Posted on by Jon Voisey

More Images of HR 8799

HR 8799 system
One of the discovery images of the system obtained at the Keck II telescope using adaptive optics system and the NIRC2 Near-Infrared Imager. Image shows all four confirmed planets indicated as b, c, d and e in the labeled image. Planet "b" is a ~5 Jupiter-mass planet orbiting at about ~68 AU, while planets c, d, and e are ~7 Jupiter-mass companions orbiting the star at about 38, 24 and 14.5 AU. Credit: NRC-HIA, C. Marois & Keck Observatory

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Late last year, astronomers using the Keck II telescope released the first direct image of a planetary system including four planets. These planets orbited the star HR 8799 and were taken in the J and L bandpasses which are in the near-infrared portion of the spectrum. Since then the team has collected new data using the same telescope, extending the spectral range into the mid-infrared portion of the spectra.

The new images are important to astronomers because this provides a more complete understanding of the distribution of radiation that the planets are emitting. This can be compared to models of planetary formation, allowing these young planets to act as a test bed. Previous comparison to models have suggested that these planets have cool, dusty atmospheres without the presence of methane or other common absorbing molecules.

The team hopes that the new observations will help distinguish between the various models that explain this deficiency of methane. Unfortunately, getting good observations in this portion of the spectra is challenging. In particular, at the Keck telescope, the design of the telescope itself makes observations especially challenging due to portions of the instrument themselves emitting in the infrared, masking the faint signals from the planet.

To bring out the planets, the team developed a new technique to help clean the images of the unwanted noise. They estimate that their new technique is nine times more efficient than previously used techniques. To do this, they moved the telescope slightly between images, allowing the patterns of interference to change between exposures, thereby making them more apparent and easier to remove.

When the results were analyzed and compared to models, the team found that they were in good agreement with predictions of planetary evolution for planets c and d. However, for planet b, the models predicted a planet with a radius that would be too small to account for the observed luminosity. The observations could be brought into agreement with the models by increasing the metallicity of the model.

With additional future observations, the team hopes to constrain these models and further investigate the atmospheres of these planets.

NOTE: I Emailed the authors of the paper to ask permission to reproduce the new image here, but have not gotten a reply. The one used above is the K and L band images from last year. To see the new ones, feel free to go to the paper directly.

Posted on by Jon Voisey

New Planet Discovered In Trinary Star System

A planet 6 times the mass of Earth orbits around the star Gliese 667 C, which belongs to a triple system. Credit: ESO

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Until recently, astronomers were highly skeptical of whether or not planets should be possible in multiple star systems. It was expected that the constantly varying gravitational force would eventually tug the planet out of orbit. But despite doubts, astronomers have found several planets in just such star systems. Recently, astronomers announced another, this time in the trinary star HD 132563.

The detection of the new planet came as part of a larger study on the trinary star system spanning 10 years. The two main stars that comprise the system are both similar to the Sun in mass, although somewhat less prevalent in metals, and orbit each other at a distance of around 400 AU. The main star, HD 132563A is also itself, a binary. This fact was not previously recognized and also reported by the team, led by Silvano Desidera from the Astronomical Observatory in Padova, Italy.

The newly discovered planet orbits the secondary star in the system, HD 132563B. As with the binary component of the main star, the new planet was discovered spectroscopically. The planet is at least 1.3 times the mass of Jupiter, with an average distance from its parent star of 2.6 AU, and an moderately high eccentricity of 0.22.

The team also attempted to image the planet directly using adaptive optics from the Italian Telescopio Nazionale Galileo. While there was a hint in the glare of the star that may have been the planet in question, the team could not rule out that the detection was not an instrumental effect.

With the discovery of this new planet, the total number of discovered planets in multiple star systems lies at eight. while this is rather small numbers from which to draw firm conclusions, it appears that planets can be commonly found orbiting the more remote members of trinary star systems for good periods of time. On the shorter end, the stellar system is anticipated to be 1-3 billion years in aged, based on the amount of stellar activity and amount of lithium present in the star’s atmosphere (which decreases with time). However, fitting of the mass and luminosity onto isochrones suggest the stars may be as much as 5 billion years in age. In either situation, the planetary system is dynamically stable.

Also based on these eight systems, the team also suggests that planets existing around such far removed members of a multiple star system may be as common as planets around wide binaries, or even single stars.

Posted on by Nancy Atkinson

One Million Observations Now in the Books for Hubble Telescope

Artist's impression of the transiting exoplanet HAT-P-7b. Credit: NASA/ESA

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After 21 years in orbit, the Hubble Space Telescope has reached an historic milestone: the venerable HST has made its millionth observation. The telescope was used to search for the chemical signature of water in the atmosphere of planet HAT-P-7b, a gas giant larger than Jupiter which orbits the star HAT-P-7, about 1,000 light-years away from Earth. The observation was led by Dr. Drake Deming, planetary scientist and astronomer from the University of Maryland and the Goddard Space Flight Center.

With this announcement, however, there is no stunning image or unprecedented view of an exoplanet. The millionth observation will show up as squiggly lines on a graph, since the observation was done with Hubble’s spectrograph.

Spectroscopy is the technique of splitting light into its component colors, and the gases present in a planet’s atmosphere leave a fingerprint in the form of the distinctive color patterns that different gases absorb. Analyzing this data can give precise measurements of which elements are present in the exoplanet’s atmosphere.

“We are looking for the spectral signature of water vapor. This is an extremely precise observation and it will take months of analysis before we have an answer,” said Deming. “Hubble has demonstrated that it is ideally suited for characterizing the atmospheres of exoplanets and we are excited to see what this latest targeted world will reveal.”

“With a million observations and many thousands of scientific papers to its name, Hubble is one of the most productive scientific instruments ever built,” said Alvaro Gimenez, head of science and robotic exploration for the European Space Agency. “As well as changing our view of the Universe with its stunning imagery, Hubble has revolutionized whole areas of science.”

Hubble’s on-orbit history began when it was launched on the space shuttle Discovery on April 24, 1990. The HST has collected over 50 terabytes of data, enough to fill more than 10,000 DVDs. While the the data collected in the one millionth observation is now proprietary for the scientists, within a year, it will be released to the public. The huge and varied library of data Hubble has produced is made freely available to scientists and the public through an online archive at his link:

http://hla.stsci.edu/

Hubble made the millionth observation using its Wide Field Camera 3, a visible- and infrared-light imager with an on-board spectrometer. It was installed by astronauts during the Hubble Servicing Mission 4 in May 2009.

More Hubble info and images can be found at the HubbleSite, and ESA’s Hubble website.

Posted on by Tammy Plotner

Exomoons Could Be Excellent Incubators

Artist's impression of the view from a hypothetical moon around a exoplanet orbiting a triple star system. Credit: NASA

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With the arrival of the Cassini–Huygens mission in 2004 to Saturn’s satellite Titan, we terrestrials became acutely aware that similar moons could be orbiting similarly large planets in other solar systems besides our own. These extrasolar moons, or exomoons, might be a little bit difficult to distinguish with our current equipment, but our technological grasp has greatly improved in recent years. Now current studies suggest that not only can these naturally occurring satellites exist – but they also might be habitable.

As we know, there isn’t exactly a lack of planetary candidates hospitable to life. At least 40 so far discovered are within Earth-like tolerances and it’s only a matter of time before transit timings (TTV and TDV) and wobble variations will allow us to detect their moons. If the potential is there for the giant planet – then why not its companion?

“The satellites of extrasolar planets (exomoons) have been recently proposed as astrobiological targets. Since giant planets in the habitable zone are thought to have migrated there,” says Simon Porter of Lowell Observatory and William Grundy of Arizona State University. “It is possible that they may have captured a former terrestrial planet or planetesimal.”

Although we’re aware of life-possible exoplanet existence, we’re not yet sure of how they got to their current position. Simulations show they may have formed on the edge of where ice can exist, but this might also make them a bit inhospitable. Disk migration would bring them closer to the parent star – but also make them intolerably hot. Yet, there’s a theory which says during the shuffle that some planetesimals could have been “swapped” in the process.

“We therefore attempt to model the dynamical evolution of a terrestrial planet captured into orbit around a giant planet in the habitable zone of a star.” says Porter and Grundy. “We find that approximately half of loose elliptical orbits result in stable circular orbits over timescales of less than a few million years. We also find that those orbits are mostly low-inclination, but have no prograde/retrograde preference.”

Right now the most probable candidates for “living” exomoons would be around planets very similar to Neptune and orbiting a star similar to our Sun. Once these Earth-massed satellites have stabilized into a long-lived orbit, they should be within the range of findability using the transit timing variation much stronger than the duration variation – even if their orbit is tight to the parent planet.

“In addition, we calculate the transit timing and duration variations for the resulting systems, and find that potentially habitable Earth-mass exomoons should be detectable.” reports the team. “Even with these closer orbits, some exomoons are still within the range of detectability. The combination of TTV and TDV may offer a stronger detection signal than photometry for these orbits, though both could detect some of the orbits produced.”

Abstract Information: Post-Capture Evolution of Potentially Habitable Exomoons.

Posted on by Jon Voisey

Rocky, Low-Mass Planet Discovered by Microlensing

A low-mass, rocky planet orbits a distant sun
A low-mass, rocky planet orbits a distant sun

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In planet hunting today, there seems to be one burning question that nearly every new article published touches on: Where did these planets come from?

As astronomers discovered the first extrasolar planets, it quickly became obvious that the formation theories that we’d built on our own solar system were only part of the story. They didn’t predict the vast number of hot Jupiters astronomers found nearly everywhere. Astronomers went back to the drawing board to put more details into the theory, breaking formation down into quick, single collapses and more gradual accretion of gas disks, and worrying about the effects of migration. It’s likely all these effects take place to some extent, but ferreting out just how much is now the big challenge for astronomers. Hampering their efforts is the biased sample from the gravitational-wobble technique which preferentially discovered high mass, tightly orbiting planets. The addition of Kepler to planet hunter’s arsenal has removed some of this bias, readily finding planets to far lower masses, but still prefers planets in short orbits where they are more likely to transit. However, the addition of another technique, gravitational microlensing, promises to find planets down to 10 Earth masses, much further out from their parent stars. Using this technique, a team of astronomers has just announced the detection of a rocky planet just in this range.

According to the Extrasolar Planet Encyclopaedia, astronomers have discovered 13 planets using gravitational microlensing. The newly announced one, MOA-2009-BLG-266Lb, is estimated to be just over 10 times the mass of Earth and orbits at a distance of 3.2 AUs around a parent star with roughly half the mass of the Sun. The new finding is important because it is one of the first planets in this mass range that lies beyond the “snow line”, the distance during formation of a planetary system beyond which ice can form from water, ammonia, and methane. This presence of icy grains is expected to assist in the formation of planets since it creates additional, solid material to form the planetary core. Just beyond the snow line, astronomers would expect that planets would form the most quickly since, as you move further, beyond this line, the density drops. Models have predicted that planets forming here should quickly reach a mass of 10 Earth masses by accumulating most of the solid material in the vicinity. The forming planet then, can slowly accrete gaseous envelopes. If it accumulates this material quickly enough, the gaseous atmosphere may become too massive and collapse, beginning a rapid gas accretion phase forming a gas giant.

The timing of these three phases, as well as their distance dependency, makes testable predictions that can be contrasted with the observations as astronomers discover more planets in this vicinity. In particular, it has suggested that we should see few gas giants around low mass stars because the gas disk is expected to dissipate before the atmosphere collapse leading to the rapid accretion phase. This expectation has been generally supported by the findings of the 500+ confirmed extrasolar planets, as well as the 1,200+ candidates from Kepler, lending credence to this core collapse + slow accretion model. Additionally, Kepler has also reported a large population of relatively low mass planets, interior to the snow line. This too supports the hypothesis since the greater difficulty in forming cores without the presence of ice would hamper the formation of large planets. However, other predictions, such as not expecting massive planets in tight orbits, is still largely contradictory to the hypothesis and greater testing with additional discoveries will be needed.

Assisting with this, several new observing programs will be coming on line in the near future. The Optical Gravitational Lensing Experiment IV (OGLE-IV) has just entered operation and a new program at Wise Observatory in Tel Aviv will begin operation following up on microlensing events next year. Also expected in the near future is the Korean Microlensing Network (KMT-Net) which will operate telescopes in South Africa, Chile, and Australia using 1.6 meter telescopes covering 4 square degrees of the galactic bulge.

Posted on by Tammy Plotner

New Planetary System Has South African Astronomers Doing A Double Take

Artist impression (c) SAAO
Artist impression (c) SAAO

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Double your pleasure… Double your fun… Double twin planets found orbiting a double sun! Are you ready for the weird, true and freaky? Then check out what Drs. Stephen Potter and Encarni Romero-Colmenero from the South African Astronomical Observatory (SAAO) and their colleagues have found. It would appear there’s evidence pointing towards the existence of a double planetary system where a pair of giants are at home orbiting a binary star.

Known in polite social circles as UZ Fornacis, this eclipsing double star is anything but a friendly environment for a solar system. Because the pair orbits so closely, the white dwarf never stops collecting material from its red dwarf companion. This steady flow gets superheated to millions of degrees and produces copious amounts of deadly x-rays. This pair of twin stars are so small they would fit within the radius of our Sun and orbit each other within a period of hours. Because of their eclipsing nature, Dr. Potter and his collaborators were quick to notice that the periodic timing wasn’t regular. This evidence led them to theorize a pair of planets needed to be present to account for the wobble and to infer that the masses of the two planets must be at least 6 and 8 times that of Jupiter and take 16 and 5 years respectively to orbit the two stars.

“The two planet model can provide realistic solutions but it does not quite capture all of the eclipse times measurements. A highly eccentric orbit for the outer planet would fit the data nicely, but we find that such a solution would be unstable” says Potter, et al. ” It is also possible that the periodicities are driven by some combination of both mechanisms. Further observations of this system are encouraged.”

This discovery was made possible by new SAAO and Southern African Large Telescope (SALT) observations combined with archival data spanning 27 years, gathered from multiple observatories and satellites.

Original Story Source: South African Astronomical Observatory News.

Posted on by Jon Voisey

Exoplanet Kepler-7b Unexpectedly Reflective

Artist concept of Kepler in space. Credit: NASA/JPL

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Early on in the hunt for extra solar planets, the main method for discovering planets was the radial velocity method in which astronomers would search for the tug of planets on their parent stars. With the launch of NASA’s Kepler mission, the transit method is moving into the spotlight, the radial velocity technique provided an early bias in the detection of planets since it worked most easily at finding massive planets in tight orbits. Such planets are referred to as hot Jupiters. Currently, more than 30 of this class of exoplanet have had the properties of their emission explored, allowing astronomers to build a picture of the atmospheres of such planets. However, one of the new hot Jupiters discovered by the Kepler mission doesn’t fit the picture.

The consensus on these planets is that they are expected to be rather dark. Infrared observations from Spitzer have shown that these planets emit far more heat than they absorb directly in the infrared forcing astronomers to conclude that visible light and other wavelengths are absorbed and reemitted in the infrared, producing the excess heat and giving rise to equilibrium temperatures over 1,000 K. Since the visible light is so readily absorbed, the planets would be rather dull when compared to their namesake, Jupiter.

The reflectivity of an object is known as its albedo. It is measured as a percentage where 0 would be no reflected light, and 1 would be perfect reflection. Charcoal has an albedo of 0.04 while fresh snow has an albedo of 0.9. The theoretical models of hot Jupiters place the albedo at or below 0.3, which is similar to Earth’s. Jupiter’s albedo is 0.5 due to clouds of ammonia and water ice in the upper atmosphere. So far, astronomers have placed upper limits on their albedo. Eight of them confirm this prediction, but three of them seem to be more reflective.

In 2002, it was reported that the albedo for υAnd b was as high as 0.42. This year, astronomers have placed constraints on two more systems. For HD189733 b, astronomers found that this planet actually reflected more light than it absorbed. For Kepler-7b, an albedo of 0.38 has been reported.

Revisiting this for the latter case, a new paper, slated for publication in an upcoming issue of the Astrophysical Journal, a team of astronomers led by Brice-Olivier Demory of the Massachusetts Institute of Technology confirms that Kepler-7b has an albedo that breaks the expected limit of 0.3 set by theoretical models. However, the new research does not find it to be as high as the earlier study. Instead, they revise the albedo from 0.38 to 0.32.

To explain this additional flux, the team proposes two models. They suggest that Kepler-7b may be similar to Jupiter in that it may contain high altitude clouds of some sort. Due to the proximity to its parent star, it would not be ice crystals and thus, would not reach as high of an albedo as Jupiter, but preventing the incoming light from reaching lower layers where it could be more effectively trapped would help to increase the overall albedo.

Another solution is that the planet may be lacking the molecules most responsible for absorption such as sodium, potassium, titanium monoxide and vanadium monoxide. Given the temperature of the planet, it is unlikely that the molecular components would be present in the first place since they would be broken apart from the heat. This would mean that the planet would have to have 10 to 100 times less sodium and potassium than the Sun, whose chemical composition is the basis for models since our star’s composition is generally representative of stars around which planets have been discovered and presumably, the cloud from which it formed and would also form into planets.

Presently there is no way for astronomers to determine which possibility is correct. Since astronomers are slowly becoming able to retrieve spectra of extrasolar planets, it may be possible in the future for them to test chemical compositions. Failing that, astronomers will need to examine the albedo of more exoplanets and determine just how common such reflective hot Jupiters are. If the number remains low, the plausibility of metal deficient planets remains high. However, if the numbers start creeping up, it will prompt a revision to models of such planets and their atmospheres with greater emphasis on clouds and atmospheric haze.

Posted on by Jason Major

Multi-Planet Systems Common in Kepler Findings

Artist's concept of Kepler in action. NASA/Kepler mission/Wendy Stenzel.

 

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Of the 1235 planetary candidates that NASA’s Kepler space telescope has found so far, 408 reside in multiple-planet systems – a growing trend that indicates planets do, in fact,  like company.

The systems observed also seem to behave quite differently than our own solar system. In particular many are flatter than ours; that is, the planets orbit their stars in more or less the same exact plane. This, of course, is what allows Kepler to see them in the first place… the planets have to transit their stars perpendicular to Kepler’s point of view in order for it to detect the oh-so-subtle change in brightness that indicates the likely presence of a planet. In our solar system there’s a variation in the orbital plane of some planets up to 7º – enough of a difference that an alien Kepler-esque telescope might very well not be able to spot all eight planets.

The reason for this relative placidity in exoplanet orbits may be due to the lack of gas giants like Jupiter in these systems. So far, all the multiple-planet systems found have planets smaller than Neptune. Without the massive gravitational influence of a Jupiter-sized world to shake things up, these exosystems likely experience a much calmer environment – gravitationally speaking, of course.

“Most likely, if our solar system didn’t have large planets like Jupiter and Saturn to have stirred things up with their gravitational disturbances, it would be just as flat. Systems with smaller planets probably had a much more sedate history.”

– David Latham, Harvard-Smithsonian Center for Astrophysics, Cambridge, MA

Slide showing Kepler multi-planet systems (blue dots). Credit: David Latham.

Systems containing large gas giants have also been found but they are not as flat as those without, and many smaller worlds are indeed out there… “probably including a lot of them comparable in size to Earth,” said planet-hunter Geoff Marcy of the University of California, Berkeley.

While multiple-planet systems were expected, the scientists on the Kepler team were surprised by the amount that have been discovered.

“We didn’t anticipate that we would find so many multiple-transit systems. We thought we might see two or three. Instead, we found more than 100,” said Latham.

A total of 171 multiple-planet systems have been found so far… with many more to come, no doubt!

Announced yesterday at the American Astronomical Society conference in Boston, these findings are the result of only the first four months of Kepler’s observations. There will be another news release next summer but in the meantime the team wants time to extensively research the data.

“We don’t want to get premature information out. There’s still a lot of analysis that needs to be done.”

– Kepler principal investigator William Borucki

Read more on the Kepler mission site, or on Science NOW.

Posted on by Tammy Plotner

A New “Spin” On Stellar Age

Artist's Conception of Hypothetical Planet courtesy of David A. Aguilar (CfA)

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It might not be polite to ask a lady her true age, but when it comes to stars it’s not as easy as checking a driver’s license. From our point of view, all stars can look pretty much the same – so how do we tell one that’s one billion years old from one that ten billion? The answer could be stellar spin rate.

In Monday’s 218th meeting of the American Astronomical Society, astronomer Soren Meibom of the Harvard-Smithsonian Center for Astrophysics presented his findings. “A star’s rotation slows down steadily with time, like a top spinning on a table and can be used as a clock to determine its age.” says Meibom. “Ultimately, we need to know the ages of the stars and their planets to assess whether alien life might have evolved on these distant worlds. The older the planet, the more time life has had to get started. Since stars and planets form together at the same time, if we know a star’s age, we know the age of its planets too.”

By determining a star’s age in advance, it assists astronomer’s working with projects like Kepler. Knowing where to begin in a galaxy filled with stars helps us to understand how planetary systems form and evolve and why they are so different from each other. In some circumstances, like galactic star clusters, we’re pretty much on the mark at knowing a star’s age because we believe they all formed about the same time. However, for a lone star that harbors planets, determining age is much more difficult. Measuring the rotation of stars in clusters with different ages reveals exactly how spin and age are related. Then by extension, astronomers can measure the spin of a single isolated star and calculate its age.

Just how is calculating stellar spin rate done? Try exactly how we know our own Sol’s rotation – sunspots. Each time a “star spot” rotates across the visible surface, it dims ever so slightly. By measuring how long these changes take place gives us substantial clues to just how fast a star rotates. Although these changes are minute and decrease as a star ages, the sensitivity of the Kepler spacecraft was designed specifically to measure stellar brightnesses very precisely in order to detect planets (which block a star’s light ever so slightly if they cross the star’s face from our point of view).

But this task was far from easy. In a four year preparatory study conducted with specially designed instrument (Hectochelle) mounted on the MMT telescope on Mt. Hopkins in southern Arizona, Meibom and his colleagues sorted out information in nearly 7000 individual stars and used Kepler data to determine how fast those stars were spinning. Their findings included stars with rotation periods between 1 and 11 days, confirming that gyrochronology is an exciting new method to learn the ages of isolated stars.

“This work is a leap in our understanding of how stars like our Sun work. It also may have an important impact on our understanding of planets found outside our solar system,” said Meibom.

Posted on by Jon Voisey

Want to Make Planets? Better Hurry.

Artist's impression of planetary formation. Image credit: NASA

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Currently, astronomers have two competing models for planetary formation. In one, the planets form in a single, monolithic collapse. In the second, the core forms first and then slowly accretes gas and dust. However, in both situations, the process must be complete before the radiation pressure from the star blows away the gas and dust. While this much is certain, the exact time frames have remained another matter of debate. It is expected that this amount should be somewhere in the millions of years, but low end estimates place it at only a few million, whereas upper limits have been around 10 million. A new paper explores IC 348, a 2-3 million year old cluster with many protostars with dense disks to determine just how much mass is left to be made into planets.

The presence of dusty disks is frequently not directly observed in the visible portion of the spectra. Instead, astronomers detect these disks from their infrared signatures. However, the dust is often very opaque at these wavelengths and astronomers are unable to see through it to get a good understanding of many of the features in which they’re interested. As such, astronomers turn to radio observations, to which disks are partially transparent to build a full understanding. Unfortunately, the disks glow very little in this regime, forcing astronomers to use large arrays to study their features. The new study uses data from the Submillimeter Array located atop Mauna Kea in Hawaii.

To understand how the disks evolved over time, the new study aimed to compare the amount of gas and dust left in IC 348’s disc to younger ones in star forming regions in Taurus, Ophiuchus, and Orion which all had ages of roughly 1 million years. For IC 348, the team found 9 protoplanetary disks with masses from 2-6 times the mass of Jupiter. This is significantly lower than the range of masses in the Taurus and Ophiuchus star forming regions which had protoplanetary clouds ranging to over 100 Jupiter masses.

If planets are forming in IC 348 at the same frequency in which they form in systems astronomers have observed elsewhere, this would seem to suggest that the gravitational collapse model is more likely to be correct since it doesn’t leave a large window in which forming planets could accrete. If the core accretion model is correct, then planetary formation must have begun very quickly.

While this case don’t set any firm pronouncements on which model of planetary formation is dominant, such 2-3 million year old systems could provide an important test bed to explore the rate of depletion of these reservoirs.