Why is it difficult to detect planets orbiting other stars?

Question

Why is it difficult to detect planets orbiting other stars?

Answer 1

The problem is they are so far away and they shine only by reflected light. Even if someone looked at our own Solar System from Alpha Centauri with the kind of telescopes we have today, he, she or it would never see Jupiter directly. Jupiter would be at most a couple of arc seconds from the Sun and billions of times fainter, and because of that it would be hidden in the Sun's glare. The turbulence in the Earth's atmosphere also blurs star images and prevents any chance of imaging planets directly, at least in visible light at present. Even then, the glare from the star would likely hide any planets due to scattering of light from moisture and dust in the air above the telescope. Earth would be even more difficult to detect, perhaps impossible. There are other techniques to detect a planet but they may take observation of the target star for years or even decades to detect any planets present. So far all searches for exo-planets have been done from the ground, but when the search is continued in space it should be possible to image planets directly around nearby stars. Until then, we have to do it indirectly.

Answer 2

Are you aware that it is only in recent years that we have had telescopes powerful enough to present an observable image of a star rather than just a point of light?  And even now it is only the nearest giant stars that present a disk in the largest telescopes; like Antares, which is wider than Earth’s orbit around the sun.  

For most of telescope history, stars only ever showed a point of light, considerably brighter in a telescope than the naked eye, but no bigger.  Also, stars are so far away that even the nearest display such a tiny shift when seen from opposite sides of Earth orbit (300 million kms across), that it took til the 20th century before any shift could be measured accurately – Alpha Centauri shifts about a 4000th of a degree when seen from opposite sides of our orbit – and that is the very nearest star.  

And those silly answers above that say astronomers can detect extra-solar planets easily, pay little respect to the massive afforts of those astronomers that search for them.  If it was easy, there would be billions of detected planets rather than the few dozen so far detected.  

Answer 3

Planets do not give off the light and make themselves clear as stars do.  They are in essence barely a reflection of light and sometimes not even that.  

It is difficult to see a dark or sometimes black rock in black space, moving at 1000's of miles per hour, depending on its distance from its sun or star.  So many go undetected and as they wiss past maybe a glimpse of them in a distant orbit.  So most we don't actually know about.

Answer 4

If a planet is in a direct line with its star (in front or behind) its reflected light can not be seen from earth because it is reflected back to the star or blocked by the star.  If the planet is elsewhere it may be too close to the star to be distinguished or its illuminated side will not be a full circle (similar to phases of the moon).  The brightness of the moon (albedo) depends upon the angle of reflection of light back to earth and is brightest at full moon with the most direct reflection.  The reflected light of a planet is much dimmer than the brilliance of a bright star and also depends upon the reflectiveness of its surface which may be dark or light rock or even slightly colored (as Mars is reddish).  If the surface absorbs most colors there will be little reflected light.  The maximum distance of a planet from its star (perhaps the distance of earth from the sun) is tiny compared with the distance from the earth (perhaps very many light years) and there may be too little separation to distinguish both bodies.  Even the North Star is a triple star system that is hard to see with powerful telescopes.

Answer 5

stars around other planets cause global warming and are depleting teh ozone layer. naturally, the government is suppressing them.

Answer 6

The stars are so much brighter than any planet that they drown out the light of their planets.  Exo-planets have been discovered (over 300 so far) by indirect means, not by direct observation.

It wasn't until technology had devekoped enough to allow scientists to detect the tiny differences in the star's light and motion to find planets.

Answer 7

because we aint no aliens

Answer 8

are you freaking kidding me???????????????

sure just whip out your abacus and calculate minute gravitational changes in an object billions and billions and billions of miles away.

jeez i wish i had your brain that advanced astrophysics was something i could doodle out like a crossword puzzle sittin' on the john

Answer 9

1. They are far from us

2. The planet would be close to its star.

3. The planet would be lost in the glare of its star.

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1.  Imagine a star like our sun that is 'only' 100 light-years away.  At that distance (which is very close, in astronomy), our Sun would not be visible by naked eye (for us humans).  However, telescopes (even small ones) do show stars similar to our Sun much further away.  So number 1 is not a big problem, except in relation to number 2.

2.  Jupiter is 5.2 astronomical units from the Sun.  That is 5.2 times 150 million kilometres or, if you prefer -- and I do for this calculation -- 5.2 times 500 light-seconds.

2600 seconds is 1/12,140 of a year.

Therefore, a distance of 2600 light-seconds is 0.0000824 light-year.

If the star is 100 light-years from us, the angle between the star and the 'Jupiter-like' planet is small (the sine of the angle is 0.0000824 divided by 100.

The angle is 0.17" (one sixth of one second of arc, where one second is one degree divided by 3600).

Still, with modern telescopes, it should be relatively easy to separate these two objects, once you get rid of all the annoying atmospheric turbulence (our atmosphere, not that of the other planet) which limits us to about 0.5"

But that still leaves problem number 3:

3.  When Jupiter is 4.2 au from us (at opposition), it has an apparent magnitude of -2.7 (about what it shows now, in August 2008).  If we were able to get at a distance of 1 au from Jupiter, it would appear brighter (inverse square distance rule) and would show up at -5.7 (twice as bright as Venus does at its maximum).

Still, the Sun is at 1 au from us (by definition) and its apparent magnitude is -26.7  (negative numbers for magnitude mean that the object is very bright).

The difference in magnitude between the Sun (at 1 au) and a theoretical Jupiter at 1 au would be (26.7 - 5.7=) 21.

A difference of 21 on the magnitude scale (which is logarithmic) means that one object is 250,000,000 times brighter than the other.

And that is what makes it difficult to see other planets.

Answer 10

Try Google Search!!!!!!

Answer 11

Because they're so small!

Consider a comparison with a pebble. Imagine a piece of pea gravel which is spherical and one centimeter in diameter. How far away could you see it? On a plain unform surface, you might see it from perhaps ten meters away, which would be 1000 times its own diameter (ten meters is 1000 centimeters). The Earth, on the other hand, is about 12756 kilometers in diameter. Imagine that a planet the same size as Earth (which is a good size for life to develop on) were orbiting Proxima Centauri, the closest star to the Sun. Proxima Centauri is about 4.2 light years away, or approximately 3115000000 times as far away as its own diameter. So in terms of scale, trying to see the planet at that distance would be like trying to see the piece of pea gravel 31150 kilometers away. That is almost two and a half times the diameter of the Earth! This is why scientists need extremely sensitive instruments in order to detect planets, and the detection is usually not done by directly seeing the light from the planet but rather by either measuring the wobble in the star the planet orbits or by measuring the change in light coming from the star as the planet passes in front of it (although this latter method only works for planets that happen to orbit their stars such that we're directly on their orbital plane).

Answer 12

Because they are simply soooo small and so insignificant in comparison to their parent star, that they are out shined and out weighed. Oh yeah...and how exactly are we going to spot something SOO tiny SOOOOO far away, I mean seriously they are plenty of light years away, that means, the distance light travels in one year. Thats a h**l of a long way...think about it, light is the fastest moving thing there is, and they are years away at those speeds...thats why.

Answer 13

That pesky recent discovery of cosmic dust. just f's the whole viewing of other solar systems up. We can see the stars, but not what's orbiting them if anything at all.  

Answer 14

The simple answer is the size of the planets and the distance involved. Stars are easy to see because they are very large, compared to planets, and they give off tons of radiation in the form of light and various other kinds.

Planets on the other hand are relatively small, on a cosmic scale, and do not produce any noticeable emissions. Since the closest stars to the Earth are light years away, that large distance combined with the small size of planets makes detecting them very difficult.

Also, the emissions of the stars that planets would be orbiting could easily obscure the view of the planets.

Answer 15

It isn't watch Nova.

Answer 16

Because of distance and size. There are two popular ways to discover extra-solar planets. 1) We look for interferences in a sun's light. If we see a dot move across a star, then we can conclude that it is a planet, because comets are far too small, usually. These planets, though, tend to be huge, typically gas giants. Smaller planets are difficult and usually impossible to discover this way.

2) We use the gravitational effects on a star to detect planets. Because gravity goes both ways, with not only a planet affected by a sun's gravity but also a sun affected by a planet's gravity, we can conclude a star has planets if it wobbles. This also makes it dificult to discover small planets because mass creates gravity, and only giant planets can create the gravity needed to make a star noticably wobble from such a distance. And, you have to consider that the closest star is 4.2 light years away. Light travels 300,000 km/s. So, how many seconds are in a year? In 4.2? Multiply that by 300,000 km and you have the distance to the closest star.  

Answer 17

First three answers are wrong. It is hard to find planets orbiting other stars because they are so far away. The closest star is over 4 light years away. Because they are so far away, a planet has to reflect a lot of the light. For this, the planet needs a thick atmosphere, or consist of mostly gas on the first layers to reflect a lot of the light. So it either has to be a gas giant, or a very large terrestrial planet that has a thick atmosphere. That light has to travel a VERY long way.

Answer 18

The brightness ratio of the star to planets are million times.Because of the very high brightness of the star, we can not see the planet. Only through observingsmall positional shift of the stars, we are finding the planets indirectly or through the transists on the disk.

Take a simple case. Jupiters moons are of about 5magnitude theoritically they should be visible to naked  eye,But due to bright jupiter interfearing the area, we can not see the moons by naked eye.

Answer 19

It's not.. New planets are discovered almost daily.