Life in Our Solar System

Although we can imagine life based on something other than carbon chemistry, we know of no examples to tell us how such life might arise and survive.

Although we can imagine life based on something other than carbon chemistry, we know of no examples to tell us how such life might arise and survive.

Although we can imagine life based on something other than carbon chemistry, we know of no examples to tell us how such life might arise and survive.

Although we can imagine life based on something other than carbon chemistry, we know of no examples to tell us how such life might arise and survive.

Although we can imagine life based on something other than carbon chemistry, we know of no examples to tell us how such life might arise and survive.

Although we can imagine life based on something other than carbon chemistry, we know of no examples to tell us how such life might arise and survive.

We must limit our discussion to life as we know it and the conditions it requires.

We must limit our discussion to life as we know it and the conditions it requires.

We must limit our discussion to life as we know it and the conditions it requires.

We must limit our discussion to life as we know it and the conditions it requires.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The most important requirement is the presence of liquid water, not only as part of the chemical reactions of life, but also as a medium to transport nutrients and wastes within the organism.

The water requirement automatically eliminates many worlds in our solar system.

The water requirement automatically eliminates many worlds in our solar system.

The water requirement automatically eliminates many worlds in our solar system.

The moon is airless, and although some data suggest ice frozen in the soil at its poles, it has never had liquid water on its surface.

The moon is airless, and although some data suggest ice frozen in the soil at its poles, it has never had liquid water on its surface.

The moon is airless, and although some data suggest ice frozen in the soil at its poles, it has never had liquid water on its surface.

The moon is airless, and although some data suggest ice frozen in the soil at its poles, it has never had liquid water on its surface.

In the vacuum of the lunar surface, liquid water would boil away rapidly.

In the vacuum of the lunar surface, liquid water would boil away rapidly.

In the vacuum of the lunar surface, liquid water would boil away rapidly.

Mercury too is airless and cannot have had liquid water on its surface for long periods of time.

Venus has some traces of water vapor in its atmosphere, but it is much too hot for liquid water to survive.

Venus has some traces of water vapor in its atmosphere, but it is much too hot for liquid water to survive.

If there were any lakes or oceans of water on its surface when it was young, they must have evaporated quickly.

The Jovian planets have deep atmospheres, and at a certain level, they have moderate temperatures where water might condense into liquid droplets.

The Jovian planets have deep atmospheres, and at a certain level, they have moderate temperatures where water might condense into liquid droplets.

The Jovian planets have deep atmospheres, and at a certain level, they have moderate temperatures where water might condense into liquid droplets.

The Jovian planets have deep atmospheres, and at a certain level, they have moderate temperatures where water might condense into liquid droplets.

The Jovian planets have no surfaces where oceans could nurture the beginning of life, and currents in the atmosphere seem destined to circulate gas and water droplets from regions of moderate temperature to other levels that are much too hot or too cold for life to survive.

The Jovian planets have no surfaces where oceans could nurture the beginning of life, and currents in the atmosphere seem destined to circulate gas and water droplets from regions of moderate temperature to other levels that are much too hot or too cold for life to survive.

The Jovian planets have no surfaces where oceans could nurture the beginning of life, and currents in the atmosphere seem destined to circulate gas and water droplets from regions of moderate temperature to other levels that are much too hot or too cold for life to survive.

A few of the satellites of the Jovian planets might have suitable conditions for life.

A few of the satellites of the Jovian planets might have suitable conditions for life.

Jupiter’s moon Europa seems to have a liquid-water ocean below its icy crust, and minerals dissolved in that water would provide a rich broth of possibilities for chemical evolution.

Jupiter’s moon Europa seems to have a liquid-water ocean below its icy crust, and minerals dissolved in that water would provide a rich broth of possibilities for chemical evolution.

Jupiter’s moon Europa seems to have a liquid-water ocean below its icy crust, and minerals dissolved in that water would provide a rich broth of possibilities for chemical evolution.

Jupiter’s moon Europa seems to have a liquid-water ocean below its icy crust, and minerals dissolved in that water would provide a rich broth of possibilities for chemical evolution.

Jupiter’s moon Europa seems to have a liquid-water ocean below its icy crust, and minerals dissolved in that water would provide a rich broth of possibilities for chemical evolution.

Jupiter’s moon Europa seems to have a liquid-water ocean below its icy crust, and minerals dissolved in that water would provide a rich broth of possibilities for chemical evolution.

Nevertheless, Europa is not a promising site to search for life because conditions may not have remained stable for the billions of years needed for life to evolve beyond the microscopic stage.

Nevertheless, Europa is not a promising site to search for life because conditions may not have remained stable for the billions of years needed for life to evolve beyond the microscopic stage.

Nevertheless, Europa is not a promising site to search for life because conditions may not have remained stable for the billions of years needed for life to evolve beyond the microscopic stage.

Nevertheless, Europa is not a promising site to search for life because conditions may not have remained stable for the billions of years needed for life to evolve beyond the microscopic stage.

Nevertheless, Europa is not a promising site to search for life because conditions may not have remained stable for the billions of years needed for life to evolve beyond the microscopic stage.

Nevertheless, Europa is not a promising site to search for life because conditions may not have remained stable for the billions of years needed for life to evolve beyond the microscopic stage.

Nevertheless, Europa is not a promising site to search for life because conditions may not have remained stable for the billions of years needed for life to evolve beyond the microscopic stage.

If Jupiter’s moons interact gravitationally and modify their orbits, Europa may have been frozen solid at some points in history.

If Jupiter’s moons interact gravitationally and modify their orbits, Europa may have been frozen solid at some points in history.

If Jupiter’s moons interact gravitationally and modify their orbits, Europa may have been frozen solid at some points in history.

Chemical reactions occur slowly or not at all at such low temperatures, so the chemical evolution needed to begin life may never have occurred on Titan.

Mars is the most likely place for life in our solar system.

The evidence, however, is not encouraging.

The evidence, however, is not encouraging.

It was probably part of debris ejected into space by a large impact on Mars.

It was probably part of debris ejected into space by a large impact on Mars.

It was probably part of debris ejected into space by a large impact on Mars.

It was probably part of debris ejected into space by a large impact on Mars.

ALH84001 is important because a team of scientists studied it and announced in 1996 that it contained chemical and physical traces of ancient life on Mars.

ALH84001 is important because a team of scientists studied it and announced in 1996 that it contained chemical and physical traces of ancient life on Mars.

ALH84001 is important because a team of scientists studied it and announced in 1996 that it contained chemical and physical traces of ancient life on Mars.

ALH84001 is important because a team of scientists studied it and announced in 1996 that it contained chemical and physical traces of ancient life on Mars.

ALH84001 is important because a team of scientists studied it and announced in 1996 that it contained chemical and physical traces of ancient life on Mars.

ALH84001 is important because a team of scientists studied it and announced in 1996 that it contained chemical and physical traces of ancient life on Mars.

Scientists were excited too, but being professionally skeptical, they began testing the results immediately.

Scientists were excited too, but being professionally skeptical, they began testing the results immediately.

In many cases, the results did not confirm the conclusion that life once existed on Mars.

In many cases, the results did not confirm the conclusion that life once existed on Mars.

In many cases, the results did not confirm the conclusion that life once existed on Mars.

Some chemical contamination from water on Earth has occurred, and some chemicals in the meteorite may have originated without the presence of life.

The physical features that look like fossil bacteria may be mineral formations in the rock.

The physical features that look like fossil bacteria may be mineral formations in the rock.

The physical features that look like fossil bacteria may be mineral formations in the rock.

Nevertheless, conclusive evidence may have to wait until a geologist in a space suit can wander the dry streambeds of Mars cracking open rocks and searching for fossils.

Nevertheless, conclusive evidence may have to wait until a geologist in a space suit can wander the dry streambeds of Mars cracking open rocks and searching for fossils.

Nevertheless, conclusive evidence may have to wait until a geologist in a space suit can wander the dry streambeds of Mars cracking open rocks and searching for fossils.

We are left to conclude that, so far as we know, our solar system is bare of life except for Earth.

Consequently, our search for life in the universe takes us to other planetary systems.

Consequently, our search for life in the universe takes us to other planetary systems.