why is it so hard to find a planet like Earth around another star?

Answer 1

Because the technological techniques to discover exoplanets has only existed since 1992.

Are you in a hurry?

Answer 2

They are so far away. We couldn't even begin to see an earth-like planet in another star system, even with our best equipment. The only way we know there are planets is by the perturbations in the motion of the star they orbit. This may prove the existence of large planets but it would be hard to get much information about small ones that way.
But even if we did have a good way of detecting earth-sized planets at an optimum distance from another star, we still don't know whether they would be at all hospitable. One could have a runaway greenhouse effect like Venus, or some other feature which would make life unlikely.

Answer 3

Well, they're very, very, very, very, very far away. It's a wonder that planets of any kind can be found at such a distance, but they aren't actually seeing planets through telescopes. What they are seeing is the tiny doppler shift in the light from the planet's star, caused by the gravitation of the planet as it orbits. This can also give an indication of the planet's size, and distance from primary, but even if those two numbers are Earthlike, that doesn't mean the planet is. To know if there is an atmosphere and what it consists of, we would need to see light from the planet itself, and we can't yet do that in most cases.

Answer 4

We can see distant objects like stars and galaxies because of the light or other electromagnetic radiation that they emit.

If two masses are orbiting each other, we can detect different redshifts in the light from each as they move towards and away from us. Or, one object can move in front of the other and change the brightness.

The problem is that, compared to a star, an earth-like planet is incredibly tiny. And it does not generate light of its own, but only reflects light from its sun. Therefore, the gravitational effects of the planet on the sun are minimal, and it is practically invisible in the glare of the star.

fantastically sensitive experiments are required to even detect the light or gravitational effects of an orbiting planet, and the effects can be completely swamped by innumerable factors and limitations in our instruments and techniques, and naturally the effect of the atmosphere.

It's just pretty hard.

Answer 5

Firstly because other stars and their planets are at such enormous distances from us. That means we currently cannot see planets directly through a telescope. We have to detect their presence by more subtle means such as their gravitational tug on their star. Big planets such as those larger than Jupiter have more gravity than small planets so their gravitational effect on their star is detectable. Small planets like the earth produce too small a tug on their star to be generally detectable using earth based equipment.

However, earth sized planets have been detected around pulsars. This is made possible due to the precise radio signals emitted by the pulsar. These signals allow us to detect the minute movements of the pulsar due to the gravity of the planet.

Secondly because the light given off by the star is vastly brighter than that reflected by, or blocked by small planets. Space based telescopes will allow us to detect the changes in light output of the star-planet as the planet reflects the star's light or moves across it's face as seen from Earth.

Answer 6

If you have The History Channel there is a series called The Universe. One is about alien worlds and it explains how planets are found. Over 200 planets have been detected and all are massive in size. Distance is the biggest factor but astronomers are working on it.

Answer 7

there is a distinct (tho perhaps overcomable[is that even a word?]) problem of resolution in the detection process.

terrestrial planets are smaller than jovian and correspondingly less massive. less massive means smaller gravity fluctuations.

BUT we really shouldnt look at what they HAVEN'T found. Look at what they HAVE... like a Jovian Planet with an orbit 1/10 of an AU? Yikes! I don't remember any models that showed that could happen. The implications are scary.

Well, to me, to you 'Star Trekers' I suppose it doesnt matter.

Answer 8

because if a planet like earth is too close to another start (like the sun) the conditions would not be suitable for vegitation and human life forms (like on earth)