Universe - Alien Worlds
Universe - Alien Worlds

Universe – Alien Worlds: The Search for Second Earth episode 2

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  • Post published:November 1, 2021
  • Post category:Science

Universe – Alien Worlds: The Search for Second Earth episode 2: Humans have long gazed up at the night sky, wondering whether other lifeforms and intelligences could be thriving on worlds far beyond our own.



Answering that question seemed fated to remain pure speculation. But over the last few decades, ultra-sensitive telescopes and dogged detective work have transformed alien planet-hunting from science fiction into hard fact. Gone are the days of speculation; the hunt for extraterrestrials has become a matter of serious scientific inquiry.

As the hunt for alien worlds began, we expected to find worlds similar to the planets in our own solar system, but we instead discovered a riot of exotic worlds. Vivid animation based on data from the most successful planet hunter of them all, the Kepler space telescope, brings these worlds into view: puffy planets with the density of polystyrene, unstable worlds orbiting two suns and 1,000-degree, broiling gas giants with skies whipped into titanic winds.

But perhaps the most startling discovery was the number of worlds that may be contenders for a second Earth. Our latest survey of the galaxy estimates that there are billions of rocky planets at the right distance from their sun to have that ingredient so crucial for life as we know it, liquid water. Amongst them, we witness the most tantalizing discovery of all: a so-called ‘super-Earth’, situated in the Goldilocks zone – the area just the right distance from a sun to potentially support life – and with the faint signal of water in its atmosphere.

With over 2,800 exoplanets confirmed by Kepler and discoveries still rolling in, Brian Cox lays out his own answer to the age-old question with thrilling new science: are we alone?


Universe – Alien Worlds: The Search for Second Earth episode 2



An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917, but was not recognized as such. The first confirmation of detection occurred in 1992. This was followed by the confirmation of a different planet, originally detected in 1988. As of 1 October 2021, there are 4,843 confirmed exoplanets in 3,579 planetary systems, with 797 systems having more than one planet.

There are many methods of detecting exoplanets. Transit photometry and Doppler spectroscopy have found the most, but these methods suffer from a clear observational bias favoring the detection of planets near the star; thus, 85% of the exoplanets detected are inside the tidal locking zone. In several cases, multiple planets have been observed around a star. About 1 in 5 Sun-like stars have an “Earth-sized” planet in the habitable zone. Assuming there are 200 billion stars in the Milky Way, it can be hypothesized that there are 11 billion potentially habitable Earth-sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included.

The least massive planet known is Draugr, which is about twice the mass of the Moon. The most massive planet listed on the NASA Exoplanet Archive is HR 2562 b, about 30 times the mass of Jupiter, although according to some definitions of a planet (based on the nuclear fusion of deuterium), it is too massive to be a planet and may be a brown dwarf instead. Known orbital times for exoplanets vary from a few hours (for those closest to their star) to thousands of years.

Some exoplanets are so far away from the star that it is difficult to tell whether they are gravitationally bound to it. Almost all of the planets detected so far are within the Milky Way. There is evidence that extragalactic planets, exoplanets farther away in galaxies beyond the local Milky Way galaxy, may exist. The nearest exoplanets are located 4.2 light-years (1.3 parsecs) from Earth and orbit Proxima Centauri, the closest star to the Sun.

Kepler space telescope

The Kepler space telescope was a space telescope launched by NASA to discover Earth-size planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched on March 7, 2009, into an Earth-trailing heliocentric orbit. The principal investigator was William J. Borucki. After nine and a half years of operation, the telescope’s reaction control system fuel was depleted, and NASA announced its retirement on October 30, 2018.

Designed to survey a portion of Earth’s region of the Milky Way to discover Earth-size exoplanets in or near habitable zones and estimate how many of the billions of stars in the Milky Way have such planets, Kepler’s sole scientific instrument is a photometer that continually monitored the brightness of approximately 150,000 main sequence stars in a fixed field of view. These data were transmitted to Earth, then analyzed to detect periodic dimming caused by exoplanets that cross in front of their host star. Only planets whose orbits are seen edge-on from Earth could be detected. Kepler observed 530,506 stars and detected 2,662 planets.

Professor Brian Cox – Universe – Alien Worlds

Brian Edward Cox (born 3 March 1968) is an English physicist and former musician who is a professor of particle physics in the School of Physics and Astronomy at the University of Manchester. He is best known to the public as the presenter of science programmes, especially the Wonders of… series and for popular science books, such as Why Does E=mc²? and The Quantum Universe.

Cox has been described as the natural successor for the BBC’s scientific programming by both David Attenborough and Patrick Moore. Before his academic career, Cox was a keyboard player for the British bands D:Ream and Dare.