The possibility of life elsewhere in the universe has always

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FEATURE ARTICLE

HARI OM VATS

The possibility of life elsewhere in the universe has always fascinated humans. Over the years, however, space probes to most planets have busted several myths. Till such time as we gather concrete evidence let us be logical and base our arguments on scientific evidence.

HUMANS have always been fascinated by the concept of life on planets and stars other than the earth. Highly evolved humans, strange looking creatures, complex machine-like forms or even a mixture of all these have always been conjured.

Long back there were stories and even reports in newspapers claiming that there were plants and animals on the moon and that through a big telescope we could see them. Some believed that there were trees. Big melons grew on them. Animals that looked like small buffaloes grazed beneath the trees. Animals looking like bears walked around on their hind legs.

There were stories claiming the presence of people on the moon too. They had hair all over their bodies and wings. The moon people were friendly, one such story said. Some of them sat near a pond feeding melons to one another. For a long time people believed in these moon creatures.

There was once a radio story that said Martians had landed on Earth. That they had big heads and small bodies. They came in space ships. They were not friendly. Once they landed, they spread out and attacked people in towns and villages.

One such supposed event was discussed among a group of physicists at the University of Chicago during a lunch meeting in 1950 with physicist Enrico Fermi. A group of neighbourhood kids had apparently stolen garbage can lids and tossed them like Frisbees in front of

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people's windows. Neighbours thought the whizzing disks were UFOs from otherworldly visitors.

SCIENCE REPORTER, MAY 2014

FEATURE ARTICLE

By the 1960s, only a few people still believed there were Martians or moon people. In 1969, however, everyone knew for sure that there was no life of any kind on the moon. That was the year Neil Armstrong and Edwin Aldrin walked on the moon. The astronauts found nothing alive. They found no sign that plants or animals had ever lived there. The moon is a dead world and it always has been so.

But still people believed that the moon landing did not mean there was no life on other planets. Many believed that Mars was habitable and hosted standing bodies of water several billion years ago. Mars is like Earth in many ways. Pictures of Mars show places where water once flowed. Where there is water, there may also be plants and animals. Did plants and animal once live on Mars? Could they be living still?

Space probes were sent to Mars, pictures were taken. The soil of Mars was tested. No plants or animals of any kind were seen. The temperature on Mars varies from -140o?C to 20o?C. No signs of life were found in the soil. In some aquifers of Mars there may hopefully be water that erupts episodically to the surface, and so there may be extant life in those locations. Recent measurements by Curiosity Rover have shown evidence of small amount of water in the soil and fine dust of Mars.

Mercury and Venus are the planets closest to the Sun. Probes were sent to Mercury to get a closer look. Mercury does not look like a place where plants or animals could live. It looks like the dead world of the moon. Mercury is the planet closest to the Sun, so one would assume that it is a burning furnace. While the

SCIENCE REPORTER, MAY 2014

Long back there were stories and even reports in newspapers claiming that there were plants and animals on the moon and that through a big telescope we could see them.

temperature on Mercury can reach 465o?C, it can also drop to frigid temperatures of -184o?C. There is such a big variation in Mercury's temperature because the planet has no atmosphere. Mercury gets very hot, much too hot for anything to live there.

Venus, the second closest planet to the Sun, has the highest average temperatures of any planet in our Solar System, regularly reaching temperatures over 460o?C. Venus is so hot because of its proximity to the Sun and its thick atmosphere. Venus' atmosphere is composed of thick clouds containing carbon dioxide and sulphur dioxide. This creates a strong greenhouse effect, trapping the Sun's heat in the atmosphere and turning the planet into a furnace. No signs of life have ever been found on Venus.

Uranus is the coldest planet with the lowest recorded temperature of about -224o?C. Although Uranus is far from the Sun, that is not the only reason why it is so cold. All of the other gas giants in our Solar System give off more heat from their cores than they receive from the Sun. Uranus has a core of about 4,737o?C, which is only one-fifth the temperature of Jupiter's core, thus giving out much less heat from its core.

With temperatures dropping to -218o?C in Neptune's upper atmosphere, the planet is one of the coldest in our Solar System. Like all the gas giants, Neptune has a much hotter core, which is around 7,000o?C. Jupiter, Saturn, Uranus and Neptune are made up of gases and are also very cold, much colder than any place on Earth.

After Earth, the four outer planets in our solar system are gas giants. Jupiter has no solid surface. At the top of Jupiter's clouds, the temperature is around -145o?C. As you descend closer to the centre of the planet, the temperature increases. At the point where atmospheric pressure is ten times greater than it is on Earth, the temperature is 21o?C, which scientists call "room temperature." At the core of the planet, the temperature is much higher, reaching approximately 24,000o?C at the core. The core of Jupiter is hotter than the surface of the Sun.

Because of Saturn's tilt, the southern and northern hemispheres are heated differently causing seasonal and temperature changes. Like on Jupiter, the temperature in the upper atmosphere of Saturn is cold ? up to approximately -175o?C and increases closer to the centre of the planet.

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Thus in our solar system, Earth seems to be the only planet where we know for sure there is life.

Europa and a number of other moons in the outer Solar System have interior water. Titan could host an alternative mode of biochemistry based on ethane and methane.

The Drake equation is a probabilistic argument used to estimate the number of active civilizations in the Milky Way galaxy. The equation was written in 1961 by Frank Drake. It has four factors. Though the values of these factors in the Drake equation are not known, it is still a useful tool for organizing our thinking.

The factors are the number of habitable planets in the galaxy, fraction of life bearing planets, fraction of civilizations capable of interstellar communication and fraction of such

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Hotter Stars Sunlike Stars Cooler Stars

Fahrenheit Celsius

Venus Mercury

There may perhaps be millions of such worlds in the universe where

creatures may know as much as we do. Some may be a lot smarter.

civilization now as opposed to millions and billions of years in the past. With pure conjecture it predicts ~10,000 detectable civilizations in our own galaxy "the Milky Way". There are billions of stars beyond our solar system. There are planets around some of these stars, just as Earth goes around the Sun.

The decades old (~50 years), Search for Extra Terrestrial Intelligence (SETI) experiment has not yet detected any radio signal. But it is argued that this is too short a time in comparison to billions of years that the universe has been around. The civilizations must have come and gone without our knowing that they existed. The absence of evidence is not evidence of absence.

The discovery of extraterrestrial intelligence would be one of the most important ones in human history. To communicate would require means and motivation. After all we can talk to animals that share 99% of our DNA.

May be new facilities, like the Allen Array Radio Telescope which includes 350 antennas, each with diameter of 6 metres will help us get in touch with the technologies of other worlds soon.

The Kepler mission was launched in March 2009. This is a part of the Exoplanet Exploration Program of NASA to find planets (one-half to twice the size of the Earth). The main aim is to search for planets in the habitable zone of a star in our galaxy. The habitable zone of a star is the area around the star where the composition and atmospheric pressure can maintain liquid water on its surface.

There life can be supported as we know.

The Kepler mission has a specially designed 0.95 meter telescope with a photometer. The detection is based on the principle of transit. When a planet crosses in front of its star as viewed by an observer, the event is called transit. The transit by an earth-size planet produces a small change (~100 part per million (ppm)) in the light curve of the star. The change must be periodic if it is caused by a planet.

From the detailed analysis of a planet's orbital size, characteristic temperature can be estimated. These are essential to learn whether or not the planet is in a habitable zone. The telescope simultaneously and continuously monitors the brightness of more than 100,000 stars. This can detect planets as small as 0.8-2.2 times the size of the Earth.

The mission has already discovered more than 3000 candidate and confirmed planets, more recently three more planets, in the habitable zone of their star. The astronomers are focussing their search mainly on stars of F, G and K types. These have longer lifetimes

The major biogenic elements are carbon, nitrogen, oxygen, sulphur and phosphorous. These are routinely created within stars and then ejected out into the interstellar space where they become part of the next generation of stars and planets. Models suggest that biochemistry could have begun within a billion years of the Big Bang. As the universe ages, and more carbon is produced, it gets more hospitable for life.

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Earth

Mars

Jupiter

Saturn

Uranus

Neptune Pluto

Planets not shown to scale

Although not discovered until now, it might be possible that somewhere out among the billions of stars, there must be plants and animals living on other worlds. There may perhaps be millions of such worlds in the universe where creatures may know as much as we do. Some may be a lot smarter. One day we may be able to talk with them. Many years from now we may even travel to those far-off planets and land on them.

But till such time as we gather concrete evidence let us be logical and base our arguments on scientific evidence. Prof. Hari Om Vats is Course Director at the Space Science CSSTEAP, Physical Research Laboratory, Ahmedabad-380009; Email: vats@prl.res.in

SCIENCE REPORTER, MAY 2014

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