Planetary Science and Media

Mohammad Abuzar Sikandar Malik

103945170

Assignment 2 – Planetary science and Media

The night sky is littered with stars, most not even bright enough to see with the naked eye. The Milky Way alone has an estimated 400-100 billion stars. Contemplating these huge numbers it is hard to not think about the possibility that there might be planets orbiting these stars. Are these planets similar to earth and can they sustain life? Surely planets outside of our solar system exist? Given how unimaginably vast the universe and even our galaxy is, it is mathematically impossible for our solar system and its eight planets to be an isolated incident. People wonder about these kinds of existential question from time to time and in order to quench their curiosity they turn to mainstream media or the internet. The average person doesn’t have enough time and knowledge to properly research and thus must rely on whatever the top Google search answer is on the topic, which usually is an article from a news website. News media affects our reality by persuading us that news in not a form of entertainment, but rather something significantly more commendable, imperative stuff that we consume in an attempt to better make sense of our world.

In 1995 51 Pegasi b was discovered, approximately 50 million light years away this planet with the mass of Jupiter was the first ever exoplanet orbiting a sun-like star to be discovered. Its discovery was made by using the Doppler spectroscopy method (Mayor & Queloz 1995), an indirect method for discovering extra-solar planets. As the planet orbits around its parent star the planet’s gravitational influence causes the star to periodically moves towards and away from us. The Doppler Effect causes the light we receive from the star to be blue shifted when the star moves towards us and a red shifted when the moves away from us. The alternating blue and red shifts indicate orbital motion around the star.

The Doppler method is effective when searching for planets that orbit near their parent star and is less sensitive to planets with larger orbits and smaller sizes; therefore the Doppler method should be supplemented by another approach, The Transit method or the photometric method.

The transit method relies on the fact that the orbital tilt of the exoplanet is aligned with that of earth. As a result the planet transits across the face of its parent star. As a consequence of this transit there is measurable dip in the brightness of the star. As stars naturally show a variation in their brightness this fall in brightness must be observed periodically. Transiting planets also cause a perceptible eclipse, when the planet goes behind the star there is a decline in the total brightness of the system. Eclipse observations are more profound in infrared as planets have greater infrared footprints than stars.    

HD 209458b, confirmed in 1999, was the first know transiting planet (initially discovered by Doppler method but transit method confirmed its status as an exoplanet). It orbits the sun-like star HD 209458 some 150 million light-years away. Every 3.5 days, because of the transit of HD 209458b, the star is dimmed by about 2%.  (Charbonneau et al 2000). The first planet discovered purely by the transit method was  OGLE-TR-56b, in 2002.

A major fraction of planets will go undiscovered because of the transit methods biggest flaw, that it can only detect planets that by chance have their orbit in the same inclination as ours. There is no way around this problem and is only counterbalanced by observing large number of stars.

Another major disadvantage of the transit method is its high rate of false positive result, as much as 40%. Thus other methods must be used in conjunction with the transit method. Many other techniques and methods can be used in the search for exoplanets, but doppler and transit methods have proven to be the most successful by indentifying around 3000 confirmed planets.

Since the 90s exoplanet discovery missions using all detection methods have been indentified and confirmed 3,621 extra solar planets. And perhaps the most famous of these missions are the Kepler mission and the upcoming James Webb space telescope (JWST).

The Kepler space observatory was launched by NASA in 2009 and as of July 2017 has discovered more than 2,300 planets. Its primary method of detection is the transit method, and is circumvents the flaws of the aforementioned method by observing huge number of stars. Originally pointed at the northern constellations of Cygnus, Lyra and Draco, the Kepler observed around 145,000 main sequence stars in the Milky Way. In order to catalog planets with longer orbits the original mission was planned for about 4 years but has elapsed for around 8 years and is projected to continue until 2018.

The Kepler mission was designed with the sole purpose of looking for terrestrial and larger planets in or near the habitable zone around a sun like star. Looking for terrestrial planets, specifically the ones in the habitable zone of their stars where water might exist in liquid form on the surface of the planet, is the first step towards finding life on another planet or suitable new world away from earth.

The exoplanets are abundant and diverse. With smaller more dense worlds being prevalent and larger Jupiter, Neptune and Saturn size planets begin less common. Akin to our solar system, where there is plethora of terrestrial bodies (planets, moons and asteroids) and only four Jovian giants. The biggest planet discovered has twice the radius of Jupiter despite having the same mass and the smallest one being only as big as our moon. Majority Extra-solar planets have been discovered orbiting very close to their parent star, in orbits smaller (with quite unconventional and out-stretched shapes) than that of mercury and none of them orbit as far out as the Jovian planets. Orbiting that close to the star means that they have high temperatures and have heated and extended atmospheres. Atmospheric compositions were determined by studying transmission photometry and direct emission data from some planets. Water, carbon dioxide, carbon monoxide and sulfur have been found in the atmosphere of these planets. With the JWST our study of atmospheric composition would improve greatly as scientists, with the JWST’s infrared capabilities, will be able to tell what molecules and chemicals there are in the atmosphere.