A newly installed planetary radar system on the Green Bank Radio Telescope will probe the solar system in detail.
This may look like an ordinary visible-light image . . . in reality, it’s anything but.
The image was constructed using a new 700-watt transmitter installed at the Green Bank Observatory in West Virginia, which sent the radar signal to the Moon. A network of radio telescopes caught the reflected signal to create the image of the Hadley Rille feature snaking near the Apollo 15 landing site.
The image shows features as small as five meters across; for context, the base of the descent stage — the largest piece of hardware left on the lunar surface during the Apollo missions — is just shy of five meters.
A Next-generation Planetary Radar
The loss of the Arecibo radio telescope in Puerto Rico late last year left a gap in terms of planetary radar. The instruments suspended above Arecibo's 305-meter dish were the most powerful planetary radar system in the world. The 1-megawatt transmitter actively pinged near-Earth asteroids to paint their ghostly profiles, revealing astonishing detail such as binary systems and even tiny moonlets.
The new radar at Green Bank is the result of a two-year collaboration between the National Radio Astronomy Observatory (NRAO), the Green Bank Observatory, and Raytheon Intelligence & Space. Raytheon designed the powerful radio transmitter installed at Green Bank.
Green Bank transmits the signal that’s received by the NRAO's Very Long Baseline Array, a collection of 10 radio telescopes spanning the contiguous United States, Hawaii and St. Croix in the Caribbean. These individual telescopes work together via radio interferometry to achieve the resolution of a single giant radio telescope. The team hopes to share additional radar results late this summer.
A New Road for Green Bank
With a 100-meter (328-foot) dish located in the National Radio Quiet Zone in eastern West Virginia, Green Bank Observatory hosts the largest fully steerable radio telescope in the world. The observatory began operations in 1956, and astronomers have used the radio dish to study galactic evolution, pulsars, compact radio sources and more. Closer to home, Green Bank has also been used to track spacecraft, follow comets, and measure the spin rate of solar system objects such as Mercury and Europa.
The Green Bank Telescope suffered its own collapse in 1988 before returning to full operation. In 2016, the facility separated from the NRAO due to funding issues. Green Bank and the NRAO now operate under separate contracts with the National Science Foundation, in partnership with Associated Universities Incorporated.
“This project opens a whole new range of capabilities,” says Tony Beasley (NRAO) in a recent press release. “We’ve participated before in important radar studies of the solar system, but turning the Green Bank Telescope into a steerable planetary radar transmitter will greatly expand our ability to pursue intriguing new lines of research.”
A Look Ahead
The ultimate plan is to incorporate a 500-kilowatt high-power radar to produce radar images with an unprecedented level of resolution. The Green Bank and VLBA system will be capable of imaging solar system objects out to the orbit of Neptune.
“The planned system will be a leap forward in radar science, allowing access to never-before-seen features of the solar system from right here on Earth,” says Karen O’Neil (Green Bank Observatory site director) in a recent press release.
If the amazing Apollo 15 landing site image is any indication, we can expect to see some impressively high-resolution radar in the years to come.