Resolving the planetesimal belt around HR8799

Resolving the Planetesimal Belt around HR8799
A submillimeter image of the planetesimal disk around the star HR8799, the first directly imaged system of four exoplanets and their dust disk. The insert shows the innermost region of the system and the location of the four exoplanets. Credit: ALMA; Booth et al.

Planets develop from the dusty placental disk of material that surrounds a star after it begins to shine. The dust in that disk, according to most models, starts to stick to itself until clumps develop large enough to attract other clumps gravitationally. Astronomers believe the process of building planets and dissipating the disk takes about ten million years. Many mysteries remain, however, including the tendency of dust not to stick together, and the likelihood that colliding clumps could break apart rather than agglomerate. Recent discoveries of exoplanets have begun to overlap with studies of planetesimal disks, and enable astronomers to probe the development and evolution of a star's system of planets and their interactions with the disk.

Direct imaging of dust disks has been very limited, and so far has principally probed regions in disks at the outer zones of – analogous to the Kuiper Belt in our own solar system. At the same time, the vast majority of exoplanets discovered and studied so far have been very close to the star, even within a distance that in the solar system would be within the orbit of Mercury. The star HR8799 is so far the only star around which direct imaging has found multiple . Its circumstellar disk has been known to exist for several decades, and has been modeled as having three zones: an inner asteroid belt analogue, a planetesimal belt from about one hunded astronomical units (au) to about 430 au, and a halo region extending out to over 1500 au.

CfA astronomer Denis Barkats has joined a team of colleagues to use the giant ALMA submillimeter array to image the disk around HR8799 with a spatial scale as small as only thirty-two au, enough to probe the inner zones of the disk. The team has determined that the inner edge of the planetesimal belt actually starts at around 145 au, and that the belt extends out to 430 au.

The known four exoplanets in this system orbit within this inner edge. The most distant of these four planets, planet b, has a chaotic orbit that is expected to take it beyond this inner edge, which therefore poses a stability problem in this interpretation.

The astronomers propose two interesting suggestions: either that the orbit of planet b has varied over time more than thought, or that there is a fifth, so-far undetected small planet in a larger whose gravity provides some stability.

Whichever the answer, the new paper marks the dawn of a new age in imaging and analyzing .


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More information: "Resolving the Planetesimal Belt of HR 8799 with ALMA," Mark Booth, Andres Jordan, Simon Casassus, Antonio S. Hales, William R. F. Dent, Virginie Faramaz, Luca Matra, Denis Barkats, Rafael Brahm and Jorge Cuadra, MNRAS 460, L10, 2016.
Citation: Resolving the planetesimal belt around HR8799 (2016, August 15) retrieved 20 August 2019 from https://phys.org/news/2016-08-planetesimal-belt-hr8799.html
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Aug 15, 2016
"Astronomers believe the process of building planets and dissipating the drive takes about one million years."
The claim in the range that the whole Paris costs 1 cent.
For asteroids that they fell to Earth the same Astronomers claim to have the old 4.5 Gy. When telling the truth?
HR 8799 is 1.47 of the Sun, radius 1.37, which means that the faster the rotation .. is expected proportionally faster events but not scenes from Hitchcock. Rare gas would have to flow in rivers that form planets 1.2, Jupiter (x 4 -5).
Of course the truth we see in our solar system (Earth picks up ~ 70 tons of cosmic material per day). When these results and redouble, we have the numbers well above 10 ^ 24, it is a more realistic time due to the in the gravity grasp.

RNP
Aug 15, 2016
Current theory suggests that planets took a lot longer than 1 million years to form. The link below is for a paper abstract that gives a brief, but clear, outline of the current thinking:

http://adsabs.har...98...39M

Aug 15, 2016
In 2006 it is made sense, today do not. There are more than 95% of the stars with no disc of gas.
The planet's composition and the composition nebulae are not at all similar. The composition of the nebula is mainly H2 and something He remained in traces the composition any body in our system does not have this the composition.
Reflections are past, today we have the evidence yet only that we start use them. Today we know calculate how much material falls to Earth for a million years.
Gravity is not a quick Gonzales, already force which millions and billions of years are insignificant value.

RNP
Aug 16, 2016
@wduckss

In 2006 it is made sense, today do not.

The general (and I note approximate) details given are still valid today. Give a reference if you have read differently.

There are more than 95% of the stars with no disc of gas.

But they all had one when they first formed.

The planet's composition and the composition nebulae are not at all similar. The composition of the nebula is mainly H2 and something He remained in traces the composition any body in our system does not have this the composition.

You are right, in the sense that the planets are composed of material that condensed into the planets from the nebula. The rest of the nebula, including a lot of the hydrogen and helium you mention, was blown away by the young star.

Reflections are past.......
I am not sure what you are trying to say here.

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