Birth of Alien Planets are “Laboratories of Life –Chemical Experiments on a Vast Planetary Scale”

 
Protoplanetary-Disks-640x320

 

"Alma has been really wonderful in allowing us to image the distribution of organics in protoplanetary discs,’ said Harvard University astrochemist Karin Öberg. ‘It is amazing that we can actually take images of the organic distribution of discs that are many hundreds of light years away – this is something I think should be mind-blowing." Before the Alma Observatory was completed in Chile in 2014, efforts to image molecules in protoplanetary discs only produced ‘unresolved blobs’, Öberg recalled. With Alma they can now produce ‘gorgeous pictures’ that show a clear chemical gradation across protoplanetary discs.


‘There must be an active organic chemistry going on in these discs to give us this diversity of distributions, and this is the chemistry that we need to understand if we want to be able to predict the organic composition of nascent planets,’ Öberg said. The Atacama Large Millimeter/submillimeter Array (Alma) in Chile – a giant radio telescope created as part of a global partnership – has given astronomers a new way of investigating these protoplanetary discs.

 

The latest telescopes are now helping to develop a deeper understanding of the chemical processes at the heart of planet formation reports Rebecca Traeger in today's Chemistry World. This in turn is helping in the search for planets which support a complex range of chemistries and, as a result, might just host life.

Stars form when an interstellar cloud collapses into a protostar, and then protoplanetary discs – made of gas and dust – begin to form around the protostar. These discs are the birthplace of planets. Astronomers at a session of the American Association for the Advancement in Science (AAAS) annual meeting in Austin, Texas called them chemical laboratories, where experiments are taking place on a planetary scale. Powerful radio telescopes are now revealing that a wealth of organic molecules and other volatiles are present in these planetary nurseries. This intense scrutiny is now providing insight into how planets form and which ones might be habitable.

It is amazing that we can actually take images of the organic distribution of discs that are many hundreds of light years away. The Atacama Large Millimeter/submillimeter Array (Alma) in Chile – a giant radio telescope created as part of a global partnership – has given astronomers a new way of investigating these protoplanetary discs.

Alma is an exceptional tool for studying the formation conditions of exoplanets because it provides an order of magnitude increase in sensitivity, as well as resolution, compared with other radio telescopes. This allows scientists to map out the chemistry that is present during the early stages of planet formation in exquisite detail.

Alma is now helping astronomers in their search for planets that are suitable for life and have similar organic material to that which is thought to have given rise to life on Earth. So far, the instrument has identified formaldehyde and methanol in these protoplanetary discs.

Öberg said the fact that Alma can detect formaldehyde has revealed that the distribution of the chemical is not uniform across the discs examined. This means that these organics are not simply inherited from the earlier stages, as one might assume for the more abundant volatiles. ‘There must be an active organic chemistry going on in these discs to give us this diversity of distributions, and this is the chemistry that we need to understand if we want to be able to predict the organic composition of nascent planets,’ Öberg said.

In order to image molecules in these protoplanetary discs and examine ones of interest, astronomers take advantage of the fact that these molecules have rotational transitions at millimetre wavelengths. However, most of the volatiles in these protoplanetary discs are in ices, which are not directly observable with Alma as rotation is restricted.

There is a workaround though: scientists can observe what these ices look like before and after protoplanetary discs form. To do this they examine comets in our solar system that offer a preserved record of the icy grains that existed in our protoplanetary disc. Lab observations of ice absorption bands, along with cometary analysis, confirm that water, carbon dioxide and carbon monoxide are the most abundant molecules in protostars and comets. It is therefore reasonable to infer that these are also the three most important molecules in protoplanetary discs, Öberg stated.

Continue reading…

 

"The Galaxy" in Your Inbox, Free, Daily