First evidence of icy comets orbiting a sun-like star

May 18, 2016
Illustration of the dust ring surrounding HD 181327. Credit: Amanda Smith, University of Cambridge

An international team of astronomers have found evidence of ice and comets orbiting a nearby sun-like star, which could give a glimpse into how our own solar system developed.

Using data from the Atacama Large Millimeter Array (ALMA), the researchers, led by the University of Cambridge, detected very low levels of around the star, in amounts that are consistent with the comets in our own solar system.

The results, which will be presented today at the 'Resolving Planet Formation in the era of ALMA and extreme AO' conference in Santiago, Chile, are a first step in establishing the properties of clouds around sun-like stars just after the time of their birth.

Comets are essentially 'dirty snowballs' of ice and rock, sometimes with a tail of dust and evaporating ice trailing behind them, and are formed early in the development of stellar systems. They are typically found in the outer reaches of our solar system, but become most clearly visible when they visit the inner regions. For example, Halley's Comet visits the inner solar system every 75 years, some take as long as 100,000 years between visits, and others only visit once before being thrown out into .

It's believed that when our solar system was first formed, the Earth was a rocky wasteland, similar to how Mars is today, and that as comets collided with the young planet, they brought many elements and compounds, including water, along with them.

The star in this study, HD 181327, has a mass about 30% greater than the sun and is located 160 light years away in the Painter constellation. The system is about 23 million years old, whereas our solar system is 4.6 billion years old.

ALMA image of the ring of comets around HD 181327 (colours have been changed). The white contours represent the size of the Kuiper Belt in the Solar System. Credit: Amanda Smith, University of Cambridge

"Young systems such as this one are very active, with comets and asteroids slamming into each other and into planets," said Sebastián Marino, a PhD student from Cambridge's Institute of Astronomy and the paper's lead author. "The system has a similar ice composition to our own, so it's a good one to study in order to learn what our looked like early in its existence."

Using ALMA, the astronomers observed the star, which is surrounded by a ring of dust caused by the collisions of comets, asteroids and other bodies. It's likely that this star has planets in orbit around it, but they are impossible to detect using current telescopes.

"Assuming there are planets orbiting this star, they would likely have already formed, but the only way to see them would be through direct imaging, which at the moment can only be used for very large planets like Jupiter," said co-author Luca Matrà, also a PhD student at Cambridge's Institute of Astronomy.

In order to detect the possible presence of comets, the researchers used ALMA to search for signatures of gas, since the same collisions which caused the dust ring to form should also cause the release of gas. Until now, such gas has only been detected around a few , all substantially more massive than the sun. Using simulations to model the composition of the system, they were able to increase the signal to noise ratio in the ALMA data, and detect very low levels of carbon monoxide gas.

"This is the lowest gas concentration ever detected in a belt of asteroids and comets—we're really pushing ALMA to its limits," said Marino.

"The amount of gas we detected is analogous to a 200 kilometre diameter ice ball, which is impressive considering how far away the star is," said Matrà. "It's amazing that we can do this with exoplanetary systems now."

The results have been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

Explore further: Cometary belt around distant multi-planet system hints at hidden or wandering planets

More information: S. Marino et al. 'Exocometary gas in the HD 181327 debris ring.' Paper presented to the Resolving Planet Formation in the era of ALMA and extreme AO conference, Santiago, May 16-20, 2016. www.eso.org/sci/meetings/2016/ … ion2016/program.html

Related Stories

Complex organic molecules discovered in infant star system

April 8, 2015

For the first time, astronomers have detected the presence of complex organic molecules, the building blocks of life, in a protoplanetary disk surrounding a young star, suggesting once again that the conditions that spawned ...

Proto-planet has two masters

February 13, 2016

A Rice University researcher will discuss images that may show the formation of a planet—or a planetary system—around a distant binary star at the annual meeting of the American Association for the Advancement of Science ...

Recommended for you

NASA telescope studies quirky comet 45P

November 22, 2017

When comet 45P zipped past Earth early in 2017, researchers observing from NASA's Infrared Telescope Facility, or IRTF, in Hawai'i gave the long-time trekker a thorough astronomical checkup. The results help fill in crucial ...

Uncovering the origins of galaxies' halos

November 21, 2017

Using the Subaru Telescope atop Maunakea, researchers have identified 11 dwarf galaxies and two star-containing halos in the outer region of a large spiral galaxy 25 million light-years away from Earth. The findings, published ...

Cassini image mosaic: A farewell to Saturn

November 21, 2017

In a fitting farewell to the planet that had been its home for over 13 years, the Cassini spacecraft took one last, lingering look at Saturn and its splendid rings during the final leg of its journey and snapped a series ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.