Star’s ‘Dust Trap’ May Solve Planet Formation Mystery

In recent years, astronomers have discovered a multitude of exoplanets around distant stars, but there are still many unanswered questions about how many of these planets form. Recently, researchers captured images of the outer regions of a young solar system known as Oph IRS 48. The observations provide new clues about how rocky planets could form and evolve from disks of gas and dust.

In models of planetary formation, astronomers have run into a problem concerning the size limit of growing objects. When pebbles and boulders grow to a certain size, they tend to ‘self-destruct’ as they collide or are drawn into their host star. Astronomers have theorized that swirling eddies in planetary disks could create dust traps where particles cling together, allowing larger and larger objects to form. The new study may have identified one of these dust traps around Oph IRS 48. Observations were made using the the new Atacama Large Millimeter/submillimeter Array (ALMA) telescope, located in the Atacama desert in northern Chile. 

"At first the shape of the dust in the images was a complete surprise for us. Instead of the ring we had expected to see, we found a very clear cashew-nut shape. We had to convince ourselves that this feature was real, but the strong signal and sharpness of the ALMA observations left no doubt about the structure."
– Lead author Nienke van der Marel, Leiden Observatory in the Netherlands

 

Some facts about ALMA:

  • The Atacama Large Millimeter/submillimeter Array (ALMA) is an international partnership of Europe, North America and East Asia in cooperation with the Republic of Chile.
  • ALMA is a single telescope composed of 66 antennas.
  • ALMA  is located on the Chajnantor plateau at 5000 meters altitude in the Atacama desert of northern Chile.
  • ALMA’s first scientific observations were made in 2011, and the first images were released in October of 2011. The array officially became fully operational in March of 2013.

 

ALMA image of the dust trap around Oph IRS 48. The distinctive crescent-shaped feature comes from the accumulation of larger dust grains in the outer regions of the disk. This provides the safe haven dust grains need to grow into larger and larger objects. Credit: ALMA (ESO/NAOJ/NRAO) / Nienke van der Marel
ALMA image of the dust trap around Oph IRS 48. The distinctive crescent-shaped feature comes from the accumulation of larger dust grains in the outer regions of the disk. This provides the safe haven dust grains need to grow into larger and larger objects. Credit: ALMA (ESO/NAOJ/NRAO) / Nienke van der Marel
 
Upcoming conjunction between Proxima Centauri and a background star
Artist’s impression of the proposed disk structure of Oph IRS 48. The brown spots represent the large and small grains. The larger grains detected by ALMA are concentrated in the dust trap at the bottom of the image. The blue represents the distribution of carbon monoxide gas. The gap in the disk is shown with the proposed planetary body that is sweeping the area clear and providing the conditions necessary to form the dust trap. Credit: Nienke van der Marel

 

How far away are we talking?
Oph IRS 48 is located about 390 light-years from Earth in the constellation Ophiuchus.

 

Why is this research important to Astrobiology?

The search for small planets around distant stars is of major importance to NASA’s Astrobiology Program. So far, Earth is our only example of a habitable planet. Discovering planets of similar size to Earth is a step toward identifying habitable worlds beyond the Solar System.

Many extrasolar planets have been discovered, but most are gas giants similar to Jupiter. It’s much more difficult to spot small planets, but new technology and techniques are now making this possible. For some information on possible habitable worlds out amongst the stars, check out the Habitable Exoplanets Catalog.

 

Where can you read more about this research?

The paper, "A Major Asymmetric Dust Trap in a Transition Disk," was published in the journal Science. Click here to view the abstract.

The press release from the National Radio Astronomy Observatory is available at: http://www.nrao.edu/pr/2013/dusttrap/

 


This artist’s rendering shows the behaviour of different sized particles in the disc of dust that surrounds Oph-IRS 48 system. The bigger particles, millimetres in diameter, tend to clump together in a safe haven that allows them to grow even further, eventually forming boulders and then comets. Credit: ESO/L. Calçada


Nienke van der Marel, Leiden Observatory
Nienke van der Marel of the Leiden Observatory. Credit: van der Marel

Astrobiology Magazine contacted Nienke van der Marel of the Leiden Observatory in the Netherlands with some additional questions:

Astrobiology Magazine (AM): Is this is the first time such a ‘crescent-shaped’ feature that has been spotted around a distant star?

van der Marel: No, this is not the case. These kinds of asymmetries have been seen in other disks around young stars, but it is the first time that we see an asymmetry with such a high contrast between the two sides of the disk (more than a factor 130 south-north in our case), and that the origin of the asymmetry was entirely modeled using the observed gas distribution in the disk as well.

I have to add here that many of the previous observations were taken with telescope arrays with much less antennas than ALMA, and therefore have lower image quality, so the asymmetries were never very clear. ALMA is finally providing us with very detailed and high quality images.

AM: Have other features that deviate from a uniform disk of debris been spotted before?

van der Marel : Yes, there are other disks that show for example spiral like structures which we do not entirely understand yet. Disks are likely formed in a uniform way (although also this is under debate) but evolve very differently from each other. Our task is to find these differences, understand them and put them in a broader picture of disk evolution and planet formation.

AM: Will you be making further observations of the system when the full compliment of ALMA antennae become operational?

van der Marel : Yes, absolutely, we would like to get even more information about the gas distribution of this disk and hopefully observe the vortex in the gas as well. Also, we would like to see if larger dust particles are even more concentrated in this dust trap.


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