Cassini: A Distant Outpost for Exploration
F. Michael Flasar
Cassini Composite Infrared Spectroscopy Experiment
NASA Goddard Space Flight Center
About the Lecture
With its instruments selected in 1990, it itself launched in 1997, arriving at Saturn in July 2004 and jettisoning a probe named Huygens onto Titan at the end of that year, Cassini represents a long-term endeavor in planetary exploration. This talk provides an overview of this amazing observatory, the questions it was sent to answer, and the surprises it sent back. It will stress Saturn and its giant moon Titan. On Saturn, there are new mysteries: How fast does Saturn’s interior really spin? Have its rapid (475 m/s) equatorial winds slowed by nearly half the last few years? What are the giant storms that seem to be solidly planted over both poles? Titan, with a molecular nitrogen atmosphere, is an Earth analog, but rich in organics. It has a hydrological cycle, and its surface exhibits channels and “lakes” that are likely associated with liquefied natural gas. Its middle atmosphere rotates over ten times faster than its surface, quite unlike Earth, but its strong winter circumpolar winds have many of the same properties associated with the terrestrial ozone holes.
About the Speaker
F. MICHAEL FLASAR received the Ph.D. in Physics from the Massachusetts Institute of Technology in 1972. After time as a research fellow at Harvard University, he came to Goddard Space flight Center in 1975. His primary research is the dynamic meteorology of planetary atmospheres, including those of Mars, the giant planets, and Saturn’s moon Titan. He was a co-investigator on the Voyager infrared spectroscopy experiment (IRIS), a member of the Galileo Radio Propagation team, and a Participating Scientist on the Mars Global Surveyor Radio Science team. Currently, he is a member of the Cassini Radio Science team and the principal investigator of the Cassini Composite Infrared Spectroscopy experiment. He is a member of the American Geophysical Union, the American Astronomical Society, and the AAS/Division for Planetary Sciences.
President Kenneth Haapala called the 2,235th meeting to order at 8:15 pm March 14, 2008 in the Powell Auditorium of the Cosmos Club. The minutes of the 2,234th meeting were read and approved, after a discussion about degrees of freedom or actuators in fingers or toes.
Mr. Haapala introduced the speaker of the evening, Mr. F. Michael Flaser of the NASA Goddard Space Flight Center. Mr. Flaser spoke on “Cassini: A Distant Outpost for Exploration.”
Cassini is the craft sent to orbit Saturn. Huygens was piggybacked on Cassini and sent to probe Titan, a moon of Saturn. The purpose of the mission was to explore the Saturn system, the planet, its major moons, and rings. Over 4 years, there were to be 76 orbits of the planet, 44 Titan flybys and 52 flybys of icy moons, and a probe released into Titan’s atmosphere. This was an international effort involving NASA, the European Space Agency, and the Italian Space Agency.
The satellite was announced in 1989. It is a spindly-looking thing, big on top, weighing 12,600 lbs and standing 22 feet high. There are 12 science instruments on the Saturn Orbiter and 6 on the Huygens Titan probe.
Cassini was launched in October of 1997 and took a circuitus path toward Saturn. It did a deep space maneuver, two swings by Venus in 1998 and ‘99, and a final swing by earth in August of 1999. Then it was on its way, with a swing by Jupiter in December of 2000. It arrived at Saturn in July of 2004.
The instruments on Cassini cover a range of spectrum. There is an ultraviolet imaging spectrograph and two cameras, one narrow angle and one wide angle. There are visible and infrared mapping spectrometers and a composite infrared spectrometer.
This equipment has produced some very nice and interesting pictures. He showed one picture of Saturn with the sun behind it which looked like Saturn had jumped toward the camera and left it’s rings behind.
Both of Saturn’s poles show tropospheric and stratosphereic cyclonic hot spots. The centers are circled by rings of temperature gradients. The north pole’s inner ring is distinctly hexagonal. The pole centers are quite hot.
He explained that because Saturn’s atmosphere is mostly hydrogen, the scale of heights related to millibars of pressure is much higher than that of earth.
The hot spots at the poles are probably caused by air moving toward the poles at high altitudes and then descending, compressing, and warming. He showed how the distribution of temperature varied with altitude. The spot was hottest at the lowest point. The south pole spot is warmer than the north pole spot.
Titan is Saturn’s largest moon. It has a diameter 40% or earth’s and its surface gravity is only 14% of earths. Primarily its atmosphere is nitrogen with a few percent of methane. It has a surface pressure 1.5 times earth’s and a surface temperature of 95K (-289F). The atmosphere is rich in organics. It is shrouded in petrochemical smog and the surface may have lakes of liquified natural gas. They have used false colors to try to show what is on the surface. They have seen ices. One shot of the surface showed ridges similar to ridges in the Namib desert on earth.
Both Titan and Saturn have long years, equal to 29 earth years.
The Titan natural gas inventory looks pretty impressive. There seems to be a great abundance of acetylene, propane, ethane, and related compounds. Alas, in this abundance of energy, there is little oxygen, which is scarce. If there is water, oxygen might be extracted, and the north polar region has spots that look like lakes. Mr. Flaser thinks they are lakes of natural gas.
He showed a picture of Enceladus, another of Saturn’s moons. Enceladus is cleaner-looking. Its temperature is similar, ranging from 65 - 85K.
Enceladus has some marks that look like meteorite craters, but its most distinctive feature is its long, meandering ridges. These structures seem to go at least halfway around the globe.
The south pole is hot. It reaches 140K. There are also higher temperatures over the long, meandering fissures. The ice is thin there, too.
Cassini flew by Enceladus, within 50 miles, just two days before Mr. Flaser spoke to us. He showed us a movie it made as it flew by.
What lies ahead for the mission? The prime mission ends in July of 2008. An extended mission, which they are calling the Equinox Mission, would continue until July of 2010. A further extension, which they are calling the Solstice Mission, would continue after that. The Equinox Mission would include 60 orbits of Saturn, 26 passes near Titan, and 7 Enceladus passes.
In the question period, someone asked, is there anything about Titan or Enceladus to make us want to send a manned mission there? Although he said hope springs eternal, he thought not in the next 20 years. He did not think Exxon would want to go there to bring back the hydrocarbon. They are pretty hostile places. In another century or two, perhaps.
He noted that, although the mission ends July of 2008, the craft still out there. Titan controls it. It doesn’t use much fuel.
If we did nothing, what would happen? It would probably hit something. We want to avoid that, as it gets the planetary protection people excited. Up to now, they have optimized the flybys. In the future, they will turn to conserving fuel as the main objective.
Out of that overwhelming set of data, what can you summarize? Enceladus is tiny, he said. Titan is more like earth. It has a hydrologic cycle and weather like earth. However, its chemistry does not encourage the simplistic theories we developed after Voyager.
After the talk, Mr. Haapala presented a plaque to Mr. Flaser commemorating the occasion.
Mr. Haapala announced that Society member Maurice Shapiro passed away recently. He recounted that Mr. Shapiro had a son born at Los Alamos back in the supersecret days. This son had a birth certificate that said he was born in a post office box in New Mexico.
From the parking announcement, we learned more of the weak dollar. Parking at the Club now costs nonmembers $10.50. He made a pitch for support. He announced the 2236th meeting. Finally, at 9:50 pm, he adjourned the 2,235th meeting to the social hour.
The weather: Misty
The temperature: 8°C
Ronald O. Hietala,