Dublin Institute for Advanced Studies contact@dias.ie 00353 (0) 16140100

The ‘comet factory’ that could explain how planets formed – DIAS astronomer in team using the world’s biggest array

eso1325c 7 June 2013 – A ‘comet factory’, that could help explain how planets form, has been discovered by an international team of scientists that includes a member of DIAS.


An unusual cloud of dust around a young star is a breeding ground for comets and could help explain how planets form.  The ‘comet factory’ was discovered by a team of international scientists, including an astronomer from the Dublin Institute for Advanced Studies (DIAS).  They were observing the star with the world’s biggest and newest telescope in Chile’s Atacama desert, called ALMA. [For the accompanying press release from the European Southern Observatory (ESO) see: http://www.eso.org/public/news/eso1325/]

The discovery, published on June 7 in the prestigious US journal, Science, is an exciting early result for ALMA, which was less than half completed at the time of this discovery.  The news means hopes are high for even more exciting discoveries, now that the telescope array has  become fully operational in March of this year.

According to Dr Vincent Geers, from the School of Cosmic Physics at DIAS, the problem is that: “We know planets exist – after all we live on one!  But still we don’t understand how they form.

We know that for a planet to form, dust particles in orbit around a star must collide and stick.”  But under normal conditions, once objects grow to form rocks about 1 metre across, “they should spiral in fast and get eaten up by their star”.

New millimeter images from ALMA, of a young star about 400 light years from Earth, in the Serpent Bearer constellation (Ophiuchus, of Oph for short), reveal something unexpected however.  The team, led by Nienke van der Marel (a PhD student at Leiden Observatory, in the Netherlands) found a crescent-shaped cloud of dust to one side of the star, and not the symmetrical dust ring they expected.

They were looking at the star Oph-IRS 48, because Dr Geers and others previously saw an interesting dust ring around it.  “At the time, we suggested that an unseen companion star might be causing this ring, but we needed better images and we had to wait for ALMA to get those.”

According to Dr Geers, thanks to the new images, scientists now think that there is a ‘dust trap’ there.  “We think it’s a region of high pressure.  A kind of vortex, where the dust is captured and can stick, and grow to form objects as big as maybe a few kilometres across.”

So, not yet big enough to be planets, and more like comets– but certainly bigger than a 1 metre rock.  Hence the team have dubbed their dust cloud the ‘comet factory’.

“What’s really exciting is that we saw this using only part of ALMA.  Now that the full telescope array is working, we should be able to see so much more . . . By finding dust traps orbiting even closer to their star, we may be able to see planets forming.”


Dr Vincent Geers, School of Cosmic Physics, DIAS: +353 (0)1 6621333

ALMA image of dust trap/comet factory around Oph-IRS 48 (annotated)


ALMA and VLT image of comet factory around Oph-IRS 48


ALMA image of comet factory around Oph-IRS 48


Video: Dust trap animation

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.


The team is composed of Nienke van der Marel (Leiden Observatory, Leiden, the Netherlands), Ewine F. van Dishoeck (Leiden Observatory; Max-Planck-Institut für Extraterrestrische Physik Garching, Germany [MPE]), Simon Bruderer (MPE), Til Birnstiel (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA [CfA]), Paola Pinilla (Heidelberg University, Heidelberg, Germany), Cornelis P. Dullemond (Heidelberg University), Tim A. van Kempen (Leiden Observatory; Joint ALMA Offices, Santiago, Chile), Markus Schmalzl (Leiden Observatory), Joanna M. Brown (CfA), Gregory J. Herczeg (Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing, China), Geoffrey S. Mathews (Leiden Observatory) and Vincent Geers (Dublin Institute for Advanced Studies, Dublin, Ireland).

About DIAS: the Dublin Institute for Advanced Studies, founded in 1940, is Ireland’s premier independent research institute, with schools of Cosmic Physics, Theoretical Physics, and Celtic Studies, and a Geophysics unit  www.dias.ie

About ALMA: The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Southern Observatory (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

About ESO: The European Southern Observatory (ESO) is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning the 39-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.