Titan

Saturn’s largest moon (the solar system’s second largest moon), Titan, was discovered in 1655 by Dutch astronomer Christiaan Huygens. In 1944, Gerard Kuiper demonstrated that Titan’s dense atmosphere has the spectral signature of methane. Up until the arrival of the voyager 1 in 1980 and Cassini-Huygens in 2004, Titan was somewhat of a mystery with its surface features hidden beneath thick layers of clouds and haze.

Although the surface was still hidden, Voyager was able to learn much about the moon’s planet-like atmosphere. Titan’s huge atmosphere creates a surface pressure of 1.5 bars, a temperature of 94K, and a density of 5.3kg/m3. This surface temperature is close to the triple point of methane, which could mean that Titan has a methane cycle similar to Earth’s hydrological cycle.

In 2005, ESA’s Huygens Probe was released from Cassini and entered Titan’s atmosphere. It discovered that Titan and Earth’s atmosphere share a similar altitude/temperature relationship. On Earth, the temperature decreases with altitude in the troposphere, increases in the stratosphere due to the absorption of UV rays in the ozone, decreases in the mesosphere due to decreasing atmospheric density, and finally increases in the thermosphere due to the release of thermal energy caused by the breakup of molecules by solar radiation. On Titan, the temperature decreases with altitude in the troposphere, and increases in the stratosphere.

With several Cassini flybys, Titan’s mysterious surface is finally being revealed. Titan’s surface is incredibly Earth-like with rain-cut river beds, hydrocarbon lakes, and giant equatorial sand dunes. Much is still unknown about the surface, such as the depth of the lakes, and how the sand dunes are formed. Cassini Radar observations also confirmed that the entire crust of Titan is floating on top of a massive water ocean.

On April 2008 a large storm cell, approximately the size of India, was observed using the combined technologies of several observatories, such as NASA’S Infrared Telescope located on Mauna Kea in Hawaii. This storm was observed over a tropical region which would be a typical place for tropical storms to develop. More recently, a second large storm system was observed over a more arid region, where such storms are less expected to develop. These storms could be capable of producing large amounts of precipitation which would sculpt the moon’s surface, creating the surface geology which we are just beginning to see.

With a continuing Cassini mission, including 20 plus Titan fly-bys, there is definitely more discoveries to come. Titan is a moon well worth exploring with complex orbiters and robotic landers, not only for further observations of Titan’s exotic surface features, but also to look for signs of extremophiles. Any such mission will be expensive and several years into the future, so in the meantime we can enjoy the only sounds ever recorded on a body other than Earth. These sounds were recorded by the Huygens Probe as it descended through Titan’s atmosphere: Sounds of Titan�

The Kepler Mission

Since the dawn of intelligent man, we as a race have asked several questions pertaining to the heavens, and to the meaning of life. In 2012, NASA’S Kepler Mission will bring us one step closer to answering one of these timeless questions: “are we alone?” Launched in March of this year, the Kepler Mission was not only named after the great mathematician and astronomer, Johannes Kepler, it also celebrates the 400th anniversary of the publication of his first two laws on planetary motion.

The Kepler spacecraft will search for Earth-like planets using a technique known as the Transit Method of Detecting Extrasolar Planets. A transit occurs when a planet crosses in front of its host star as viewed by an observer. These transits dim the brightness of a star which allow for the detection of extrasolar planets. This change in brightness is very difficult to detect by terrestrial planets, such as Earth, because they only dim their host star by 100 parts per million, lasting only 2 to 16 hours. In order for an extrasolar transit to be observed from our solar system, the orbit must be viewed edge on. The probability of observing such a planet is less than 1%. To increase the chances of observing a transiting terrestrial planet, the Kepler spacecraft will observe 100,000 of our neighboring stars. Because any planet in the habitable zone will require an orbit close to that of one Earth year, Kepler will need to observe any transits discovered amongst these 100,000 stars for at least 3.5 years to determine if the transit is periodic enough to be a planet.

The precision of the spacecraft was recently tested by observing a known exoplanet called HAT-P-7. This planet orbits a star 1000 light years away in approximately 2.2 days. Not only was Kepler able to observe transit with the precision necessary for the detection of an Earth sized planet, the light given off by this planet was also observed. This is the first time light from an exosolar planet has been observed, this light can provide information about the planet’s atmosphere.

The Kepler Mission may not be able to directly determine whether or not we are alone in the universe, but it will be able to tell us if we have neighboring planetary systems, containing planets, capable of sustaining life. When compared to all the stars in the universe, even one discovery amongst the relatively small sample space of 100,000 stars will be significant enough for us to rethink our meaning and place in the universe.