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Comets orbiting nearby sunlike star

Astronomers have found the first evidence of icy comets orbiting a sunlike star 160 light-years from Earth.

Illustration of the dust ring surrounding HD 181327. Image via Amanda Smith, University of Cambridge.

Illustration of the dust ring surrounding HD 181327. Image via Amanda Smith, University of Cambridge.

An international team of astronomers have found the first evidence of icy comets orbiting a nearby sunlike star.

Their study, published May 23, 2016 in Monthly Notices of the Royal Astronomical Society, is a first step in establishing the properties of comet clouds around sunlike stars just after the time of their birth, and could give a glimpse into how our own solar system developed.

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

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 interstellar space.

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. Image via Amanda Smith, University of Cambridge.

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. Image via Amanda Smith, University of Cambridge.

It’s believed that when our solar system was first formed, the Earth was a rocky wasteland, similar to Mars today, and that comets colliding with the young planet 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 [Pictor] constellation. The system is about 23 million years old, whereas our solar system is 4.6 billion years old.

Sebastián Marino is a PhD student from Cambridge’s Institute of Astronomy and the paper’s lead author. Marino said in a statement:

Young systems such as this one are very active, with comets and asteroids slamming into each other and into planets. The system has a similar ice composition to our own, so it’s a good one to study in order to learn what our solar system 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.

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 stars, 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.

Study co-author Luca Matrà is a PhD student at Cambridge’s Institute of Astronomy. Matrà said:

This is the lowest gas concentration ever detected in a belt of asteroids and comets … The amount of gas we detected is analogous to a 200 kilometer diameter ice ball, which is impressive considering how far away the star is. It’s amazing that we can do this with exoplanetary systems now.

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Bottom line: An international team of astronomers have found the first evidence of icy comets orbiting a sunlike star 160 light-years from Earth. Their study results, published May 23, 2016 in Monthly Notices of the Royal Astronomical Society, could give a glimpse into how our own solar system developed.

Read more from the University of Cambridge

Eleanor Imster

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