Signs of the formation of a planetary system around the star HD 169142

Image at 7 mm wavelength of the dusty disk around the star HD 169142 obtained with the Very Large Array (VLA) at 7 mm wavelength. The positions of the protoplanet candidates are marked with plus signs (+) (Osorio et al. 2014, ApJ, 791, L36). The insert in the upper right corner shows, at the same scale, the bright infrared source in the inner disk cavity, as observed with the Very Large Telescope (VLT) at 3.8 micron wavelength (Reggiani et al. 2014, ApJ, 792, L23). 

Young star HD169142 displays a disk of gas and dust with two annular gaps possibly due to the formation of planets

Planets are formed from disks of gas and dust that orbit around young stars. Once the “seed” of the planet —composed of a small aggregate of dust— is formed, it will continue to gather material and it will carve out a cavity or gap in the disk along its orbital path.

This transitional stage between the original disk and the planetary system, difficult to study and as yet little known, is precisely what has been observed in the star HD169142 and is discussed in two articles published in The Astrophysical Journal Letters.

"Although in recent years more than seventeen hundred extrasolar planets have been discovered, few of them have been directly imaged, and so far we have never been able to capture an unequivocal image of an still-forming planet”, says Mayra Osorio, researcher at the Institute of Astrophysics of Andalusia (IAA-CSIC) heading one of the articles. “In HD 169142 we may be seeing indeed those seeds of gas and dust which will later become planets."

HD169142 is a young star with twice the mass of the Sun and whose disk extends up to two hundred and fifty astronomical units (an astronomical unit, or AU, is a unit equivalent to the distance between the Sun and the Earth: one hundred and fifty million kilometers). The system is in an optimal orientation for the study of planet formation because the disk is seen face-on.

The first article explores the disk of HD169142 with the Very Large Array radio telescope, which can detect centimeter-sized dust grains. The results, combined with infrared data which trace the presence of microscopic dust, reveal two gaps in the disk, one in the inner region (between 0.7 and 20 AU) and another, farther out and less developed, between 30 and 70 AU. 

"This structure already suggested that the disk was being modified by two planets or sub-stellar objects, but, additionally, the radio data reveal the existence of a clump of material within the external gap, located approximately at the distance of Neptune’s orbit, which points to the existence of a forming planet”, says Mayra Osorio (IAA-CSIC).

ONE (OR TWO) COMPANIONS AROUND HD169142

The second study focused on searching for infrared sources in the gaps of the disk, using the Very Large Telescope. They found a bright signal in the inner gap, which could correspond to a still-forming planet or to a young brown dwarf (a sort of failed star that never reached the threshold mass to trigger the nuclear reactions characteristic of stars).

Infrared data did not, however, corroborate the presence of an object in the outer gap as radio observations suggested. This non detection could be due to technical limitations: the researchers have calculated that an object with a mass between one tenth and 18 times the Jupiter’s mass surrounded by a cold envelope may well remain undetected at the observed wavelength.   

"In future observations we will be able to verify whether the disk harbors one or two objects. In any case, HD 169142 remains as a promising object since it is one of the few known transitional disks and it is revealing to us the environment where planets are formed", says Mayra Osorio (IAA-CSIC).

An artist's impression of a protoplanetary disk

Credit: ESO/L. Calçada

Reference:

M. Osorio et al. "Imaging the Inner and Outer Gaps of the Pre-Transitional Disk of HD 169142 at 7 mm". The Astrophysical Journal ApJ 791 L36. DOI: 10.1088/2041-8205/791/2/L36

M. Reggiani et al. "Discovery of a companion candidate in the HD169142 transition disk and the possibility of multiple planet formation". The Astrophysical Journal. 792, L23, DOI: 10.1088/2041-8205/792/1/L23

Contact:

Instituto de Astrofísica de Andalucía (IAA-CSIC)
Unidad de Divulgación y Comunicación
Silbia López de Lacalle - Email:  sll@iaa.es - 958230532

Instituto de Astrofísica de Andalucía - (IAA- CSIC)
http://www-divulgacion.iaa.es

The Birth of a Giant Planet?

 PR Image eso1310a

Artist's impression of a gas giant planet forming in the disc around the young star HD 100546 

PR Image eso1310b

VLT and Hubble images of the protoplanet system HD 100546

 

PR Image eso1310c

VLT image of the protoplanet around the young star HD 100546

PR Image eso1310d

NASA/ESA Hubble Space Telescope view of the dust disc around the young star HD 100546

PR Image eso1310e

The young star HD 100546 in the southern constellation of Musca 

PR Image eso1310f

Wide-field view of the sky around the young star HD 100546

Videos

PR Video eso1310a

Flying through the HD 100546 system

Candidate protoplanet spotted inside its stellar womb

Astronomers using ESO’s Very Large Telescope have obtained what is likely the first direct observation of a forming planet still embedded in a thick disc of gas and dust. If confirmed, this discovery will greatly improve our understanding of how planets form and allow astronomers to test the current theories against an observable target.

An international team led by Sascha Quanz (ETH Zurich, Switzerland) has studied the disc of gas and dust that surrounds the young star HD 100546, a relatively nearby neighbour located 335 light-years from Earth. They were surprised to find what seems to be a planet in the process of being formed, still embedded in the disc of material around the young star. The candidate planet would be a gas giant similar to Jupiter.

“So far, planet formation has mostly been a topic tackled by computer simulations,” says Sascha Quanz. “If our discovery is indeed a forming planet, then for the first time scientists will be able to study the planet formation process and the interaction of a forming planet and its natal environment empirically at a very early stage.”

HD 100546 is a well-studied object, and it has already been suggested that a giant planet orbits about six times further from the star than the Earth is from the Sun. The newly found planet candidate is located in the outer regions of the system, about ten times further out [1].

The planet candidate around HD 100546 was detected as a faint blob located in the circumstellar disc revealed thanks to the NACO adaptive optics instrument on ESO’s VLT, combined with pioneering data analysis techniques. The observations were made using a special coronagraph in NACO, which operates at near-infrared wavelengths and suppresses the brilliant light coming from the star at the location of the protoplanet candidate [2].

According to current theory, giant planets grow by capturing some of the gas and dust that remains after the formation of a star [3]. The astronomers have spotted several features in the new image of the disc around HD100546 that support this protoplanet hypothesis. Structures in the dusty circumstellar disc, which could be caused by interactions between the planet and the disc, were revealed close to the detected protoplanet. Also, there are indications that the surroundings of the protoplanet are potentially heated up by the formation process.

Adam Amara, another member of the team, is enthusiastic about the finding. “Exoplanet research is one of the most exciting new frontiers in astronomy, and direct imaging of planets is still a new field, greatly benefiting from recent improvements in instruments and data analysis methods. In this research we used data analysis techniques developed for cosmological research, showing that cross-fertilisation of ideas between fields can lead to extraordinary progress.”

Although the protoplanet is the most likely explanation for the observations, the results of this study require follow-up observations to confirm the existence of the planet and discard other plausible scenarios. Among other explanations, it is possible, although unlikely, that the detected signal could have come from a background source. It is also possible that the newly detected object might not be a protoplanet, but a fully formed planet which was ejected from its original orbit closer to the star. When the new object around HD 100546 is confirmed to be a forming planet embedded in its parent disc of gas and dust, it will become an unique laboratory in which to study the formation process of a new planetary system.

Notes

[1] The protoplanet candidate orbits about 70 times further from its star than the Earth does from the Sun. This distance is comparable to the size of the orbits of outer Solar System dwarf planets such as Eris and Makemake. This location is controversial, as it does not fit well with current theories of planet formation. It is unclear at present whether the newfound planet candidate has been in its current position for the whole time since it formed or whether it could have migrated from the inner regions.

[2] The team made use of a special feature called an apodised phase plate that increases the contrast of the image close to the star.

[3] To study planet formation, astronomers cannot look at the Solar System, as all the planets in our neighborhood were formed more than four billion years ago. But for many years, theories about planet formation were strongly influenced by what astronomers could see in our local surroundings, as no other planets were known. Since 1995, when the first exoplanet around a sunlike star was discovered, several hundred planetary systems have been found, opening up new opportunities for scientists studying planetary formation. Up to now however, none have been “caught in the act” in the process of being formed, whilst still embedded in the disc of material around their young parent star.

More information

This research was presented in a paper “A Young Protoplanet Candidate Embedded in the Circumstellar disc of HD 100546”, by S. P. Quanz et al., to appear online in the 28 February 2013 issue of Astrophysical Journal Letters.

The team is composed of Sascha P. Quanz (ETH Zurich, Switzerland), Adam Amara (ETH), Michael R. Meyer (ETH), Matthew A. Kenworthy (Sterrewacht Leiden, Netherlands), Markus Kasper (ESO, Garching, Germany) and Julien H. Girard (ESO, Santiago, Chile).

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”.

Links

• Research paper
• Photos of the VLT

Contacts

Sascha P. Quanz
ETH Zurich
Zurich, Switzerland
Tel: +41 (0) 44 63 32830
Email: sascha.quanz@astro.phys.ethz.ch

Julien H. Girard
ESO
Santiago, Chile
Tel: +56 2 2463 5342
Email: jgirard@eso.org

Richard Hook
ESO, Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

Source: ESO

Youngest Planet Seen As It’s Forming

Artist’s conception of the view at LkCa 15 b
Credit: Karen L. Teramura, UH IfA
Click here for enlarged version

Kamuela, HI – The first direct image of a planet in the process of forming around its star has been captured by astronomers who combined the power of the 10-meter Keck telescopes with a bit of optical sleight of hand.

What astronomers are calling LkCa 15 b, looks like a hot “protoplanet” surrounded by a swath of cooler dust and gas, which is falling into the still-forming planet. Images have revealed that the forming planet sits inside a wide gap between the young parent star and an outer disk of dust.

“LkCa 15 b is the youngest planet ever found, about 5 times younger than the previous record holder,” said astronomer Adam Kraus of the University of Hawaii’s Institute for Astronomy. “This young gas giant is being built out of the dust and gas. In the past, you couldn’t measure this kind of phenomenon because it’s happening so close to the star. But, for the first time, we’ve been able to directly measure the planet itself as well as the dusty matter around it.”

Kraus will be presenting the discovery at an Oct. 19 meeting at NASA’s Goddard Space Flight Center. The meeting follows the acceptance of a research paper on the discovery by Kraus and Michael Ireland (of Macquarie University and the Australian Astronomical Observatory), in The Astrophysical Journal (available at http://arxiv.org/abs/1110.3808)

Figure 1 Left: The transitional disk around the star LkCa 15. All of the light at this wavelength is emitted by cold dust in the disk. the hole in the center indicates an inner gap with radius of about 55 times the distance from the Earth to the Sun. Right: An expanded view of the central part of the cleared region, showing a composite of two reconstructed images (blue: 2.1 microns, from November 2010; red: 3.7 microns) for LkCa 15. The location of the central star is also marked. Credit: Kraus & Ireland 2011. Click here for enlarged version of Fig. 1

The optical sleight of hand used by the astronomers is to combine the power of Keck’s Adaptive Optics with a technique called aperture mask interferometry. The former is the use of a deformable mirror to rapidly correct for atmospheric distortions to starlight. The latter involves placing a small mask with several holes in the path of the light collected and concentrated by a giant telescope. With that, the scientists can manipulate the light waves.

“It’s like we have an array of small mirrors,” said Kraus. “We can manipulate the light and cancel out distortions.” The technique allows the astronomers to cancel out the bright light of stars. They can then resolve disks of dust around stars and see gaps in the dusty layers where protoplanets may be hiding.

“Interferometry has actually been around since the 1800’s, but through the use of adaptive optics has only been able to reach nearby young suns for about the last 7 years.” said Dr. Ireland. “Since then we’ve been trying to push the technique to its limits using the biggest telescopes in the world, especially Keck.”

The discovery of LkCa 15 b began as a survey of 150 young dusty stars in star forming regions. That led to the more concentrated study of a dozen stars.

“LkCa 15 was only our second target, and we immediately knew we were seeing something new,” said Kraus. “We could see a faint point source near the star, so thinking it might be a Jupiter-like planet we went back a year later to get more data.”

Figure 2: The location of LkCa 15 can be found using this chart.
Credit: Adam Kraus/IAU/Sky & Telescope
Click here for enlarged version of Fig. 2

In further investigations at varying wavelengths, the astronomers were intrigued to discover that the phenomenon was more complex than a single companion object.

“We realized we had uncovered a super Jupiter-sized gas planet, but that we could also measure the dust and gas surrounding it. We’d found a planet, perhaps even a future solar system at its very beginning” said Kraus.

Drs. Kraus and Ireland plan to continue their observations of LkCa 15 and other nearby young stars in their efforts to construct a clearer picture of how planets and solar systems form.

***

The W. M. Keck Observatory operates two 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Big Island of Hawaii. The twin telescopes feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectroscopy and a world-leading laser guide star adaptive optics system which cancels out much of the interference caused by Earth’s turbulent atmosphere. The Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

When is an Asteroid Not an Asteroid?

This image shows a model of the protoplanet Vesta, using scientists' best guess to date of what the surface of the protoplanet might look like. Image credit: NASA/JPL-Caltech/UCLA/PSI. Full image and caption

On March 29, 1807, German astronomer Heinrich Wilhelm Olbers spotted Vesta as a pinprick of light in the sky. Two hundred and four years later, as NASA's Dawn spacecraft prepares to begin orbiting this intriguing world, scientists now know how special this world is, even if there has been some debate on how to classify it.

Vesta is most commonly called an asteroid because it lies in the orbiting rubble patch known as the main asteroid belt between Mars and Jupiter. But the vast majority of objects in the main belt are lightweights, 100-kilometers-wide (about 60-miles wide) or smaller, compared with Vesta, which is about 530 kilometers (330 miles) across on average. In fact, numerous bits of Vesta ejected by collisions with other objects have been identified in the main belt.

"I don't think Vesta should be called an asteroid," said Tom McCord, a Dawn co-investigator based at the Bear Fight Institute, Winthrop, Wash. "Not only is Vesta so much larger, but it's an evolved object, unlike most things we call asteroids."

The layered structure of Vesta (core, mantle and crust) is the key trait that makes Vesta more like planets such as Earth, Venus and Mars than the other asteroids, McCord said. Like the planets, Vesta had sufficient radioactive material inside when it coalesced, releasing heat that melted rock and enabled lighter layers to float to the outside. Scientists call this process differentiation.

McCord and colleagues were the first to discover that Vesta was likely differentiated when special detectors on their telescopes in 1972 picked up the signature of basalt. That meant that the body had to have melted at one time.

Officially, Vesta is a "minor planet" -- a body that orbits the sun but is not a proper planet or comet. But there are more than 540,000 minor planets in our solar system, so the label doesn't give Vesta much distinction. Dwarf planets – which include Dawn's second destination, Ceres -- are another category, but Vesta doesn't qualify as one of those. For one thing, Vesta isn't quite large enough.

Dawn scientists prefer to think of Vesta as a protoplanet because it is a dense, layered body that orbits the sun and began in the same fashion as Mercury, Venus, Earth and Mars, but somehow never fully developed. In the swinging early history of the solar system, objects became planets by merging with other Vesta-sized objects. But Vesta never found a partner during the big dance, and the critical time passed. It may have had to do with the nearby presence of Jupiter, the neighborhood's gravitational superpower, disturbing the orbits of objects and hogging the dance partners.

Other space rocks have collided with Vesta and knocked off bits of it. Those became debris in the asteroid belt known as Vestoids, and even hundreds of meteorites that have ended up on Earth. But Vesta never collided with something of sufficient size to disrupt it, and it remained intact. As a result, Vesta is a time capsule from that earlier era.

"This gritty little protoplanet has survived bombardment in the asteroid belt for over 4.5 billion years, making its surface possibly the oldest planetary surface in the solar system," said Christopher Russell, Dawn's principal investigator, based at UCLA. "Studying Vesta will enable us to write a much better history of the solar system's turbulent youth."

Dawn's scientists and engineers have designed a master plan to investigate these special features of Vesta. When Dawn arrives at Vesta in July, the south pole will be in full sunlight, giving scientists a clear view of a huge crater at the south pole. That crater may reveal the layer cake of materials inside Vesta that will tell us how the body evolved after formation. The orbit design allows Dawn to map new terrain as the seasons progress over its 12-month visit. The spacecraft will make many measurements, including high-resolution data on surface composition, topography and texture. The spacecraft will also measure the tug of Vesta's gravity to learn more about its internal structure.

"Dawn's ion thrusters are gently carrying us toward Vesta, and the spacecraft is getting ready for its big year of exploration," said Marc Rayman, Dawn's chief engineer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "We have designed our mission to get the most out of this opportunity to reveal the exciting secrets of this uncharted, exotic world."

The Dawn mission to Vesta and Ceres is managed by the Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, for NASA's Science Mission Directorate, Washington. The Dawn mission is part of the Discovery Program managed by NASA's Marshall Space Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission science. Orbital Sciences Corporation of Dulles, Va., designed and built the Dawn spacecraft. The German Aerospace Center, the Max Planck Society, the Italian Space Agency and the Italian National Astrophysical Institute are part of the mission team.

For more information about Dawn, visit http://www.nasa.gov/dawn and http://dawn.jpl.nasa.gov .

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov