New solar systems

Not that many years ago, we believed we would never be able to detect planets orbiting other stars, or to see planets forming around a newborn star.

Planets would be impossible to see because it would be like trying to spot a firefly next to a searchlight, viewed from a few kilometres away.

If anything, seeing the birth of new stars and planets would be even more difficult, because these births are discreetly hidden in the middle of the huge clouds of gas and dust from which those new stars and planets are forming.

We first detected extra-solar planets by detecting the slight wobbling of a star as its planets orbited around it. Then, we found an easier method: searching for the slight dimming of a star as a planet moves across in front of it.

Today, extra-solar planets are being detected by amateur astronomers by using this method.

Finally, surprisingly, we now have the technology to detect that firefly hovering by the searchlight, or a faint planet orbiting a distant star.

Space is filled with clouds of cold gas and dust. This is the raw material for making new stars and planets. In places where the clouds are thicker and denser, parts of the interiors of the clouds become unstable and collapse.

Our calculations suggested the collapsing material would form a disc, with the core of the disc becoming a new star and the rest of the material forming planets.

However, our optical telescopes could show us nothing, because the fog of cloud material discreetly hid the birth process from view.

We only get to see the new star and planetary system when it starts shining and evaporates and blows away its birth cloud.

The problem is a process called scattering. This happens when light passes through fog. Details just become a blurred glow.

However, scattering is more pronounced at shorter wavelengths. If instead of light, we make our observations at longer wavelengths, such as infrared or radio, we should be able to see through the fog.

Luckily, as the cloud material collapses into a disc, it gets warm, not much, but enough to glow at millimetre wavelengths, which can be observed by means of radio telescopes.

Unfortunately, there is a catch — our damp atmosphere is really good at blocking these wavelengths.

There are two ways to deal with this problem. One is to put our radio telescope in space, above the atmosphere, and above the problem.

However, to make a detailed image, radio telescopes have to be extremely large, certainly far too large to put on top of a rocket.

A second option is to find the highest, driest place we can find, and put our instrument there. This is what has been done. The site is the Atacama Plateau, which straddles Chile and Argentina.

A large radio telescope, one of the largest on Earth, has been built there, about five kilometres above sea level, at a location where rain is almost unknown.

The instrument, known as the Atacama Large Millimetre Array, is an array of more than 60-dish radio telescopes that can emulate an antenna about 16 km across.

It can image to a higher degree of detail at millimetre wavelengths than the Hubble Space Telescope can with visible light.

The resulting images look like golden bull’s eyes: concentric circles of gold and black. Some were golden discs with only one dark ring; others had more. Most bull’s eyes are a bit elliptical, because we're not seeing them face-on.

Initially the cloud forms a disc, then lumps in the disc start growing into planets. As they orbit their young star they sweep up material, each forming a dark ring.

By looking at these bull’s-eye images, we can count the young planets — one per ring, and from the width of the ring get an idea how big each planet has become.

Growth will continue until the disc material is used up or blown away by the star.

• Mars is high in the southwest after dark.
• Jupiter and Saturn lie low in the southeast before dawn.
• The Moon will be full on the 26th.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.