Philosophical Society of Washington

Minutes of the 2318th Meeting

President John Ingersoll called the 2,318th meeting to order at 8:28pm May 10, 2013 in the Powell Auditorium of the Cosmos Club. Mr. Ingersoll announced the order of business and introduced three new members of the Society, including the speaker of the evening.

The minutes of the 2,317th meeting were read and approved.

Mr. Ingersoll then introduced the speaker, Mr. John Grotzinger of the California Institute of Technology. Mr. Grotzinger spoke on "Curiosity's Robotic Exploration of Mars' Gale Crater."


Mr. Grotzinger began by acknowledging his colleagues on the Mars Science Laboratory team, with a total of 457 members from over 15 countries. He explained that early rover missions, such as Sojourner in 1997, focused on efficient, inexpensive construction combined with technology demonstrations such as robust suspension systems. Curiosity's expanded scientific instrumentation is designed to determine whether Mars ever had habitable environments by looking for traces of ancient chemistry. Additionally, Curiosity's success will help NASA prepare for a future Mars mission in 2020 that will involve eventually returning samples to Earth.

Mr. Grotzinger then described the components of the Curiosity rover and noted that Curiosity possesses many advanced sensing capabilities, including cameras, drills, and sample collection and processing systems. These sensitive instruments have been developed and miniaturized for deployment, some costing many tens of millions of dollars, he said. They are controlled by two redundant computer systems and powered by a battery-supported nuclear thermoelectric system. Finally, a thermal fluid loop keeps the rover within operating temperatures during the cold night.

Mr. Grotzinger described the successful November 2011 launch and eight month cruise to Mars. He explained that the selected landing site inside Gale Crater, in a moat between the rim of the crater and the mysterious mountain at the center informally called Mount Sharp, required an ambitious landing procedure referred to as the "seven minutes of terror." This procedure involved ballast-controlled aeroshell lift, real-time course correction with thrusters at hypersonic speeds, a parachute, and finally a powered descent vehicle gently lowering the rover to the surface. A landing of this kind had never been attempted before and its difficulty captured the public's imagination, he said. A NASA video visualizing the landing procedure with discussion by responsible engineers received millions of views online.

Mr. Grotzinger explained that the science team began work immediately after the successful landing, with early images from the rover showing Mount Sharp, the nearby crater rim, and spectacular nearby terrain. The team very carefully and thoroughly tested each instrument and aspect of the rover's capabilities, since it is now is effectively a priceless national asset on the surface of Mars that cannot be replaced, he said. The fourteen minute communication delay requires the rover to be nearly autonomous, with a main command message sent near Martian sunrise and a main results message received at Martian sunset. The science team has spent months working during the Martian night, staying synchronized regardless of local Earth time.

Mr. Grotzinger described the three different kinds of terrain observed near the landing site and noted that the intersection point was only a few hundred meters away, a geological jackpot for the mission scientists and a sufficiently compelling reason to drive in the opposite direction from that originally planned. While en route, Curiosity encountered rock outcrops that appeared very similar to concrete, containing rounded pebbles in a hardened matrix, which implied the rover was traveling through an ancient streambed. The rover then followed the streambed downhill to discover rock formations that had been fractured in a manner suggesting fluid flow, along with the presence of sulfate which is an indicator of water. After drilling a hole in the surface, Curiosity found grayish-green rock that contained significant amounts of clay minerals, implying that neutral pH, low salinity water had once accumulated there. This provided the first strong evidence that Mars was once a habitable environment and accomplished the principle mission goal, he said.

Mr. Grotzinger concluded by explaining that microbes do not leave morphologic fossils like dinosaurs but they do leave a kind of "chemofossil." This occurs when complex organic molecules such as those found in the structure of a cell membrane chemically degrade into simpler molecules that can be detected. Mr. Grotzinger believes Mars was habitable in at least one place and at one time, so now the mission emphasis is to reconstruct the ancient chemical environment to find the chemical remnants from any life that might have existed. To do so, Curiosity will drive toward the nearby foothills of Mount Sharp where it should arrive in approximately one year.

With that, he closed his talk and Mr. Ingersoll invited questions.

Someone wondered about the odds of finding a meteorite while exploring the surface of Mars. Mr. Grotzinger confirmed that Curiosity has not yet encountered a meteorite but noted that the Opportunity rover encountered many during its 30km exploration. He suspects that Curiosity's position near a crater rim means that most nearby surface rocks are actually secondary impact ejecta, but is confident that a meteorite will soon be observed by Curiosity.

Another question concerned the possibility of ancient cosmic ray bombardment affecting the evolution of any microbial life on Mars. Mr. Grotzinger explained that any evolving microorganisms would be safe from ultraviolet radiation just below the sediment layer and safe from cosmic radiation about a meter further below the surface, an explanation also potentially relevant to Earth.


After the question and answer period, Mr. Ingersoll thanked the speaker, made the usual housekeeping announcements, and invited guests to apply for membership. At 10:04pm, President John Ingersoll adjourned the 2,318th meeting to the social hour.

Attendance: 120
The weather: Clear
The temperature: 26°C

Respectfully submitted,

Justin Stimatze,
Recording secretary


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