**5. Evolution of solar system building material**

In NASA's DEEP IMPACT mission a 820 pound impactor collided with Comet Tempel 1. By the study of Comet material it was concluded that it was made of the pristine constituents of early solar system. This pristine material consisted of fragile organic material. This material includes polycyclic aromatic hydrocarbons(carbon based molecules found on charred barbeque grills and automobile exhaust on Earth).

On the other hand, the asteroids are the leftovers of planet formation and they therefore represent a more evolved form of matter. About 4000 Asteroids have been categorized. The Asteroid belt exists from 2.1AU to 3.3AU. Asteroids are coplanar with Ecliptic Plane. They move in the same direction as the Planets.

In terrestrial planets there is a metallic core and surrounding basaltic-granitic mantle.

But a Solar System which is in transition like HD113766 and which has a dusty disk has material in between the primitive kind contained in comets and more evolved kind found in asteroids.

Planet bearing Extra Solar Systems invariably have an environment rich in metal[Santos 2005]. The stars with twice the metallicity have 25% chance of harbouring a planet whereas stars with Sun's metallicity has only 5% chance.

There is a very narrow time slot of tens of millions of year in which Gas Giants birth and growth must take place. The dust part is continuously spiraling inward due to Poynting - Robertson photo assisted drag and gas-dust particle smaller than 0.1 micron are pushed out by the solar radiation insolation also known as photo evaporation.. Thus the gas-dust circumstellar disc is dissipated after tens of millions of years. If the opportunity is not seized for the birth and evolution of Gas Giants then no planetary formation would take place. The formation of Gas Giants is essential for Earth- like terrestrial planets.

## **6. The difficulties in discovering exo-planets**

Doppler shift technique is the most convenient method of detecting Jupiter sized planets in tight orbits around their parent stars. The other methods are enumerated in Table 5.

80 Space Science

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

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

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

In NASA's DEEP IMPACT mission a 820 pound impactor collided with Comet Tempel 1. By the study of Comet material it was concluded that it was made of the pristine constituents of early solar system. This pristine material consisted of fragile organic material. This material includes polycyclic aromatic hydrocarbons(carbon based molecules found on charred

On the other hand, the asteroids are the leftovers of planet formation and they therefore represent a more evolved form of matter. About 4000 Asteroids have been categorized. The Asteroid belt exists from 2.1AU to 3.3AU. Asteroids are coplanar with Ecliptic Plane. They

But a Solar System which is in transition like HD113766 and which has a dusty disk has material in between the primitive kind contained in comets and more evolved kind found

Planet bearing Extra Solar Systems invariably have an environment rich in metal[Santos 2005]. The stars with twice the metallicity have 25% chance of harbouring a planet whereas

There is a very narrow time slot of tens of millions of year in which Gas Giants birth and growth must take place. The dust part is continuously spiraling inward due to Poynting - Robertson photo assisted drag and gas-dust particle smaller than 0.1 micron are pushed out by the solar radiation insolation also known as photo evaporation.. Thus the gas-dust circumstellar disc is dissipated after tens of millions of years. If the opportunity is not seized for the birth and evolution of Gas Giants then no planetary formation would take place. The

Doppler shift technique is the most convenient method of detecting Jupiter sized planets in

tight orbits around their parent stars. The other methods are enumerated in Table 5.

In terrestrial planets there is a metallic core and surrounding basaltic-granitic mantle.

our Asteroid belt debris and Kuiper belt debris.

cooler stars but they are all in Goldilock zone.

**5. Evolution of solar system building material** 

barbeque grills and automobile exhaust on Earth).

move in the same direction as the Planets.

stars with Sun's metallicity has only 5% chance.

**6. The difficulties in discovering exo-planets** 

formation of Gas Giants is essential for Earth- like terrestrial planets.

given exoplanet.

in asteroids.


Enigma of the Birth and Evolution of Solar Systems

apparent radial velocity.

method for discovering a new planet.

terrestrial planets. So there are two scenarios:

following:

May Be Solved by Invoking Planetary-Satellite Dynamics 83

As seen from the Table(6), with decreasing mass of the planet and increasing mass of the host star, the amplitude of oscillation of the radial velocity decreases. As the amplitude of oscillation decreases it becomes increasingly difficult to decipher the periodic planetary signal in the presence of various noise sources that produce random fluctuations in star's

Recently HARPS spectrometer has been developed by the Swiss team which discovered the first exoplanet Pegasi 51. This spectrometer has the required precision to decipher the tiny Doppler shift due to 0.1 m/s radial velocity of the host star harboring an earthlike planet. The instrument is kept in high vacuum and precisely controlled low temperature so that the sources of noise can be eliminated and optical stability may be imparted for obtaining the required precision. Through HARPS only Mu Arae's planet, 14 times ME, was detected.

By Astrometric measurements , the inclination of the planetary orbit and orbit-globe parameters can be determined. Astrometry is the precise measurement of two-dimensional stellar positions on the celestial sphere. The astrometric studies complement the radial velocity method. Through this method the ellipse traced by the centroid of the star during one orbital period of the planet can be exactly determined. From this ellipse the angle of

Space Interferometry Mission scheduled for 2009 will give sufficient accuracy to astrometric

From the three new Neptune-like planets [Schwarzschild 2004] the scientists conclude the

i. The shock waves of a Supernova explosion sets a giant cloud of gas and dust , passing nearby, into a spinning mode. The rapid spin cannot be accommodated by one hydrostatic star hence it results into the fragmentation of the cloud into binary or multiple star system. Even the new multiple system cannot accommodate the excess angular momentum and the individual clouds are flattened out as pancake shaped disc of accretions. The central part collapses into a proto-star surrounded by a thick disk of gas and dust. From these Keplerian debris disks the planets are born. The solar insolation is causing the photoevaporation of gas out of the system and the dust particles are spiraling inward due to Poynting-Richardson Drag and settling down in the midplane of the disc. Thus gas is blown out and the host star vicinity is filled with heavy suspension of dust particles larger than a micron size. These micron size dust randomly collide and stick together building up km-sized planetismals. But before the build up can take place the random collision may result in repeated breakups preventing the formation of planetismals. But if there is heavy dust suspension, with the gas blown out, runaway gravitational accretion takes place resulting into full scale

a. The first scenario is the earliest stage of planet formation when the protostar is not experiencing full scale thermonuclear fusion . At that stage there is a very light density suspension of dust in a thick envelope of gas. The gravitation is too weak and

inclination α and other globe-orbit parameters can be determined.

**7. The classical model of the birth and evolution of a solar system** 


Table 5. Various methods of detecting exo-planets.[Shiga 2004],

Time is the greatest difficulties. The orbital periods of Jupiter and Saturn are 12 and 29.5 years. Hence one will have to wait for that long to measure its periodicity.

Second is the resolution of the Doppler Technique. With the present resolution we could keep looking for century and not detect a Saturn of that mass and of that semi-major axis.

The masses of Jupiter and Saturn are 318 and 95ME and those of Neptune and Uranus are 17.2 and 14.6 ME . The amplitude of Doppler oscillation is proportional to (MSinα)/a1/2. Hence observational bias is towards heavier masses and shorter semi-major axis.


Table (6) gives the radial velocity which have been detected [Schwarzschild 2004].

Table 6. A comparative study of the radial velocity of the host star for different combinations of star-planets.

82 Space Science

period of fluctuation in the image of the source is the orbital period

Suppresses 98.5% of the starlight by the use of a coronagraph and images the companion planet at near-IR wavelength or images the starlight reflected by the companion planet or by the circumstellar

Large binocular telescope is used for canceling the starlight by nulling interference and image the exo-planet or the debris disk. Starlight are

wavelength. This results into destructive interference along the central line of sight but it is constructive interference off the line of sight.

and the amount of fluctuation gives the mass of the planet.

collected by two mirrors but with a path difference of half

Radio emissions similar to those from Jupiter could reveal the

Time is the greatest difficulties. The orbital periods of Jupiter and Saturn are 12 and 29.5

Second is the resolution of the Doppler Technique. With the present resolution we could keep looking for century and not detect a Saturn of that mass and of that semi-major axis. The masses of Jupiter and Saturn are 318 and 95ME and those of Neptune and Uranus are 17.2 and 14.6 ME . The amplitude of Doppler oscillation is proportional to (MSinα)/a1/2.

> Semi-major axis a (AU)

> > 0.028AU <sup>18</sup>

0.084AU <sup>4</sup>

0.04AU <sup>6</sup>

15AU 12.5

20AU 2.7

Amplitude of oscillation of Radial velocity of the host star (meter/second)

Method Description

debris disk.

presence of planets.

Table 5. Various methods of detecting exo-planets.[Shiga 2004],

Mass of the planet (×ME)

1 14 9.5 days

1 18 2.8 days

Sun Jupiter 11.86 yrs

Sun Saturn 30 yrs

years. Hence one will have to wait for that long to measure its periodicity.

Hence observational bias is towards heavier masses and shorter semi-major axis. Table (6) gives the radial velocity which have been detected [Schwarzschild 2004].

<sup>21</sup>2.6 days

<sup>1</sup>1 1AU 0.1

Table 6. A comparative study of the radial velocity of the host star for different

Lyot method

interferometry.

Radio emissions similar to those from Jupiter.

Mass of the host star (×MΘ)

Red dwarf –Gliese 436 0.5

μ- Arae

ρ Cancri sun-like

Sun-like star

combinations of star-planets.

Nulling

As seen from the Table(6), with decreasing mass of the planet and increasing mass of the host star, the amplitude of oscillation of the radial velocity decreases. As the amplitude of oscillation decreases it becomes increasingly difficult to decipher the periodic planetary signal in the presence of various noise sources that produce random fluctuations in star's apparent radial velocity.

Recently HARPS spectrometer has been developed by the Swiss team which discovered the first exoplanet Pegasi 51. This spectrometer has the required precision to decipher the tiny Doppler shift due to 0.1 m/s radial velocity of the host star harboring an earthlike planet. The instrument is kept in high vacuum and precisely controlled low temperature so that the sources of noise can be eliminated and optical stability may be imparted for obtaining the required precision. Through HARPS only Mu Arae's planet, 14 times ME, was detected.

By Astrometric measurements , the inclination of the planetary orbit and orbit-globe parameters can be determined. Astrometry is the precise measurement of two-dimensional stellar positions on the celestial sphere. The astrometric studies complement the radial velocity method. Through this method the ellipse traced by the centroid of the star during one orbital period of the planet can be exactly determined. From this ellipse the angle of inclination α and other globe-orbit parameters can be determined.

Space Interferometry Mission scheduled for 2009 will give sufficient accuracy to astrometric method for discovering a new planet.
