An artist's illustration of an Earth-like planet. The search for planets that are similar to Earth is one of NASA's main goals. Many planets have already been discovered orbiting other stars, but so far only larger planets (the size of Jupiter or larger) have been found. New missions are being planned by NASA which will be able to detect smaller Earth-sized planets. Some of these missions will also try to detect signs of life on these planets by studying emissions in their atmospheres.


'Fifty planets' could have life

BBC News Online science staff
By Helen Briggs
1 April, 2004

Astronomers estimate about half the planetary systems so far discovered in our galaxy could contain Earth-like worlds.

And they say that space telescopes will be capable of observing these planets and investigating them to see if they support life in about 15 years' time.

Scientists have recently discovered more than 100 stars other than our Sun with planets circling about them.
But they are all giant planets like Jupiter that cannot sustain life.
Planets more like the Earth should, in theory, exist too. But they are too small to be seen using current technology.

Computer modelling

Research work by the UK's Open University suggests there are perhaps 50 or so of these small, rocky bodies on which there is liquid water and possibly life.

"We would certainly expect them to be something like Earth in size and in mass, to have a reasonable atmosphere; they'll have oceans and continents, they'll be potential abodes of life, but the big question is - has there actually been life there?" OU astronomer Professor Barrie Jones told BBC News Online.

His team used computer modelling to calculate the likely number of habitable planets, based on what we know about how planets form and the conditions needed for life.

The planets would exist in what is sometimes referred to as the "Goldilocks" zone, a region set back from the parent star where it is neither too hot for liquid water, nor too cold.

By launching "Earths" into a variety of orbits in this zone and following their progress with the computer model, the small planets have been found to suffer a variety of fates.

Read more:


Smallest "Earth-like" Planet Seen

25 August, 2004
By Pallab Ghosh
BBC science correspondent in Stockholm, Sweden

European scientists have discovered what they describe as the smallest Earth-like planet orbiting a star outside our Solar System.
The planet is 14 times the size of Earth - not so large that it qualifies as a gas giant - and is close enough to the star that it is unlikely to be icy.

Dr Nuno Santos, of the University of Lisbon, said the new planet could be thought of as "super-Earth-like".

He was speaking at the EuroScience Open Forum in Stockholm, Sweden.
Dr Santos claimed the discovery set a new record for the smallest planet discovered around a solar type star, "further extending European Leadership in the field".

The discovery was made using the highly sensitive Harps spectrograph on the European Southern Observatory's 3.6m telescope at La Silla.

The planet was found to be orbiting the star mu Arae in the southern constellation of Altar. It is the second planet discovered round the star and completes a full revolution in 9.5 days.

Mu Arae was already known to harbour a Jupiter-sized planet with a 650-day orbital period. Previous observations hinted that the giant planet may have a smaller companion much further away.

According to Francois Bouchy, of the Marseille Astrophysics Laboratory, "not only did the Harps measurements confirm what we previously believed to know about this star, but they also showed that an additional planet on a short orbit was present".
This makes mu Arae a very exciting new planetary system.

To learn about Mu Arae.


Scientists estimate 30 billion Earths

By Dr David Whitehouse
BBC News Online science editor
Monday, 1 July, 2002

There could be billions of Earths out there.
Astronomers say there could be billions of Earths in our galaxy, the Milky Way. Earth is not alone.
Their assessment comes after the discovery of the 100th exoplanet - a planet that circles a star other than our own.

The latest find is a gas giant, just like all the other exoplanets so far detected, and orbits a Sun-like star 293 light-years away.

Scientists say they are now in a position to try to estimate how many planets may exist in the galaxy and speculate on just how many could be like the Earth. The answer in both cases is billions.

Virtually all the stars out to about 100 light-years distant have been surveyed. Of these 1,000 or so stars, about 10% have been found to possess planetary systems.

So, with about 300 billion stars in our galaxy, there could be about 30 billion planetary systems in the Milky Way alone; and a great many of these systems are very likely to include Earth-like worlds, say researchers.

Better grasp

The 100th new planet circles the star HD 2039. It was found by astronomers using the Anglo-Australian Telescope as part of the Carnegie Institution Planet Search Program.

The Jupiter-sized world circles its star every 1,210 days at a distance of about 320 million kilometres (200 million miles).

Astronomer Dr Jean Schneider, who compiles the Extrasolar Planets Catalogue, told BBC News Online: "The 100th planet is symbolic and important.

"The first discoveries concentrated on short orbital periods because of the limited timebase of observations. Now, we are learning more about the statistics of long orbital periods and know to what extent our own Jupiter is exceptional or not."

New telescopes

With the new world, astronomers say that they have just about finished surveying all the Sun-like stars out to a distance of 100 light-years from Earth.

Current planet detection technology - based on the "wobble" induced in the parent star by the gravitational pull of the orbiting planet - can only detect worlds about the mass of Saturn or larger. Earth-sized worlds are too small to be seen.

But even in this "biased" survey of giants, the smaller worlds predominate - which makes astronomers think that Earth-like worlds do exist. They may even be as common as Jupiter-sized exoplanets.

And if stellar statistics gathered in our local region of space are applied to our galaxy of 300 billion stars, then there may be 30 billion Jupiter-like worlds and perhaps as many Earth-like worlds as well.

Astronomers will have to wait for a new generation of space-based telescopes incorporating advanced detectors before they can detect Earth-sized worlds orbiting other stars.


30 Billion Earths? New Estimate of Exoplanets in Our Galaxy

By Robert Roy Britt
Senior Science Writer
29 January 2002

Chances are you haven't spent a whole lot of time wondering how many Jupiter-like planets exist in our galaxy. But Charley Lineweaver has, because it bears on a more important question: How many potentially habitable planets are there?

New calculations by Lineweaver and Daniel Grether, both of the University of New South Wales in Australia, provide an encouraging answer to this question. The researchers expect a flood of Jupiters will be found, perhaps 50 percent more than currently expected.

Each such discovery would be significant in the hunt for planets that could harbor life.

Why? Because much of the evolution of our own solar system, including the formation of Earth, was orchestrated or affected by Jupiter, the largest planet with by far the bulk of the solar system's mass, excepting the Sun, of course.

"Our solar system is Jupiter and a bunch of junk," as Lineweaver puts it.

Our protector

When Jupiter developed, it simply bullied other objects into position or out of existence. Then the mighty gas giant became Earth's protector.

Though the fledgling Earth was pummeled by asteroids and comets, making it difficult for life to take hold, it could have been much worse. Jupiter shielded Earth from an even heavier bombardment of debris that made its way from the outskirts of the new system toward its central star.

That protective role continues. In 1994, Jupiter used its immense gravity to lure comet Shoemaker-Levy into a death plunge. Had the comet hit Earth, it would have sterilized much or all of the planet.

For now, no one knows whether our solar system represents a common method of formation and evolution. In fact, discoveries over the past six years seem to indicate otherwise. Most of the roughly 80 planets discovered outside our solar system are much more massive than Jupiter. They also orbit perilously close to their host stars, locations that would likely prevent rocky planets from forming in so-called habitable orbits.

But experts attribute these findings to the limitations of technology. Smaller planets in more comfortable orbits around other stars simply can't be detected. Yet.

How many Jupiters?

All this in mind, Lineweaver and Grether worked out some new calculations for the prevalence of planets that are about Jupiter's size at about the same distance from their host stars. The calculations are based on some of the most recent extrasolar planet discoveries, in which ever-smaller objects are being detected at ever-greater distances from their host stars.

So how many Jupiters are out there orbiting Sun-like stars in the Milky Way Galaxy?

"At least a billion, but probably more like 30 billion," Lineweaver told

And the math behind that?

"There are about 300 billion stars in our galaxy. About 10 percent (or 30 billion) are roughly Sun-like," he explained. "At least 5 percent (1.5 billion) but possibly as many as 90 percent or 100 percent (about 30 billion) of these have Jupiter-like planets."

These estimates would vary based on exactly what you call Jupiter-like or Sun-like, Lineweaver said.

What about Earths?

The calculations, which are part of a paper that has been submitted to the journal Astrobiology, don't bear directly on worlds like our own. But with what's known of planet formation, some speculation is possible.

"A reasonable guess is the same number of Earths as Jupiters," Lineweaver said.

That, however, depends heavily on how one defines Earth-like. If one includes rocky planets in general, like Mercury, Venus and Mars, "then they are probably more common than Jupiters," he said. If, however, you mean rocky planets with liquid water at the surface, "then we really can't answer that very well. They may be as common as Jupiters, or they may be much less common."

Alan Boss, an expert in planetary system formation at the Carnegie Institution of Washington, said the new calculations for Jovian twins seem reasonable. Trying then to estimate the number of Earth-like planets requires "a leap of faith, but one which appears to be plausible," he said.

"As the veil covering the unseen portions of discovery space is lowered in the next decade, I expect we will find that Jupiter-like planets are commonplace," said Boss, who was not involved in the new study. "Whether or not that also means Earth-like planets are common can only be proven by NASA's Kepler mission."

Kepler, recently approved to launch in 2006, will monitor 100,000 stars for telltale dips in light indicating an Earth-sized planet in an Earth-like orbit has crossed in front of the star. While it would not take photographs, Kepler could provide the first census of planets that have the potential to support life.


Looking into the Future!

An artist's impression of the new worlds. If mankind survives another 1000 years the human race will have great knowledge and power to make new worlds. (Click image to enlarge)

Can a planet have two Suns? "YES"

News articles about a planet have 2 or 3 suns.

Many planets may have double suns
Worlds with double sunsets common
Planets with Two Suns Likely Common
First Planet Under Three Suns Is Discovered
Planet-Forming Disk Discovered Orbiting Twin Suns
Surprise Discovery: Two Planets, Two Stars, One System

Quest for New Life

Recent discoveries of new planets in far-distant constellations have pushed scientists to search for signs of intelligent life among the stars of the Milky Way galaxy. Within the next ten years scientists will incerase their power of signal-detection equipment at least a thousand-fold. Scientists at the SETI Institute (Search for Extraterrestrail Intelligence) will try to discovery evidence of intelligence elsewhere in the universe. Researchers also plan to broaden their search to 10 Million stars.

The universe is infinite and the chance of other life forms existing is quite likely, especially when 10 Million stars are scanned. What does this mean to us here on Earth? If distant life is discovered on planets that are suitable for humans we may find ourselves moving off of this earth and heading out to "new worlds", maybe even just for a vacation. Some people say the universe is a living being. In all this excitement about new planet discoveries there is one thing not to be taken for granted. The Earth. For the earth is where the beings of today evolved and we will consciously (or subconsciously) maintain a connection to our life giving planet somewhere deep in our hearts.

Learn How You Can Help Search For Extraterrestrial Intelligence.
  1. SETI Institute - SETI News Home page
  2. SETI Institute - News
  3. SETI Home
Alien Radiotelescope probes the sky for signs of Intelligent Life.


The four basic types of terrestrial planets (Most earth-like planets)

There are four basic types of terrestrial planets imaginable around other stars. Upper left: A dry, barren desert world in a system devoid of water. Upper right: A warm and moist jungle world covered with plant life and a rich carbon dioxide atmosphere, and located at the inner edge of the habitable zone. Lower left: A frozen, ice-covered planet just outside the habitable zone. Lower right: A water world with large oceans and little land mass in the middle of the habitable zone. (Click image to enlarge) Image Credit: NASA.