For the second time, Vladtepesblog has been honoured with a new Fjordman essay. Read, enjoy, pass around. We may well be at the end of an era of free thinking rational science, unencumbered by the oversight of voodoo practitioners and other forms of religious and political censors. Fjordman is a refreshingly honest and courageous historian who has helped shape my world view like very few authors have been able to do. Thank you again Fjordman for this.
Eeyore for Vlad:
I touched briefly upon the subject of astrobiology in my history of geology, Earth science and planetary science, but I will expand upon this here. The best-explored planet next to our own is without doubt Mars, which has been visited by several orbiters as well as by a number of robotic probes on the surface. The most successful ones to date have been the twin Mars Exploration Rovers Spirit and Opportunity from the United States. Originally intended for just a 90-day mission, the rovers landed on opposite sides of the planet in January 2004, but were still exploring the Martian surface as of 2010. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in the USA, manages the rovers on behalf of NASA.
Next to Mars, the most promising candidates for primitive life in our immediate neighbourhood might not be the planets but rather some of their natural satellites. Jupiter’s huge moon Ganymede is the largest moon in our Solar System. Like Saturn’s moon Titan it is larger in diameter than the innermost planet Mercury but has less mass. Ganymede is the only natural satellite in the Solar System known to possess a magnetosphere, which is suspected to be generated through convections within a liquid, iron-rich core, not too different from the Earth.
While it is the least massive of Jupiter’s major Galilean moons, Europa is one of the most interesting bodies in the entire Solar System for astrobiologists and is strongly suspected to harbor a subsurface liquid water ocean. The same could be true of Ganymede and possibly Callisto, although this is considered less likely. If water contains a little bit of ammonia this has an antifreeze effect that could enable liquid water to exist at temperatures significantly below those of liquid freshwater or even seawater here on Earth. With a diameter of over 4,800 km, Callisto is almost the size of Mercury. Unlike Io, Europa and Ganymede, Callisto does not experience much tidal heating and orbits beyond Jupiter’s main radiation belts. “It is thought to be a long dead world, with a nearly complete absence of any geologic activity on its surface.” Any heat generated within it would have to come from radioactive decay alone.
In contrast, the gravitational influence of Jupiter squeezes Europa as it orbits from one side of the planet to the other. This “tidal flexing” should keep its core molten and result in volcanic activity, just like at its neighbor Io which is closer to Jupiter. The downside is that Europa orbits within the unfriendly radiation environment of its planet’s powerful magnetosphere.
Io, the innermost of the Galilean moons, is the most volcanically active body in the Solar System, with volcanoes spewing out sulfur and sulfur dioxide (SO2) to a height of hundreds of kilometers. The heat is caused by massive tidal forces generated by Jupiter and its moons. Volcanism exists on other bodies, too, but not necessarily in the form of molten rock (lava).
The American probes Pioneer 10 and Pioneer 11, launched in 1972 and 1973, were the first spacecraft to visit Jupiter and Saturn in the Outer Solar System. NASA’s Galileo spacecraft orbited Jupiter from 1995 to 2003, sent pictures and data back to the Earth and dropped a probe into the Jovian atmosphere to sample its composition. It also found evidence of what could be an ocean on Europa. New research suggests that there may be plenty of oxygen available there, possibly great enough to support not only microorganisms but perhaps also “macrofauna,” or more complex organisms like fishes. Maybe Europa has hydrothermal vents like the ones we know from the ocean floors of our planet, although this remains pure speculation. Some scientists think the origin of life on Earth occurred at such volcanic vents.
Europa’s ocean, if it does exist, is covered by ice many kilometers thick. Lake Bonney, an ice-covered lake in Antarctica’s Dry Valleys, has been explored by a robot funded by NASA through its astrobiology program as a possible dress rehearsal for future space probes. Europa is covered with sulfur-rich materials concentrated along cracks on its icy surface. Researchers have found one region at Ellesmere Island in the Canadian High Arctic where springs stain the surrounding glacier yellow with sulfur, gypsum and calcite. It is not a perfect analog for Europa, as the radiation is much lower and the temperature and oxygen content higher, but it’s the closest analog we can find here on Earth. Likewise, expeditions to the Norwegian-ruled Svalbard archipelago high in the Arctic are used to test robotic equipment intended for Mars.
NASA, along with the European Space Agency and with possible Japanese and Russian involvement, are pushing ahead with proposals for multiple spacecraft to the Jupiter and Saturn systems to explore the giant planets and their unique satellites Europa, Ganymede, Callisto and Titan in greater detail. The spacecraft would launch in 2020 from different spaceports, provided, of course, that they get the necessary funding for this big undertaking.
One moon besides our own has already been visited by a dedicated space probe, namely Saturn’s giant moon Titan. The temperature at its surface hovers around 94 degrees Kelvin (minus 179 C). Instruments on NASA’s Cassini spacecraft and images captured by ESA’s Huygens probe have revealed a world with a complete liquid cycle, much like the hydrologic cycle on Earth. Rivers and lakes of methane-ethane evaporate to form clouds and the clouds rain hydrocarbons back down onto the surface, flowing through rivers and lakes. It is the only moon with a thick atmosphere and contains hundreds of times more liquid hydrocarbons than all the known oil and natural gas reserves on the Earth. Just like Jupiter’s moon Ganymede, Titan is so big that it would probably have been called a planet if it orbited the Sun directly.
There are a few known organisms on the Earth that can survive without oxygen. While certain terrestrial microbes might conceivably survive on Mars, at least below its surface, Titan is almost certainly far too cold for any life forms we know of. If life does exist there, which is considered unlikely, it will be radically different from anything we have seen before. “This idea that you can walk up to the alien ambassador and shake their hand is very unlikely,” says biochemist William Bains of MIT in the USA and the England-based Rufus Scientific. Other worldly life forms coming into contact with us could prove hazardous for both parties. Titan life’s metabolism might involve chemical compounds such as phosphine and hydrogen sulfide, foul-smelling gases that are toxic to humans. Hypothetical life forms there might have blood based on liquid methane, which would instantly boil on the much warmer Earth.
Enceladus has a diameter of only 500 km, yet it is surprisingly geologically active for such a small body and arguably the most intriguing of Saturn’s many moons next to Titan. Its powerful water vapor geysers were first spotted in 2005 by NASA’s Cassini orbiter and contribute to creating Saturn’s huge E-ring. Several close flybys, where Cassini has been only a few dozen kilometers above its surface, have revealed the presence of ammonia in the icy plumes of Enceladus, as well as carbon dioxide and carbon monoxide, nitrogen, methane, complex hydrocarbons such as propane (C3H8), ethane and acetylene (C2H2) and other organic materials. It is suspected that the moon might harbor a salty ocean. Scientists believe the internal heat could be explained by a combination of radioactive decay and tidal heating.
The path-breaking American Voyager 2 spacecraft in 1989 observed cryovolcanoes (ice volcanoes) on Triton, Neptune’s largest moon. The mean temperature at its surface is around 34.5 K (-235 C). In this extreme cold methane, nitrogen and carbon dioxide freeze solid. The geysers Voyager 2 observed there are probably nitrogen geysers, maybe driven by seasonal heating by the Sun. At 2700 km in diameter – bigger than Pluto – it is the seventh-largest moon in the Solar System after Ganymede, Titan, Callisto, Io, the Earth’s Moon and Europa.
The atmosphere of Triton varies with Neptune’s very long seasons. A team at the European Southern Observatory’s Very Large Telescope made infrared observations which show that the warmth of the Sun causes Triton’s very thin atmosphere to thicken. As the surface warms up, a thin layer of frozen nitrogen, methane and carbon monoxide on its surface sublimates into gas. Sublimation is the transition of a substance directly from the solid phase to the gas phase. Ice can sublime on the Earth and become water vapor directly, without first being liquid water. “We have found real evidence that the sun still makes its presence felt on Triton, even from so far away,” said Emmanuel Lellouch of the Observatoire de Paris in France in 2010. The telescope also discovered the presence of carbon monoxide (CO) in its atmosphere.
Triton is the only large natural satellite in the Solar System with a retrograde orbit, in the opposite direction to its planet’s rotation. Whereas the tides on Earth cause our Moon to spiral outward, the tides on Neptune cause Triton to spiral inward. Many millions of years from now it will eventually reach Neptune’s Roche limit. Named after the nineteenth century French astronomer Édouard Roche who first calculated it this is the distance at which a planet creates tides on the solid surface of an object high enough to pull that object apart. Triton will then either crash into Neptune or be pulled apart to create a new ring system around that planet.
A recent advance of tremendous importance is the discovery of the first extrasolar planets or exoplanets, planets orbiting other stars. Hundreds of these have been found during the first generation alone. This has led to the establishment of a new branch within planetary science dubbed exoplanetology or exoplanet science. Most of the planets discovered so far have been gas giants detected through indirect means by observing the effects they have on the stars they orbit, but methods are rapidly improving and Earth-like rocky planets have been identified.
Aleksander Wolszczan, a Polish-born USA-based radio astronomer, became the co-discoverer of some of the first extrasolar planets. In 1992, together with the Canadian-born astronomer Dale Frail, he found evidence of planets orbiting around a pulsar (neutron star), one of the first confirmed discoveries of extrasolar planets of any kind. Michel Mayor, a Swiss professor of astronomy at the University of Geneva in Switzerland, together with his associate Didier Queloz in 1995 discovered the first exoplanet orbiting a Sun-like main sequence star. Michel Mayor and his team have discovered many additional extrasolar planets since then.
It is highly unlikely whether we in the foreseeable future, if ever, will have the technological capability to send robotic probes to explore these extrasolar planets, let alone manned missions. Nevertheless, by studying them from a distance we can learn a great deal about planet formation and about how common Earth-like planets are in our galaxy.
Several extrasolar planets have been discovered to be orbiting backwards – that is, they revolve in the opposite direction that their host star rotates. Planets are thought to form in the cloud of gas and dust that surrounds a young star. This proto-planetary disc rotates in the same direction as the star, and it was believed that any planets that formed out of this nebula would revolve in their orbits in that same direction. “The new results really challenge the conventional wisdom that planets should always orbit in the same direction as their star’s spin,” said Andrew Cameron of the University of St. Andrews in Scotland to SPACE.com.
The German astronomer Otto Heckmann (1901-1983), educated at the University of Bonn, worked at the University of Göttingen from 1927-41 and directed the Hamburg Observatory from 1941-62. After World War II, Heckmann joined with other leaders in European astronomy to promote the idea of a joint observatory in the Southern Hemisphere, and from 1962 to 1969 he served as the first director general of the European Southern Observatory (ESO). ESO operates several large, world-class observing sites in the dry Atacama Desert region of Chile, South America. The ESO headquarters are located near Munich, Germany.
Unlike most chemical elements lighter than iron, the alkali metal lithium with atomic number three (three protons in the nucleus) is not easily produced in stars. According to current theories, most of it was probably created after the Big Bang itself. Yet astronomers see a wide range of different lithium levels in Sun-like stars. With the ESO’s HARPS spectrograph survey of hundreds of stars, astronomer Garik Israelian of Spain’s Instituto de Astrofisica de Canarias in Tenerife and his colleagues found that those that had an orbiting planetary system had lithium levels similar to the Sun’s while those that did not had higher levels. If this insight is correct it might suggest an easier way to look for undiscovered planetary systems around other stars. Jorge Meléndez at the University of Porto in Portugal has identified 15 elements that are more abundant in Sun-size stars with giant planets orbiting very close to the stars. But these elements are scarce in our Sun, which hosts distant giants and small, rocky inner planets. A chemical signature similar to the Sun’s could be a clue to finding Earth-like worlds.
By the twenty-first century, astronomy has progressed to the point where we can use spectroscopy not only to determine the chemical composition of stars, but even to study the atmospheres of planets orbiting other stars than our own. In 2010 it was reported that the first direct capture of a spectrum of light from a planet outside of our Solar System had been obtained by the European Southern Observatory, from a planet 130 light-years away from us.
Although we now possess the technological capability to send probes to physically explore the other planets in our Solar System, as the Americans in particular have done in recent generations, it will remain impossible for us in the foreseeable future to visit planets orbiting other stars. The only way we have of studying them is through telescopes and spectroscopy.