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Hubble replacement

Date: Thu Jun 6 16:13:39 1996
Posted by: Edward Colon
Grade level: grad
School/Organization: Howard University
City: Washington, D.C. State/Province: No state given.
Country: USA
Area of science: Astronomy


With the detection of planets orbiting other stars like 51 Pegasus, I was wondering if the next generation space telescopes would be powerful enough to obtain crude visual images of these planets. If the resolution is too poor would it be possible sometime in the next century to establish an observatory on the outskirts of the solar system which would utilize the sun as a gravitational lens to enhance telescope resolutions to the point where observing distant planets would be possible as was postulated by Carl Sagan in his book "Pale Blue Dot"?

Detecting new planets is a very hot topic in astronomy right now. One of the more interesting aspects is that there are so many ways to do it! All of the planets outside our solar system that have been found to date have not been directly imaged (with the exception of Gliese 229B, which is a very large planet, bordering on being a brown dwarf). The new planets have been found by taking very high precision spectra of the stars and looking for the gravitational tug from the planet (check here for a look at how that was done).

Larger telescopes in space may be able to actually take pictures of these planets. Right now, these types of telescopes are still in the planning stages. Even when built, they will probably not be able to see any detail of the surface of these planets, but will probably just be able to see them as points of light. The trouble is that a star like the Sun is something like 30 billion times brighter than Jupiter, making it hard to detect the planet from far away.

However, that ratio is for visible wavelengths. In the infrared, planets are still bright while stars dim considerably, and that ratio drops to a factor of a few hundred thousand. The SIRTF, or Space InfraRed Telescope Facility is a big telescope scheduled to be launched by NASA in 2001. One of its primary goals is to detect brown dwarfs. According to their web site, SIRTF will be able to detect brown dwarfs as far away as 40 parsecs (about 130 light years)!

The next jump in technology is to use an optical interferometer, which is a highly complicated instrument capable of extraordinary resolution. The test 'scopes on the ground have been able to achieve extremely high resolution images, far higher than even Hubble or any conventional telescope. These types of telescopes should be able to find planets as small as the Earth, even if they are a hundred light years away. Again, we won't be able to see surface detail; we'll just be able to say it's there. I am not familiar with Sagan's idea of using the Sun as a gravitational lens to detect planets (I haven't had a chance to read Pale Blue Dot yet, but I will!). But there is another way to detect planets, which is more subtle. If a planet or brown dwarf somewhere in the outskirts of the Milky Way comes between us and an even more distant star, the gravity of the planet will bend the starlight, making the star get suddenly brighter. This idea is being tested right now. The MACHO project (for MAssive Compact Halo objects: these planets are compact, massive, and may reside in the halo of our Galaxy) has found 49 candidate objects after taking 27000 images and determining the characteristics of 18 million stars!

Thanks to Keith Irish for pointing out a minor error in this page (which I have corrected; I originally said SIRTF was the next big 'scope to be launched by NASA, when actually AXAF is).

©2008 Phil Plait. All Rights Reserved.

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