How to detect How to detect planets beyond planets beyond

our Solar system our Solar system

THE SUN THAT WE KNOWTHE SOLAR SYSTEM

THE NIGHT SKYThe Night Sky

PLANETS derive their name from the term “Wandering Stars”

Planets have been known even to the early cultures. But were viewed as emissaries of god .

Mayan Astronomy

The stone henge

Astronomers star gazing

Intensive telescope search (1930) - based on incorrect prediction!

Predicted by Newtonian Mechanics (1846)

“Naked Eye” planets

Telescope (1781)

Only few planets are visible to the unaided eye , while most remain undetected

Hence astronomers use indirect methods to discover planets beyond our Solar system.

THE METHODS INCLUDE:

a.Transit method.

a.Radial velocity method.

a.Pulsar timing.

TRANSIT METHODTRANSIT METHODOne of the simplest methods

Uses fundamental concepts like:

i.Concept of eclipseii.Variation in luminous intensity during

eclipseiii.Parallax method.

Understanding transiting motionUnderstanding transiting motion

The luminous intensity of the star observed by us changes when planet transits before the parent star.

Variation in the intensity α The size of planet.

Luminous intensity of star HD209458 dims by 1.7%

Applications of transit Applications of transit methodmethod

1.Determining the radius of the planet.

Makes use of light curve and parallax method

2. Study of planets upper atmosphere.

• Light emanating from the upper atmosphere is studied under high resolution stellar spectrum.

• Thus detecting elements in the atmosphere.

•3. Temperature of the planet

• Observed during secondary eclipse(when planet behind the star).

• Original light signal of star is obtained.

Light intensity of planet = a-b a= light intensity during secondary eclipse

b= intensity with planet transiting the star

The reading estimates the temperature and

Possibility of cloud formation.

Temperatures of various planets found using Transit method

Could this indicate presence of life.......................?

............Well the research is going on

ADDITIONAL INFORMATIONADDITIONAL INFORMATIONTemperature of some exoplanets:

TrES-1 = 1060k.

HD209458 = 1130k.

DISADVANTAGES OF DISADVANTAGES OF TRANSIT METHODTRANSIT METHOD

1.Planets need to be aligned with the astronomer’s vantage point.

Only about 10% of planets with small orbits have these alignment and this percentage decreases with size of the planet.

Probability of random alignment producing transit is mere 0.47%

This method suffers from high rate of false detection.

Hence transit method requires additional conformation

AND…….. radial velocity method provides this !

THE RADIAL VELOCITY METHOD

RADIAL VELOCITY METHODRADIAL VELOCITY METHOD• Radial velocity method too makes use of basic concepts such as :

1.Centre of mass.2.Spectral lines.3.Radial velocity.4.Dopplers effect.

• The motion of the planet and star system

A system of parent star and it’s planets is studied , with planet moving around the star.

Parent star wobbles(spins around the common cm)

During primary eclipse star moves towards us .

During secondary eclipse the planet tugs the star away from earth.

Starlight so obtained during this motion is studied under a spectrograph.

The absorption lines so obtained exhibit variation in the radial velocity of the star

These stellar spectral lines shift

towards the red end of spectrum as star moves away from earth

And towards the blue end of spectrum as it moves towards the earth

Variation in the radial velocity being measured

An actual observatory

The variation in the velocity up to 1m/s can be measured with modern spectrometers example: HARPS,HIRES etc.

HIRESHIRES

Radial velocity method has been the most productive technique used by planet hunters.

This method determines minium mass of the planet.

LIMITATIONSLIMITATIONSOnly sensitive towards large

Jupiter sized planets.

Insensitive towards rocky planets. Large investment of time & resources

Few planets discovered using radial velocity method

THE PULSAR TIMING

• Pulsars are dense remnant of stars that exploded as supernova.

• Pulsars emit electromagnet radiations at regular intervals.

•

Slight anomaly in the timing of the radio pulsars is. used to track the pulsar’s motion This forms the basis of pulsar timing.

Working of the pulsar motion

• Pulsar timing is very sensitive method

• Can detect planets as small as a 10th of the earth’s mass.

LimitationsLimitations• Pulsars are rare to find in the

universe hence it’s to detect planets is restricted

• The surrounding of pulsars contains intense em radiation, which is unsuitable for life forms.