TITAN, THE SATURN'S LARGEST MOON IS DISCOVERED

Joseph & The Grandma in Castelltallat, Bages

Today, Joseph de Ca'th Lon has invited The Grandma to go to Castelltallat, in Sant Mateu de Bages, near Barcelona. In this beautiful town, there is an Astronomical Observatory. Joseph wants to explain to The Grandma more things about Titan, the Saturn's moon, and about Christiaan Huygens, the astronomer who discovered it on a day like today in 1655.

During the travel from Barcelona to Castelltallat, The Grandma has studied a new lesson of her Intermediate Language Practice manual (Grammar 44).

More information: Verbs followed by preposition

Titan is the largest moon of Saturn and the second-largest natural satellite in the Solar System. It is the only moon known to have a dense atmosphere, and the only object in space, other than Earth, where clear evidence of stable bodies of surface liquid has been found.

Titan is the sixth gravitationally rounded moon from Saturn. Frequently described as a planet-like moon, Titan is 50% larger than Earth's moon and 80% more massive. It is the second-largest moon in the Solar System after Jupiter's moon Ganymede, and is larger than the planet Mercury, but only 40% as massive. Discovered in 1655 by the Dutch astronomer Christiaan Huygens, Titan was the first known moon of Saturn, and the sixth known planetary satellite, after Earth's moon and the four Galilean moons of Jupiter. 

Titan orbits Saturn at 20 Saturn radii. From Titan's surface, Saturn subtends an arc of 5.09 degrees and would appear 11.4 times larger in the sky than the Moon from Earth.

Titan & Saturn

Titan is primarily composed of ice and rocky material. Much as with Venus before the Space Age, the dense opaque atmosphere prevented understanding of Titan's surface until the Cassini–Huygens mission in 2004 provided new information, including the discovery of liquid hydrocarbon lakes in Titan's polar regions. The geologically young surface is generally smooth, with few impact craters, although mountains and several possible cryovolcanoes have been found. The atmosphere of Titan is largely nitrogen; minor components lead to the formation of methane and ethane clouds and nitrogen-rich organic smog.

The climate -including wind and rain- creates surface features similar to those of Earth, such as dunes, rivers, lakes, seas -probably of liquid methane and ethane-, and deltas, and is dominated by seasonal weather patterns as on Earth. With its liquids, both surface and subsurface, and robust nitrogen atmosphere, Titan's methane cycle is analogous to Earth's water cycle, at the much lower temperature of about 94 K (−179.2 °C; −290.5 °F).

More information: NASA Science-Solar System Exploration

Titan was discovered on March 25, 1655, by the Dutch astronomer Christiaan Huygens. Huygens was inspired by Galileo's discovery of Jupiter's four largest moons in 1610 and his improvements in telescope technology. Christiaan, with the help of his older brother Constantijn Huygens, Jr., began building telescopes around 1650 and discovered the first observed moon orbiting Saturn with one of the telescopes they built. It was the sixth moon ever discovered, after Earth's Moon and the Galilean moons of Jupiter.

Christiaan Huygens

Huygens named his discovery Saturni Luna or Luna Saturni, Latin for Saturn's moon, publishing in the 1655 tract De Saturni Luna Observatio Nova, A New Observation of Saturn's Moon. After Giovanni Domenico Cassini published his discoveries of four more moons of Saturn between 1673 and 1686, astronomers fell into the habit of referring to these and Titan as Saturn I through V, with Titan then in fourth position.

Other early epithets for Titan include Saturn's ordinary satellite. Titan is officially numbered Saturn VI because after the 1789 discoveries the numbering scheme was frozen to avoid causing any more confusion, Titan having borne the numbers II and IV as well as VI. Numerous small moons have been discovered closer to Saturn since then.

The name Titan, and the names of all seven satellites of Saturn then known, came from John Herschel, son of William Herschel, discoverer of two other Saturnian moons, Mimas and Enceladus, in his 1847 publication Results of Astronomical Observations Made during the Years 1834, 5, 6, 7, 8, at the Cape of Good Hope.

He suggested the names of the mythological Titans (Ancient Greek: Τῑτᾶνες), brothers and sisters of Cronus, the Greek Saturn. In Greek mythology, the Titans were a race of powerful deities, descendants of Gaia and Uranus, that ruled during the legendary Golden Age.

More information: Space I & II

Titan is the only known moon with a significant atmosphere, and its atmosphere is the only nitrogen-rich dense atmosphere in the Solar System aside from Earth's.

Observations of it made in 2004 by Cassini suggest that Titan is a super rotator, like Venus, with an atmosphere that rotates much faster than its surface. Observations from the Voyager space probes have shown that Titan's atmosphere is denser than Earth's, with a surface pressure about 1.45 atm. It is also about 1.19 times as massive as Earth's overall, or about 7.3 times more massive on a per surface area basis.

Opaque haze layers block most visible light from the Sun and other sources and obscures Titan's surface features. Titan's lower gravity means that its atmosphere is far more extended than Earth's. The atmosphere of Titan is opaque at many wavelengths and as a result, a complete reflectance spectrum of the surface is impossible to acquire from orbit. It was not until the arrival of the Cassini–Huygens spacecraft in 2004 that the first direct images of Titan's surface were obtained.

Spotting dust storms on Titan

Titan's surface temperature is about −179.2 °C. At this temperature, water ice has an extremely low vapor pressure, so the little water vapor present appears limited to the stratosphere.

Titan receives about 1% as much sunlight as Earth. Before sunlight reaches the surface, about 90% has been absorbed by the thick atmosphere, leaving only 0.1% of the amount of light Earth receives. Atmospheric methane creates a greenhouse effect on Titan's surface, without which Titan would be far colder. Conversely, haze in Titan's atmosphere contributes to an anti-greenhouse effect by reflecting sunlight back into space, cancelling a portion of the greenhouse effect and making its surface significantly colder than its upper atmosphere.

Titan's clouds, probably composed of methane, ethane or other simple organics, are scattered and variable, punctuating the overall haze. The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto its surface.

More information: Science Daily

Titan is never visible to the naked eye, but can be observed through small telescopes or strong binoculars. Amateur observation is difficult because of the proximity of Titan to Saturn's brilliant globe and ring system; an occulting bar, covering part of the eyepiece and used to block the bright planet, greatly improves viewing.

Titan has a maximum apparent magnitude of +8.2, and mean opposition magnitude 8.4. This compares to +4.6 for the similarly sized Ganymede, in the Jovian system.

Observations of Titan prior to the space age were limited. In 1907 Catalan astronomer Josep Comas i Solà observed limb darkening of Titan, the first evidence that the body has an atmosphere. In 1944 Gerard P. Kuiper used a spectroscopic technique to detect an atmosphere of methane.

Even with the data provided by the Voyagers, Titan remained a body of mystery -a large satellite shrouded in an atmosphere that makes detailed observation difficult. The mystery that had surrounded Titan since the 17th-century observations of Christiaan Huygens and Giovanni Cassini was revealed by a spacecraft named in their honor.

The Cassini–Huygens spacecraft reached Saturn on July 1, 2004, and began the process of mapping Titan's surface by radar. A joint project of the European Space Agency (ESA) and NASA, Cassini–Huygens proved a very successful mission. The Cassini probe flew by Titan on October 26, 2004, and took the highest-resolution images ever of Titan's surface, at only 1,200 kilometers, discerning patches of light and dark that would be invisible to the human eye.

More information: The Cassini–Huygens last mission in Space

 What a wonderful and amazing Scheme have we here 
of the magnificent Vastness of the Universe! 
So many Suns, so many Earths.
 

Christiaan Huygens

THE CASSINI-HUYGENS LAST MISSION IN SPACE

The Cassini–Huygens

The Cassini–Huygens mission was a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class unmanned robotic spacecraft comprised both NASA's Cassini probe, and ESA's Huygens lander which would be landed on Saturn's largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit. The craft were named after astronomers Giovanni Cassini and Christiaan Huygens.

Launched aboard a Titan IVB/Centaur on October 15, 1997, Cassini was active in space for more than 18 years, with 13 years spent orbiting Saturn, studying the planet and its system after entering orbit on July 1, 2004. The voyage to Saturn included flybys of Venus, Earth , the asteroid 2685 Masursky, and Jupiter. 

Its mission ended on September 15, 2017, when Cassini was commanded to fly into Saturn's upper atmosphere and burn up, in order to prevent any risk of contaminating Saturn's moons, some of whose environments could potentially bear life, with stowaway terrestrial microbes. 

The Cassini–Huygens

The mission is widely perceived to have been successful beyond expectation. Cassini-Huygens has been described by NASA's Planetary Science Division Director as a mission of firsts, that has revolutionized human understanding of the Saturn system, including its moons and rings, and our understanding of where life might be found in the Solar System.

Cassini's original mission was planned to last for four years, from June 2004 to May 2008. The mission was extended for another two years until September 2010, branded the Cassini Equinox Mission. The mission was extended a second and final time with the Cassini Solstice Mission, lasting another seven years until September 15, 2017, on which date Cassini was de-orbited by being allowed to burn up in Saturn's upper atmosphere.

More information: NASA

The Huygens module traveled with Cassini until its separation from the probe on December 25, 2004; it was successfully landed by parachute on Titan on January 14, 2005. It successfully returned data to Earth for around 90 minutes, using the orbiter as a relay. This was the first landing ever accomplished in the outer Solar System and the first landing on a moon other than our own. Cassini continued to study the Saturn system in the following years.

Landed on Saturn's largest moon Titan

At the end of its mission, the Cassini spacecraft executed the Grand Finale of its mission: a number of risky passes through the gaps between Saturn and Saturn's inner rings. 

The purpose of this phase was to maximize Cassini's scientific outcome before the spacecraft was destroyed. The atmospheric entry of Cassini effectively ended the mission, although data analysis and production will continue afterwards.

Until September 2017 the Cassini probe continued orbiting Saturn at a distance of between 8.2 and 10.2 astronomical units from the Earth. It took 68 to 84 minutes for radio signals to travel from Earth to the spacecraft, and vice versa. Thus ground controllers could not give real-time instructions for daily operations or for unexpected events. Even if response were immediate, more than two hours would have passed between the occurrence of a problem and the reception of the engineers' response by the satellite.

More information: Cassini-The Grand Finale

We must believe then, that as from hence we see Saturn and Jupiter; 

if we were in either of the Two, 

we should discover a great many Worlds which we perceive not; 

and that the Universe extends so in infinitum.
 

Cyrano de Bergerac