̽��ֱ�� of Cambridge - Luca Matra

Icy ring around young planetary system has similar chemical fingerprint to our solar system

sc604 — Thu, 18 May 2017 15:00:00 +0000

Earlier observations of the star, known as Fomalhaut and located 25 light years from Earth, were taken in 2012 by astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA), located in Chile. ̽��ֱ��2012 results were gathered when the telescope was still under construction, and while they only revealed about half of the debris disc, the observations provided hints about the nature and possible origin of the disc.

̽��ֱ��new observations offer a far more complete view of this glowing band of debris, a band of rubble resulting from comets smashing together near the outer edges of the planetary system. ̽��ֱ��gases observed within the ring by the team suggest that there are chemical similarities between its icy contents and comets in our own solar system.

“We can finally see the well-defined shape of the disc, which may tell us a great deal about the underlying planetary system responsible for its highly distinctive appearance,” said Meredith MacGregor, an astronomer at the Harvard-Smithsonian Center for Astrophysics, and lead author on one of two papers accepted for publication in the Astrophysical Journal describing these observations.

Fomalhaut is a relatively nearby star system and one of only about 20 in which planets have been imaged directly. ̽��ֱ��entire system is approximately 440 million years old, or about one-tenth the age of our solar system. As revealed in the new ALMA image, a brilliant band of icy dust about two billion kilometres wide has formed approximately 20 billion kilometres from the star.

Debris discs are common features around young stars and represent a dynamic and chaotic period in the history of a solar system. Astronomers believe they are formed by the ongoing collisions of comets and other solid objects, known as planetesimals, in the outer reaches of a recently formed planetary system. ̽��ֱ��leftover debris from these collisions absorbs light from its central star and re-radiates that energy as a faint glow that can be studied with ALMA.

Using the new ALMA data and detailed computer modelling, the researchers could calculate the precise location, width, and geometry of the disc. These parameters confirm that such a narrow ring is likely produced through the gravitational influence of planets in the system.

̽��ֱ��new observations are also the first to definitively show “apocenter glow,” a phenomenon predicted in a 2016 paper by Margaret Pan, a scientist at the Massachusetts Institute of Technology and co-author on the new papers. Like all objects with elongated orbits, the dusty material in the Fomalhaut disc travels more slowly when it is farthest from the star. As the dust slows down, it piles up, forming denser concentrations in the more distant portions of the disc. These dense regions can be seen by ALMA as brighter millimetre-wavelength emission.

Using the same dataset, but focusing on distinct millimetre-wavelength signals naturally emitted by molecules in space, the researchers also detected vast stores of carbon monoxide gas in precisely the same location as the debris disc.

“These data allowed us to determine that the abundance of carbon monoxide plus carbon dioxide around Fomalhaut is about the same as found in comets in our own solar system,” said Dr Luca Matrà of Cambridge’s Institute of Astronomy, and lead author of the team’s second paper. “This chemical kinship may indicate a similarity in comet formation conditions between the outer reaches of this planetary system and our own.” Matrà and his colleagues believe this gas is either released from continuous comet collisions or the result of a single, large impact between ‘supercomets’ hundreds of times more massive than Hale-Bopp.

̽��ֱ��presence of this well-defined debris disc around Fomalhaut, along with its curiously familiar chemistry, may indicate that this system is undergoing its own version of the Late Heavy Bombardment, a period approximately four billion years ago when the Earth and other planets were routinely struck by swarms of asteroids and comets left over from the formation of our solar system.

“Twenty years ago, the best millimetre-wavelength telescopes gave the first fuzzy maps of sand grains orbiting Fomalhaut. Now with ALMA’s full capabilities the entire ring of material has been imaged,” said Paul Kalas, an astronomer at the ̽��ֱ�� of California at Berkeley and principal investigator on these observations. “One day we hope to detect the planets that influence the orbits of these grains.”

Adapted from a National Radio Astronomy Observatory press release.

References:
Meredith A. MacGregor et al. 'A Complete ALMA Map of the Fomalhaut Debris Disk.' arXiv:1705.05867
L. Matrà et al. 'Detection of exocometary CO within the 440 Myr-old Fomalhaut belt: a similar CO+CO2 ice abundance in exocomets and Solar System comets.' arXiv:1705.05868

An international team of astronomers, including researchers from the ̽��ֱ�� of Cambridge, has made the most detailed image of the ring of dusty debris surrounding a young star and found that the ice content of colliding comets within it is similar to comets in our own solar system.

̽��ֱ��chemical kinship may indicate a similarity in comet formation conditions between the outer reaches of this planetary system and our own.

Luca Matra

ALMA (ESO/NAOJ/NRAO), M. MacGregor; NASA/ESA Hubble, P. Kalas; B. Saxton (NRAO/AUI/NSF)

Composite image of the Fomalhaut star system. ̽��ֱ��ALMA data, shown in orange, reveal the distant and eccentric debris disk in never-before-seen detail. ̽��ֱ��central dot is the unresolved emission from the star, which is about twice the mass of our sun.

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

First evidence of icy comets orbiting a sun-like star

sc604 — Thu, 19 May 2016 09:20:14 +0000

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 ̽��ֱ�� of Cambridge, detected very low levels of carbon monoxide gas around the star, in amounts that are consistent with the comets in our own solar system.

̽��ֱ��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 comet 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 interstellar space.

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.

̽��ֱ��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. ̽��ֱ��system is about 23 million years old, whereas our solar system is 4.6 billion years old.

“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. “ ̽��ֱ��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.

“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 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.

“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.

“ ̽��ֱ��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.”

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

Reference:
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. http://www.eso.org/sci/meetings/2016/Planet-Formation2016/program.html

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

Astronomers have found the first evidence of comets around a star similar to the sun, providing an opportunity to study what our solar system was like as a ‘baby’.

̽��ֱ��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.

Sebastián Marino

Amanda Smith, ̽��ֱ�� of Cambridge

Illustration of the dust ring surrounding HD 181327

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes