Venus imaged with the Hat Creek interferometer in the J = 1 − 0 CO line

Abstract

We have observed the J = 1 − 0 transition of carbon monoxide and the 2.7-mm continuum emission from Venus with the three-element millimeter interferometer of the Hat Creek Radio Observatory. The observations were carried out during January 1987, when Venus was at Western elongation. The 2.7-mm image shows a 10% increase in brightness temperature from the day to the night side. Since the variation in brightness temperature is larger than expected from physical variations in temperature, it is most likely to be associated with opacity variations in the atmosphere, perhaps related to atmospheric clouds. The CO line was observed at low (1.25 MHz) and high (40 kHz) spectral resolution. The shape of the spectra varies across the disk of the planet, with broad and shallow lines on the dayside and deep and narrow lines on the nightside. CO model fits to these spectra suggest that the CO at high altitudes (> 90 km) decreases from night to day on the planet, while the CO at low altitudes (< 85 km) may show a general increase.