Scientists estimate 30 billion Earths

bbc ^ | 3 Jul 02 | Dr David Whitehouse

[RightWhale]

Scientists estimate 30 billion Earths

By Dr David Whitehouse , BBC News Online science editor

Astronomers say there could be billions of Earths in our galaxy, the Milky Way.

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.

[RightWhale]

this Universe is mind-boggling

It is. The Hubble Deep Field image of galaxies is just about all the imagination can handle. Kind of puts a different scale to our problems on earth.

[rmmcdaniell]

If we ever get off this mudball, we can go for a long time without worrying about running out of places to go and things to do. A very long time.

Yes, what is the estimate of time until the last star has burn out? 100 billion years?

[RightWhale]

We have trillions of years of happy, carefree life ahead until the whole thing colapses to a point and starts over. It will get kind of dark and quiet toward the end, which might not be all bad.

[El Gato]

There might be other planets about the size of earth, but none of them, not one, would be like earth in any other way

Why do you say that? I'm sure if they have life it will be very different from life on earth, probably at a fundamental level. But no mild seasons? That's mostly a function of distance and inclination of the orbit, surely some of them will be in the sweet spot. Until recently I thought that there would be lots of earthlike worlds, but with the recent knowledge of how the earth moon system was formed, and knowing that having a large moon may have helped or made possible the developement of life on earth, I've become somewhat less optimistic. If ET is anywhere nearby, within say 50 light years, we should be hearing them, and we are not. Still hope springs eternal.

[El Gato]

So how can they possibly make the claim of earth-like planets? EVERY other planet found has been a gas giant. I'll start to believe this nonsense when they actually do find a planet remotely similar to ours.

At the present state of the art, they couldn't detect and earthlike world if it was there. Too small and too close to the star. Too close to resolve from the (rather brighter) star, and too small to have enough effect on the motion of the star to detect.

[El Gato]

If you belive in evolution, that sounds logical, but if you belive in God and that he created all things,

It is logically possible to believe both (or is it all three). God could very well have created everything by using evolution as His tool. He, after all, created the universe with it's physical laws, laws which probably allow for the possibility of life and evolution.

[teeman8r]

there are two earths orbiting the sun in the same orbital pattern, one on either end, dual existence and parallel realities... we cannot see each other but the proof is they send their probes here every so often and we label them ufos... or weather balloons, depends on their budget... but there, there are no democrats.... they are much more advanced than us.

[The KG9 Kid]

(ChilePepper)"... The number of stars in OUR universe completely overwhelms your argument..."

(RightWhale)"... Add all the zeros you want. It's still zero."

The debate between you two can logically go no further.

I have to agree with RightWhale on scientific priciple: Until we see reproducible results -- that there are other planets like Earth that could sustain life -- the size of the sample only serves to prove that chances of actually finding reproducible results are increasingly negative.

Chile, you do understand the difference between a 'Universe' and a 'Galaxy', correct? ;)

[El Gato]

For a budding space-faring race, Humans got dealt a folding hand. The biggest burn is the dead ball that orbits our planet. A living moon would have been critical to our chances.

On the contrary having any moon, especially a large one like ours, is a big plus. It gives you somewhere close to aim for. Then when you know you can do it, you can think about going farther. An airless world even has some advantages as a staging point for further explorations. The jury is still out on Europa, (IO is a sulpherous ball, heated by tidal friction resembling nothing so much as hell).

[El Gato]

For a budding space-faring race, Humans got dealt a folding hand. The biggest burn is the dead ball that orbits our planet. A living moon would have been critical to our chances.

On the contrary having any moon, especially a large one like ours, is a big plus. It gives you somewhere close to aim for. Then when you know you can do it, you can think about going farther. An airless world even has some advantages as a staging point for further explorations. The jury is still out on Europa, (IO is a sulpherous ball, heated by tidal friction resembling nothing so much as hell).

[Sabertooth]

Astronomers say there could be billions of Earths in our galaxy, the Milky Way.

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.

It appears in the discovery of 100 exoplanetary gas-giants, Astronomers have mastered the ability to talk out of their asses.

100 exoplanets, not a one is rocky like Earth, and the feel they can estimate billions?

Woe to science. This is Dark Age hokey-pokey.

[The KG9 Kid]

Point taken, El Gato, but I think that we can already see that even if there were a New World we just can't sail to it like Columbus did his.

[Ahban]

Kid, your 113 and 114 put a lock on it, and there are a lot of limitations they don't mention. For example, only K and G stars will have a habitable zone for billions of years. The larger ones will swell after a relatively short life, roasting any Earths-in-the-making long before advanced life comes along.

Instead of calculating how many other Earth's there are, they should be scratching their heads trying to figure out how THIS ONE ever got here. It's too perfect. Everything has to work out just right. The odds of another planet that harbors intellignet life in this galaxy is just about zero. Multiply those odds by 100 billion and it is still about zero. With 100 billion galaxies in the universe, the odds that there is another Earth are still just about zero.

The Earth itself is a miracle. If it is the result of chance, it beat incredible odds, even with 100 billion galaxies in the universe.

[El Gato]

You've got the R and r defined wrong. R is the average distance to the center of the torus. r is the radius of the circle that is the cross section of the torus. A torus is likely to be a bad model anyway. I suspect that the "life zone" is bigger along the radial from the core than is the thickness of the galatic disk at those distances. Probably a better approximation would be (Rmax- Rmin)* T * 2 * Pi
With Rmax and Rmin being the outside and inside limits of the life zone, and T the thickness of the galactic disk. (Which isn't constant, but close enough that the average value between Rmax and Rmin from the core would be good enough.)

[My back yard]

At least. 8^)

[El Gato]

My point was that they cannot logically make a guesstimate of "earth-like" planets when none have been found.

But they can, if the large planets they have found fit some model of planet formation. You could then use that model to estimate the number of earth sized and even earthlike if you define that as being in the "water zone" of the primary and of roughtly earth size. Of course some of those will be Venus like, which is about the same size as earth, but trapped in a runaway greenhouse hell. Maybe all of them, except those with large moons, like our own. But your model should help you estimate what fraction of the earth sized planets in the "life zone" would have large moons. I don't think all that was done in this case, but it could be.

[The KG9 Kid]

I propose a name for the Earth-like planet that we'll never find:

'Tantalus'

[The KG9 Kid]

Of course, if you're saying that those posts lend scientific proof to the fact that the Supreme Being designed our Earth, then I have to wonder why He decided to place our planet inside a cosmic shooting gallery.

Our situation is anything but perfect, but I am still happy about it anyway.

[El Gato]

Point taken, El Gato, but I think that we can already see that even if there were a New World we just can't sail to it like Columbus did his

But at least we won't be worrying about fallig off the edge of the solar system. :) No we can't just sail to distant stars, but at least to ones not too far away, we can at least envision the technology to enable us to get there. Lots of different technologies in fact. Bussard ramjet is my favorite, but there are many others. Generation ships if we must, but I suspect before doing something like that, we'd send probes first, which would also take generations to get there. Speed of light is the only real limitation set by physics, but it's a big one given the size of the galaxy, let alone the universe.