Why can't the Hubble Space telescope take a decent picture of Pluto?

Question

It can take brilliant pictures of nebulas, supernovas, and galaxies many light years from us, but cannot take a proper picture of Pluto, which is about 5.8 billion miles from earth. Is there a certain reason?

yeah anonoymous...i sure do know that already....
then tell me why the heck I would be asking this question???

Answer 1

This isn't really an answer to your question, but we should have much better-than-decent pictures of Pluto after July 15, 2015, some 7 1/2 years from now.

The "New Horizons" craft is due to fly by Pluto at that time, taking pics and info as it goes into the Kuiper belt.

Answer 2

A perfect analogy is why you can see a skyscraper from 40 miles away, but not see a bug from 40 feet. It's a matter of simple geometry. While Pluto is indeed much closer than the galaxies Hubble views, it is smaller by a very large magnitude. Pluto's angular size is far too small for the Hubble to get a clear picture of.

Answer 3

The answer is that Pluto is small and distant, but we can be more quantitative.

The Hubble telescope has a diameter of 94.5 inches. The resolving power of a telescope is given by
4.57/D seconds of arc
where D is the diameter in inches. Plug in the numbers and you get

resolving power of Hubble = 0.048 seconds of arc

Pluto has a diameter of 2390 km. Its typical distance is about 40 astronomical units (AU), where an AU is 1.5e8 kilometers. Therefore, the disk of Pluto subtends an angle of

Pluto angular diameter = 2390 / (40 * 1.5e8) radians
= 4.0e-7 radians
= 0.082 seconds of arc

The size of Pluto is less than twice the resolving power of the Hubble. A photo of Pluto would effectively have only three pixels! Imagine a photo from a camera that has only 3 pixels instead of 10,000,000 pixels -- it would just be a blur.

For a good picture, therefore, we need a bigger telescope or a closer view.

The dark surface of Pluto is not the problem; you can solve this simply by taking a longer exposure and accumulating more photons.

Answer 4

Nebulas and Galaxies may be much farther away but they are also much bigger. Pluto just got demoted to dwarf planet because of its size. Nebulas can be several light years across and galaxies may be hundreds of thousands of light years in diameter. As such they take up a larger portion of the night sky. Amateur astronomers use their most powerful lenses for planets but switch to less power full ones for galaxies and nebulas; otherwise the image would more than fill up their view port.

Also those deep sky objects shine with their own light while Pluto has to do with reflected light from a distant sun and besides, its surface is not very reflective.

Answer 5

Nebulae and stars are self illuminating. Pluto is DARK. It's a dirty snowball. The reflected light from Pluto is more than 55000 times dimmer than the Earth's reflected light.

Additionally, what you see of stars in pictures is simply a point of light; there's no detail. The detail that you do see is spread out over thousands and millions of light years.

Answer 6

Those galaxies may be a billions of times farther away, but they are a quadrillions of times bigger than Pluto.

It is like how a regular camera can take a fine picture of mountains 20 miles away but cannot take clear picture of an ant only 20 feet away.

Answer 7

Pluto is too embarrassed to have it's picture taken ever since it was demoted from full planet status.

Answer 8

Dr Bob always gets me hot when he says "Subtends an angle"

rrrrrrrowl!

Answer 9

Because it is smaller than our moon and 3 billion miles away maybe...

Answer 10

Because it doesn't have the resolution necessary, pluto is very small.