Where does Mass Come From? Announcement July 4th, 2012!

On July 4th in Melbourne, Australia, the 5000 physicists of the ATLAS and CMS collaborations from the Large Hadron Collider in Geneva, Switzerland are going to announce their results on the search for a particle that has to do with the origin of mass—the Higgs boson.

In December of 2011, these two giant groups of scientists, engineers, computer programers and support staff, announced their first concrete results on the search for the Higgs boson.  Now, they have about twice the data, and they will be able to make a much more definitive claim.  Scientists and nonscientists around the globe are waiting excitedly for the unveiling of the results.

So what is the Higgs boson?

Imagine a world where everything is like light, able to zip around at 300,000 km/s (186,000 mi/hr).  Light is made up of just one kind a particle, called a photon.  If all the particles were like that, they would be massless.  They would not form into atoms and molecules.  Except for the frequency (color) of the various kinds of light, everything would be much the same.

It turns out our understanding of particle physics is very much like that, except that there is a mechanism which gives the particle mass so most things can't travel at the speed of light, and so they aren't all the same, and they can form atoms and molecules.  That "except" part is all due to a mechanism called "spontaneous symmetry breaking" (never mind the big term for now).  So we have a beautiful theory of lightlike massless particles which is "fixed" to explain the world as we see it by this mechanism.  The theory has been tested backwards and forwards—all of it except for this crucial mechanism.

And that's where the Higgs boson comes in.  The mechanism predicts that this particle must be there.  The trouble is, it requires an enormous amount of energy (on the scale of elementary particles) to make one, and so our biggest colliders have not been big enough to produce it.  Until now.

The Large Hadron Collider is big enough and collides enough particles per second to see it.  If the Higgs is there, as predicted in the simplest model, the LHC should see it and report evidence or even observation of it on July 4th.  If they don't see it (contrary to the rumors), then the simplest model is wrong.

So this July 4th, keep an ear and eye peeled for news about the origin of mass and the Higgs boson.


P.S.: Please never refer to the Higgs boson as the "God particle", a term made up by a PR guy, because it simultaneously insults religion and science. (It's particularly ironic because the Higgs boson doesn't do anything, not even give mass to particles—it is the smoking gun for the mechanism which does.)

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Sometimes It's Just Hay

Last December I wrote about rumors that an experiment called CDMS had found evidence for direct detection of the Dark Matter. I called my post "Searching for Unusual Hay in a Haystack" because the "needle" they were looking for (the dark matter) is so close in appearance to the "hay" (background events) that it is really hard to tell them apart. At the time, I said that it was quite likely that the "signal" of two events was just some background events that happened to look a lot like the signal they were looking for---that they had just found normal hay that looked a little unusual. And I concluded, "So we await future experiments with more signal and less background".

Well, that data has just been published in the journal Physical Review Letters. Here is a nice writeup of the results. In brief, an experiment called XENON100, which is much more powerful than CDMS, was able to take enough data in just its first 11 days of running to basically rule out the CDMS signal (in the plot pictured above, the solid black XENON100 line is below the dotted CDMS line on the left half of the plot, where CDMS signal events were found). Another way to put that is this: if the CDMS signal were real (not just a background fluctuation), XENON100 would easily have seen it. But XENON100 saw nothing unusual.

This is often the pattern on the frontiers of science. There is a hint of a signal, and then it is either confirmed or it is ruled out by a more powerful experiment. Alas, this time it was ruled out. So it's back to waiting for a hint of a signal from somewhere else.

[the plot is taken from the journal article, which is available here]

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Searching for Unusual Hay in a Haystack: The Case of CDMS

Over the past two weeks, rumors have swirled around the web that the CDMS collaboration had discovered particles of "dark matter". [I have not yet written a promised post on dark matter, but there is this.] It all started with a single blog post which contained "facts", such as the statement that there was a paper in press at the journal Nature, which turned out to be false. One very connected person tweeted about the post, and it spread like wildfire. Soon the Nature editor sent the blogger a snarky letter denying the claim, which the blogger posted. Others speculated that the Nature editor was just trying to throw them off track. The next day the Nature editor posted a comment on the blog apologizing for the snarky nature of the letter, but again refuting the claims. Still rumors shot around the net about what result there might be.

So there was much anticipation Thursday when the CDMS collaboration gave two simultaneous talks announcing their results.

I watched a live stream of one of them. It proceeded in a halting fashion from the strain of the web traffic. Then, when the speaker got to the point of announcing their results, the stream froze for ten solid minutes. When it recovered, it zipped straight to her conclusions (how many of you were assuming the speaker was male--come on admit it), and I was left to guess a number of the details. But the bottom line is this: they saw 2 events with a background of 0.8. What does that mean, you ask?

The experiment looked for a very rare signal: that a particle of dark matter, which rarely interacts with anything, leaves a small ripple in the detector. The detector is located at the bottom of a mine to shield it from most cosmic rays. But there are still background events: interactions in the detector from particles which come from radioactive elements in the rock or particles which somehow survive going through hundreds of meters of rock. There are telltale signatures of dark matter particles (such as the energy and timing of the event) which help distinguish them from background particles, but occasionally a background particle mimics those signatures by chance. In the CDMS experiment, they calculate that over two years of running, that happened on average 0.8 times ( it took heroic efforts to keep it this small) . Maybe this helps: if they ran for 20 years with the same detector, i.e. 10 times longer, then they'd expect it to happen 8 times.

Now they saw 2 events. So what is the chance that those events are really signals of dark matter particles? Well, it is easier to ask "what is the chance they are background events?". If you ran for 20 years, what is the chance that 2 of the background events happened in the first two years. Using something called the Poisson distribution, they find that there is about a 1/4 chance those 2 events are both just background events. That's not a strong signal. As good as their efforts were at reducing backgrounds, it was not enough. If there were no dark matter particles and you ran the experiment for 20 years and divided them into ten two year periods, about two or three of those ten periods would happen to have 2 background events in them.

Still, if the events do turn out to be really from dark matter, it will begin to explain one of the great mysteries of science. So we await future experiments with more signal and less background.

UPDATE: Sometimes It's Just Hay

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The Two Cultures

Fifty years ago, C. P. Snow lamented in his famous lecture, The Two Cultures, that there was a rift in understanding  between the sciences and the humanities.  He noted that ignorance of the laws of thermodynamics is akin to never having read a work of Shakespeare, and that such scientific illiteracy could prove harmful to society.  How can our leaders solve our problems if they don't understand them?

So it was with great interest that I went last Saturday (9 May) to the New York Academy of Sciences, at the top of the world, to attended a conference exploring the current state of the Two Cultures and what could be done about it.   There were many fascinating people there.

The 192 year old NY Academy of Sciences now resides in the gleaming new building at 7 World Trade Center.  Forty stories up, there is a panoramic view of Manhattan, and an overlook on the unimproved hole of ground zero.  

Actually, one feels the presence of 9/11 as soon as one steps in the elevator.  Each wall of the elevator is roughly polished metal, so that one's reflection is distorted  as it is bounced back and forth, and one is surrounded by ghostly images.

There were two main topics discussed: the nature of the divide between scientists and nonscientists (both in the humanities and the general public), and what one could do to bridge the gap.

  

E. O. Wilson, the famous biologist, described his idea of consilience, and argued that the walls between fields were illusions because of the interdisciplinary bridges which already exist.  He is a hardcore reductionist who believes that complex sociological behavior can be mapped to chemical reactions in the brain.  On the other hand, the historian Ann Blair argued that having walls between fields was important so they can flourish independently.

But most of the day was spent discussing how to bridge the gap between science and the larger society (such as you, dear reader).   There was a panel on "How to more effectively communicate science issues to the public," with the executive producer of Nova, Paula Apsell, and the host of Science Friday, Ira Flatow.   There was a panel on science and politics with the founders of Science Debate 2008.  And there was a concluding keynote address by Segway inventor, Dean Kamen.  I have to say that I was impressed with his organization, FIRST, which sponsors a robot competition that makes science cool for kids.  In just 20 years, it has gone from a handful of people, to something which won't fit in the Houston Astrodome!

Science is  increasingly important for our society.  For democracy to work in such an environment, it is essential that the average citizen be at least somewhat scientifically literate.  For example, everyone should have some vague idea why a perpetual motion machine can't work (thermodynamics says, "there ain't no free lunch").  So I hope we can all work on bridges of understanding between ourselves.

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Report from the 'April meeting'

Scientific conferences have personalities. They shift locations and take on the color of the locale, but the canvass of a given conference is the same. I write this from a hotel room in Denver, CO, site of my society's annual meeting. It does not matter that it is in Denver, or that it's May, it is still the 'April meeting'.  The April Meeting is not a cozy specialized meeting, nor is it a zoo that the largest meetings become. It covers just the subjects of particle physics, nuclear physics and astrophysics. So it is a chimera of the small and the large, the specialized and the very broad.

There is the same rhythm of expansive plenary talks in darkened ballrooms, and frenzied cryptic parallel session talks in small rooms which either are empty or overfull. There are talks on science and society. There are all the organizational meetings. There are the booths and posters. Yet at 1400 people it feels sparse.

The most exciting results this year are from the Fermi Gamma-ray Space Telescope (formerly called GLAST). Launched in June 2008, it is already changing our view of the high-energy sky. Its main instrument, the Large Area Telescope, or LAT, has made a precise measurement of ultra-high energy electrons and positrons. A previous experiment had shown indications of an excess in number of particles detected, which was hard to explain with known physics. LAT has shown that that "bump" was likely just a statistical fluctuation. Alas, this is what usually happens--most coincidences are actually just coincidences. LAT also showed that there is some new source of high-energy positrons out there, which will surely launch a thousand papers.

Fun anecdote: One of the talks was given by a senior physicist  (he received the Nobel prize for work done in 1964). He admitted that he had a habit of showing data before the large collaboration of which he is a part was ready to release it. After his talk, someone asked a question about the composition of the cosmic rays his collaboration had detected. He excitedly jumped to a slide he'd prepared because he "knew someone would ask that question". He explained that the collaboration would release the data soon, after further analysis, but he'd show the figure now. When the figure popped up there was a big "X" in place of the plot. He was astonished and confused and wondered aloud how it could have happened. Then one of his collaborators raised her hand and admitted to have hacked into his talk. She said, "we knew you might show this but we're not ready to release it yet".   He laughed at being thwarted.

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2008 Nobel Prize in Physics

The 2008 Nobel Prize in Physics goes to two different achieve- ments.  Both relate to symmetry breaking, but in very different ways.  All three recipients, Yoichiro Nambu, Makoto Kobayashi and Toshihide Maskawa, certainly deserved the prize, but Nambu should have gotten the prize years ago, and they should given the prize to Nicola Cabibbo as well—after all it is called the Cabibbo-Kobayashi-Maskawa mechanism!

In brief, this is what they did.

Nambu explained how protons and neutrons could get mass in the same way that superconductivity happens.  If that doesn't sound ground-breaking, I don't know what does!  He showed that a symmetry in something called a quantum field theory can be "spontaneously broken".   

Think of looking down at a pencil from above.  What is the most symmetric way of placing the pencil?  Why on its point!  That way, if you rotate your view, it looks the same.  But of course that is not a stable situation.  The pencil immediately falls over.  Which way?  Well, it goes spontaneously in a random direction.  And after it falls, the situation isn't invariant under rotations—the symmetry is broken.  That is in essence what Nambu showed worked in a quantum field theory—that the most stable state need not be the most symmetric one.

Now on to a completely different topic.  There are three families of quarks: up-down, charm-strange, and top-bottom (yes, these are silly names).  Back when we knew about only two of them, Nicola Cabibbo realized that they could mix together—that if you started a process with a strange quark, there was a chance you could end it with a down quark.  Such mixing is controlled by just one parameter, the Cabibbo angle.  (It's an angle of rotation in quark mixing space.)

A puzzle at the time was how to explain CP violation—the observation that the symmetries of charge conjugation (C, switching + and -) and parity (P, switching left and right) were not actually good symmetries of nature.   In other words, if you took some processes and switched both + and - charges and left and right, you didn't get the same result (trust me, that's odd).

Kobayashi and Maskawa realized in 1973 that if there were a third family of quarks (there is, but no one knew it then), one would get not only other mixing angles, but something called a phase.  This phase was just what one needed to explain CP violation.

In brief, they came up with a mechanism which explained the existing observation of CP violation by proposing that there was a third family of quarks—and lo and behold a third family of quarks was found a few years later!  Come to think of it, Cabibbo, Kobayashi, and Maskawa should have won years ago.

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Is the Large Hadron Collider safe?

The Large Hadron Collider, usually referred to by scientists as the LHC, had its first preliminary test today.  All went well.  But what does the LHC do, and is it safe?

What is the LHC?

The LHC is a "particle collider".  It has two main parts: beams and detectors.  Two beams of protons will be channeled at near the speed of light around a tunnel 27 km in circumference, one clockwise, one counterclockwise, by a pair of rings made of 9000 superconducting magnets.  The beams will cross in several places, allowing the particles within them to collide (hence the term "collider").  The by-products of those collisions will be observed by two enormous detectors (as well as two somewhat smaller ones).  It short, it collides beams of particles and detects what happens.

What is the LHC for?

Physicists have learned a lot about the fundamental constituents of matter by bashing particles together.  The higher the energy scale of the collisions, the deeper, in a sense, one can probe.  We now understand what particles make up all the matter we can see, and what particles are responsible for forces.  For example, as I said in a previous post, we understand about electrons and their siblings (yes, I know I haven't gotten around to doing the followup posts yet), and we understand that the electromagnetic force comes from the particle of light, the photon.  In fact, we have understood how these particles and forces behave in terms of some rather beautiful symmetries.  A symmetry is an invariance, as in "looks the same in a mirror", or "runs the same if you switch all the red and black cables for one another".   A key point is that a symmetry can be broken.  For example, you don't look the same in a mirror.  Even if you part your hair down the middle, there is always some freckle to give away that it is a mirror image.

Our theory of particle physics using symmetries works great, except for understanding why most of the particles have mass.  If the symmetries of the theory were not broken,  these particles would have to be massless.  We need to understand how the symmetries are broken—we have to find the freckles.   The main freckle is called the Higgs boson (please, can we stop using the awful term "God particle"!).  It has never been seen.  We think that is how the electron gets its mass, but we don't know for sure.  And we don't understand how the Higgs boson might fit into a more complete theory.

The LHC is designed to find the Higgs boson, and we hope it will point us to a more complete theory of matter and energy.  It may also shed light on the dark matter, but that is a post for another day.

Is the LHC Safe?

Sometimes the LHC is described as "recreating the Big Bang".  This sort of language is colorful, and conveys the grand nature of the endeavor, but it also makes it sound scary, and, more to the point, is completely inaccurate.  The LHC will probe a new frontier for humans, but the kinds of collisions that will take place in it happen in and around the Earth all the time.  Cosmic ray protons hit protons in the atmosphere and create sprays of particles just like in the LHC.  If you were to wait in one location, it would be quite rare that you would see a collision at the same energies as the LHC, but across the whole atmosphere they happen all the time.  If these collisions were dangerous, they would have done their damage long ago.  

One worry that has been stated in the press is that the LHC might produce mini black holes.  Well, that is a possibility if there are extra dimensions of space that become visible just at the LHC energy scale, but that is unlikely (not quite as crazy as it sounds though).  But such mini black holes would not be like the monsters you may have seen in Sci Fi.  They would be tiny (way smaller than protons) and would decay in a fraction of a second.

Could these mini black holes be stable?  First of all, even if they were, a mini black hole would take hundreds of millions of years to grow appreciably in size in the Earth, so it could not be the doomsday machine some have feared.  But everything we know about the theory says that such mini black holes must decay very rapidly due to quantum processes.   Mini black holes are essentially  just another kind of particle that decays. 

If all of that is not enough to convince you that the LHC is safe, here is a final comfort:  we have seen pulsars.  Comforting eh?  You see, pulsars are like canaries in the coal mine.  They are spinning neutron stars.  Neutron stars are dense cinders of dying stars that just barely avoided collapsing on themselves into black holes (the large kind).  They would feel the effects of a mini black hole much much faster than the Earth would.  They too are bombarded by cosmic rays all the time.  They recreate the LHC experiments each second.  If particle collisions created mini black holes that somehow were stable, all neutron stars would quickly be triggered into collapsing.  We see pulsars, so that can't have happened.

So the LHC is not a threat.  It is just a tool to look for freckles.

An engineer leans on a magnet in the 27km-long tunnel that houses the Large Hadron Collider (BBC News; Image: Cern/Maximilien Brice)

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Ice on Mars!!

On Sunday, I posted that the Phoenix probe uncovered a white substance which might be frozen water, though it could have been a salt.  Turns out it IS water.  The evidence?  Some of it disappeared by the time the next picture was taken--it must have evaporated.  You can see that white chunks in the Sol 20 picture have disappeared within 4 Martian days.   Salt doesn't do that.  So Phoenix has found water ice on Mars!

As I said Sunday, this is the first contact with alien water.  The probe will now look for evidence of the building blocks for life.

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Mars Phoenix Probe Hits White Gold?

The Mars Phoenix probe, which touched down on the north polar region of Mars twenty days ago, has begun digging with its robotic arm.  Dirt from the first scoop was "stickier" than expected perhaps due to moisture?  Where would moisture come from on that dry world?  Scientists chose the polar landing site because orbital imaging indicated that there is ice underneath the surface.  But could it be this close to the surface?  Pictured above is the trench that Phoenix has enlarged.  You can see light patches in the trenches.  They are either streaks of some salt, or water ice--white gold, if you will.  If turns out to be ice, it will be the first alien water we've ever had a chance to study. We should find out very soon. [It IS ice!]

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Mars Phoenix Probe Sees Permafrost Pattern

The Mars Phoenix probe has just landed safely on the polar region of Mars.  The terrain exhibits "polygonal cracking"—it looks like it has been shaped by repeated melting and freezing of ice below the surface.  If Phoenix's digging arm can detect that ice, it would be the first contact with alien water.

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Spy Satellite and Space Junk

The US military just destroyed a spy satellite with a missile strike.  Let's forget, how unlikely it was that the satellite would have hit near anyone if they had just let it reenter the atmosphere on its own.  Let's also forget that this strike was a simple way to make a flawed missile defense system look good (I am sure that the path of the satellite was much more predictable than any real incoming ordinance).  Let's also forget about the worry that the strike could contribute to the militarization of space.  What I want to concentrate on is the possible effect of all the junk that the explosion produced, and the resulting danger to satellites and astronauts.

The photo above shows about 10,000 objects of baseball size or larger in low Earth orbit tracked by NASA.   There are perhaps 600,000 objects  larger than a centimeter which are too small to track.  

Now if that doesn't sound worrying to you, note that objects in such orbits move around the Earth at more than 17,000 mph (27,000 kph), and the energy of an object goes as the velocity squared.  That means being slammed with a 1 kg object at orbital speed involves as much energy as a 60,000 kg 18-wheeled truck crashing into you at 70 mph (113 kph), except that in the former case the energy is concentrated into a much smaller object.  This is what being hit by a tiny object going 17,000 mph looks like:

So how many pieces of space junk did the spy satellite strike create?  Well, it is estimated that the Chinese destruction of one of their satellites in 2007 increased the amount of space junk by about 30%.  

[It is fair to note, as Rampant Clam's Comment points out, that the Chinese satellite was in a more stable orbit than the US satellite, so what the Chinese did was far worse because it created much more long-lived debris.]

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More on Why Asteroid Will Miss Mars

I decided my previous post on the Mars asteroid was not clear enough.  Above is a figure from NASA's Near Earth Asteroid site  from 9 January.  The thin white line with the orange circle on it is the orbit of Mars.  The blue line is the most likely path, which corresponds to s=0 on the bell curve of the previous post.   The bunch of white dots are the possible points of closest approach given the error in the measurements (the path of the asteroid for each dot would be a line parallel to the blue line going through that dot).  

As you can see, the dots are bunched around the most probable value and taper off in either direction—in the same way that the the area under a bell curve decreases away from the center.  s, the distance from the blue line to Mars divided by the size of the error, is 3.7, giving a probability of 10,000:1.

 

Here is what the asteroid figure looked like two weeks ago:

Notice that the scale here is 500,000 km, so this is zoomed out by a factor of 5 from the 9 January picture.  Two things have happened in the fortnight.  First, the position of the blue line has changed a little.  More importantly, the size of the error was a lot bigger two weeks ago.  Back then the error was large enough so that the distance from the blue line to Mars divided by the error was only 2.2, giving a probability of 25:1.

So the probability changed from 25:1 to 10,000:1 over the last two weeks mainly because the error in the path decreased, making  s  increase (again, s is the distance from the blue line to Mars divided by the error, and it is also the position on the bell curve of the previous post).

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Why Asteroid Will Miss Mars

Last month, it was reported that a very small asteroid had a 1-in-75 chance of hitting Mars, which was very exciting.  It would be awesome to see the effects of such a collision.  Then the number was 1-in-25, which was even more exciting.  Now the number has dropped to 1-in-10,000, so it is very unlikely to happen.  How could the numbers change that much?

[see also next post, More on Why Asteroid Will Miss Mars]

Suppose it was your job to calculate the probability the asteroid would hit.  You would take the most accurate measurements of the asteroid, extrapolate its position, and come up with your best estimate of the path for the asteroid.  Now there would be some uncertainty in your estimate for the path.  Let's call s the distance of closest approach to Mars of your best guess for the path.  The plot of  probabilities is given by this bell curve (also called a Gaussian curve):

If you calculated that s=0, that the most likely path just grazes the surface of Mars, then all paths to the right of s=0 would hit Mars, and you'd say that the probability of hitting was 1/2 (half the area under the curve is to the right of s=0).  If you calculated that s=2.2 (which they did in December), then only paths more than 2.2 standard deviations from the most likely path would hit Mars, a chance of 75 to 1 (less than 2.1%).  And if your calculation shifted just a little, so that s=3.7 (the value now), then only the paths more than 3.7 standard deviations from the most likely path would hit Mars, a chance of 10,000 to 1.  It takes only a little shift out on a bell curve to make the probability plummet.   

And so a small refinement in measurements of the asteroid positions made the impact probability... crash.

 

[Notice that I did not put any units on s, because s is really distance/error-in-path-estimation, so that s=1 corresponds to whatever 1 standard deviation is in this case.  We don't need the actual distances in km because we are taking a ratio.]

[image from here, arrows and text added by me (feel free to use)]

[confidence: likely, my qualifications: informed]

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"One small step for man..."

The explorer was getting low on food.  He was in a desolate landscape of sand and rocks.  His lame leg tore a ragged trench as he doggedly dragged it through the sand.  How long could he last?  Would he find the treasure, or would he expire first?  Then he came upon it without warning.   Ironically, it had been uncovered by his lame foot.  There glistening in the sunlight was a streak of "white gold", evidence for an ancient hot spring on Mars.

 

 

 

The explorer is 4'11" tall, weighs 384 lbs, and rides on six wheels.  

It is the Mars Rover Spirit.  It gets its "food" from the sun.  As the Martian sand builds up on its solar panels, less sunlight get through, and it "starves".  At one point recently, a lucky gust of wind cleared its panels, but now they are dusty again and  Mission Managers are unsure whether Spirit will make it through the cold dim Martian winter.  One of Spirit's six wheels stopped turning in 2006, so they have had to drive it backwards through the sand since then.  The "lame leg" digs a trench wherever it goes.  It just happened to uncover a patch of white silica, the stuff of window glass.

 

The NASA Press Release states

 

"It could have come from either a hot-spring environment or an environment called a fumarole, in which acidic steam rises through cracks. On Earth, both of these types of settings teem with microbial life."

 

This was originally announced in May of 2007, but the conclusion has been bolstered by the finding that a rock called "Innocent Bystander" has an interior rich in silica and is probably thus a siliceous sinter.

 

While I am fascinated with these hints that ancient Mars may have been more hospitable to life, that's not what I wanted to stress in this post.  I anthropomorphized Spirit to make a point.  We respond viscerally to humans meeting challenges.  (Actually, the public was quite interested in the Mars rovers when they landed, which surprised me.  But that interest has faded.)  If there were a human whose survival on Mars was in doubt, it would be the top story on every news outlet (and rightly so).  If a human had dug up the silica, we'd be hearing all about her personal history and idiosyncrasies. 

 

Humans are also much more adept than a robot in a setting, like Mars, where autonomous actions are required.  A human could probably do the work the rovers have performed in a few days.

 

BUT, human space travel is very expensive.  It would cost many, many more times the rover program to get a human to and from Mars (perhaps as much as a few months of the Iraq war).  When the human part of the space program is expanded, other programs suffer, and there is often less science done.

 

Further, robotic vehicles are becoming more and more sophisticated.   They may be all we need to accomplish our scientific goals.

So, until we are willing to commit the resources for both an intensive robotic science program and an expensive human space flight program, I think we should concentrate on sending robots, not humans. 

 

[confidence level: likely,  my qualifications: informed]

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