Tag: Fomalhaut

The return of Sauron’s planet

By Phil Plait | October 27, 2012 7:00 am

First it was there, then it wasn’t, and now it just may be back again: the first exoplanet directly observed orbiting a normal star, Fomalhaut b, has had quite a ride.

[This post has a bit of detail to it, so here's the tl;dr version: new analysis shows an object orbiting the star Fomalhaut may actually be a planet, enveloped in a cloud of dust. We can't for sure it exists, but we can't say it doesn't, either! Earlier claims of it not existing may have been premature. Also, at the bottom of this post is a gallery of direct images of exoplanets.]

First a brief history. In 2008, astronomers revealed huge news: they had successfully taken images of planets orbiting other stars. Up until then, the only evidence we had of exoplanets was indirect, either by their tugging on their stars which affects the starlight, or by having them pass between their stars and us, dimming the starlight.

But, along with Gemini telescope pictures of a family of planets orbiting HR 8799, Fomalhaut b was the first planet ever seen directly, as a spark of light in a picture. Here is that historic shot:

It’s Sauron’s eye! [Click to embiggen.]

The object is labeled. It doesn’t look like much, but the important thing to note is that it moved between 2004 and 2006 (see picture below), and it was definitely in both images taken two years apart. That means it wasn’t some bit of noise or detector error. Moreover, the movement was consistent with what you’d expect from a planet. Not only that but the star Fomalhaut is surrounded by a vast ring of dust – Sauron’s eye – and the inner edge of the ring is sharp. That’s what you would expect if a planet was orbiting inside the ring; its gravity sweeps up the dust on the inside of the ring. Given the brightness, we were looking at an object with a few times Jupiter’s mass, much smaller than a star, so definitely a planet.

All in all, it looked good, and it looked real.

Then, in early 2012, some astronomers threw a Pluto-esque wet blanket on the news. A planet that big should be bright in the infrared. Fomalhaut is a youngish star, only a few hundred million years old. Any planet more massive than Jupiter should still be hot, radiating away the heat of its formation. They looked for it in the infrared, and it wasn’t there.

Uh oh.

To make things worse, they found that if you extrapolate the orbit of the supposed planet using its movement, it should cross the ring. That’s bad, because its gravity would disrupt the ring after a few million years tops. The ring is there, so that planet means the planet must not be.

Their conclusion: this object is a clump of dust, a cloud, orbiting the star. That fits the data, and a planet doesn’t. Cue the sad trombone.

But wait! We’re not done!
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Another direct picture of a planet orbiting an alien star confirmed!

By Phil Plait | June 30, 2010 10:39 am

Astronomers have confirmed that an object in an image from 2008 — thought at the time to possibly be a direct image of a planet orbiting another star — is in fact a planet.

I’ll explain in a sec, but 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.

First, the planet picture:

This image, taken in 2008 by the Gemini North telescope in Hawaii, shows the star 1RXS J160929.1-210524 (I’ll call it 1RXS 1609) in the center, and the planet (1RXS 1609b) indicated by the red circle. As I wrote about this in 2008:
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