Two families of exocomets found around nearby star Beta Pictoris

This artist's impression shows exocomets orbiting the star Beta Pictoris.

Astronomers analysing observations of nearly 500 individual comets made with the HARPS instrument at ESO's La Silla Observatory have discovered two families of exocomets around this nearby young star.

The first consists of old exocomets that have made multiple passages near the star.

The second family, shown in this illustration, consists of younger exocomets on the same orbit, which probably came from the recent breakup of one or more larger objects.

Credit: ESO/L. Calçada

Beta Pictoris is a young star located about 63 light-years from the Sun. It is only about 20 million years old and is surrounded by a huge disc of material, a very active young planetary system where gas and dust are produced by the evaporation of comets and the collisions of asteroids.

Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study sets the scene: "Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system."

For almost 30 years astronomers have seen subtle changes in the light from Beta Pictoris that were thought to be caused by the passage of comets in front of the star itself.

Comets are small bodies of a few kilometres in size, but they are rich in ices, which evaporate when they approach their star, producing gigantic tails of gas and dust that can absorb some of the light passing through them.

The dim light from the exocomets is swamped by the light of the brilliant star so they cannot be imaged directly from Earth.

To study the Beta Pictoris exocomets, the team analysed more than 1000 observations obtained between 2003 and 2011 with the HARPS instrument on the 3.6-metre telescope at the ESO's La Silla Observatory in Chile.

The researchers selected a sample of 493 different exocomets. Some exocomets were observed several times and for a few hours.

Careful analysis provided measurements of the speed and the size of the gas clouds.

Some of the orbital properties of each of these exocomets, such as the shape and the orientation of the orbit and the distance to the star, could also be deduced.

This analysis of several hundreds of exocomets in a single exo-planetary system is unique. It revealed the presence of two distinct families of exocomets: a) one family of old exocomets whose orbits are controlled by a massive planet, and b) another family, probably arising from the recent breakdown of one or a few bigger objects. Different families of comets also exist in the Solar System.

The exocomets of the first family have a variety of orbits and show a rather weak activity with low production rates of gas and dust.

This suggests that these comets have exhausted their supplies of ices during their multiple passages close to Beta Pictoris.

The exocomets of the second family are much more active and are also on nearly identical orbits.

This suggests that the members of the second family all arise from the same origin: probably the breakdown of a larger object whose fragments are on an orbit grazing the star Beta Pictoris.

Flavien Kiefer concludes: "For the first time a statistical study has determined the physics and orbits for a large number of exocomets. This work provides a remarkable look at the mechanisms that were at work in the Solar System just after its formation 4.5 billion years ago."

More information: "Two families of exocomets in the Beta Pictoris system" Nature, 23 October 2014. dx.doi.org/10.1038/nature13849

Gemini Planet Imager: Powerful exoplanet camera turns skyward

Gemini Planet Imager's first light image of Beta Pictoris b, a planet orbiting the star Beta Pictoris. 

The star, Beta Pictoris, is blocked in this image by a mask so its light doesn't interfere with the light of the planet. 

In addition to the image, GPI obtains a spectrum from every pixel element in the field of view to allow scientists to study the planet in great detail. 

Beta Pictoris b is a giant planet – several times larger than Jupiter -- and is approximately ten million years old. 

These near-infrared images (1.5-1.8 microns) show the planet glowing in infrared light from the heat released in its formation. 

The bright star Beta Pictoris is hidden behind a mask in the center of the image. 

Credit: Processing by Christian Marois, NRC Canada.

After nearly a decade of development, construction, and testing, the world's most advanced instrument for directly imaging and analyzing planets around other stars is pointing skyward and collecting light from distant worlds.

The instrument, called the Gemini Planet Imager (GPI), was designed, built, and optimized for imaging faint planets next to bright stars and probing their atmospheres.

It will also be a powerful tool for studying dusty, planet-forming disks around young stars. It is the most advanced such instrument to be deployed on one of the world's biggest telescopes – the 8-meter Gemini South telescope in Chile.

Bruce Macintosh

"Even these early first-light images are almost a factor of 10 better than the previous generation of instruments. In one minute, we are seeing planets that used to take us an hour to detect," says Bruce Macintosh of the Lawrence Livermore National Laboratory who led the team that built the instrument.

GPI detects infrared (heat) radiation from young Jupiter-like planets in wide orbits around other stars, those equivalent to the giant planets in our own Solar System not long after their formation. Every planet GPI sees can be studied in detail.

"Most planets that we know about to date are only known because of indirect methods that tell us a planet is there, a bit about its orbit and mass, but not much else," says Macintosh.

"With GPI we directly image planets around stars – it's a bit like being able to dissect the system and really dive into the planet's atmospheric makeup and characteristics."

Stephen Goodsell

GPI carried out its first observations last November – during an extremely trouble-free debut for an extraordinarily complex astronomical instrument the size of a small car.

"This was one of the smoothest first-light runs Gemini has ever seen" says Stephen Goodsell, who manages the project for the observatory.

This is Gemini Planet Imager's first light image of the light scattered by a disk of dust orbiting the young star HR4796A. 

This narrow ring is thought to be dust from asteroids or comets left behind by planet formation; some scientists have theorized that the sharp edge of the ring is defined by an unseen planet.

The left image (1.9-2.1 microns) shows normal light, including both the dust ring and the residual light from the central star scattered by turbulence in the Earth's atmosphere. 

The right image shows only polarized light. Leftover starlight is unpolarized and hence removed from this image. 

The light from the back edge of the disk is strongly polarized as it scatters towards us.

Credit: Processing by Marshall Perrin, Space Telescope Science Institute.

For GPI's first observations, the team targeted previously known planetary systems, including the well-known Beta Pictoris system; in it GPI obtained the first-ever spectrum of the very young planet Beta Pictoris b.

The first-light team also used the instrument's polarization mode – which can detect starlight scattered by tiny particles – to study a faint ring of dust orbiting the very young star HR4796A.

With previous instruments, only the edges of this dust ring, (which may be the debris remaining from planet formation), could be seen, but with GPI astronomers can follow the entire circumference of the ring.