Re: Looking for "New Earth" around Alpha Centauri
From: Joseph Lazio (jlazio_at_adams.patriot.net)
Date: 10/28/04
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Date: 28 Oct 2004 18:30:21 -0400
>>>>> "AI" == AA Institute <abdul.ahad@ntlworld.com> writes:
AI> "New Earth" is just my favourite way of referring to a
AI> hypothetical planet orbiting around either one of the two
AI> principal stars in the Alpha Centauri system, within their
AI> respective *habitable* zones. So... assuming such a planet does
AI> exist, I'd like to know if we could hope to see it *directly*
AI> through a telescope [...]
AI> Focusing on Alpha Centauri 'A', which is of spectral type G2V -
AI> exactly like the Sun - and whose habitable zone is located at
AI> between 1.2 to 1.3 AUs out, is there a projected *magnitude* that
AI> an Earth-sized planet is expected to have?
The rough number that I remember is that the contrast between a star
and a terrestrial planet in the optical is something approaching 1
billion. That is, the star is 1 billion times (or about 23
magnitudes) brighter than its planet.
AI> If indeed it exists, at maximum elongation from the star New Earth
AI> would wander a total of 2.7 arc-seconds out and be amply within
AI> astrometric resolution limits for even amateur sized telescopes!
AI> Since *resolution* is not an issue
Correct, resolution per se is not the issue, particularly not for
Alpha Centauri.
AI> and *masking* out the star itself in a telescope is no problems,
No, masking, to this level of precision, is incredibly difficult. Any
imperfections within the optics of the telescopes can scatter light.
When one is trying to work at the 1 part in 1 billion level of
precision, even small imperfections could end up swamping the expected
signal.
Take a look at the documentation on the Terrestrial Planet Finder
mission, which is going to try to do exactly this.
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