Hubble Watches Massive Exoplanet Stir Stellar Dust

By watching how an exoplanet orbiting the star Beta Pictoris interacts with circumstellar dust, astronomers are beginning to understand how to look for the dusty fingerprints of hidden alien worlds. Continue reading →

Owed to its long-duration mission, Hubble can spot short-duration changes in celestial objects, revealing unprecedented detail in an otherwise ‘unchanging' sky. Take Beta Pictoris for example. This 20 million year-old star sports an extensive edge-on protoplanetary disk and Hubble has been watching motion in this dust, stirred up by the presence of a massive exoplanet.

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This is yet another cosmic first for the veteran space telescope; astronomers have been able to compare Hubble observations of Beta Pictoris 1997 and 2012 and would therefore be able to track any morphological changes in its protoplanetary disk.

As the exoplanet's orbit is predicted to have an orbital period of between 18-20 years, over the 15 years between observations, the exoplanet would have shifted considerably, but Hubble has noticed little change in the distribution of dust in the protoplanetary disk, confirming some models about how protoplanetary disks mingling with exoplanets work.

"Some computer simulations predicted a complicated structure for the inner disk due to the gravitational pull by the short-period giant planet," said Daniel Apai of the University of Arizona. "The new images reveal the inner disk and confirm the predicted structures. This finding validates models, which will help us to deduce the presence of other exoplanets in other disks."

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From these observations, astronomers can see that the circumstellar dust is orbiting in unison with the exoplanet "like a carousel," according to a Hubble news release. This suggests that the inner dusty disk is "smooth and continuous" as it orbits the star.

Beta Pictoris, however, isn't believed to be a ‘typical' young star with a protoplanetary disk.

"The Beta Pictoris disk is the prototype for circumstellar debris systems, but it may not be a good archetype," said co-author Glenn Schneider of the University of Arizona.

Beta Pictoris was the first star to be discovered to have a bright circumstellar disk. It's believed that asteroids and comets in the system are continuously colliding, populating the disk with copious quantities of dust. Also, a lobe-like feature in the disk is thought to be the dusty remains of a pulverized Mars-sized body.

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Located only 63 light-years from Earth, Beta Pictoris is the closest circumstellar disk system, so it is a protoplanetary Petri-dish of sorts, providing astronomers with a smorgasbord of planetary phenomena.

Interestingly, the researchers suggest that by studying star systems with circumstellar disks known also to contain exoplanets, we may begin to fathom the ‘fingerprint' in these disks so previously hidden exoplanets may be revealed around other stars.


The photo at the bottom is the most detailed picture to date of a large, edge-on, gas-and-dust disk encircling the 20-million-year-old star Beta Pictoris. The new visible-light Hubble image traces the disk in closer to the star to within about 650 million miles of the star (which is inside the radius of Saturn's orbit about the sun).

Astronomers using the Hubble Space Telescope recently completed the largest and most sensitive survey of dust surrounding young star systems. The survey zoomed-in on stars that are between 10 million to 1 billion years old and the source of the dust is thought to be the left-over debris from planet, asteroid and comet collisions after systems of planets have formed.

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The research is akin to looking far back into the history of our solar system, seeing the inevitable dusty mess left over after the Earth and other planets evolved. "It's like looking back in time to see the kinds of destructive events that once routinely happened in our solar system after the planets formed," said Glenn Schneider, of the University of Arizona's Steward Observatory and lead scientist on the survey team.

Read on to see some of the beautiful variety of circumstellar disks observed by Hubble.

One of the major findings to come from this survey is the stunning diversity of dust surrounding these young stars. Traditionally, circumstellar dust is thought to settle into an orderly disk-like shape -- but it turns out that the opposite is true.

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"We find that the systems are not simply flat with uniform surfaces," said Schneider. "These are actually pretty complicated three-dimensional debris systems, often with embedded smaller structures. Some of the substructures could be signposts of unseen planets."

One stunning observation of the star HD 181327 exhibits a bright ring of dust containing irregularities, potential evidence of a massive collision that has scattered debris far and wide. "This spray of material is fairly distant from its host star — roughly twice the distance that Pluto is from the Sun," said Christopher Stark of NASA's Goddard Space Flight Center, Greenbelt, Md., and co-investigator in the survey team. "Catastrophically destroying an object that massive at such a large distance is difficult to explain, and it should be very rare. If we are in fact seeing the recent aftermath of a massive collision, the unseen planetary system may be quite chaotic."

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Another interpretation for the irregularities could be some kind of interaction with unseen interstellar material. "Our team is currently analyzing follow-up observations that will help reveal the true cause of the irregularity," added Schneider.

Like the diversity of exoplanetary systems astronomers have discovered, it appears the accompanying dust disks also share this characteristic, possibly indicative of gravitational interactions with planets orbiting the stars surveyed by Hubble.

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"How are the planets affecting the disks, and how are the disks affecting the planets? There is some sort of interdependence between a planet and the accompanying debris that might affect the evolution of these exoplanetary debris systems," said Schneider.

Since 1995, thousands of exoplanets have been discovered orbiting stars in our galaxy. Over the same period, however, only a couple of dozen circumstellar disks have been imaged directly. This is down to the fact that the scattered light off these disks is extremely faint (around 100,000 times fainter than the parent star's light). The technology and techniques are only recently becoming available for scientists to not only block the star's blinding light, but to also boost the sensitivity of observations to pick out this scattered light that would otherwise be obscured from view. Fortunately, Hubble's high-contrast imaging has been key in making this survey a success.

By studying these disks of dust and their surprising variety of morphologies may help astronomers better understand how the Earth-moon and Pluto-Charon systems formed. Through planetary collisions, the debris from the early solar system may have coalesced to create many of the natural satellites we see today, 4.6 billion years later. The results of this survey have been published in The Astrophysical Journal.

For more information about this Hubble survey and high-resolution images, browse the news release.