New computer simulations show how special the solar system is

Aug 07, 2008

Prevailing theoretical models attempting to explain the formation of the solar system have assumed it to be average in every way. Now a new study by Northwestern University astronomers, using recent data from the 300 exoplanets discovered orbiting other stars, turns that view on its head.

The solar system, it turns out, is pretty special indeed. The study illustrates that if early conditions had been just slightly different, very unpleasant things could have happened -- like planets being thrown into the sun or jettisoned into deep space.

Using large-scale computer simulations, the Northwestern researchers are the first to model the formation of planetary systems from beginning to end, starting with the generic disk of gas and dust that is left behind after the formation of the central star and ending with a full planetary system. Because of computing limitations, earlier models provided only brief glimpses of the process.

The researchers ran more than a hundred simulations, and the results show that the average planetary system's origin was full of violence and drama but that the formation of something like our solar system required conditions to be "just right."

The study, titled "Gas Disks to Gas Giants: Simulating the Birth of Planetary Systems," will be published in the Aug. 8 issue of the journal Science.

Before the discovery in the early 1990s of the first planets outside the solar system, our system's nine (now eight) planets were the only ones known to us. This limited the planetary formation models, and astronomers had no reason to think the solar system unusual.

"But we now know that these other planetary systems don't look like the solar system at all," said Frederic A. Rasio, a theoretical astrophysicist and professor of physics and astronomy in Northwestern's Weinberg College of Arts and Sciences. He is senior author of the Science paper.

"The shapes of the exoplanets' orbits are elongated, not nice and circular. Planets are not where we expect them to be. Many giant planets similar to Jupiter, known as 'hot Jupiters,' are so close to the star they have orbits of mere days. Clearly we needed to start fresh in explaining planetary formation and this greater variety of planets we now see."

Using the wealth of exoplanet data collected during the last 15 years, Rasio and his colleagues have been working to understand planet formation in a much broader sense than was possible previously. Modeling an entire planetary system -- the varied physical phenomena associated with gas, gravity and grains of material, on such a variety of scales -- was a daunting challenge.

The work required very powerful computers. The researchers also had to judiciously decide what information was important and what was not, so as to speed up the calculations. They decided to follow the growth of planets, the gravitational interaction between planets, and the whole planetary system in its entire spatial extent. They chose not to follow the gas disk's fluid dynamics in fine detail, but rather more generally. As a result, they were able to run simulations spanning a planetary system's entire formation.

The simulations suggest that an average planetary system's origin is extremely dramatic. The gas disk that gives birth to the planets also pushes them mercilessly toward the central star, where they crowd together or are engulfed. Among the growing planets, there is cut-throat competition for gas, a chaotic process that produces a rich variety of planet masses.

Also, as the planets approach each other, they frequently lock into dynamical resonances that drive the orbits of all participants to be increasingly elongated. Such a gravitational embrace often results in a slingshot encounter that flings the planets elsewhere in the system; occasionally, one is ejected into deep space. Despite its best efforts to kill its offspring, the gas disk eventually is consumed and dissipates, and a young planetary system emerges.

"Such a turbulent history would seem to leave little room for the sedate solar system, and our simulations show exactly that," said Rasio. "Conditions must be just right for the solar system to emerge."

Too massive a gas disk, for example, and planet formation is an anarchic mess, producing "hot Jupiters" and noncircular orbits galore. Too low-mass a disk, and nothing bigger than Neptune -- an "ice giant" with only a small amount of gas -- will grow.

"We now better understand the process of planet formation and can explain the properties of the strange exoplanets we've observed," said Rasio. "We also know that the solar system is special and understand at some level what makes it special."

"The solar system had to be born under just the right conditions to become this quiet place we see. The vast majority of other planetary systems didn't have these special properties at birth and became something very different."

Source: Northwestern University

Explore further: Gravitational waves according to Planck

add to favorites email to friend print save as pdf

Related Stories

NASA's Maven spacecraft reaches Mars this weekend

Sep 17, 2014

Mars, get ready for another visitor or two. This weekend, NASA's Maven spacecraft will reach the red planet following a 10-month journey spanning 442 million miles (711 million kilometers).

'Hot Jupiters' provoke their own host suns to wobble

Sep 11, 2014

Blame the "hot Jupiters." These large, gaseous exoplanets (planets outside our solar system) can make their suns wobble when they wend their way through their own solar systems to snuggle up against their ...

Ten years of Cassini

Sep 09, 2014

Ten years ago, the Cassini-Huygens mission entered the Saturnian System and in January 2005, the Huygens probe landed softly on the surface of Saturn's largest moon, Titan. These historic events, which revolutionized ...

Solar system simulation reveals planetary mystery

Sep 08, 2014

When we look at the Solar System, what clues show us how it formed? We can see pieces of its formation in asteroids, comets and other small bodies that cluster on the fringes of our neighborhood (and sometimes, ...

Recommended for you

Gravitational waves according to Planck

11 hours ago

Scientists of the Planck collaboration, and in particular the Trieste team, have conducted a series of in-depth checks on the discovery recently publicized by the Antarctic Observatory, which announced last spring that it ...

Infant solar system shows signs of windy weather

11 hours ago

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have observed what may be the first-ever signs of windy weather around a T Tauri star, an infant analog of our own Sun. This may help ...

Finding hints of gravitational waves in the stars

18 hours ago

Scientists have shown how gravitational waves—invisible ripples in the fabric of space and time that propagate through the universe—might be "seen" by looking at the stars. The new model proposes that ...

How gamma ray telescopes work

19 hours ago

Yesterday I talked about the detection of gamma ray bursts, intense blasts of gamma rays that occasionally appear in distant galaxies. Gamma ray bursts were only detected when gamma ray satellites were put ...

The frequency of high-energy gamma ray bursts

20 hours ago

In the 1960s a series of satellites were built as part of Project Vela.  Project Vela was intended to detect violations of the 1963 ban on above ground testing of nuclear weapons.  The Vela satellites were ...

User comments : 30

Adjust slider to filter visible comments by rank

Display comments: newest first

defunctdiety
4.6 / 5 (14) Aug 07, 2008
The problem here seems to be that we don't know what most (any) other solar systems are truly like in detail because at this point we can only detect large planets... am I wrong that this article is based entirely on incomplete data, and is little more than a barely-educated guess?
earls
3 / 5 (6) Aug 07, 2008
I wish there was a video so we could analyze what assumptions they made.

I assume:

1. This was the formation of the entire solar system (including the sun).

2. It relies strictly on classical physics instead of quantum physics.

3. Electromagnetism played no role in the simulation.

4. They could tweak the simulation to produce the same amount of planets we have.

I'd like to know how the seeds of the planets were produced.
Modernmystic
3 / 5 (3) Aug 07, 2008
My feeling is that as far as the solar system goes that the Copernican principle is about to be turned on its head. Any feeling to the contrary while looking at the evidence we've seen both in the math of the computer models and the abundance of hot Jupiters is wishful thinking at best.

Even if we can only detect large planets we're detecting them in the wrong places...period. Most of what we're seeing out there is nothing like what we see here.
fleem
4.5 / 5 (6) Aug 07, 2008
I question the conclusion of the researchers. To say what is said here requires that we know a lot about the degree of correlation between disorderly/orderly planetary systems and the presence of detectable exoplanets. We don't know that relationship. In fact it seems to me that a detectable exoplanet (a giant rocky planet with a very tight orbit) will ONLY occur from catastrophic events--otherwise the heavy elements that would have created that planet would have fallen into the protosun because those heavy molecules have lower velocity than lighter molecules at the same temperature. So detectable planets might only be those that were placed there through some catastrophe. Since the probability of a given star system revealing a detectable exoplanet is very low, we might presume chaotic star systems are rare. i think the bottom line, though, is we don't have enough info yet.
ruebi
1.5 / 5 (6) Aug 07, 2008
our planets are waste products of the sun. seeds of semi hard matter that couldnt be further broken buy the suns currents. eventually ejected. some planets like ours, still house a burning core that continues to alter the ecosystem. others like saturn barley had enough hard matter to be ejected and eventually were eaten from the inside out, growing into gas giants.

having your own theorys is fun
winkler
3.7 / 5 (3) Aug 07, 2008
The problem here seems to be that we don't know what most (any) other solar systems are truly like in detail because at this point we can only detect large planets... am I wrong that this article is based entirely on incomplete data, and is little more than a barely-educated guess?


This is my view as well. The data we have on exoplanets is based on very specific types of planets that fall within our ability to detect. The assumption here seems to be that those planets (and the systems that harbor them) represent the majority of the planets in the universe, and I fail to see how that conclusion is anything but a guess at this point.
menkaur
1 / 5 (1) Aug 07, 2008
The problem here seems to be that we don't know what most (any) other solar systems are truly like in detail because at this point we can only detect large planets... am I wrong that this article is based entirely on incomplete data, and is little more than a barely-educated guess?

1
also, in chaotic system you can't decide that some information is irrelevant. with time you'll get extreme flaws
DoctorKnowledge
1 / 5 (2) Aug 07, 2008
Yes, defunctdiety, it's guesswork. There various theories, and none is outstanding. What's a little worrying (I guess) is that this is published in "Science". That means they've probably investigated some new or ill-defined aspect of the problem, and found negative results there. Many of the points made above are pretty valid and reasonable -- and we don't have to give up hope, yet.
NewDimension
2.5 / 5 (2) Aug 07, 2008
The sentence: The researchers also had to judiciously decide what information was important and what was not, so as to speed up the calculations.
Guess they played kind of God in this case deciding what is important or not - in my opinion every tiny bit was important to get just the right conditions and assuming that nearby stars and the overall galaxy gravitation also may have played a role together with the position of this 'flat gas disk' in correspondence to the up and down relative to the galactic plane I would guess it takes a long time for the human race till it really can be calculated.
RAL
3.8 / 5 (5) Aug 08, 2008
While poking around with computer modeling is a reasonable thing to do in many cases, there seems to be a disturbing trend toward equating it with experimental evidence. Given the paucity of real data involved, the researchers appear to have gotten caught up by the power of their computers and conflated that with reality.
MrFred
4.2 / 5 (6) Aug 08, 2008
So, planetary systems like ours are hard to make yet, somehow defying the astronomical odds, we have a planetary system here that is just right. However, when we see something as simple as a stone arrowhead we automatically assume that something intelligent made it, it didn't just happen.
Such an intelligent bunch we are...
CreepyD
2.5 / 5 (2) Aug 08, 2008
Once we can discover smaller planets, systems like our own might be just as common as those chaotic ones.
In simulations, it's always going to be easier to produce a choatic system, but that doesn't mean it will really be like that.
Modernmystic
3.3 / 5 (3) Aug 08, 2008
Ok I'm sorry I just don't understand how some of the posters here are just not getting it, maybe I'm missing something. The fact of the matter is that no matter how "inept" our detection methods are now, and despite the fact that we can only detect large planets...WE ARE DETECTING THEM IN THE WRONG PLACES with respect to our own system. We have no gas giants near our sun, most of the systems we look at DO. Something should tell you that our system is different from most others right there.

Most other systems have highly elliptical orbits, our system doesn't. Again something should click for you right there. Now despite the fact that computer models are the least convincing argument here they represent our extrapolated knowledge and they're telling us that we're pretty rare, and so are our OBSERVATIONS.

So what if the Copernican principle fails one or two times, it was bound to be wrong about something at some point because rarely is anything COMPLETELY average and run of the mill. I don't know why a lot of you seem to be afraid to admit that despite all the evidence blaring in your face. Hey I might be wrong, but based on observation alone (despite the fact that our data is woefully incomplete) I really don't think I am.

Is it because it somehow threatens your scientific prejudice that we should not be special in any way, or that some of you are disappointed that the galaxy isn't going to be all Star Trek and brimming with intelligent life? I don't know how our being special would pose that kind of problem but if I'm honest I think that's EXACTLY what I see going on here...just a little bit of intellectual dishonesty.
Latrosicarius
1 / 5 (1) Aug 08, 2008
The problem here seems to be that we don't know what most (any) other solar systems are truly like in detail because at this point we can only detect large planets... am I wrong that this article is based entirely on incomplete data, and is little more than a barely-educated guess?


yeah. it's like saying: through my binoculars I can see people, but not ants. Therefore i conclude that there are no ants.
earls
3 / 5 (1) Aug 08, 2008
Echoing Latrosicarius in response to Modernmystic & Mr. Fred - Because we can't see the "ants" suddenly we're at the center of a God created Universe? What?!

I guess time travel *is* possible, because here I am in the middle of the Dark Ages.
Modernmystic
2 / 5 (2) Aug 08, 2008
No sir. The problem is not that we can't see ants, the problem is that we're not even seeing people.

This does NOT mean we're at the center of the universe, nor even that we occupy any "special" place in it based on a purely scientific evaluation of the concept. What it DOES mean is that solar systems like ours are very likely quite rare...period.
Modernmystic
1 / 5 (1) Aug 08, 2008
Oh and FTR, I never mentioned God. I don't think God even has a place in this discussion. In fact notihing would please me more than having the nearby universe teaming with intelligent life...or failing that life of any kind.

The COLD HARD FACTS however are beating down my hopes to almost nil. So what though? The universe is as it is...not as I wish it to be.
RAL
3 / 5 (1) Aug 08, 2008
Modernmystic you raise a good point regarding highly elliptic orbits.

Could it be easier to detect planets with highly elliptical orbits using current planet detection techniques? I raise but cannot answer the question.

My remark up page about conflating computer projection with data points still stands. Saying our own system is atypical in some way is a long way from implying a detailed undertanding of how it formed.

Modernmystic
1 / 5 (1) Aug 08, 2008
Couldn't agree more RAL, I'm not overly fond of computer simulations even if they have good data. I'm downright skeptical if they don't, and we don't.

That said we don't need perfect data to start drawing some rather gloomy pictures of how the rest of the star systems in the galaxy seem to tick. Who knows tho, it could be an anomaly of being in our particular spot of the galaxy, or the kind of galaxy we're in...but I'm leaning towards the fact that this is not the case.
earls
5 / 5 (1) Aug 08, 2008
"Could it be easier to detect planets with highly elliptical orbits using current planet detection techniques?"

Yes, absolutely. Exoplanets are detected by the gravitational wobble they cause on their host star. Much less massive rocky planets evade this technique.

Modernmystic, however, has apparently given up all hope of improving our detection techniques and has resigned us to a cold, empty Universe.

And Mystic, I know it you never made any reference to God, it was "Mr. Fred" who was implying an "intelligent designer." I was simply tying (what I consdier) to obscene ideas together with Latrosicarius that "there's a lot more to see than what we're seeing."

As much as some like to trumpet how "perfect" and "unusual" our spec of existence is (see yet another article on the front page), I know without a doubt in my mind that our solar system is just one of a million million pathetically common natural occurrences.

Our worldview is simply not even a fraction of a fraction of a fraction of 1% complete.
Modernmystic
1 / 5 (1) Aug 08, 2008
Modernmystic, however, has apparently given up all hope of improving our detection techniques and has resigned us to a cold, empty Universe.


Not at all, but with the vast majority of systems having highly elliptically orbiting planets it hardly matters if we can detect small rocky ones or not...they're probably going to be borked for the purposes of supporting complex life.

As much as some like to trumpet how "perfect" and "unusual" our spec of existence is (see yet another article on the front page), I know without a doubt in my mind that our solar system is just one of a million million pathetically common natural occurrences.

Our worldview is simply not even a fraction of a fraction of a fraction of 1% complete.


Huh you lost me. On the one hand your SURE that our solar system is simply one of millions, yet then you say our worldview is a fraction of a fraction of 1% complete. I presume that you include your own worldview in that statement...

Moreover other than the Copernican principle/isotropic universe (which truth be told both have served us well so far) what hard DATA, if any, are you basing that assumption on?
ezezz
not rated yet Aug 09, 2008
Mystic is right on here. The real moral of this article is in the comments section: 'science' inclined people can be just as biased as the religious.

That said, while I'm a big fan of computer simulations (working on my degree in applied math), I wouldn't trust this simulation further than I can throw the supercomputer that ran it. If they gave some quantitative matches to observation that would be great, like: average size of Jupiters, average orbit distance and eccentricity, etc. It's possible they have done extensive validation, I'd have to read the paper to know for sure.
ZeroDelta
not rated yet Aug 09, 2008
(Athiest) "I'm not suprised"

Predict the unknown eh....
twango
not rated yet Aug 10, 2008
New releases of this sort which make predictions and even reach specific conclusions based on *computer modellling* really need to include basic specifics about the model. The words 'computer model' mean very little ... could be highly sophisticated, could be based in physics 101.
AJJ
4 / 5 (1) Aug 10, 2008
There was an interesting book that came out a while ago called "Rare Earth" that was written on a similar subject that Earth is rare. I guess this computer simulation will help validate those authors (Peter Ward & Donald Brownlee) theory.
Damon_Hastings
2 / 5 (1) Aug 10, 2008
ModernMystic: we see hot Jupiters with small orbits because our technology is incapable of seeing the ones with large orbits. This does not mean that most Jupiters have small orbits. Same goes for the elliptical orbits. Future technology will be able to see smaller planets with larger, more circular orbits.

That said, it's still possible that the simulation could be right. I'm skeptical, given that their fluid dynamics model was so coarsely grained; my own experience with writing physics simulations has demonstrated that the granularity level can have a profound impact on the final results, even at the most general level of description. And of course there's the wildcard of dark matter. But even if these guys are right, there are still over a sextillion other star systems out there, so there should still be plenty which are enough like ours to harbor similar life. Not to mention the possibility of dissimilar life.
Modernmystic
1 / 5 (1) Aug 10, 2008
ModernMystic: we see hot Jupiters with small orbits because our technology is incapable of seeing the ones with large orbits.


Patently false. Epsilon Eridani b is a 1.55 Jupiter mass planet that orbits at 3.39 AU. Epsilon Eridani c is far less massive and orbits at a whopping 40 AU. Go fish.
jeffsaunders
not rated yet Aug 10, 2008
Our searches for planets does in fact limit us to what we can see with our current level of technology.

What we do see is not necessarily a complete picture of what we could see, should our vision be better.

That said we have seen a lot of examples of planets that are both quite large and quite close to the sun they orbit. Of those stars in between do we conclude anything at all at this stage.

I suggest, and it is only a suggestion that we try several scenarios.

1) That every single star we have seen so far that we cannot see any planets circling it - does in fact have smaller planets circling it. How many star systems is that by the way?

2) That we take a statistical sample of those stars we have looked at where we have found massive planets circling in close to the sun and compare that number of stars to those that we have not seen massive planets in close. This gives a statistical number that you can expect to find all over the galaxy with the simple assumption that what we have seen is a reasonable statistical sample.

Both above statements may lead to an incorrect view of the galaxy yet both may be correct and not in conflict with each other.

The in close massive planets may mean that habitable planets around those stars would be rare - then again maybe not. Sure a massive planet in close to the sun is nothing like ours and yes there is a good chance that these large planets have scrubbed clean the chances of small rocky planets staying in orbit around these stars if they could form at all. But the chance is NOT zero and there ARE plenty of other stars out there without massive planets orbiting them.

For a planet to sustain life it probably should not have been too close to a super novae within the last few millions of years either or it may have lost its atmosphere or been sterilized in other ways.
Modernmystic
1 / 5 (1) Aug 10, 2008
There is one thing for certian, the eccentricity of the orbits we see in exoplanets is NOT an observational selection effect. A planet can be detected around a star equally well regardless of the eccentricty of it's orbit.

Planets with highly elliptical orbits don't bode well for life, but more to the point (other than Mercury) do not jibe well at all with what we see in our own system.
EarthScientist
1 / 5 (1) Aug 11, 2008
Oh boy, It sure is fun to read all of your assertions and co-hesion with your favorite gurus,try some independent thought,for once,as that might make you more whole.

Papa here knows that the system is grown ,and music is the key just as your DOT works on the same process. Each planet provides part ofthe process,there re no big bangs that provided the system,just planet process men,that grew the planetoids,with simple science. Just simple science.