Wednesday, March 30, 2016

Using 'smoothed light' to Detect ExoEarths?

Physicists of MIPT (Moscow Institute of Physics and Technology) and the Space Research Institute of the Russian Academy of Sciences developed optical technology for the "correction" of light coming from distant stars, which will significantly improve the "seeing" of telescopes and therefore will enable us to directly observe exoplanets as Earth-twins. Their work has been published in the Journal of Astronomical Telescopes, Instruments, and Systems (JATIS).

The first exoplanets (extra solar planets), which are the planets outside our solar system, had been discovered in the late 20th century, and now we have detected of more than two thousand of them. It is almost impossible to see the faint light of the planets themselves without special tools -- it is saturated "overshadowed" by the radiation of parent star. Therefore exoplanets are discovered by indirect methods: by registration of the weak periodic fluctuations in the luminosity of the star when a planet passes in front of its disk (the transit method), or by spectral translational vibrations of the star itself from the impact of the planet's gravity (the radial-velocity method). For the first time, in the late 2000s, astronomers were able to directly obtain images of exoplanets. So far we have about 65 of such images. To obtain them, the scientists use stellar coronagraphs first created in 1930s for observations of the solar corona outside eclipses known as solar coronagraphs. These devices have a focal mask - an "artificial moon" inside them, which blocks some part of the field of view -- ultimately, it covers the solar disk, allowing you to see the dim solar corona.

To repeat this technique for the stars, we need a much higher level of accuracy and much higher resolution of the telescope, which accommodates a coronagraph. Apparent size of the orbit of Earth-type planets, nearest to us, is about 0.1 arcseconds. This is close to the resolution limit of modern space telescopes (for example, the resolution of the space telescope Hubble is about 0.05 seconds). To remove the effects of atmospheric distortions in ground-based telescopes, scientists use adaptive optics -- mirrors that can change shape while adjusting to the state of the atmosphere. In some cases, the mirror shape can be maintained with an accuracy of 1 nanometer, but such systems do not keep pace with the dynamics of atmospheric changes and are extremely expensive.

A team led by Alexander Tavrov, an associate professor at MIPT and the Head of the Planetary Astronomy Laboratory at the Space Research Institute of the Russian Academy of Sciences, has found a way to obtain the highest resolution, while using relatively simple and inexpensive systems of adaptive optics.

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