Observing the Surface of Venus with the Arecibo Telescope

This past summer I had the opportunity to operate the world’s largest single-dish telescope at the Arecibo Observatory in Puerto Rico. Before my current position as a postdoctoral researcher at the Museum’s Center for Earth and Planetary Studies (CEPS), I had never operated such a large instrument, much less a 305 meter- (1,000 feet-) wide telescope. During my 10-day observation trip, I used the telescope to take measurements of Venus. My research at the Museum centers on investigating the radar properties of planetary surfaces using a combination of orbital and telescopic data. For my research on Venus, I have used radar data collected by the Magellan Mission, a spacecraft that orbited Venus in the early 1990s, and the Arecibo Observatory.

Venus is sometimes referred to as Earth’s twin because the two planets are similar in size, density, and average composition. Many of the same geologic processes are observed on the two planets as well. For instance, Venus has many shield volcanoes, mountain belts, and lava flows like Earth. Here at CEPS we are particularly interested in the distribution of crater ejecta, the material ejected while a crater is being formed. Typically on Venus, crater ejecta are deposited on the surface in parabola (curved) shapes that open to the west. If this material is deposited onto tesserae (highly deformed, radar-bright terrains that represent the oldest surface materials on Venus; see the Arecibo image of Alpha Regio below), it can obscure measurement of the true composition of tesserae. We are working to detect tesserae not contaminated by crater ejecta that could be targeted by future orbital and landed missions to Venus.

Before arriving in Puerto Rico, I had seen the Arecibo Telescope in movies (like Contact) and pictures and thought it looked rather impressive, but nothing compared to seeing it in person. The telescope is HUGE, built inside a depression left by a sinkhole. The sinkhole provided a natural location for the telescope and it also helps to shield the telescope from unwanted radio noise that would interfere with measurements. I fully appreciated the size of the telescope once I was standing above it on the platform that houses all of the instrumentation required to send and receive radio signals. Since the dish is immobile, the suspended platform can be moved to track different objects as they traverse the sky. The instruments are mounted on a linear track, which itself is attached to a circular platform that can rotate 360°, allowing the receiver to move from one side of the dish to the other.

  The 305 meter-wide dish does not have a smooth surface, but is made up of thousands of aluminum panels that are supported by a mesh of steel cables. Everything has to be tightened by hand. I got to the telescope operations center early on an observation day and was treated to a quick tour underneath the collecting dish. It looks like another world. The vegetation is lush, but it’s pretty shady, and there is a metal ceiling above you. Being directly above or below the dish emphasizes the lattice spacing of the dish panels.

We had 10 observation days lined up to measure Venus. We needed all of that time in order to make several repeat observations during our allotted window. Repeat measurements enable us to produce a higher resolution data product. Venus was in inferior conjunction, meaning that the planet was closest to Earth at this time, giving us the highest possible resolution views of the surface. Our telescope time usually started mid-morning and involved warming up and positioning the telescope for observations and ended in the early afternoon after Venus moved outside of the view of the telescope. The observation run was highly successful and I am excited for all of the interesting science that will come out of these measurements!