Tag Archives: radar

A projection of the radar data of Venus collected in 2012. Striking surface features -- like mountains and ridges -- are easily seen. The black diagonal band at the center represents areas too close to the Doppler “equator” to obtain well-resolved image data. Credit: B. Campbell, Smithsonian, et al., NRAO/AUI/NSF, Arecibo

NRAO Image Release: Venus, If You Will, as Seen in Radar with the GBT

Radar astronomy is a bit different from radio astronomy as in radar astronomy active observations are performed means a signal is sent from Earth which bounces back from an object and then this signal is analyzed to obtain images or other relevant information. In case of radio astronomy we perform passive observations and no signal is sent from earth and only signals from various sources are received to perform analysis. Radar astronomy is more suitable for nearby celestial objects as sending and receiving the bounced back signal in reasonable time is impossible for objects many light years away.


 

From earthbound optical telescopes, the surface of Venus is shrouded beneath thick clouds made mostly of carbon dioxide. To penetrate this veil, probes like NASA’s Magellan spacecraft use radar to reveal remarkable features of this planet, like mountains, craters, and volcanoes. 

Recently, by combining the highly sensitive receiving capabilities of the National Science Foundation’s (NSF) Green Bank Telescope (GBT) and the powerful radar transmitter at the NSF’s Arecibo Observatory, astronomers were able to make remarkably detailed images of the surface of this planet without ever leaving Earth. 

The radar signals from Arecibo passed through both our planet’s atmosphere and the atmosphere of Venus, where they hit the surface and bounced back to be received by the GBT in a process known as bistatic radar.

A projection of the radar data of Venus collected in 2012. Striking surface features -- like mountains and ridges -- are easily seen. The black diagonal band at the center represents areas too close to the Doppler “equator” to obtain well-resolved image data. Credit: B. Campbell, Smithsonian, et al., NRAO/AUI/NSF, Arecibo
A projection of the radar data of Venus collected in 2012. Striking surface features — like mountains and ridges — are easily seen. The black diagonal band at the center represents areas too close to the Doppler “equator” to obtain well-resolved image data. Credit: B. Campbell, Smithsonian, et al., NRAO/AUI/NSF, Arecibo


This capability is essential to study not only the surface as it appears now, but also to monitor it for changes. By comparing images taken at different periods in time, scientists hope to eventually detect signs of active volcanism or other dynamic geologic processes that could reveal clues to Venus’s geologic history and subsurface conditions.

High-resolution radar images of Venus were first obtained by Arecibo in 1988 and most recently by Arecibo and GBT in 2012, with additional coverage in the early 2000s by Lynn Carter of NASA’s Goddard Spaceflight Center in Greenbelt, Md. The first of those observations was an early science commissioning experiment for the GBT.

“It is painstaking to compare radar images to search for evidence of change, but the work is ongoing. In the meantime, combining images from this and an earlier observing period is yielding a wealth of insight about other processes that alter the surface of Venus,” said Bruce Campbell, Senior Scientist with the Center for Earth and Planetary Studies at the Smithsonian’s National Air and Space Museum in Washington, D.C. A paper discussing the comparison between these two observations was accepted for publication in the journal Icarus.  

The 100-meter Green Bank Telescope is the world’s largest fully steerable radio telescope. Its location in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone protects the incredibly sensitive telescope from unwanted radio interference, enabling it to perform unique observations.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

These three images, created from Cassini Synthetic Aperture Radar (SAR) data, show the appearance and evolution of a mysterious feature in Ligeia Mare, one of the largest hydrocarbon seas on Saturn's moon Titan.
Image Credit: NASA/JPL-Caltech/ASI/Cornell

Cassini Watches Mysterious Feature Evolve in Titan Sea

By Preston Dyches


 

NASA’s Cassini spacecraft is monitoring the evolution of a mysterious feature in a large hydrocarbon sea on Saturn’s moon Titan. The feature covers an area of about 100 square miles (260 square kilometers) in Ligeia Mare, one of the largest seas on Titan. It has now been observed twice by Cassini’s radar experiment, but its appearance changed between the two apparitions.

Images of the feature taken during the Cassini flybys are available at:

http://photojournal.jpl.nasa.gov/catalog/PIA18430

The mysterious feature, which appears bright in radar images against the dark background of the liquid sea, was first spotted during Cassini’s July 2013 Titan flyby. Previous observations showed no sign of bright features in that part of Ligeia Mare. Scientists were perplexed to find the feature had vanished when they looked again, over several months, with low-resolution radar and Cassini’s infrared imager. This led some team members to suggest it might have been a transient feature. But during Cassini’s flyby on August 21, 2014, the feature was again visible, and its appearance had changed during the 11 months since it was last seen.

Scientists on the radar team are confident that the feature is not an artifact, or flaw, in their data, which would have been one of the simplest explanations. They also do not see evidence that its appearance results from evaporation in the sea, as the overall shoreline of Ligeia Mare has not changed noticeably.

The team has suggested the feature could be surface waves, rising bubbles, floating solids, solids suspended just below the surface, or perhaps something more exotic.

The researchers suspect that the appearance of this feature could be related to changing seasons on Titan, as summer draws near in the moon’s northern hemisphere. Monitoring such changes is a major goal for Cassini’s current extended mission.

“Science loves a mystery, and with this enigmatic feature, we have a thrilling example of ongoing change on Titan,” said Stephen Wall, the deputy team lead of Cassini’s radar team, based at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We’re hopeful that we’ll be able to continue watching the changes unfold and gain insights about what’s going on in that alien sea.”

These three images, created from Cassini Synthetic Aperture Radar (SAR) data, show the appearance and evolution of a mysterious feature in Ligeia Mare, one of the largest hydrocarbon seas on Saturn's moon Titan. Image Credit: NASA/JPL-Caltech/ASI/Cornell
These three images, created from Cassini Synthetic Aperture Radar (SAR) data, show the appearance and evolution of a mysterious feature in Ligeia Mare, one of the largest hydrocarbon seas on Saturn’s moon Titan.
Image Credit: NASA/JPL-Caltech/ASI/Cornell

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and ASI, the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the United States and several European countries.

Source: NASA