/geodss.htm
[13]http://www.astro.uwo.ca/~wiegert/3753/3753.html

Sunday, 26 September 2010

A very quick note: Presented by Brian Cox, Wonders of the Solar System[1] is being repeated over the next few weeks, from six to seven Sunday evenings. Well worth catching, either on BBC two or on BBC iplayer. I'm a bit late with this but even coming in halfway through its very accessible, and Cox manages to be clear on some quite complex ideas without dumbing them down. I hope to have 'Rise of the Oligarchs' up in the next week.

All the best.

John Freeman

[1]http://www.bbc.co.uk/programmes/b00qyxfb

Friday, 24 September 2010

A light that cuts the primordial darkness.....

All links are numbered, and the web addresses listed in order at the end.

Mysteries in the dark:

A few weeks back I posted on the earliest days of the solar system, and how many details are unknown. In large part this is because star systems, that are still collapsing(or even yet to) out of the dust and gas clouds[1] that bear them, are visible only as a darkness against the background stars- a cloak of dust that no light can penetrate [2].
Well that changed this week, with the discovery of 'coreshine'[3]. Coreshine appears to be a common phenomena in dense molecular clouds across the galaxy. It is invisible to our limited human eyes, but abundantly clear to the infra red detectors aboared the SPITZER[4] space telescope.

Image above: The SPITZER space telescope awaiting launch. Image courtesy of NASA archives.

Mysteries illuminated:
Coreshine is light scattered off of dust particles of a particular size- roughly 1 micron (millionth of a meter) across. Light can be a quirky phenomena: it will only reflect and scatter off of particles that exceed a minimum size. You can see why in the bath tub: pick up a sponge and dribble water into the full bath, the waves will reflect off the walls, and off a big bath toy. But if you put a small rubber duck in the bath then it wil bob up and down with the waves without affecting them very much. The dust in the icy black core of a cold molecular cloud is typically 0.1 microns or less- like the small duck it moves with light waves rather than reflecting them.
So seeing into the core of a pre-stellar cloud has a catch 22 problem- any light that is of the right wavelength to penetrate the outer layers is also just the right wavelength to go right through the core without stopping!

SPITZER picked up an unexpected glow in mid infra red light[5] (light with wavelengths of around 2 to 8 millionths of a meter)coming from a pre-stellar cloud 360 lightyears away, known by the catchy handle of L-183. There are many possible sources for such a glow, but none of the possibilities seemed to fit the bill.

Image above: A false colour view of coreshine in L-183. Image courtesy of JPL,

Theory has suggested that dust grains in the cores of such clouds should be able to grow in size- and computer models of grains growing in thw densest regions of molecular clouds predicted that they would reach the right size to scatter mid infrared radiation, which is emitted by so many sources, incuding dust itself our galaxy is bathed in a gentle, continuos, glow of it.

SPITZER followed up this curious, and possibly fluke, find with a survey of 110 similar clouds[6] of dust and gas across the sky: the results left the investigateing team in no doubt that the effect is both real and widespread- half the clouds obsrved showed coreshine.

This is a very exciting find for scientists researching the earlyiest stages of star gestation. Illuminated by the galaxies ruddy mid infra red glow this larger, slowly growing[7], dust acts like dye droppered into the seemingly still water of a slowly flowing stream; suddenly complex structure is revealed where before only the streambed could be seen. Study of the spectrum[8] of scattered infra red light could reveal details about the conditions in the dark wombs of starbirth that were previously unguessable-not only SPITZER but the under-construction James Webb Space Telescope[9] to wil doubtless have a slew of coreshine projects to begin working through soon.
So watch this dust filled segment of space!


Image above: Some of the team working on the James Webb Space Telescope, in front of a ful sized model of the sattelite. Image courtesy of NASA.


List of links:
[1]http://www.universetoday.com/18282/solar-nebula/
[2]http://astronomy.swin.edu.au/cms/astro/cosmos/B/Bok+Globule
[3]http://www.mpia.de/Public/menu_q2e.php?Aktuelles/PR/2010/PR100923/PR_100923_en.html
[4]http://www.spitzer.caltech.edu/
[5]http://www.ipac.caltech.edu/Outreach/Edu/Regions/irregions.html
[6]http://www.sciencemag.org/cgi/content/abstract/329/5999/1622
[7]http://adsabs.harvard.edu/full/1993A%26A...280..617O
[8]http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm
[9]http://www.jwst.nasa.gov/

Monday, 20 September 2010

All links are numbered, and listed at the end.

Of tiny shrapnel, zombie stars, and out of place isotopes.

Science often needs three difficult traits: faith that what you’re doing is worthwhile, tenacity enough to convince others of this, and patience enough to see it through. It appears that Nicolas Dauphas[1] and his co-authors have proved that they’ve got the mettle. He and his team have just passed a tiny but significant milestone in an 8 year quest to shed more light on our solar systems earliest epoch [2], and explain why the concentrations of certain rare isotopes vary between the various planets and meteorites.
To do this needs a careful analysis of samples from the most unaltered type of meteorite, carbonaceous chondrites[3], and to give you an idea of just how painstaking this research has been; Dauphas began preparing samples of the Murchison[4] and Orgueil[5] meteorites, a pair of space rocks older than our Earth, in 2002.

He only got to actually use them in 2009.



Image above: a section of the Murchison meteorite, showing white aluminium rich chondrules, some of the first solid objects ever to form in our solar system. Image courtesy of meteorites.com.

Science so long in the preparation can be a tense business when it finally gets going. Dauphas research was something that cosmochemists[6] have been wanting to try for over 20 years, but it was only relatively recently that the technology to do so became available. His aim was to use the California institute of technology ion microprobe[7] to very accurately measure the abundance of a particular isotope of chromium (Cr 54) in minute grains, or nanoparticles, embedded in the rock of the meteorites.



Image above: a pre-solar nanodiamond, less than 100 atoms across, imaged by high resolution TEM. The diamond is the pentagonal symmetric arrangement of atoms (seen as light and dark dots) near the middle of the image). Image courtesy of Washington University.

The right tool for the job...
The ion microprobe operates a bit like a combination of a microscopic sandblaster and sensitive nose: The sample being analysed is held in a high quality vacuum, and ‘sand blasted’ with a stream of energetic ions (electrically charged particles). This smashes a small section of the sample into plasma, a gas where the atoms are ionised. This ionised gas is then analysed by a mass spectrometer (the ‘nose’ part) which uses electric and magnetic fields to separate and identify the atoms present by their mass. Because it measures atoms by mass the ion microprobe can distinguish between different isotopes of a chemical element- something otherwise impossible as the chemical behaviour of isotopes of the same element is almost identical.
As the supply of material from suitably primitive meteorites is limited, the experiment so long in the preparation, and time on such an advanced and complex piece of kit so hard to come by a little bit of nerves on Dauphas part would be understandable: “ Time is very precious on those instruments, and three weeks of instrument time is very hard to come by” he said.
Dauphas used an electron microscope and the microprobe to search through minute grains, some only 0.0000001 meters (100 nanometers) across, looking for one with an excess of Cr54.

But why?

Dauphas is looking for a piece of shrapnel, a grain forged by the death of a ‘zombie’ star. Grains from supernova have been identified in the material brought to Earth by meteorites before, such as nanodiamonds[8], and grains of silicon carbide[9]. The proportions of rare isotopes of aluminium and iron (aluminium 26 and iron 60) they carry have bolstered the idea that our solar system was hit by a supernova around the time it began to form. The leading theory, the nebular hypothesis[10], on our solar systems origin suggest that this supernova explosion triggered the collapse of the pre-solar nebula (if you just thought ‘the what?’ go to the first entry on this blog and start reading). In a sense that explosion was the very start of year zero for our solar system.

But supernova come in different types[11]. True the type most people think of is simply the immense implosion ,then rebounding explosion, of a terrifyingly powerful star that makes our sun look like a pocket torch- type II, or core collapse supernova. But another type, type 1a, can occur when the super dense corpse of dead star attempts to reanimate itself; by ghoulishly tearing the flesh off a nearby companion and wearing it!

No I’m not joking! The situation starts with two stars orbiting each other: one of them dies in a relatively modest way, a planetary nebula. It leaves behind a corpse as big as Earth and as heavy as a full grown sun. This is the stars burnt out core, full of carbon and oxygen, known as a white dwarf[12]. This dwarf continues to orbit its companion, and under the right circumstances its intensely focused gravity (the dwarf is denser than only a few things known to science) strips material off its companion, and layers it onto itself. As the material builds up its mass, under the dwarfs crushing gravity, compresses the core of the dwarf until things there are hot and dense enough for nuclear fusion to begin again, this time using carbon as fuel, bringing the dead star snarling back to life!

Yet the attempt to revive itself is not only vain, it’s doomed to catastrophe: the dead star lacks the thermal pressure feed back mechanism[13] that living stars use to stabilise themselves, and the reaction goes runaway in only seconds- the temperature of the white dwarf goes up to billions of degrees Kelvin, and the white dwarf becomes an Earth sized thermonuclear bomb.
It is torn entirely apart: The intense pulse of radiation is followed by a demonic shockwave moving at 20,000 km per second, or 3% of light speed- awesome velocity for such a huge phenomena. This is known as a type 1a supernova, and in the brief moments it takes to happen, high energy nuclear alchemy produces rare isotopes, such as chromium 54 and calcium 48, in quantities that no other natural phenomena does.



Image above: A 1a supernova ignites in a distant galaxy. Image courtesy of the University of Toronto.

Back to labouring Dauphas and his sections of meteorite: Over three weeks, using the ion probe, he sifted through grains embedded in the meteorite samples (1500 in all!). In the first session his search began promisingly, with hints of the Cr54 excess he was seeking, but he had to search for a full three weeks, until he found one definitively rich in chromium 54. This makes it a possible candidate for a fragment made during a type Ia supernova. If he can confirm this he will have found proof that our star system was subjected to at least one type Ia explosion, and will have solved a mystery that has plagued cosmochemists: Different planets, and different meteorites, have different concentrations of Cr 54. If they all came from the same proto-planetary disk[14], which should have been well mixed, then they should all have the same amount.

But if Cr 54 was injected into the disk, by a type 1a supernova explosion, as minute fragments then the processes in the disk would have sorted them by size, concentrating them into the young objects in the proto-planetary disk– some which would eventually form the planets. The same processes would have left the rest of the disk depleted in Cr54, explaining the modern day difference in concentrations.
Confirming this fragments origin will mean searching for another rare isotope- this time of calcium, calcium 48, which is relatively easy to make in 1a blasts, and hard to make in type 2 blasts. If there is a lot of calcium 48 in this grain then Dauphas and his eight co-authors will have filled in a blank in the earliest chapter of our solar systems history- an academic feat worth showing eight years of passion, tenacity and patience for .

List of Links:
[1] http://geosci.uchicago.edu/~dauphas/
[2] http://www.lpi.usra.edu/books/MESSII/9005.pdf
[3] http://www.daviddarling.info/encyclopedia/C/carbchon.html
[4] http://news.bbc.co.uk/1/hi/8516319.stm
[5] http://www.daviddarling.info/encyclopedia/O/Orgueil.html
[6] http://www.nhm.ac.uk/nature-online/space/meteorites-dust/studying-meteorites/cosmochemistry/index.html
[7] http://ccm.caltech.edu/Instrument.aspx
[8] http://www.journalamme.org/papers_vol37_2/37279.pdf
[9] http://www.lpi.usra.edu/meetings/LPSC98/pdf/1126.pdf
[10] http://csep10.phys.utk.edu/astr161/lect/solarsys/nebular.html
[11] http://imagine.gsfc.nasa.gov/docs/science/know_l1/sn_overview.html
[12] http://www.daviddarling.info/encyclopedia/W/whitedwarf.html
[13] http://www.astronomynotes.com/starsun/s7.htm#A5.3
[14] http://www.daviddarling.info/encyclopedia/P/protoplandisk.html

Tuesday, 14 September 2010

Note: As always, a list of links is at the end.
Our solar system- where the ancient past really is present (sometimes as big rocks less than a hundred kilometers above your head).

I've found myself with some time on my hands, so I'd like to direct your attention to the video below on youtube. This oddly beautiful piece of animation comes to us from Scott Manley and [1]Armagh Observatory, [2]orbital elements by Ted Bowell. It did the rounds of the space community last week, and I've been meaning to post about it:




This video shows the discoveries of small objects, asteroids mainly, since 1980. Red blips are Earth orbit crossers, yellow are Earth orbit approachers, anything giving us a fairly wide berth is green.

Not only is the image beautiful, and the choice of soundtrack right up my street, but by the time 2010 rolls around its impossible to hold onto the view that our eight planets move through the dark in serene isolation. In fact we're clearly embedded in a swirling disk of meter and kilometer sized chunks of matter- the descendant of the protoplanetary disk and its planetesimals. Each of those chunks carries a story leading back to our solar systems creation. And as this video of a meteorite coming down over Edmonton, Canada shows, the violent process of planet building by accretion hasn't stopped, its just slowed down a tad:



This one was less than meter across, and pieces of it made it to the ground to be collected by hunters of space rocks. Video courtesy of a Canadian police officers dashboard camera.



Image above: A fragment of the Edmonton meteorite sits on the surface of a frozen lake. This bit is about 30cm long.

The modern disk is much much sparser, but it goes to show- the night sky is a far busier place than anyone would think just by looking up at night.

Worryingly the first video gave me a nice serene feeling, which it really shouldn't given the number of red blips....

Before I sign off I'd also like to direct every ones attention to [3]this excellent blog entry by Emily Lakdawalla on the flight of the falcon (Hayabusa), and its attendant podcast.

List of links:

[1]http://www.arm.ac.uk/
[2]http://www.naic.edu/~nolan/astorb.html
[3]http://www.planetary.org/blog/article/00002659/

Thursday, 9 September 2010

Note: All links are numbered, with a full list of web addresses in order at the end.

The Ancient Solar System - going there.


Image above: One cloudy morning the Giotto spacecraft splits the sky, on the first leg of its 8 year mission to explore comets Halley and Grigg Skjellerup. Image courtesy of ucl.co.uk.

There are many sources of information on our solar systems deep past, but few are as anticipated or as exciting as space missions to explore ancient chunks of matter, like asteroids and comets, left almost unaltered since that time. So lets give our ancient solar system story context, lets tip our hats to, and marvel at, some of these missions to survivors from geologically distant eons.

Past:
First stop in this series, which will run concurrently with the ancient solar system story, are some of the missions that have completed their main objective, furnishing us with stunning images and tantalising data...

1984 and 1985: Giotto and VEGA


Image above: Giotto under construction. Image courtesy of ESA.

Image above : A mock up of the Vega spacecraft, which dropped balloon probes on the planet Venus, then went on to Halley's comet. Image courtesy of mentallandscape.com

The first up close and personal glimpse of a wanderer from the deep past was [1]ESAs [2]Giotto mission, which became the first space craft to perform a close fly by of the [3]nucleus of a comet. Sending back incredible images, the little cylindrical robot opened up a whole new vista on these frozen, nomadic, time capsules. The Giotto and [4]VEGA 1 and 2 missions revealed [5]Halleys comet to be a tiny, dark skinned, peanut shaped world, barely 15km from end to end. The VEGA mission found the crust to be almost totally black with a temperature between 300 and 400 degrees kelvin, suggesting it is made of space weathered [6]organic compounds1. Reflectively brilliant jets of water vapour, carbon monoxide, and carbon dioxide burst through the surface, laced with traces of methane and ammonia. Dust particles swept like black bullets away from the surface by the vents were found, from the size of small hailstones down to the smaller than the unaided eye can perceive. These particles contained complex compounds based on carbon, hydrogen, oxygen, and nitrogen, mashed together: The presence of such material has suggested to scientists watching from Earth that comets were a possible source of organic material for pre-biotic chemistry here, billions of years ago.

Image above: The nucleus of Haleys comet, a 15km long piece of rock, organic chemicals, and ice broken by jets of evaporating ices. Image courtesy of johnstonarchive.com

Giottos visit to the Halleys comet was a perilous one: A piece of gravel, shot away from the comet by the jets, smashed its camera. But, even with an eye put out, Giotto soldiered on to visit another comet, the fainter [7]Grigg-Skjellerup, in 1992.

Giotto and VEGA exceeded expectations, and paved the way for many further missions to small objects.

1996: NEAR


Image above: Technicians at work on the NEAR spacecraft in its clean room. Image courtesy of Aerospace-technology.com

[8]NEAR (Near Earth Asteroid Rendezvous) was the [9]first mission to orbit, and then land on, a near Earth asteroid. The target was [10]433 Eros, one of the first near Earth asteroids discovered. On the way NEAR flew by 253 Mathilde, taking spectacular images:


Image above: The slightly ominous face of 253 Mathilde, a carbon rich main belt asteroid about 66 km across at its widest. The surface is covered in phyllosilicate materials, which often form in relation to liquid water. This image was taken by NEAR from around 2400km. Image courtesy of NASA.

Eros was shown by NEAR to be a tiny, stony, desert 33 km from end to end, with a granite cracking difference in temperature between the night and day side: 250 degrees kelvin (123 kelvin on the night side, 373 kelvin maximum on the day side. The asteroids surface held [11]hard to explain smoothed areas-perhaps related to a collision with another asteroid that sent shock waves through its internals structure, shaking the outer layers of Eros like sand in a 'quake and erasing ancient craters from its records. The mission also revealed Eros to be layered internally, with a solid core topped by rubble from countless collisions and eons of thermal weathering.

Image above: The S-type (stony) asteroid Eros looms out of the darkness like an interplanetary whale. Image courtesy of Jet Propulsion Laboratory (JPL) NASA.

Image above: A density map of 433 Eros. Red is denser, shading to dark blue as least dense. Image courtesy of Jet Propulsion Laboratory (JPL) NASA.


Image above: Odd 'ponded' regions on Eros, where fine dust appears to have settled into the bottom of craters. This is odd given Eros tiny size and low gravity, and may be related to disturbances from collisions with smaller asteroids. Image courtesy of astro.cornell.edu

Part of the rationale behind NEAR was that missions like it could literally save our planet: 433 Eros isn't likely to hit Earth, but it is very similar to some that could- and if a vindictive cousin of Eros came calling on our skies one day....

Image above: Depiction of the crater from the blast that wiped out the dinosaurs (or at least a lot of them). I could have put a very dramatic special effect here. I didn't - think about what this picture represents if centered over say, London, Washington, Moscow, Beijing...... special effects would be selling it short.
Image courtesy of athenapub.com

Knowing how an asteroid like Eros works is a step towards being able to prevent such rare but apocalyptic disasters.

2005: Deep Impact

Image above: Ball Aerospace technicians work on the Deep Impact probe. Image courtesy of Ball Aerospace .

Image above: The battered, alien , surface of Tempel 1 appears out of the darkness as the Deep Impact mission approaches. Image courtesy of NASA.

The [12]Deep Impact mission could have been subtitled 'Earth strikes back!' as this was a uniquely explosive mission: its goal was to smash a 370 kg copper slug into the surface of comet [13]Tempel 1, pulverizing the crust and ejecting it into space. The blast was equivalent to roughly 5 tons of TNT, and would have given astronomers their first good look at the interior of a comet.
Image above: The impact and resulting dust plume from the Deep Impact copper 'bullet' slamming into Tempel 1 at space craft speeds. The resulting crater is obscured by the plume (although probably wouldn't be visible at this resolution anyway). Image courtesy of wvi.com, and JPL NASA.

On the 4th of July 2005 the impactor flashed down through the comets rarefied coma, crossing its skies with speed a human eye could not even register, and slammed into the comets fragile crust- but Tempel 1 had the last laugh: the blast threw up a plume of dust so large it totally whited out the blast site!


Image above: The plume of dust blasted into space by Deep Impact. From this angle it is clear how extensive the plume is, ad why imaging the impact site is no easy proposition on this pass of the nucleus. Image courtesy of NASA.

Still, observations of the dust cloud found some surprising things: Tempel 1 contained less water than expected, and held [14]phyllosilicates, [15]carbonates, (both often formed by liquid water), metal sulfides (like fools gold), sodium (a rare find in space), and Polycyclic Aromatic Hydrocarbons ([16]PAHs) which some theories implicate in the origins of life.

And as for that crater? It is thought to be about 100 meters wide, 30 deep, and not to worry- [17]Stardust NExT is due to drop by Tempel 1 in 2011 to get a better look at it. Meanwhile the main Deep Impact spacecraft has been assigned two new missions: using one of its cameras to study distant [18]extrasolar planets, and a visit to comet [19]Hartley 2 this November.

1999: Stardust

Image above: The Stardust spacecraft is inspected. Image courtesy of Life magazine.

Bringing us to the [20]Stardust mission, which I have written about numerous times before. Stardust's first mission was to comet [21]Wild 2. Wild 2 is believed to be newcomer in the warmer inner solar system, and has spent most of its existence in the frigid volumes of the outer solar system space until the huge gravity of Jupiter rudely perturbed it.

Image above: The nucleus of wild 2, an alien landscape of towering spires, steep sided pits and twisted canyons. Image courtesy of NASA.

Early in 2004 the small ship flew through the coma of Wild 2 and collected samples of the dust in specially designed [22]aerogel collectors. On the 15th of January 2006 [23]it faithfully delivered its sample capsule into Earths atmosphere, and continued on to become the stardust NExT mission.

Image above: Stardusts sample return capsule safely on the ground after the nail biting tension of re-entry. Image courtesy of the Open University.

Image above: Tracks from the 6km/second impact of particles with the aerogel collector on Stardust. The particle's themselves are trapped in the bulb shaped track ends. Image courtesy of JPL NASA.

Studies of these samples have revealed a range of organic molecules, including [24]remarkably long chain hydrocarbons and [25]glycine a fundamental building block of proteins. High temperature materials such as olivine and pyroxene, that suggest some unknown mixing mechanism was at work in the early solar system, were also found. The results add to the mystery of cometary water, as Wild 2 seems to have little in the way of carbonates, unlike other comets studied. To top all this off, one very special grain dubbed [26]'Orion' by its stardust@home discoverer, may be from a lot further away than anything else ever recognized by human eyes: a grain from interstellar space.

The chemistry was not the only fascinating result: Wild 2 was revealed to be one of the most alien landscapes ever seen: A bizarrely folded place of scarps, spires and degraded depressions. Pillars of vapour from vents stud the landscape, and a truly alien geology with no simple analogue on Earth at play here.

2003: Hayabusa, Per Ardua Ad Astra.
In the recent past one mission has stood out, for sheer drama and nail biting intensity- and for the tenacity and inventiveness of the mission control team here on earth:
[27]JAXAs [28]Hayabusa space craft. If ever a mission deserved the title of 'the little ship that could' it’s this one.
The mission launched aboard an [29]M-V rocket on the 9th of may 2003. The 520 kg probe was equipped with four ion engines, powered by large solar panels, and carried the tiny [30]MINERVA lander. This was the first attempt by humans to land a probe on the surface of an asteroid, collect samples, and then return them to Earth. The craft itself was a testbed for several new technologies, including the [31]ion engines themselves.

But only months after launch, while still en-route, [32]a monster solar flare struck the spacecraft, frying its solar panels, and reducing the power available to the ion drives. The damage wasn't lethal, but the limping probe couldn't reach the asteroid by its scheduled June 2005 date, and instead had to wait until September to rendezvous. Since orbital mechanics demanded that the probe leave the asteroid by November 2005 to reach Earth, the amount of time the probe could spend at the [33]Itokawa asteroid was cut in half.

Image above: As Hayabusa approaches the surface of Itokawa his (Japenese ships are 'he') shadow is cast by the distant sun onto the regolith beneath him. image courtesy of JAXA.

A hard road....:
When the probe struggled eventually into a sun centred station keeping orbit, 20km off Itokawas surface, the probe began mapping the surface using infra red and x-ray spectrometers. But when it tried to launch the coffee jar sized MINERVA lander catastrophe struck: a problem with the spacecrafts navigation sent the little lander tumbling into deep space.
[34]Glitches plagued the mission: A navigation problem left the probe stranded on the asteroids baking surface for 30 minutes, over heating it. A propellant tank began to leak, an onboard battery discharged its power threatening the spacecrafts systems, the sample collecting system malfunctioned, and the probes small chemical engine was catastrophically damaged during a landing attempt.
Some of the malfunctions began to threaten the probes ability to return to Earth: two of the reaction control fly wheels used by the probe to orient itself had jammed, and then the ion engines, one of which was already found to be unstable shortly after launch, began to give out.

The Hayabusa team refused to say die: they compensated for the loss of one fly wheel by orienting the craft using its ion engines and for the loss of the other by inventively using [35]solar sailing. As the conditions of the ion engines worsened the team began a running battle to keep at least two working, eventually resorting to [36]using the undamaged parts of two malfunctioning thrusters together, as one cobbled together engine.
After seven years in space, in a testament to the strength of will and ingenuity of the ground team and the tenaciousness of the little probe, [37]Hayabusa delivered its sample return capsule to Earth on the 13 of June 2010 before being immolated in Earths atmosphere. Japanese scientists are still studying the small amount of material in the capsule to determine if it is indeed material from the asteroid, so stay tuned for news on that front.

Image above: Hayabusa splits open the night sky over the Australian desert, literally going down in flames to bring its cargo home Image courtesy of National Geographic.

A surprising find:

Image above: Itokawa, a rubble pile that should not by rights have been able to form and hold together. Image courtesy of JAXA.


The mission revealed Itokawa itself to be something very different than the image of a single huge cratered rock many were expecting. Itokawa was shown to be a 535m by 209m by 294 m pile of [38]iron and magnesium silicates, and seems to be a rubble pile, made from smaller asteroids which have come together and stuck. [39]The surface is a mixture of broken up rock, pebble and boulders with [40]odd smooth patches, and its density is way to low for it to be solid rock- it must be filled with caverns. This information is vital baseline data for future asteroid missions, as well as any attempt to move or destroy an asteroid on a collision course with Earth. And if even a tiny amount of its surface has been captured we can use more powerful instruments on earth to learn about how this lonely rock and others like it came to be, hence shedding further light on how rocky bodies that went toward building Earth were born.

Recently JAXA has announced that Hayabusa 2 has been greenlighted, and that it will be headed to asteroid [41] 1999JU3- a [42]c type asteroid that may have a history of organic chemistry and alteration by water, so watch this space eagerly!

List of links:
[1]www.esa.int/esaCP/index.html
[2]http://sci.esa.int/science-e/www/area/index.cfm?fareaid=15
[3]http://www.weather.gov.hk/gts/event/event-comet_e.htm
[4]http://starbrite.jpl.nasa.gov/pds/viewMissionProfile.jsp?MISSION_NAME=VEGA%201
[5]http://www.solarviews.com/eng/halley.htm
[6]http://www.organic-chemistry.org/
[7]http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31877
[8]http://near.jhuapl.edu/
[9]http://nssdc.gsfc.nasa.gov/planetary/near.html
[10]http://astroprofspage.com/archives/1508
[11]http://www.nature.com/nature/journal/v436/n7049/full/nature03855.html
[12]http://www.nasa.gov/mission_pages/deepimpact/main/
[13]http://www.planetary.org/explore/topics/asteroids_and_comets/tempel1.html
[14]http://ssed.gsfc.nasa.gov/gunther/gunther/lisseetal2007.pdf
[15]http://www.lpi.usra.edu/meetings/acm2008/pdf/8382.pdf
[16]http://www.space.com/scienceastronomy/051018_science_tuesday.html
[17]http://stardustnext.jpl.nasa.gov/
[18]http://planetquest.jpl.nasa.gov/
[19]http://www.sciencedaily.com/releases/2007/12/071215203737.htm
[20]http://stardust.jpl.nasa.gov/photo/top20.html
[21]http://www.solarviews.com/eng/cometwild2.htm
[22]http://stardust.jpl.nasa.gov/tech/aerogel.html
[23]http://www.space.com/missionlaunches/0601_stardust_archive.html
[24]http://infrared.als.lbl.gov/pubs/Stardust-IR-Science2006.pdf
[25]http://science.gsfc.nasa.gov/691/analytical/PDF/Elsila2009.pdf
[26]http://www.nature.com/news/2010/100303/full/news.2010.106.html
[27]http://www.jaxa.jp/index_e.html
[28]http://www.isas.jaxa.jp/e/enterp/missions/hayabusa/index.shtml
[29]http://www.isas.jaxa.jp/e/enterp/rockets/vehicles/m-v/index.shtml
[30]http://www.planetary.org/explore/topics/hayabusa/facts.html
[31]http://www.bbc.co.uk/science/space/exploration/futurespaceflight/ionengines.shtml
[32]http://www.space.com/scienceastronomy/xtreme_flare_031105.html
[33]http://www.newscientist.com/article/dn9257-rubbly-itokawa-revealed-as-impossible-asteroid.html
[34]http://www.planetary.org/blog/article/00002530/
[35]http://5thstar.air-nifty.com/blog/2009/02/hayabusas-retur.html
[36]http://www.nasa.gov/offices/oce/appel/ask-academy/issues/volume3/AA_3-6_F_outside.html
[37]http://www.universetoday.com/66330/hayabusa-returns/
[38]http://www.spaceref.com/news/viewpr.html?pid=19991
[39]http://www.jaxa.jp/article/special/hayabusa_sp3/index_e.html
[40]http://www.planetary.org/blog/article/00000969/
[41]http://www.lpi.usra.edu/meetings/lpsc2008/pdf/1594.pdf
[42]http://www.planetary.org/explore/topics/asteroids_and_comets/facts.html