Abstract Details
| Name: Nithin Mohan Affiliation: Vikram Sarabhai Space Center, ISRO, Trivandrum Conference ID: ASI2015_570 Title : Radio Observation of Venus at Meter Wavelengths using the GMRT Authors and Co-Authors : Subhashis Roy(2), Govind Swarup(2), Divya Oberoi(2), Niruj Mohan Ramanujam(2), C. Suresh Raju(1), and Anil Bhardwaj(1) 1-Space Physics Laboratory, VSSC, Trivandrum,  695022, Kerala, India; 2-National Center for Radio Astrophysics, TIFR, Pune, 411007, Maharashtra, India. Abstract Type : Oral Abstract Category : Sun and the Solar System Abstract : The dense atmosphere of Venus limits the use of visible light for probing the surface of Venus. The temperature of the surface of Venus has been measured by Venera landers as about 740 K, with little variation during the day and night, due to the greenhouse effect by its dense Carbon Dioxide dominated atmosphere. The surface of Venus has been explored by measuring radar reflections and thermal radio emission at microwave frequencies (cm/decimeter wavelengths) by several observers using the Earth-based and the space borne observations. Models based on these observations have not been able to explain values of the brightness distribution of Venus at metre wavelengths. We describe observations of Venus made at 610, 325 and 244 MHz using the Giant Metrewave Radio Telescope (GMRT). Observations were made during March 21-27, 2004 when the Venus had a diameter of ~ 21.5 arcsec. The resulting beamwidth of the GMRT was ~ 6, ~ 12 and ~ 24 arcsec at 610, 325 and 244 MHz, respectively. The derived brightness temperature (Tb) of Venus was 485 K, 430 K and < 330 K with errors of < 10 %, respectively, for the above frequencies. These values are consistent with values of about 550 K measured at 608 MHz and 430 MHz during 1970s by previous workers (see Condon et al. 1973) and are much lower than those measured at higher frequencies, e.g. 679.9 K +/- 13.6 at 4.86 GHz by Butler et al. 2001 using the VLA. The microwave observations (cm wavelengths) of Tb of Venus have been explained in the literature by considering emission from its atmosphere, surface and sub-surface. For explaining lower values of Tb at frequencies < 1 GHz (metre wavelengths), we propose a new model in which heat flows from the hot surface of Venus towards the interior and radiation arises at longer wavelengths further down from the surface of Venus at lower physical temperature. It is planned to develop a detailed radiation transfer model. |