If the Centauri exoplanet is so close why didn’t we see it sooner?

Friday, 19 October, 2012

You didn’t think that the discovery earlier this week of an exoplanet orbiting Alpha Centauri, the star nearest to Earth, would go unmentioned here?

Star isn’t really the right word to use though as Alpha Centauri is a binary system, made up of two stars known as Alpha Centauri A and Alpha Centauri B. Even calling the system a binary may not be correct however as a third star, a red dwarf, that also lurks in the vicinity, Proxima Centauri, might also be part of the system.

The planet in question orbits Alpha Centauri B, and while it is too close to its host star to be habitable, the find has raised the prospect that other, more conducive to life, planets could be present in the system. But if Alpha Centauri – at a distance of some four light years from us – is so close, why haven’t planets been detected there sooner?

Needless to say finding exoplanets is no small ask, and when you consider the difficulty, it is surprising that we have found any at all:

Viewed over interstellar distances in visible light, the Earth is some ten billion times fainter than the Sun, meaning that for every photon bouncing off Earth’s atmosphere or surface, ten billion more are flying out from our star. About the same ratio would apply for any habitable planet around Alpha Centauri’s stars. Distinguishing such faint planetary light from that powerful stellar glare is rather like spotting a firefly hovering a centimeter away from the world’s most powerful spotlight, when the spotlight is in Los Angeles and you are in New York. To see the firefly, that overwhelming ten-billion-to-one background light must be suppressed.

Related: , ,

First photographed exoplanet not first photographed exoplanet

Tuesday, 6 July, 2010

Reports circulating last week that the first ever photograph of an exoplant – a planet orbiting a star other than the Sun – had been taken, have turned out to be inaccurate, though the actual photo in question is notable for another reason.

I want people to understand that this discovery is being touted as the first direct image of a planet around another star. It isn’t. Nor is it the first direct image of a planet orbiting a sun-like star. What this is is the first direct image of a planet orbiting a sun-like star taken using a ground-based telescope. While that may sound overly picky, it’s actually a significant achievement, and worth noting.

Related: , , ,