Thursday, December 16, 2010

Donald Mount Hunten 1925-2010

One of the leading planetary scientists of the Space Age, Prof. Donald M. Hunten of the Lunar and Planetary Laboratory of the University of Arizona, has died of a stroke at age 85.

I have known Don since 1967, when I was still a graduate student in La Jolla. Don, a refugee from Canadian winters, was already well established in the field as a professor at the University of Arizona. He had arrived there in time to join the fledgling Lunar and Planetary Laboratory at its inception, in 1964. His work to that point had centered on the chemistry and physics of Earth’s auroras.

By the time I met him, planetary exploration by spacecraft was under way, and Don had broadened the scope of his research to include the upper atmospheres of the planets. He focused on the interaction of the Sun with the outer fringes of planetary atmospheres; I worked on the chemistry of atmosphere-surface interactions at MIT. Our overlapping interests led to us serving together on a number of NASA advisory committees and on advisory panels of the National Academy of Science, spanning the exploration of Venus and the giant planets, including the potential role of entry probes on the planets and Titan.

Don was a no-nonsense researcher with a keen critical sense; he was always a font of ideas and a hard worker, a researcher whose work merited membership in the prestigious National Academy of Science. Those who got to know him well found a deeper and richer persona: a bassoonist in various groups in Tucson with a deep love of classical music; someone endowed with a sense of humor that merged British and American sensibilities; a respected and successful mentor of generations of outstanding graduate students. I look back on our 43 years of professional interaction and personal friendship, 30 of them as colleagues at LPL, with gratitude for having known him.

I extend my sympathies and condolences to his wife Ann Sprague and his family. They may take some solace from knowing that his professional legacy and his “second family” of students will carry on the work he began and loved.

The Solar System is no longer the limit

Voyager 1 was launched in 1977 on a mission to fly by Jupiter and Saturn. Barring damaging encounters with cosmic dust or Saturn’s ring debris, Voyager was expected to last a few years, after which the slow decay of its radioisotope power supply would make its radio transmissions inaudibly faint. That was then.

This is now: radio detection technology has advanced more rapidly than Voyager’s transmissions have faded. Now, 33 years after launch, Voyager 1 is still on line. It is now operating 17,400,000,000 kilometers from the Sun, nearly three times as far away as Pluto, receding from us at a rate of 17 kilometers per second. Its signals take 16 hours at the speed of light to reach us. Its instruments have monitored the outward rush of the Solar Wind since launch, but now it is so far from the Sun that the interstellar medium is getting in the way. The Solar Wind sweeps out an immense “bubble” in the interstellar plasma, within which the flow is steadily outward from the Sun. Next comes a relatively thin region of interaction of the Solar Wind with interstellar plasma, a turbulent shock front. (This turbulent sheath streams out behind the Sun as it travels through the interstellar plasma at 20 kilometers per second like the tail of a comet.) Next comes the outer edge of the bow shock, beyond which no trace of the Sun’s influence survives.

Voyager 1 is now in the turbulent shock region. The plasma flow it is now measuring is at right angles to the flow from the Sun. It is leaving the heliosphere, the region in which the Sun is dominant. It is already in the disputed realm where the Sun is losing its struggle against the interstellar medium. A vast, sparse cloud of Kuiper Belt Objects lies around it, and the Oort cloud of frozen, inactive comets lies ahead, but they are so widely scattered and so faint that Voyager will not see them. To its sensors, it is leaving the Solar System behind. In 4 or 5 years it will be beyond the shock front, cruising the void between the stars. This is interstellar space, the stuff of science fiction.

But space is vast. If Voyager had been aimed at the nearest star (it wasn’t), it would be less than 0.1% of the way there. On its present course it will be as far away as the nearest star in about 50,000 years. Will we still be listening then?

Monday, December 13, 2010

What Everybody Knows about Newton

Isaac Newton, during his exile in the English countryside during the plague year of 1666, conceived the idea that the force that caused things to fall to the ground might be the very same force that held the Moon in orbit around Earth.  He seems to have arrived at this hypothesis without reference to apples.

Newton, being a scientist, was not content to make a qualitative generalization.  Instead, he constructed a quantitative description of his idea, an equation intended to predict how the force of gravitation depends on the mass of the attracting body and its distance.  Then Newton, being a scientist, solved the equation for the two cases of interest.  

The first case was that of the acceleration of a falling body near the ground (at a distance of one Earth radius from Earth’s center).  For this calculation he used the best available measurement of Earth’s radius.  The second case, the motion of the Moon, specifically the acceleration required to bend the Moon’s trajectory into a closed orbit around Earth, required using the best available measurement of the Moon’s distance from Earth.  Both calculations also depended on the exact mass of Earth, since both accelerations were, by his hypothesis, proportional to Earth’s mass.  Newton realized that  the ratio of these two accelerations was therefore independent of Earth’s mass, which was fortunate because Earth’s mass was not well known.  Indeed, in both calculations the predicted  acceleration was proportional to the product GM, where G was a very poorly known constant called the Universal Gravitational Constant, and M was the equally poorly known mass of Earth.  But the numerical value of the product of G times M could be calculated with good precision from measuring the acceleration of falling objects in the laboratory-- and in the ratio of the two accelerations, the product GM cancelled out perfectly.

Newton did the calculation with the best available data and found to his chagrin that there was a small but significant discrepancy.  In effect, the product GM estimated from the Moon’s motion and the value of GM deduced from laboratory measurements were not exactly the same.  Being a scientist, Newton concluded that his hypothesis was in error, and tucked it away in a drawer.  

Several years later an astronomer made new observations of the parallax of the Moon (the apparent displacement of its position seen when two observers in different places simultaneously measured the Moon’s position precisely against the background of distant stars), from which the Moon’s distance can easily be calculated.   He published his more accurate determination of the Moon’s distance.  Newton read the article and remembered his old hypothesis, gathering dust in a drawer.  He pulled it out, inserted the new measurement of the Moon’s distance, and found that it worked!  GM was the same for the Moon and for cannonballs in the laboratory!  Encouraged by this success, Newton published the Theory of Universal Gravitation, and immediately the motions of Solar System bodies became predictable!

A contemporary of Newton, Edmund Halley, was fascinated by the apparently unpredictable motions of comets.  All contemporary wisdom held that comets were not even physical objects; they were signs from God, not subject to any law understood or even understandable by mere humans.  But Halley found in ancient records reports of a series of comet appearances that very nearly fit the same orbit, and very nearly the same orbital period.  He suspected that they were all the same comet.  Halley found by laborious calculations that the comet’s orbit changed whenever it passed close to Jupiter.  Using Newton Law of Universal Gravitation, he showed that the gravitational influence of Jupiter accounted for the changes in the comet’s orbit.  Halley then predicted the next appearance of the comet.  When the comet reappeared in accordance with his prediction, years after Halley’s death, the comet was named after him.  Comets ceased to be regarded as “signs” and became Solar System bodies with predictable orbits.  This was an astonishing verification of Universal Gravitation.

Back in his day and using this law, Newton showed that a body sent from Earth with a high enough velocity, such as a projectile from a giant cannon fired from a mountain top, could enter orbit around Earth just above the atmosphere.  That critical speed was called “circular orbital velocity”  With twice as much energy (a velocity greater by a factor of the square root of 2) the projectile would coast out to infinite distance from Earth.  Any speed equal to or above this “escape velocty” would guarantee that the projectile would never return to Earth.

Everybody knows that Newton said “what goes up must come down”.  But, like almost everything that “everybody knows”, this is errant nonsense.  In the history of the human race, the first person to prove that what goes up does not have to come down was Newton.  In doing so, he paved the way for launching Earth satellites, interplanetary probes, and the Pioneer and Voyager missions into interstellar space.

For more about comets and their interaction with Earth, see Rain of Iron and Ice and Physics and Chemistry of the Solar System.

What Everybody Knows about Einstein

Back in 1905 a young clerk at the Swiss Patent Office thought deeply about the behavior of bodies traveling close to the speed of light.  He showed mathematically that the observed properties of such bodies could be powerfully affected by the relative motion of observer and observed, with the observations deviating ever more profoundly from low-speed observations as the relative velocity approached the speed of light.

Specifically, observations of lengths, masses, and time duration could all be dramatically affected by relative motion. It follows that different observers of the same event would observe very different masses, times, and distances. But Einstein did not stop there. He provided a set of transformation equations by which different observers could correct for these effects and “translate” their observations into a form comprehensible to others. Having provided a precise quantitative means for observers to understand each other’s observations, Einstein summarized the situation by propounding the Relativity Principle: “The laws of the Universe are the same for all observers”.

Everybody known that Einstein said that “everything is relative.”  He most certainly did not.  That would provide a convenient excuse for not trying to understand anything; for maintaining that all perspectives are equally valueless, and the Universe is fundamentally incomprehensible. Such sloppy thinking permits newspaper readers to conclude that there are no absolutes and that this generalization extends to morality as well as physics.  But this understanding of the Relativity Principle is precisely backwards, and its application to human behavior is almost hilariously inept.  

Everybody also knows that “Einstein showed that Newton was wrong”.  This is another example of why people should not use newspapers as science text books.  The classical example of how Newton was wrong is mass dilation.  Einstein showed that observations of the mass of an object traveling close to the speed of light show a dramatically increased apparent mass.  Experiments bear this out: the faster a body is moving, the more energy is required to increase its speed by a given amount.  The apparent inertial mass of a body becomes infinite at the speed of light, which means that infinite energy would be required to accelerate a body to the speed of light.  Now Newton surely never said or suspected any such thing.  Let’s go back and look at what Newton said about accelerating bodies.

Everybody knows that Newton said “F = ma”; the force required to accelerate a body at rate a is equal to the inertial mass of the body.  Curiously, however, Newton did not say that (thousands of textbooks notwithstanding).  Newton actually stated his Second Law in the following terms: “force is the rate of change of momentum”.  In calculus (co-invented by Newton and Leibnitz) the statement is F = d(mv)/dt, which mathematically implies F = v(dm/dt) + (dv/dt).  Generations of introductory physics texts have said in effect, either explicitly or implicitly, “if the mass is constant, then dm/dt is zero, so the term v(dm/dt) is also zero.  Then F = m(dv/dt), and the rate of change of v, (dv/dt), is obviously the acceleration, a.  Thus F = ma, and the acceleration of a body of mass m acted upon by a force F is a = F/m.

But Newton did not go there.  In his theory, a body with mass m would obey the equation F = v(dm/dt) + ma, so the acceleration of the body under the action of force F would be a = [F - v(dm/dt)]/m.  This equation holds as well in relativistic (Einsteinian) physics as in classical (Newtonian) physics!  What Einstein provided was the concept that the energy imparted to a body in the process of acceleration to high speeds adds equivalent mass to the particle: the more energy imparted to the particle, the greater its effective mass, the greater its inertia, and the less its acceleration under the action of a constant force.  In other words, the change in mass of a particle caused by a change in its energy is the energy change divided by the square of the speed of light.  The newspapers report this as E = mc2

Relativity is based not only on the “rest” properties of an object (mass, dimensions, and time intervals measured by an observer at rest relative to the object) but also on the equations used to translate the observations of different observers and the universal, absolute principle that not only are there laws, they are the same for all observers.

The next time someone tells you that everything is relative or that the Universe has no absolutes, fell free to laugh.


Wednesday, December 8, 2010

Venus: Not this Time

            The Akatsuki probe, launched last May on a mission by the Japanese space agency JAXA, has failed to enter orbit around Venus.  Akatsuki’s planned mission, to study the clouds and atmospheric dynamics of Venus, therefore cannot proceed as planned.  The spacecraft is, however, still alive and communicating, and will, in its present orbit around the Sun, again approach Venus six years from now.  JAXA has begun a study of the feasibility of injecting Akatsuki into Venus orbit at that time.  Since the mission was designed for an operational lifetime of only two years, this “Plan B” must be regarded as a long-shot.

            Ironically, NASA had recently announced the formation of a team of American scientists to work with JAXA on the interpretation of the Venus data expected to be acquired starting today.

            The difficulties with this ambitious mission, following on the heels of the 1998 loss of JAXA’s  Nozomi Mars mission and the disappointment of the Hayabusa asteroid sample return mission launched in 2003, are a big problem for JAXA.  Their tradition of highly sophisticated, relatively low-cost missions is seriously undercut by the apparent failure of Akatsuki, a $300 million investment.

Space-X’s Falcon 9 Soars into Orbit

            This morning’s successful flight of the commercial, privately-developed Falcon 9 launch vehicle placed a mockup of its Dragon orbital vehicle into low Earth orbit (LEO).  Falcon 9 is a serious contender for the role of a medium- to heavy-lift launch vehicle to be marketed to NASA (and all comers) for use in servicing the International Space Station (ISS) and for other future programs.  Variants of this booster can deliver 10 to 25 metric tonnes of payload to LEO, making it comparable at the high end with the lifting capacity of the Space Shuttle, the Atlas V, Ariane 5 (ESA), Long March 5 (PRC), and Proton (Russia).

            Competition with other promising launch providers will help keep customer costs down.  Two companies have focused on the short-term market for suborbital flights with “airline-style” operations.  Keep your eyes on XCOR for flights of its booster which uses high-performance, highly reusable engines.  XCOR has recently signed a marketing agreement with KLM Airlines and a lease contract with a company in Curacao for commercial use of its Lynx suborbital vehicle..  Also watch for news on the SpaceShip2 system developed by Mohave Aerospace for commercial suborbital tourist flights by Virgin Galactic.  The latter’s prospects hang on the successful development of the hybrid engine for the SpaceShip2 passenger vehicle.  Its White Knight 2 carrier aircraft has already been extensively flight-tested.

Mercury as a Puzzle

            The innermost planet in the Solar System, Mercury, is unique in many ways.  It is surprisingly dense, reflecting a massive metallic core that has 60% of the mass of the planet (versus less than 31% for Earth, Venus, and Mars).  It has a highly eccentric orbit, approaching as close as 0.3236 AU to the Sun and retreating as far as 0.4506 AU on each orbit, covering the entire range in half an orbital period, 44 Earth days.  The intensity of sunlight striking Mercury’s orbit drops off with the square of the distance from the Sun, so it varies by nearly a factor of two. 

            Even odder, the rotation of Mercury is locked onto its orbital period.  Most examples of spin-orbit resonances in the Solar System are 1:1 (one rotation per orbit), which means that the smaller body always keeps the same side toward the larger body.  Examples include Earth’s Moon and the large Galilean satellites of Jupiter.  The most extreme example of a strong lock between rotation and orbit is Pluto and its satellite Charon:  they are locked into a 1:1:1 spin-spin-orbit state, in which both Charon and Pluto always keep exactly the face toward each other.  Mercury is noteworthy in that it has a 3:2 spin-orbit resonance: Mercury rotates exactly 3 times every 2 Mercury years, or 1 ½ times per year.  Thus in consecutive closest approaches to the Sun (perihelion), opposite sides of the planet get baked.  This situation is understandable if Mercury is elongated along one of its equatorial axes: the planet then points the ends of this long axis (the so-called tidal bulges) at the Sun alternatingly at each perihelion passage.

            Mercury shows no trace having ever had a significant atmosphere or oceans.  The faint wisp of gases surrounding Mercury today is in part due to solar wind gases from the Sun temporarily captured by Mercury’s gravity, and in part to atoms, such as sodium, baked out of the surface by the extreme heat and the impact of high-speed solar wind ions.  Gases released from Mercury’s interior, such as argon-40 from the radioactive decay of potassium-40 in the crust and mantle, can easily be ionized by ultraviolet radiation from the Sun, entrapped in the magnetic field of the solar wind, and swept away.

            How did Mercury get to be like this?  The spin-orbit resonance is essentially unavoidable for a planet that orbits so close to a star.  The absence of atmosphere and oceans is also unavoidable for a planet with such weak gravity in so hostile an environment.  But the high density of Mercury is a continuing puzzle.  The smaller bodies that accreted to form Mercury may have collided so violently that brittle silicates were preferentially crushed to dust, while tough grains of metal survived.  Dissipation of the finest dust would then leave behind the ingredients of a metal-rich, dense planet.  A second possibility is that the material in the zone where Mercury was to accrete was so strongly heated by the early superluminous Sun that the most volatile minerals were evaporated and lost from Mercury’s formation zone, leaving dense, involatile solids behind to form the planet.  A third scenario is that Mercury formed normally with a composition similar to that of the other terrestrial planets, but that post-accretion impacts of comets and asteroids eroded away the crust and much of the mantle, blasting them off at high speeds and leaving behind a part of the lower mantle and the well-protected dense metallic core.  Each of these three scenarios predicts different surface compositions for present-day Mercury.  The goal of the MESSENGER spacecraft, which is due to enter orbit around Mercury in January, is to test these hypotheses by analyzing the crust by means of gamma-ray spectroscopy and probing the interior of the planet by means of measuring its gravitational and magnetic fields and the interaction of Mercury’s core with the magnetic field of the solar wind.

            If all goes well, the answers to these puzzles will soon be in our hands.

Tuesday, December 7, 2010

The New Space Race: China and India

Since 1998 there have been only five missions sent to explore the Moon. Two were  Chinese, one was Japanese, one was Indian, and one was American.


China  Chang’e 1 lunar orbiter
Japan  SELENE lunar orbiter with two small subsatellites.


US      Lunar Reconnaissance Orbiter (LRO) and polar ice probe LCROSS
India   Chandrayaan 1 lunar orbiter with international assortment of scientific instruments


China  Chang’e 2 lunar orbiter for mapping

(After 20 months in orbit, SELENE was intentionally crashed into the lunar surface, targeted on the ice deposits found near the lunar poles.)  

The prospect for the American for the next few years has recently changed significantly as a result of the restructuring of NASA’s exploration program to emphasize Mars and asteroids over the Moon.  NASA’s two GRAIL orbiters, devoted to study of the Moon’s gravitational field and interior structure, which are scheduled for launch in 2011, were paid for before this change in policy.  Also, NASA’s LADEE orbital mission to study the Moon’s tenuous atmosphere and dust environment is scheduled for launch in May 2012.  Two lunar missions are presently scheduled for launch in 2013: China’s Chang’e 3 lander and rover, and India’s Chandrayaan 2 orbiter, lander, and rover.  Japan’s SELENE 2 lander with a surface penetrator probe including a seismometer and possibly an autonomous rover is presently scheduled for launch before 2015.

China has targeted 2017 for the launch of an automated (unmanned) lunar surface sample return mission, Chang’e 4.  The European Space Agency (ESA) is planning a lunar polar lander for the 2019 time frame.

Both China and India have announced their intention to land astronauts on the Moon around 2025.  China has released its plans for the development of several new large launch vehicles (Long March 5, 8, and 9), including specific and realistic performance and schedule goals, that would permit carrying out such an ambitious program.  India has so far demonstrated its commitment to a series of unmanned precursor missions that pave the way for eventual manned lunar landings, but has not announced any plans for the development of the necessary giant rocket boosters.

So far, it looks as though India has a goal and China has a plan.  The cost of such a program is immense; indeed, budgetary constraints, not lack of technical capability, have kept Japan on the sidelines in this new space race.

In the interests of full disclosure, I must mention that I have served as a regular commentator on China Central Television (CCTV-9) since 2005, including lunar missions in the Chang’e program and manned missions in the Shenzhou series.  My role has been to contribute an independent international and historical perspective.  I have given a lecture series at the Chinese Academy of Science’s Center for Space Science and Applied Research and its Center for Lunar Missions.  I have not advised China on what to do or how to do it.

Monday, December 6, 2010

Planets: Water, Water, Everywhere

           Nothing makes the popular science press giddier than the mention of the word “water”.  Whether it is on the Moon, Mars, Mercury, or distant planets of other stars, the mere mention of the word leads to mock-eloquent flights of fancy, in which the words “Earth-like” and “life” figure prominently  But perspective is lacking.  Here’s the real situation.

The Universe is overwhelmingly composed of hydrogen and helium.  For every atom of silicon (think rocks) there 28000 atoms of hydrogen and 2700 atoms of helium.  What about the rest of the Universe?  Add 24 atoms of oxygen, 10 atoms of carbon, and 3 atoms each of neon and nitrogen. 

Our fixation with Earth-like worlds leads us to wonder about the rest: add 1 atom each of silicon, magnesium, and iron to the mix.  All the other elements combined would add up to a single atom.  Terrestrial (rocky) planets are mostly made of these relatively rare elements in the form of oxides of these three elements plus metallic iron.  The most abundant element in Earth (and Mercury, Venus, Mars, the Moon and most asteroids) is actually oxygen.  After accounting for elemental hydrogen and helium, oxygen is next in order of abundance.  Its presence makes chemistry (the formation of chemical compounds) possible, including the formation of water (2 atoms of hydrogen combined with one of oxygen).  It also means that water is the most abundant chemical compound in the Universe.  We therefore should expect to find it everywhere.  If water is absent from a planet, we need to explain why.

Consider this week’s feeding frenzy about water in the atmosphere of an extrasolar plant (GJ 1214b) with about 6.5 times the mass of Earth.  This planet is in a very close orbit (about 2 million km, or 1.2 million miles) around a faint red M4.5-class star with a luminosity of only 0.003 times that of the Sun.  The planet is so close to its star that its orbital period (year) is only 38 hours long. 

Such a faint star imposes certain limitations on its solar system: Any planet of such a faint star must be very close in order for it to have “Earthlike” temperatures (in the liquid water range; not boiled, not frozen).  Any such planet must be despun by tidal interactions with its parent star.  Even worse, the planet and sun must be so close that they are on the verge of being torn apart by those tidal forces.   The best data show no evidence of a massive hydrogen (and helium) atmosphere, which has almost certainly been stripped away by the tidal influence.  So what should be left behind?  Throughout the Universe, candidate #1 is water.  What we see is probably water clouds.  The interior is likely much hotter and may or may not have a global ocean, the reality depending on factors not yet known from observation. 

This planet is not the first, and certainly not the last, to be implicated as water-rich.  The first such “super-Earth” was discovered several years ago.  I also wrote about them in my 1998 book, Worlds without End.  But “water” is not a synonym for “ocean” or “inhabited” or “life-supporting”.

Mercury: MESSENGER Spacecraft in Future Headlines

Paradoxically, Mercury is the hardest planet to land on (or in) in the Solar System.  Only a single mission from Earth has flown by Mercury, the Mariner 10 spacecraft launched by NASA in 1973.  Mariner 10 used a flyby of Venus  to bend its orbital path inward to Mercury and to shorten its orbital period, eventually placing the spacecraft in an orbit around the Sun that repeatedly passed by Mercury at close range.  That orbit had a period of 176 days, exactly two Mercury years, assuring that it would fly by Mercury at close range that often.  Because Mercury is locked into a resonance with the Sun, the planet rotates exactly 3 times every 2 Mercury years—meaning that the exact same face of Mercury is presented to the Sun (and illuminated for imaging purposes) on every flyby date.  Mariner 10 carried out three brief high-speed flybys of Mercury (and one of Venus) during its operational lifetime.

Placing a spacecraft in orbit around Mercury is made very difficult by the high speed of a fly-by spacecraft.  After falling in the Sun’s gravitational field in from Earth’s orbit to Mercury’s orbit, the spacecraft is traveling so fast that it would require impractically large masses of rocket propellant to slow it down enough to be captured.  Landing is even harder, since it requires additional propellant to resist the planet’s gravitational field and decelerate to zero velocity upon arrival at the planetary surface. Instead, other deceleration methods need to be undertaken.

A second spacecraft mission, MESSENGER, uses planetary swing-bys to slow the probe. MESSENGER will soon arrive at Mercury after a 6.6 year journey and no less than six planetary flybys.  After its launch in August 2004, there were close encounters with Earth (August 2005), Venus (October 2006 and June 2007), and Mercury (January and October 2008 and September 2009), putting MESSENGER into an orbit around the Sun that will arrive at Mercury with a low relative speed on March 18, 2011.  MESSENGER will then fire its rocket engine and drop into orbit around Mercury.  The orbit will be eccentric (to permit both large-scale mapping and close-up imagery) and highly inclined (to permit coverage of the entire surface as Mercury rotates beneath the spacecraft’s orbit). 

Even with this clever trajectory design, most of MESSENGER’s launched mass (55%) had to be rocket propellant. By the end of the mission it will have been used for mid-course trajectory tweaks, to slow it down, and to bring about orbital insertion, and to maintain the desired orbit. By far the most costly of these maneuvers in terms of fuel consumption is orbital insertion. To keep posted on this exciting mission consult the website maintained by Johns Hopkins University’s Applied Physics Laboratory, the managers of the mission:  
 If you are interested in the instruments carried to Mercury to explore its atmosphere, magnetic and gravitational fields, radiation environment, and surface composition and structure, go the The Mission and click on Instruments on this same site.

Venus: Revisited

Did you know that there is a spacecraft mission on the way to Venus? Such missions were common in the days of the Soviet-American (US/SU) space race, from 1961 to 1984. But the world is different now. Not only has the US/SU space race ended, but other players are now in the game. On May 20 of this year the Japanese space agency JAXA launched the Akatsuki spacecraft (known before its successful launch as Planet-C) on a planned two-year mission to orbit around Venus. The purpose of the mission is to study the clouds, climate, and atmospheric circulation of “Earth’s twin”. With a surface baking at about 750 K (900oF) and clouds of sulfuric acid droplets, a better name for Venus might be “Earth’s evil twin”.

Akatsuki (“dawn” in Japanese) is scheduled to arrive at Venus and enter orbit on December 7, 2010. Along the way to Venus it dropped off a secondary payload named Ikaros, an experimental solar sail which is propelled by the momentum carried by sunlight (not the solar wind!). By late Tuesday we should know whether it entered Venus orbit successfully. Since this is the first Venus mission since NASA’s Magellan radar mapper in 1989, we can hope that the media will pay some attention!

Friday, December 3, 2010

Life as We Don't Know It

A fascinating discovery reported at the Science magazine website reports on a microorganism that not only tolerates arsenate, a classically recognized toxin, but actually uses it in its metabolism. The genetic code used by all life on Earth consists of “letters”, called nucleosides, which each contain a single sugar molecule (deoxyribose) attached to a single organic base (adenine, cytosine, guanine or thymine). These nucleosides are linked into very long chains by means of phosphate (HPO4=) ions, each of which is bonded to two sugars in two consecutive nucleosides: sugar-phosphate-sugar-phosphate-sugar- etc.

This microorganism freely substitutes arsenate (HAsO4=) for phosphate in the DNA molecule. The element arsenic is chemically similar to phosphorus, both of which belong to the family nitrogen-phophorus-arsenic-antimony-bismuth. Nitrates are strong oxidizing agents and react readily with organic matter to “burn” it. Phosphates are readily available in nature and quite stable. Arsenic is about 200 times less abundant than phosphorus in the universe, but can be concentrated by geochemical processes on Earth. Antimony is far less abundant than arsenic, but may possibly follow arsenic into DNA in tiny traces. Bismuth is less similar to phosphorus and even rarer.

But phosphates have another major role in biochemistry: the energy management of cells depends on adenosine diphosphate and adenosine triphosphate (ADP and ATP). So the big question is, are the ADP and ATP molecules in the mitochondria of this strange organism also tolerant of arsenate: do they actually use it the power-generating system of the cell?

Truly, one cell’s food is another cell’s poison.

Obama and NASA

Obama and NASA 

      Recently I was accosted by a young couple on the street in Anacortes, Washington.  They were campaigning to have President Obama impeached.  I took the time to ask why, and they responded that his recent decisions regarding NASA, especially his removal of a lunar base from the agenda and the cancellation of the boosters needed for that program, could kill NASA.  Having been interested in this issue since the creation (of NASA), I naturally donned my Socratic persona and asked a series of questions:

      Did they think that NASA was doing a good job on booster development, since all evidence suggested the Ares program was way over budget and behind schedule?  Yes, they did. 

      Did they think that NASA’s designing and building of boosters in the past had been a great success?  Yes again.  They cited the Saturn 1 and Saturn 5, which were of course designed by the former Army Redstone Arsenal team that had recently been moved into NASA as Marshall Space Flight Center.  The Saturns, moreover, were built by industry, not NASA. 

      They also approved of the Space Shuttle, a creature that I was astonished to find still had some public appeal after all its shortcomings have become public news.  The STS hardware was, however, designed and built by industry in response to very different NASA and Air Force specifications, a sort of hybridized offshoot of a moving van and a sports car. 

      Did they think there were things NASA did exceptionally well?  They fumbled about, but when I suggested basic technology development, astronomy, and Solar System exploration as examples, they agreed enthusiastically.  I pointed out that this good science and technology stuff was a few percent of the NASA budget.  The lion’s share of the budget has long gone to manned spaceflight (Mercury, Gemini, Apollo, STS, ISS, and the abortive Lunar Base).

      They were appalled that the Space Shuttle was being phased out.  I suggested that the STS had a compromised design process, a depressing fatality record, serious metal fatigue problems, and a huge budget.  They still loved it.  I asked whether they supported manned exploration of space, and they of course said yes.  Socrates Jr. then asked, “When was the last time humans explored anything new in space?”  After a bit of consideration, they stipulated that exploration ceased with the end of the Apollo program.  If so, I asked, why transfer their love for Apollo to a program that can’t get a person out of Low Earth Orbit?  (BTW, several polls have shown that many people believe that the Space Shuttle routinely flies to the Moon.)

      Finally, I asked them what they thought of privatization of launch services, putting governmental payloads on launches on boosters designed by private industry and marketed competitively.  They laughed uproariously, painting Richard Branson as a wealthy nut case riding an outlandish hobby horse.  When I pointed out that the cost of the energy needed to put a pound of payload into orbit was less than 50 cents, and that there was a lot of room for improvement over present STS launch costs of about $10,000 per pound, they simply didn’t believe me. 

      I suppose that at some level they recognized that having a giant National Goal is a recipe for the continuing existence of NASA, protecting it from brutal dismemberment by the wolves that prowl the corridors of Washington, and assuring political support from Congressmen whose distracts are home to large, wealthy aerospace corporations.  But couldn’t we have a NASA that spends less and accomplishes more?  Maybe such a NASA would have greater public appeal than one driven by corporate campaign contributions.