Why Haven’t Planets Been Detected Around Alpha Centauri?

by Fraser Cain on April 19, 2008

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Question: Why aren’t astronomers looking for planets around nearby stars like Alpha Centauri?
Answer: That’s a great question. Since Alpha Centauri is only a little over 4 light-years away, why aren’t astronomers studying it for planets, instead of the more distant stars.

Astronomers have included stars like Alpha Centauri in their search for extrasolar planets, they just haven’t found them yet. That’s because the techniques used to find extra solar planets require very large planets orbiting very close to their parent stars.

The first technique is called the radial velocity method. This is where the gravity of the planet yanks its parent star back and forth. The changes in the star’s velocity are measurable in the light that reaches the Earth.

The second technique looks for transits. This is where the planet passes in front of the parent star, dimming it slightly. By measuring the amount the light dims, astronomers are able to know if there’s a planet there, calculate its size and even determine what’s in its atmosphere.

A third technique detects microlensing events. A closer star focuses the light from a more distant star with its gravity. From Earth, we see a flare in brightness as the two stars line up perfectly. If the closer star has a planet orbiting it, that will change the light curve that astronomers detect, allowing them to calculate the size of the planet.

Most of the planets discovered to date are known as Hot Jupiters. These are planets much larger than Jupiter that orbit within the orbit of Mercury.

A team of astronomers led by Javiera Guedes from the University of California think that an Earth-sized planet should be detectable orbiting Alpha Centauri. They’re working to get a single dedicated telescope to watch the star, and work out if there are planets there. According to their calculations, it should only take about 5 years of intense observations by a dedicated telescope to work out the answer.


Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

pradipta April 20, 2008 at 12:11 PM

We can see original space objects within 150 million kilometer. Ahade of it everything is mere image into space mirror. It can not explain in short. . Therefore it invites to visit http://www.spacemirrormystery.com to know the original truth

Adam April 21, 2008 at 9:04 PM

Hi Fraser

Nice summary.

A good question, as follow up, might be: if Alpha Centauri hosts an earth-like planet what can we do to get a closer look?

Dark Gnat April 23, 2008 at 6:56 AM

I looked at the “space mirror” website….

I guess the probes that we have sent to other planets, confirming their sizes are wrong as well? All the other stars in the sky are actually mirror images of the sun? What happens when one goes supernova?

Space mirror = bad science.

Really bad science.

El Sofista - ¿Hay planetas alrededor de Alfa Centauri? April 23, 2008 at 5:59 PM

[...] En esta ocasión, Fraser Cain, de Universe Today, responde “¿Por qué no se han detectado planetas alrededor de Alfa Centauri?”:

Como Alpha Centauri está a poco más de 4 años luz de distancia, por qué no están los astrónomos investigando si hay planetas en ese sistema, en lugar de observar estrellas más distantes. [...]

Liam April 28, 2008 at 2:34 PM

I agree with Dark Gnat. The space mirrors? Come on, who ever created this theory is whack and going back to the pre-Copernicus era, thinking that humans are the center of everything. If people believe this ridiculous theory, they’ll be doubting Einstein and every other brilliant astronomer/physicist who definitely knew what they were talking about.

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