**Enigma of the Birth and Evolution of Solar Systems May Be Solved by Invoking Planetary-Satellite Dynamics**

Bijay Sharma

*Electronics and Communication Department, National Institute of Technology, Patna India* 

## **1. Introduction**

72 Space Science

No impact solutions were found for (144898) VD17 in the next 100 year in the future. Similar

To compute precisely the impact solutions of (99942) Apophis and (144898) 2004 VD17 it is necessary to include small effects like relativistic effects, close approaching asteroids, the Yarkovsky/YORP effect. The use of the software OrbFit is helpful in computing exact possible impacts of asteroids with the Earth. Thanks for the OrbFit Consortium. Also the

Thank you to the researches from OrbFit Consortium working in four research laboratories: http://adams.dm.unipi.it/~orbmaint/orbfit/OrbFit/doc/help.html#authors for theirs free

Thank you very much for Andrea Milani and Geny Sansaturio for discussions during

I would like to thank Grzegorz Sitarski from the Space Research Center, of the Polish Academy of Sciences in Warsaw for his impact solutions of (99942) Apophis and (144898)

Giorgini, J. D., Benner, L. A. M., Ostro, S. J., Nolan, M. C., Busch, M. W. (2008). *Icarus*, 193, 1

Milani, A., Chesley, S. R., Chodas, P. W., Valsecchi, G. B. (2002). In *Asteroids III*, ed.: W.F.

Milani, A., Chesley, S.R., Sansaturio, M. E., Tommei, G., Valsecchi, G.B. (2005a). *Icarus* 173,

Milani, A., Sansaturio, M. E., Tommei, G., Arratia, O., Chesley, S. R. (2005b). *Astron.* 

Bottke Jr., A. Cellino, P. Paolicchi, and R. P. Binzel (eds), Univ. of Arizona Press,

I also thank Aldo Vitagliano for his discussion about Solex during Mace 2006.

I would like to thank Fabrizio Bernardi for his help in the OrbFit v.4.2.

I am also grateful for the suggestions given by Leonard Kornos.

Chesley, S. R., Baer, J., Monet, D. G. (2010). *Icarus*, 210, 158

solution, no possible impact, were detected by the JPL NASA and by the NEODyS.

**5. Conclusion** 

**6. Acknowledgment** 

software and source code.

**7. References** 

Tucson, 55

*Astrophys.* 431, 729 Sitarski, G. (2002). *Acta Astron.* 52, 471

Wlodarczyk, I. (2001). *Acta Astron.* 51, 357

362

free software Solex was useful in this work.

MACE 2006 and for the help through e-mails.

2004 VD17 and profound and fruitful help.

Michalak, G. (2001). *Astron. Astrophys.* 374, 703

Vitagliano, A. (1997). *Cel. Mech. Dyn. Astron.* 66, 293

Vitagliano, A. and Stoss, R. (2006). *Astron. Astrophys.* 455, L29

Yeomans, D.K., Ostro, S.J., Chodas, P.W. (1987). *Astron. J.* 94, 189

From ancient times there has been a quest to understand the position of human kind in the cosmic order and to develop predictive system which could warn us of the impending natural calamity. In a continuing quest for an accurate predictive system, in Greek times Ptolemy kept our Planet at the center of the Universe and propagated the Geo-centric World View [Gale (2005-2006), Lawson (2004)]. In 16th century at the height of Renaissance, in a paradigm shift work but which was very much in keeping with common-sense , Nicolaus Copernicus, mathematician, astronomer and catholic monk, presented his book "*De revolutionibus orbium coelestium* (on the Revolution of the Heavenly Spheres)" first printed in 1542 in Nuremberg, Holy Roman Empire of the German Nation[Hawking (2005), Kuhn (1957), Windleband (1958), Crowe (1990)]. It offered a new framework for calculating the positions of the planets and this computational framework was tied to a Helio-centric World View [Hawking (2005)].

This Helio-centric Model was a natural consequence of common sense logic because the Sun was the heaviest object. The mass of Sun had been established during the renaissance by Sir Issac Newton [Hawking (2005)].This simple model at one stroke removed all the anomalies observed in the motion of the planets till then. But still it stood against a wall. The concept of helio-centrism was very much there in Greek Times [ Gomez 2011] but the religious dogma and over-possessiveness of the idea of superiority of human-kind over all living kinds compelled geo-centric world view as the correct and the official tenant of the Greek times.

This dogma persisted. Such were the dogmatism of the Dark Mediaeval Period that in 1553 Michael Servetus [Goldstone & Goldstone(2002), Janz (1953)] was burnt at stake for advancing new ideas contrary to those of the Church. New ideas were considered heretical ideas.

In 1584 a young theologioan and naturalist by the name of Giordano Bruno [Singer (1950), Yates (1964), Brix (1998)] came on the European Scene. He boldly proclaimed the correctness of Helio-centric Model and he went a step forward saying that all stars were like our Sun, that there may be many more *extra terrestrial solar systems , many more exo-planets and many more extra terrestrial intelligence*. There was nothing sacrosanct about Man and his Earth just as there is nothing special about Chinese Civilization and their Middle Kingdom. This was the final nail in his coffin.

Enigma of the Birth and Evolution of Solar Systems

churning atmosphere.

Type of object Planet

Hydrogen

Deuterium

Distinguishing feature of star.

May Be Solved by Invoking Planetary-Satellite Dynamics 75

Adaptive Optics overcomes the atmospheric turbulence. Adaptive optics measures the scrambling due to air turbulence with a special sensor, then sends the information to a flexible mirror that deforms and undulates many times a second to tidy up the image. The rapid changes in the shape of the mirror exactly compensates the distorting effect of the

Recently extreme adaptive optics has been developed. It replaces hundreds of tiny pistons that reshape current flexible mirrors with thousands of smaller ones, and correct the incoming light not hundreds but thousands of times a second. This would spot a young glowing Jupiter in a much wider orbits. The road to another earth lies through another Jupiter, hence the presence of wide orbit Jupiter will mark the stars which should be closely

In 1991 the first extra-solar system around a Pulsar was discovered by Alexander Wolszczan and Dale Frail. This pulsar is PSR1257+12, a rapidly rotating neutron star about 1.4MΘ and at a distance of 2000 to 3000 light years of our Earth. In this solar-system three planets were observed. The two planets have orbital period of a few months, small eccentricities and masses a few times as large as the mass of Earth. Third planet, innermost planet, has a

Name Jupiter Gliese 229B Teide1 Gliese229A SUN

Mass(×MJ) 1 30 55 300 1,000 Radius(km) 71,500 65,000 150,000 250,000 696,000 Temperature(k) 100 1,000 2,600 3,400 5,800 Age(years) 4.5Gy 2-4Gy 120My 2-4Gy 4.5Gy

fusion No No No Yes Yes

fusion No Yes Yes Yes Yes

Not hot enough for Hydrogen Fusion but deuterium fusion starts and after that the fusion fizzles out. Hence we say it is a failed star.

Failed star Brown Dwarf

M type Main Sequence Star Red Dwarf

Full scale fusion takes place from Hydrogen onward till Iron is nucleosynthesized. It can't go beyond Iron since Iron has the maximum binding energy.

G type Main Sequence Star, Yellow Dwarf

Full scale fusion takes place from Hydrogen onward till Iron is nucleosynthesized. It can't go beyond Iron since Iron has the maximum binding energy.

examined first for earth like planets and then for life and intelligence.

Failed star Brown Dwarf

Not hot enough for Hydrogen Fusion but deuterium fusion starts and after that the fusion fizzles out. Hence we say it is a failed star.

Table 2. Distinction among Planets, Brown Dwarfs and Main Sequence Stars.

period of one month and the mass is that of our Moon.

Gas Giant

No fusion whatsoever

In 1592 Bruno was arrested by the Inquisition, a Church Court. His philosophical and political views were censored and he himself was burnt at stake in 1600. He was the martyr of "Free Thought and Modern Scientific Ideas". He was the bold harbinger of a New Cosmology during the Italian Renaissance.

*De Revolutionibus* was banned "until corrected". In 1620 nine sentences were deleted and then it was brought into circulation.

The debate about **extraterrestrial intelligence** continued and it was argued that if indeed there is **extraterrestrial intelligence** elsewhere there must be Earth-like planets in our Milky Way Galaxy. It was also argued that SETI must concentrate in those regions of our Galaxy where Earth-like planets are most likely to be found by anthromorphic principles. By anthromorphic principles the best places to find life in our galaxy could be on planets that orbit the Red Dwarf Star. Gliese 876 falls in this category. It is one-third the mass of our Sun and only 15 light years distant from us. It is three planet system. The planets falling in "Goldilocks Zone" around these Red Dwarfs will have maximum probability of **extraterrestrial intelligence**. These zones are the area around the star which is neither hot nor cold for liquid water to stay. The full lifecycle of a star is dependent on its mass. The lifecycle is inversely proportional to the mass. The massive stars are short lived, their life being of million years. The light stars like Red Dwarf star are very long lived, their life cycle extend up to 100 billion years. Therefore Red Dwarf planetary system has a greatest chance of harboring an evolved form of life. Thus the idea of Extra-Solar Systems and Exo-Planets were born. Extra-Solar Systems are the Solar –Systems around other main-sequence stars and members of the extra solar –systems are exo-planets.

M Dwarf or Red dwarf stars are most abundant outnumbering sun-like G Type stars by 10 to 1. Since these stars are likely to have earth like planets falling in Goldilocks Zone hence they are the primary target for SETI missions.


The following table gives the types of Stars and the likelihood of finding extra-solar systems:

Table 1. The types of stars and the likelihood of extra-solar systems with different types. [Zimmerman 2004]

### **2. The discovery of first extra-solar system1**

In 1986, two proposals came from the University of Arizona and the University of Perkin-Elmer for space based direct imaging of Extra-Solar Systems using 16m- infrared telescope and optical telescope respectively.[Shiga 2004, Zimmerman 2004]. Atmospheric turbulence smears the star's light into an arcsecond blob and reduces the resolution therefore ground based imaging of exo-planets was impossible.

<sup>1 [</sup>Lissauer 2002]

74 Space Science

In 1592 Bruno was arrested by the Inquisition, a Church Court. His philosophical and political views were censored and he himself was burnt at stake in 1600. He was the martyr of "Free Thought and Modern Scientific Ideas". He was the bold harbinger of a New

*De Revolutionibus* was banned "until corrected". In 1620 nine sentences were deleted and

The debate about **extraterrestrial intelligence** continued and it was argued that if indeed there is **extraterrestrial intelligence** elsewhere there must be Earth-like planets in our Milky Way Galaxy. It was also argued that SETI must concentrate in those regions of our Galaxy where Earth-like planets are most likely to be found by anthromorphic principles. By anthromorphic principles the best places to find life in our galaxy could be on planets that orbit the Red Dwarf Star. Gliese 876 falls in this category. It is one-third the mass of our Sun and only 15 light years distant from us. It is three planet system. The planets falling in "Goldilocks Zone" around these Red Dwarfs will have maximum probability of **extraterrestrial intelligence**. These zones are the area around the star which is neither hot nor cold for liquid water to stay. The full lifecycle of a star is dependent on its mass. The lifecycle is inversely proportional to the mass. The massive stars are short lived, their life being of million years. The light stars like Red Dwarf star are very long lived, their life cycle extend up to 100 billion years. Therefore Red Dwarf planetary system has a greatest chance of harboring an evolved form of life. Thus the idea of Extra-Solar Systems and Exo-Planets were born. Extra-Solar Systems are the Solar –Systems around other main-sequence stars

M Dwarf or Red dwarf stars are most abundant outnumbering sun-like G Type stars by 10 to 1. Since these stars are likely to have earth like planets falling in Goldilocks Zone hence

The following table gives the types of Stars and the likelihood of finding extra-solar systems:

K-Type 0.3 to 0.7 M<sup>Θ</sup> 3 to 4% M-Type 0.1 to 0.3 M<sup>Θ</sup> Unlikely. Table 1. The types of stars and the likelihood of extra-solar systems with different types.

 In 1986, two proposals came from the University of Arizona and the University of Perkin-Elmer for space based direct imaging of Extra-Solar Systems using 16m- infrared telescope and optical telescope respectively.[Shiga 2004, Zimmerman 2004]. Atmospheric turbulence smears the star's light into an arcsecond blob and reduces the resolution therefore ground

**Types Mass Likelihood**  F- Type 1.3 to 1.5 M<sup>Θ</sup> 10% G- Type (sun like) 1 M<sup>Θ</sup> 7%

Cosmology during the Italian Renaissance.

and members of the extra solar –systems are exo-planets.

they are the primary target for SETI missions.

**2. The discovery of first extra-solar system1**

based imaging of exo-planets was impossible.

[Zimmerman 2004]

1 [Lissauer 2002]

then it was brought into circulation.

Adaptive Optics overcomes the atmospheric turbulence. Adaptive optics measures the scrambling due to air turbulence with a special sensor, then sends the information to a flexible mirror that deforms and undulates many times a second to tidy up the image. The rapid changes in the shape of the mirror exactly compensates the distorting effect of the churning atmosphere.

Recently extreme adaptive optics has been developed. It replaces hundreds of tiny pistons that reshape current flexible mirrors with thousands of smaller ones, and correct the incoming light not hundreds but thousands of times a second. This would spot a young glowing Jupiter in a much wider orbits. The road to another earth lies through another Jupiter, hence the presence of wide orbit Jupiter will mark the stars which should be closely examined first for earth like planets and then for life and intelligence.

In 1991 the first extra-solar system around a Pulsar was discovered by Alexander Wolszczan and Dale Frail. This pulsar is PSR1257+12, a rapidly rotating neutron star about 1.4MΘ and at a distance of 2000 to 3000 light years of our Earth. In this solar-system three planets were observed. The two planets have orbital period of a few months, small eccentricities and masses a few times as large as the mass of Earth. Third planet, innermost planet, has a period of one month and the mass is that of our Moon.


Table 2. Distinction among Planets, Brown Dwarfs and Main Sequence Stars.

Enigma of the Birth and Evolution of Solar Systems

**3. The menagrie of exo-planets discovered till date2**

55Cancri. Its MSini = 4MJ and its orbital period is 14 years.

1992 Arecibo Radio Telescope

2001 Hubble Space Telescope.

2003 Keck Interferometer

2009 Space Interferometry

2014-2020 Terrestrial Planet

studies.[Appenzellar 2004]

2 [Shiga 2004, Zimmerman 2004]

2006 Large Binocular

Telescope

Mission (SIM)

Finder (TPF)

1995 Haute –Provence

1999 STARE Project.

Observatory

May Be Solved by Invoking Planetary-Satellite Dynamics 77

708 exo-planets have been discovered till 17th December, 2011. 81 multiple exo-planet systems have been discovered till now. 10 earth and super-earths discovered. 2 of these are in Goldilock zone.[ "Coming Soon, Earth's Twin." The Economic Times on Sunday. December 11-17, 2011 Pg.15.] Generally the exo-planets have eccentricities equal to zero. That is they are orbiting in perfect circular orbits like our nine planets. But there are other exo-planets which are in highly elliptical orbits like comets. Planets have been found orbiting binary stars, in circum-binary configuration, as well as in three star-systems.

The only exoplanet with an orbital period larger than that of Jupiter is the one orbiting

Planet as massive as 14ME have been discovered around Mu Arae [Appenzellar

[Doyle et. al. (2011), Welsh et.al(2012)]. Planets have been found orbiting pulsars.

2004].Orbital period is 9.5 days. Hence it is very close to the parent star.

*found.* 

*sodium.* 

*the transit method.* 

*Jupiter-size planets.* 

2007 Kepler Mission. *This space-based telescope is surveying more than 100,000 stars* 

2025? Life Finder *The space- based Life Finder will search newfound Earths for signs of biological activity.* 

Table 3. Chronological Order of the milestones achieved in exo-planetary

*seek planets almost as small as Earth.* 

*and search for signs of habitability.* 

*Scientists announce the discovery of planets around a pulsar – a spinning neutron star. They are unlike any known planets and almost certainly hostile to life but are the first exo-planets to be* 

*Astronomers discover a planet around a sunlike star, 51 Pegasi, by tracking stellar motions. This is the Doppler Shift method. The*

*For the first time the shadow of a Jupiter-size planet is detected as the planet passes across the face of the star , HD 209458. This is* 

*same technique has revealed more than 130 planets.* 

*By observing light from HD 209458 as its planet passes, astronomers see hints of a planetary atmosphere containing* 

*The interferometer combines light from two existing Keck telescopes, eliminating atmospheric " noise" with adaptive optics. It will search for debris disk around stars, which could signal* 

*Its twin mirrors will search for debris disk and for newly formed* 

*SIM will combine light from multiple telescopes to map stars and* 

*A two part space mission, TPF will detect from Earth-size planets*

*for dimming that hints at the presence of Earth-size planets.* 

*planet formation, and look directly for giant planets.* 

In 1994, 60-inch telescope on Palomar Mountain, coupled with primitive adaptive-optics system, imaged a brown dwarf orbiting the star Gliese 229. The brown dwarf was orbiting the host star at a semi-major axis of 40AU(Astronomical Unit) where 1AU is 1.5×108 km. The same system was photographed by Hubble Space Telescope. The ground-based imaging of this binary-star was confirmed by space image. This established the technical feasibility of taking ground-based images of sub-stellar objects using telescopes fitted with adaptiveoptics.

In 1995 Mayor and Quiloz discovered the first exo-planet orbiting the star 51Pegasi. They used ELODIE spectrograph. In this the wobbling motion of the host star is used to detect the companion object. The wobbling motion of the host star gives rise to an effective radial velocity along the line-of-sight. Hence light coming from the host star experiences Doppler Effect. When the host star is approaching us , we record a blue shifted light and when host star is receding we record a blue shifted light. The recording of the alternate blue and red shift along the time axis gives the orbital period of the exo-planet and the magnitude of the shift gives us the mass of the host star. Since we may not be having an edge-on view of the orbital plane and the orientation radius vector of the orbital plane may be at an angle i, the angle of inclination of the orientation vector with respect to the line-of-sight, therefore the mass observed is MSini. We do not get the true mass of the exo-planet unless we have an edge-on view.

In 51Pegasi extra-solar system, we have the exo-planet orbiting the host star at a semi-major axis of 4.8 million miles. The orbital period is 4.2 days. This exo-planet is named 51 Pegasi.b. The mass observed, i.e. MSini , was more massive than that of Saturn.

One of the biggest drawback of Doppler Method of detection is that only Gas Giants of the size of Jupiter and Saturn can be detected.

ELODIE spectrograph has been further improved into CORALIE echlie spectrograph mounted on the 1.2m-Euler Swiss telescope at La Silla Observatory, ESO, Chile. This has been refined and exo-planets of Uranus mass have also been detected.

In 1999, a planet around HD209458 was detected by transit method. The actual mass and the size of the planet orbiting HD 209458 has been determined by combining the transit method and Doppler shift method. The density has been inferred and it is established that HD 209458b is a gas giant primarily constituted of Hydrogen just as Jupiter and Saturn are.

In 2001 the exoplanet OGLE-TR-56b detected by transit method. A polish team using 1.3m Warsaw Telescope at the Las Campanas Observatory in Chile made this discovery. In the transit method a dip in star light is caused while the exo-planet is transiting across the host star just as we record a solar eclipse when Moon is transiting across the face of Sun on NO MOON day. In the case of OGLE-TR-56b the dip occurred for 108 minutes and repeated every 1.2 days. Using 10m Keck I telescope on Mount Kea, Hawaii, the finding was confirmed by Doppler Method in January, 2003.

Both these discoveries were too close to the host star for comfort. In the classical model there was no place for gas giants to be orbiting closer than 1 to 2 AU. These exo-planets were called hot-jupiters and they defied the conventional wisdom.

76 Space Science

In 1994, 60-inch telescope on Palomar Mountain, coupled with primitive adaptive-optics system, imaged a brown dwarf orbiting the star Gliese 229. The brown dwarf was orbiting the host star at a semi-major axis of 40AU(Astronomical Unit) where 1AU is 1.5×108 km. The same system was photographed by Hubble Space Telescope. The ground-based imaging of this binary-star was confirmed by space image. This established the technical feasibility of taking ground-based images of sub-stellar objects using telescopes fitted with adaptive-

In 1995 Mayor and Quiloz discovered the first exo-planet orbiting the star 51Pegasi. They used ELODIE spectrograph. In this the wobbling motion of the host star is used to detect the companion object. The wobbling motion of the host star gives rise to an effective radial velocity along the line-of-sight. Hence light coming from the host star experiences Doppler Effect. When the host star is approaching us , we record a blue shifted light and when host star is receding we record a blue shifted light. The recording of the alternate blue and red shift along the time axis gives the orbital period of the exo-planet and the magnitude of the shift gives us the mass of the host star. Since we may not be having an edge-on view of the orbital plane and the orientation radius vector of the orbital plane may be at an angle i, the angle of inclination of the orientation vector with respect to the line-of-sight, therefore the mass observed is MSini. We do not get the true mass of the exo-planet unless we have an

In 51Pegasi extra-solar system, we have the exo-planet orbiting the host star at a semi-major axis of 4.8 million miles. The orbital period is 4.2 days. This exo-planet is named 51 Pegasi.b.

One of the biggest drawback of Doppler Method of detection is that only Gas Giants of the

ELODIE spectrograph has been further improved into CORALIE echlie spectrograph mounted on the 1.2m-Euler Swiss telescope at La Silla Observatory, ESO, Chile. This has

In 1999, a planet around HD209458 was detected by transit method. The actual mass and the size of the planet orbiting HD 209458 has been determined by combining the transit method and Doppler shift method. The density has been inferred and it is established that HD 209458b is a gas giant primarily constituted of Hydrogen just as Jupiter and Saturn are.

In 2001 the exoplanet OGLE-TR-56b detected by transit method. A polish team using 1.3m Warsaw Telescope at the Las Campanas Observatory in Chile made this discovery. In the transit method a dip in star light is caused while the exo-planet is transiting across the host star just as we record a solar eclipse when Moon is transiting across the face of Sun on NO MOON day. In the case of OGLE-TR-56b the dip occurred for 108 minutes and repeated every 1.2 days. Using 10m Keck I telescope on Mount Kea, Hawaii, the finding was

Both these discoveries were too close to the host star for comfort. In the classical model there was no place for gas giants to be orbiting closer than 1 to 2 AU. These exo-planets were

The mass observed, i.e. MSini , was more massive than that of Saturn.

been refined and exo-planets of Uranus mass have also been detected.

size of Jupiter and Saturn can be detected.

confirmed by Doppler Method in January, 2003.

called hot-jupiters and they defied the conventional wisdom.

optics.

edge-on view.

#### **3. The menagrie of exo-planets discovered till date2**

708 exo-planets have been discovered till 17th December, 2011. 81 multiple exo-planet systems have been discovered till now. 10 earth and super-earths discovered. 2 of these are in Goldilock zone.[ "Coming Soon, Earth's Twin." The Economic Times on Sunday. December 11-17, 2011 Pg.15.] Generally the exo-planets have eccentricities equal to zero. That is they are orbiting in perfect circular orbits like our nine planets. But there are other exo-planets which are in highly elliptical orbits like comets. Planets have been found orbiting binary stars, in circum-binary configuration, as well as in three star-systems. [Doyle et. al. (2011), Welsh et.al(2012)]. Planets have been found orbiting pulsars.

The only exoplanet with an orbital period larger than that of Jupiter is the one orbiting 55Cancri. Its MSini = 4MJ and its orbital period is 14 years.

Planet as massive as 14ME have been discovered around Mu Arae [Appenzellar 2004].Orbital period is 9.5 days. Hence it is very close to the parent star.


Table 3. Chronological Order of the milestones achieved in exo-planetary studies.[Appenzellar 2004]

<sup>2 [</sup>Shiga 2004, Zimmerman 2004]

Enigma of the Birth and Evolution of Solar Systems

are cooler than expected.

much larger debris disk.

HD 100546 <500My ?

Beta Pictoris 15My

HD 141569 < 20My

Fomalhaut

Au Mic (M Type star)

Name of the

May Be Solved by Invoking Planetary-Satellite Dynamics 79

the ground observatories have established that a dozen stars possess the dusty debris disk including Beta Pictoris. These debris disks are the analogue of Kuiper belt debris and hence

The debris disk depend on the age. Young stars in formative stage possess a much larger and heavier dusty debris disk as compared to our Solar System which is 4.56Gy.In our Solar System much of the debris has been used up in planet formation and the residual has spiraled in due to Poynting-Robertson(PR) drag or photoevaporated. The dust presently seen in asteroid belt and Kuiper belt is the result of collision and evaporation of comets and asteroids. They are continuously being removed by PR drag and by photoevporation and they are also being replenished by collisions and evaporation. Hence the young stars have a

So far the stars with debris disk have not given the confirmation of the presence of planets

disk implications

parent star.

sun.

micron.

15My 50 AU to 210AU Excess of far-IR radiation points to the

A protoplanet might be orbiting the

10,000 times as much dust as our solar system does. This means it has 100 times more planetismals as compared to our

The companion stars could have created

Observed at 70 microns by SPITZER. The inner warm ring is akin to asteroid belt and its IR glow was observed at 24

existence circumstellar dust grains;

these features. It could be due to

accompanying planets.

and stars with extra- solar systems have not shown up any debris disk.

Revealed a gap at 10AU

debris disk detected at optical and near IR.

Long spiral arms of dust. Debris disk detected at optical and near IR.

200AU in radius , edge on ring of dust is observed. Debris disk detected at

A ring of warm materials detected very near the star.

optical and near IR.

thermal IR.

thermal IR. Table 4. Stars with dusty debris disk and the implications.

star Age Extent of the dusty debris

1400AU edge-on disk

thermal IR.

HR4967A < 20My debris disk detected at

Vega debris disk detected at

<sup>ε</sup> Eridani debris disk detected at

Planets have been orbiting very close to their parent star so much so that they are slowly evaporating due to the heat and solar wind from their parent star. These are the hot Jupiters referred to above. As mentioned these defy the common wisdom of planet formation. By the year 2000, dozen exoplanets discovered and majority of them were hot Jupiters.

The catalog of exoplanets is growing and hot-jupiters seem to be an exception. The average planet size is falling and orbital distance is growing. That is exo-planets are being discovered farther and farther away from their parent star.

Table 3. gives a chronological order of the milestones achieved in exo-planetary studies

## **4. Conditions conducive to exo-planet growth**

In general it is found that single star system favour planet growth. Heavier stars favor giant planet growth while lighter stars favour terrestrial planet growth [Thommes et.al.(2008)]

The extra- solar systems have a much larger probability in younger and more metal-rich regions of the spiral galaxies. The parent stars of exo-planets have higher metallicity [Santos 2005]. They have a higher abundance of elements heavier than hydrogen and helium.

The time factor is also very important. There is a very narrow time slot of few million years after the birth of the solar nebula in which the planets can be formed. The building blocks of planets are dust and gas. The dust particles of the accretion disc are continuously spiraling into the parent star by Poynting-Robertson drag and gas-dust smaller than 0.1 micron are being pushed out by solar radiation insolation by the process known as photo-evaporation [Ardila 2004].

In our Solar System there exists dusty debris disk in the asteroid belt. This causes the zodiacal light hence it is called zodiacal belt of dusty debris. This extends from 3AU to 10AU. There also exists Kuiper Belt of dusty debris from 30AU to 100AU. Similar dusty debris disk surround the stars with planetary system. These have been imaged by IRAS(infra red astronomical satellites) in 1983.It carried out complete survey of the sky in mid to far infra-red wavelength from 12 to 100 microns. The star itself is too hot, about 1000 Kelvin, to emit at far IR. But an accompanying debris disk will heat up and reradiate at far IR. This will give a bump in the stellar spectrum. The excess energy at infrared wavelength invariably indicate the presence of dusty debris disk. These debris disks are tenuous and faint but they have definite IR hazy glow. A gap in the debris disk is the signature of a protoplanet orbiting the parent star. The planet is in formative stage.

The dust in the debris disk either comes from the collisions of the initial leftover planetismals during planet formation or could be coming from collisions of comets and asteroids much after the formation has been completed. This debris disk generally range from 100AU to 1000AU and their composition is similar to that of our comets. The central part is a gap.

Ground based detectors cannot observe IR because of the absorption effect of the atmosphere. Milllimetric radiations reach the surface of the Earth. Therefore Submillimeter Common-User Bolometer Arrays (SCUBA) are used on the ground observatory for detecting the mm radiation coming from the debris disk of the stars. A combination of IR and mm wavelengths observations made by Hubble Space Telescope, SCUBA and IR detectors from 78 Space Science

Planets have been orbiting very close to their parent star so much so that they are slowly evaporating due to the heat and solar wind from their parent star. These are the hot Jupiters referred to above. As mentioned these defy the common wisdom of planet formation. By the

The catalog of exoplanets is growing and hot-jupiters seem to be an exception. The average planet size is falling and orbital distance is growing. That is exo-planets are being

In general it is found that single star system favour planet growth. Heavier stars favor giant planet growth while lighter stars favour terrestrial planet growth [Thommes et.al.(2008)]

The extra- solar systems have a much larger probability in younger and more metal-rich regions of the spiral galaxies. The parent stars of exo-planets have higher metallicity [Santos 2005]. They have a higher abundance of elements heavier than hydrogen and helium.

The time factor is also very important. There is a very narrow time slot of few million years after the birth of the solar nebula in which the planets can be formed. The building blocks of planets are dust and gas. The dust particles of the accretion disc are continuously spiraling into the parent star by Poynting-Robertson drag and gas-dust smaller than 0.1 micron are being pushed out by solar radiation insolation by the process known as photo-evaporation

In our Solar System there exists dusty debris disk in the asteroid belt. This causes the zodiacal light hence it is called zodiacal belt of dusty debris. This extends from 3AU to 10AU. There also exists Kuiper Belt of dusty debris from 30AU to 100AU. Similar dusty debris disk surround the stars with planetary system. These have been imaged by IRAS(infra red astronomical satellites) in 1983.It carried out complete survey of the sky in mid to far infra-red wavelength from 12 to 100 microns. The star itself is too hot, about 1000 Kelvin, to emit at far IR. But an accompanying debris disk will heat up and reradiate at far IR. This will give a bump in the stellar spectrum. The excess energy at infrared wavelength invariably indicate the presence of dusty debris disk. These debris disks are tenuous and faint but they have definite IR hazy glow. A gap in the debris disk is the signature of a

The dust in the debris disk either comes from the collisions of the initial leftover planetismals during planet formation or could be coming from collisions of comets and asteroids much after the formation has been completed. This debris disk generally range from 100AU to 1000AU and their composition is similar to that of our comets. The central

Ground based detectors cannot observe IR because of the absorption effect of the atmosphere. Milllimetric radiations reach the surface of the Earth. Therefore Submillimeter Common-User Bolometer Arrays (SCUBA) are used on the ground observatory for detecting the mm radiation coming from the debris disk of the stars. A combination of IR and mm wavelengths observations made by Hubble Space Telescope, SCUBA and IR detectors from

protoplanet orbiting the parent star. The planet is in formative stage.

Table 3. gives a chronological order of the milestones achieved in exo-planetary studies

year 2000, dozen exoplanets discovered and majority of them were hot Jupiters.

discovered farther and farther away from their parent star.

**4. Conditions conducive to exo-planet growth** 

[Ardila 2004].

part is a gap.

the ground observatories have established that a dozen stars possess the dusty debris disk including Beta Pictoris. These debris disks are the analogue of Kuiper belt debris and hence are cooler than expected.

The debris disk depend on the age. Young stars in formative stage possess a much larger and heavier dusty debris disk as compared to our Solar System which is 4.56Gy.In our Solar System much of the debris has been used up in planet formation and the residual has spiraled in due to Poynting-Robertson(PR) drag or photoevaporated. The dust presently seen in asteroid belt and Kuiper belt is the result of collision and evaporation of comets and asteroids. They are continuously being removed by PR drag and by photoevporation and they are also being replenished by collisions and evaporation. Hence the young stars have a much larger debris disk.

So far the stars with debris disk have not given the confirmation of the presence of planets and stars with extra- solar systems have not shown up any debris disk.


Table 4. Stars with dusty debris disk and the implications.

Enigma of the Birth and Evolution of Solar Systems

Terrestrial direct

imaging

Space direct imaging

Radial Velocity technique or

Radiovelocimetry or reflex motion of solar type stars

Astrometric method

Transit photometry

method

Gravitational microlensing

May Be Solved by Invoking Planetary-Satellite Dynamics 81

Easier to detect gas giants in wide orbits like ours.

William SPARKS(Space Telescope Science Institute)

Easier to detect gas giants in wide orbits like ours.

known as Doppler Shift technique.

Easier to detect gas giants in tight orbit.

hence a longer timeline of observations.

Most sensitive for gas giants in nearby stars.

Largest telescopes such as Keck, Gemini and Subaru are being used for direct imaging. Orbital architecture can be determined hence true

Young stars are ideal target as their companion planet would be glowing brightly in infra red wavelength because of the accretion

Young stars are ideal target as their companion planet would be glowing brightly in infra red wavelength because of the accretion

A color change in the star light betrays the wobble caused by the companion planet. When star is approaching, light experiences a blue shift and when star is receding, light experiences red shift. This is also

There is uncertainty about the orbital angle of inclination hence real mass is indeterminent. Only the lower limit of the true mass is

Recording the proper motion of the star on the celestial sphere i.e. the

Since 2-D picture is obtained therefore actual mass is determined. Wide orbit planets produce larger amplitude of the proper motion of stars hence easier to detect but wide orbit means longer orbital period

If the planet lies in the orbital plane of the star and we have an edge on view then the planet transit or Venus transit-like will cause a periodic square-well shaped dip in the star's brightness. It gives the estimate of planet size and the orbital period. The mass will have to

This method is used for detecting very faint stellar and sub-stellar bodies within our galaxy. A massive body intervening the space between the source and observer causes gravitational bending of light from the source leading to the brightening of the image of the source. If the intervening body is a star with a planet then the lining up of the

be determined by astrometric or Doppler shift technique.

source planet, intervening star and the observer will lead to considerable brightening up of the image of the source. As planet moves out of the line of sight, the brightening will diminish. The

is using Hubble Space Telescope's Advanced Camera for Surveys for direct imaging. Orbital architecture can be determined hence true

Method Description

mass is known.

generated heat.

mass is known.

generated heat.

determined.

dome of the sky.

The debris disks have definite large scale features such as rings, warps , blobs and, in one case, a large spiral. All the extra-debris disks so far detected are much more massive than our Asteroid belt debris and Kuiper belt debris.

Till date(1.01.2012) in last 16 months, since the Kepler Program was started, 2,326 planet candidates have been discovered out of which 31 have been have been confirmed. Kepler 22b is orbiting Sun-like star whereas Gliese-581d and HD 85512b are orbiting smaller and cooler stars but they are all in Goldilock zone.

The discovery of earth-like exo-planet would be the Holy Grail of astrobiology- a place where life started from scratch independently of life on Earth. The strategy is to first detect an earth-like exoplanet in the Goldilock zone of some star nearby say within 100 lightyears and then use terrestrial planet finder (TPF) to detect the biomarkers in the atmosphere of the given exoplanet.
