In August and September 1977, two Voyager spacecraft were launched on a Grand Tour of the solar system. In 1973, the mission had been named Mariner Jupiter-Saturn 1977 (MJS ‘77) and was intended to go only as far as Jupiter and Saturn.
In March 1977 the mission name was changed to Voyager. In October 1978, a Voyager Fact Sheet mentioned the possibility of sending Voyager 2 to Uranus and Neptune. It would happen only if the primary science objectives were met at Saturn first. Even though the extended mission was not certain before launch, Voyager engineers (unofficially) designed and built the spacecraft to be capable of navigating to Uranus and Neptune, and surviving the longer trip. On-board computers were reprogrammed during the voyage, giving the spacecraft the ability to successfully return many more images and much more information than were expected. It’s unlikely the Voyager team imagined that both spacecraft would still be operating 40 years after launch.
For more information about the history of JPL, contact the JPL Archives for assistance. [Archival and other sources: Various Voyager and JPL History web pages; Voyager Fact Sheet, 10/6/1978; Section 260 photo album and index.
The end of 1609 and the first months of 1610 mark the beginning of modern astronomy. 400 years ago today, January 7th, Galileo Galilei looked up towards the constellation Orion. He aimed his telescope at an object brighter than any of the surrounding stars - the planet Jupiter.
The view through his telescope startled him. He did not see only one object, but rather, one large world, with four smaller objects nearby.
These four objects are the moons we now call Io, Europa, Ganymede and Callisto.
Galileo wrote in his book Sidereus Nuncius, which was published in 1610 the following words:
"I should disclose and publish to the world the occasion of discovering and observing four Planets, never seen from the beginning of the world up to our own times, their positions, and the observations made during the last two months about their movements and their changes of magnitude; and I summon all astronomers to apply themselves to examine and determine their periodic times, which it has not been permitted me to achieve up to this day . . . On the 7th day of January in the present year, 1610, in the first hour of the following night, when I was viewing the constellations of the heavons through a telescope, the planet Jupiter presented itself to my view, and as I had prepared for myself a very excellent instrument, I noticed a circumstance which I had never been able to notice before, namely that three little stars, small but very bright, were near the planet; and although I believed them to belong to a number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude . . .When on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night."
"I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury around the Sun; which was at length established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions around Jupiter."
On the 400th anniversary of their first sighting, use a pair of binoculars to spot Galileo's four tiny moons directly next to the planet. On the evening of January 7 look to the southwest after sunset. Europa and Ganymede will appear to the upper left and Io and Callisto on the lower right of Jupiter.
Letters with translations http://www2.jpl.nasa.gov/galileo/ganymede/discovery.html
We've had such great feedback and comments to our earlier post about the recent impact at Jupiter that we wanted to give you more details, plus answer some questions. My name is Glenn Orton, a senior research scientist at JPL. My colleague and fellow JPL blogger Leigh Fletcher is on a well-deserved vacation for a bit, and he filled in for me while I was at a conference talking about another aspect of our research and the Jupiter impact last week.
I've been on Anthony Wesley's email list (as I am for many in the amateur astronomy community) for some time, so it wasn't happenstance that I was aware of his Jupiter observation. Anthony is the Australian-based amateur astronomer who alerted the world to this big impact. When we received news of his discovery, we immediately wanted to verify it with some of the sophisticated telescopes NASA uses. Having actively observed in both the visible and infrared during the Shoemaker-Levy-9 impacts in 1994, I was aware that a quick verification was possible by looking at a wavelength with lots of gaseous absorption, which suppresses light reflected from Jupiter's deep clouds.
Luck was on our side. Several months before the impact, our JPL team had been awarded observing time on NASA's Infrared Telescope Facility (IRTF) atop Mauna Kea in Hawaii. We had the midnight to 6 a.m. shift (from our Pasadena office, which meant we started work at 3 a.m.) so much of our observing time would take place before Jupiter rose over Australian skies. Another piece of luck is that Anthony's "day job" involves software engineering so he was able to watch the same telescope instrument status and data screens as we were, while we did remote-style observing from the IRTF over the Internet. He would also be doing his own (now *very important*) post-impact observing. Weather was just as "iffy" over Mauna Kea as in Australia, so it was lucky for all of us that we could catch this event.
With Leigh, several JPL summer interns and me huddled at our side-by-side computers at JPL (one with instrument controls and one showing the data), and Anthony online from Australia, we got started. We knew the location of Anthony's dark spot would be coming over Jupiter's rising limb (edge) just as our allotted time was beginning. A near-infrared spectrometer was in the center of the telescope from the previous observer. Although it wasn't our instrument of choice (we wanted images!), it has a very nice guide camera sensitive to the near infrared, so we used it rather than waiting for the 20-40 minute hiatus needed by the telescope operator to move it out of the way and put our preferred instrument in its place. This turned out to be a good decision because the very first image showed us something brighter than anyplace else on the planet -- exactly where Anthony's dark feature was located. For me, this totally clinched the case that this was an impact. Even better was the fact that Anthony was looking on in real time. We e-mailed him what was obvious - he was *definitely* the father of a new impact!
Right after this we collected data that may help us sort out any exotic components of the impactor or of Jupiter's atmosphere and just how high the particulates have spread. Then we switched instruments to something at much longer wavelengths that told us the temperatures were higher, and that ammonia gas had probably been pushed up from Jupiter's troposphere (the lower part of the atmosphere) and ejected into its stratosphere (higher up in the atmosphere). We finished up with our preferred (more versatile) near-infrared camera and ended up, pretty tired, at 9 a.m. (this was a midnight to 6 a.m. run in Hawaii, and in California we were three hours ahead). Then we took some of the screen shots we'd been making and used them to submit a press release. Another person had already alerted a clearinghouse for important astronomical bulletins, so that was another thing that was important but that we didn't need to do.
Now some responses to posts:
Good post from Mike Salway who is another one of the cadre of the world's talented Jupiter observers. I should note that, in fact, there aren't all that many of us who track the time evolution of phenomena in the planets in the professional community, either.
Asim. Neither NASA nor JPL is capable of observing everything in the sky. There is a program to search for asteroids whose orbits will intersect the Earth's, but not at Jupiter. In fact, it's unlikely this object could have been seen, given that it may have been at most a half kilometer in size. For Shoemaker-Levy 9, we were both lucky and the disruption of the comets left a lot of very shiny material around it which made it easier to see.
Denise. It hit quite a bit further south than the Shoemaker-Levy 9 fragments, almost at 60 deg S latitude.
Patrick, Jim, BobK. I suspect that the only link between this and the SL9 fragments is the voracious appetite of Jupiter, the great gravitational vacuum cleaner in that part of the solar system! SL9 fragments impacted from the south; this was from the east.
What an incredible few hours it's been for astronomers everywhere, as we witness a chance of a lifetime event: evidence of a space rock of some sort slamming into Jupiter. Images taken after the impact show the debris field and aftermath of a gigantic collision that occurred in the southern polar region of the enormous planet.
An extremely dedicated and meticulous team of amateur astronomers observe Jupiter's changing cloud patterns on a regular basis, and it came as an amazing surprise when Anthony Wesley, near Canberra, Australia, reported his Sunday-morning (July 19, 2009) observations (http://jupiter.samba.org/jupiter-impact.html) of a dark scar that bore all the hallmarks of the Shoemaker Levy 9 impacts at Jupiter in 1994. By an amazing coincidence, I was part of a team that had already been allocated time to observe Jupiter from the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Based on Anthony's discovery, we were crowded around our computers at 3 a.m. PDT (with Anthony observing with us remotely from Australia) as the first near- and mid-infrared images started to come in... it was such an exciting moment, seeing the high altitude particles that had been lofted by the impact (they appear bright in the infrared). Anthony celebrated with us, but then the real work began. We celebrated and then rolled up our sleeves and began an exciting night of observations.
With the assistance of William Golisch at the IRTF, Glenn Orton and I viewed the impacts in as many wavelengths and spectra as we possibly could, as Jupiter rotated and carried the impact scar out of Earth's view. We used these many views to show evidence for high temperatures at the impact location, and suggestions of ammonia and aerosols that had been carried high into the atmosphere. The observations were repeated again today, Tuesday morning, to track the shape and properties of the site. The scar is extremely large, almost as big as Earth and will continue to grow as Jupiter's atmospheric winds and jet streams redistribute the material, and then, like Shoemaker-Levy 9, it will begin to fade in the coming weeks and months. Based on comparisons to SL-9, the impactor was likely to be small despite the large aftermath, maybe a few hundreds of metres across. Not only will this tell us a lot about impacts in the outer solar system, and how they contribute to the nature of the planets and icy moons, but they'll also serve as a probe for the fundamental weather patterns in Jupiter's high atmosphere.
Amateur observers continue to flood the Internet with new images of the dark spot at approximately 60 degrees south on Jupiter, and so far it looks as though the impact took place sometime in the 24 hours preceding Anthony's discovery. The debris field now extends out to the west and northwest, with additional high-resolution images from the Keck telescope (Marchis, Wong, Kalas, Fitzgerald and Graham http://keckobservatory.org/index.php/news/jupiters_adds_a_feature/) showing the detailed morphology of the impact region. The hard work continues today, as an international team of planetary astronomers scrambles for time on some of the world's largest astronomical facilities.
Finally, it's a shame but perhaps not surprising that we didn't see the collision, or the impactor itself, given the great distance to Jupiter. Like throwing a rock in a pond, we're seeing and analyzing the splash that it's made, and we can't yet infer many details about the rock itself - the detailed shape of the impact site could help determine the trajectory and energy of the collision. But it certainly made quite a splash, and we hope to learn a lot about Jupiter from this event!
Anthony's discovery is truly astounding, as it united astronomers in looking again at the gas giant Jupiter. It's overwhelming and spectacularly exciting to watch this event unfolding before our eyes!
You can follow Leigh on Twitter at http://twitter.com/LeighFletcher