# A ‘Hot Jupiter’ in Our Solar System?

by on April 22, 2008

Serendipity is a wondrous thing. Start writing about the early history of the Solar System, as I intended to do yesterday, and you wind up discussing ‘hot Jupiters’ around other stars. But there actually is a bridge between the two concepts, and it comes in the form of a question. If we find gas giants in scorchingly hot orbits around other stars, why was there no hot Jupiter in our own Solar System? Or was there? That question was what originally led me to the paper by Avi Mandell, Sean Raymond and Stein Sigurðsson that occupied yesterday’s post.

For in their analysis of how giant planets migrate through an early planetary system, wreaking havoc on newly forming worlds but also scattering them interestingly throughout nearby space, these researchers paused to examine the implications of these studies for our own system. Having demonstrated through their simulations that the migration of a gas giant through an inner system may be common, and that systems that experience it often form terrestrial worlds, why rule out earlier generations of giant planets right here in Sol space?

Image: A ‘hot Jupiter’ moves breathtakingly close to its star. Found around a number of other stars, could such a world have once moved through our own Solar System? Credit: NASA/JPL-Caltech.

If such were the case, then the natural follow-up is to ask whether it may be possible to find the signature of early planetary scattering in the system today. One problem with that concept is that although the mixing of large bodies that would occur during migration should leave traces in the makeup of elements found in the final system, this signature would be obscured by other kinds of mixing. Thus the authors give up on the idea of tracing it in the inner Solar System, saying in their paper:

…radial mixing of dust and smaller bodies is also thought to occur through a variety of other processes in the planet formation region besides planetary scattering…, and it is clear from the ﬁnal abundances of planets in our simulations and others that any signature of the scattering of massive bodies early in the formation history will be quickly erased through accretion in the inner system due to continued mixing.

But the further we move from the Sun, the more interesting things get. Here we’ve dealing with lower densities of solids and gases and longer time-frames, with accretion and other factors less likely to obscure what may be evidence of planetary movements in the early system. Finding comets whose orbits make them appear to be Oort Cloud objects, but whose physical characteristics suggest asteroids, could provide evidence for the scattering of inner disk objects by a migrating gas giant.

Even better would be an object in the right place, one made of materials showing signs of high temperature origins. From the paper:

A more conclusive sign of giant planet migration would be a classical KBO with a composition primarily composed of refractory materials; this would imply the re-circularization of a scattered inner-disk object, which would most likely only be possible in the presence of damping by signiﬁcant amounts of gas or dust for long timescales.

So there’s a lively vector for another research project, examining objects from the Edgeworth/Kuiper belt and the Oort Cloud for evidence of early planetary migration. It would take a lot of work and much more information about the outer system than we currently have before we could remotely conclude that a hot Jupiter once perturbed our own neighborhood. But the idea that extrasolar systems with these planets are necessarily of a different order than our own Solar System may one day be shown to be false. We may find that hot Jupiters are not uncommon as a system with terrestrial worlds continues its development.

Edg Duveyoung April 22, 2008 at 10:28

Question: is the spectral data of any star enough to “fingerprint it?” Seems likely that this is true, but has our technology advanced enough to see a star with such detail that it is unique amongst the trillions of stars?

Edg

Mang April 22, 2008 at 11:11

Interesting. They lay question is what happened to it. So I had a quick read of the paper as I was curious as to the fate of the migrating giant. Ok, it seems the giant planet settles in at 0.25 AU after being dragged inward. I may have missed it but I’m left to assume it boils away.

dad2059 April 22, 2008 at 12:07

Interesting hypothesis. So it is assumed that hot Jupiters occur early in planetary formation.

But does that necessarily mean hot Jupiters must form in the outer accretion disk and then migrate in, sweeping up material along the way as implied?

RonSmith April 22, 2008 at 13:45

Hot Jupiters that have been observed to be venting material do so at a very small rate, relative to the size of the planet. Based on current observations I made a ‘back of the envelope’ calculation and found it would take at least an order of magnitude longer than the age of the universe for the planet to boil away.
So the eventual fate of a Hot Jupiter is open to question. Maybe it gets swallowed by its star? Unless that is the answer I would find it hard to see how there could have been such an object in the early Solar System, because otherwise it would still be here.

Dave Moore April 22, 2008 at 14:23

There may be a piece of evidence for this scenario. If you drawn a plane through the center of the Sun and Jupiter, which I will call the solar system’s ecliptic, you will find most of the planets have orbits within one degree of this plane. This presumably is the original plane of the solar nebula. There are only 2 planets with orbital inclination’s outside this limit, Venus at 2 degrees, and Mercury at 7. Mercuriy’s orbit is aligned with the solar equator, which is what you would expect from tidal interactions with an oblate spheroid.

The question is why is the sun’s equator tilted at 7 degrees to the plane of the solar nebula? I have never heard a good answer to this and I wonder if the tilt was caused by a collision between the sun and a giant planet in close orbit around it. Possibly, we could get some idea of the planet’s mass by calculating what mass of planet is needed to tilt the sun by 7 degrees.

Dave.

Dave Weeden April 22, 2008 at 15:14

If we assume that a ‘Mars-sized body’ collided with the early Earth (the current theory of the formation of our moon), then the early solar system must have been very different to the one we have now. So, it’s an appealing hypothesis.

I’m not convinced by the strategies to test it. I don’t think we know enough about Oort cloud bodies (which are very small and very far away) to examine them in the way we’d need. There isn’t any evidence that comets (which we do know a bit about) fit this hypothesis.

I’m not aware of any ‘holes’ in current models of the formation of the Solar System. If there was some big mystery – say, computer models predicted that Jupiter should be somewhere else – and the ‘migratory giant planet’ explained things better, then this theory might have a chance. However, I think this is likely to be a stochastic process – some stellar discs produce hot Jupiters; some don’t.

FrankH April 22, 2008 at 18:28

I think it’ll be very difficult to find traces of our former hot Jupiters (if any). If one or more Jupiter sized objects were absorbed by the Sun, there may still be some trace of them, since there’s very little mixing going on in the Sun’s photosphere. Most of the gas giant will have been helium and hydrogen, so not much to see there, but the core should have contained some heavy elements, so the Sun could be slightly enriched in some elements compared to the original solar nebula (or by proxy, meteorites). The fly in the ointment is that the Sun has probably plowed through enough interstellar dust or solar nebula leftovers (including comets and asteroids) to mask any lasting effects of a Jupiter mass object.

Orbital dynamics or composition of KBO objects is probably a better way to go. The Kuiper Belt and Oort cloud are certainly populated by wild and crazy beasts.

Frank

Colin Weaver April 22, 2008 at 20:16

Seems like wishful thinking to me. We have such an orderly & stable little 8 planet system, and I get the feeling some people are feeling a bit left out and wish we had one of those wacky hot Jovians :-)

One thought – could the apparent correlation between stellar metallicity and hot Jovians imply that in some systems where hot Jupiters form, stellar metallicity is boosted by absorbtion of one or more such bodies?

MaDeR April 23, 2008 at 5:15

I don’t think so. In universe are all kinds of planets and is impossible that any solar system could contain examples of all types of planets at once. We do not have hot jupiter or superearths. So what?

ljk April 28, 2008 at 23:03

The potential impact of groove modes on Type II planetary migration

Authors: Stefano Meschiari, Gregory Laughlin

(Submitted on 22 Apr 2008)

Abstract: In this letter, we briefly describe the evolution of a variety of self-gravitating protoplanetary disk models that contain annular grooves (e.g. gaps) in their surface density. These grooves are inspired by the density gaps that are presumed to open in response to the formation of a giant planet. Our work provides an extension of the previously studied groove modes that are known in the context of stellar disks. The emergence of spiral gravitational instabilities (GI) is predicted via a generalized eigenvalue code that performs a linear analysis, and confirmed with hydrodynamical simulations.

We find the presence of a groove drives a fast-growing two-armed mode in moderately massive disks, and extends the importance of self-gravitating instabilities down to lower disk masses than for which they would otherwise occur. We discuss the potential importance of this instability in the context of planet formation, e.g. the modification of the torques driving Type II migration.

Comments: 10 pages, 5 figures. Accepted for publication in ApJ Letters. Additional color plots and movies are available at this http URL

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0804.3425v1 [astro-ph]

Submission history

From: Stefano Meschiari [view email]

[v1] Tue, 22 Apr 2008 00:21:18 GMT (1037kb)

http://arxiv.org/abs/0804.3425

ljk May 7, 2008 at 8:44

Nonuniform viscosity in the solar nebula and large masses of Jupiter and Saturn

Authors: Liping Jin

(Submitted on 6 May 2008)

Abstract: I report a novel theory that nonuniform viscous frictional force in the solar nebula accounts for the largest mass of Jupiter and Saturn and their largest amount of H and He among the planets, two outstanding facts that are unsolved puzzles in our understanding of origin of the Solar System. It is shown that the nebula model of uniform viscosity does not match the present planet masses.

By studying current known viscosity mechanisms, I show that viscosity is more efficient in the inner region inside Mercury and the outer region outside Jupiter-Saturn than the intermediate region. The more efficient viscosity drives faster radial inflow of material during the nebula evolution. Because the inflow in the outer region is faster than the intermediate region, the material tends to accumulate in Jupiter-Saturn region which is between the outer and intermediate region. It is demonstrated that the gas trapping time of Jovian planets is longer than the inflow time in the outer region.

Therefore the gas already flows to Jupiter-Saturn region before Uranus and Neptune can capture significant gas. But the inflow in the Jupiter-Saturn region is so slow that they can capture large amount of gas before the gas can flow further inward. Hence they have larger masses with larger H and He content than Uranus and Neptune. I also extend the discussion to the masses of the terrestrial planets, especially low mass of Mercury. The advantages of this theory are discussed.

Comments: 4 pages, 1 figure, A&A Letters accepted

Subjects: Astrophysics (astro-ph)

Journal reference: A&A 423, L5-L8 (2004)

DOI: 10.1051/0004-6361:200400013

Cite as: arXiv:0805.0654v1 [astro-ph]

Submission history

From: Liping Jin [view email]

[v1] Tue, 6 May 2008 07:14:04 GMT (30kb)

http://arxiv.org/abs/0805.0654

ljk May 7, 2008 at 9:21

The May, 2008 issue of Scientific American has as its cover
story the idea that planet formation is anything but an orderly
process.

The piece is not online for free, but you can see the start of
it here:

http://www.sciam.com/article.cfm?id=the-genesis-of-planets

ljk May 16, 2008 at 23:53

Infall of planetesimals onto growing giant planets: onset of runaway gas accretion and metallicity of their gas envelopes

Authors: Masakazu Shiraishi, Shigeru Ida

(Submitted on 15 May 2008)

Abstract: We have investigated the planetesimal accretion rate onto giant planets that are growing through gas accretion, using numerical simulations and analytical arguments. We derived the condition for gap opening in the planetesimal disk, which is determined by a competition between the expansion of the planet’s Hill radius due to the planet growth and the damping of planetesimal eccentricity due to gas drag. We also derived the semi-analytical formula for the planetesimal accretion rate as a function of ratios of the rates of the Hill radius expansion, the damping, and planetesimal scattering by the planet. The predicted low planetesimal accretion rate due to gap opening in early gas accretion stages quantitatively shows that “phase 2,” which is a long slow gas accretion phase before onset of runaway gas accretion, is not likely to occur.

In late stages, rapid Hill radius expansion fills the gap, resulting in significant planetesimal accretion, which is as large as several $M_{\oplus}$ for Jupiter and Saturn. The efficient onset of runaway gas accretion and the late pollution may reconcile the ubiquity of extrasolar giant planets with metal-rich envelopes of Jupiter and Saturn inferred from interior structure models.

These formulae will give deep insights into formation of extrasolar gas giants and the diversity in metallicity of transiting gas giants.

Comments: 19 pages, 9 figures, accepted for publication in ApJ

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.2200v1 [astro-ph]

Submission history

From: Shigeru Ida [view email]

[v1] Thu, 15 May 2008 03:01:01 GMT (224kb)

http://arxiv.org/abs/0805.2200

ljk May 21, 2008 at 11:48

Hot Jupiters and stellar magnetic activity

Authors: A. F. Lanza

(Submitted on 20 May 2008)

Abstract: Recent observations suggest that stellar magnetic activity may be influenced by the presence of a close-by giant planet. Specifically, chromospheric hot spots rotating in phase with the planet orbital motion have been observed during some seasons in a few stars harbouring hot Jupiters. The spot leads the subplanetary point by a typical amount of about 60-70 degrees, with the extreme case of upsilon And where the angle is about 170 degrees. The interaction between the star and the planet is described considering the reconnection between the stellar coronal field and the magnetic field of the planet. Reconnection events produce energetic particles that moving along magnetic field lines impact onto the stellar chromosphere giving rise to a localized hot spot.

A simple magnetohydrostatic model is introduced to describe the coronal magnetic field of the star connecting its surface to the orbiting planet. The field is assumed to be axisymmetric around the rotation axis of the star and its configuration is more general than a linear force-free field. With a suitable choice of the free parameters, the model can explain the phase differences between the hot spots and the planets observed in HD 179949, upsilon And, HD 189733, and tau Bootis, as well as their visibility modulation on the orbital period and seasonal time scales.

The possible presence of cool spots associated with the planets in tau Boo and HD 192263 cannot be explained by the present model. However, we speculate about the possibility that reconnection events in the corona may influence subphotospheric dynamo action in those stars producing localized photospheric (and chromospheric) activity migrating in phase with their planets.

Comments: 9 pages, 5 figures, 2 tables, 2 appendixes, accepted by Astronomy & Astrophysics

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0805.3010v1 [astro-ph]

Submission history

From: Antonino Francesco Lanza [view email]

[v1] Tue, 20 May 2008 06:30:06 GMT (148kb)

http://arxiv.org/abs/0805.3010

ljk July 1, 2008 at 13:26

Planet Migration and Disk Destruction due to Magneto-Centrifugal Stellar Winds

Authors: R.V.E. Lovelace, M.M. Romanova, A.W. Barnard

(Submitted on 25 Jun 2008)

Abstract: This paper investigates the influence of magneto-centrifugally driven or simply magnetic winds of rapidly-rotating, strongly-magnetized T Tauri stars in causing the inward or outward migration of close-in giant planets. The azimuthal ram pressure of the magnetized wind acting on the planet tends to increase the planet’s angular momentum and cause outward migration if the star’s rotation period $P_*$ is less than the planet’s orbital period $P_p$. In the opposite case, $P_* > P_p$, the planet migrates inward. Thus, planets orbiting at distances larger (smaller) than $0.06 {\rm AU}(P_*/5{\rm d})^{2/3}$ tend to be pushed outward (inward), where $P_*$ is the rotation period of the star assumed to have the mass of the sun.

The magnetic winds are likely to occur in T Tauri stars where the thermal speed of the gas close to the star is small, where the star’s magnetic field is strong, and where the star rotates rapidly. The time-scale for appreciable radial motion of the planet is estimated as $\sim 2 – 20$ Myr. A sufficiently massive close-in planet may cause tidal locking and once this happens the radial migration due to the magnetic wind ceases.

The magnetic winds are expected to be important for planet migration for the case of a multipolar magnetic field rather than a dipole field where the wind is directed away from the equatorial plane and where a magnetospheric cavity forms. The influence of the magnetic wind in eroding and eventually destroying the accretion disk is analyzed. A momentum integral is derived for the turbulent wind/disk boundary layer and this is used to estimate the disk erosion time-scale as $\sim 1-10^2$ Myr, with the lower value favored.

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0806.4197v1 [astro-ph]

Submission history

From: Richard V. E. Lovelace [view email]

[v1] Wed, 25 Jun 2008 20:52:49 GMT (619kb)

http://arxiv.org/abs/0806.4197

Shaun November 26, 2008 at 14:06

Dave Weeden, interesting that you brought up this suggestion of Jupiter having formed somewhere else for I recall reading on http://www.space.com just exactly that a few years ago. Apparently the suspicion was raised because of “abnormally” large amounts of inert gases ike argon and neon in Jupiter. The only place where these inert elements can be found in large amounts today is in the Edgeworth-Kuiper Belt. Otherwise, the solar system was a much colder place then originally thought or so these scientists say.

As for past planetary migrations within our own solar system, they probably did happened even if one or two here loathes the idea. For while most astrophysicists obviously do not share what a few of their compatriots suspect that Jupiter migrated inwards from the the EKB as mentioned in the space.com article earlier, they do think that the only logical explanation to account for the Late Heavy Bombardment was for the outward migration of the then embryonic Uranus and Neptune from in and around ~3-5 AU displacing dwarf planets, asteroids, comets and causing them to fall inwards impacting the Earth and Moon.

Now back to the topic of a past “torch”” orbit Jovian in our solar system and what could have happened to it. Though the notion that such a planet (if it did exist) could have plunged into the Sun, I think it could very well have been scattered either out into the nether regions of the Oort Cloud or even interstellar space altogether due to complex secular perturbation involving the likes of Jupiter and Saturn i.e. similar to what is proposed to have occured to Uranus and Neptune. Now some may argue that if it still lingers on in the solar system albeit in the Oort Cloud, we would surely have discovered it by now or should we or could we? There was this Extrasolar Planets & Brown Dwarfs Calculator on Prof Adam Burrows homepage, not sure if it still exists but I recall inputing random figures for mass and Ages e.g. 17 MJup and 4.57 Gyrs and the Teff that was returned was if I recall correctly a mere ~390° K. While this seems trivial and rather easy to some, and is definitely within the capability of SPITZER, let us not forget, we aren’t talking about a BD i.e. brown dwarf here. For that’s what a 17 MJup object is i.e. a BD. We are talking about a real planet albeit a Jupiter-like planet which is a a lot less massive and thus takes way shorter time to radiate away excess heat leftover from its formation.

And if the hypothetical “hot” Jupiter was really but a “hot” Saturn or worst a “hot” SuperEarth, it will be a lot colder still. Also forget not that space is a very big place, even if we can derive a likely Teff for this 4.57 Gyrs (assuming coevality with the Sun) substellar Jovian, we need to know exactly where to look. We only have to look at the case of Teegarden’s Star / SO025300.5+165258 to know how hard such a search can be. On one hand we can find and be excited about dim, dust enshrouded giant ellipticals some 11-12 billion light years away but only found Teegarden’s Star / SO025300.5+165258 in 2003. What does this tells us?

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