the extrasolar planets
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DESCRIPTIONThe extrasolar planets. Detection techniques - future possibilities Angelo Angeletti Tolentino (MC), ITALY – 31 October, 2007. Extrasolar planets. – A bit of history – Detection techniques – Present results – Our observations – Future work. A bit of history. What is a planet?. - PowerPoint PPT Presentation
Detection techniques - future possibilities
Angelo AngelettiTolentino (MC), ITALY 31 October, 2007
PLANETARY RESEARCH TEAMEXOPLANETS TRANSITSEARCH THE SKY!ASSOCIAZIONE ASTROFILICRAB NEBULA COELUM ASTRONOMIA
A bit of history
Future workExtrasolar planets
What is a planet?
The term planet stems from a Greek word meaning wanderer. All celestial objects moving across the sky were dubbed planets, as opposed to the fixed stars. The list included the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn the only planets visible to the naked eye.
On 24 August, 2005, the International Astronomical Union (IAU) defined planet every celestial body which:
- orbits around the Sun;- is massive enough to attain a spherical shape;- has swept the region of its orbit clean of all the debrisA bit of history
The Solar SystemA bit of history
How did the Solar System form?The Sun and planets are believed to have formed from a contracting nebula of interstellar gas; the process took place about 4.6 billion years ago
According to modern theories, the primordial nebula was mainly composed of hydrogen and helium (though heavier elements and solid grains were also present) and it must have been very cold (10 K)A bit of historyThe Orion nebula. This gas cloud hosts the cradle of a number of stars.
How did the Solar System form?About 4.55 billion years ago, due to self-gravity, the density at the center of the primordial nebula grew steadily; further contraction gave birth to our Sun.
The process increased at the same time the rotation velocity as well as the centrifugal force. The outer parts of the nebula flattened to a disk, while still rotating around the newly-formed star.A bit of historyProtoplanetary disks (proplyds) in the Orion nebula
How did the Solar System form?During the final stages of the collapse a strong stellar wind must have set in, dragging the lighter elements outward mostly hydrogen and helium.A bit of historyAs the temperature of proto-Sun rose high enough to ignite thermo-nuclear reactions, some bodies inside the disk began to grow by collision and gravitational capture processes, sweeping their zone clean from debris. This led to the formation of the proto-planets, from which the present planets originated.The proto-Sun became a yellow main-sequence star.
How did the Solar System form?
The Working Group on Extrasolar Planets (WGESP) of the IAU defines as an extrasolar planet (shortened exoplanet) a body whose mass lies below the threshold value for the onset of deuterium thermo-nuclear fusion (which is about 13 Jupiter masses [MJ] for a typical solar composition) and at the same time is orbiting a star or a stars remnant - no matter how evolved. The minimum mass required is Mercurys - not Pluto!
Bodies less massive than 70 MJ (but still above the 13 MJ threshold) are to be considered brown dwarfs no matter how they formed.Free bodies (as those found in young stellar clusters) with masses below the 13 MJ limit are brown subdwarfs, not planets.A bit of history
Why search for extrasolar planets?
The search for exoplanets is a most recent field in Astronomy. Being strictly related to a number of hot topics in other cultural areas such as religion, philosophy and much more else it is increasingly becoming an issue of paramount importance. In due time perhaps earlier than we might expect! it may even give an answer to a crucial question in the history of mankind...A bit of history
Do other life forms and other inhabited worlds exist?
A bit of historyIn the past, the existence of extrasolar planets was reputed a plausible scenario. The first scientific discussions about the issue date back to 17th century.
Sir Isaac Newton was the first modern scientist to give credit to the existence of exoplanets (1713).
Supposedly confirmed reports of exoplanets discoveries abounded in 19th century.IsaacNewtonThe beginnings
A bit of historyA brand new research field opened up in 1984, when a circumstellar disk around the star Pictoris was detected.The beginnings
A bit of historySeveral discovery reports were issued in the following years.
1989: Latham detects a 10 MJ body circling the star HD 114762. 1991: Alexander Wolszczan identifies two planets about the same mass as Earths, revolving around a pulsar (PSR 1257+12).
1993: Gordon Walker claims that oscillations in radial velocity of the star Cephei might be caused by a 2 MJ planet.
However, such findings were considered too weird by most scientists to be taken very seriously.The beginnings
A bit of historyThe discoverers: Michel Mayor and Didier Queloz, of the Geneva Observatory On 6 October, 1995, in Florence, the discovery of a planet near the star 51 Pegasi is announced. This star is 50 light years away, and very similar to our Sun.The mass of the planet is about 160 terrestrial masses (0.5 MJ) ; it orbits very close to its star (7.5 million kilometers), in about 4 days.An artists impression of 51 PegasiThe beginnings
A bit of historyThe date of 6 October 1995 marks the beginning of a thorough, extensive search for extrasolar planets.The beginningsAt 30 October 2007, 260 exoplanets in 224 stellar systems had been discovered, located as follows:
198 single systems
18 double systems
6 triple systems
2 quadruple systems
Most exoplanets havent been actually seen through a telescope
Direct observation of an exoplanet is an exceedingly difficult task. Its light is usually much fainter (a millionth or even less) than its parent stars.Detection techniques2M1207 b one of the four extrasolar planets discovered through direct observation The various methods
Apart from a direct observation, several methods for detecting exoplanets have been developed. These are:
The astrometrical method
The radial velocity method
The transit method
The gravitational microlensing method
The timing methodDetection techniquesThe various methods
Detection techniquesThe astrometrical methodThe position of the star is measured with the highest possible accuracy, with the purpose to detect a displacement - however slight - caused by a planet (both bodies orbit around the center of mass).
For comparison, Jupiter when seen from a distance of 10 light years makes our Sun oscillate of about 1 millionth of grade, with a period of about 12 years.
Detection techniquesThe astrometrical methodBy this technique only very massive pianets and very close to their star can be detected: the so-called hot Jupiters.The mass of a hot Jupiter is the same as Jupiters or even more, but it revolves around the parent star at a distance less than 0.05 AU (7,5 million km), which is eight times closer than Mercury to our Sun.The typical temperature on the dayside can reach a thousand degrees Celsius.An artists impression of HD 209458b. The blue tail is the planets atmosphere, evaporating into space due to the close proximity of the parent star.
The gravity of a planet close to its star induces small variations in the stars radial velocity (i.e., the velocity along the line connecting Earth and the star). Such variations can be detected in the stars spectrum, by measuring the shift of the spectral lines. This gives information about the planets mass and orbiting distance.Detection techniquesThe radial velocity methodLine shifts are very small and are proportional to the planets mass.
This method has given the best results so far.
From the collected data, and making use of Keplers laws, some fundamental properties can be deduced namely, the orbital period, the distance from the parent star, plus an estimate of the planets mass (the last parameter depending on the orbits inclination as seen by the observer)Detection techniquesThe radial velocity method
A planet crossing the disc of its parent star (in so performing a transit), it causes a small eclipse; the stars brightness drops then slightly.In order to be able to detect a transit, two conditions are to be met:
Earth, planet and parent star must be sharply aligned (this seldom happens); Observations must take place just when the alignment is achieved.Detection techniquesThe transit method
Detection techniquesThe transit method
Detection techniquesThe transit methodOnly hot Jupiters have been detected during transits so far - plus, they had all been previously discovered with radial velocity measurements.
On 30 October, 2007 only 29 planets (out of a total reckoning of 260) had been seen transiting over the disc of their parent star.
Detection techniquesThe transit methodBy observing a transit the actual size of a planet can be estimated.
The next step is spectral analysis. This means taking two spectra - one as the planet crosses the stars disc, the other when it passes behind and its eclipsed by the star.
By subtracting the spectra one can then get useful information about the planets atmosphere.Another artists impression of HD 209458b.
Detection techniquesThe gravitational microlensing methodThis method makes use of a passing star intercepting the light path from another star thats much farther away. If both stars are aligned with respect to Earth, the gravity of the nearer bends the light rays coming from the farther (gravitational lens effect), enhancing its luminosity for a short time. If the passing star hosts a planet, a second luminosity peak can be observed.
Detection techniquesThe timing meth