THE SEARCH FOR EXTRATERRESTRIAL INTELLIGENCE

Posted by admin_akashic on Jun 27th, 2022 in Space

measuring the frequencies of its light to determine how fast it is approaching or receding (Campbell, 1990). The ‘Doppler effect’ is the observed change in the wavelength emitted by a star due to its motion. Light from far-off stars, which are moving away from us because of the expansion of the universe, has a longer wavelength. This is known as the ‘red shift’. If the star were moving towards us it would exhibit a shorter wavelength or ‘blue shift’. A tiny fluctuation from a red to a blue shift indicates that something is causing the star to wobble.

The distribution of angular momentum (or the amount of spin) could provide indirect evidence of a planetary system. A slowly spinning star could be so because of the gravitational effect of its planets. The rate of spin can be detected by a study of the light it emits. Its movements affect the frequencies of light that reaches us due to the Doppler effect. A star with an orbiting companion will oscillate as it goes into its counter-orbit. This can be seen in the case of double stars. But it is harder to detect any change in velocity with presumed planets, as the oscillatory effect would be smaller. However, during the 1990s improvements in observation techniques, including spectral analysis, enabled fairly accurate measurements of the velocities of stars and their speed changes as low as 30 mph. Doppler techniques were to prove successful, leading to a spate of observations at the close of the twentieth century. Many of these announcements followed a search for wobble which showed up as Doppler shifts in a star’s spectrum due to the gravitational influence of orbiting planets.

Until 1995 no true observations of ex-solar planets had been detected, but by the end of 1996 more than twelve had been confirmed and more were expected. The American, David Latham, of the Harvard-Smithsonian Center for Astrophysics, with Michel Mayor at the Geneva Observatory, discovered that the star, HD116762, which is about 90 light years away, has a regular oscillation indicative of a massive planet about eleven times the size of Jupiter which completes its orbit in eighty-four days (Heidmann, 1995: 17). In October 1995, Mayor and Didier Queloz of the Geneva Observatory detected a wobble in the star 51 Pegasi, which is held to be caused by a Jupiter-sized planet (Mayor and Queloz, 1995). In January 1996, Geoff Marcy of San Francisco State University and Paul Butler of the University of California claimed to have detected wobbles caused by two planets; one in the constellation of Virgo which is about 6.5 times the mass of Jupiter and another in the Great Bear, which is allegedly 2.3 times the mass of Jupiter. Both are about 35 light years from the Earth. In January of 1996 Chris Burrows of the Space Telescope Institute in Baltimore, Maryland, cited supporting evidence of a planet from an image taken by the Hubble telescope which revealed a slight warp in the disk around Beta-Pictoris, which is about 50 light years away (Walker, 1996).

In June 1998, scientists reported a planet about 1.6 times as big as Jupiter orbiting the star, Gliese 876, which is 15 light years away. The alleged planet was detected by observing the ‘wobble’ of its parent star. The Gliese is a very low mass star only about one-third that of the Sun. But if there are planets so close to the solar system near an uncharacteristic star like Gliese 876, then this would

suggest that planetary systems are fairly widespread. So far, it has been mainly gas giants that have been observed, but large rocky planets are being discovered as techniques improve, and the detection of Earth-type rocky planets cannot be far off. Early in 2000 astronomers using the Keck Telescope in Hawaii found one rocky planet less than the size of Saturn orbiting the star HD46375, which is 109 light years away in the constellation Monoceros, and another planet of similar size around 79 Ceti, which is 117 light years away in the constellation Cetus. These discoveries suggest that the existence of smaller rocky planets may be fairly widespread.

An analysis of a star’s Doppler shift in December 1999 preceded claims that a planet estimated at twice the diameter and eight times the mass of Jupiter orbits the star, Tau Boötis, which is a Sun-sized star 51 light years from Earth. Its orbit is so close to the parent star that its atmosphere is 1500ºC, which, according to prevailing theory, is hot enough for its clouds to include molten iron, as well as sodium and potassium (Adler, 1999: 4). This means that the planet will absorb most of the light reaching its atmosphere. A team of astronomers from the University of St Andrews employed spectral analysis to separate the light emanating from the planet from the glare of Tau Boötis, using data from the 4.2 metre Herschel telescope at La Palma (ibid.: 4).

The detection of planets is of clear benefit to SETI research, and will have a profound effect on current theories of planetary formation. Unfortunately, if a planet is large enough to affect the motions of a star to any significant amount, it would be an unlikely candidate for life similar to that found on Earth. Observa-tional methods leading to the satisfactory detection of Earth-sized rocky planets will be greatly enhanced by successors to the Hubble space telescope and space platforms, although major technical problems still have to be solved with regard to the need to separate images of the planet from the background light of the star. For this reason, ground-based telescopes are limited to observations of wobbles and shadows of planets larger than Jupiter. However, an array of infrared telescopes on a space station could detect Earth-sized planets directly, which are currently obscured from ground-based telescopes by the glare of scattered light from their parent stars. Proposals are underway for a 50-metre array of four infrared telescopes which could be situated near Jupiter’s orbit, at an estimated cost of US$2 billion (Hecht, 1996).

Even with advances in optical equipment there are still major problems in the identification, eradication and control of systematic errors. But dramatic future developments in the technology required for planetary observation should not be ruled out in the immediate future. During the 1840s Auguste Comte outlined limits on our knowledge of heavenly bodies, stating that we could never know anything of their chemical or mineralogical structure. This was but a few decades before the invention of the spectroscope. Nowadays analysis of the chemical and mineralogical features of objects in space is one of the central tasks conducted by astronomers.