# Do planets migrate suddenly or gradually?

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Current models of the configurations of the planets conclude that Neptune once migrated outwards. AFAIK this refurbishment came about by Jupiter and Saturn gradually getting into and leaving a gravitational resonance.

Did Neptune (and possibly a fifth giant planet) redirect itself in a sudden encounter event, like comet 67P Churyumov-Gerasimenko did in 1959, halving the perihelion of its orbit since then? Or did it happen gradually over maybe millions of years? Is planetary migration in general sudden or gradual? Is it a matter of a single encounter event, or an adaptation to a changing gravity landscape?

Thommes et al. (2001) ran simulations and found that, at optimal conditions (namely, a planet of ~ 10 Earth masses), migration can be complete with ~ 100,000 years. Note that this was done before in-depth research was done on the Nice model, which is very similar. However, the mechanisms are different, as are the planet masses. The difference in timescales is dramatic.

Levison et al. (2007) did explore their own model - the Nice Model. They found that it took 60 million years to 1.1 billion years for Jupiter and Saturn to break their resonance. The period of encounters and scattering lasted for 878-885 million years, followed by a period of eccentricity damping lasting for 0.3 million years to 4 million years.

What was relatively quick was the ejection of the hypothetical 5th giant planet. The change in the other giants' orbits, however, was not.

So yes, planetary migration on this scale takes a long time. A very long time.

For some really interesting results, see the graphs of semi-major axis vs. time from the various four-, five-, and six- planet models of Nesvorný & Morbidelli (2012). There are some incredible oscillation among the orbits of Uranus and Neptune in some of the simulations, which is eventually slowly damped.

Fig. 14.- Orbit histories of the giant planets in a simulation with five initial planets. See the caption of Fig. 1 for the description of orbital parameters shown here. The five planets were started in the (3:2,3:2,2:1,3:2) resonant chain, Mdisk = 20 MEarth and B(1). The fifth planet was ejected at $t =$ 6.1 Myr after the start of the simulation.

There's another relevant passage, if you're looking at setups with six giant planets:

The instability typically occurred in two steps, corresponding to the ejection of the two planets. Sometimes, as in Fig. 18, the ejection of the two planets was nearly simultaneous, but most of the times there was a significant delay between ejections. This was useful because the first planet's ejection partially disrupted the planetesimal disk and reduced its capability to damp e55, which was then excited by the second planet's ejection. While this mode of instability can be important, we would need to increase the statistics (>100 simulations for each initial condition) to be able to properly resolve the small success fractions in the six-planet case.

## Do planets lose energy?

check out what "leap seconds" are all about. the need for an occasional leap second, here or there, is due exactly to loss of kinetic energy in the rotation of the earth.

there is kinda an odd reason (having to due with geology and the speed of the Earth's crust) for why they haven't added leap seconds in the past few years. but the rotation of the earth, as a whole, is still slowing down very minutely.

Slowing down the rotation of Earth isn't going to cause it to crash into the sun, though.

A careful answer would involve figuring out all the effects that might brake the Earth's orbital motion (there are some), plus the effects that would move the Earth into a higher orbit (there are some of those, too).

A non-careful answer would say that these effects are all so small that we can expect the Sun to turn into a red giant first, at which point the question becomes moot.

check out what "leap seconds" are all about. the need for an occasional leap second, here or there, is due exactly to loss of kinetic energy in the rotation of the earth.

there is kinda an odd reason (having to due with geology and the speed of the Earth's crust) for why they haven't added leap seconds in the past few years. but the rotation of the earth, as a whole, is still slowing down very minutely.

The loss of kinetic energy in the rotation of the Earth is due to the combined Earth-Moon system. The Earth and Moon will eventually become tidally locked with each other (the Moon already presents a virtually identical face towards the Earth). The Earth's rotation rate gradually slows down and the distance between the Earth and Moon gradually increases (the combined angular momentum has to stay constant). The varying rotation rate is why leap seconds are required.

The reason they haven't added leap seconds is buried deep in the article (it's not very well organized, even though it pulled together some good material). Primarily, it's because it's becoming more important for systems that have to communicate with each other to be using the same time and, unfortunately, leap seconds have to be added in (or subtracted) manually at irregular times. You'd think it wouldn't be that difficult to add in the leap second at 0000 Universal Time on the designated day, but . if a computer can't do it automatically, then it must not be a very good thing.

Bottom line is that computer and electronics folks hate time that doesn't update at a constant rate, forever and ever. They hate having to roll over form 99 to 00, 1024 to 0000, and especially hate having to figure out how to account for a second that can be added every 18 months, or maybe every 12 months. For computer programmers, reality is a b.

## Dry super-Earths and cold Jupiters

Scientists from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, the University of Bern and the University of Arizona have now found strong evidence that rocky planets similar to Earth occur conspicuously often together with a Jupiter-like planet that is in a wide orbit. “We call such gas giants cold Jupiters. They grow at a distance from the central star, where water exists in the form of ice,” explains Martin Schlecker, a doctoral student at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, who led the study. The Earth-like planets studied are so-called dry super-Earths, i.e. rocky planets larger and more massive than the Earth, which have only a thin atmosphere and hardly any water or ice. They populate the inner, i.e. temperate zone of the planetary systems and are very similar to the Earth except for their size. “Also, the Earth is, despite the enormous oceans and the polar regions, with a volume fraction for water of only 0.12% altogether a dry planet,” Schlecker points out.

To find a cold Jupiter together with an ice-rich super-Earth in the inner region is therefore almost impossible. Furthermore, dense, extended gas envelopes are mainly found in massive super-Earths.

## How Earth Survived Its Birth

WASHINGTON ?Just how Earth survived the process of its birth without suffering an earlydemise by falling into the sun has been something of a mystery to astronomers,but a new model has figured out what protected our planet when it was still avulnerable, baby world.

In short,temperature differences in the space around the sun, 4.6 billion years ago,caused Earth to migrate outward as much as gravity was trying to pull itinward, and so the fledgling world found equilibrium in what we now know to bea very habitable orbit.

Planetslike the Earth are thought to form from condensing clouds of gas anddust surrounding stars. The material in these disks gradually clumpstogether, eventually forming planetesimals? the asteroid-sized building blocks that eventually collide to formfull-fledged planets.

As theplanets are forming, they are also thought tomigrate within the surrounding dust disk. The classic picture of thisplanet migration suggests that planets like (and including) the Earth shouldhave plummeted into the sun while they were still planetesimals.

"Well,this contradicts basic observational evidence, like We. Are. Here," saidastronomer Moredecai-Mark Mac Low of the American Museum of Natural History in New York.

Mac Low andhis colleagues investigated this apparent paradox and came up with a new modelthat explains how planets can migrate as they're forming and still avoid afiery premature death. He presented these findings here today at the 215th meetingof the American Astronomical Society.

One problemwith the classic view of planet formation and migration is that it assumed thatthe temperature of the protoplanetary disk around a star is constant intemperature across its whole span, Mac Low explained.

It turnsout that portions of the disk are actually opaque and so cannot cool quickly byradiating heat out to space. This creates temperature differences across thedisk, and these differences have not been accounted for before in models. SoMac Low and his colleagues created new model simulations of planetmigration that include a disk with variations in temperature.

Whathappens when you change the temperatures in the disk is this: The temperaturechanges can completely alter the nature of the planet migrations, causingplanets to migrate outward instead of inward.

"Well,that is a major development," Mac Low said, because you can put it in themodel and see if outward migration cancels inward migration "and allows usto survive, or at least our progenitors."

Sureenough, that seems to be the case. Within the disk, zones of inward and outwardmigration develop that meet at equilibrium zones once planets reach these,"they more or less sit there," Mac Low said.

Andeventually the disk dissipates to a point where its gravity can no longerinfluence the planets to pull or push them into new orbits.

So themodel suggests that outward migration "allows planetoids to survive,"which explain how planets in our solar system and others that we see in galaxysurvive, Mac Low said.

## IU News Room

The rings near the center of this simulation may be protected areas where planets can start to form around a young star.

BLOOMINGTON, Ind. -- A new theory of how planets form finds havens of stability amid violent turbulence in the swirling gas that surrounds a young star. These protected areas are where planets can begin to form without being destroyed. The theory will be published in the February issue of the journal Icarus.

"This is another way to get a planet started. It marries the two main theories of planet formation," said Richard Durisen, professor of astronomy and chair of that department at Indiana University Bloomington. Durisen is a leader in the use of computers to model planet formation.

Watching his simulations run on a computer monitor, it's easy to imagine looking down from a vantage point in interstellar space and watching the process actually happen.

A green disk of gas swirls around a central star. Eventually, spiral arms of yellow begin to appear within the disk, indicating regions where the gas is becoming denser. Then a few blobs of red appear, at first just hints but then gradually more stable. These red regions are even denser, showing where masses of gas are accumulating that might later become planets.

The turbulent gases and swirling disks are mathematical constructions using hydrodynamics and computer graphics. The computer monitor displays the results of the scientists' calculations as colorful animations.

"These are the disks of gas and dust that astronomers see around most young stars, from which planets form," Durisen explained. "They're like a giant whirlpool swirling around the star in orbit. Our own solar system formed out of such a disk."

Scientists now know of more than 130 planets around other stars, and almost all of them are at least as massive as Jupiter. "Gas giant planets are more common than we could have guessed even 10 years ago," he said. "Nature is pretty good at making these planets."

The key to understanding how planets are made is a phenomenon called gravitational instabilities, according to Durisen. Scientists have long thought that if gas disks around stars are massive enough and cold enough, these instabilities happen, allowing the disk's gravity to overwhelm gas pressure and cause parts of the disk to pull together and form dense clumps, which could become planets.

However, a gravitationally unstable disk is a violent environment. Interactions with other disk material and other clumps can throw a potential planet into the central star or tear it apart completely. If planets are to form in an unstable disk, they need a more protected environment, and Durisen thinks he has found one.

As his simulations run, rings of gas form in the disk at an edge of an unstable region and grow more dense. If solid particles accumulating in a ring quickly migrate to the middle of the ring, the core of a planet could form much faster.

The time factor is important. A major challenge that Durisen and other theorists face is a recent discovery by astronomers that giant gas planets such as Jupiter form fairly quickly by astronomical standards. They have to -- otherwise the gas they need will be gone.

"Astronomers now know that massive disks of gas around young stars tend to go away over a period of a few million years," Durisen said. "So that's the chance to make gas-rich planets. Jupiter and Saturn and the planets that are common around other stars are all gas giants, and those planets have to be made during this few-million-year window when there is still a substantial amount of gas disk around."

This need for speed causes problems for any theory with a leisurely approach to forming planets, such as the core accretion theory that was the standard model until recently.

"In the core accretion theory, the formation of gas giant planets gets started by a process similar to the way planets such as Earth accumulate," Durisen explained. "Solid objects hit each other and stick together and grow in size. If a solid object grows to be about 10 times the mass of Earth, and there's also gas around, it becomes massive enough to grab onto a lot of the gas by gravity. Once that happens, you get rapid growth of a gas giant planet."

The trouble is, it takes a long time to form a solid core that way -- anywhere from about 10 million to 100 million years. The theory may work for Jupiter and Saturn, but not for dozens of planets around other stars. Many of these other planets have several times the mass of Jupiter, and it's very hard to make such enormous planets by core accretion.

The theory that gravitational instabilities by themselves can form gas giant planets was first proposed more than 50 years ago. It's recently been revived because of problems with the core accretion theory. The idea that vast masses of gas suddenly collapse by gravity to form a dense object, perhaps in just a few orbits, certainly fits the available time frame, but it has some problems of its own.

According to the gravitational instability theory, spiral arms form in a gas disk and then break up into clumps that are in different orbits. These clumps survive and grow larger until planets form around them. Durisen sees these clumps in his simulations -- but they don't last long.

"The clumps fly around and shear out and re-form and are destroyed over and over again," he said. "If the gravitational instabilities are strong enough, a spiral arm will break into clumps. The question is, what happens to them?"

Co-authors of the paper are IU doctoral student Kai Cai and two of Durisen's former students: Annie C. Mejia, postdoctoral fellow in the Department of Astronomy, University of Washington and Megan K. Pickett, associate professor of physics and astronomy, Purdue University Calumet.

## Where do Rogue Planets come from?

"Like all animals, human beings have always taken what they want from nature. But we are the rogue species. We are unique in our ability to use resources on a scale and at a speed that our fellow species can't." -Edward Burtynsky

It's really a romantic notion when you think about it: the heavens, the Milky Way, is lined with hundreds of billions of stars, each with their own unique and varied solar systems.

But beyond that -- in addition to the stars -- there are hundreds of billions of planets with no central stars at all: the rogue planets of our galaxy. We think this is true everywhere, from small star clusters to giant galaxies. As best as we can tell, there are at least as many starless planets wandering the cosmos as there are stars, meaning that for every point of light you see, there are probably more massive points that exist, but emit no visible light of their own.

We've recently discovered a number of possible rogue planet candidates, although since these are so difficult to detect (and are only visible from their heat signatures in the infrared) we know that there must be many, many more than what we've seen so far. You can't help but wonder where these rogue planets come from!

One compelling source is near and dear to us all.

We know how solar systems like our own form: you get a central star with a protoplanetary disk around it. Gravitational perturbations in the disk attract more and more matter from their surroundings, while the heat from the newly formed central star gradually blows much of the lightest gas away into the interstellar medium. Over time, these gravitational perturbations grow into asteroids, rocky planets, and eventually -- for the largest ones -- gas giants.

The thing is, these worlds don't just orbit their central star, they also gravitationally tug on one another! Over time, these planets migrate into the most stable configurations they can attain, and this usually mean the largest, most massive worlds migrating into their most stable configurations, often at the expense of other worlds.

A recent simulation shows that for every planet-rich solar system like our own (with gas giants) that forms, there's likely to be at least one gas giant planet that gets kicked out, into the interstellar medium, where it's doomed to wander the galaxy on its own as a rogue planet.

That's almost definitely a major source of rogue planets.

But here's the funny thing: when we work out the numbers of our best theoretical calculations, it's far less than 50% of all rogue planets that are expected to be accounted for by this process. To figure out where the majority of starless planets come from, we have to look at a larger scale at around the same time: not just when the Solar System formed, but at the cluster of stars (and star systems) that all formed at around the same time!

Star clusters form from the slow collapse of cold, mostly hydrogen gas, typically within a galaxy. Within these collapsing clouds, gravitational instabilities form, and the earliest, most massive instabilities preferentially attract more and more matter. When enough matter gets together, and the densities and temperatures at the core of these clouds get high enough, nuclear fusion ignites!

This results in new stars and star systems, but something else happens, too. The biggest stars that form are also the hottest and bluest, meaning they emit the most ionizing, ultraviolet radiation.

So when you look inside a star-forming nebula in the Universe, you are actually watching two processes simultaneously competing:

1. Gravity, as it attempts to pull matter in towards these young, growing gravitational overdensities, and
2. Radiation, as it works to burn off the neutral gas and blow it back into the interstellar medium.

It depends what you mean by "win," exactly. The biggest gravitational overdensities form the largest stars, but these are also the rarest of all stars. Smaller (but still large) ones form the other star types, but become more and more common as we get down to lower masses. This is why, when we look deep inside a young star cluster, it's easiest to see the brightest (blue) stars, but they're vastly outnumbered by lower mass, yellow (and especially red), dim stars.

The thing is, if it weren't for the radiation, there dim, red-and-yellow stars would have grown more massive, brighter, and burned hotter! Stars (on the main sequence, which is most stars) come in a variety of types, O-stars being the hottest, largest and bluest and M-stars being the coolest, smallest, reddest and least massive.

Even though the vast majority of stars -- 3 out of every 4 -- are M-class stars, compared to less than 1% of all stars being O-or-B stars, there's just as much total mass in O-and-B-stars as there are in M-stars.

And it turns out that some 90% of the original gas-and-dust that was in these star-forming nebula gets blown off back into the interstellar medium rather than forming stars. The most massive stars form the fastest, and then get to work blowing the star-forming material out of the nebula. By time a few million years go by, there's less and less material to form new stars at all. Eventually, all the leftover gas-and-dust will burn off completely.

Well, guess what? Not only are M-class stars -- stars between 8% and 40% of the Sun's mass -- the most common type of star in the Universe by far, but there are a whole lot more that would have been M-class stars if it weren't for the high-mass stars burning off this material!

In other words, for every star that forms, there are many, many failed stars that didn't quite make it anywhere from tens to hundreds-of-thousands of them for each star that actually forms!

These nomad planets -- or rogue planets -- may or may not have atmospheres, and they may be incredibly difficult to detect, especially the (theoretically) more common ones: the smallest objects.

So we may have a few rogue planets that were ejected from young solar systems, and there may even be a couple that came from our Solar System, but the vast majority were never attached to stars at all! Rogue planets wander the galaxy, most of them to toil forever in loneliness, never knowing the warmth of a parent star, thwarted by stellar evolution from ever becoming stars themselves. What we have, instead, is a galaxy with trillions or possibly even quadrillions of these nomad worlds, objects which we're only just beginning to discover. And that's where rogue planets come from!

### More like this

So are the masses of the Roque Planets taken into account in the tally of the mass of the Universe ? Are they part of the 4 % ? What is the best estimate for the mass difference between "trillions " and "quadrillions" ? Thanks.

Is there a reason for the power law that says that each class of stars has roughly the same total mass? It seems unlikely to be coincidence, yet there doesn't appear to be any obvious reason why there should should be any scaling law, let alone one that is so orderly.

In the hypothetical case of a gas giant booted out of its orbit by Jupiter, why is it so obvious that it would be totally expelled from the solar system? Couldn't it still remain in a very distant orbit?

Wow! Like using exclamation points, much!

Yes, a gas giant thrown into the far reaches of the solar system can get stuck there (identical to how we produce Oort cloud comets), but the chance of that happening is only a couple percent. So - probably not, unless there were dozens.

The mass of any rogue planet compared to 1 solar mass is extremely tiny. Given a galaxy you might at best get 0.1% contribution. And yes, they are in 4% part since they are made of matter like everything else.

@2
yes, you can check stellar classification. Basically it's like black body radiation. Different colors, different temperatures hence energies, hence composition, hence mass needed to produce such and such radiation.

SL, re answer to #1, it would be more complete and helpful to say that it is part of the 4% because it will, despite being "dark", it interacts with normal matter and can be captured like normal matter. It is also able, since it is a coalesced body of significant size, be able to spot a significant portion by their occlusion of starlight.

True Dark Matter (tm) doesn't interact even with itself well and therefore doesn't coalesce and, if it reacted with photons (the idea is it would not, any more than it would with normal matter, but if it did, it would be pushed out of every stellar envelope by photon pressure), it is a diffuse body and does not cause extinction in the same way.

And like Velikovsky said, when a HUGE object (we are calling them rogue planets here) comes into the influence of a star, it becomes a comet. As Jim McCanney says, the object then discharges the Solar Capacitor like a bug zapper. This causes the Sun to begin to increase its activity. The bigger the object, the more the solar activity. We do not see HUGE comets the size of Venus too often, luckily, but we have had them pass nearby on occasion. They are usually very destructive and can account for massive Earth changes simply by passing near by, without impact. Like Velikovsky proposes, Venus was a comet before it fell into its present orbit. It happened in recorded history and caused people to go underground at the time it passed by us, possibly 4K years ago. Venus even exhibited a tail.

Well, I did say it :) "And yes, they are in 4% part since they are made of matter like everything else."

@3: It's possible for a planet to be kicked into an orbit which is highly elliptical but still bound. To do that, you would have to boost its speed to somewhere between the circular orbit speed and escape speed for its previous location. IIRC, these two speeds differ by a factor of sqrt(2). The problem is whether such a planet would remain in that orbit without having nasty effects on the planets remaining in more conventional orbits whenever this planet approaches periastron. Near apastron, it wouldn't take much of a gravitational kick from a nearby star to turn this planet into an Oort cloud object (similar to how Oort cloud objects become comets), or finish the job of kicking it out of the solar system. Alternatively, the remaining planets could finish the job when this planet next approaches periastron.

No, you said it but it was implied, not explicit.

All you said in explicit form was "it's not like dark matter because it's like the regular matter".

You never explained why it would be known to be part of the 4% of normal matter and not part of the 20-ish% of dark.

true, it was implied, because Ethan's article is about it. Since they are made of the stuff that was in our solar system.

Didn't think @1 was asking if they were DM, rather if their mass contribution was accounted for in normal matter. Guess it's how you interpret the question. Anyways you added more to the answer so it's all cool :)

"Since they are made of the stuff that was in our solar system. "

sorry.. should be our/other solar system.. hence hydrogen, rocks, metals etc. or just gas giants

"Didn’t think @1 was asking if they were DM,"

Use the term rogue planet and the cranks come running in, as displayed by wally58 above.

I believe the theoretical argument that they should form, but what direct observation is there that they do form?

not likely to get "direct observation" any time soon. Think about it. How do you observe a tiny speck that doesn't emit light.. hence black.. against a black background of space?

It will be a major breakthrough when we get to "directly observe" any planet outside of our solar system. Those wandering the blackness of space.. who knows.. maybe in some other bands if they emit something.

"How do you observe a tiny speck that doesn’t emit light.. hence black.. against a black background of space?"

I'm reminded of the conversation aboard Hot Black Desiato's ship with this.

I believe a few months ago we have the first direct observation of an extrasolar planet.

Though that might have been the observation of the absorption spectra of a planetary atmosphere (dense enough neutral matter to be neither space dust nor stellar atmosphere).

@Wow #19: Direct observation of extrasolar planets goes back several years, to at least 2004. HR8799's four planets were imaged back in 2010 AB Pictoris has a companion which is either a brown dwarf or Jovian-mass planet, directly imaged in 2003. See http://en.wikipedia.org/wiki/List_of_directly_imaged_extrasolar_planets for a current list.

Thank you Michael! This is awesome. To this day I wasn't aware that this was done.

Read the paper on GJ 504. Awesome! A real image of a planet orbiting some other sun. So cool!

p.s. Ethan, why no article on that we are actually able to image exoplanets?? :D Bad Ethan!! :))

Well, I remembered a story a few months ago (earlier this year anyway) and may have been about the direct measuring of the atmosphere of the planet rather than imaging the planet directly.

Rogue planets came from bad family backgrounds?

@Wow #23: Ah! I think you're remembering the recent spectroscopic analysis of HD 189733b (http://en.wikipedia.org/wiki/HD_189733_b).

A study of the combination of absorption features derived for the planet from secondary eclispes allowed the authors to "estimate" the apparent color the planet would have if we could see it directly.

No exoplanet has yet been imaged in "true color," although, given the progress in the field, that is only a matter of time.

Everyone: ferocious criticism invited for the following:

Are there any estimates of (or any reasonable basis for estimating) the occurrence of approximately-Earth-mass rocky rogue planets?

Those might be useful for interstellar colonization as follows:

1) Locate Earth-sized rogue planet.
2) Build Dyson rings around two or more of its nearest suitable stars.
3) The Dyson rings capture energy from the stars and convert to microwave laser or similar means, directed toward artificial moons (or captured space rocks with infrastructure built) orbiting the rogue planet.
4) At the moons, incoming energy is converted to a form that can safely be beamed down to the planet's surface and used.
5) Meanwhile, the Dyson rings are inhabited by minimal populations needed to maintain them. These should be small enough populations as to easily migrate off the Dyson rings to the client planet when the stars became hazardous toward the end of their useful lives.

Why go through all that effort, when there are Earth-sized planets orbiting stars, that can be colonized?

Because then you have an inhabitable world that is not a) dependent on and b) at risk from, a single star. Its usable lifespan would be equal to the useful life of the most long-lived of the stars that provided it with energy. Assuming you need at minimum two stars to supply energy to a rogue planet, build Dyson rings around a total of three or more stars, and you have time to replace any of them that are lost in stellar explosions.

Also it would seem that rogue planets in and of themselves, could potentially have the raw materials needed to support life, but be lifeless due to lack of energy sources. Thus they are ready to colonize with zero to minimal risk of encountering indigenous microbes that could prove fatal.

G: even for sci-fi, your proposal is extremely Rube Goldberg-ish. Any civilization that can do step 2 has no need of any of the other steps it can simply move to another system when the old star is close to burning out.

Secondly, wouldn't it just be easier to locate a rogue planet with some internal heat associated with it, and just use that? Whether gas giant or rocky, the rogue planet's gravitational force on its own mass will tend to heat things up at depth. I have to think that extracting that heat as work must be a great deal easier than your set-up. A jupiter-sized geothermal generator is (speculatively) peanuts compared to ringworlds firing interstellar lasers.

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## Young Star RZ Piscium is ‘Eating’ Its Own Planets, Astronomers Say

Astronomers studying RZ Piscium, a variable Sun-like star located approximately 555 light-years away in the constellation Pisces, have found evidence suggesting its strange, unpredictable dimming episodes may be caused by orbiting clouds of gas and dust, the remains of one or more destroyed exoplanets. The research appears in the Astronomical Journal.

This illustration shows a ‘disrupted planet’ broken up into a cloud of gas and dust as it orbits RZ Piscium. Image credit: NASA.

“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 lead author Kristina Punzi, a doctoral student at the Rochester Institute of Technology.

“Although there could be other explanations, we suggest this material may have been produced by the break-up of massive orbiting bodies near the star.”

“We know it’s not uncommon for planets to migrate inward in young solar systems since we’ve found so many solar systems with hot Jupiters,” added Dr. Catherine Pilachowski, an astronomer with Indiana University.

“This is a very interesting phase in the evolution of planetary systems, and we’re lucky to catch a solar system in the middle of the process since it happens so quickly compared to the lifetimes of stars.”

Doomed worlds that fly too close to their parent star — only to be ripped apart by its tidal forces — are officially known as ‘disrupted planets.’ In the case of RZ Piscium, the material near the star is being slowly pulled apart to create a small circle of debris about the same distance from the star as the planet Mercury’s orbit is from our Sun.

“Based on our observations, it seems either that we’re seeing a fairly massive, gaseous planet being pulled apart by the star, or perhaps two gas-rich planets that have collided and been torn apart,” Dr. Pilachowski said.

“Even planetary systems whose planets are not lost to their host star are unstable in their early history, since newly born planets interact strongly with one another — as well as their star — through gravity.”

“In our Solar System, for example, some astronomers speculate that Uranus and Neptune swapped orbits about 4 billion years ago. But erratic orbits tend to stabilize over time, falling into regular patterns.”

The astronomers observed RZ Piscium using ESA’s XMM-Newton satellite, the Shane 3-m telescope at Lick Observatory in California and the 10-m Keck I telescope at W. M. Keck Observatory in Hawaii.

The observations revealed the star’s surface temperature to be about 9,600 degrees Fahrenheit (5,330 degrees Celsius), only slightly cooler than the Sun’s.

They also show the star is enriched in the tell-tale element lithium, which is slowly destroyed by nuclear reactions inside stars.

“The amount of lithium in a star’s surface declines as it ages, so it serves as a clock that allows us to estimate the elapsed time since a star’s birth,” explained co-author Dr. Joel Kastner, director of the Rochester Institute of Technology’s Laboratory for Multiwavelength Astrophysics.

“Our lithium measurement for RZ Piscium is typical for a star of its surface temperature that is about 30 to 50 million years old.”

Another sign of RZ Piscium’s relative youth – the star produces X-rays at a rate roughly 1,000 times greater than our Sun.

“This discovery really gives us a rare and beautiful glimpse into what happens to many newly formed planets that don’t survive the early dynamical chaos of young solar systems,” Dr. Pilachowski said.

“It helps us understand why some young solar systems survive — and some don’t.”

Very Interesting!
However, I believe that the sentence in 3rd paragraph,

For example, the farther-out planet might circle its star three times every time the other, closer-in planet goes around twice.

For example, the farther-out planet might circle its star TWO times every time the other, closer-in planet goes around THREE TIMES.

since an inner planet has an shorter orbital period than an outer planet.

Hi David, you're of course right, the inner planet would be traveling faster - it's the law! (Kepler's 3rd, to be exact.) I've fixed this in the text.

If tilted exoplanets explain the odd orbits, being near the galaxy's bar might explain the tipsy planets.

When I read exoplanet reports like this, I wonder how did Earth avoid forming like this? It seems Earth is precariously balanced, some slight change in a myriad of variables (giant impact for example) during its evolutionary formation - we are lifeless here.

Hmmm. "rolling on their sides"? Rather hard to imagine up/down/sides in three dimensional space! bwa

## Observations fuel speculation as to whether a pole reversal is imminent

In addition to all above, according to the ESA data, the Earth’s magnetic field has weakened by an average of around 9%ent over the past two centuries, with the decline in the area of ​​the South Atlantic Anomaly being particularly strong: there, the minimum field strength has fallen from around 24,000 nanoteslas to 22,000 nanoteslas since 1970 (Tesla is the unit for the flux density of alternating magnetic fields).

These observations are fueling speculation as to whether the Earth is about to make another pole reversal. Previously, the earth has experienced many pole shifts. In the past, the field reversed at intervals of 200,000 to 300,000 years. The last pole shift happened 780,000 years ago (and lasted about 22,000 years), so the next one is more than overdue.

Earth’s magnetic field during a Geomagnetic reversal: NASA computer simulation using the model of Glatzmaier and Roberts. The tubes represent magnetic field lines, blue when the field points towards the center and yellow when away. The rotation axis of the Earth is centered and vertical. The dense clusters of lines are within the Earth’s core. Image: Wikipedia

The aforementioned magnetic field reversal 41,000 years ago only partly counts, as it lasted less than 1000 years. If early humans had a compass at that time, its needle would have been pointing south. The magnetic north pole’s current migration may serve as yet another hint.

In fact, the point at which the Earth’s magnetic field lines run perpendicularly into the Earth is rapidly changing its position. This traveled 16 kilometers (10 miles) a year in a north-north-westerly direction at the start of the 20th century. The speed increased to 55 kilometers (34 miles) a year in the 1990s, and it is 48 kilometers (30 miles) today.

That’s why there’s a Declination Diagram on military maps and nautical charts – it indicates the angular relationship of true north, grid north (north that is established by the vertical grid lines on the map – the variation between grid north and true north is due to the curvature of the earth), and magnetic north. And it should be regularly updated.

## Earth

Earth (IPA: /ɝθ/) is the third planet from the Sun and is the largest of the terrestrial planets in the Solar System, in both diameter and mass. Home to the human species, it is also referred to as "the Earth", "Planet Earth", "Gaia", "Terra", and "the World".

The Earth is the first planet known to have liquid water on the surface and is the only place in the universe known to harbor life. Earth has a magnetic field that, together with a primarily nitrogen-oxygen atmosphere, protects the surface from radiation that is harmful to life. The atmosphere also serves as a shield that causes smaller meteors to burn up before they strike the surface.

The Earth formed around 4.57 billion years[1] ago and its only known natural satellite, the Moon, began orbiting it around 4.53 billion years ago. At present, the Earth orbits the Sun once for every roughly 366.26 times it rotates about its axis (which is equal to 365.26 solar days).[2] The Earth's axis of rotation is tilted 23.5°[3] (away from the perpendicular to its orbital plane), producing seasonal variations on the planet's surface.

Atmospheric conditions on Earth have been significantly altered by the presence of life forms, which create an ecological balance that modifies the surface conditions. About 71% of the surface is covered with salt-water oceans. The remaining 29% consists of continents and islands. The planet's outer surface is divided into several rigid segments, or tectonic plates, that gradually migrate across the surface over periods of many millions of years. Earth's interior remains active, with a thick layer of relatively solid mantle, a liquid outer core that generates a magnetic field, and a solid-iron inner core.

Earth interacts with outer space to a significant degree. Its relatively large moon provides ocean tides, stabilizes the axial tilt and has gradually modified the length of the planet's rotation period. A cometary bombardment during the early history of the planet played a role in the formation of the oceans. Later, asteroid impacts caused significant changes to the surface environment. Long term periodic changes in the orbit of the planet are believed to have caused the ice ages that have covered significant portions of the surface in glacial sheets.