THE OTHER PLANETARY SYSTEMS AND THE SEARCH FOR LIFE

The search for life in our Solar System has always been disappointing. Venus revealed to be a dry and corrosive environment, Mars is much colder and hostile than thought, and the gaseous giants and their frozen satellites offer prohibitive conditions for the development of life as we know it. Nevertheless, the finding of living organisms in the Solar System, even bacteria or their fossil traces, recently speculated by NASA scientists, should represent an extraordinarily important event not only from the scientific point of view, but also psychological and philosophical.
Our interest though also goes to the search for other evolved civilizations, in the conviction (or in the hope) that we are not alone in the Universe. Seeing as the existence of intelligent forms of life on the other planets of our Solar System can be excluded, the most interesting possibilities, as to the research of intelligent life in the Universe, are connected to the study of planetary systems that orbit around stars of our galaxy.

THE SEARCH FOR EXTRA SOLAR PLANETS

The planets are objects with very weak luminosity compared to their star, and so far no extra solar planet has ever been directly observed. Nevertheless their presence can be determined by studying the effects of their gravitational field on the motion of the central star. By using such technique 3 extra solar planets have been discovered in the last year, which orbit around normal stars ( two of which very similar to the Sun).
 

The 51 Pegasi planet

51 Pegasi B is a planet that orbits around the central star. Its mass is approximately 180 times that of the Earth. The planet does not appear able to host living organisms; the temperature on its surface, in fact, is approximately 1,000 degrees. 
 

The planet 47 Ursa Majoris.

47 UMa B is the name of the planet that orbits around a star of the Ursa Major. Its mass is approximately 900 times that of the Earth, the orbital period is approximately 3 years, and its distance from the central star 300 million km. Scientists think that the surface temperature is similar to that of Mars, therefore not very different from that of the Earth. 47 Ursa Majoris is a star that resembles the Sun. 
 

The planet 70 Virginis.

The planet that orbits around the 70 Virginis star has a mass that is approximately 2,000 times that of the Earth. Its distance from the central star is 75 million km, and a complete revolution takes about 4 months. Its surface temperature should be approximately 80 degrees centigrade, which is not incompatible with the existence of water in the liquid phase. 70 Virginis is a star that resembles the Sun.
 

THE SETI PROJECT

How would you look for other intelligent beings? The most direct method is to look for the signals that a technological civilization emits towards space: radio waves. Hence the SETI project (Search for Extra Terrestrial Intelligence), with the aim of both "listening" to the Universe with large radio telescopes, hoping to receive signals of artificial origin, and "sending" terrestrial messages that, hopefully, could demonstrate our intelligence to whom receives them.
The main problems with these forms of communication are the large distances and the low speed of radio waves, that, just as light or in general all electromagnetic radiation, travel at 300 thousand km/sec. This means that if we send now a message towards a star at the distance of 1,000 light years, which is a small distance in astronomical terms, a hypothetical civilization would receive our message at the beginning of the 4th millennium.
If the aliens then decided to reply, we would receive their message in the year 3997. We would have to wait 2,000 years only to establish the first contact! The second problem is: where should we start searching? There are so many stars that even considering only the near ones we would have to choose among thousands of directions for the pointing of the telescopes and the sending of the messages. It is important to have a well structured organization, plenty of time, adequate funding, and a lot of fortune: it can be demonstrated that it is easier to look for a needle in a haystack!

The Goldstone (California) radio antenna for the transmission and reception of "intelligent" signals.  (JPEG, 381 K) (Caltech-JPL)

 

An other planetary system? This star, concealed by a mask in order to study the surrounding material with weaker luminosity, has a disc, 60 billion km large, probably made of ice, silicates, and carbonaceous organic substances, the same materials that form our Solar System. It is the star Beta Pictoris, 50 light years from us, photographed in false colours to better highlight the areas with different luminosities. The density of the material that forms the ring, seen here edgewise, indicates that the formation of some planets could have occurred.   (JPEG, 597 K) (University of Arizona-JPL)

 

A detail of the "fingers" that are formed in the nebula of the Eagle, 7,000 light years from us. The intense ultraviolet radiation of the surrounding stars disperses the weakest gases, discovering the nuclei of dense gases or dust that represent embryos of stars. The cocoon that wraps them is the material that maybe will originate the planetary bodies. New stellar systems will therefore originate from those globules.  (JPEG, 82 K) (NASA-STScI)

 

The Orion nebula, a huge cluster of gas and dust at a distance of 1,500 light years, is the best known "cradle" of stars in the Milky Way. The new stars that are formed here emit a large amount of radiations that energize the surrounding gases that shine with these spectacular colours. It was recently noted that over a hundred stars are surrounded by clouds of gas and dust the size of which is comparable with that of our Solar System. Some of these globules have the shape of a flat disc that orbits around the star. It is a long time that astronomers think that our planetary system originated from similar material that orbited around the Sun. The presence of planets around the stars could therefore be a common phenomenon in our galaxy as well as in others.  (JPEG, 345 K) (NASA-STScI)

TRACES OF LIFE ON MARS

Fragments of the planet Mars, that detached due to violent impacts on the surface, reached us in the form of meteorites. We definitely recognized 12 by analyzing the gases trapped inside them, that corresponded to those found by the Viking probes in the atmosphere of Mars. Almost all these rocks come from martian soil, and their age ranges between 180 million and 1.3 billion years. Only one sample, ALH84001, is very old, and it gives us precious information about the beginning of the history of Mars, seeing as it crystallized from the magma soon after the formation of the planet, 4.5 billion years ago. Many of the martian meteorites indicate the presence, in the past, of water in the liquid phase, since among their components are salts and clay. The atmosphere, most of it now dispersed in space, must have been dense, since heavy isotopes of gaseous atmospheric molecules were found in the meteorites.  

The search for rocky samples on Mars. The meteorites we have are all volcanic rocks, and surely are not the best material for the search for fossil traces.

The future missions on Mars will also have the task to look for soil samples of the sedimentary kind, that is rocks that originated from stratified sediments, the rocks that enabled us to trace the history of the evolution of the living beings on our planet.
Therefore the beginning of the next millennium will maybe bring us the confirmation that we have not always been alone in the Solar System.  (JPEG, 557 K)
(NASA-Johnson Space Center)

The ALH84001 meteorite fell on the Antarctic approximately 13,000 years ago, and was discovered in 1984 in an area called Allan Hills. Only recently detailed analyses revealed:   1) the presence of organic molecules that are thought to be of martian origin;  2) many mineral characteristics that on the Earth are connected to biological activities;  3) the possible presence of micro fossils, very small organisms similar to our bacteria. (JPEG, 62 K) (NASA-Johnson Space Center)

 

ALH84001. Globules of carbonaceous minerals, probably dating back to 3.6 billion years ago, settled in the clefts of the meteorite. The coin shapes and the stratified edges remind the terrestrial primitive fossils.  (JPEG, 363 K) (NASA-Johnson Space Center)

 

ALH84001. The most striking pictures, those that most suggest a trace of fossil life, are those revealed by a high resolution electronic microscope: ovoid forms that resemble very small nanobacteria.  (JPEG, 390 K) (NASA-Johnson Space Center)