The same region on Ganymede, as seen by Voyager-1 in 1979 and Juno in 2021
Click for full image.
When the Jupiter orbiter Juno did a close pass of the moon Ganymede on June 7, 2021, it took four pictures, covering regions mostly photographed for the first time by Voyager-1 in its close fly-by in 1979.
Scientists have now published the data from this new fly-by. Though Juno’s higher resolution pictures revealed many new details when compared with the Voyager-1 images from four decades earlier, the scientists found no changes. The comparison image, figure 2 of their paper, is to the right, reduced and sharpened to post here.
A flicker comparison between the registered JunoCam and Voyager reprojected mosaics revealed no apparent new impact features. Given the high albedo of fresh craters on Ganymede, with high albedo ejecta deposits two or three times the diameter of the craters themselves, we argue that new craters as small as 250 m diameter would be detectable in images at these 1 km per pixel scales. Extrapolating Ganymede cratering rates from Zahnle et al. (2003) below 1 km, the probability of JunoCam observing a new crater over 12.2 million km2 in 42 years is 1 in 1500, consistent with none being observed.
In other words, at these resolutions finding no new impacts is not a surprise.
Of the new features detected, the Juno images could see more details in the bright rays emanating from the crater Tros (in the lower center of both images), and thus found “…terrain boundaries previously mapped as ‘undivided’ or as ‘approximate’, several large craters, and 12 paterae newly identified in this region.”
Paterae resemble craters but are thought to be a some form of volcanic caldera. Their geological origin however is not yet completely understood.
The paper’s conclusion is actually the most exciting:
The insight gained from this handful of images makes it likely in our opinion that new observations from the upcoming JUICE and Europa Clipper missions will revolutionize our understanding of Ganymede.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Click for full image.
When the Jupiter orbiter Juno did a close pass of the moon Ganymede on June 7, 2021, it took four pictures, covering regions mostly photographed for the first time by Voyager-1 in its close fly-by in 1979.
Scientists have now published the data from this new fly-by. Though Juno’s higher resolution pictures revealed many new details when compared with the Voyager-1 images from four decades earlier, the scientists found no changes. The comparison image, figure 2 of their paper, is to the right, reduced and sharpened to post here.
A flicker comparison between the registered JunoCam and Voyager reprojected mosaics revealed no apparent new impact features. Given the high albedo of fresh craters on Ganymede, with high albedo ejecta deposits two or three times the diameter of the craters themselves, we argue that new craters as small as 250 m diameter would be detectable in images at these 1 km per pixel scales. Extrapolating Ganymede cratering rates from Zahnle et al. (2003) below 1 km, the probability of JunoCam observing a new crater over 12.2 million km2 in 42 years is 1 in 1500, consistent with none being observed.
In other words, at these resolutions finding no new impacts is not a surprise.
Of the new features detected, the Juno images could see more details in the bright rays emanating from the crater Tros (in the lower center of both images), and thus found “…terrain boundaries previously mapped as ‘undivided’ or as ‘approximate’, several large craters, and 12 paterae newly identified in this region.”
Paterae resemble craters but are thought to be a some form of volcanic caldera. Their geological origin however is not yet completely understood.
The paper’s conclusion is actually the most exciting:
The insight gained from this handful of images makes it likely in our opinion that new observations from the upcoming JUICE and Europa Clipper missions will revolutionize our understanding of Ganymede.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The print edition can be purchased at Amazon or from any other book seller. If you want an autographed copy the price is $60 for the hardback and $45 for the paperback, plus $8 shipping for each. Go here for purchasing details. The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Yet another example of the importance of having a decent optical camera on any deep space mission. I will remind listeners that Junocam was an afterthought, the original mission was planned without any form of optical camera.
The public loves ( us included ) pretty pictures from distant places… The scientific value of Junos photos Vs it’s gravitational measurements, ( which is why it is there in the first place…) Is debatable… The outreach value, and the PR is undoubtedly massive, and the science being returned by that little webcam is now shining in its own light.
Never, ever send something to the stars without a good optical camera…. For us, and for science!
Voyager had better optics-no matter how good your chip-cameras are-the lens make all the difference. Lots of places got rid of good, toggled, zoomable cameras in favor of chip cams hooked to desktops. A step down. I have learned to have litle trust in computer wunderkinds. Yes, Juno’s an add-on afterthought-I get it.
@Jeff, you are kinda correct.
A combination of high quality optics made of high quality glass and a super high resolution landing pad for the final image will never be beaten.
BUT… a cell phone scale camara , duckt taped to the outside of a probe ( as Junocam is essentially..) is still better than no cam.
As SpaceX launches show us, cam tech is amazing these days, we truly are living in the future!