Astronomy

If a solar system were surrounded by a cloud of debris, is it possible for a planet's orbit to intersect it?

If a solar system were surrounded by a cloud of debris, is it possible for a planet's orbit to intersect it?


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I'm doing research for a story that I'm writing and I'd like some physics advice on whether a hypothetical system of celestial bodies is possible.

Suppose the following:

  • A system of planets orbiting a star, similar in size to our own.
  • A cloud of debris (Asteroids, technological refuse, and dust) surrounds the entire system, similar to the description of a Dyson swarm.
  • The outermost planet orbiting on a path that intersects the cloud during a small portion of it's year, but is within the cloud for the majority of it's year.

Is this configuration possible within our understanding of physics, or would gravity cause the objects of the cloud and the outermost planet to 'snap' to an orbit that does not intersect? Would the planet 'capture' objects within the swarm in it's own orbit?

My story takes place on the inside of a Dyson swarm or bubble, where interplanetary travel has developed to a reasonable degree, but cannot escape the swarm. An area of intrigue might be the outermost planet. If it can be landed upon while it's orbit is within the swarm, people could 'ride' the planet through to the other side if they stayed there for a number of years or went into stasis there.

Any thoughts or opinions are greatly appreciated.


The solar system IS surrounded by a cloud of debris,left over from its formation. This debris is called the Oort Cloud,& consists of thousands of comet-like bodies,sometimes described as dirty snowballs. None of the known major planets passes through them,but a few years ago some astronomers seemed certain that they had detected signs of a 9th major planet much further out than the others. They predicted it was only a matter of time before this planet would be discovered,but so far it hasn't been. If there is indeed such a planet & part of its orbit passes through the Oort Cloud,it would probably sweep a lane through it eventually. The planet would not be a nice place to live,as the likelihood is that it has a temperature close to that of liquid nitrogen,& is frequently struck by comets & other debris.


'Dirty' Collisions Shed Light on Planet Formation

Imperfect collisions can help explain discrepancies in planet formation models.

The early solar system was a violent, chaotic place, with debris slamming into growing planets. Sometimes, the material would fall onto a planetary embryo, and other times, it would obliterate the would-be world. Now, new research into these collisions is helping to shine light on how planets came to be — or didn't — in the early solar system.

Planetary models are incredibly complex, requiring scientists to account for everything that happens to a growing planet on timescales spanning a few days to millions of years. In the past, astronomers would simplify their models of colliding objects by assuming that all of the material from both the impactor and its target perfectly merged into a single object — an unrealistic expectation, since at least some pieces would most likely be flung into space and lost. But because computers of the past were less powerful than those today, scientists were forced into the simplification.

In the past decade, however, improvements in computational power have allowed researchers to begin studying more-realistic collision scenarios. Now, scientists can model so-called hit-and-run collisions, where two bodies scraped each other in passing, or even the total annihilation that could occur when two planetary embryos slammed together. These imperfect "dirty collisions" not only affect how large planets grow to be but also help to explain their orbits.

"Accounting for hit-and-run impacts and the gravitational perturbations of ejected fragments in our models lead to more realistic final orbits for Earth and Venus," lead author Matt Clement, a planet modeler at the University of Oklahoma, told Space.com by email.


A beloved exoplanet turns to dust

Images of Fomalhaut from the Hubble Space Telescope. Fomalhaut b, previously thought to be a massive planet, is now known to be an expanding dust cloud. A Kuiper belt-like ring of icy debris surrounds the star. Image via NASA/ ESA/ A. Gáspár/ G. Rieke (University of Arizona)/ Hubblesite.

When is a planet not really a planet? Many new exoplanets – over 4,000 now so far – have been discovered and confirmed orbiting other stars. But, sometimes, all might not be quite as it first appears. Meet Fomalhaut b, thought to be a massive world and thought to be one of the only exoplanets to be directly imaged to date. This world orbits the bright star Fomalhaut in the southern constellation Piscis Austrinus. It’s only 25 light-years away and so well loved that it was among the first group of exoplanets to be given proper names, in this case Dagon. Alas. New observations from the Hubble Space Telescope showed that Fomalhaut b or Dagon has apparently disappeared. The results suggest that the well-loved planet wasn’t a planet at all, but rather an expanding dust cloud that formed after two large icy bodies collided.

The disappointing, yet still fascinating, peer-reviewed findings from researchers at the University of Arizona were published on April 20, 2020, in the Proceedings of the National Academy of Sciences.

The announcement that Fomalhaut b or Dagon had been photographed caused a sensation in 2008. Until now, it was thought to be a massive planet. But the new study refutes that:

Although originally thought to be a massive exoplanet, the faintness of Fomalhaut b in the infrared and its failure to perturb Fomalhaut’s debris ring indicate a low mass. We use all available data to reveal that it has faded in brightness and grown in extent, with motion consistent with an escaping orbit. This behavior confirms suggestions that the source is a dispersing cloud of dust, produced by a massive collision between two planetesimals. The visible signature appears to be very fine dust escaping under the influence of radiation pressure.

Based on data from the Hubble Space Telescope (HST), researchers now think that the Fomalhaut b dust cloud resulted from the collision of 2 large icy bodies. Image via ESA/ NASA/ M. Kornmesser/ Hubble Space Telescope.

Many will be disappointed at this news about Fomalhaut b. Astronomer András Gáspár of the University of Arizona was lead author of the new study paper. He was clearly trying to make lemonade out of lemons when he said in a statement:

These collisions are exceedingly rare, and so this is a big deal that we actually get to see one. We believe that we were at the right place at the right time to have witnessed such an unlikely event with NASA’s Hubble Space Telescope.

Our study, which analyzed all available archival Hubble data on Fomalhaut, revealed several characteristics that together paint a picture that the planet-sized object may never have existed in the first place.

Bah! Curses! Rats! And so on.

George Rieke of the University of Arizona’s Steward Observatory added:

The Fomalhaut system is the ultimate test lab for all of our ideas about how exoplanets and star systems evolve. We do have evidence of such collisions in other systems, but none of this magnitude has been observed in our solar system. This is a blueprint of how planets destroy each other.

The star Fomalhaut as seen by Earth-based telescopes on November 13, 2008. Image via NASA/ ESA/ Digitized Sky Survey 2/ Davide De Martin (ESA/Hubble)/ Hubble Space Telescope.

Okay. Instead of a huge planet, the object photographed and labeled Fomalhaut b, subsequently named Dagon, was an expanding cloud of dust. Since it is so far away from us, it still basically looks like just a bright dot in the images, but Hubble’s additional analysis, not previously possible, revealed Fomalhaut b for what it really is. A dust cloud from a collision would also help explain its very eccentric orbit.

Images from 2014 showed that the object had virtually disappeared, as compared to how it appeared in the earlier images. Gáspár said:

Clearly, Fomalhaut b was doing things a bona fide planet should not be doing.

The researchers estimate that the collision occurred fairly recently, not too long before the first images were taken. Since then, the dust cloud has expanded and dispersed, and can no longer be detected by Hubble. It is now much larger than any planet could ever be (but extremely diffuse), around the size of Earth’s orbit around the sun. The dust particles are estimated to be about 1 micrometre (1/50th the diameter of a human hair) in size.

Not only does Fomalhaut b not look like a planet anymore, it also isn’t moving like one. It isn’t going around its star in a nice elliptical orbit like a planet would, but instead appears to be on an escape trajectory that will eventually take it away from its star. This also fits with Fomalhaut b being a dust cloud. Gáspár said:

A recently created massive dust cloud, experiencing considerable radiative forces from the central star Fomalhaut, would be placed on such a trajectory. Our model is naturally able to explain all independent observable parameters of the system: its expansion rate, its fading, and its trajectory.

Artist’s concept of Fomalhaut b when it was thought to be an exoplanet. Image via ESA/ NASA/ L. Calcada (ESO for STScI)/ Wikipedia.

There are also clues from the ring of icy debris that surrounds the star, which is much like the Kuiper Belt that surrounds our sun out beyond Neptune. The researchers estimate that many of those frozen bodies are about 125 miles (200 kilometers) across. Collisions between them could create dust clouds like Fomalhaut b, which resides inside this ring. In fact, sophisticated dust dynamical modeling done by the researchers showed that practically all characteristics of the dust cloud could be explained this way. Such collisions are probably rare, however, occurring only once every 200,000 years or so.

Although Hubble has pretty much put the nail in the coffin for Fomalhaut b as a planet, scientists are still eager to continue observing it. The upcoming James Webb Space Telescope (JWST) will study the Fomalhaut system during its first year of operations, including additional direct imaging. For the first time, scientists will be able to resolve the asteroid belt of an extrasolar planetary system.

Just because Fomalhaut b turned out to be a non-planet doesn’t mean that there can’t be other planets in the system, still waiting to be discovered. Fomalhaut is still surrounded by its circumstellar disk, after all. Observations from missions like Kepler and others have shown that almost all stars have at least one planet, and many stars, like our sun, have multiple planets. In fact, there are now estimated to be more planets in our galaxy than stars! So the chances are still good that Fomalhaut has at least one planet as well.

So don’t worry. Although Fomalhaut b may have lost its status as an exoplanet, there are still thousands of other known (and confirmed) exoworlds out there, and many more still waiting to be found.

András Gáspár of The University of Arizona, lead author of the new study paper. Image via The University of Arizona.

Bottom line: The well-loved exoplanet Fomalhaut b or Dagon – thought to be the first exoworld to be imaged directly – now appears not to be a planet after all, according to new observations from the Hubble Space Telescope.


Young Jupiter wiped out solar system’s early inner planets, study says

Before Mercury, Venus, Earth and Mars occupied the inner solar system, there may have been a previous generation of planets that were bigger and more numerous – but were ultimately doomed by Jupiter, according to a new study.

If indeed the early solar system was crowded with so-called super-Earths, it would have looked a lot more like the planetary systems found elsewhere in the galaxy, scientists wrote Monday in the Proceedings of the National Academy of Sciences.

NASA’s Kepler space telescope has found more than 1,000 planets in orbit around other stars, along with more than 4,000 other objects that are believed to be planets but haven’t yet been confirmed. Kepler finds these planets by watching their host stars and registering tiny drops in their brightness – a sign that they are being ever-so-slightly darkened by a planet crossing in front of them.

In addition, ground-based telescopes have detected hundreds of exoplanets by measuring the wiggles of distant stars. Those stars wiggle thanks to the gravitational pull of orbiting planets, and the Doppler effect makes it possible to estimate the size of these planets.

The more planetary systems astronomers discovered, the more our own solar system looked like an oddball. Exoplanets – at least the ones big enough for us to see – tended to be bigger than Earth, with tight orbits that took them much closer to their host stars. In multi-planet systems, these orbits tended to be much closer together than they are in our solar system. For instance, the star known as Kepler-11 has six planets closer to it than Venus is to the sun.

Why does our solar system look so different? Astrophysicists Konstantin Batygin of Caltech and Greg Laughlin of UC Santa Cruz summed it up in one word: Jupiter.

Here’s what could have happened, according to their models:

In Solar System 1.0, the region closest to the sun was occupied by numerous planets with masses several times bigger than that of Earth. There were also planetesimals, “planetary building blocks” that formed within the first million years after the birth of the sun, Batygin and Laughlin wrote.

This is how things might have stayed if the young Jupiter had stayed put at its initial orbit, between 3 and 10 astronomical units away from the sun. (An astronomical unit, or AU, is the distance between the Earth and the sun. Today, Jupiter’s orbit ranges between 5 and 5.5 AUs from the sun.)

But Jupiter was restless, according to a scenario known as the “Grand Tack.” In this version of events, Jupiter was swept up by the currents of gas that surrounded the young sun and drifted toward the center of the solar system.

Jupiter, however, was too big to travel solo. All manner of smaller objects would have been dragged along too. With so many bodies in motion, there would have been a lot of crashes.

The result was “a collisional cascade that grinds down the planetesimal population to smaller sizes,” the astrophysicists wrote. For the most part, these planetary crumbs were swept toward the sun and ultimately destroyed, like disintegrating satellites falling back to Earth.

The planetesimals wouldn’t have been Jupiter’s only victims. Assuming the early solar system resembled the planetary systems spied by Kepler and other telescopes, there would have been “a similar population of first-generation planets,” the pair wrote. “If such planets formed, however, they were destroyed.”

Jupiter probably got about as close to the sun as Mars is today before reversing course, pulled away by the gravity of the newly formed Saturn. That would have ended the chaos in the inner solar system, allowing Earth and the other rocky planets to form from the debris that remained.

“This scenario provides a natural explanation for why the inner Solar System bears scant resemblance to the ubiquitous multi-planet systems” discovered by Kepler and other survey efforts, Batygin and Laughlin wrote.

Although their models show that this is what might have happened, they don’t prove that it actually did. But there may be a way to get closer to the truth.

The scientists’ equations suggest that if a star is orbited by a cluster of close-in planets, there won’t be a larger, farther-out planet in the same system. As astronomers find more exoplanetary systems, they can see whether this prediction holds up.

Also, if far-away solar systems are experiencing a similar series of events, telescopes ought to be able to detect the extra heat thrown off by all of the planetesimal collisions, they added.

Sadly for those hoping to find life on other planets, the pair’s calculations also imply that most Earth-sized planets are lacking in water and other essential compounds that can exist in liquid or solid form. As a result, they would be “uninhabitable,” they wrote.

For more science news that’s out of this world, follow me on Twitter @LATkarenkaplan and “like” Los Angeles Times Science & Health on Facebook.


If a solar system were surrounded by a cloud of debris, is it possible for a planet's orbit to intersect it? - Astronomy

Key points: How planets are detected or inferred to be present around other stars how common they are how the known planet systems compare with the Solar System

We are finding evidence for massive planets around many stars from Doppler shifts indicating something unseen orbiting the star . This animation is based on a real system ( from Sylvain G. Korzennik, http://cfa-www.harvard.edu/afoe/orbits/ ) . If you watch closely, you can see a small movement of the star around the common center of mass of it and the massive planet orbiting it. The resulting Doppler shift of the stellar lines is shown in the graph at the bottom. The net effect is just over + 50 m/s, about + 0.00002%. It is just possible to detect such a tiny shift in the wavelengths of the spectral lines. An earth-sized planet would produce shifts more than a hundred times smaller, less than we can measure. Also, a large planet too far from the star would produce too slow a recoil for us to have detected it. These systems must be examples where a gas giant planet formed far from the star and migrated inward as described above.

This diagram shows what is happening in more detail. (From The Essential Cosmic Perspective, by Bennett et al.)

Here is a sampling of the planets found (mostly) in this way. The vertical column of yellow disks to the left represents the stars, while the other disks with black shading are planets. Masses are compared with that of Jupiter. There are 178 planets in 150 systems in this figure, but the TOTAL number of planets we know about has just topped 700! (from Exoplanet Encyclopedia, http://exoplanet.eu/ )

How did so many giant planets end up so close to their stars? All of these planets are about as massive as Jupiter, yet most of them lie closer to their stars than the earth lies to the sun.

Around other stars, some of the planetesimals that did not stick together to form planets still had a big influence on their systems. The giant planets had to plow through swarms of them, and they slowed the planets a bit like lots and lots of bugs hitting the windshield of your car would slow it down. These planetesimals got thrown into eccentric orbits or ejected from the systems, but the giant planets migrated inward, often to orbits very close to the stars.

raymonsn/graphics.html Raymond, Mandell & Sigurdsson (2006, Science, 313, 1413-1416), Sean Raymond

Fortunately, this did not happen in the Solar System. (from Stephan Kane, IPAC, via http://exep.jpl.nasa.gov/newsletterImages/issue9comic.gif )

Another approach to finding planets is to look for the small reduction in the light from a star when a planet passes between us and it -- a transit. This requires that the planet orbit be lined up just so, but we do know of about three dozen examples. One is when Mercury or Venus pass between us and the sun:

The Kepler satellite was built to look for transiting planets (and some were found by the earlier CoROT mission also). Here is an example - a planet that takes out nearly 1% of the light of the star when it passes in front of it. This planet orbits its star in a little less than 5 days, and has a mass about 40% as large as that of Jupiter.
This animation shows the multiple-planet system candidates found by the Kepler mission as of February 2012: 885 candidates in 361 systems. The orbit radii are to scale with respect to each other, but the orbits and planet sizes are different scales. The colors are in order of orbit size: two-planet systems (242 in all) have a yellow outer planet 3-planet systems (85) green 4-planet (25) light blue 5-planet (8) dark blue 6-planet (1, Kepler-11, purple). (from Kepler Mission website, http://kepler.nasa.gov/multimedia/animations/?ImageID=219)
The most spectacular in some ways is the system around the star HD 10180, a star similar to the sun. The complex radial velocity changes of this star require at least five planets to explain, at distances of 0.06 to 1.42 AU from the star and with masses similar to those of Uranus and Neptune. There may be another planet nearly as small as the earth very close to the star (if this planet is really there, it orbits the star in just over a day) and another like Saturn 3.4 AU from it. In this artist's concept, we look over the limb of this giant planet back toward the star just at the moment that two of the smaller planets are moving across in front of it and the rest are lined up to either side. (this work uses the HARPS radial velocity spectrometer at the European Southern Observatory).

Although we could give Bruno credit for being way ahead of his time scientifically, he really had no evidence - and was outspoken about other matters that ran contrary to religious doctrine. He spent the last seven years of his life in prison (while at trial) and was then burned at the stake. Nonetheless, we are now gathering scientific evidence that his statements were correct!

More than 700 planets are now known for sure and there are thousands more that are likely (from Kepler). Almost all of these examples are giant planets that have migrated inward to orbits very close to their stars. As many as 10% of stars like the Sun have such planets, so the process must be common. Why didn't this happen in the Solar System (with potentially disastrous consequences for Earth)? It is proposed that we were saved by the accident of forming two massive planets close to each other, and that the orbital resonance that caused the Late Heavy Bombardment also stabilized Jupiter's and Saturn's orbits out where they are to this day.

None of these systems let us look at how ones like ours evolved all of them are too different from ours, and we see them at some random late time in their evolution. We need a different approach to learn about the evolution of systems like ours. We are interested in systems where massive planet migration did not take place, that is systems that evolved more like the Solar System did.

In fact, we would like to take pictures of other planets. However, s eeing normal planets orbiting even the nearest stars is much more difficult than observing Doppler recoils or transits, both because the planets are so faint, and because they tend to be lost in the glare from the star itself. The stars are more than a billion times brighter. The challenge is like trying to take a picture of a firefly circling the beam of a lighthouse - except it is harder because the stars never turn off. (from Navigator Program Public Engagement Team, NASA, http://planetquest.jpl.nasa.gov)
We are developing instruments that can block the light of the star however, they are not good enough to probe the planets that have migrated into tight orbits. Fortunately, there are also many examples of stars surrounded by circumstellar disks of debris. The dust and small grains in these disks will either be blown away from the star or will fall into it in only about a million years. Therefore, the debris has to be renewed - we think this happens when small planets, typically on the scale of large asteroids in the solar system - collide with each other (from Robert Hurt, SSC). The debris disks therefore require systems where the small planets are on large orbits, hinting that there might also be large planets far from the stars in these systems. This has turned out to be correct! An example is in the Hubble Telescope (HST) images to the right. Fomalhaut is about 200 million years old. The narrow ring is a system of debris from recent collisions that produced a cloud of dust we now see spread in orbit around the star. The sharp inner edge is maintained by a massive planet, whose orbital motion can be seen in the inset to the lower right. (From NASA, ESA, P. Kalas et al. http://apod.nasa.gov/apod/ap081114.html)
The debris disk was first discovered because of the infrared emission from its heated dust. These images are rotated to the true orientation on the sky (the HST one was fixed horizontal). They are at 70 microns ( Herschel Telescope, from Acke et al.) showing pretty much the same ring as seen by HST, but at lower resolution) and at about 1 mm (ALMA, from Sky & Telescope)). At 70 microns, we see the side of the ring closer to the star heated to a higher temperature this offset of the ring can be seen in the HST image above. The 1 mm image (just part of the ring) is in blue superimposed on the HST one in the optical. At 1 mm we see the larger particles (sand and gravel) that produce the dust seen heated at 70 microns and scattering light in the visible (we also see the star at both wavelengths).
A second example is HR 8799. Four massive planets were discovered by Marois and others (see below), while Su, Rieke, and others imaged the huge debris system (artist's concept to right). This star is much younger than Fomalhaut, perhaps 30 million years old. It is not thought that the four planets can stay in stable orbits and that one of them may be ejected from the system. They are also stirring up the small bodies in the debris disk causing a lot of collisions so the disk is very bright small, weakly bound dust grains are on very eccentric orbits extending to 1000 AU from the star, while tiny grains are being ejected altogether through impacts with photons from the star. (planet image from Marois et al., http://solarsystemwatch.blogspot.com/2010/12/hr-8799-hosts-jumbo-planetary-system.html, disk concept by G. Rieke)

We know of about 300 stars with debris disks, indicating planet systems actively evolving (and colliding) around them. The intense debris disk stage appears to last about 100 million years, after which most planetary systems seem to have "settled down" and have a lower rate of collisions and debris generation. This time period matches pretty well the theoretical estimates for the time required for our Solar System to have settled down. Like the three examples above, perhaps all of these stars harbor planetary systems, but the rest are too faint for us to image yet.


Recent Developments

As of today, no missions have been sent to explore the Oort Cloud, but five spacecrafts will eventually get there, according to NASA. 3 These spacecrafts include Voyager 1 and 2, New Horizons, and Pioneer 10 and 11. A major obstacle, as discussed in this paper, is that the Oort Cloud is so distant. Consequently, the power source for all five spacecrafts will be dead centuries before they reach the inner edge of the Oort Cloud. To put things into perspective, Voyager 1 is the fastest and farthest of the interplanetary space probes currently leaving the solar system. Even though Voyager 1 travels at approximately a million miles per day, it will take the spacecraft about 300 years to reach the inner boundary of the Oort Cloud and an estimated 30,000 years to exit the far side. 3 This lengthy expedition is something Astronomers are currently devising.

Figure 10: Voyager 1 Courtesy NASA/JPL-Caltech https://voyager.jpl.nasa.gov/galleries/images-of-voyager/

The exploration and study of the Oort Cloud and the materials that have originated from the Oort Cloud continues to be pursued by the astronomical community around the world. For instance, the European Space Agency has proposed a Comet Interceptor mission for launch in 2028 which aims to become the first spacecraft to get a close-up of a “dynamically new” comet or interstellar object that has not passed near the sun before. 17 So far, spacecrafts have only visited comets that have made repeated passages close to the sun, where solar radiation breaks down ice and other material that are evidence from the birth of the solar system. The type of comets sought by this mission have originated in the Oort Cloud. Professor Colin Snodgrass, an astronomer at the University of Edinburgh and deputy lead of the Comet Interceptor science team, believes that the Large Synoptic Survey Telescope (LSST), currently under construction in Chile, will be critical in finding a comet destination. 17 The new telescope is set to be operative by the end of 2022, and will be able to detect smaller asteroids and comets farther from the sun than ever before. With this development, “scientists expect to find comets with up to five or six years of warning before they reach perihelion, the closest point to the sun in their trajectories." 3 This forewarning will allow enough time to study the object, plot the trajectory, and reach it.


Contents

In 1984 a debris disk was detected around the star Vega using the IRAS satellite. Initially this was believed to be a protoplanetary disk, but it is now known to be a debris disk due to the lack of gas in the disk and the age of the star. The first four debris disks discovered with IRAS are known as the "fabulous four": Vega, Beta Pictoris, Fomalhaut, and Epsilon Eridani. Subsequently, direct images of the Beta Pictoris disk showed irregularities in the dust, which were attributed to gravitational perturbations by an unseen exoplanet. [6] That explanation was confirmed with the 2008 discovery of the exoplanet Beta Pictoris b. [7]

Other exoplanet-hosting stars, including the first discovered by direct imaging (HR 8799), are known to also host debris disks. The nearby star 55 Cancri, a system that is also known to contain five planets, also was reported to have a debris disk, [8] but that detection could not be confirmed. [9] Structures in the debris disk around Epsilon Eridani suggest perturbations by a planetary body in orbit around that star, which may be used to constrain the mass and orbit of the planet. [10]

On 24 April 2014, NASA reported detecting debris disks in archival images of several young stars, HD 141943 and HD 191089, first viewed between 1999 and 2006 with the Hubble Space Telescope, by using newly improved imaging processes. [11]

In 2021, observations of a star, VVV-WIT-08, that became obscured for a period of 200 days may have been the result of a debris disk passing between the star and observers on Earth. [12] Two other stars,Epsilon Aurigae and TYC 2505-672-1, are reported to be eclipsed regularly and it has been determined that the phenomenon is the result of disks orbiting them in varied periods, suggesting that VVV-WIT-08 may be similar and have a much longer orbital period that just has been experienced by observers on Earth. VVV-WIT-08 is ten times the size of the Sun in the constellation of Sagittarius.

During the formation of a Sun-like star, the object passes through the T-Tauri phase during which it is surrounded by a gas-rich, disk-shaped nebula. Out of this material are formed planetesimals, which can continue accreting other planetesimals and disk material to form planets. The nebula continues to orbit the pre-main-sequence star for a period of 1–20 million years until it is cleared out by radiation pressure and other processes. Second generation dust may then be generated about the star by collisions between the planetesimals, which forms a disk out of the resulting debris. At some point during their lifetime, at least 45% of these stars are surrounded by a debris disk, which then can be detected by the thermal emission of the dust using an infrared telescope. Repeated collisions may cause a disk to persist for much of the lifetime of a star. [13]

Typical debris disks contain small grains 1–100 μm in size. Collisions will grind down these grains to sub-micrometre sizes, which will be removed from the system by radiation pressure from the host star. In very tenuous disks such as the ones in the Solar System, the Poynting–Robertson effect can cause particles to spiral inward instead. Both processes limit the lifetime of the disk to 10 Myr or less. Thus, for a disk to remain intact, a process is needed to continually replenish the disk. This can occur, for example, by means of collisions between larger bodies, followed by a cascade that grinds down the objects to the observed small grains. [14]

For collisions to occur in a debris disk, the bodies must be gravitationally perturbed sufficiently to create relatively large collisional velocities. A planetary system around the star can cause such perturbations, as can a binary star companion or the close approach of another star. [14] The presence of a debris disk may indicate a high likelihood of exoplanets orbiting the star. [15] Furthermore, many debris disks also show structures within the dust (for example, clumps and warps) that point to the presence of one or more exoplanets within the disk. [7]

Belts of dust or debris have been detected around many stars, including the Sun, including the following:

Star Spectral
class [16]
Distance
(ly)
Orbit
(AU)
Notes
Epsilon Eridani K2V 10.5 35–75 [10]
Tau Ceti G8V 11.9 35–50 [17]
Vega A0V 25 86–200 [18] [19]
Fomalhaut A3V 25 133–158 [18]
AU Microscopii M1Ve 33 50–150 [20]
HD 181327 F5.5V 51.8 89-110 [21]
HD 69830 K0V 41 <1 [22]
HD 207129 G0V 52 148–178 [23]
HD 139664 F5IV–V 57 60–109 [24]
Eta Corvi F2V 59 100–150 [25]
HD 53143 K1V 60 ? [24]
Beta Pictoris A6V 63 25–550 [19]
Zeta Leporis A2Vann 70 2–8 [26]
HD 92945 K1V 72 45–175 [27]
HD 107146 G2V 88 130 [28]
Gamma Ophiuchi A0V 95 520 [29]
HR 8799 A5V 129 75 [30]
51 Ophiuchi B9 131 0.5–1200 [31]
HD 12039 G3–5V 137 5 [32]
HD 98800 K5e (?) 150 1 [33]
HD 15115 F2V 150 315–550 [34]
HR 4796 A A0V 220 200 [35] [36]
HD 141569 B9.5e 320 400 [36]
HD 113766 A F4V 430 0.35–5.8 [37]
HD 141943 [11]
HD 191089 [11]

The orbital distance of the belt is an estimated mean distance or range, based either on direct measurement from imaging or derived from the temperature of the belt. The Earth has an average distance from the Sun of 1 AU.


Planets

The planets and the solar system were formed from a huge cloud of gases and dust particles left over when a massive star exploded as a supernova.

The gas drifted in space and it's thought that another supernova explosion nearby may have caused a pressure wave to pass through the cloud that caused clumping to occur. As the matter clumped together, gravity in that area got stronger which attracted more matter which in turn increased the gravitational pull. As more and more matter fell toward the high density area, due to conservation of momentum it began to spin - rather like water going down a plug hole. The result was that as the gravity intensified, the spin became faster resulting in a flat disk of gas and dust surrounding a central high density sphere of gas.

Gravity was also working within the disk of rotating gas and dust pulling matter together to form primitive planets within the gas disk.

Eventually the temperature and pressures in the central sphere became so high that the atoms began fusing together (nuclear fusion) and the Sun ignited producing heat and light and also the solar wind - an out streaming of subatomic particles.

The heat of the Sun and the solar wind immediately began to have an effect on the huge cloud of gas and particles in the disk. Volatile substances such as water ice near the Sun would heat and sublimate into gas, and these and other gases such as hydrogen would be gently accelerated away from the Sun by the solar wind.

At the distance of Jupiter, the temperature the Sun was not high enough to cause water ice to evaporate and so this meant that large quantities of solid material were available to build larger planets. These planets could therefore attract and keep hold of more of gas from the gas disk. This is one theory as to why the gas giants became so large, and why there is a divide in planet size between the small inner rocky planets and the outer gas giants.

As time continued, the workings of gravity and the solar wind eventually resulted in the solar system becoming as we know it today. A mostly empty space with eight surviving planets, five dwarf planets, a band of possibly millions of asteroids. All of this is thought to be surrounded by a cloud of icy comets - preserved remains of that early dust from which the solar system formed.


Do the orbits of the planets in our solar system intersect?

On diagrams and whatnot all the planets are always on this 2D plane when orbiting around the sun, which I always just figured was to make it easier to recreate. But in my mind there's no reason why the planets can't orbit freely like electrons. Then again, Saturn has a 2D orbit of rings, and the Milky Way is the same shape. So what is this phenomenon, and is it present in our very own solar system?

This Astronomy FAQ entry answers why the planets all orbit in roughly the same plane--because of conservation of angular momentum.

While not a planet per se Pluto's orbit intersection's Neptune's, but at an angle of almost 30 degrees out of the plane, so it's not like they ever share the same traffic lane. Here's the top view of the "intersection."

The other planets are all well spaced.

Many of your questions can be traced back to the formation of the Solar System and the formation of the planets from the Sun's accretion disk.

At one time during the formation of the solar system, yes, they did indeed intersect. If I recall correctly, something like 20 planets were whizzing past the sun from the current day orbit of Neptune towards the current day inner solar system. These orbits were very chaotic as the planets had just coalesced from the astral gases and debris. Over time, the planets with the most chaotic orbits would eventually collide with other planets and would then consolidate their masses in an orbit that would eventually become more or less circular around the sun.


The pre-solar nebula

I can't help but start with: In the beginning, there was nothing. But it wasn't quite nothing. All stars form from the collapse of nebulae, which are loose clouds of gas and dust, and our sun &mdash and solar system &mdash are no different. Astronomers call it the "pre-solar nebula" and of course it isn't around today, but we've seen enough solar systems forming throughout the galaxy to get the general picture.

But a nebula on its own won't collapse into a solar system without something to set it in motion. In our case, we can thank a nearby supernova explosion, whose shockwave ripped through the pre-solar nebula, causing it to begin its contraction. We can tell that such a supernova went off nearby, because supernovae release great quantities of certain radioactive elements &mdash elements that aren't normally found inside nebulae &ndash but which we can see in our solar system today.

Once underway, the transition from nebula to solar system was irreversible. Over the course of millions of years, the nebula contracted and cooled, eventually reaching the point where a proto-sun was surrounded by a thin, rapidly rotating disk of gas and dust.


Astronomers think 'winking' star is consuming cloud of planetary debris

Dec. 22 (UPI) -- New data suggests a unique 'winking' star located 550 light-years from Earth is consuming remnants of wrecked planets.

Astronomers believe the periodic dimming of RZ Piscium, a star found in the constellation Pisces, is caused by a giant orbiting cloud of dust formed by the debris of one or more disintegrating planets.

Normally, the large discs of dust and debris found around young stars disperse after a few million years. But RZ Piscium is between 30 million and 50 million years old and the dimming episodes persist, sometimes last a couple of days.

"I've been studying young stars near Earth for 20 years and I've never seen anything like this one," Benjamin Zuckerman, a professor of astronomy at UCLA, said in a news release. "Most sun-like stars have lost their planet-forming disks within a few million years of their birth. The fact that RZ Piscium hosts so much gas and dust after tens of millions of years means it's probably destroying, rather than building, planets."

RZ Piscium produces larger amounts of infrared radiation than the sun, which suggests the star is surrounded by a warm ring of dust. Roughly 8 percent of the star's radiation is emitted in the form of infrared wavelengths, putting the star in rare company. Only a handful of other stars within a few hundred light-years of the solar system emit similar amount of infrared radiation.

Scientists detailed their analysis of RZ Piscium in the Astronomical Journal.

"Our observations show there are massive blobs of dust and gas that occasionally block the star's light and are probably spiraling into it," said Kristina Punzi, a doctoral student at the Rochester Institute of Technology.

Spectral analysis revealed the star's lithium levels, which allowed scientists estimate the star's age. Analysis also revealed the star's surface temperature, 9,600 degrees Fahrenheit, just a bit cooler than the sun. Scientists were also able to measure the temperature of the dust, 450 degrees Fahrenheit, which suggests the cloud is orbiting 30 million miles from the star.

While astronomers believe planetary collisions are the most likely source of the dust cloud surrounding RZ Piscium, they suggest it's also possible the star is stealing material from a stellar companion.