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Being Busy
Wow it has been almost 5 months since my last post!  Really sorry to all those who have been checking during this time and finding no updates at all :/  I have been really really busy with various things, perhaps too busy for my own good. 

Among the many things that I got involved in is a SEDS trip up to Mt. Wilson Observatory.  It is nice to see a different observatory after being to Palomar back in Ay20, and Mt. Wilson probably has a much richer history.  It is unfortunate that we had to rush off that day, partly because of transport problems.  The most interesting thing for me is when I found out they use the Zeeman effect to measure the strength of the magnetic field in the Sun, and it just happened that I did an experiment on Zeeman effect for my Ph7 lab course just a week ago!  For those who have not heard of it, the Zeeman effect is essentially a change in the energy levels in atoms due to the different magnetic moments of the electrons.  Thus in the presence of a magnetic field, originally equal energy levels (degenerate) will no longer be equal due to their different orientations in the magnetic field, causing the spectral line to split.  The degree of splitting is linearly related to the magnetic field. 

Another interesting project that I have been involved in is the RASC-AL Exploration Robo-Ops Competition.  This is a national competition bringing together teams from various universities to build a working rover that will roam the rock yard at Johnson Space Center.  It has really been an eye-opening and enriching experience for me, especially as someone coming from a more scientific background.  I learnt how to use the various machines in the ME prototyping shop, some basic design principles, how motors and servos work among many other things!  The competition will take place later this week, and I have just sent off the three to Houston this morning (the rest are staying back here in Caltech where we remotely control the rover).  Really excited about the competition. 

I haven't really been able to read up some of the papers that I found online about various things (I downloaded a paper on the origin of Iapetus's equatorial ridge a few months back but never got the chance to read).  Life will be much less busy after this term ends, and then I will start my SURF with Mike Lamb studying waterfalls.  Also looking forward to that. 

On the Dark Side
I am back from my month-long hiatus due to finals and winter break!  School just started this Wednesday, and it looks like this term I would not be taking courses that are too unusual: just my last term of core math (Ma2b), my physics core Ph12b and Ph6 lab, computational math ACM95b and my philosophy Pl151 on Immanuel Kant. 

As I mentioned, I started this blog partly for my Ay20 class, and also because I want to share with the world my experiences as I walk down this path towards my dual Physics and Planetary Science majors in Caltech, and also beyond to my life as a graduate student and eventually starting my career wherever I may end up.  It would be interesting I think for readers further down the path than I am to look back on my experiences and perhaps see parallels to their own (and perhaps just leave a comment!), and also for readings behind me to see the challenges I face and how I managed to (or fail to) overcome them and anticipate these same challenges in their own futures. 

Anyway, the end of the Christmas-New Year holidays means the start of start of a whole bunch of astronomy-related events.  I attended an Astronomy Colloquium about dark matter by Annika Peter from UC Irvine yesterday and although I admit I perhaps understood less than half of what is said, I shall attempt to present what I have learnt, hopefully in a manner that would be understandable and interesting for non-astronomy readers. =) 

And before I start, I would like to say that it is perfectly okay to not understand things.  No one completely understand something he is exposed to for the first time.  As my Ph12b professor said today concerning quantum mechanics but actually applies to everything, the first time you read about it you probably would go what on earth is this guy talking about.  The fifth time you learn about something you start to get the general idea how it works, and you only start to really appreciate what it is about after having gone through it twenty times.  Personally, I find that the best way to learn something is just to immerse yourself in it, to throw yourself into the deep end of the pool and figure out your way from there.  And one way to do this is to attend real technical lectures. 

So dark matter came about as the solution to a missing mass problem for galaxies.  Essentially, the matter that we can observe using light ranging from radiowaves to gamma rays does not seem sufficient to provide the gravity required to hold galaxies together.  So astronomers suggested that there is a class of matter that we cannot see (hence dark) that contributes the additional gravitational force.  This hypothesis was floated in 1934 by Fritz Zwicky (a Caltech professor!) and since then astronomers and physicists have been trying to characterize this mysterious dark matter. 

Much progress has been made since then, but we still are pretty much in the dark about dark matter.  Dark matter makes up about 24% of all mass-energy in the universe (Einstein suggested that mass and energy are essentially equivalent and related through his famous equation E=mc^2).  Current models of how baryons (particles such as protons and neutrons) are formed since the Big Bang give a baryon density that could still not account for all the mass.  This leads to the conclusion that dark matter is mostly not baryonic in nature (baryonic dark matter makes up at most 1/6 of all dark matter).  Furthermore, we also know that dark matter is electrically neutral (hence they do not interact with electromagnetic waves or light), dark matter is relatively stable in the sense that they don't decay quickly on their own, and they form small, dense structures. 

Methods to characterize dark matter tend to fall under two approaches: the particle physics approach and the astrophysics approach.  The particle physics approach involves investigating dark matter using known particles (what particle physicists call the Standard Model particles, or the whole array of particles that is thought to make up all known matter today).  We can look at how dark matter interacts with these Standard Model particles, how dark matter interacts with itself to produce these Standard Model particles, or how these Standard Model particles can interact with each other to produce dark matter.  Important characteristics for investigation include the energy distribution of the dark matter particles, their mass and cross-sectional area (here cross-sectional area is pi multiplied by the square of the distance from the center of the particle at which it would interact with another particle).  Although a lot of effort has been spent in this approach to understand dark matter, it seems like the experiments conducted so far returned either negative or inconclusive results. 

The astrophysics approach involves simply observing through telescopes and studying through numerical simulations how dark matter behave out there in space.  Dark matter "candidates" are generally classified according to its energy level into cold, warm and hot.  The most popular candidate today is the low-energy cold dark matter, especially in the form of weakly interacting massive particles (WIMPs).  Such cold dark matter is favored as they would theoretically be able to resolve the outstanding problems about dark matter, and they also arise "naturally" from the various cosmological models we have today.  Numerical models of WIMPs and another candidate, Self-interacting Cold Dark Matter, are able to produce large and small scale structures similar to those observed.  There are certainly other candidates, such as axions, but interest and correspondingly funding has been low and thus not much work has been done on them. 

Chaotic Terrain in an Icy World
Earth is unique.  However, as we move out to explore and understand other worlds, we have to have some starting point.  These worlds may look very different from our home planet, but physical laws (should) apply universally, so it isn't too unreasonable to put out our best model based on the most familiar planet to us in a first step to understanding these exotic alien worlds. 

Comparative geology is exactly about this.  We see an interesting feature on say Mars, then we look for a similar feature back here on Earth.  Perhaps the processes that gave rise to both features are similar?  We cannot study Mars readily (on a side note, go Curiosity!), but we definitely can just walk out on Earth and study it as much as we want, then go back to our computers and figure out a model that takes into account the differences between Mars and Earth. 

A team of scientists did exactly that for Europa.  Europa, the smallest of the Galilean moons around Jupiter, has a relatively young surface (result from crater counts - older surfaces have more craters) striated by cracks, suggesting recent resurfacing events.  Its orbital characteristics suggest a liquid layer just below the surface.  Given the composition of Europa, this is very likely water, kept in the liquid state due to tidal flexing as the moon goes around Jupiter in a slightly eccentric orbit, resulting in varying stresses due to gravity at different parts of its orbit. 

It now seems natural that the authors of a recent paper in Nature drew their inspiration from processes occurring in the glaciers of Iceland and Antarctica to explain some chaotic terrain (a term scientists often use for phenomena they cannot explain on first sight) they found on Europa.  Specifically, they tried to explain the geomorphology of two regions: Conamara Chaos (8 N 274 W) and Thera Macula (46 S 181 W).

Conamara Chaos (left) and Thera Macula (right): Warmer colors indicate higher features (Schmidt et al.)

Using images taken from two different angles from Galileo, the authors were able to create topographical maps of the areas.  As can be seen above, these areas have very small features rising and dropping below the mean elevation in green.  They suggested the following mechanism:

4-Step Process to Forming Chaotic Terrains

Thermal plumes are not unusual, whether on Earth (in hotspots such as Hawaii) or on Europa.  Such a rising thermal plume compresses the ice above it, and the additional pressure melts the ice (water is different from many other substances in this way), resulting in a melt lens.  The smaller volume occupied by the liquid water results in sinking of the surface (b).  This process is similar to what occurs in glaciers on Icelandic volcanoes, where the melt lens is created by an increase in temperature due to volcanic activity rather than an increase in pressure due to a thermal plume.  In fact, such lens-shaped subglacial lakes in Iceland are known to exist. 

Now we turn to Antarctic ice shelves.  Seawater can enter ice shelves through cracks and percolate for tens of kilometers, reducing their shear strength and causing them to fracture.  Thus here on Europa, the authors hypothesize that a similar process occurs, causing the ice above the lens ("plains material") to fracture and the brine from the melt lens to seep upwards.  The brine and lens then refreeze, resulting in the observed swelling matrix of domes.  At Conamara Chaos, the entire terrain is raised, corresponding to the last phase of the process.  However, at Thera Macula, we still see blocks of plains material above the average elevation, against a topographically lower surface due to the brine, corresponding to phase c. 

The authors also pointed out that the size of the blocks of plains material can give an idea to the depth of the liquid water in which they formed (ie the depth of the melt lens) by considering their tilt and stability.  In this way they were able to conclude that the lens occur at 3 km below the surface for Thera Macula. 

From Afar
One of the considerations that has always been at the front of my mind is the dilemma between pursuing a career in astronomy and being able to be permanently back in Singapore.  Having spent more than a year now here in the US, I feel that Singapore is still the better place for starting a family due to the easy access to educational opportunities for the first few years.  However, at the higher levels, opportunities there become much more restricted due to limitations in resources, and astronomy with its lack of clearly tangible economic benefits is very much neglected in Singapore. 

But that is quite a while later, when I have finished my undergraduate degree here and perhaps also have gotten my PhD.  I have always taken for granted that I have to go all the way to that if I want to go into academics and research.  And it just happens that last week was registration for next term's courses, and so I met up with my two (yes two ^^) advisors and talked to them about what lies ahead of me. 

Caltech has often been amazing in that you can throw a stone and perhaps hit someone who is a heavyweight in his field.  When I found out that my Physics advisor was Ed Stone my jaw dropped.  Yes, Ed Stone, project scientist for the Voyagers and former director of Jet Propulsion Lab (JPL).  My Planetary Science advisor is younger (and as a result not as well-known).  Bethany Elhmann got her PhD and did her postdoc at Brown before coming to Caltech as an assistant professor. 

Ask me a week ago what exactly is meant by that last line I wrote, and I would probably struggle for an answer.  What is a postdoc or an assistant professor?  That was one of the questions I asked both of them. 

So assuming everything goes well, I will get my undergraduate degree.  If I choose not to perhaps go around the world (or to one particular exotic place) for a year or more, I can continue with my graduate degree or go out to some research institute.  For the latter, probably I will be a research scientist in a team.  Going the graduate school track I will probably get my PhD in 3-4 years, after which I can again choose to go out to the research institute or continue as a postdoc.  Should I choose the former, it will almost be the same as only having an undergraduate degree, only that I will have a more senior position and correspondingly higher pay. 

Postdoc is a transitional period, as Bethany put it, and usually lasts 3 years.  It is a time when you learn a new area that is related to what you did for your PhD, and essentially is a waiting period before you take up a more permanent job as a research scientist at a research institute or as an assistant professor at a university.  My time as an assistant professor will also be limited.  After about 5 years there will be a review that will take into account what my colleagues in the field think about my work.  If the review turns out bad, I will have to go elsewhere, otherwise I will be promoted and given tenure as a professor. 

What is the difference between going to a research institute and doing research at a university as a professor?  At the research institute, it is less likely that I will be the one leading a team, and even if I am, my area of research is likely to be determined by external factors such as by contracts or by the direction of the institute.  However, there is perhaps less job security due to a lack of the tenure and your research institute may unfortunately close down if it is private due to funding issues (this would be rare for a university).  At the research institute my life will be more about research, without my attention diverted to other responsibilities such as teaching, being on various administrative committees and, as both my advisors remembered to point out, advising. 

How important is it to be physically around colleagues in your field?  Bethany replied that it is just convenient to walk down the hallway to ask Dave Stevenson a question instead of sending a email and waiting several days for a reply.  However, Caltech is unique in that it is rare to have such a large planetary science department.  In other places, it (or the entire astronomy department) may be much smaller, and you will be the only authority around for your field there.  Wherever you are, you also have to travel to conferences, and being in Singapore perhaps just add 10 hours for each flight to and from.  But technology is improving.  I remember how Rob Phillips conducted one of our Bi1x classes via Skype. 

Research is exploration.  True that exploration is cool that you will find and see things no one has seen before, but it is cooler to be able to share it with others.  Research at research institutes does not have as much of the "cozy scientific community" feeling.  And I like teaching, to light this fire in people and to guide them.  Opportunities in Singapore may not be abundant for astronomy, but definitely at least one person will be needed for variety, and it could be me, that is if I am good enough.  In that position, I will become the bridge to expose my students to opportunities available elsewhere through the colleagues I work with, and being the only one, I am perhaps less "dispensible" than the rest?  I may also end up being well-known, but I am not sure if that is what I want. 

But the pressure will certainly be on. 

The Path Forward
Astronomy is unique among the sciences.  It is perhaps the oldest science, playing an integral role in the cultures of ancient civilizations.  Today, just as it has been through human history, astronomy is the science that is most relevant to our lives, the most accessible to us.  We can perhaps not be aware of how levers work, that when you heat water it vaporizes, or how plants would die if you deprive them of water, but we will always be aware of the blazing Sun in the afternoon and the starry sky at night, punctuated every evening by a beautiful sunset. 

Accessibility means that even today, the ordinary layperson can in fact be crucial to advances in astronomy.  You don't need a billion-dollar particle accelerator that spans the border of two countries, or a strange-looking machine which you put something into and display some squiggly lines on a screen.  You can easily get a telescope in your backyard for less than $1k, but that is not even necessary.  To be an amateur astronomer, you would need just your eyes. 

In 2010, an amateur discovered a storm in the Northern Hemisphere of Saturn, and only after that were there observations by the Cassini spacecraft.  Also in 2010, a British amateur captured the breakup of the icy nucleus of comet C2007 C3 as it approached the Sun.  Another British amateur Tom Boles holds the record for discovering more than 120 supernovas. 

Then what does a professional astronomer do?  Many amateurs are in fact very informed in the field, perhaps the only difference is that they are not full-time.  Are professional astronomers merely people who are paid to periodically publish journal papers and once in a while lob a telescope into space?  Perhaps I am putting down the professional astronomers - there are certainly large fields, such as X-ray astronomy,  that are generally inaccessible to amateurs. 

My Summer Undergraduate Research Fellowship (SURF) project saw me working on Cassini data under Andrew Ingersoll and Shawn Ewald.  Certainly I learnt a lot about atmospheric dynamics and IDL (I still find it a sloppy language), but what is most interesting is that I saw the breadth of options open to a Physics graduate who wishes to go into academics (of course there is always finance, or the dark side as the joke goes).  Andy is perhaps the stereotypical professor leading various teams working in different research areas, and collaborating with other professors like himself from other universities to contribute various instruments for spacecraft.  Shawn, however, seemed more like a programmer.  In fact I was surprised at first when I found out he was also Physics trained.  His role is simply to process the data from the spacecraft, and pass it on to the various research teams.  He hardly does any theoretical studies or attempt to interpret the data he handles. 

I often like to cite Michael Malin as another person whom I would not have guessed to be a Physics graduate.  He graduated from UC Berkeley with a BA in Physics, and came to Caltech to get a PhD in Geology and Planetary Sciences.  After 11 years of teaching at Arizona State University, he set up his own Malin Space Science Systems devoted to building camera systems for spacecraft.  Notable contributions include the Color Imager on board the Mars Reconnaissance Orbiter, the Mars Science Laboratory Mastcam, and the Mars Orbiter Camera on the now lost Mars Global Surveyor.  It would seem that he has a stable job after getting his professorship at Arizona State University, but he left that job to enter industry.  Perhaps he felt he could accomplish much more with more funds available outside the university?  It would be interesting to find out. 

Which brings me to the latest assignment we have for Ay20.  I look forward to all the interviews with various people, and have my eyes opened to the options that lay before me. 

On a somewhat related note, I once again realize that I know next to nothing about building stuff.  I took part in Caltech Space Challenge, and was exposed to the design process which seemed so natural to the engineers present there.  I thought perhaps the reason why I was kinda clueless was that I was the most junior there.  Last Friday I held a meeting for a rover building competition, and I had to ask someone next to me what CAD stands for.  And this time, most of the engineers in the room were freshmen. 

Being able to build an instrument and then fly it in space would be really cool, but looks like I have a long long way to go. 

And for all the other scientists out there who are as ignorant as I was, CAD stands for computer aided design.  I still don't know how the process work though. 

...And More Water
Another Herschel paper about water!  This time from Science and just a few days back.

And this time it is from outside our solar system, around the 10 million years old TW Hydrae.  Michiel Hogerheijde and his team reported findings from the Heterodyne Instrument for the Far-IR spectrometer (HIFI) on the Herschel Space Observatory.  They measured the amount of water in the 196-AU radius dust disk around TW Hydrae.  Making use of a single model based on previous observations (rather than two in the previous study), and playing with various gas-to-dust ratios, they found an equilibrium column of water vapor throughout the disk from 100 to 196 AU with an abundance 0.5-2 x 10^-7 relative to H2.  Above the layer closer to the star, the water is photodissociated, and below the layer, little photodesorption occurs and the water is frozen out. 

The detected water vapor suggests an ice reservoir.  According to the authors, this reservoir lies in the giant planet formation zone.  100-196 AU in our own solar system will place us in the Oort cloud, certainly not where Jupiter and Saturn were formed.  TW Hydrae is a 0.6 solar mass star, and I would actually expect this giant planet formation zone to be even nearer than that for our own solar system. 

Anyway, they also determined the ortho-to-para ratio (OPR) based on the two spin states of water vapor.  They found a OPR of 0.77, much lower than the OPR of 2-3 found in solar system comets.  The associated spin temperatures are 13.5K and 20K.  This spin temperature may reflect the actual temperature of the originating grain, but the effects of photodesorption on the OPR is not well understood.  For comets, the OPR does reflect the actual temperature, and is also supported by similar spin temperatures of NH3. 

Linking back to the previous paper, this work opens a window to where water is in the formation stages of a planetary system.  Translated to our own solar system, this water would have existed where the Oort cloud currently is, and where, as mentioned, many comets originate.  However, as pointed out in the other paper, water on Earth may have originated from sources closer to the Sun, and it would be interesting but difficult to determine the variation of water content going closer to the star (due to the huge signal from the star itself). 

Finally I have the time to sit down and read through some science papers.  So the first was published about two weeks ago on results from the Herschel Space Observatory. 

Water on Earth has long been hypothesized to originate from impact events from asteroids and comets after the Earth has cooled.  However, properties of asteroids and comets span a huge spectrum, and it is still not known which kinds of asteroids/comets contributed to our water and where these bodies originated.

A commonly studied parameter that offers some clues to this puzzle is the deuterium-hydrogen ratio of the water.  Earth has a ratio of about 1.558 x 10^-4.  Measurements of Oort cloud comets gave a ratio of 2.96 x 10^-4, while carbonaceous chondrites (asteroids with high carbon content that are believed to have delivered volatiles to the Earth) had a ratio of 1.4 x 10^-4.  These results, together with numerical simulations, suggest that about 10% of Earth's water probably came from comets, with the rest from asteroids. 

Paul Hartogh and his team presented in the paper results from Herschel observations of the Jupiter-family comet Hartley 2.  They found a D/H ratio of 1.61 +- 0.24 x 10^-4, much closer to Earth's value than the Oort cloud comets and the C-type asteroids. 

The measurement of the ratio is not straightforward though.  Most of us students who haven't done remote spectroscopy are probably more used to putting the sample into the spectrometer and then applying Beer-Lambert's law.  Here, we have to somehow figure out the column density (and we don't have a 1cm x 1cm cuvette), the excitation modes, and production rates.  This is where the models come in, and there is often not one best model given all the uncertainties.  So the team eventually obtained their D/H value by using two models with a total of 6 different sets of parameters. 

The paper explained that the D/H ratio is very sensitive to temperature.  Ices far from the Sun are enriched in deuterium due to non-equilibrium chemistry, however, the temperature rise going towards the Sun allows isotopic exchange reactions that lead to a decrease in deuterium content (as we can see from comparing Oort cloud comets and asteroids above).  The D/H ratio is then preserved when the ice is captured by planetesimals or cometesimals, thus a good indicator of where the body originated.  The intermediate D/H ratio of Hartley 2 seems to suggest it may have originated closer to the Sun than the Oort cloud comets, perhaps the Kuiper belt.  However, the D/H gradient from the Sun is still poorly characterized, with a total of less than 20 data points from comets, asteroids and planets.  Nonetheless, the discovery of a D/H ratio on a comet close to that of the Earth's oceans gives a third source for the water on Earth after Oort cloud comets and carbonaceous asteroids. 

New ESA Missions
The European Space Agency (ESA) has chosen two medium class space missions to launch in the future as part of the Cosmic Vision 2015-2025 Plan.  This Cosmic Vision Plan lays out the goals to be achieved in the next decade, serving to provide the stability needed for activities which typically take over two decades to go from initial concept to the production of scientific results (unfortunately such stability is something that NASA lacks, given that its goals have a tendency to shift with every new administration.  Case in point, Constellation program).  The Cosmic Vision Plan includes 3 M-class missions, with a cost ceiling of 470 million euros, and a L-class mission with a cost ceiling of 900 million euros. 

The first M-class mission, Euclid, will be launched in 2019 to the L2 Lagrangian point (where it will be pointing away from the Sun).  It is a 1.2m telescope with three instruments. 
1. Visible light CCD down to 24.5 magnitude sensitivity
2. Near-IR photometer in J, Y and H bands for observing galaxies
3. Near-IR spectrometer for looking at galaxies

It will conduct a survey covering 20000 sq degrees of the of the sky, about half the sky not covered by the Milky Way, and also a 40 sq degree deep field.  It seeks to use gravitational lensing to map the distribution of dark matter and characterize dark energy in the universe. 

The second mission is the Solar Orbiter, launching in 2017 to as close as 60 Sun radii to perform in situ and remote measurements to study solar wind plasma, energetic particles, the magnetic field and the solar dynamo.  It will carry
1. Solar wind analyzer
2. Energetic particle detector
3. Magnetometer
4. Radio and plasma wave analyzer
5. Polarimetric and Helioseismic Imager (I am not sure how one can learn solar seismology from imaging)
6. EUV full-Sun and high-resolution imager
7. EUV spectral imager
8. X-ray spectrometer/telescope
9. Coronagraph
10. Heliospheric Imager

The difference in the number of instruments between the two missions is pretty glaring.  The NIR instruments on Euclid would possibly require a liquid helium cooling system (otherwise noise caused by the heat from the electronics would overwhelm the signals).  Furthermore, the large mirror would jack up the cost.  Comparatively, Spitzer Space Telescope (with a diameter of 0.85m and also 3 similar instruments) cost 540 million euros (720 million USD).  While the Solar Orbiter is the first to be such close to the Sun, it would have heritage technology and instruments, especially from the MESSENGER mission to Mercury.  The Solar Orbiter will be about 90% closer to the Sun than MESSENGER, meaning that it will be getting about 20% energy from the Sun.  Clearly, as the mission designers assumed, a decade would be sufficient to develop the cooling system for the Solar Orbiter, planned to stay at least 7 years around the Sun. 

SpaceX Reusable Falcon 9

Looks really cool eh?  Reusability will definitely lower the cost of spaceflight by a lot, and the technology will make it easier to launch spacecraft into space (perhaps the envisioned fuel depots in LEO for deep space missions?)  SpaceX CEO Elon Musk has predicted earlier that the cost of a Falcon 9 flight will come down to as low as $50k.  That is 10 tons of payload to LEO.  In comparison, the Russian Soyuz rocket launches 7 tons to LEO, with the launch vehicle each costing 400 million rubles ($12 million USD).  For each seat on the   Soyuz NASA pays Roscosmos about $56 million.  So if we use the same scaling factor (which would be on the high side due to the minimal competition in man-rated launch vehicles), we end up $200k for a seat on the Dragon. 

Which is still on the high side for an average person.  I still believe though that just as plane flights were exorbitant in our grandparents' days and hardly so now, spaceflight would be cheap enough in my lifetime for me to go up at least semiregularly. 

The Small Rocks Around Us
Weekend!  Which means I finally have the time to put up another entry or two. 

What a month for near-Earth asteroid studies!  First there was the Caltech Space Challenge, where undergraduate and graduates from all over the world came together to study a manned sample return mission from a near-Earth asteroid/object (NEA/NEO).  Then this week was the start of a professional workshop to study moving a small asteroid to a the L1 Lagrangian point (Lagrangian points are locations in a two-body system (say Sun-Earth) such that any body at that location will remain stationary in the Earth's rotating frame), where it can then act as a staging area/refuelling station for missions into deeper space.  Asteroids at Lagrangian points are not new - we have known of the Jovian Trojans, and just recently the Wide-Field Infrared Survey Explorer (WISE) spacecraft found an asteroid at Earth-Sun L4.  (http://blogs.discovermagazine.com/badastronomy/2011/07/27/wise-finds-the-very-first-earth-trojan-asteroid/)

Source: Wikipedia

So the workshop began with a public panel discussion organized by the Keck Institute of Space Studies (KISS) and the Planetary Society (TPS) right here in Caltech Cahill Hameetman Auditorium.  The discussion was moderated by Lou Friedman, the co-leader of the Keck Institute Asteroid Retrieval Mission Study (ie the workshop I was referring to) and the former Executive Director of TPS, and the panel included Rusty Schweickart, former Apollo astronaut and Chairperson of the B612 Foundation (a private organization to protect Earth from asteroid strikes), Tom Jones, former shuttle astronaut, John Lewis, planetary scientist, and Bill Nye, the current Executive Director of TPS. 
The discussion started with Rusty explaining the hazard posed by asteroids.  Asteroids impact events at the Tunguska scale have a period of several hundred years, more than the typical lifetime of a human and thus it may feel "remote" to some people.  Nonetheless, asteroids present a natural hazard that can be predicted many years in advance, and mitigation measures can be taken.  These measures can be classified into two kinds: civil defense (ie to run xD) or to deflect the asteroid by some means, perhaps by kinetic impact (send an impactor hurtling into the asteroid) or by gravity tractor (send a spacecraft near the asteroid to pull it off course by mutual gravity).  He pointed out that both technologies are in fact available now, and should there be an asteroid coming towards Earth, what is stopping us from doing anything would mostly be politics.  The uncertainty in the orbit of the asteroid, the deflection method and possible unintended consequences would lead to long discussions that may delay any action before it is too late.  He gave an example.  Say an asteroid is believed to impact the Earth with its landing eclipse centered in the Atlantic Ocean but spanning from the US to Russia.  Should we slow the asteroid (ie move it to the West) or speed up the asteroid (move it to the East)?  What if the deflection attempt is aborted halfway, and the asteroid is insufficiently slowed down, and thus its landing eclipse is squarely over the US and not off the planet as intended?  Deflection of the asteroid off its orbital plane would be ineffective, resulting in mostly a cyclic motion about its original orbit.

Rusty then gave the example of the asteroid 99942 Apophis, which will pass close to the Earth on 13 April 2029 2100 UTC.  At this close pass, the Earth's gravity will change the orbit of the asteroid.  This change may in fact result in the asteroid orbit intersecting with Earth's orbit, and lead to a future impact.  Such narrow windows have been termed "keyholes".  Fortunately, Apophis is not expected to go through any keyhole in its 2029 pass, but it highlights the threats we have due to the NEA around us.

Source: Rusty's Presentation

Tom Jones proceeded to talk about mission to study asteroids.  The complexity of any manned mission and the uncertainty with the topology and spin characteristics of the asteroid requires robotic scout missions.  Studies of the radiation environment shows that radiation effects of staying 180 days in deep space do not have too adverse effects on the astronauts, and Tom also outlined various technologies that can be used (e.g. jetpacks (Manned Maneuvering Units), ropes and exploration vehicles).  Such technologies can be tested on the International Space Station (ISS), and perhaps since not all components of the ISS expire by 2025, some components can be reused instead of being sent to burn up in the atmosphere. 

Credit: NASA
John Lewis took a different approach, describing asteroids as places of opportunity for science and resources.  Not only are asteroids made up of primitive material from the formation of the solar system, they also have abundant resources.  Carbonaceous (C-type) asteroids have 6% organic matter and 10% water, useful for sustaining astronauts and also as a source of fuel.  He pointed out that the smallest known asteroids contain more metals than what has been mined on Earth so far, and that NEAs, with their orbits going out to the asteroid belt, can serve as traveling hotels for astronauts to hitch a ride to further destinations. 

Bill Nye then suggested other interesting ideas for asteroid deflection, including the use of a swarm of small small satellite equipped with mirrors, cutely named "Mirror Bees", to deflect the asteroid using radiation pressure. 

Thursday also saw the release of new results from the WISE mission (NASA news conference here).  While originally designed to look at cool stars, WISE has turned out to be very useful in searching for asteroids in our solar system.  The low temperatures of the asteroids make it easier to observe them in IR (Wien/Planck's law), but apparently IR observations also give a more accurate measurement of the size of the asteroid. 

Credit: NASA/JPL-Caltech
I am not so sure how this works though.  True I can understand why chalk will appear much brighter than charcoal in optical and perhaps of similar brightness in the IR, but certainly IR is not any more special from optical and minerals/molecules can appear very different in IR too.  A direct conclusion that a brighter objects in IR means a larger object seems as naive as a similar conclusion in optical.  Perhaps someone can enlighten me about this. 

Nonetheless, WISE completed a one-year survey of the sky, cataloging more than 90% of NEAs with diameters greater than 1 km.  While the estimated number of asteroids agree with the number detected at this size, there seems to be about 40% fewer asteroids at smaller diameters than previously expected as estimated from WISE data. 

Credit: NASA/JPL-Caltech

While the smaller number of estimated asteroids may mean that Earth may be safer than we originally thought, we have to remember that it does not take that large an asteroid to devastate large areas on the Earth.  Meteor crater was due to an asteroid ~50m across, and the line of "?" for that size category in the chart above is certainly not very comforting. 

Asteroid studies have just started.  There are new discoveries every day, but they merely highlight how much we do not know about them.  As Rusty pointed out, the understanding of these NEAs and an ability to manipulate them would be an "entrance exam" into the league of space-faring civilizations.  It is only in this way that we can take the first step in protecting our survival as a species against threats from space.